JP6292037B2 - Construction machinery - Google Patents

Description

  The present invention relates to a construction machine having a hydraulic cylinder.

  For example, a hydraulic excavator described in Patent Document 1 is known as the construction machine.

  The hydraulic excavator described in Patent Literature 1 includes an arm that is rotatably attached to the tip of a boom, an arm cylinder that rotationally drives the arm, and an arm cylinder that adjusts the supply and discharge of hydraulic oil to and from the arm cylinder. And a back pressure valve provided in a lead-out oil passage that connects the control valve and the tank.

  This hydraulic excavator branches from an oil passage that connects the bottom side chamber of the arm cylinder and the control valve to a quick return oil passage that is connected to the tank without going through a control valve (back pressure valve), and a quick return oil passage. And a quick return valve provided. The quick return valve allows the hydraulic oil to flow in the quick return oil passage only when operating the contraction side of the arm cylinder. When the flow of the hydraulic oil is allowed by the quick return valve, the hydraulic oil is guided to the tank through the quick return oil path having a lower pressure than the outlet oil path having the back pressure valve. Therefore, during operation on the contraction side of the arm cylinder, the flow rate of return oil from the bottom side chamber is larger than the supply flow rate of hydraulic oil to the rod side chamber due to the difference in cross-sectional area between the bottom side chamber and the rod side chamber of the arm cylinder. An increase in the pressure loss of the return oil in the outlet oil passage on the side can be suppressed.

  The hydraulic excavator has a reclaimed oil passage that branches from a portion on the downstream side of the quick return valve in the quick return oil passage and is connected to the rod side chamber of the arm cylinder, and a check valve provided in the reclaimed oil passage. . The check valve only allows the flow of hydraulic oil from the quick return oil passage toward the rod side chamber of the arm cylinder. Thereby, for example, it is possible to suppress cavitation of the arm cylinder when the arm cylinder contracts in the direction in which the weight of the arm acts (when the arm is pushed). Specifically, the pressure in the rod side chamber of the arm cylinder decreases during the above-described contraction operation, but hydraulic fluid is supplied from the quick return oil passage to the rod side chamber of the arm cylinder through the regenerative oil passage and the check valve. Can be suppressed.

JP 2013-137062 A

  However, in the hydraulic excavator described in Patent Document 1, since the regeneration oil passage is directly connected to the tank through the downstream portion of the quick return valve of the quick return oil passage, the primary side of the check valve in the regeneration oil passage The pressure is low.

  Therefore, if the pressure in the rod side chamber of the arm cylinder does not fall below the pressure in the regenerated oil passage, hydraulic oil is not supplied from the quick return oil passage to the rod side chamber, and cavitation of the arm cylinder is effectively prevented. I can't.

  An object of the present invention is to provide a construction machine that can more effectively prevent cavitation of a hydraulic cylinder while reducing pressure loss of hydraulic oil during a contraction operation of the hydraulic cylinder.

In order to solve the above-mentioned problems, the present invention is a construction machine, which is a machine body, a boom attached to the machine body so as to be able to undulate, and a rotating end of the boom so that it can be pushed and pulled. An arm that is attached to the arm, a bucket that is rotatably attached to the tip of the arm, a hydraulic pump that can discharge hydraulic oil, and a hydraulic cylinder that can be expanded and contracted by the hydraulic oil from the hydraulic pump , A hydraulic cylinder provided between the boom and the arm so that the pushing operation of the arm is performed by a contracting operation of the hydraulic cylinder, and the pulling operation of the arm is performed by an extending operation of the hydraulic cylinder; A tank to which hydraulic oil derived from the hydraulic cylinder is guided, supply of hydraulic oil from the hydraulic pump to the hydraulic cylinder, and from the hydraulic cylinder A control valve for controlling the operation of the hydraulic cylinder by adjusting the derivation of the hydraulic oil to the tank, and the hydraulic oil derived from the hydraulic cylinder during the extension operation of the hydraulic cylinder so as to be guided to the tank. A back pressure valve provided in a main return oil passage connecting the control valve and the tank; and hydraulic oil led out from a bottom side chamber of the hydraulic cylinder during the contraction operation of the hydraulic cylinder, bypassing the back pressure valve, A quick return oil path that can be guided to the tank; a reclaimed oil path that connects the quick return oil path and the rod side chamber of the hydraulic cylinder; and the reclaimed oil path that is provided from the quick return oil path to the hydraulic cylinder. A check valve that allows the flow of hydraulic oil toward the rod side chamber while restricting the flow in the opposite direction; and Together provided at a position of the tank side than the connection point of the oil passage, and a pressure increasing device capable of increasing the pressure of the hydraulic fluid in the connection point, and detecting means for detecting the contraction speed of the hydraulic cylinder The pressure raising means includes an electromagnetic opening adjustment valve capable of adjusting an opening area, and a cavitation generation condition set in advance as a condition that the cavitation of the hydraulic cylinder is highly likely to occur. A controller that outputs to the opening adjustment valve a command for adjusting the opening area to be smaller than the opening area when the cavitation generation condition is not satisfied, and the cavitation generation condition is detected by the detection means A construction machine in which the contraction speed of the hydraulic cylinder is set to a condition that is equal to or higher than a preset reference speed is provided. Provide.

