JP2015172394A - Shovel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shovel on which a hydraulic circuit is mounted for allowing efficient operation of two hydraulic pumps and one pump motor.SOLUTION: The shovel includes a first pump 14L for discharging first working oil, a second pump 14R for discharging second working oil, and a pump motor 14A for receiving working oil flowing out of a boom cylinder 7 to produce a back pressure in the boom cylinder 7 and to generate rotating torque. When an arm cylinder 8 and the boom cylinder 7 operate at the same time, the arm cylinder 8 is driven at least by the first working oil and the boom cylinder 7 is driven at least by the second working oil, and the pump motor 14A produces the back pressure to control the operating speed of the boom cylinder 7 and to increase the discharge amount of the first pump 14L with the generated rotating torque or assist an engine 11.

Description

  The present invention relates to an excavator equipped with a hydraulic circuit including a plurality of hydraulic pumps and at least one hydraulic device functioning as at least one of a hydraulic pump and a hydraulic motor.

  There is known a hydraulic system for a construction machine including a boom cylinder, an arm cylinder, and a bucket cylinder that are simultaneously driven by hydraulic oil supplied from each of three hydraulic pumps (see, for example, Patent Document 1).

  In this hydraulic system, hydraulic oil supplied from each of the three hydraulic pumps is combined to flow into the corresponding cylinders in order to increase the drive speed of the work device including the boom, arm, and bucket. ing.

JP 2010-48417 A

  However, the above-described hydraulic system does not mention the difference in load pressure when the boom cylinder, the arm cylinder, and the bucket cylinder are simultaneously driven. Therefore, the occurrence of energy loss due to the load pressure difference cannot be prevented, and it cannot be said that the three hydraulic pumps are operated efficiently.

  In view of the above, it is desirable to provide a shovel equipped with a hydraulic circuit capable of operating a plurality of hydraulic pumps and at least one hydraulic device functioning as at least one of a hydraulic pump and a hydraulic motor more efficiently.

  An excavator according to an embodiment of the present invention includes a first pump that discharges first hydraulic fluid, a second pump that discharges second hydraulic fluid, a first hydraulic actuator into which at least the first hydraulic fluid can flow, At least a second hydraulic actuator through which the second hydraulic oil can flow, and a hydraulic motor that receives the hydraulic oil flowing out from the second hydraulic actuator to generate a back pressure of the second hydraulic actuator and generate a rotational torque When the first hydraulic actuator and the second hydraulic actuator operate simultaneously, the first hydraulic actuator is driven by at least the first hydraulic oil, and the second hydraulic actuator is at least the second hydraulic actuator. Driven by hydraulic oil, the hydraulic motor generates the back pressure to control the operating speed of the second hydraulic actuator. And, to assist the increased allowed or engine discharging amount of the first pump by the rotation torque is generated.

  By the above-described means, it is possible to provide a shovel equipped with a hydraulic circuit capable of operating a plurality of hydraulic pumps and at least one hydraulic device functioning as at least one of a hydraulic pump and a hydraulic motor more efficiently. .

It is a side view of an excavator. It is the schematic which shows the structural example of the hydraulic circuit mounted in the shovel of FIG. It is the schematic which shows another structural example of the hydraulic circuit mounted in the shovel of FIG. The state of the hydraulic circuit of FIG. 2 when excavation operation is performed is shown. The state of the hydraulic circuit of FIG. 2 when excavation operation is performed is shown. The state of the hydraulic circuit of FIG. 2 when excavation operation is performed is shown. The state of the hydraulic circuit of FIG. 3 in the case where excavation operation is performed is shown. The state of the hydraulic circuit of FIG. 2 in the case where excavation operation accompanied by engine assist by back pressure regeneration is performed is shown. The state of the hydraulic circuit of FIG. 3 in the case where excavation operation accompanied by engine assist by back pressure regeneration is performed is shown. The state of the hydraulic circuit of FIG. 2 when excavation operation with accumulator assistance is performed is shown. The state of the hydraulic circuit of FIG. 3 in the case where excavation operation with accumulator assistance is performed is shown. The state of the hydraulic circuit of FIG. 2 in the case where excavation operation with assistance of the hydraulic actuator by back pressure regeneration is performed is shown. The state of the hydraulic circuit of FIG. 3 in the case where excavation operation with assistance of the hydraulic actuator by back pressure regeneration is performed is shown. FIG. 3 shows the state of the hydraulic circuit in FIG. 2 when a soil removal operation accompanied by engine assist by back pressure regeneration is performed. The state of the hydraulic circuit of FIG. 3 in the case where the earth removal operation accompanied by the engine assist by back pressure regeneration is performed is shown. The state of the hydraulic circuit of FIG. 2 in the case where the soil removal operation accompanied by the assist of the hydraulic actuator by back pressure regeneration is performed is shown. The state of the hydraulic circuit of FIG. 3 in the case where the soil removal operation accompanied by the assist of the hydraulic actuator by back pressure regeneration is performed is shown. The state of the hydraulic circuit of FIG. 2 in the case where the earth discharging operation accompanied by accumulator pressure accumulation by back pressure regeneration is performed is shown. The state of the hydraulic circuit of FIG. 3 in the case where the earth removal operation accompanied by accumulator pressure accumulation by back pressure regeneration is performed is shown. FIG. 3 shows the state of the hydraulic circuit in FIG. 2 when a boom lowering turning deceleration operation accompanied by accumulator pressure accumulation is performed. FIG. 4 shows a state of the hydraulic circuit in FIG. 3 when a boom lowering turning deceleration operation accompanied by accumulator pressure accumulation is performed.

  FIG. 1 is a side view showing an excavator to which the present invention is applied. An upper swing body 3 is mounted on the lower traveling body 1 of the excavator via a swing mechanism 2. A boom 4 is attached to the upper swing body 3. An arm 5 is attached to the tip of the boom 4, and a bucket 6 is attached to the tip of the arm 5. The boom 4, the arm 5, and the bucket 6 as work elements constitute a drilling attachment that is an example of an attachment, and are hydraulically driven by the boom cylinder 7, the arm cylinder 8, and the bucket cylinder 9, respectively. The upper swing body 3 is provided with a cabin 10 and is mounted with a power source such as the engine 11 and a controller 30.

  The controller 30 is a control device as a main control unit that performs drive control of the shovel. In the present embodiment, the controller 30 is configured by an arithmetic processing unit including a CPU (Central Processing Unit) and an internal memory, and realizes various functions by causing the CPU to execute a drive control program stored in the internal memory.

  FIG. 2 is a schematic diagram illustrating a configuration example of a hydraulic circuit mounted on the shovel of FIG. In the present embodiment, the hydraulic circuit mainly includes a first pump 14L, a second pump 14R, a pump / motor 14A, a control valve 17, and a hydraulic actuator. The hydraulic actuator mainly includes a boom cylinder 7, an arm cylinder 8, a bucket cylinder 9, a turning hydraulic motor 21, and an accumulator 80.

  The boom cylinder 7 is a hydraulic cylinder that raises and lowers the boom 4. A regeneration valve 7 a is connected between the bottom side oil chamber and the rod side oil chamber, and a holding valve 7 b is installed on the bottom side oil chamber side. . The arm cylinder 8 is a hydraulic cylinder that opens and closes the arm 5. A regeneration valve 8a is connected between the bottom side oil chamber and the rod side oil chamber, and a holding valve 8b is installed on the rod side oil chamber side. Is done. The bucket cylinder 9 is a hydraulic cylinder that opens and closes the bucket 6, and a regeneration valve 9a is connected between the bottom side oil chamber and the rod side oil chamber.

  The turning hydraulic motor 21 is a hydraulic motor for turning the upper turning body 3, and ports 21L and 21R are connected to the hydraulic oil tank T via relief valves 22L and 21R, respectively, and a regeneration valve 22G via a shuttle valve 22S. And is connected to the hydraulic oil tank T via check valves 23L and 23R.

  The relief valve 22L opens when the pressure on the port 21L side reaches a predetermined relief pressure, and discharges the hydraulic oil on the port 21L side to the hydraulic oil tank T. The relief valve 22R opens when the pressure on the port 21R side reaches a predetermined relief pressure, and discharges the hydraulic oil on the port 21R side to the hydraulic oil tank T.

  The shuttle valve 22S supplies the regenerating valve 22G with hydraulic oil having a higher pressure on the port 21L side and the port 21R side.

  The regeneration valve 22G is a valve that operates in response to a command from the controller 30, and switches communication / blocking between the turning hydraulic motor 21 (shuttle valve 22S) and the pump / motor 14A or the accumulator 80.

  The check valve 23L opens when the pressure on the port 21L side becomes negative, and supplies hydraulic oil from the hydraulic oil tank T to the port 21L side. The check valve 23R opens when the pressure on the port 21R side becomes negative, and replenishes hydraulic oil from the hydraulic oil tank T to the port 21R side. Thus, the check valves 23L and 23R constitute a supply mechanism that supplies hydraulic oil to the suction side port when the swing hydraulic motor 21 is braked.

  The first pump 14L is a hydraulic pump that sucks and discharges hydraulic oil from the hydraulic oil tank T. In the present embodiment, the first pump 14L is a swash plate type variable displacement hydraulic pump. The first pump 14L is connected to a regulator. The regulator controls the discharge amount of the first pump 14L by changing the swash plate tilt angle of the first pump 14L in accordance with a command from the controller 30. The same applies to the second pump 14R.

  A relief valve 14aL is installed on the discharge side of the first pump 14L. The relief valve 14aL opens when the pressure on the discharge side of the first pump 14L reaches a predetermined relief pressure, and discharges the hydraulic oil on the discharge side to the hydraulic oil tank. The same applies to the relief valve 14aR installed on the discharge side of the second pump 14R.

  The pump motor 14A is a hydraulic device that functions as both a hydraulic pump (third pump) and a hydraulic motor. In this embodiment, the pump motor 14A is a swash plate type variable displacement hydraulic pump / motor. The pump motor 14A is connected to a regulator in the same manner as the first pump 14L and the second pump 14R. The regulator changes the swash plate tilt angle of the pump / motor 14A in accordance with a command from the controller 30 to control the discharge amount of the pump / motor 14A.

  A relief valve 70a is installed on the discharge side of the pump / motor 14A. The relief valve 70a opens when the pressure on the discharge side of the pump / motor 14A reaches a predetermined relief pressure, and discharges the discharge side hydraulic oil to the hydraulic oil tank.

  In the present embodiment, the first pump 14L, the second pump 14R, and the pump / motor 14A are mechanically connected to their respective drive shafts. Specifically, each drive shaft is connected to the output shaft of the engine 11 through the transmission 13 at a predetermined speed ratio. Therefore, if the engine speed is constant, each speed is also constant. However, the first pump 14L, the second pump 14R, and the pump motor 14A may be connected to the engine 11 via a continuously variable transmission or the like so that the rotation speed can be changed even if the engine rotation speed is constant. Good.

  The control valve 17 is a hydraulic control device that controls a hydraulic drive system in the excavator. The control valve 17 mainly includes variable load check valves 51 to 53, a merging valve 55, unified bleed-off valves 56L and 56R, switching valves 60 to 63, and flow control valves 170 to 173.

  The flow control valves 170 to 173 are valves that control the direction and flow rate of hydraulic oil flowing into and out of the hydraulic actuator. In the present embodiment, each of the flow control valves 170 to 173 is a 4-port 3 position that operates by receiving pilot pressure generated by an operating device (not shown) such as a corresponding operating lever at either the left or right pilot port. This is a spool valve. The operating device causes the generated pilot pressure corresponding to the operation amount (operation angle) to act on the pilot port on the side corresponding to the operation direction.

  Specifically, the flow control valve 170 is a spool valve that controls the direction and flow rate of the hydraulic oil flowing into and out of the turning hydraulic motor 21, and the flow control valve 171 is the hydraulic oil flowing into and out of the arm cylinder 8. A spool valve that controls the direction and flow rate.

  The flow control valve 172 is a spool valve that controls the direction and flow rate of the hydraulic oil flowing into and out of the boom cylinder 7, and the flow control valve 173 controls the direction and flow rate of the hydraulic oil flowing into and out of the bucket cylinder 9. This is a spool valve.

  The variable load check valves 51 to 53 are valves that operate in response to a command from the controller 30. In this embodiment, the variable load check valves 51 to 53 are two ports that can switch communication / blocking between each of the flow control valves 171 to 173 and at least one of the first pump 14L and the second pump 14R. This is a two-position solenoid valve. Note that the variable load check valves 51 to 53 have a check valve that blocks the flow of hydraulic oil returning to the pump side at the first position. Specifically, when the variable load check valve 51 is in the first position, the flow control valve 171 communicates with at least one of the first pump 14L and the second pump 14R and is in the second position. In that case, the communication is cut off. The same applies to the variable load check valve 52 and the variable load check valve 53.

  The junction valve 55 is an example of a junction switching unit, and is a valve that operates in response to a command from the controller 30. In the present embodiment, the merging valve 55 is a hydraulic oil discharged from the first pump 14L (hereinafter referred to as “first hydraulic oil”) and a hydraulic oil discharged from the second pump 14R (hereinafter referred to as “second hydraulic oil”). ").” Is a 2-port 2-position solenoid valve capable of switching whether or not to join. Specifically, the merging valve 55 merges the first hydraulic oil and the second hydraulic oil when in the first position, and merges the first hydraulic oil and the second hydraulic oil when in the second position. Do not let it.

  The unified bleed-off valves 56 </ b> L and 56 </ b> R are valves that operate in response to a command from the controller 30. In this embodiment, the unified bleed-off valve 56L is a 2-port 2-position electromagnetic valve capable of controlling the discharge amount of the first hydraulic oil to the hydraulic oil tank T. The same applies to the unified bleed-off valve 56R. With this configuration, the unified bleed-off valves 56L and 56R can reproduce the combined opening of the associated flow control valve among the flow control valves 170 to 173. Specifically, when the merging valve 55 is in the second position, the unified bleed-off valve 56L can reproduce the combined opening of the flow control valve 170 and the flow control valve 171, and the unified bleed-off valve 56R includes the flow control valve 172 and the flow control valve 172. The synthetic opening of the flow control valve 173 can be reproduced.

  The switching valves 60 to 63 are valves that operate in response to a command from the controller 30. In this embodiment, the switching valves 60 to 63 are three-port, two-position solenoid valves that can switch whether or not the hydraulic oil discharged from each of the hydraulic actuators flows to the upstream side (supply side) of the pump motor 14A. It is. Specifically, when the switching valve 60 is in the first position, the hydraulic oil discharged from the turning hydraulic motor 21 through the regeneration valve 22G flows to the supply side of the pump motor 14A and is in the second position. In addition, the hydraulic oil discharged from the turning hydraulic motor 21 through the regeneration valve 22G is caused to flow to the accumulator 80. Further, when the switching valve 61 is in the first position, the hydraulic oil discharged from the arm cylinder 8 flows into the hydraulic oil tank T, and when it is in the second position, the hydraulic oil discharged from the arm cylinder 8 is allowed to flow. Flow to the supply side of the pump motor 14A. The same applies to the switching valve 62 and the switching valve 63.

  The accumulator 80 is a hydraulic device that accumulates pressurized hydraulic oil. In this embodiment, the accumulator 80 is controlled to store and release hydraulic oil by the switching valve 81 and the switching valve 82.

  The switching valve 81 is a valve that operates in response to a command from the controller 30. In the present embodiment, the switching valve 81 is a two-port two-position electromagnetic valve that can switch communication / blocking between the first pump 14L, which is a supply source of pressurized hydraulic oil, and the accumulator 80. Specifically, the switching valve 81 communicates between the first pump 14L and the accumulator 80 when in the first position, and blocks the communication when in the second position. Note that the switching valve 81 has a check valve that blocks the flow of hydraulic oil that returns to the first pump 14L side in the first position.

