KR102156447B1 - Hydraulic system of construction machinery - Google Patents

Abstract

The present invention relates to a hydraulic system for a construction machine.
In the hydraulic system of a construction machine according to an embodiment of the present invention, when in the driving mode, hydraulic oil discharged from the first main pump is joined to the hydraulic oil discharged from the second main pump, and the combined hydraulic oil is provided to the driving motor to improve driving performance. Improve.
In addition, the hydraulic system of the construction machine according to the embodiment of the present invention, even if a situation in which the control of the first and third control valve units 51 and 53 is not properly controlled for an unknown reason occurs, the first main By limiting the maximum discharge flow rate discharged from the pump, driving overspeed can be prevented, thereby ensuring driving stability, and preventing deterioration of the durability of the driving system.

Description

Hydraulic system of construction machinery

The present invention relates to a hydraulic system of a construction machine, and more particularly, in a hydraulic system provided with a first main pump and a second main pump, the hydraulic oil discharged from the first main pump in the running mode is supplied to the second main pump. The present invention relates to a hydraulic system of a construction machine that combines hydraulic oil discharged from the hydraulic oil and provides the combined hydraulic oil to a driving motor to improve driving performance.

In general, construction machinery is equipped with a power source and a hydraulic system. The power source may be an engine or an electric motor. The hydraulic system consists of a main pump, a main control valve, an actuator, a sub pump and a joystick.

The main pump is operated by the above-described power source to discharge hydraulic oil having a pressure generated toward the main control valve. In addition, a plurality of main pumps may be provided. In addition, the main pump may be a variable displacement type in which the discharge flow rate is variable.

A plurality of control valve units are disposed on the main control valve. Each control valve unit is connected to each actuator by a hydraulic line.

The sub pump is operated by the power source described above to discharge pilot hydraulic oil. The sub-pump may be to maintain a set pressure and a set flow rate. Pilot fluid is provided to the joystick.

The joystick can be operated by an operator, and a control signal is generated when the joystick is operated. The control signal is a signal corresponding to the operating displacement of the joystick. The control signal is provided to the spool of the corresponding control valve unit via pilot hydraulic oil.

That is, when the operator manipulates the joystick, the spool of the control valve unit is moved, thereby providing the above-described high-pressure hydraulic oil to the actuator. The actuator is actuated by the supplied hydraulic oil to perform the desired operation.

The actuator has a linear type of linear actuation, and there is a rotary type of pivot actuation. The linear type actuator may be a boom actuator, an arm actuator, a bucket actuator, or the like. In addition, the rotary type may be a traveling motor or a swing motor of a construction machine.

In addition, the actuator may further include an optional actuator, an outrigger, and a dozer to perform additional functions.

Meanwhile, the above-described main control valve includes a first hydraulic line connected to the first main pump and a second hydraulic line connected to the second main pump. That is, actuators mainly responsible for the first main pump and the second main pump are determined.

For example, an optional control valve unit, a bucket control valve unit, a second boom control valve unit, and a first arm control valve unit may be disposed in the first hydraulic line.

In addition, a travel control valve unit, an optional control valve unit, a swing control valve unit, a first speed boom control valve unit, and a second arm control valve unit may be disposed in the second hydraulic line.

However, the hydraulic system of a general construction machine has the following problems.

When the engine is driven, the first and second main pumps and sub-pumps are driven, and the driving control valve unit receives hydraulic oil from the first main pump.

On the other hand, the construction machine can select either a work mode or a driving mode. The work mode prioritizes work and mainly operates the boom, arm, bucket, and upper body turning. In the driving mode, driving is prioritized, and the driving motor is mainly operated.

When driving is performed by selecting the driving mode, the hydraulic system of a general construction machine is connected to the second main pump and the driving control valve unit, so the hydraulic oil discharged from the first main pump is not utilized for driving and is immediately discharged. There is a problem.

On the other hand, during driving, the engine may be driven at a higher engine speed (rpm) than in the normal working mode, for example, 2,000 rpm in order to supply sufficient hydraulic oil to the driving motor.