  According to the present invention, since the return oil from the hydraulic cylinder can be guided to the tank by bypassing the back pressure valve by the quick return oil passage, it is possible to avoid pressure loss of the return oil in the back pressure valve during the contraction operation of the hydraulic cylinder. Can do.

  In addition, since the pressure of the hydraulic oil at the connection point between the quick return oil passage and the regenerated oil passage can be increased by the pressure increasing means, the pressure on the primary side of the check valve compared to the conventional case without the pressure increasing means. Can be raised. Thereby, it is possible to positively guide the hydraulic oil in the quick return oil passage to the rod side chamber in a situation where the pressure in the rod side chamber of the hydraulic cylinder is relatively high.

Therefore, according to the present invention, it is possible to more effectively prevent cavitation of the hydraulic cylinder while preventing pressure loss of the hydraulic oil during the contraction operation of the hydraulic cylinder.
Specifically, the construction machine includes an airframe, a boom attached to the airframe so as to be raised and lowered, an arm rotatably attached to a tip portion of the boom so as to be capable of pushing and pulling, and an arm. A bucket rotatably attached to the tip of the hydraulic cylinder, wherein the hydraulic cylinder is pushed by the arm by a contraction operation of the hydraulic cylinder, and the arm is pulled by an extension operation of the hydraulic cylinder. It is provided between the boom and the arm so as to operate.
Therefore, when the arm is pushed (the hydraulic cylinder is retracted) with the weight of the arm acting as if the arm is pushed from the state where the arm is pulled toward the boom, the arm It is possible to effectively prevent cavitation of the hydraulic cylinder accompanying an increase in the speed of the pushing operation.
Such an arm pushing operation is frequently performed as a preparatory operation at the time of excavation by the bucket. Therefore, the operability of the excavation work can be significantly improved by effectively preventing cavitation during the preparatory operation.

It said pressure-increasing device of the present invention is adjustable aperture adjustment valve opening area.

As a result , the opening area can be changed between a scene where cavitation is likely to occur and a scene where cavitation is unlikely to occur. Therefore, it is possible to effectively prevent the occurrence of cavitation in a scene where the possibility of cavitation is high while maintaining the original function of the quick return oil passage that reduces pressure loss in a scene where the possibility of cavitation is low. it can.

Specifically, the opening adjustment valve is an electromagnetic valve, and the pressure raising means is configured to cause the cavitation when the cavitation generation condition set in advance as a condition that the cavitation of the hydraulic cylinder is likely to occur is satisfied. condition is that further comprise a controller that outputs to the opening regulating valve a command for adjusting the smaller opening area than the opening area when not satisfied.

Thereby, when the cavitation generation condition is satisfied, the opening area of the opening adjustment valve is adjusted to be small, thereby increasing the pressure on the primary side of the check valve and effectively preventing the occurrence of cavitation. On the other hand, when the cavitation generation condition is not established, the original function of the quick return oil passage is achieved by reducing the return oil pressure loss by adjusting the opening area to be larger than when the cavitation generation condition is established. be able to.