  The switching valve 82 is a valve that operates in response to a command from the controller 30. In this embodiment, the switching valve 82 is a 2-port 2-position electromagnetic valve that can switch communication / blocking between the supply side of the pump / motor 14A to which pressurized hydraulic oil is supplied and the accumulator 80. is there. Specifically, the switching valve 82 communicates between the pump motor 14A and the accumulator 80 when in the first position, and blocks the communication when in the second position. Note that the switching valve 82 has a check valve that blocks the flow of hydraulic oil that returns to the accumulator 80 side in the first position.

  The switching valve 90 is a valve that operates in response to a command from the controller 30. In this embodiment, the switching valve 90 is a three-port, two-position electromagnetic valve capable of switching the supply destination of hydraulic oil discharged from the pump / motor 14A (hereinafter referred to as “third hydraulic oil”). Specifically, the switching valve 90 allows the third hydraulic oil to flow toward the switching valve 91 when in the first position, and allows the third hydraulic oil to flow toward the hydraulic oil tank T when in the second position. .

  The switching valve 91 is a valve that operates in response to a command from the controller 30. In this embodiment, the switching valve 91 is a four-port, three-position electromagnetic valve that can switch the supply destination of the third hydraulic oil. Specifically, the switching valve 91 directs the third hydraulic oil toward the arm cylinder 8 when in the first position, and directs the third hydraulic oil toward the turning hydraulic motor 21 when in the second position. When in position, the third hydraulic fluid is directed to the accumulator 80.

  Next, another configuration example of the hydraulic circuit will be described with reference to FIG. FIG. 3 is a schematic view showing another configuration example of a hydraulic circuit mounted on the excavator of FIG. The hydraulic circuit in FIG. 3 mainly flows in and out of the bottom side oil chamber of the boom cylinder 7 in that the direction and flow rate of the hydraulic oil flowing into and out of the arm cylinder 8 are controlled by the two flow control valves 171A and 171B. From the point that the flow rate of the hydraulic oil is controlled by the two flow rate control valves 172A and 172B, the point where the merging switching unit is configured by a variable load check valve instead of the merging valve (the point where the merging valve is omitted), 2 is different from the hydraulic circuit of FIG. 2 in that it can be stored in the accumulator 80, but is common in other points. Therefore, the difference will be described in detail while omitting the description of the common points.

  The flow control valves 171A and 172B are valves that control the direction and flow rate of the hydraulic oil flowing into and out of the arm cylinder 8, and correspond to the flow control valve 171 in FIG. Specifically, the flow control valve 171 </ b> A supplies the first hydraulic oil to the arm cylinder 8, and the flow control valve 171 </ b> B supplies the second hydraulic oil to the arm cylinder 8. Therefore, the first hydraulic oil and the second hydraulic oil can flow into the arm cylinder 8 at the same time.

  The flow control valve 172A is a valve that controls the direction and flow rate of hydraulic oil flowing into and out of the boom cylinder 7, and corresponds to the flow control valve 172 in FIG.

  The flow control valve 172B is a valve that allows the first hydraulic oil to flow into the bottom side oil chamber of the boom cylinder 7 when the boom raising operation is performed. When the boom lowering operation is performed, the boom cylinder 7 The hydraulic oil flowing out from the bottom side oil chamber can be merged with the first hydraulic oil.

  The flow control valve 173 is a valve that controls the direction and flow rate of the hydraulic oil flowing into and out of the bucket cylinder 9 and corresponds to the flow control valve 173 in FIG. 3 includes a check valve for regenerating hydraulic oil flowing out from the rod side oil chamber of the bucket cylinder 9 into the bottom side oil chamber.

  The variable load check valves 50, 51A, 51B, 52A, 52B, 53 are respectively flow rate control valves 170, 171A, 171B, 172A, 172B, 173 and at least one of the first pump 14L and the second pump 14R. It is a 2-port 2-position valve that can be switched between communication and blocking. These six variable load check valves operate in conjunction with each other, thereby functioning as a merging switching unit and realizing the function of the merging valve 55 of FIG. Therefore, the junction valve 55 of FIG. 2 is omitted in the hydraulic circuit of FIG. For the same reason, the switching valve 91 of FIG. 2 is omitted.

  The unified bleed-off valves 56L and 56R are 2-port 2-position valves capable of controlling the discharge amount of the first hydraulic oil to the hydraulic oil tank T, and correspond to the unified bleed-off valves 56L and 56R in FIG.

  Each of the six flow control valves in FIG. 3 is a spool valve at a 6-port 3-position, and has a center bypass port unlike the flow control valve in FIG. Therefore, the unified bleed-off valve 56L in FIG. 3 is disposed downstream of the flow control valve 171A, and the unified bleed-off valve 56R is disposed downstream of the flow control valve 171B.

  The switching valve 61A is a 2-port 2-position valve capable of switching whether or not to flow the hydraulic oil discharged from the rod-side oil chamber of the arm cylinder 8 to the upstream side (supply side) of the pump / motor 14A. Specifically, the switching valve 61A communicates between the rod-side oil chamber of the arm cylinder 8 and the pump / motor 14A when in the first position, and shuts off the communication when in the second position.

  The switching valve 62A is a three-port, three-position valve that can switch whether or not the hydraulic oil discharged from the boom cylinder 7 flows to the upstream side (supply side) of the pump / motor 14A. Specifically, the switching valve 62A communicates between the bottom side oil chamber of the boom cylinder 7 and the pump motor 14A when in the first position, and the rod side of the boom cylinder 7 when in the second position. The oil chamber and the pump / motor 14A are communicated with each other, and the communication between the oil chamber and the pump / motor 14A is blocked when the oil chamber is in the third position (neutral position).

  The switching valve 62 </ b> B is a 2-port 2-position variable relief valve capable of switching whether to discharge the hydraulic oil discharged from the rod side oil chamber of the boom cylinder 7 to the hydraulic oil tank T. Specifically, the switching valve 62B communicates between the rod-side oil chamber of the boom cylinder 7 and the hydraulic oil tank T when in the first position, and blocks communication when in the second position. The switching valve 62B has a check valve that blocks the flow of hydraulic oil from the hydraulic oil tank T in the first position.

  The switching valve 62C is a 2-port 2-position variable relief valve capable of switching whether or not to discharge the hydraulic oil discharged from the bottom side oil chamber of the boom cylinder 7 to the hydraulic oil tank T. Specifically, the switching valve 62C communicates between the bottom side oil chamber of the boom cylinder 7 and the hydraulic oil tank T when in the first position, and shuts off the communication when in the second position. Note that the switching valve 62C has a check valve that blocks the flow of hydraulic oil from the hydraulic oil tank T at the first position.

  The switching valve 90 is a 3-port 2-position electromagnetic valve capable of switching the supply destination of the third hydraulic oil discharged from the pump / motor 14A, and corresponds to the switching valve 90 of FIG. Specifically, the switching valve 90 allows the third hydraulic oil to flow toward the control valve 17 when in the first position, and causes the third hydraulic oil to flow toward the switching valve 92 when in the second position.

The switching valve 92 is a four-port, three-position electromagnetic valve that can switch the supply destination of the third hydraulic oil. Specifically, when the switching valve 92 is in the first position, the third hydraulic oil is directed to the replenishment mechanism of the turning hydraulic motor 21, and when it is in the second position, the third hydraulic oil is directed to the accumulator 80, When in the third position, the third hydraulic oil is directed to the hydraulic oil tank T.

[Drilling operation]
Next, the state of the hydraulic circuit in FIG. 2 when the excavation operation is performed will be described with reference to FIGS. 4 to 6 show the state of the hydraulic circuit in FIG. 2 when the excavation operation is performed. Moreover, the black thick solid line of FIGS. 4-6 represents the flow of the hydraulic fluid which flows in into a hydraulic actuator, and represents that the flow volume is so large that the thickness of a solid line is thick.

  The controller 30 determines the operation content of the operator on the shovel based on the output of an operation detection unit such as an operation pressure sensor (not shown) that detects the pilot pressure generated by the operation device. The controller 30 also includes a discharge pressure sensor (not shown) that detects the discharge pressure of each of the first pump 14L, the second pump 14R, and the pump / motor 14A, and a load pressure that detects each pressure of the hydraulic actuator. Based on the output of a load detector such as a sensor (not shown), the operation state of the shovel is determined. In the present embodiment, the load pressure sensor includes a cylinder pressure sensor that detects respective pressures of the bottom side oil chamber and the rod side oil chamber of the boom cylinder 7, the arm cylinder 8, and the bucket cylinder 9. Further, the controller 30 detects the pressure of hydraulic oil accumulated in the accumulator 80 (hereinafter referred to as “accumulator pressure”) based on the output of an accumulator pressure sensor (not shown).

  If the controller 30 determines that the arm 5 has been operated, the merging valve 55 at the second position is moved in the direction of the first position in accordance with the operation amount of the arm operation lever, as shown in FIG. Then, the first hydraulic oil and the second hydraulic oil are merged, and the first hydraulic oil and the second hydraulic oil are supplied to the flow rate control valve 171. The flow control valve 171 receives the pilot pressure corresponding to the operation amount of the arm operation lever, moves to the right position in FIG. 4, and causes the first hydraulic oil and the second hydraulic oil to flow into the arm cylinder 8.

  Further, when it is determined that the boom 4 and the bucket 6 are operated, the controller 30 determines whether the excavation operation or the floor excavation operation is performed based on the output of the load pressure sensor. The floor excavation operation is an operation of leveling the ground with the bucket 6, for example, and the pressure in the bottom side oil chamber of the arm cylinder 8 is lower than that during the excavation operation.

  When it is determined that the excavation operation is performed, the controller 30 responds to the operation amounts of the boom operation lever and the bucket operation lever based on pump discharge amount control such as negative control control, positive control control, load sensing control, and horsepower control. A discharge amount command value for the second pump 14R is determined. Then, the controller 30 controls the corresponding regulator so that the discharge amount of the second pump 14R becomes the command value.

  Further, the controller 30 uses the pump discharge amount control described above to flow between the discharge amount calculation value and the discharge amount command value in consideration of the operation amount of the arm operation lever in addition to the operation amount of the boom operation lever and the bucket operation lever. The difference is calculated, and the hydraulic oil having a flow rate corresponding to the flow rate difference is discharged to the pump motor 14A. In this discharge amount calculation value, the arm 5 is operated with a full lever (for example, an operation amount of 80% or more when the neutral state of the lever is 0% and the maximum operation state is 100%) as in the excavation operation. The maximum discharge amount of the second pump 14R. Specifically, as shown in FIG. 5, the controller 30 operates the pump / motor 14A as a hydraulic pump, controls the corresponding regulator, and the discharge amount of the pump / motor 14A is a flow rate corresponding to the flow rate difference. Control to be. Then, the controller 30 directs the third hydraulic oil toward the switching valve 91 with the switching valve 90 in the first position, and directs the third hydraulic oil toward the arm cylinder 8 with the switching valve 91 in the first position.

  Further, the controller 30 controls the opening area of the junction valve 55 based on the above-described flow rate difference, the discharge pressure of the first pump 14L, the discharge pressure of the second pump 14R, and the like. In the example of FIGS. 4 to 6, the controller 30 determines the opening area of the merging valve 55 with reference to the opening map registered in advance, and outputs a command corresponding to the opening area to the merging valve 55. The controller 30 may determine the opening area of the merging valve 55 using a predetermined function instead of the opening map.

  For example, when the flow rate of the third hydraulic oil discharged from the pump / motor 14A reaches a flow rate corresponding to the above-described flow rate difference, the controller 30 sets the merging valve 55 to the second position as shown in FIG. The merge of the first hydraulic oil and the second hydraulic oil is shut off.

  In addition, even when it is determined that the floor excavation operation is performed, the controller 30 closes the merging valve 55 as quickly as possible as long as the excavator movement does not become unstable, as shown in FIG. This is to improve the operability of the boom 4 and the bucket 6 by allowing only the second hydraulic oil to flow into the boom cylinder 7 and the bucket cylinder 9.

  4 to 6, the maximum discharge amount of the pump / motor 14A is smaller than the maximum discharge amount of the second pump 14R. Therefore, when the above-described flow rate difference exceeds the maximum discharge amount of the pump / motor 14A, the controller 30 operates the pump / motor 14A functioning as a hydraulic pump and the first pump 14L with the maximum discharge amount, 2 The discharge amount of the pump 14R is increased. Then, the difference between the maximum discharge amount of the second pump 14R and the actually increased discharge amount is set to be equal to or less than the maximum discharge amount of the pump / motor 14A. This is to prevent the operating speed of the arm 5 from falling below the operating speed of the arm 5 when the first hydraulic oil and the second hydraulic oil are used.

  However, when the maximum discharge amount of the pump / motor 14A is equal to or larger than the maximum discharge amount of the second pump 14R, the controller 30 closes the merging valve 55 during the excavation operation (second state) as shown in FIG. Position). This is because the operating speed of the arm 5 when the first hydraulic oil and the third hydraulic oil are used does not fall below the operating speed of the arm 5 when the first hydraulic oil and the second hydraulic oil are used. In this case, the controller 30 always causes only the first hydraulic oil and the third hydraulic oil to flow into the arm cylinder 8 and allows only the second hydraulic oil to flow into the boom cylinder 7 and the bucket cylinder 9 during the excavation operation. Therefore, the hydraulic oil for moving the arm 5 and the hydraulic oil for moving the boom 4 and the bucket 6 can be completely separated, and the operability of each can be improved.

  Next, the state of the hydraulic circuit in FIG. 3 when excavation operation is performed will be described with reference to FIG. FIG. 7 shows the state of the hydraulic circuit in FIG. 3 when excavation is performed. Moreover, the black and gray thick solid lines in FIG. 7 represent the flow of hydraulic oil flowing into the hydraulic actuator, and the larger the solid line thickness, the greater the flow rate. Further, the gray solid line in FIG. 7 additionally indicates that the flow of hydraulic oil can be reduced or eliminated.

  As in the case of the hydraulic circuit in FIG. 2, the controller 30 determines the operation content of the operator on the shovel based on the output of the operation detection unit, and determines the operation state of the shovel based on the output of the load detection unit.

  When the arm 5 is operated, the flow control valve 171A receives the pilot pressure corresponding to the operation amount of the arm operation lever and moves to the left position in FIG. 7, and the flow control valve 171B corresponds to the operation amount of the arm operation lever. Under the pilot pressure, it moves to the right position in FIG.

  When the controller 30 determines that the arm 5 has been operated, the controller 30 sets the variable load check valve 51A to the first position so that the first hydraulic oil reaches the flow control valve 171A through the variable load check valve 51A. Further, the variable load check valve 51B is set to the first position so that the second hydraulic oil reaches the flow control valve 171B through the variable load check valve 51B. The first hydraulic oil that has passed through the flow control valve 171A merges with the second hydraulic oil that has passed through the flow control valve 171B, and flows into the bottom side oil chamber of the arm cylinder 8.

  Thereafter, when it is determined that the boom 4 and the bucket 6 have been operated, the controller 30 determines whether the excavation operation or the floor excavation operation is performed based on the output of the load pressure sensor. When it is determined that the excavation operation is performed, the controller 30 determines a discharge amount command value of the second pump 14R corresponding to the operation amounts of the boom operation lever and the bucket operation lever. Then, the controller 30 controls the corresponding regulator so that the discharge amount of the second pump 14R becomes the command value.

  At this time, the flow control valve 172A receives the pilot pressure corresponding to the operation amount of the boom operation lever and moves to the left position in FIG. Further, the flow control valve 173 receives the pilot pressure corresponding to the operation amount of the bucket operation lever and moves to the right position in FIG. Then, the controller 30 sets the variable load check valve 52A to the first position so that the second hydraulic oil reaches the flow control valve 172A through the variable load check valve 52A. Further, the variable load check valve 53 is set to the first position so that the second hydraulic oil reaches the flow control valve 173 through the variable load check valve 53. The second hydraulic oil that has passed through the flow control valve 172A flows into the bottom side oil chamber of the boom cylinder 7, and the second hydraulic oil that has passed through the flow control valve 173 flows into the bottom side oil chamber of the bucket cylinder 9. To do.