That is, the engine speed during driving is relatively very high compared to setting the engine speed to 1,500 rpm to 1,800 rpm during normal operation.

Therefore, in the related art, an engine having a large engine output must be selected so as to output a high rotation speed to satisfy the driving performance, and this has a problem in that fuel efficiency is disadvantageous due to an increase in loss when the engine is driven.

On the other hand, there is a difficulty in determining the main pump volume specification in consideration of both driving performance and work machine performance. For example, when the volume of the traveling motor is determined in consideration of the traveling performance and the traction force, the traveling speed may be designed according to the engine speed and the volume of the main pump.

However, since the volume of the main pump is determined by the performance of the work machine, the engine speed to satisfy the driving speed must be determined regardless of the intention of the designer.

As a result, there is no performance factor for efficiently designing the driving system to meet the driving target performance (traction force and driving speed) of the construction machine, so there is a problem that the driving system efficiency is very bad compared to the work machine efficiency.

On the other hand, as a technology related to the hydraulic system of a conventional construction machine, when in the running mode, the hydraulic oil discharged from the first main pump is joined to the hydraulic oil discharged from the second main pump, and the combined hydraulic oil is provided to the traveling motor. Thus, a technology has been proposed to improve driving performance. Driving is performed by a driving system, which includes a number of components related to driving in addition to a travel motor.

However, in the conventional hydraulic system of a construction machine, for reasons unknown, a problem may occur in the control unit controlled by the current value. If a problem occurs in the control unit, the control of the first main pump may be abnormal, and in particular, when the hydraulic oil discharged from the first main pump merges with the hydraulic oil discharged from the second main pump, the hydraulic oil discharged from the first main pump May be excess.

In other words, there is a problem that driving safety is impaired because there is a concern that the vehicle may run at a higher speed than the driving speed designed by the manufacturer of the construction equipment. In addition, when hydraulic oil is excessively provided to the driving motor, a problem may occur in durability of the driving system.

Japanese Laid-Open Patent Publication No. 2004-27706 (2004.01.29.)

Accordingly, it is an object of the present invention to provide a hydraulic system for a construction machine capable of preventing deterioration in durability of a traveling system while improving the running performance of the construction machine.

The technical problem to be achieved by the present invention is not limited to the technical problem mentioned above, and another technical problem that is not mentioned can be clearly understood by those of ordinary skill in the technical field to which the present invention belongs from the following description. There will be.

The hydraulic system of a construction machine according to the present invention for achieving the above technical problem comprises: first and second main pumps 11 and 12 through which high-pressure hydraulic oil is discharged, respectively; A sub pump 70 from which pilot hydraulic oil is discharged; A first hydraulic line 21 connected to the first main pump 11; A second hydraulic line 22 connected to the second main pump 12; A traveling control valve unit 31 disposed on the second hydraulic line 22 to control the traveling motor 80; A first relief valve 41 disposed on the first hydraulic line 21 to maintain the pressure of the first hydraulic line 21 as a relief pressure; When the driving mode is selected, the first control valve unit 51 is opened to pass the pilot hydraulic oil; A second control valve unit 52 that connects hydraulic oil discharged from the first main pump 11 to the second hydraulic line 22 operated by the pilot hydraulic oil passing through the first control valve unit 51 ); And a shuttle valve 60 for connecting the hydraulic oil having a relatively high pressure to the first regulator 13 of the first main pump 11 by competing with the pressure of the pilot hydraulic oil at both ends.

In addition, in the hydraulic system of a construction machine according to an embodiment of the present invention, the relief pressure set in the first relief valve 41 and the pressure of the pilot hydraulic oil discharged from the sub pump 70 may be set equally. .

In addition, in the hydraulic system of a construction machine according to an embodiment of the present invention, if any one of the first main pump 11 or the second main pump 12 is higher than a set pressure, the first regulator ( It may further include a third control valve unit 53 for reducing the pressure of the hydraulic oil provided to 13).