  In the case where it is possible to achieve both prevention of hydraulic oil pressure loss and prevention of cavitation, the pressure raising means has a fixed throttle having an opening area smaller than a cross-sectional area of the quick return oil passage. It may be.

  According to this aspect, the configuration of the construction machine can be further simplified by omitting the configuration for adjusting the opening area (configuration for operating the above-described opening adjusting valve).

In the construction machine, the opening adjustment valve has a position where the opening area is set to the minimum and a fully open position where the opening area is set to the maximum, and the controller, when the cavitation generation condition is satisfied Outputs a command for switching the opening adjustment valve to a position where the opening area is set to the minimum, and outputs a command for switching the opening adjustment valve to the fully opened position when the cavitation generation condition is not satisfied. It is preferable to do.

  ADVANTAGE OF THE INVENTION According to this invention, the cavitation of a hydraulic cylinder can be prevented more effectively, preventing the hydraulic oil pressure loss at the time of the shrinking | contraction operation | movement of a hydraulic cylinder.

1 is a side view showing an overall configuration of a hydraulic excavator according to a first embodiment of the present invention. It is a circuit diagram which shows the hydraulic circuit provided in the hydraulic shovel shown in FIG. It is a flowchart which shows the process performed by the controller shown in FIG. It is a graph which shows the relationship between the command current of the controller of the hydraulic shovel which concerns on 2nd Embodiment of this invention, and the pressure of a rod side chamber. It is a graph which shows the relationship between the command electric current shown in FIG. 4, and the opening area of an opening adjustment valve. It is a circuit diagram which shows the hydraulic circuit of the hydraulic shovel which concerns on 3rd Embodiment of this invention. It is a graph which shows the relationship between the pressure of the rod side chamber of the hydraulic cylinder shown in FIG. 6, and the stroke of an opening adjustment valve. It is a graph which shows the relationship between the stroke of the opening adjustment valve shown in FIG. 7, and the opening area of an opening adjustment valve. It is a circuit diagram which shows the hydraulic circuit of the hydraulic shovel which concerns on 3rd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The following embodiments are examples embodying the present invention, and are not of a nature that limits the technical scope of the present invention.

<First Embodiment (FIGS. 1 to 3)>
Referring to FIG. 1, a hydraulic excavator 1 as an example of a construction machine according to an embodiment of the present invention includes a lower traveling body 2 having a pair of crawlers 2a, and an upper portion provided on the lower traveling body 2 so as to be turnable. A revolving unit 3 and a work machine 4 attached to the upper revolving unit 3 so as to be displaceable are provided. The lower traveling body 2 and the upper swing body 3 correspond to a machine body to which the work machine 4 is attached.

  The work machine 4 is attached to the upper swing body 3 so that it can be raised and lowered (can be raised and lowered), and the work machine 4 is rotatably attached to the tip of the boom 5 so that it can be pushed and pulled. An arm 6 and a bucket 7 rotatably attached to the tip of the arm 6 are provided.

  Further, the work machine 4 includes a boom cylinder 8 that drives the boom 5 up and down relative to the upper swing body 3, an arm cylinder (an example of a hydraulic cylinder) 9 that rotates the arm 6 relative to the boom 5, and an arm 6. A bucket cylinder 10 that rotates the bucket 7 is provided. The arm cylinder 9 is pushed between the boom 5 and the arm 6 so that the arm 6 is pushed by the contraction operation of the arm cylinder 9 and the arm 6 is pulled by the extension operation of the arm cylinder 9. Is provided.

  As shown in FIG. 2, the upper swing body 3 includes a swing motor 11 for driving the upper swing body 3 to rotate relative to the lower traveling body 2, and the swing motor 11 and the cylinders 8 to 10 (in FIG. A hydraulic circuit 12 including a cylinder 9 only) and a controller (pressure raising means) 13 for controlling the hydraulic circuit 12.

  The hydraulic circuit 12 includes a hydraulic pump 14 that can discharge hydraulic oil, a swing control valve 15 that controls driving of the swing motor 11, an arm control valve 16 that controls driving of the arm cylinder 9, the swing motor 11, and And a tank 17 to which hydraulic oil led out from the arm cylinder 9 is guided.