  Further, the controller 30 calculates a flow rate difference between the maximum discharge amount of the second pump 14R and a discharge amount command value, and causes the pump / motor 14A to discharge hydraulic oil having a flow rate corresponding to the flow rate difference. Specifically, as shown in FIG. 7, the controller 30 operates the pump / motor 14A as a hydraulic pump, controls the corresponding regulator, and sets the discharge amount of the pump / motor 14A to a flow rate corresponding to the flow rate difference. Control to be. Then, the controller 30 sets the switching valve 90 to the first position and directs the third hydraulic oil to the control valve 17.

  Further, the controller 30 controls the opening area of the variable load check valve 51B based on the flow rate difference, the discharge pressure of the first pump 14L, the discharge pressure of the second pump 14R, and the like. In the example of FIG. 7, the controller 30 determines the opening area of the variable load check valve 51B with reference to the opening map registered in advance, and outputs a command corresponding to the opening area to the variable load check valve 51B. Thereby, the 2nd hydraulic fluid which flows into the bottom side oil chamber of the arm cylinder 8 reduces or lose | disappears. The gray solid line in FIG. 7 indicates that the second hydraulic fluid flowing into the bottom side oil chamber of the arm cylinder 8 decreases or disappears as the flow rate of the third hydraulic fluid discharged from the pump / motor 14A increases. Represents what to do.

  As described above, the controller 30 operates the pump motor 14A as a hydraulic pump when excavation operations including boom raising, arm closing, and bucket closing are performed. Then, the third hydraulic oil discharged from the pump / motor 14A is caused to flow into the hydraulic actuator (arm cylinder 8) having a high load pressure. When the hydraulic actuator having a high load pressure can be operated at a desired speed using the first hydraulic oil and the third hydraulic oil, the merging valve 55 is closed and the first hydraulic oil and the second hydraulic oil are Block the merge. Therefore, the shovel according to the embodiment of the present invention operates the hydraulic actuator (arm cylinder 8) having a high load pressure with the first hydraulic oil, and the load hydraulic pressure with the second hydraulic oil having a lower pressure than the first hydraulic oil. Low hydraulic actuators (boom cylinder 7 and bucket cylinder 9) can be operated. Specifically, it is not necessary to operate a hydraulic actuator having a low load pressure with the second hydraulic oil pressurized to the same pressure as the first hydraulic oil for merging with the first hydraulic oil. That is, it is not necessary to reduce the flow rate of the second hydraulic oil with a throttle in order to operate the hydraulic actuator with a low load pressure at a desired speed using the pressurized second hydraulic oil. As a result, it is possible to reduce or prevent pressure loss from occurring in the throttle, and to reduce or prevent energy loss.

The controller 30 may increase the discharge amount of the first pump 14L by individual flow control instead of causing the pump / motor 14A to discharge the third hydraulic oil. Specifically, the maximum discharge flow rate of the first pump 14L (the amount of discharge of the second pump 14R is reduced by closing the merging valve 55 and shutting off the merging of the first hydraulic oil and the second hydraulic oil. The maximum swash plate tilt angle) may be increased.

[Excavation with engine assist by back pressure regeneration]
Next, the state of the hydraulic circuit in FIG. 2 when the excavation operation with the assist of the engine 11 by back pressure regeneration is performed will be described with reference to FIG. FIG. 8 shows a state of the hydraulic circuit of FIG. 2 when excavation operation accompanied by assist of the engine 11 by back pressure regeneration is performed. Also, the black thick solid line in FIG. 8 represents the flow of hydraulic oil flowing into the hydraulic actuator, and the larger the solid line, the greater the flow rate. Moreover, the black and gray thick dotted lines in FIG. 8 represent the flow of hydraulic oil flowing out from the hydraulic actuator.

  Back pressure regeneration is a process executed when a plurality of hydraulic actuators operate simultaneously and when the load pressures of the plurality of hydraulic actuators are different. For example, when a complex excavation operation by a boom raising operation and an arm closing operation is performed, the load pressure of the arm cylinder 8 (the pressure of the bottom oil chamber of the arm cylinder 8) is the load pressure of the boom cylinder 7 (the bottom of the boom cylinder 7). Higher than the pressure in the side oil chamber). This is because the bucket 6 is grounded during excavation, and the weights of the boom 4, the arm 5, and the bucket 6 are supported by the ground, and the excavation reaction force against the excavation operation (closing operation) of the arm 5 is caused by the boom 4. To receive.

  Therefore, when a combined excavation operation is performed, the controller 30 increases the system pressure of the hydraulic circuit (the discharge pressures of the first pump 14L and the second pump 14R) to cope with the relatively high load pressure of the arm cylinder 8. Let On the other hand, the controller 30 controls the flow rate of the hydraulic oil flowing into the bottom side oil chamber of the boom cylinder 7 in order to control the operating speed of the boom cylinder 7 that operates at a load pressure lower than the system pressure. At this time, when the flow rate is controlled by the restriction of the flow control valve 172, a pressure loss (energy loss) is generated. Therefore, the controller 30 realizes control of the operating speed of the boom cylinder 7 while increasing the pressure (back pressure) of the rod side oil chamber of the boom cylinder 7 while avoiding the occurrence of pressure loss in the flow control valve 172. To do. Further, in order to increase the pressure (back pressure) of the rod side oil chamber of the boom cylinder 7, the controller 30 supplies hydraulic oil flowing out from the rod side oil chamber to the pump motor 14A, and the pump motor 14A is hydraulically ( (Regenerative) Let it function as a motor. Note that, when executing the back pressure regeneration, the controller 30 largely moves the flow control valve 172 to the right position in FIG. 8 regardless of the operation amount of the boom operation lever. This is because the opening area of the flow control valve 172 is maximized to minimize pressure loss. For example, the controller 30 assists the amount of movement of the flow control valve 172 by increasing the pilot pressure acting on the pilot port of the flow control valve 172 using a pressure reducing valve (not shown).

  Specifically, the controller 30 determines the operation content of the operator for the shovel based on the output of the operation detection unit, and determines the operation state of the shovel based on the output of the load detection unit.

  When the controller 30 determines that the combined excavation operation by the boom raising operation, the arm closing operation, and the bucket closing operation is being performed, the controller 30 determines which hydraulic actuator has a minimum load pressure. Specifically, the controller 30 determines which hydraulic actuator has the maximum energy loss (pressure loss) when the flow rate of hydraulic fluid flowing into each of the hydraulic actuators is controlled by restricting the flow control valve. To do.

  When the controller 30 determines that the pressure (load pressure) in the bottom side oil chamber of the boom cylinder 7 is the minimum, the controller 30 sets the switching valve 62 to the second position, as shown by the black thick dotted line, on the rod side of the boom cylinder 7. The hydraulic oil flowing out from the oil chamber is directed to the supply side of the pump / motor 14A. Further, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 172 by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172 is opened to the maximum, and the flow control valve Reduce pressure loss at 172. Further, the controller 30 directs the hydraulic oil flowing out from the rod side oil chamber of the bucket cylinder 9 to the hydraulic oil tank T with the switching valve 63 in the first position.

  Thereafter, the controller 30 controls the amount of hydraulic oil absorbed (push-out volume) by the pump motor 14 </ b> A as a hydraulic motor so that the operation speed of the boom cylinder 7 becomes a speed corresponding to the operation amount of the boom operation lever. Specifically, the controller 30 controls the displacement volume by adjusting the swash plate tilt angle of the pump motor 14A with a regulator. For example, when the pump / motor 14A is rotated at a constant speed, the controller 30 can reduce the flow rate of hydraulic fluid flowing out from the rod side oil chamber of the boom cylinder 7 as the push-out volume is reduced. The pressure (back pressure) of the oil chamber can be increased. Using this relationship, the controller 30 can control the back pressure so that the back pressure becomes a pressure commensurate with a desired load pressure of the boom cylinder 7 (pressure in the bottom side oil chamber).

  The hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 generates rotational torque by rotating the pump motor 14A. This rotational torque is transmitted to the rotating shaft of the engine 11 via the transmission 13, and can be used as the driving force of the first pump 14L and the second pump 14R. That is, the rotational torque generated by the pump motor 14A is used to assist the rotation of the engine 11, and has an effect of suppressing the load on the engine 11 and thus the fuel injection amount. 8 indicates that the rotational torque is transmitted to the rotating shaft of the engine 11 via the transmission 13 and can be used as the driving force of the first pump 14L and the second pump 14R. Further, for the output control of the engine 11, it is desirable to use one that applies transient load control (torque base control).

  In addition, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the rod side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62 to an intermediate position between the first position and the second position, or completely switches the switching valve 62 to the first position, so that the rod side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T. When the CT opening of the flow control valve 172 is large (when the operation amount of the boom raising operation is large and the operator's intention to quickly raise the boom 4 is estimated), or when the load is applied to the boom cylinder 7 and the back pressure is increased. The same applies to the case where it is no longer necessary to generate them. 8 indicates that the hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 is discharged to the hydraulic oil tank T when the switching valve 62 is moved in the direction of the first position. Represents that.

  In the above description, the case where the pressure (load pressure) in the bottom side oil chamber of the boom cylinder 7 is determined to be minimum will be described. However, the pressure (load pressure) in the bottom side oil chamber of the bucket cylinder 9 is determined to be minimum. The same description applies to the case of the case. Specifically, when the controller 30 determines that the pressure (load pressure) in the bottom side oil chamber of the bucket cylinder 9 is the minimum, the controller 30 sets the switching valve 63 to the second position, and the controller 30 flows out from the rod side oil chamber of the bucket cylinder 9. Direct the oil to the supply side of the pump motor 14A. Further, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 173 by the pressure reducing valve regardless of the operation amount of the bucket operation lever, thereby setting the flow control valve 173 to the maximum opening. Reduce pressure loss at 173. Further, the controller 30 directs the hydraulic oil flowing out from the rod-side oil chambers of the arm cylinder 8 and the boom cylinder 7 to the hydraulic oil tank T with the switching valve 61 and the switching valve 62 set to the first positions, respectively. Further, the operation speed of the bucket cylinder 9 is controlled in the same manner as described above.

  When the controller 30 determines that the pressure (load pressure) in the bottom side oil chamber of the arm cylinder 8 is the minimum, the controller 30 sets the switching valve 61 to the second position and pumps the hydraulic oil flowing out from the rod side oil chamber of the arm cylinder 8.・ Direct toward the supply side of the motor 14A. Further, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 171 by the pressure reducing valve regardless of the operation amount of the arm operation lever so that the flow control valve 171 is opened to the maximum. Reduce pressure loss at 171. Further, the controller 30 directs the hydraulic oil flowing out from the rod-side oil chambers of the boom cylinder 7 and the bucket cylinder 9 to the hydraulic oil tank T with the switching valve 62 and the switching valve 63 being in the first positions. Further, the operating speed of the arm cylinder 8 is also controlled in the same manner as described above.

  Next, the state of the hydraulic circuit in FIG. 3 when the excavation operation with the assist of the engine 11 by back pressure regeneration is performed will be described with reference to FIG. FIG. 9 shows the state of the hydraulic circuit of FIG. 3 when excavation operation accompanied by assist of the engine 11 by back pressure regeneration is performed. Moreover, the black thick solid line of FIG. 9 represents the flow of the hydraulic fluid which flows into a hydraulic actuator, and represents that the flow volume is so large that the thickness of a solid line is thick. Moreover, the black thick dotted line of FIG. 9 represents the flow of the hydraulic fluid which flows out from a hydraulic actuator.

  Specifically, when the controller 30 determines that the combined excavation operation by the boom raising operation, the arm closing operation, and the bucket closing operation is performed, the controller 30 sets the switching valve 62A to the second position, as indicated by a black thick dotted line. The hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 is directed to the supply side of the pump / motor 14A. Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172A by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172A is opened to the maximum, and the flow control valve Reduce pressure loss at 172A. Further, the controller 30 causes the hydraulic oil tank T to discharge the hydraulic oil flowing out from the rod side oil chamber of the bucket cylinder 9 through the flow rate control valve 173.

  Thereafter, the controller 30 controls the amount of hydraulic oil absorbed (push-out volume) by the pump motor 14 </ b> A as a hydraulic motor so that the operation speed of the boom cylinder 7 becomes a speed corresponding to the operation amount of the boom operation lever.

  Further, for example, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 may control the rod side oil chamber of the boom cylinder 7. At least a part of the hydraulic oil flowing out of the hydraulic oil is discharged to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62B to an intermediate position between the first position and the second position, or completely switches the switching valve 62B to the first position, so that the rod side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T. The controller 30 may block the communication between the rod-side oil chamber of the boom cylinder 7 and the pump / motor 14A by setting the switching valve 62A to the third position (neutral position) as necessary. 9 represents that the hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 is discharged to the hydraulic oil tank T when the switching valve 62B is switched to the first position. .

  As described above, the controller 30 additionally realizes the following effects in addition to the effects described in [Excavation Operation].

  Specifically, when the boom raising operation is performed, the controller 30 generates the back pressure by rotating the pump motor 14A with the hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7. Therefore, the excavator according to the embodiment of the present invention can use the rotational torque obtained when generating the back pressure for assisting the engine 11. As a result, it is possible to realize energy saving by reducing the engine output by the amount of the assist output, speeding up the operation and shortening the cycle time by adding the assist output to the engine output and increasing the output of the hydraulic pump. 9 indicates that the rotational torque is transmitted to the rotating shaft of the engine 11 via the transmission 13 and can be used as the driving force of the first pump 14L and the second pump 14R.

Further, since the controller 30 generates the back pressure by rotating the pump / motor 14A, it is not necessary to restrict the flow of hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 with a restriction, and the pressure loss is reduced with the restriction. It is not generated. Therefore, it is possible to suppress or prevent the hydraulic energy of the hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 from being consumed as heat energy, and to suppress or prevent energy loss.

[Drilling operation with accumulator assist]
Next, with reference to FIG. 10, the state of the hydraulic circuit in FIG. 2 when excavation operation with accumulator assistance is performed will be described. FIG. 10 shows the state of the hydraulic circuit in FIG. 2 when excavation operation with accumulator assistance is performed. Also, the black thick solid line in FIG. 10 represents the flow of hydraulic oil flowing into the hydraulic actuator, and the larger the solid line, the greater the flow rate.

  The accumulator assist is a process of assisting the movement of the hydraulic actuator using the hydraulic oil accumulated in the accumulator 80, and includes a case where the hydraulic actuator is operated using only the hydraulic oil accumulated in the accumulator 80.

  Specifically, when the controller 30 determines that the arm 5 has been operated, the merging valve 55 at the second position is moved in the direction of the first position in accordance with the amount of operation of the arm operation lever, as shown in FIG. Move. Then, the first hydraulic oil and the second hydraulic oil are merged, and the first hydraulic oil and the second hydraulic oil are supplied to the flow rate control valve 171. The flow control valve 171 receives the pilot pressure corresponding to the operation amount of the arm operation lever, moves to the right position in FIG. 10, and causes the first hydraulic oil and the second hydraulic oil to flow into the arm cylinder 8.

  Thereafter, when it is determined that the boom 4 and the bucket 6 are operated, the controller 30 determines whether the excavation operation or the floor excavation operation is performed based on the output of the load pressure sensor.

  When it is determined that the excavation operation is performed, the controller 30 responds to the operation amounts of the boom operation lever and the bucket operation lever based on pump discharge amount control such as negative control control, positive control control, load sensing control, and horsepower control. A discharge amount command value for the second pump 14R is determined. Then, the controller 30 controls the corresponding regulator so that the discharge amount of the second pump 14R becomes the command value.

  Further, the controller 30 calculates a flow rate difference between the maximum discharge amount of the second pump 14R and a discharge amount command value, and causes the pump / motor 14A to discharge hydraulic oil having a flow rate corresponding to the flow rate difference. Specifically, the controller 30 places the switching valve 82 in the first position to allow communication between the accumulator 80 and the pump / motor 14A, and discharges hydraulic oil accumulated in the accumulator 80 toward the pump / motor 14A. .