In addition, in the hydraulic system of a construction machine according to an embodiment of the present invention, the third control valve unit 53 is proportional to the difference between the pump pressure and the set pressure, the hydraulic oil provided to the first regulator 13. It may be an electronic proportional control valve that reduces pressure.

In addition, in the hydraulic system of a construction machine according to an embodiment of the present invention, when the work mode is selected, the first control valve unit 51 connects the spool pressure receiving part of the second control valve unit 52 to the drain tank, The second control valve unit 52 may be to disconnect the connection between the first hydraulic line 21 and the second hydraulic line 22.

Details of other embodiments are included in the detailed description and drawings.

In the hydraulic system of a construction machine according to an embodiment of the present invention made as described above, when in the driving mode, the hydraulic oil discharged from the first main pump is joined to the hydraulic oil discharged from the second main pump, and the combined hydraulic oil is added to the driving motor. By providing it to improve driving performance.

In addition, the hydraulic system of a construction machine according to an embodiment of the present invention, even if a situation in which the control of the first and third control valve units is not properly controlled for an unknown reason occurs, the maximum discharged from the first main pump in the driving mode. By limiting the discharge flow rate, driving overspeed can be prevented, thereby ensuring driving stability, and further, it is possible to prevent the durability of the driving system from deteriorating.

1 is a hydraulic circuit diagram for explaining a working mode in a hydraulic system of a construction machine according to an embodiment of the present invention.
2 is a hydraulic circuit diagram for explaining a driving mode in the hydraulic system of a construction machine according to an embodiment of the present invention.
3 is a hydraulic circuit diagram for explaining when an overload is applied in a driving mode in the hydraulic system of a construction machine according to an embodiment of the present invention.

Advantages and features of the present invention, and a method of achieving them will become apparent with reference to the embodiments described below in detail together with the accompanying drawings.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below are illustratively shown to aid understanding of the present invention, and it should be understood that the present invention may be variously modified and implemented differently from the embodiments described herein. However, in describing the present invention, when it is determined that a detailed description of a related known function or component may unnecessarily obscure the subject matter of the present invention, the detailed description and detailed illustration thereof will be omitted. In addition, the accompanying drawings are not drawn to scale to aid understanding of the invention, but the sizes of some components may be exaggerated.

Meanwhile, terms to be described later are terms set in consideration of functions in the present invention and may vary according to the intention or custom of the producer, so the definition should be made based on the contents throughout the present specification.

The same reference numerals refer to the same elements throughout the specification.

Hereinafter, a hydraulic system of a construction machine according to an embodiment of the present invention will be described with reference to FIG. 1.

1 is a hydraulic circuit diagram for explaining a working mode in a hydraulic system of a construction machine according to an embodiment of the present invention.

The hydraulic system according to the embodiment of the present invention includes first and second main pumps 11 and 12, a main control valve 30, and a sub pump 70.

The first and second main pumps 11 and 12 are operated by power output from the engine 17 to discharge high-pressure hydraulic oil, respectively.

In addition, the first and second main pumps 11 and 12 are provided with respective first and second regulators 13 and 14 to control the swash plate angle. That is, the flow rate and pressure of the hydraulic oil discharged from the first and second main pumps 11 and 12 are controlled by the first and second regulators 13 and 14.

In addition, the first and second main pumps 11 and 12 may be provided to the control unit by measuring the respective pump pressures. Each pump pressure can be detected by the first and second pressure sensors 15 and 16. The first and second pressure sensors 15 and 16 may be disposed on the side where hydraulic oil is discharged from the first and second main pumps 11 and 12, respectively.

The sub pump 70 may be operated by the above-described engine 17 or a separate electric motor. The sub pump 70 discharges the pilot hydraulic oil, and the pressure pc of the pilot hydraulic oil is detected on the discharge side of the sub pump 70. The pilot hydraulic oil is provided to the joystick and generates a control signal corresponding to the operating displacement of the joystick as the joystick is operated, and the control signal is transmitted to the spools of a plurality of control valves provided in the main control valve 30 by the pilot hydraulic oil. Works.