  The hydraulic pump 14 is connected to a center bypass passage provided in the turning control valve 15 and the arm control valve 16 through a tandem oil passage R1, and is connected to a tank 17 through a return oil passage R4. Yes. The return oil passage R4 is provided with a back pressure valve 18 for generating a back pressure on the secondary side of the control valves 15 and 16.

The turning control valve 15 is connected to the hydraulic pump 14 in parallel with the arm control valve 16 via a parallel oil passage R2. Similarly, the arm control valve 16 is connected to the hydraulic pump 14 in parallel with the turning control valve 15 via a parallel oil passage R3. Therefore, the hydraulic oil discharged from the hydraulic pump 14 can be supplied to both control valves 15 and 16 via the parallel oil passages R2 and R3.

  The turning control valve 15 controls the turning drive of the turning motor 11 by adjusting the supply and discharge of hydraulic oil to and from the turning motor 11. Specifically, the turning control valve 15 includes a neutral position (center position in the figure), a right turning position (right position in the figure) for driving the turning motor 11 to turn right, and the turning motor 11 left. It is possible to switch between a left turn position (left position in the figure) for driving to turn in the direction. The turning control valve 15 is a pilot-type switching valve that is normally biased to the neutral position and is switched to the right turning position or the left turning position by supplying the pilot pressure.

  Further, the turning control valve 15 is connected to the right port of the turning motor 11 through the right oil passage R5 and is connected to the left port of the turning motor 11 through the left oil passage R6. The right oil passage R5 and the left oil passage R6 are connected to each other via a connection oil passage R7, and two supply check valves 19a and 19b are provided in the connection oil passage R7. Between the position between the replenishment check valves 19a and 19b of the connecting oil path R7 and the upstream position of the back pressure valve 18 of the return oil path R4, the working oil in the return oil path R4 is placed in the oil paths R5 and R6. A replenishment oil path R8 is provided for replenishment. The replenishment check valve 19a allows the flow of hydraulic oil from the replenishment oil path R8 to the right oil path R5, and the replenishment check valve 19b allows the flow of hydraulic oil from the replenishment oil path R8 to the left oil path R6. . Therefore, at the time of turning braking when the turning control valve 15 is switched to the neutral position, the return oil is supplied to the suction side oil passage (right oil passage R5 or left oil passage R6) of the turning motor 11 via the replenishment oil passage R8. Hydraulic oil can be replenished from the path R4. Here, since the back pressure by the back pressure valve 18 is generated in the return oil path R4, it becomes possible to replenish hydraulic oil promptly during turning braking. In addition, between the turning control valve 15 and the return oil passage R4, it is connected to the return-side oil passage (the right oil passage R5 or the left oil passage R6) while being switched to the right turning position or the left turning position. A return oil passage is provided.

  The arm control valve 16 controls the operation of the arm cylinder 9 by adjusting the supply of hydraulic oil from the hydraulic pump 14 to the arm cylinder 9 and the derivation of hydraulic oil from the arm cylinder 9 to the tank 17. Specifically, the arm control valve 16 includes a neutral position (center position in the figure), a contraction position (right side position in the figure) for performing a contraction operation of the arm cylinder 9 (pushing operation by the arm 6), an arm It is possible to switch between an extension position (left side position in the figure) for executing an extension operation of the cylinder 9 (a pulling operation by the arm 6). The arm control valve 16 is a pilot-type switching valve that is normally urged to a neutral position and is switched to a contracted position or an extended position by supplying a pilot pressure. The pilot circuit of the arm control valve 16 is provided with a pilot sensor 16a capable of detecting a pilot pressure for contracting the arm control valve 16. A detection signal from the pilot sensor 16a is output to the controller 13 described later.

  The arm control valve 16 is connected to the bottom side chamber of the arm cylinder 9 via the bottom side oil passage R9, and is connected to the rod side chamber of the arm cylinder 9 via the rod side oil passage R10. The rod side oil passage R10 is provided with a pressure sensor 20 for detecting the pressure in the rod side chamber of the arm cylinder 9 (pressure in the rod side oil passage R10). A detection signal from the pressure sensor 20 is output to the controller 13 described later.