  Then, when the load pressure of the arm cylinder 8 (the pressure in the bottom side oil chamber) is higher than the accumulator pressure, the controller 30 operates the pump / motor 14A as a hydraulic pump to reduce the pressure of the supply side hydraulic oil (accumulator pressure). The pressure is increased to the load pressure, and the corresponding regulator is controlled so that the discharge amount of the pump motor 14A becomes a flow rate corresponding to the flow rate difference. Compared with the case where the hydraulic oil is sucked from the hydraulic oil tank T, the pump motor 14A that operates as a hydraulic pump can discharge the hydraulic oil with a small pump load. As a result, energy saving can be realized by reducing the load on the engine 11.

  In addition, when the load pressure of the arm cylinder 8 (the pressure of the bottom side oil chamber) is equal to or less than the accumulator pressure, the controller 30 operates the pump motor 14A as a hydraulic motor to reduce the pressure of the supply side hydraulic oil (accumulator pressure). The pressure is reduced to the load pressure, and the corresponding regulator is controlled so that the discharge amount of the pump motor 14A becomes a flow rate corresponding to the flow rate difference. The pump motor 14A that operates as a hydraulic motor can assist the engine 11 and bear a part of the driving force for rotating the first pump 14L. As a result, the controller 30 can increase the absorption horsepower of the first pump 14L, or can suppress the load of the engine 11 and the fuel injection amount when the absorption horsepower is not increased.

  Note that the black dashed-dotted arrow in FIG. 10 indicates that the rotational torque generated by the pump motor 14A operating as a hydraulic motor is transmitted to the rotating shaft of the engine 11 via the transmission 13, and the first pump 14L and the second pump It represents that it can be used as the driving force of the pump 14R. Further, a gray dot-dash line arrow indicates that the pump motor 14 </ b> A operating as a hydraulic pump uses a part of the output of the engine 11.

  Then, the controller 30 directs the third hydraulic oil toward the switching valve 91 with the switching valve 90 in the first position, and directs the third hydraulic oil toward the arm cylinder 8 with the switching valve 91 in the first position.

  Further, the controller 30 controls the opening area of the junction valve 55 based on the above-described flow rate difference, the discharge pressure of the first pump 14L, the discharge pressure of the second pump 14R, and the like. In the example of FIG. 10, the controller 30 determines the opening area of the merging valve 55 with reference to a previously registered opening map, and outputs a command corresponding to the opening area to the merging valve 55. The controller 30 may determine the opening area of the merging valve 55 using a predetermined function instead of the opening map.

  On the other hand, if it is determined that the excavation operation is a floor excavation operation, the controller 30 closes the merging valve 55 as soon as possible as long as the excavator movement does not become unstable. This is to improve the operability of the boom 4 and the bucket 6 by allowing only the second hydraulic oil to flow into the boom cylinder 7 and the bucket cylinder 9.

  In the example of FIG. 10, the maximum discharge amount of the pump / motor 14A is smaller than the maximum discharge amount of the second pump 14R. Therefore, when the above-described flow rate difference exceeds the maximum discharge amount of the pump / motor 14A, the controller 30 operates the pump / motor 14A functioning as a hydraulic pump and the first pump 14L with the maximum discharge amount, 2 The discharge amount of the pump 14R is increased. The difference between the maximum discharge amount of the second pump 14R and the actually increased discharge amount is set to be equal to or less than the maximum discharge amount of the pump motor 14A, and the operating speed of the arm 5 is the first hydraulic oil and the second operation. This is to prevent the operating speed of the arm 5 from being lowered when oil is used.

  However, when the maximum discharge amount of the pump motor 14A is equal to or greater than the maximum discharge amount of the second pump 14R, the controller 30 can maintain the junction valve 55 in the closed state (second position) during the excavation operation. This is because the operating speed of the arm 5 when the first hydraulic oil and the third hydraulic oil are used does not fall below the operating speed of the arm 5 when the first hydraulic oil and the second hydraulic oil are used. In this case, the controller 30 always causes only the first hydraulic oil and the third hydraulic oil to flow into the arm cylinder 8 and allows only the second hydraulic oil to flow into the boom cylinder 7 and the bucket cylinder 9 during the excavation operation. Therefore, the hydraulic oil for moving the arm 5 and the hydraulic oil for moving the boom 4 and the bucket 6 can be completely separated, and the operability of each can be improved.

  Next, with reference to FIG. 11, the state of the hydraulic circuit in FIG. 3 when excavation operation with accumulator assistance is performed will be described. FIG. 11 shows the state of the hydraulic circuit in FIG. 3 when excavation operation with accumulator assistance is performed. In addition, black and gray thick solid lines in FIG. 11 represent the flow of hydraulic oil flowing into the hydraulic actuator, and the larger the solid line thickness, the greater the flow rate. Further, the gray solid line in FIG. 11 additionally indicates that the flow of hydraulic oil can be reduced or eliminated.

  As in the case of the hydraulic circuit of FIG. 10, the controller 30 determines the operation content of the operator on the shovel based on the output of the operation detection unit, and determines the operation state of the shovel based on the output of the load detection unit.

  When the arm 5 is operated, the flow control valve 171A receives the pilot pressure corresponding to the operation amount of the arm operation lever and moves to the left position in FIG. 11, and the flow control valve 171B corresponds to the operation amount of the arm operation lever. It receives the pilot pressure and moves to the right position in FIG.

  When the controller 30 determines that the arm 5 has been operated, the controller 30 sets the variable load check valve 51A to the first position so that the first hydraulic oil reaches the flow control valve 171A through the variable load check valve 51A. Further, the variable load check valve 51B is set to the first position so that the second hydraulic oil reaches the flow control valve 171B through the variable load check valve 51B. The first hydraulic oil that has passed through the flow control valve 171A merges with the second hydraulic oil that has passed through the flow control valve 171B, and flows into the bottom side oil chamber of the arm cylinder 8.

  Thereafter, when it is determined that the boom 4 and the bucket 6 have been operated, the controller 30 determines whether the excavation operation or the floor excavation operation is performed based on the output of the load pressure sensor. When it is determined that the excavation operation is performed, the controller 30 determines a discharge amount command value of the second pump 14R corresponding to the operation amounts of the boom operation lever and the bucket operation lever. Then, the controller 30 controls the corresponding regulator so that the discharge amount of the second pump 14R becomes the command value.

  At this time, the flow control valve 172A receives the pilot pressure corresponding to the operation amount of the boom operation lever and moves to the left position in FIG. Further, the flow control valve 173 receives a pilot pressure corresponding to the operation amount of the bucket operation lever and moves to the right position in FIG. Then, the controller 30 sets the variable load check valve 52A to the first position so that the second hydraulic oil reaches the flow control valve 172A through the variable load check valve 52A. Further, the variable load check valve 53 is set to the first position so that the second hydraulic oil reaches the flow control valve 173 through the variable load check valve 53. The second hydraulic oil that has passed through the flow control valve 172A flows into the bottom side oil chamber of the boom cylinder 7, and the second hydraulic oil that has passed through the flow control valve 173 flows into the bottom side oil chamber of the bucket cylinder 9. To do.

  Further, the controller 30 calculates a flow rate difference between the maximum discharge amount of the second pump 14R and a discharge amount command value, and causes the pump / motor 14A to discharge hydraulic oil having a flow rate corresponding to the flow rate difference. Specifically, the controller 30 places the switching valve 82 in the first position to allow communication between the accumulator 80 and the pump / motor 14A, and discharges hydraulic oil accumulated in the accumulator 80 toward the pump / motor 14A. .

  Then, when the load pressure of the arm cylinder 8 (the pressure in the bottom side oil chamber) is higher than the accumulator pressure, the controller 30 operates the pump / motor 14A as a hydraulic pump to reduce the pressure of the supply side hydraulic oil (accumulator pressure). The pressure is increased to the load pressure, and the corresponding regulator is controlled so that the discharge amount of the pump motor 14A becomes a flow rate corresponding to the flow rate difference. Compared with the case where the hydraulic oil is sucked from the hydraulic oil tank T, the pump motor 14A that operates as a hydraulic pump can discharge the hydraulic oil with a small pump load. As a result, energy saving can be realized by reducing the load on the engine 11.

  In addition, when the load pressure of the arm cylinder 8 (the pressure of the bottom side oil chamber) is equal to or less than the accumulator pressure, the controller 30 operates the pump motor 14A as a hydraulic motor to reduce the pressure of the supply side hydraulic oil (accumulator pressure). The pressure is reduced to the load pressure, and the corresponding regulator is controlled so that the discharge amount of the pump motor 14A becomes a flow rate corresponding to the flow rate difference. The pump motor 14A that operates as a hydraulic motor can assist the engine 11 and bear a part of the driving force for rotating the first pump 14L. As a result, the controller 30 can increase the absorption horsepower of the first pump 14L, or can suppress the load of the engine 11 and the fuel injection amount when the absorption horsepower is not increased.

  Note that the black dot-and-dash line arrow in FIG. 11 indicates that the rotational torque generated by the pump motor 14A operating as a hydraulic motor is transmitted to the rotating shaft of the engine 11 via the transmission 13, and the first pump 14L and the second It represents that it can be used as the driving force of the pump 14R. Further, a gray dot-dash line arrow indicates that the pump motor 14 </ b> A operating as a hydraulic pump uses a part of the output of the engine 11.

  Further, the controller 30 controls the opening area of the variable load check valve 51B based on the flow rate difference, the discharge pressure of the first pump 14L, the discharge pressure of the second pump 14R, and the like. In the example of FIG. 11, the controller 30 determines the opening area of the variable load check valve 51B with reference to the opening map registered in advance, and outputs a command corresponding to the opening area to the variable load check valve 51B. Thereby, the 2nd hydraulic fluid which flows into the bottom side oil chamber of the arm cylinder 8 reduces or lose | disappears. The gray solid line in FIG. 11 indicates that the second hydraulic oil flowing into the bottom side oil chamber of the arm cylinder 8 decreases or disappears as the flow rate of the third hydraulic oil discharged from the pump / motor 14A increases. Represents what to do.

  As described above, the controller 30 additionally realizes the following effects in addition to the effects described in [Excavation operation] and [Excavation operation with engine assist by back pressure regeneration].

Specifically, the controller 30 supplies hydraulic oil accumulated in the accumulator 80 to the pump motor 14A when an excavation operation is performed. Then, it is switched whether the pump / motor 14A is operated as a hydraulic pump or a hydraulic motor, and the displacement of the third hydraulic oil discharged by the pump / motor 14A is controlled by controlling the displacement volume of the pump / motor 14A. Change the pressure. Therefore, regardless of the magnitude relationship between the load pressure of the hydraulic actuator to which the third hydraulic oil is supplied and the accumulator pressure, the third hydraulic oil can flow into the hydraulic actuator. As a result, the flow rate balance between the first hydraulic oil and the third hydraulic oil can be flexibly controlled, and the hydraulic energy accumulated in the accumulator 80 can be efficiently reused.

[Excavation operation with assist of hydraulic actuator by back pressure regeneration]
Next, with reference to FIG. 12, the state of the hydraulic circuit of FIG. 2 in the case where excavation operation with assistance of the hydraulic actuator by back pressure regeneration is performed will be described. FIG. 12 shows the state of the hydraulic circuit in FIG. 2 when excavation operation with assist of the arm cylinder 8 by back pressure regeneration is performed. Moreover, the black thick solid line of FIG. 12 represents the flow of the hydraulic fluid which flows into a hydraulic actuator, and represents that the flow volume is so large that the thickness of a solid line is thick. Moreover, the black and gray thick dotted lines in FIG. 12 represent the flow of hydraulic oil flowing out from the hydraulic actuator.

  Specifically, when the controller 30 determines that the combined excavation operation by the boom raising operation, the arm closing operation, and the bucket closing operation is being performed, the controller 30 determines which hydraulic actuator has a minimum load pressure. When the controller 30 determines that the pressure (load pressure) in the bottom side oil chamber of the boom cylinder 7 is the minimum, the controller 30 sets the switching valve 62 to the second position, as shown by the black thick dotted line, on the rod side of the boom cylinder 7. The hydraulic oil flowing out from the oil chamber is directed to the supply side of the pump / motor 14A. Further, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 172 by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172 is opened to the maximum, and the flow control valve Reduce pressure loss at 172. Further, the controller 30 directs the hydraulic oil flowing out from the rod side oil chamber of the bucket cylinder 9 to the hydraulic oil tank T with the switching valve 63 in the first position.

  Thereafter, the controller 30 controls the amount of hydraulic oil absorbed (push-out volume) by the pump motor 14A so that the operating speed of the boom cylinder 7 becomes a speed corresponding to the operating amount of the boom operating lever. Specifically, when the load pressure of the arm cylinder 8 (pressure in the bottom side oil chamber) is higher than the desired back pressure of the boom cylinder 7 (pressure in the rod side oil chamber), the controller 30 hydraulically controls the pump motor 14A. The pump is operated as a pump to increase the pressure of hydraulic oil on the supply side (pressure in the rod side oil chamber of the boom cylinder 7) to the load pressure of the arm cylinder 8. In addition, when the load pressure of the arm cylinder 8 (pressure in the bottom side oil chamber) is equal to or lower than the desired back pressure of the boom cylinder 7, the controller 30 operates the pump motor 14A as a hydraulic motor to supply hydraulic oil on the supply side. The pressure (pressure in the rod side oil chamber of the boom cylinder 7) is reduced to the load pressure. The controller 30 adjusts the swash plate tilt angle of the pump motor 14A by a regulator to control the displacement volume. For example, when the pump / motor 14A is rotated at a constant speed, the controller 30 can reduce the flow rate of hydraulic fluid flowing out from the rod side oil chamber of the boom cylinder 7 as the push-out volume is reduced. The pressure (back pressure) of the oil chamber can be increased. Using this relationship, the controller 30 can control the back pressure so that the back pressure becomes a pressure commensurate with a desired load pressure of the boom cylinder 7 (pressure in the bottom side oil chamber).

  The hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 generates rotational torque by rotating the pump motor 14A that functions as a hydraulic motor. This rotational torque is transmitted to the rotating shaft of the engine 11 via the transmission 13, and can be used as the driving force of the first pump 14L and the second pump 14R. That is, the rotational torque generated by the pump motor 14A is used to assist the rotation of the engine 11, and has an effect of suppressing the load on the engine 11 and thus the fuel injection amount. For output control of the engine 11, it is desirable to use torque base control.

  In addition, the pump motor 14A functioning as a hydraulic pump sucks in the hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 so that the hydraulic oil can be operated with a smaller pump load than when the hydraulic oil is sucked in from the hydraulic oil tank T. Can be discharged. As a result, energy saving can be realized by reducing the load on the engine 11.

  In FIG. 12, the black dot-and-dash line arrow indicates that the rotational torque generated by the pump motor 14A operating as a hydraulic motor is transmitted to the rotation shaft of the engine 11 via the transmission 13, and the first pump 14L and the second pump It represents that it can be used as the driving force of the pump 14R. Further, a gray dot-dash line arrow indicates that the pump motor 14 </ b> A operating as a hydraulic pump uses a part of the output of the engine 11.

  In addition, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the rod side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62 to an intermediate position between the first position and the second position, or completely switches the switching valve 62 to the first position, so that the rod side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T. The same applies when the CT opening of the flow control valve 172 is large, or when it is no longer necessary to generate a back pressure by applying a load to the boom cylinder 7. Note that the gray thick dotted line in FIG. 12 indicates that the hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 is discharged to the hydraulic oil tank T when the switching valve 62 is moved in the direction of the first position. Represents that.

  Further, when the operating speed of the arm cylinder 8 cannot be controlled to a speed corresponding to the operation amount of the arm operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 sets the merging valve 55 to the first position. The second hydraulic oil discharged from the second pump 14R is caused to flow into the arm cylinder 8.

  In the above description, the case where the pressure (load pressure) in the bottom side oil chamber of the boom cylinder 7 is determined to be minimum will be described. However, the pressure (load pressure) in the bottom side oil chamber of the bucket cylinder 9 is determined to be minimum. The same description applies to the case of the case. Specifically, when the controller 30 determines that the pressure (load pressure) in the bottom side oil chamber of the bucket cylinder 9 is the minimum, the controller 30 sets the switching valve 63 to the second position, and the controller 30 flows out from the rod side oil chamber of the bucket cylinder 9. Direct the oil to the supply side of the pump motor 14A. Further, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 173 by the pressure reducing valve regardless of the operation amount of the bucket operation lever, thereby setting the flow control valve 173 to the maximum opening. Reduce pressure loss at 173. Further, the controller 30 directs the hydraulic oil flowing out from the rod-side oil chambers of the arm cylinder 8 and the boom cylinder 7 to the hydraulic oil tank T with the switching valve 61 and the switching valve 62 set to the first positions, respectively. Further, the operation speed of the bucket cylinder 9 is controlled in the same manner as described above.