Meanwhile, the first hydraulic line 21 is connected to the first main pump 11. Similarly, the second hydraulic line 22 is connected to the second main pump 12.

The first and second hydraulic lines 21 and 22 are connected to the above-described main control valve 30. The main control valve 30 may be provided with a plurality of control valves therein. To further explain this, a plurality of control valves may be successively disposed on the first hydraulic line 21, and a plurality of control valves may be successively disposed on the second hydraulic line 22. Each of the control valves is operated by pilot hydraulic oil having a control signal formed thereon, and the pilot hydraulic oil is applied to the spool of the corresponding control valve, thereby moving the spool of the corresponding control valve to operate the corresponding actuator.

The travel control valve unit 31 may be one of a plurality of control valves disposed on the second hydraulic line 22 described above. The travel control valve unit 31 controls the travel motor 80.

Meanwhile, the first relief valve 41 may be disposed on the first hydraulic line 21, and similarly, the second relief valve 42 may be disposed on the second hydraulic line 22. In more detail, the first hydraulic line 21 is provided with a plurality of control valves, and the first relief valve 41 described above is disposed at the most downstream. Likewise, the second hydraulic line 22 is provided with a plurality of control valves, and the second relief valve 42 is disposed at the most downstream.

A relief pressure may be set in the above-described first and second relief valves 41 and 42. Accordingly, when an abnormal high pressure is formed in the first hydraulic line 21, the first relief valve 41 is opened, and the first hydraulic line 21 maintains the relief pressure. Likewise, when an abnormal high pressure is formed in the second hydraulic line 22, the second relief valve 42 is opened so that the second hydraulic line 22 maintains the relief pressure. The relief pressure may be 40 kgf/cm ² , for example.

In addition, a first control valve unit 51 is disposed on the pilot hydraulic oil discharge line of the sub pump 70.

On the other hand, the relief pressure set in the above-described first relief valve 41 and the pressure pc of the pilot hydraulic oil discharged from the above-described sub-pump 70 may be set equally.

Accordingly, since the discharge flow rate of the hydraulic pump is the minimum value at the pressure (pc) of the pilot hydraulic oil, the discharge flow rate of the first main pump 11 is minimum when the hydraulic oil discharged from the first and second main pumps 11 and 12 merges. It can be discharged at a flow rate. By maintaining the discharge flow rate of the first main pump 11 to a minimum, the stability of running is improved.

In addition, a second control valve unit 52 is provided on the first hydraulic line 21.

In addition, the third hydraulic line 23 connects the pressure receiving portion of the first control valve unit 51 and the second control valve unit 52. To further explain this, when the first current signal is not input, the first control valve unit 51 is connected to the water pressure portion of the second control valve unit 52 and the drain tank, and the second control valve unit 52 The water pressure unit and the sub pump 70 are disconnected.

Conversely, when the first current signal is input to the first control valve unit 51, the pressure receiving unit of the second control valve unit 52 and the sub pump 70 are connected. That is, when the first control valve unit 51 is opened, the pilot hydraulic oil passes through, and the pilot hydraulic oil acts on the pressure receiving portion of the second control valve unit 52. The above-described first current signal is a signal that determines whether hydraulic oil is joined.

In addition, the fourth hydraulic line 24 connects the second control valve unit 52 and the second hydraulic line 22.

The second control valve unit 52 is operated by the pilot hydraulic oil via the first control valve unit 51 described above. That is, when the pilot hydraulic oil is not provided to the second control valve unit 52, the hydraulic oil discharged from the first main pump 11 flows toward the first relief valve 41 along the first hydraulic line 21. Conversely, when pilot hydraulic oil is provided to the second control valve unit 52, the flow path from the first hydraulic line 21 toward the main control valve 30 is cut off, and the hydraulic oil discharged from the first main pump 11 is It joins the second hydraulic line 22 along the fourth hydraulic line 24.