  Further, the arm control valve 16 is connected to a return oil passage R11 that is connected to the return-side oil passage (rod-side oil passage R10) in a state where the arm control valve 16 is switched to the extended position. . The return oil passage R11 is connected to a position upstream of the back pressure valve 18 in the return oil passage R4. The return oil passages R4 and R11 correspond to main return oil passages that connect the arm control valve 16 and the tank 17 so that the hydraulic oil led out from the arm cylinder 9 is guided to the tank 17 when the arm cylinder 9 extends. To do.

  The arm control valve 16 is connected to a quick return oil passage R12 that is connected to the return-side oil passage (bottom side oil passage R9) in a state where the arm control valve 16 is switched to the contracted position. Yes. The quick return oil path R <b> 12 can guide the hydraulic oil led out from the bottom side chamber of the arm cylinder 9 during the contraction operation of the arm cylinder 9 to the tank 17 by bypassing the back pressure valve 18. Specifically, the quick return oil passage R12 is connected to the tank 17 without passing through the return oil passage R4.

  The quick return oil passage R12 and the rod-side oil passage R10 of the arm cylinder 9 are connected to each other by a regeneration oil passage R13. The regeneration oil path R13 is provided with a check valve 22 that allows the flow of hydraulic oil from the quick return oil path R12 toward the rod-side oil path R10 while restricting the flow in the opposite direction. Accordingly, when the arm cylinder 9 is contracted and the weight of the arm 6 acts, the hydraulic oil can be supplied from the quick return oil path R12 to the rod side oil path R10. Cavitation can be prevented.

  Here, when the regenerated oil passage R13 is directly connected to the tank 17 via the quick return oil passage R12 as in the conventional case, the pressure on the primary side of the check valve 22 is low. Therefore, if the pressure in the rod side oil passage R10 does not fall below the pressure in the regenerated oil passage R13, the hydraulic oil is not supplied from the quick return oil passage R12 to the rod side oil passage R10, and the cavitation of the arm cylinder 9 occurs. Cannot be effectively prevented.

  Therefore, an opening adjustment valve (pressure increasing means) 21 capable of increasing the pressure of the hydraulic oil at the connection point is provided at a position closer to the tank 17 than the connection point of the regeneration oil path R13 of the quick return oil path R12. Yes. The opening adjustment valve 21 is an electromagnetic valve capable of adjusting the opening area. Specifically, the opening adjustment valve 21 is normally urged to the fully open position (left side position in the figure) and is switched from the fully open position to the throttle position (right side position in the figure) by a command current from the controller 13 described later. The opening adjustment valve 21 is a proportional valve whose opening area is adjusted to be small as the command current from the controller 13 increases.

  The controller 13 controls the operation of the opening adjustment valve 21 so as to prevent the occurrence of cavitation during the contraction operation of the arm cylinder 9. Specifically, the controller 13 controls the opening adjustment valve 21 so that the opening area becomes smaller in a situation where cavitation of the arm cylinder 9 is likely to occur than in a situation where the possibility of cavitation is low.

  Hereinafter, processing executed by the controller 13 will be described with reference to FIGS. 2 and 3.

  First, based on the detection result by the pilot sensor 16a, it is determined whether or not an arm pushing operation by an operation lever (not shown) has been performed (whether or not the arm control valve 16 has been switched to the retracted position) (step S1). ). When it is determined that the arm pushing operation is not performed, the quick return oil passage R12 is closed (not used) by the arm control valve 16, and therefore the opening adjustment valve 21 is switched to the throttle position (the command current The maximum value is output: Step S3).

  On the other hand, if it is determined in step S1 that the arm pressing operation has been performed, it is determined whether or not a cavitation generation condition set in advance as a condition that the cavitation is likely to occur in the arm cylinder 9 is satisfied. (Step S2).

  The cavitation generation condition is set such that the pressure in the rod side oil passage R10 of the arm cylinder 9 is equal to or lower than a preset reference pressure. In step S2, the controller 13 determines whether or not the pressure in the rod side oil passage R10 detected by the pressure sensor 20 is equal to or lower than the reference pressure. The cavitation generation condition is not limited to the pressure in the rod-side oil passage R10, and can be set to a condition in which, for example, the contraction speed of the arm cylinder 9 is equal to or higher than a preset reference speed. In this case, instead of the pressure sensor 20, a means (stroke sensor or potentiometer) for detecting the contraction speed of the arm cylinder 9 is required.