  When the controller 30 determines that the pressure (load pressure) in the bottom side oil chamber of the arm cylinder 8 is the minimum, the controller 30 sets the switching valve 61 to the second position and pumps the hydraulic oil flowing out from the rod side oil chamber of the arm cylinder 8.・ Direct toward the supply side of the motor 14A. Further, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 171 by the pressure reducing valve regardless of the operation amount of the arm operation lever so that the flow control valve 171 is opened to the maximum. Reduce pressure loss at 171. Further, the controller 30 directs the hydraulic oil flowing out from the rod-side oil chambers of the boom cylinder 7 and the bucket cylinder 9 to the hydraulic oil tank T with the switching valve 62 and the switching valve 63 being in the first positions. Further, the operating speed of the arm cylinder 8 is also controlled in the same manner as described above.

  Next, referring to FIG. 13, the state of the hydraulic circuit in FIG. 3 in the case where excavation operation with assistance of the hydraulic actuator by back pressure regeneration is performed will be described. FIG. 13 shows the state of the hydraulic circuit of FIG. 3 when excavation operation accompanied by the assist of the arm cylinder 8 by back pressure regeneration is performed. Moreover, the black and gray thick solid lines in FIG. 13 represent the flow of hydraulic oil flowing into the hydraulic actuator, and the larger the solid line thickness, the greater the flow rate. Moreover, the black and gray thick dotted lines in FIG. 13 represent the flow of hydraulic oil flowing out from the hydraulic actuator. Moreover, the thick gray solid line and the thick dotted line in FIG. 13 additionally indicate that the flow of hydraulic oil can be reduced or eliminated.

  Specifically, when the controller 30 determines that the combined excavation operation by the boom raising operation, the arm closing operation, and the bucket closing operation is performed, the controller 30 sets the switching valve 62A to the second position, as indicated by a black thick dotted line. The hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 is directed to the supply side of the pump / motor 14A. Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172A by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172A is opened to the maximum, and the flow control valve Reduce pressure loss at 172A. Further, the controller 30 causes the hydraulic oil tank T to discharge the hydraulic oil flowing out from the rod side oil chamber of the bucket cylinder 9 through the flow rate control valve 173.

  Thereafter, the controller 30 controls the amount of hydraulic oil absorbed (push-out volume) by the pump motor 14A so that the operating speed of the boom cylinder 7 becomes a speed corresponding to the operating amount of the boom operating lever. Specifically, when the load pressure of the arm cylinder 8 (pressure in the bottom side oil chamber) is higher than the desired back pressure of the boom cylinder 7 (pressure in the rod side oil chamber), the controller 30 hydraulically controls the pump motor 14A. The pump is operated as a pump to increase the pressure of hydraulic oil on the supply side (pressure in the rod side oil chamber of the boom cylinder 7) to the load pressure of the arm cylinder 8. In addition, when the load pressure of the arm cylinder 8 (pressure in the bottom side oil chamber) is equal to or lower than the desired back pressure of the boom cylinder 7, the controller 30 operates the pump motor 14A as a hydraulic motor to supply hydraulic oil on the supply side. The pressure (pressure in the rod side oil chamber of the boom cylinder 7) is reduced to the load pressure. The controller 30 adjusts the swash plate tilt angle of the pump motor 14A by a regulator to control the displacement volume.

  The black dot-and-dash line arrow in FIG. 13 indicates that the rotational torque generated by the pump motor 14A operating as a hydraulic motor is transmitted to the rotating shaft of the engine 11 via the transmission 13, and the first pump 14L and the second It represents that it can be used as the driving force of the pump 14R. Further, a gray dot-dash line arrow indicates that the pump motor 14 </ b> A operating as a hydraulic pump uses a part of the output of the engine 11.

  Further, for example, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 may control the rod side oil chamber of the boom cylinder 7. At least a part of the hydraulic oil flowing out of the hydraulic oil is discharged to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62B to an intermediate position between the first position and the second position, or completely switches the switching valve 62B to the first position, so that the rod side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T. The controller 30 may block the communication between the rod-side oil chamber of the boom cylinder 7 and the pump / motor 14A by setting the switching valve 62A to the third position (neutral position) as necessary. 13 indicates that the hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 is discharged to the hydraulic oil tank T when the switching valve 62B is switched to the first position. .

  If the operating speed of the arm cylinder 8 can be controlled to a speed corresponding to the operation amount of the arm operation lever by controlling the displacement of the pump / motor 14A, the controller 30 moves the variable load check valve 51B to the second position. Thus, the flow of the second hydraulic oil into the arm cylinder 8 may be blocked. The gray solid line in FIG. 13 represents that the flow of the second hydraulic oil into the arm cylinder 8 is blocked when the variable load check valve 51B is switched to the second position.

  As described above, the controller 30 additionally realizes the following effects in addition to the effects described in [Excavation operation] and [Excavation operation with engine assist by back pressure regeneration].

Specifically, the controller 30 supplies hydraulic oil flowing out from the rod side oil chamber of the boom cylinder 7 to the pump motor 14A when excavation operation is performed. Then, it is switched whether the pump / motor 14A is operated as a hydraulic pump or a hydraulic motor, and the displacement of the third hydraulic oil discharged by the pump / motor 14A is controlled by controlling the displacement volume of the pump / motor 14A. Change the pressure. Therefore, regardless of the magnitude relationship between the load pressure of the hydraulic actuator to which the third hydraulic oil is supplied and the desired back pressure in the rod side oil chamber of the boom cylinder 7, the third hydraulic oil is allowed to flow into the hydraulic actuator. Can do. As a result, the flow rate balance between the first hydraulic oil and the third hydraulic oil can be flexibly controlled, and the regenerated energy can be efficiently reused.

[Soil removal with engine assist by back pressure regeneration]
Next, referring to FIG. 14, the state of the hydraulic circuit in FIG. 2 in the case where the soil removal operation with the assist of the engine 11 by back pressure regeneration is performed will be described. FIG. 14 shows the state of the hydraulic circuit in FIG. 2 when a soil removal operation with the assist of the engine 11 by back pressure regeneration is performed. Moreover, the black thick solid line of FIG. 14 represents the flow of the hydraulic fluid which flows into a hydraulic actuator, and represents that the flow volume is so large that the thickness of a solid line is thick. Moreover, the black thick dotted line of FIG. 14 represents the flow of the hydraulic fluid which flows out from a hydraulic actuator.

  The earth removal operation is an operation including boom lowering, arm opening, and bucket opening. Further, the boom 4 is lowered by its own weight, and the lowering speed of the boom 4 is controlled by adjusting the flow rate of the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7. Specifically, the lowering speed of the boom 4 increases as the flow rate of the hydraulic oil flowing out from the bottom side oil chamber increases.

  When the boom lowering operation is performed, the flow control valve 172 receives the pilot pressure corresponding to the operation amount of the boom operation lever and moves to the left position in FIG. Further, when the arm opening operation is performed, the flow control valve 171 receives a pilot pressure corresponding to the operation amount of the arm operation lever and moves to the left position in FIG. 14, and when the bucket opening operation is performed, the flow control valve 173. 14 receives the pilot pressure corresponding to the operation amount of the bucket operating lever and moves to the left position in FIG.

  When the controller 30 determines that the boom lowering operation has been performed, the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 with the opening of the regeneration valve 7a maximized as shown in FIG. Let flow into the oil chamber on the rod side.

  When the opening of the regenerative valve 7a is maximized, the pressure in the bottom side oil chamber of the boom cylinder 7 is directly applied to the rod side oil chamber, so that the pressure in the bottom side oil chamber is further increased and installed in the control valve 17. The relief pressure of the released relief valve may be exceeded. Therefore, when the pressure in the bottom oil chamber of the boom cylinder 7 approaches its relief pressure, the controller 30 reduces the opening of the regeneration valve 7a so that the pressure in the bottom oil chamber does not exceed the relief pressure. To.

  Further, the controller 30 sets the switching valve 62 to the second position, and directs the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 toward the supply side of the pump / motor 14A, as shown by a black thick dotted line. Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172 by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172 is opened to the maximum. Reduce pressure loss at 172. In addition, the controller 30 places the variable load check valve 52 in the second position, and blocks communication between the second pump 14R and the flow control valve 172.

  Further, the controller 30 controls the discharge amount of the pump motor 14A according to the operation amount of the boom operation lever and the opening degree of the regeneration valve 7a. Specifically, the controller 30 operates the pump motor 14A as a hydraulic motor, and controls the corresponding regulator so that the pressure in the bottom oil chamber of the boom cylinder 7 does not change suddenly and does not exceed the relief pressure. Thus, the displacement of the pump motor 14A is controlled. Then, the controller 30 sets the switching valve 90 to the second position and causes the hydraulic oil tank T to discharge the third hydraulic oil discharged from the pump motor 14A.

  Further, the controller 30 maintains the merging valve 55 in the second position so as not to merge the first hydraulic oil and the second hydraulic oil, and the movements of the arm cylinder 8 and the bucket cylinder 9 are operated separately. Be controlled independently with oil. In this case, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the arm cylinder 8 can be directly controlled by the first pump 14L, and therefore does not need to be limited by the restriction in the flow rate control valve 171. Similarly, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the bucket cylinder 9 can be directly controlled by the second pump 14R, and therefore does not need to be limited by the restriction in the flow rate control valve 173. Therefore, as in the case of the flow control valve 172 corresponding to the boom cylinder 7, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valves 171 and 173 by the pressure reducing valve, thereby controlling the flow control valves 171 and 173. May be the maximum opening, and the pressure loss at the flow control valves 171 and 173 may be reduced. Note that when a soil removal operation involving an arm opening operation and a bucket opening operation is performed, the arm operation lever and the bucket operation lever are typically full levers (for example, the neutral state of the lever is set to 0%, and the maximum operation state is set). The operation amount is 80% or more of 100%). Therefore, both of the flow control valves 171 and 173 have a maximum opening.

  The hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 generates rotational torque by rotating the pump motor 14A. This rotational torque is transmitted to the rotating shaft of the engine 11 via the transmission 13 as shown by the black dashed-dotted arrow in FIG. 14, and can be used as the driving force of the first pump 14L and the second pump 14R. That is, the rotational torque generated by the pump motor 14A is used to assist the rotation of the engine 11, and has an effect of suppressing the load on the engine 11 and thus the fuel injection amount.

  Further, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the bottom side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62 to an intermediate position between the first position and the second position, or completely switches the switching valve 62 to the first position, so that the bottom side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T.

  Next, referring to FIG. 15, the state of the hydraulic circuit in FIG. 3 in the case where the soil removal operation with the assist of the engine 11 by back pressure regeneration is performed will be described. FIG. 15 shows the state of the hydraulic circuit of FIG. 3 when a soil removal operation with the assist of the engine 11 by back pressure regeneration is performed. Further, the black thick solid line in FIG. 15 represents the flow of hydraulic oil flowing into the hydraulic actuator, and the larger the solid line, the greater the flow rate. Moreover, the black and gray thick dotted lines in FIG. 15 represent the flow of hydraulic oil flowing out from the hydraulic actuator.

  Specifically, when the controller 30 determines that the boom lowering operation has been performed, the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 with the opening of the regeneration valve 7 a being maximized is discharged to the rod side oil chamber of the boom cylinder 7. To flow into.

  Further, the controller 30 sets the switching valve 62A to the first position, and directs hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 toward the supply side of the pump / motor 14A. Further, the controller 30 reduces the pilot pressure acting on the pilot port on the right side of the flow control valve 172A by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172A is in the neutral position, and the boom cylinder 7 The flow of hydraulic oil from the bottom side oil chamber to the hydraulic oil tank T through the flow rate control valve 172A is cut off. In addition, the controller 30 places the variable load check valve 52A in the second position, and blocks communication between the second pump 14R and the flow control valve 172A.

  Further, when the arm opening operation is performed, the flow control valve 171A receives the pilot pressure corresponding to the operation amount of the arm operation lever and moves to the right position in FIG. When the bucket opening operation is performed, the flow control valve 173 receives the pilot pressure corresponding to the operation amount of the bucket operation lever and moves to the left position in FIG.

  Further, when the controller 30 determines that the arm opening operation has been performed, the controller 30 sets the variable load check valve 51A to the first position, and communicates between the first pump 14L and the flow control valve 171A. Further, when the controller 30 determines that the bucket opening operation has been performed, the controller 30 sets the variable load check valve 53 to the first position, and communicates between the second pump 14R and the flow control valve 173.

  Further, the controller 30 controls the discharge amount of the pump motor 14A according to the operation amount of the boom operation lever and the opening degree of the regeneration valve 7a. Specifically, the controller 30 operates the pump / motor 14A as a hydraulic motor and controls the corresponding regulator so that the pressure in the bottom side oil chamber of the boom cylinder 7 does not change suddenly. To control. Then, the controller 30 sets the switching valve 90 to the second position and sets the switching valve 92 to the third position to discharge the third hydraulic oil discharged from the pump motor 14A to the hydraulic oil tank T.

  Further, the controller 30 maintains the variable load check valve 51B in the second position so that the first hydraulic fluid and the second hydraulic fluid do not merge, and the movements of the arm cylinder 8 and the bucket cylinder 9 are different. Independently controlled by hydraulic fluid. In this case, since the flow rate of the hydraulic oil flowing into the rod side oil chamber of the arm cylinder 8 can be directly controlled by the first pump 14L, it is not necessary to be limited by the restriction in the flow rate control valve 171A. Similarly, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the bucket cylinder 9 can be directly controlled by the second pump 14R, and therefore does not need to be limited by the restriction in the flow rate control valve 173. Therefore, as in the case of the flow control valve 172A corresponding to the boom cylinder 7, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 171A by the pressure reducing valve so that the flow control valve 171A becomes the maximum opening. In addition, the pressure loss at the flow control valves 171A and 173 may be reduced by increasing the pilot pressure acting on the pilot port on the left side of the flow control valve 173 with the pressure reducing valve so that the flow control valve 173 becomes the maximum opening.

  The hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 generates rotational torque by rotating the pump motor 14A. This rotational torque is transmitted to the rotating shaft of the engine 11 via the transmission 13 as shown by the black dashed-dotted arrow in FIG. 15, and can be used as the driving force of the first pump 14L and the second pump 14R. That is, the rotational torque generated by the pump motor 14A is used to assist the rotation of the engine 11, and has an effect of suppressing the load on the engine 11 and thus the fuel injection amount.

  Further, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the bottom side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62C to an intermediate position between the first position and the second position, or completely switches the switching valve 62C to the first position, so that the bottom side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T.

  Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172B by the pressure reducing valve regardless of the operation amount of the boom operation lever, so that the flow control valve 172B is set to the left position in FIG. The hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 may be merged with the first hydraulic oil.

  Note that the gray thick dotted line in FIG. 15 indicates that the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 is discharged to the hydraulic oil tank T when the switching valve 62C is moved in the direction of the first position. And when the flow control valve 172B is moved to the left position, the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 joins the first hydraulic oil at the flow control valve 172B.

  As described above, when the boom lowering operation is performed, the controller 30 generates the back pressure by rotating the pump motor 14 </ b> A with the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7. Therefore, the excavator according to the embodiment of the present invention can use the hydraulic energy obtained when the back pressure is generated for assisting the engine 11. As a result, it is possible to realize energy saving by reducing the engine output by the amount of the assist output, speeding up the operation and shortening the cycle time by adding the assist output to the engine output and increasing the output of the hydraulic pump.

  Further, since the controller 30 generates the back pressure by rotating the pump / motor 14A, it is not necessary to restrict the flow of the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 with the restriction, and the pressure loss is reduced with the restriction. It is not generated. Therefore, it can suppress or prevent that the positional energy of the boom 4 is consumed as heat energy, and can suppress or prevent energy loss.