The fifth and sixth hydraulic lines 25 and 26 are connected to both sides of the shuttle valve 60, respectively. The fifth hydraulic line 25 is connected to the third hydraulic line 23. The sixth hydraulic line 26 is connected to the downstream of the first hydraulic line 21. That is, the sixth hydraulic line 26 is connected at the inlet of the first relief valve 41.

In addition, the shuttle valve 60 is connected to the first regulator 13 by a seventh hydraulic line 27.

Accordingly, the pressure of the pilot hydraulic oil and the relief pressure compete at both ends of the shuttle valve 60, and a hydraulic oil having a relatively higher pressure is selected, and the selected hydraulic oil is applied to the first regulator 13.

On the other hand, the eighth hydraulic line 28 is connected to the seventh hydraulic line 27. A third control valve unit 53 is provided on the eighth hydraulic line 28. The third control valve unit 53 is opened when the pump pressure of either the first main pump 11 or the second main pump 12 is higher than the set pressure. The high or low pump pressure is determined by the controller, and the second current signal is applied to the third control valve unit 53 according to the determined result.

When the third control valve unit 53 is opened, the hydraulic oil of the seventh hydraulic line 27 is drained. Accordingly, when the third control valve unit 53 is opened, the pressure of the seventh hydraulic line 27 is reduced.

Increasing the pump pressure means that a larger work load is applied and a higher hydraulic oil flow rate is required. On the other hand, when the pressure of the seventh hydraulic line 27 decreases, the pressure applied to the first regulator 13 decreases, and the first regulator 13 forms a large swash plate tilt angle of the first main pump 11 The first main pump 11 is controlled to increase the discharge flow rate.

On the other hand, when the pressure applied to the second regulator 14 decreases, the second regulator 13 forms the swash plate tilt angle of the second main pump 12 to increase the second main pump 12 so that the discharge flow rate increases. ) To control.

On the other hand, the third control valve unit 53 may be an electronic proportional control valve. In more detail, the third control valve unit 53 is proportional to the difference between the pump pressure ps1 of the first main pump 11 and the set pressure at the first relief valve 41, and the first regulator 13 It proportionally decreases the pressure of the hydraulic oil supplied to it. Accordingly, when the minimum flow rate is discharged from the first main pump 11, as the load increases, the discharge flow rate can be gradually increased in proportion.

<Work mode>

Hereinafter, a working mode in a hydraulic system according to an embodiment of the present invention will be described with reference to FIG. 1.

When the work mode is selected by the operator's selection, the pilot hydraulic oil is cut off by the first control valve unit 51 and the second control valve unit 52 does not operate.

Accordingly, the hydraulic oil discharged from the first main pump 11 flows toward the first relief valve 41 via the first hydraulic line 21. When the pressure formed in the first hydraulic line 21 is higher than the relief pressure, the first relief valve 41 is opened.

Meanwhile, the hydraulic oil flowing in the first hydraulic line 21 is applied to the shuttle valve 60 via the first hydraulic line 21 and the sixth hydraulic line 26. In the shuttle valve 60, the pressure formed in the sixth hydraulic line 26 and the pressure formed in the fifth hydraulic line 25 compete. Since the fifth hydraulic line 25 is connected to the drain tank, the actual pressure may be atmospheric pressure. have. However, the sixth hydraulic line 26 has a pressure equal to or lower than the relief pressure. Accordingly, the pressure of the sixth hydraulic line 26 is selected for the shuttle valve 60.

Accordingly, the maximum pressure in the sixth hydraulic line 26 is the relief pressure, and this relief pressure is transmitted to the first regulator 13 of the first main pump 11 via the sixth and seventh hydraulic lines 26 and 27 do.

On the other hand, the hydraulic oil discharged from the second main pump 12 is provided to each control control unit provided in the second hydraulic line 22 including the travel control valve unit 31. That is, in the work mode, the spool of the control valve unit corresponding to the adjustment of the joystick is operated to provide high pressure hydraulic oil to the actuator to perform a desired operation.