  If it is determined that the cavitation generation condition is satisfied (YES in step S2), the opening adjustment valve 21 is switched to the throttle position in step S3 (step S3). That is, in step S3, the opening area is set to the minimum, thereby generating a back pressure in the quick return oil passage R12 (the pressure on the primary side of the check valve 22 increases). As a result, the hydraulic oil is guided from the quick return oil path R12 to the rod-side oil path R10 that tends to run out of hydraulic oil. Therefore, cavitation of the arm cylinder 9 can be effectively prevented.

  On the other hand, if it is determined in step S2 that the cavitation generation condition is not satisfied, the opening adjustment valve 21 is switched to the fully open position (the minimum value of the command current is output: step S4). That is, the opening area is set to the maximum. Thereby, the original function of the quick return oil passage R12 that reduces the pressure loss of the return oil when the arm cylinder 9 is contracted can be realized.

  After execution of steps S3 and S4, the process returns to step S1.

  As described above, the return oil from the arm cylinder 9 can be guided to the tank 17 by bypassing the back pressure valve 18 by the quick return oil passage R12, so that the return oil in the back pressure valve 18 is retracted when the arm cylinder 9 is contracted. Can be avoided.

  Further, since the pressure of the hydraulic oil at the connection point between the quick return oil passage R12 and the regenerated oil passage R13 can be increased by the opening adjustment valve 21, the check valve 22 is compared with the conventional case without the opening adjustment valve 21. The primary side pressure can be increased. Thereby, the hydraulic oil in the quick return oil passage R12 can be actively guided to the rod side chamber in a situation where the pressure in the rod side chamber of the arm cylinder 9 is relatively high.

  Therefore, cavitation of the arm cylinder 9 can be more effectively prevented while preventing pressure loss of the hydraulic oil during the contracting operation.

  Moreover, according to 1st Embodiment, there can exist the following effects.

  Since the opening adjusting valve 21 is provided, the opening area can be changed between a scene where cavitation is highly likely to occur and a scene where cavitation is unlikely to occur. Therefore, it is possible to effectively prevent the occurrence of cavitation in a scene where cavitation is highly likely to occur while maintaining the original function of the quick return oil passage that reduces pressure loss in a scene where cavitation is unlikely to occur. it can.

  Specifically, when the cavitation generation condition is satisfied (YES in step S2), the opening area of the opening adjustment valve 21 is adjusted to be small so that the pressure on the primary side of the check valve 22 is increased to effectively generate cavitation. Can be prevented. On the other hand, when the cavitation generation condition is not satisfied (NO in step S2), the quick return oil path reduces the pressure loss of the return oil by adjusting the opening area to be larger than that when the cavitation generation condition is satisfied. It can fulfill the original function of R12.

  In the first embodiment, a quick return oil passage R <b> 12 is provided for the boom cylinder 8. Therefore, as in the case where the arm 6 is pushed from the state in which the arm 6 is pulled toward the boom 5, the pushing operation of the arm 6 (hydraulic cylinder contraction operation) is performed with the weight of the arm 6 acting. In this case, it is possible to effectively prevent cavitation of the arm cylinder 9 accompanying an increase in the speed of the pushing operation of the arm 6.

  Since such an arm pushing operation is frequently performed as a preparation operation during excavation by the bucket 7, operability of excavation work can be significantly improved by effectively preventing cavitation during the preparation operation.

<Second Embodiment (FIGS. 4 and 5)>
In the first embodiment, when the cavitation generation condition is satisfied (YES in step S2), the opening adjustment valve 21 is switched to the throttle position in step S3, but depending on the pressure in the rod side oil passage R10. The opening area of the opening adjusting valve 21 can also be set.

  Specifically, as shown in FIG. 4, the controller 13 according to the second embodiment outputs a smaller command current as the pressure in the rod-side oil passage R10 increases. As a result, as shown in FIG. 5, the opening area of the opening adjusting valve 21 can be reduced as the command current increases, that is, as the pressure in the rod side oil passage R10 decreases.