Further, the controller 30 does not cause the first hydraulic oil and the second hydraulic oil to merge even when the boom lowering operation, the arm opening operation, and the bucket opening operation are performed at the same time. Each movement of the cylinder 9 is independently controlled by separate hydraulic oil. Therefore, one of the flow rate of the first hydraulic oil required for moving the arm cylinder 8 and the flow rate of the second hydraulic oil required for moving the bucket cylinder 9 is not affected by the other. . Therefore, it is possible to prevent the hydraulic pump from discharging hydraulic oil more than necessary.

[Soil removal operation with hydraulic actuator assist by back pressure regeneration]
Next, with reference to FIG. 16, the state of the hydraulic circuit of FIG. 2 in the case where the soil removal operation with the assistance of the hydraulic actuator by back pressure regeneration is performed will be described. FIG. 16 shows the state of the hydraulic circuit in FIG. 2 when a soil removal operation with the assist of the arm cylinder 8 by back pressure regeneration is performed. Moreover, the black thick solid line of FIG. 16 represents the flow of the hydraulic fluid which flows into a hydraulic actuator, and represents that the flow volume is so large that the thickness of a solid line is thick. Moreover, the black thick dotted line of FIG. 16 represents the flow of the hydraulic oil which flows out from a hydraulic actuator.

  When the boom lowering operation is performed, the flow control valve 172 receives the pilot pressure corresponding to the operation amount of the boom operation lever and moves to the left position in FIG. When the arm opening operation is performed, the flow control valve 171 receives a pilot pressure corresponding to the operation amount of the arm operation lever and moves to the left position in FIG. 16, and when the bucket opening operation is performed, the flow control valve 173. 16 receives a pilot pressure corresponding to the operation amount of the bucket operation lever and moves to the left position in FIG.

  When the controller 30 determines that the boom lowering operation has been performed, the hydraulic fluid flowing out from the bottom side oil chamber of the boom cylinder 7 with the opening of the regeneration valve 7a maximized as shown by the thick black dotted line. 7 into the oil chamber on the rod side.

  Further, the controller 30 sets the switching valve 62 to the second position, and directs the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 toward the supply side of the pump / motor 14A, as shown by a black thick dotted line. Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172 by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172 is opened to the maximum. Reduce pressure loss at 172. In addition, the controller 30 places the variable load check valve 52 in the second position, and blocks communication between the second pump 14R and the flow control valve 172.

  Further, the controller 30 controls the discharge amount of the pump motor 14A according to the operation amount of the boom operation lever and the opening degree of the regeneration valve 7a. Specifically, when the load pressure of the arm cylinder 8 (the pressure in the rod side oil chamber) is higher than the desired back pressure (the pressure in the bottom side oil chamber) of the boom cylinder 7, the controller 30 hydraulically drives the pump motor 14A. The pump is operated as a pump to increase the pressure of hydraulic oil on the supply side (the pressure in the bottom oil chamber of the boom cylinder 7) to the load pressure of the arm cylinder 8. In addition, when the load pressure of the arm cylinder 8 (pressure in the rod side oil chamber) is equal to or lower than the desired back pressure of the boom cylinder 7, the controller 30 operates the pump motor 14A as a hydraulic motor to supply the hydraulic fluid on the supply side. The pressure (pressure in the rod side oil chamber of the boom cylinder 7) is reduced to the load pressure. Then, the controller 30 controls the displacement volume by adjusting the tilt angle of the swash plate of the pump motor 14A with a corresponding regulator so that the pressure in the bottom oil chamber of the boom cylinder 7 does not change suddenly. For example, when the pump / motor 14A is rotated at a constant speed, the controller 30 can reduce the flow rate of hydraulic fluid flowing out from the bottom side oil chamber of the boom cylinder 7 as the push-out volume is reduced. The pressure (back pressure) of the oil chamber can be increased. Using this relationship, the controller 30 can set the pressure of the hydraulic fluid on the supply side of the pump / motor 14A so that the pressure of the hydraulic fluid on the discharge side of the pump / motor 14A becomes the load pressure of the arm cylinder 8. The pump motor 14 </ b> A can be controlled so as to have a back pressure of ˜. The controller 30 does not adjust the swash plate tilt angle and the rotational speed of the pump / motor 14A, but the pressure of the hydraulic oil on the discharge side of the pump / motor 14A is changed to the load of the arm cylinder 8 by the diversion control using a throttle. The pump / motor 14A may be controlled so that the pressure of the hydraulic oil on the supply side of the pump / motor 14A becomes a desired back pressure. In this case, the swash plate tilt angle of the pump motor 14A may be fixed.

  Compared with the case where the hydraulic oil is sucked from the hydraulic oil tank T, the pump motor 14A that operates as a hydraulic pump can discharge the hydraulic oil with a small pump load. As a result, energy saving can be realized by reducing the load on the engine 11. Further, the controller 30 reduces the discharge amount of the first hydraulic oil discharged by the first pump 14L by the discharge amount of the third hydraulic oil discharged by the pump / motor 14A. As a result, energy saving can be realized by reducing the load on the engine 11 without changing the flow rate of the hydraulic oil flowing into the rod side oil chamber of the arm cylinder 8.

  Further, the pump motor 14A operating as a hydraulic motor can assist the engine 11 and bear a part of the driving force for rotating the first pump 14L. As a result, the controller 30 can increase the absorption horsepower of the first pump 14L, or can suppress the load of the engine 11 and the fuel injection amount when the absorption horsepower is not increased. 16 indicates that the pump motor 14A that operates as a hydraulic pump uses a part of the output of the engine 11. 16 indicates that the pump motor 14A operating as a hydraulic motor assists the engine 11 and bears a part of the driving force of the first pump 14L.

  Then, the controller 30 turns the switching valve 90 to the first position to direct the third hydraulic oil discharged from the pump motor 14A to the switching valve 91, and sets the switching valve 91 to the first position to arm the third hydraulic oil. Turn to cylinder 8.

  Further, the controller 30 maintains the merging valve 55 in the second position so as not to merge the first hydraulic oil and the second hydraulic oil, and the movements of the arm cylinder 8 and the bucket cylinder 9 are operated separately. Be controlled independently with oil. In this case, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the arm cylinder 8 can be directly controlled by the first pump 14L, and therefore does not need to be limited by the restriction in the flow rate control valve 171. Similarly, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the bucket cylinder 9 can be directly controlled by the second pump 14R, and therefore does not need to be limited by the restriction in the flow rate control valve 173. Therefore, as in the case of the flow control valve 172 corresponding to the boom cylinder 7, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valves 171 and 173 by the pressure reducing valve, thereby controlling the flow control valves 171 and 173. May be the maximum opening, and the pressure loss at the flow control valves 171 and 173 may be reduced.

  Further, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the bottom side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62 to an intermediate position between the first position and the second position, or completely switches the switching valve 62 to the first position, so that the bottom side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T.

  Next, referring to FIG. 17, the state of the hydraulic circuit in FIG. 3 when the soil removal operation accompanied by the assist of the hydraulic actuator by back pressure regeneration is performed will be described. FIG. 17 shows the state of the hydraulic circuit of FIG. 3 when a soil removal operation accompanied by the assist of the arm cylinder 8 by back pressure regeneration is performed. Moreover, the black thick solid line of FIG. 17 represents the flow of the hydraulic fluid which flows into a hydraulic actuator, and represents that the flow volume is so large that the thickness of a solid line is thick. Moreover, the black and gray thick dotted lines in FIG. 17 represent the flow of hydraulic oil flowing out from the hydraulic actuator.

  Specifically, when the controller 30 determines that the boom lowering operation has been performed, the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 with the opening of the regeneration valve 7 a being maximized is discharged to the rod side oil chamber of the boom cylinder 7. To flow into.

  Further, the controller 30 sets the switching valve 62A to the first position, and directs hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 toward the supply side of the pump / motor 14A. Further, the controller 30 reduces the pilot pressure acting on the pilot port on the right side of the flow control valve 172A by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172A is in the neutral position, and the boom cylinder 7 The flow of hydraulic oil from the bottom side oil chamber to the hydraulic oil tank T through the flow rate control valve 172A is cut off. In addition, the controller 30 places the variable load check valve 52A in the second position, and blocks communication between the second pump 14R and the flow control valve 172A.

  When the arm opening operation is performed, the flow control valve 171A receives the pilot pressure corresponding to the operation amount of the arm operation lever and moves to the right position in FIG. When the bucket opening operation is performed, the flow control valve 173 receives the pilot pressure corresponding to the operation amount of the bucket operation lever and moves to the left position in FIG.

  Further, when the controller 30 determines that the arm opening operation has been performed, the controller 30 sets the variable load check valve 51A to the first position, and communicates between the first pump 14L and the flow control valve 171A. Further, when the controller 30 determines that the bucket opening operation has been performed, the controller 30 sets the variable load check valve 53 to the first position, and communicates between the second pump 14R and the flow control valve 173.

  Further, the controller 30 controls the discharge amount of the pump motor 14A according to the operation amount of the boom operation lever and the opening degree of the regeneration valve 7a. Specifically, when the load pressure of the arm cylinder 8 (the pressure in the rod side oil chamber) is higher than the desired back pressure (the pressure in the bottom side oil chamber) of the boom cylinder 7, the controller 30 hydraulically drives the pump motor 14A. The pump is operated as a pump to increase the pressure of hydraulic oil on the supply side (the pressure in the bottom oil chamber of the boom cylinder 7) to the load pressure of the arm cylinder 8. In addition, when the load pressure of the arm cylinder 8 (pressure in the rod side oil chamber) is equal to or lower than the desired back pressure of the boom cylinder 7, the controller 30 operates the pump motor 14A as a hydraulic motor to supply the hydraulic fluid on the supply side. The pressure (pressure in the rod side oil chamber of the boom cylinder 7) is reduced to the load pressure. Then, the controller 30 controls the displacement volume by adjusting the tilt angle of the swash plate of the pump motor 14A with a corresponding regulator so that the pressure in the bottom oil chamber of the boom cylinder 7 does not change suddenly. For example, when the pump / motor 14A is rotated at a constant speed, the controller 30 can reduce the flow rate of hydraulic fluid flowing out from the bottom side oil chamber of the boom cylinder 7 as the push-out volume is reduced. The pressure (back pressure) of the oil chamber can be increased. Using this relationship, the controller 30 can set the pressure of the hydraulic fluid on the supply side of the pump / motor 14A so that the pressure of the hydraulic fluid on the discharge side of the pump / motor 14A becomes the load pressure of the arm cylinder 8. The pump motor 14 </ b> A can be controlled so that the back pressure becomes equal to the above.

  Compared with the case where the hydraulic oil is sucked from the hydraulic oil tank T, the pump motor 14A that operates as a hydraulic pump can discharge the hydraulic oil with a small pump load. As a result, energy saving can be realized by reducing the load on the engine 11. Further, the controller 30 reduces the discharge amount of the first hydraulic oil discharged by the first pump 14L by the discharge amount of the third hydraulic oil discharged by the pump / motor 14A. As a result, energy saving can be realized by reducing the load on the engine 11 without changing the flow rate of the hydraulic oil flowing into the rod side oil chamber of the arm cylinder 8.

  Further, the pump motor 14A operating as a hydraulic motor can assist the engine 11 and bear a part of the driving force for rotating the first pump 14L. As a result, the controller 30 can increase the absorption horsepower of the first pump 14L, or can suppress the load of the engine 11 and the fuel injection amount when the absorption horsepower is not increased. 17 indicates that the pump / motor 14A operating as a hydraulic pump uses a part of the output of the engine 11. 17 indicates that the pump motor 14A operating as a hydraulic motor assists the engine 11 and bears a part of the driving force of the first pump 14L.

  Further, the controller 30 maintains the variable load check valve 51B in the second position so that the first hydraulic fluid and the second hydraulic fluid do not merge, and the movements of the arm cylinder 8 and the bucket cylinder 9 are different. Independently controlled by hydraulic fluid. In this case, since the flow rate of the hydraulic oil flowing into the rod side oil chamber of the arm cylinder 8 can be directly controlled by the first pump 14L, it is not necessary to be limited by the restriction in the flow rate control valve 171A. Similarly, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the bucket cylinder 9 can be directly controlled by the second pump 14R, and therefore does not need to be limited by the restriction in the flow rate control valve 173. Therefore, as in the case of the flow control valve 172A corresponding to the boom cylinder 7, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 171A by the pressure reducing valve so that the flow control valve 171A becomes the maximum opening. In addition, the pressure loss at the flow control valves 171A and 173 may be reduced by increasing the pilot pressure acting on the pilot port on the left side of the flow control valve 173 with the pressure reducing valve so that the flow control valve 173 becomes the maximum opening.

  Further, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the bottom side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62C to an intermediate position between the first position and the second position, or completely switches the switching valve 62C to the first position, so that the bottom side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T.

  Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172B by the pressure reducing valve regardless of the operation amount of the boom operation lever, so that the flow control valve 172B is set to the left position in FIG. The hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 may be merged with the first hydraulic oil.

  Note that the gray thick dotted line in FIG. 17 indicates that the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 is discharged to the hydraulic oil tank T when the switching valve 62C is moved in the direction of the first position. And when the flow control valve 172B is moved to the left position, the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 joins the first hydraulic oil at the flow control valve 172B.

  As described above, the controller 30 additionally realizes the following effects in addition to the effects described in the section “Soil discharging operation with engine assist by back pressure regeneration”.

Specifically, the controller 30 switches whether the pump / motor 14A is operated as a hydraulic pump or a hydraulic motor, and controls the displacement of the pump / motor 14A, thereby discharging the pump / motor 14A. The discharge pressure of the third hydraulic oil is changed. Therefore, regardless of the magnitude relationship between the load pressure of the hydraulic actuator to which the third hydraulic oil is supplied and the desired back pressure of the boom cylinder 7, the third hydraulic oil can flow into the hydraulic actuator. As a result, the flow rate balance between the first hydraulic oil and the third hydraulic oil can be flexibly controlled, and the regenerated energy can be efficiently reused.

[Soil removal with accumulator pressure accumulation by back pressure regeneration]
Next, the state of the hydraulic circuit in FIG. 2 in the case where the soil removal operation with accumulator pressure accumulation by back pressure regeneration is performed will be described with reference to FIG. FIG. 18 shows the state of the hydraulic circuit in FIG. 2 when a soil removal operation involving accumulator pressure accumulation by back pressure regeneration is performed. Moreover, the black thick solid line of FIG. 18 represents the flow of the hydraulic oil which flows into a hydraulic actuator, and represents that the flow volume is so large that the thickness of a solid line is thick. Moreover, the black thick dotted line of FIG. 18 represents the flow of the hydraulic oil which flows out from a hydraulic actuator.

  When the boom lowering operation is performed, the flow control valve 172 receives the pilot pressure corresponding to the operation amount of the boom operation lever and moves to the left position in FIG. When the arm opening operation is performed, the flow control valve 171 receives a pilot pressure corresponding to the operation amount of the arm operation lever and moves to the left position in FIG. 18, and when the bucket opening operation is performed, the flow control valve 173 is operated. 18 receives a pilot pressure corresponding to the operation amount of the bucket operation lever and moves to the left position in FIG.

  When the controller 30 determines that the boom lowering operation has been performed, the hydraulic fluid flowing out from the bottom side oil chamber of the boom cylinder 7 with the opening of the regeneration valve 7a maximized as shown by the thick black dotted line. 7 into the oil chamber on the rod side.

  Further, the controller 30 sets the switching valve 62 to the second position, and directs the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 toward the supply side of the pump / motor 14A, as shown by a black thick dotted line. Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172 by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172 is opened to the maximum. Reduce pressure loss at 172. In addition, the controller 30 places the variable load check valve 52 in the second position, and blocks communication between the second pump 14R and the flow control valve 172.