<driving mode>

Hereinafter, a driving mode will be described with reference to FIG. 2. 2 is a hydraulic circuit diagram for explaining a driving mode in the hydraulic system of a construction machine according to an embodiment of the present invention.

The driving mode may be selected by the operator's selection. When the driving mode is selected, the first current signal is input to the first control valve unit 51. Thereby, the first control valve unit 51 provides pilot hydraulic oil to the pressure receiving portion of the second control valve unit 52 and the shuttle valve 60.

The second control valve unit 52 is switched by the provided pilot hydraulic oil so that the flow path from the first hydraulic line 21 to the main control valve 30 is cut off, and the hydraulic oil discharged from the first main pump 11 is It joins the second hydraulic line 22 along the fourth hydraulic line 24.

That is, since the driving motor 80 can be provided with hydraulic oil of a higher flow rate, driving performance is improved.

On the other hand, in the shuttle valve 60, the relief pressure and the pilot pressure compete. As described above, as the first hydraulic line 21 is disconnected, no pressure or very low pressure is formed in the sixth hydraulic line 26. do. On the other hand, since the pilot hydraulic oil is provided to the fifth hydraulic line, the pressure of the pilot hydraulic oil is formed.

Therefore, in the running mode, the shuttle valve 60 selects the pressure of the fifth hydraulic line 25.

Accordingly, the pilot hydraulic oil is transmitted to the first regulator 13 of the first main pump 11 via the fifth hydraulic line 25, the shuttle valve 60, and the seventh hydraulic line 27.

On the other hand, the pressure of the pilot hydraulic oil is significantly lower than that of the hydraulic oil discharged from the first and second main pumps 11 and 12. For a more specific example, the pressure of the pilot hydraulic oil may be 40kgf/cm ² .

Therefore, in the hydraulic system according to the embodiment of the present invention, the maximum flow rate discharged from the first main pump 11 is limited. In addition, the first control valve 51 is controlled by a current value, and even if any unknown error occurs in the first control valve 51, the pressure to control the first regulator 13 is controlled by the pilot hydraulic oil pressure. Therefore, the driving speed of construction machinery is prevented from overspeeding abnormally, thereby improving driving stability.

In addition, by preventing abnormal speeding, it is possible to prevent abnormal deterioration of the durability of the components related to the driving system.

<Driving mode-Overload>

Hereinafter, a case where an overload is applied to driving in the driving mode will be described with reference to FIG. 3. 3 is a hydraulic circuit diagram for explaining when an overload is applied in a driving mode in a hydraulic system of a construction machine according to an embodiment of the present invention.

When construction equipment is running, it can travel uphill. In this case, a more hydraulic oil flow rate may be required from the driving motor 80.

On the other hand, when a load is applied to the traveling motor 80, the pump pressure of the first main pump 11 or the second main pump 12 increases. The pump pressure may be detected as ps1 pressure by the first pressure sensor 15 and as ps2 pressure by the second pressure sensor 16.

When the pump pressure of the first main pump 11 or the second main pump 12 increases, the third control valve unit 53 is opened.

When the third control valve unit 53 is opened, the hydraulic oil of the seventh and eighth hydraulic lines 27 and 28 is drained, so that the pressure of the seventh and eighth hydraulic lines 27 and 28 is lowered. To further explain this, it means that the pressure applied to the first regulator 13 is lower than the pressure of the pilot hydraulic oil.

As the pressure applied to the first regulator 13 decreases, the swash plate angle of the first main pump 11 increases, thereby increasing the discharge flow rate of hydraulic oil from the first main pump 11.

Further, as the flow rate of the hydraulic oil discharged from the first main pump 11 is increased, the increased hydraulic oil is joined from the first hydraulic line 21 to the second hydraulic line 22 and provided to the traveling motor 80. Therefore, even if the driving load is increased, such as climbing uphill, more hydraulic oil can be provided to the driving motor 80, so that the driving performance can be maintained satisfactorily.