  Therefore, also in the second embodiment, the occurrence of cavitation of the arm cylinder 9 can be effectively prevented while reducing the pressure loss in the quick return oil passage R12 as much as possible.

  In FIG. 4, the command current I0 smaller than the command current I1 and the command current I3 larger than the command current I2 are output even when the individual difference of the opening adjustment valve 21 is taken into account. This is in order to ensure the state that has been set and the state that has been switched to the aperture position.

  That is, the above-mentioned “output a smaller command current as the pressure in the rod-side oil passage R10 increases” includes the case shown in FIG. 4 and conversely, if the individual difference of the opening adjustment valve 21 can be ignored, The controller 13 may output a command current of the command currents I1 and I2.

<Third Embodiment (FIGS. 6 to 8)>
In the first and second embodiments, the electromagnetic opening adjustment valve 21 has been described. However, as shown in FIG. 6, a pilot opening adjustment valve (pressure increasing means) 23 may be employed.

  The opening adjusting valve 23 according to the third embodiment is normally biased to the throttle position (left side position in the figure) and can be switched to the fully open position (right side position in the figure) by supplying pilot pressure. is there.

  The pilot port of the opening adjustment valve 23 and the rod side oil passage R10 of the arm cylinder 9 are connected to each other by a pilot oil passage R14. Thereby, the opening adjustment valve 23 can be switched using the pressure in the rod side oil passage R10 as a pilot pressure.

Specifically, as shown in FIG. 4, the stroke from the throttle position of the opening adjustment valve 23 toward the fully open position increases as the pressure in the rod side oil passage R <b> 10 increases. As shown in FIG. 5, the larger the stroke of the opening adjustment valve 23, the larger the opening area of the opening adjustment valve 23. As a result, the lower the pressure in the rod side oil passage R10, the smaller the opening area of the opening adjustment valve 23. Becomes smaller.

  In FIG. 8, the region where the opening area is constant in the region where the stroke of the opening adjusting valve 23 is smaller than ST1 and the region where ST2 is larger than ST2 is a design error of the opening adjusting valve 23. This is to ensure the state where the opening area is the maximum and the state where the opening area is the minimum, even if considered.

  That is, “the lower the pressure in the rod-side oil passage R10, the smaller the opening area of the opening adjusting valve 23” includes the case shown in FIG. If it can be ignored, the opening area of the opening adjusting valve 23 only needs to increase continuously when the stroke is from 0 to FULL.

  According to the third embodiment, the lower the pressure in the rod side chamber of the arm cylinder 9, that is, the higher the possibility that cavitation occurs, the smaller the opening area of the opening adjustment valve 23, the primary side of the check valve 22. By increasing the pressure, it is possible to effectively prevent the occurrence of cavitation. Moreover, since the controller 13 described above is not necessary, the configuration of the excavator 1 can be simplified.

<Fourth Embodiment (FIG. 9)>
In the first to third embodiments, the opening adjusting valves 21 and 23 capable of adjusting the opening area are exemplified as the pressure increasing means. However, when both the prevention of hydraulic oil pressure loss and the prevention of cavitation can be achieved. As shown in FIG. 9, a fixed throttle 24 may be employed as the pressure raising means.

  In this case, the opening area of the fixed throttle 24 is set smaller than the cross-sectional area of the quick return oil passage R12.

  According to the fourth embodiment, the configuration of the hydraulic excavator 1 can be further simplified by omitting the configuration for adjusting the opening area (configuration for operating the above-described opening adjusting valves 21 and 23). it can.

  In addition, this invention is not limited to embodiment mentioned above, For example, the following aspects can also be employ | adopted.

  The configuration in which the return oil of the arm cylinder 9 is caused to flow through the quick return oil passage R12 through the contracted position (for example, the right position in FIG. 2) of the arm control valve 16 during the contracting operation of the arm cylinder 9 has been described. As disclosed in the publication, a valve for opening and closing the quick return oil passage may be separately provided. In this case, the contracted position of the arm control valve 16 allows connection between the bottom side oil passage R9 and the return oil passage R11, and the quick return oil passage R12 is located at the upstream side of the arm control valve 16 at the bottom side. Branch from oil path R9. Further, at a position upstream of the connection point of the quick return oil path R12 with the regenerated oil path R13, between the state where the flow of hydraulic oil through the quick return oil path R12 is allowed and the state where this flow is restricted. A switchable valve is provided.