  Further, the controller 30 controls the discharge amount of the pump motor 14A according to the operation amount of the boom operation lever and the opening degree of the regeneration valve 7a. Specifically, when the accumulator pressure is higher than the desired back pressure (the pressure in the bottom side oil chamber) of the boom cylinder 7, the controller 30 operates the pump / motor 14A as a hydraulic pump to increase the pressure of the hydraulic fluid on the supply side. (The pressure in the bottom oil chamber of the boom cylinder 7) is increased to the accumulator pressure. Further, when the accumulator pressure is equal to or lower than the desired back pressure of the boom cylinder 7, the controller 30 operates the pump motor 14A as a hydraulic motor to supply the supply side hydraulic oil pressure (the pressure in the rod side oil chamber of the boom cylinder 7). ) To the accumulator pressure. Then, the controller 30 controls the displacement volume by adjusting the tilt angle of the swash plate of the pump motor 14A with a corresponding regulator so that the pressure in the bottom oil chamber of the boom cylinder 7 does not change suddenly. For example, when the pump / motor 14A is rotated at a constant speed, the controller 30 can reduce the flow rate of hydraulic fluid flowing out from the bottom side oil chamber of the boom cylinder 7 as the push-out volume is reduced. The pressure (back pressure) of the oil chamber can be increased. Using this relationship, the controller 30 ensures that the pressure of the hydraulic oil on the discharge side of the pump / motor 14A becomes the accumulator pressure, and the pressure of the hydraulic oil on the supply side of the pump / motor 14A becomes the desired back pressure. Thus, the pressure of the hydraulic oil can be controlled.

  The pump motor 14 </ b> A that operates as a hydraulic pump can accumulate the accumulator 80 with a small pump load, compared to the case where the hydraulic oil is sucked from the hydraulic oil tank T and accumulated in the accumulator 80. As a result, energy saving can be realized by reducing the load on the engine 11. Further, the pump motor 14A operating as a hydraulic motor can assist the engine 11 and bear a part of the driving force for rotating the first pump 14L. As a result, the controller 30 can increase the absorption horsepower of the first pump 14L, or can suppress the load of the engine 11 and the fuel injection amount when the absorption horsepower is not increased. 18 indicates that the pump / motor 14A operating as a hydraulic pump uses a part of the output of the engine 11. 18 indicates that the pump motor 14A operating as a hydraulic motor assists the engine 11 and bears a part of the driving force of the first pump 14L.

  Then, the controller 30 sets the switching valve 90 to the first position, directs the third hydraulic oil discharged from the pump motor 14A to the switching valve 91, and sets the switching valve 91 to the third position to supply the third hydraulic oil to the accumulator. Turn to 80. In addition, the controller 30 sets the switching valve 81 in the first position to allow communication between the first pump 14L and the accumulator 80.

  Further, the controller 30 maintains the merging valve 55 in the second position so as not to merge the first hydraulic oil and the second hydraulic oil, and the movements of the arm cylinder 8 and the bucket cylinder 9 are operated separately. Be controlled independently with oil. In this case, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the arm cylinder 8 can be directly controlled by the first pump 14L, and therefore does not need to be limited by the restriction in the flow rate control valve 171. Similarly, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the bucket cylinder 9 can be directly controlled by the second pump 14R, and therefore does not need to be limited by the restriction in the flow rate control valve 173. Therefore, as in the case of the flow control valve 172 corresponding to the boom cylinder 7, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valves 171 and 173 by the pressure reducing valve, thereby controlling the flow control valves 171 and 173. May be the maximum opening, and the pressure loss at the flow control valves 171 and 173 may be reduced.

  Further, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the bottom side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62 to an intermediate position between the first position and the second position, or completely switches the switching valve 62 to the first position, so that the bottom of the boom cylinder 7 is reached. At least a part of the hydraulic oil flowing out from the side oil chamber is discharged to the hydraulic oil tank T.

  Next, referring to FIG. 19, the state of the hydraulic circuit in FIG. 3 in the case where the soil discharging operation with accumulator 80 accumulating by back pressure regeneration is performed will be described. FIG. 19 shows the state of the hydraulic circuit in FIG. 3 when a soil removal operation with the assist of the arm cylinder 8 by back pressure regeneration is performed. Moreover, the black thick solid line of FIG. 19 represents the flow of the hydraulic fluid which flows into a hydraulic actuator, and represents that the flow volume is so large that the thickness of a solid line is thick. Further, black and gray thick dotted lines in FIG. 19 represent the flow of hydraulic oil flowing out from the hydraulic actuator.

  Specifically, when the controller 30 determines that the boom lowering operation has been performed, the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 with the opening of the regeneration valve 7 a being maximized is discharged to the rod side oil chamber of the boom cylinder 7. To flow into.

  Further, the controller 30 sets the switching valve 62A to the first position, and directs hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 toward the supply side of the pump / motor 14A. Further, the controller 30 reduces the pilot pressure acting on the pilot port on the right side of the flow control valve 172A by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172A is in the neutral position, and the boom cylinder 7 The flow of hydraulic oil from the bottom side oil chamber to the hydraulic oil tank T through the flow rate control valve 172A is cut off. In addition, the controller 30 places the variable load check valve 52A in the second position, and blocks communication between the second pump 14R and the flow control valve 172A.

  When the arm opening operation is performed, the flow control valve 171A receives the pilot pressure corresponding to the operation amount of the arm operation lever and moves to the right position in FIG. When the bucket opening operation is performed, the flow control valve 173 receives a pilot pressure corresponding to the operation amount of the bucket operation lever and moves to the left position in FIG.

  Further, when the controller 30 determines that the arm opening operation has been performed, the controller 30 sets the variable load check valve 51A to the first position, and communicates between the first pump 14L and the flow control valve 171A. Further, when the controller 30 determines that the bucket opening operation has been performed, the controller 30 sets the variable load check valve 53 to the first position, and communicates between the second pump 14R and the flow control valve 173.

  Further, the controller 30 controls the discharge amount of the pump motor 14A according to the operation amount of the boom operation lever and the opening degree of the regeneration valve 7a. Specifically, when the accumulator pressure is higher than the desired back pressure (the pressure in the bottom side oil chamber) of the boom cylinder 7, the controller 30 operates the pump / motor 14A as a hydraulic pump to increase the pressure of the hydraulic fluid on the supply side. (The pressure in the bottom oil chamber of the boom cylinder 7) is increased to the accumulator pressure. Further, when the accumulator pressure is equal to or lower than the desired back pressure of the boom cylinder 7, the controller 30 operates the pump motor 14A as a hydraulic motor to supply the supply side hydraulic oil pressure (the pressure in the rod side oil chamber of the boom cylinder 7). ) To the accumulator pressure. Then, the controller 30 controls the displacement volume by adjusting the tilt angle of the swash plate of the pump motor 14A with a corresponding regulator so that the pressure in the bottom oil chamber of the boom cylinder 7 does not change suddenly. For example, when the pump / motor 14A is rotated at a constant speed, the controller 30 can reduce the flow rate of hydraulic fluid flowing out from the bottom side oil chamber of the boom cylinder 7 as the push-out volume is reduced. The pressure (back pressure) of the oil chamber can be increased. Using this relationship, the controller 30 ensures that the pressure of the hydraulic oil on the discharge side of the pump / motor 14A becomes the accumulator pressure, and the pressure of the hydraulic oil on the supply side of the pump / motor 14A becomes the desired back pressure. Thus, the pump motor 14A can be controlled.

The pump motor 14 </ b> A that operates as a hydraulic pump can accumulate the accumulator 80 with a small pump load, compared to the case where the hydraulic oil is sucked from the hydraulic oil tank T to accumulate the accumulator 80.
As a result, energy saving can be realized by reducing the load on the engine 11. Further, the pump motor 14A operating as a hydraulic motor can assist the engine 11 and bear a part of the driving force for rotating the first pump 14L. As a result, the controller 30 can increase the absorption horsepower of the first pump 14L, or can suppress the load of the engine 11 and the fuel injection amount when the absorption horsepower is not increased. 19 represents that the pump motor 14A that operates as a hydraulic pump uses a part of the output of the engine 11. 19 indicates that the pump motor 14A operating as a hydraulic motor assists the engine 11 and bears a part of the driving force of the first pump 14L.

  Further, the controller 30 maintains the variable load check valve 51B in the second position so that the first hydraulic fluid and the second hydraulic fluid do not merge, and the movements of the arm cylinder 8 and the bucket cylinder 9 are different. Independently controlled by hydraulic fluid. In this case, since the flow rate of the hydraulic oil flowing into the rod side oil chamber of the arm cylinder 8 can be directly controlled by the first pump 14L, it is not necessary to be limited by the restriction in the flow rate control valve 171A. Similarly, the flow rate of the hydraulic oil flowing into the rod side oil chamber of the bucket cylinder 9 can be directly controlled by the second pump 14R, and therefore does not need to be limited by the restriction in the flow rate control valve 173. Therefore, as in the case of the flow control valve 172A corresponding to the boom cylinder 7, the controller 30 increases the pilot pressure acting on the pilot port on the right side of the flow control valve 171A by the pressure reducing valve so that the flow control valve 171A becomes the maximum opening. In addition, the pressure loss at the flow control valves 171A and 173 may be reduced by increasing the pilot pressure acting on the pilot port on the left side of the flow control valve 173 with the pressure reducing valve so that the flow control valve 173 becomes the maximum opening.

  Further, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the bottom side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62C to an intermediate position between the first position and the second position, or completely switches the switching valve 62C to the first position, so that the bottom side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T.

  Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172B by the pressure reducing valve regardless of the operation amount of the boom operation lever, so that the flow control valve 172B is set to the left position in FIG. The hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 may be merged with the first hydraulic oil.

  Note that the gray thick dotted line in FIG. 19 indicates that the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 is discharged to the hydraulic oil tank T when the switching valve 62C is moved in the direction of the first position. And when the flow control valve 172B is moved to the left position, the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 joins the first hydraulic oil at the flow control valve 172B.

  As described above, the controller 30 has the following effects in addition to the effects described in [Soil discharging operation with assist of engine by back pressure regeneration] and [Soil discharging operation with assist of hydraulic actuator by back pressure regeneration]. Is realized additionally.

Specifically, the controller 30 switches whether the pump / motor 14A is operated as a hydraulic pump or a hydraulic motor, and controls the displacement of the pump / motor 14A, thereby discharging the pump / motor 14A. The discharge pressure of the third hydraulic oil is changed. Therefore, the third hydraulic oil can flow into the accumulator 80 regardless of the magnitude relationship between the pressure of the accumulator 80 to which the third hydraulic oil is supplied and the desired back pressure of the boom cylinder 7. As a result, the positional energy of the boom 4 can be flexibly stored in the accumulator 80 as hydraulic energy, and the stored hydraulic energy can be efficiently reused. Further, when the boom lowering operation is performed and it is not necessary to assist the engine 11 or when it is not necessary to increase the operating speed of the arm cylinder 8, the potential energy of the boom 4 is used as hydraulic energy. It can be stored in the accumulator 80. Moreover, even if the positional energy of the boom 4 is small, it can be stored in the accumulator 80 as hydraulic energy.

[Boom lowering turning deceleration operation with accumulator pressure accumulation]
Next, referring to FIG. 20, the state of the hydraulic circuit in FIG. 2 when the boom lowering turning deceleration operation with accumulator 80 pressure accumulation is performed will be described. FIG. 20 shows the state of the hydraulic circuit in FIG. 2 when the boom lowering turning deceleration operation with accumulator 80 pressure accumulation is performed. 20 represents the flow of hydraulic oil flowing into the accumulator 80, and the black thick dotted line in FIG. 20 represents the flow of hydraulic oil flowing out from the hydraulic actuator.

  The boom lowering turning deceleration operation is an operation including boom lowering and turning deceleration. The upper swing body 3 continues to rotate due to inertia, and the deceleration of the upper swing body 3 is controlled by adjusting the pressure of hydraulic oil on the discharge port side of the swing hydraulic motor 21. Specifically, the deceleration of the upper swing body 3 increases as the pressure of the hydraulic fluid on the discharge port side increases.

  When the boom lowering operation is performed, the flow control valve 172 receives the pilot pressure corresponding to the operation amount of the boom operation lever and moves to the left position in FIG.

  When the controller 30 determines that the boom lowering operation has been performed, the hydraulic fluid flowing out from the bottom side oil chamber of the boom cylinder 7 with the opening of the regeneration valve 7a maximized as shown by the thick black dotted line. 7 into the oil chamber on the rod side.

  Further, the controller 30 sets the switching valve 62 to the second position, and directs the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 toward the supply side of the pump / motor 14A, as shown by a black thick dotted line. Further, the controller 30 increases the pilot pressure acting on the pilot port on the left side of the flow control valve 172 by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172 is opened to the maximum. Reduce pressure loss at 172. In addition, the controller 30 places the variable load check valve 52 in the second position, and blocks communication between the second pump 14R and the flow control valve 172.

  Further, the controller 30 controls the discharge amount of the pump motor 14A according to the operation amount of the boom operation lever and the opening degree of the regeneration valve 7a. Specifically, the controller 30 operates the pump / motor 14A as a hydraulic motor and controls the corresponding regulator so that the pressure in the bottom side oil chamber of the boom cylinder 7 does not change suddenly. To control. Then, the controller 30 sets the switching valve 90 to the second position and causes the hydraulic oil tank T to discharge the third hydraulic oil discharged from the pump motor 14A.

  The controller 30 may direct the third hydraulic oil discharged from the pump / motor 14A to the accumulator 80 or the hydraulic actuator that is operating. Specifically, when the accumulator pressure is higher than the desired back pressure (the pressure in the bottom side oil chamber) of the boom cylinder 7, the controller 30 operates the pump / motor 14A as a hydraulic pump to increase the pressure of the hydraulic fluid on the supply side. (The pressure in the bottom oil chamber of the boom cylinder 7) is increased to the accumulator pressure. Further, when the accumulator pressure is equal to or lower than the desired back pressure of the boom cylinder 7, the controller 30 operates the pump motor 14A as a hydraulic motor to supply the supply side hydraulic oil pressure (the pressure in the rod side oil chamber of the boom cylinder 7). ) To the accumulator pressure. Then, the controller 30 controls the displacement volume by adjusting the tilt angle of the swash plate of the pump motor 14A with a corresponding regulator so that the pressure in the bottom oil chamber of the boom cylinder 7 does not change suddenly. Further, the controller 30 sets the switching valve 90 to the first position to direct the third hydraulic oil discharged from the pump motor 14A to the switching valve 91, and sets the switching valve 91 to the third position to supply the third hydraulic oil to the accumulator. Turn to 80. In this way, the controller 30 ensures that the pressure of the hydraulic oil on the discharge side of the pump / motor 14A becomes the accumulator pressure, and the pressure of the hydraulic oil on the supply side of the pump / motor 14A becomes the desired back pressure. The pump motor 14A is controlled. The same applies to the case where the third hydraulic oil is directed to the operating hydraulic actuator.

  Compared with the case where the hydraulic oil is sucked from the hydraulic oil tank T, the pump motor 14A that operates as a hydraulic pump can discharge the hydraulic oil with a small pump load. As a result, energy saving can be realized by reducing the load on the engine 11. Further, the pump motor 14A operating as a hydraulic motor can generate a rotational torque to assist the engine 11 and bear a part of the driving force for rotating the first pump 14L. As a result, the controller 30 can increase the absorption horsepower of the first pump 14L, or can suppress the load of the engine 11 and the fuel injection amount when the absorption horsepower is not increased.

  In the example of FIG. 20, when the pump / motor 14A is operated as a hydraulic motor and the third hydraulic oil is discharged to the hydraulic oil tank T, the controller 30 is driven by the rotational torque of the pump / motor 14A. Causes the first hydraulic oil discharged from the engine to flow into the accumulator 80. In this case, the controller 30 controls the displacement volume of the first pump 14L by a corresponding regulator so that the discharge pressure of the first pump 14L becomes the accumulator pressure. In addition, the controller 30 sets the switching valve 81 in the first position to allow communication between the first pump 14L and the accumulator 80. 20 indicates that the rotational torque of the pump motor 14A that operates as a hydraulic motor drives the first pump 14L, and the gray solid line in FIG. 20 indicates that the pump motor 14A This represents that the first hydraulic oil of the driven first pump 14 </ b> L flows into the accumulator 80.