On the other hand, the third control valve 53 is controlled by the current value, and even if any unknown error occurs in the third control valve 53, the pressure to control the first regulator 13 is controlled by the pilot hydraulic oil pressure. Therefore, the driving speed of construction machinery is prevented from overspeeding abnormally, thereby improving driving stability.

In addition, by preventing abnormal speeding, it is possible to prevent abnormal deterioration of the durability of the components related to the driving system.

As described above, in the hydraulic system of a construction machine according to an embodiment of the present invention, the hydraulic oil discharged from the first main pump 11 joins and merges the hydraulic oil discharged from the second main pump 12 in the running mode. It is possible to improve the driving performance by providing the hydraulic oil to the driving motor 80.

In addition, the hydraulic system of the construction machine according to the present invention is the first main pump 11 in the running mode even if a situation in which the control of the first and third control valve units 51 and 53 is not properly controlled for an unknown reason occurs. ) By limiting the maximum discharge flow rate discharged from the vehicle, it is possible to prevent overspeed driving, thereby ensuring driving stability, and further preventing the durability of the driving system from deteriorating.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains can understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features. will be.

Therefore, the embodiments described above are to be understood as illustrative and non-limiting in all respects, and the scope of the present invention is indicated by the claims to be described later, and from the meaning and scope of the claims and the concept of equivalents thereof. All changes or modified forms derived should be interpreted as being included in the scope of the present invention.

The hydraulic system of a construction machine according to the present invention can be used to improve the running performance of the construction machine.

11, 12: first and second main pumps
13, 14: 1st and 2nd regulator
15, 16: first and second pressure sensors
17: engine
21, 22, 23, 24, 25, 26, 27, 28: hydraulic lines 1 to 8
30: main control valve (MCV)
31: drive control valve unit
41, 42: first and second relief valves
51, 52, 53: 1st, 2nd, 3rd control valve unit
60: shuttle valve
70: sub pump
80: drive motor

Claims (5)

First and second main pumps 11 and 12 through which high-pressure hydraulic oil is discharged, respectively;
A sub pump 70 from which pilot hydraulic oil is discharged;
A first hydraulic line 21 connected to the first main pump 11;
A second hydraulic line 22 connected to the second main pump 12;
A traveling control valve unit 31 disposed on the second hydraulic line 22 to control the traveling motor 80;
A first relief valve 41 disposed on the first hydraulic line 21 to maintain the pressure of the first hydraulic line 21 as a relief pressure;
When the driving mode is selected, the first control valve unit 51 is opened to pass the pilot hydraulic oil;
A second control valve unit 52 that connects hydraulic oil discharged from the first main pump 11 to the second hydraulic line 22 operated by the pilot hydraulic oil passing through the first control valve unit 51 ); And
Shuttle valve 60 for connecting the hydraulic oil having a relatively high pressure to the first regulator 13 of the first main pump 11 by competing with the pressure of the pilot hydraulic oil at both ends
Including,
When the working mode is selected,
The first control valve unit 51 connects the spool pressure receiving part of the second control valve unit 52 to the drain tank,
The second control valve unit (52) disconnects the connection between the first hydraulic line (21) and the second hydraulic line (22).
The method of claim 1
The relief pressure set in the first relief valve 41 and
Hydraulic system of a construction machine, characterized in that the pressure of the pilot hydraulic oil discharged from the sub pump 70 is set equally
The method of claim 1,
A third control valve unit for reducing the pressure of hydraulic oil provided to the first regulator 13 when any one of the first main pump 11 or the second main pump 12 is higher than a set pressure (53);
Hydraulic system of a construction machine further comprising a.
The method of claim 3,
The third control valve unit 53 is an electronic proportional control valve for reducing the pressure of hydraulic oil provided to the first regulator 13 in proportion to the difference between the pump pressure and the set pressure. Hydraulic system
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