  Although the arm cylinder 9 has been illustrated as an example of the hydraulic cylinder, the hydraulic cylinder is not particularly limited as long as it is a hydraulic cylinder that drives a driving object that may move by potential energy when the hydraulic cylinder is contracted.

  Although the hydraulic excavator 1 is illustrated as the construction machine, the present invention can also be applied to other construction machines (crane, demolition machine, etc.).

R4, R11 return oil passage (example of main return oil passage)
R12 Quick return oil passage R13 Reclaimed oil passage 1 Hydraulic excavator (an example of construction machinery)
2 Lower traveling body (an example of the aircraft)
3 Upper revolving structure (an example of the aircraft)
5 Boom 6 Arm 7 Bucket 9 Arm cylinder (example of hydraulic cylinder)
13 Controller (Example of pressure riser)
14 Hydraulic pump 16 Arm control valve (an example of control valve)
17 Tank 18 Back pressure valve 21, 23 Opening adjustment valve (an example of pressure increasing means)
22 Check valve 24 Fixed throttle (an example of pressure increase means)

Claims (3)

A construction machine,
The aircraft,
A boom attached to the airframe in a undulating manner;
An arm rotatably attached to the tip of the boom so that it can be pushed and pulled;
A bucket rotatably attached to the tip of the arm;
A hydraulic pump capable of discharging hydraulic oil;
A hydraulic cylinder that can be expanded and contracted by hydraulic oil from the hydraulic pump, wherein the arm is pushed by a contraction operation of the hydraulic cylinder, and the arm is pulled by an extension operation of the hydraulic cylinder. A hydraulic cylinder provided between the boom and the arm ,
A tank to which hydraulic oil derived from the hydraulic cylinder is guided;
A control valve that controls the operation of the hydraulic cylinder by adjusting the supply of hydraulic oil from the hydraulic pump to the hydraulic cylinder and the derivation of hydraulic oil from the hydraulic cylinder to the tank;
A back pressure valve provided in a main return oil passage that connects the control valve and the tank so that hydraulic oil derived from the hydraulic cylinder is guided to the tank during the extension operation of the hydraulic cylinder;
A quick return oil path capable of guiding the hydraulic oil led out from the bottom side chamber of the hydraulic cylinder during the contraction operation of the hydraulic cylinder to the tank, bypassing the back pressure valve;
A regenerative oil passage connecting the quick return oil passage and the rod side chamber of the hydraulic cylinder;
A check valve that is provided in the regenerative oil passage and that allows the flow of hydraulic oil from the quick return oil passage toward the rod side chamber of the hydraulic cylinder, while restricting the reverse flow;
A pressure increasing means that is provided at a position closer to the tank than the connection point of the regeneration oil path of the quick return oil path, and capable of increasing the pressure of hydraulic oil at the connection point ;
Detecting means for detecting the contraction speed of the hydraulic cylinder ,
The pressure raising means is configured to generate the cavitation when a cavitation generation condition set in advance as a condition that the cavitation of the electromagnetic cylinder and the hydraulic cylinder is highly likely to occur is established. A controller that outputs to the opening adjustment valve a command for adjusting the opening area to be smaller than the opening area when the condition is not satisfied,
The construction machine, wherein the cavitation generation condition is set such that a contraction speed of the hydraulic cylinder detected by the detection means is equal to or higher than a preset reference speed .   The construction machine according to claim 1, wherein the pressure increasing means includes a fixed throttle having an opening area smaller than a cross-sectional area of the quick return oil passage. The opening adjustment valve has a position where the opening area is set to the minimum, and a fully open position where the opening area is set to the maximum,
The controller outputs a command for switching the opening adjustment valve to a position where the opening area is set to a minimum when the cavitation generation condition is satisfied, while the fully open position is not satisfied when the cavitation generation condition is not satisfied. The construction machine according to claim 1 or 2, wherein a command for switching the opening adjusting valve is output to the construction machine.

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