  Further, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the bottom side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62 to an intermediate position between the first position and the second position, or completely switches the switching valve 62 to the first position, so that the bottom side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T.

  When the turning deceleration operation is performed, the flow rate control valve 170 moves to the neutral position in FIG. 20 because the operation amount of the turning operation lever decreases and the pilot pressure decreases.

  When the controller 30 determines that the turning deceleration operation has been performed, the regeneration valve 22G is opened and the hydraulic oil on the discharge port 21L side of the turning hydraulic motor 21 is directed to the switching valve 60, as indicated by the thick black dotted line. And let it flow. In addition, the controller 30 sets the switching valve 60 to the second position, and causes the hydraulic oil flowing out from the turning hydraulic motor 21 to flow into the accumulator 80 as indicated by a black thick dotted line.

  Further, the controller 30 adjusts the opening degree of the regeneration valve 22G or the opening degree of the switching valve 60 at the second position according to the pressure of the hydraulic oil on the discharge port 21L side of the turning hydraulic motor 21 and the accumulator pressure. . And the pressure of the hydraulic fluid by the side of the discharge port 21L is controlled so that the desired deceleration torque for stopping the turning of the upper turning body 3 can be generated. The controller 30 detects the pressure of hydraulic fluid on each side of the two ports 21L and 21R of the turning hydraulic motor 21 based on the output of the turning pressure sensor (not shown).

  Further, when the controller 30 determines that the turning deceleration operation has been performed, the controller 30 may set the switching valve 60 to the first position and allow the hydraulic oil flowing out from the turning hydraulic motor 21 to flow into the supply side of the pump / motor 14A. In this case, since the controller 30 generates the braking pressure by rotating the pump motor 14A, it is not necessary to throttle the flow of the hydraulic oil flowing out from the turning hydraulic motor 21, and the pressure loss is generated by the throttle. There is nothing. Therefore, it can suppress or prevent that the inertial energy of the upper revolving body 3 is consumed as heat energy, and can suppress or prevent energy loss.

  Next, referring to FIG. 21, the state of the hydraulic circuit in FIG. 3 when the boom lowering turning deceleration operation with accumulator 80 pressure accumulation is performed will be described. FIG. 21 shows the state of the hydraulic circuit of FIG. 3 when the boom lowering turning deceleration operation with accumulator 80 pressure accumulation is performed. 21 represents the flow of hydraulic oil flowing into the accumulator 80, and the black thick dotted line in FIG. 21 represents the flow of hydraulic oil flowing out from the hydraulic actuator.

  Specifically, when the controller 30 determines that the boom lowering operation has been performed, the hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 with the opening of the regeneration valve 7 a being maximized is discharged to the rod side oil chamber of the boom cylinder 7. To flow into.

  Further, the controller 30 sets the switching valve 62A to the first position, and directs hydraulic oil flowing out from the bottom side oil chamber of the boom cylinder 7 toward the supply side of the pump / motor 14A. Further, the controller 30 reduces the pilot pressure acting on the pilot port on the right side of the flow control valve 172A by the pressure reducing valve regardless of the operation amount of the boom operation lever so that the flow control valve 172A is in the neutral position, and the boom cylinder 7 The flow of hydraulic oil from the bottom side oil chamber to the hydraulic oil tank T through the flow rate control valve 172A is cut off. In addition, the controller 30 places the variable load check valve 52A in the second position, and blocks communication between the second pump 14R and the flow control valve 172A.

  Further, the controller 30 controls the discharge amount of the pump motor 14A according to the operation amount of the boom operation lever and the opening degree of the regeneration valve 7a. Specifically, the controller 30 operates the pump / motor 14A as a hydraulic motor and controls the corresponding regulator so that the pressure in the bottom side oil chamber of the boom cylinder 7 does not change suddenly. To control. The controller 30 turns the switching valve 90 to the second position and turns the switching valve 92 to the first position to direct the third hydraulic oil discharged from the pump motor 14 </ b> A to the replenishment mechanism of the turning hydraulic motor 21.

  The controller 30 may direct the third hydraulic oil discharged from the pump / motor 14A to the accumulator 80 or the hydraulic actuator that is operating. Specifically, when the accumulator pressure is higher than the desired back pressure (the pressure in the bottom side oil chamber) of the boom cylinder 7, the controller 30 operates the pump / motor 14A as a hydraulic pump to increase the pressure of the hydraulic fluid on the supply side. (The pressure in the bottom oil chamber of the boom cylinder 7) is increased to the accumulator pressure. Further, when the accumulator pressure is equal to or lower than the desired back pressure of the boom cylinder 7, the controller 30 operates the pump motor 14A as a hydraulic motor to supply the supply side hydraulic oil pressure (the pressure in the rod side oil chamber of the boom cylinder 7). ) To the accumulator pressure. Then, the controller 30 controls the displacement volume by adjusting the tilt angle of the swash plate of the pump motor 14A with a corresponding regulator so that the pressure in the bottom oil chamber of the boom cylinder 7 does not change suddenly. In addition, the controller 30 sets the switching valve 90 to the first position and the switching valve 92 to the second position, and causes the third hydraulic oil discharged from the pump motor 14 </ b> A to flow into the accumulator 80. In this way, the controller 30 ensures that the pressure of the hydraulic oil on the discharge side of the pump / motor 14A becomes the accumulator pressure, and the pressure of the hydraulic oil on the supply side of the pump / motor 14A becomes the desired back pressure. The pump motor 14A is controlled. The same applies to the case where the third hydraulic oil is directed to the operating hydraulic actuator.

  Compared with the case where the hydraulic oil is sucked from the hydraulic oil tank T, the pump motor 14A that operates as a hydraulic pump can discharge the hydraulic oil with a small pump load. As a result, energy saving can be realized by reducing the load on the engine 11. Further, the pump motor 14A operating as a hydraulic motor can generate a rotational torque to assist the engine 11 and bear a part of the driving force for rotating the first pump 14L. As a result, the controller 30 can increase the absorption horsepower of the first pump 14L, or can suppress the load of the engine 11 and the fuel injection amount when the absorption horsepower is not increased.

  In the example of FIG. 21, when the pump / motor 14A is operated as a hydraulic motor and the third hydraulic oil is discharged to the hydraulic oil tank T, the controller 30 is driven by the rotational torque of the pump / motor 14A. Causes the first hydraulic oil discharged from the engine to flow into the accumulator 80. In this case, the controller 30 controls the displacement volume of the first pump 14L by a corresponding regulator so that the discharge pressure of the first pump 14L becomes the accumulator pressure. In addition, the controller 30 sets the switching valve 81 in the first position to allow communication between the first pump 14L and the accumulator 80. 21 indicates that the rotational torque of the pump motor 14A that operates as a hydraulic motor drives the first pump 14L, and the gray thick solid line in FIG. 21 indicates that the pump motor 14A This represents that the first hydraulic oil of the driven first pump 14 </ b> L flows into the accumulator 80.

  Further, when the operating speed of the boom cylinder 7 cannot be controlled to a speed corresponding to the operation amount of the boom operating lever only by controlling the displacement of the pump / motor 14A, the controller 30 starts from the bottom side oil chamber of the boom cylinder 7. At least a part of the flowing hydraulic oil is directed to the hydraulic oil tank T. Specifically, the controller 30 sets the switching valve 62C to an intermediate position between the first position and the second position, or completely switches the switching valve 62C to the first position, so that the bottom side oil of the boom cylinder 7 is changed. At least part of the hydraulic oil flowing out of the chamber is discharged to the hydraulic oil tank T.

  When the turning deceleration operation is performed, the flow control valve 170 moves to the neutral position in FIG. 21 because the operation amount of the turning operation lever decreases and the pilot pressure decreases.

  When the controller 30 determines that the turning deceleration operation has been performed, the regeneration valve 22G is opened and the hydraulic oil on the discharge port 21L side of the turning hydraulic motor 21 is caused to flow into the accumulator 80 as indicated by the thick black dotted line. .

  Further, the controller 30 adjusts the opening degree of the regeneration valve 22G according to the hydraulic oil pressure and the accumulator pressure on the discharge port 21L side of the turning hydraulic motor 21. And the pressure of the hydraulic fluid by the side of the discharge port 21L is controlled so that the desired deceleration torque for stopping the turning of the upper turning body 3 can be generated.

  In the example of FIG. 21, when the turning deceleration operation is performed, the pressure of the hydraulic oil on the suction port 21R side becomes negative, and the check valve 23R in the supply mechanism supplies hydraulic oil to the suction port 21R side. At this time, the controller 30 sets the switching valve 90 to the second position and the switching valve 92 to the first position so that the third hydraulic oil discharged from the pump motor 14A is directed to the replenishment mechanism of the turning hydraulic motor 21. Yes. Therefore, the check valve 23R can supply the third hydraulic oil discharged from the pump / motor 14A to the suction port 21R side, as indicated by a thick gray dotted line. As a result, the replenishment mechanism does not generate cavitation even when the amount of hydraulic oil in the hydraulic oil tank T decreases and it becomes difficult to suck hydraulic oil from the hydraulic oil tank T. The hydraulic oil can be supplied to the motor 21. Note that the amount of hydraulic fluid in the hydraulic fluid tank T decreases as the amount of hydraulic fluid accumulated in the accumulator 80 increases.

  As described above, the controller 30 performs the [soil discharging operation with the assist of the engine by the back pressure regeneration], [the soil discharging operation with the assist of the hydraulic actuator by the back pressure regeneration], and [accumulator pressure accumulation by the back pressure regeneration]. In addition to the effects described in the accompanying earth removal operation, the following effects are additionally realized.

Specifically, when the boom lowering turning deceleration operation is performed, the controller 30 causes the hydraulic oil flowing out from the turning hydraulic motor 21 to flow into the accumulator 80 and to flow out from the bottom side oil chamber of the boom cylinder 7. Oil flows into the supply side of the pump motor 14A. Therefore, the excavator according to the present embodiment can store the hydraulic energy generated at the time of turning deceleration in the accumulator 80 and can use the hydraulic energy generated at the time of boom lowering for assisting the engine 11. Further, the first pump 14L is driven by assisting the engine 11 using hydraulic energy generated when the boom is lowered, and the first hydraulic oil discharged from the first pump 14L is caused to flow into the accumulator 80. The hydraulic energy generated when the boom is lowered can be stored in the accumulator 80. Therefore, even when the hydraulic energy generated when the boom is lowered is large, by increasing the discharge amount of the first pump 14L and increasing the absorption horsepower of the first pump 14L, all of the hydraulic energy is regenerated. it can.

In the above description, eight states (four states during excavation operation, three states during soil removal operation, and one state during boom lowering turning deceleration operation) are described in the hydraulic circuits of FIGS. 2 and 3. However, the controller 30 determines which state to realize based on the operation amount of the operation lever corresponding to each hydraulic actuator, the load pressure of each hydraulic actuator, the pressure accumulation state of the accumulator 80, and the like.

  For example, when the controller 30 determines that there is no need to generate back pressure in the rod side oil chamber of the boom cylinder 7 during excavation and that sufficient hydraulic fluid is accumulated in the accumulator 80, the accumulator assist An excavation operation involving the above may be performed.

  Further, when the controller 30 determines that it is necessary to generate a back pressure in the rod side oil chamber of the boom cylinder 7 during the excavation operation and the arm cylinder 8 needs to be operated quickly, the back pressure regeneration is performed. The excavation operation with the assistance of the hydraulic actuator may be performed.

  Further, when the controller 30 determines that it is necessary to generate a back pressure in the rod side oil chamber of the boom cylinder 7 during the excavation operation and it is not necessary to operate the arm cylinder 8 quickly, the back pressure regeneration is performed. The excavation operation with the assist of the engine may be performed.

  Further, when the controller 30 determines that it is necessary to generate a back pressure in the bottom oil chamber of the boom cylinder 7 during the soil discharging operation and the arm cylinder 8 needs to be operated quickly, the back pressure is determined. A soil removal operation accompanied by assist of the hydraulic actuator by regeneration may be performed.

  Further, the controller 30 needs to generate a back pressure in the bottom oil chamber of the boom cylinder 7 during the soil discharging operation, and it is not necessary to operate the arm cylinder 8 quickly, and sufficient hydraulic oil is supplied to the accumulator 80. When it is determined that the pressure is accumulated, a soil discharging operation accompanied by engine assist by back pressure regeneration may be performed.

  Further, the controller 30 needs to generate a back pressure in the bottom oil chamber of the boom cylinder 7 during the soil discharging operation, and it is not necessary to operate the arm cylinder 8 quickly, and sufficient hydraulic oil is supplied to the accumulator 80. When it is determined that the pressure is not accumulated, a soil discharging operation accompanied by accumulator pressure accumulation by back pressure regeneration may be performed.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the above-described embodiment, the hydraulic actuator may include a left traveling hydraulic motor (not shown) and a right traveling hydraulic motor (not shown). In this case, the controller 30 may accumulate hydraulic energy at the time of traveling deceleration in the accumulator 80. Further, the turning hydraulic motor 21 may be an electric motor.

  Further, the excavator according to the above-described embodiment includes a motor generator (not shown) that assists the engine 11, and a capacitor (not shown) that accumulates electric power generated by the motor generator and supplies electric power to the motor generator. .), An inverter or the like for controlling the movement of the motor generator may be mounted.

  Further, the pump motor 14A may be driven by a motor generator instead of being driven by the engine 11. In this case, when operating as a hydraulic motor, the pump motor 14 </ b> A may operate the motor generator as a generator with the generated rotational torque to charge the accumulator with the generated power. Further, the motor generator may operate as a motor using the electric power charged in the capacitor, and the pump / motor 14A may be operated as a hydraulic pump.

  DESCRIPTION OF SYMBOLS 1 ... Lower traveling body 2 ... Turning mechanism 3 ... Upper turning body 4 ... Boom 5 ... Arm 6 ... Bucket 7 ... Boom cylinder 8 ... Arm cylinder 9 ... Bucket cylinders 7a, 8a, 9a ... regeneration valves 7b, 8b ... holding valves 10 ... cabin 11 ... engine 13 ... transmission 14A ... pump motor 14L ... first Pump 14R ... Second pump 14aL, 14aR ... Relief valve 17 ... Control valve 21 ... Turning hydraulic motor 21L, 21R ... Port 22L, 22R ... Relief valve 22S ... Shuttle Valve 22G ... Regenerative valve 23L, 23R ... Check valve 30 ... Controller 50, 51, 51A, 51B, 52, 52A, 52B, 53 ... Variable load check valve 55 ... Junction valve 56L, 56R ... Unified bleed-off valve 60, 61, 61A, 62, 62A, 62B, 62C, 63, 81, 82, 90, 91, 92 ... Switching valve 70a ... Relief valve 80 ... Accumulator 170, 171, 171A, 171B, 172, 172A, 172B, 173 ... Flow control valve T ... Hydraulic oil tank

Claims (2)

A first pump for discharging the first hydraulic oil;
A second pump for discharging the second hydraulic oil;
A first hydraulic actuator into which at least the first hydraulic oil can flow;
A second hydraulic actuator into which at least the second hydraulic oil can flow; and
A hydraulic motor that receives hydraulic oil flowing out from the second hydraulic actuator, generates a back pressure of the second hydraulic actuator, and generates a rotational torque;
When the first hydraulic actuator and the second hydraulic actuator operate simultaneously, the first hydraulic actuator is driven by at least the first hydraulic oil, the second hydraulic actuator is driven by at least the second hydraulic oil, The hydraulic motor generates the back pressure to control the operating speed of the second hydraulic actuator, and increases the discharge amount of the first pump or assists the engine by the generated rotational torque;
Excavator. A switching valve for switching between flowing the hydraulic oil flowing out from the second hydraulic actuator to the hydraulic motor or the hydraulic oil tank;
When the first hydraulic actuator and the second hydraulic actuator operate simultaneously, the switching valve causes a part of the hydraulic oil flowing out from the second hydraulic actuator to flow to the hydraulic motor.
The excavator according to claim 1.