KR20150121506A - Hydraulic system of construction machinery - Google Patents

Abstract

The present invention relates to a hydraulic system for a construction equipment. According to the embodiment of the present invention, the hydraulic system for the construction equipment improves a driving performance by enabling a hydraulic fluid discharged from a first main pump in a driving mode to meet the hydraulic fluid discharged from a second main pump, and provides a hydraulic oil met in a driving motor. The hydraulic system for the construction equipment in accordance to the embodiment of the present invention prevents speeding by limiting a maximum discharge rate discharged from the first main pump in the driving mode even if a first control valve unit (51) and a third control valve unit (53) cannot be correctly controlled due to an unknown reason. As such, the hydraulic system for the construction equipment obtains stability, and prevents degradation of durability of a driving system.

Description

[0001] Hydraulic system of construction machine [0002]

The present invention relates to a hydraulic system of a construction machine. More particularly, the present invention relates to a hydraulic system having a first main pump and a second main pump, To a hydraulic system of a construction machine that improves the running performance by providing hydraulic oil that joins to the traveling motor.

Generally, a construction machine 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 the working hydraulic fluid to the main control valve side. Further, the main pump may be provided in plural. Further, the main pump may be a variable capacity type in which the discharge flow rate is variable.

A plurality of control valve units are arranged in the main control valve. Each control valve unit is connected to the hydraulic line of each actuator.

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

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

That is, when the operator operates the joystick, the spool of the control valve unit is moved, whereby the above-mentioned high-pressure hydraulic fluid is supplied to the actuator. The actuator is operated by the supplied hydraulic fluid to perform the desired operation.

The actuator has a linear type that operates linearly, and a rotary type that operates swivel. The linear type actuator may be a boom actuator, a female actuator, a bucket actuator, or the like. The rotary type may be a running motor of a construction machine, a swing motor, or the like.

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

The 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, the first main pump and the second main pump mainly define the actuators to take charge.

For example, the first hydraulic line may be provided with an option control valve unit, a bucket control valve unit, a boom second-speed control valve unit, and a first-speed control valve unit.

In addition, the second hydraulic line may be provided with a travel control valve unit, an option control valve unit, a swing control valve unit, a boom first-speed control valve unit, and a second-speed control valve unit.

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 drive control valve unit is supplied with the hydraulic oil from the first main pump.

On the other hand, the construction machine can select either the working mode or the traveling mode. Work mode is work priority, boom, arm, bucket, upper body turn, etc. mainly operate. The driving mode is primarily for driving, which mainly drives the traveling motor.

When the traveling mode is selected and the traveling is performed, the hydraulic system of the general construction machine is connected to the second main pump and the travel control valve unit, so that the hydraulic fluid discharged from the first main pump can not be utilized for traveling and is discharged immediately There is a problem.

On the other hand, there is a case where the engine is driven at a higher engine speed (rpm), for example, 2,000 rpm, than in the normal operation mode in order to sufficiently supply the operating oil to the traveling motor during traveling.

In other words, the number of revolutions of the engine during running is relatively high as compared with the case where the number of revolutions of the engine is set to 1,500 rpm to 1,800 rpm when the normal operation is performed during traveling.

Therefore, in order to satisfy the driving performance, it is necessary to select an engine having a large engine output so as to be capable of outputting a high rotational speed. This causes a problem that the loss increases when driving the engine and fuel efficiency becomes worse.

On the other hand, it is difficult to determine the main pump volume specification considering both the running performance and the performance of the working machine. For example, if the volume of the traveling motor is determined in consideration of the traveling performance and the traction force, the traveling speed can be designed by 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 working machine, the number of revolutions of the engine for satisfying the running speed can not be determined regardless of the designer's intention.

As a result, there is no performance factor that can efficiently design the traveling system to satisfy the target performance (the traction force and the traveling speed) of the construction machine. Therefore, the efficiency of the traveling system is inferior to the efficiency of the working machine.

On the other hand, as a technique related to a hydraulic system of a conventional construction machine, in a traveling mode, hydraulic oil discharged from a first main pump is joined to hydraulic oil discharged from a second main pump, Thereby improving the running performance. Driving is carried out by a driving system, which includes a number of components related to driving besides driving motors.

However, in a hydraulic system of a conventional construction machine, a problem may arise in a control unit controlled by a current value for an unknown reason. When a problem occurs in the control unit, the control on the first main pump may be abnormal. In particular, when the operating oil discharged from the first main pump joins the operating oil discharged from the second main pump, May be excessive.

That is, there is a concern that the traveling speed may be higher than the traveling speed designed by the maker of the construction machine, thereby hindering the traveling safety. Further, if the operating fluid is excessively supplied to the traveling motor, there may be a problem in the durability of the traveling system.

Japanese Laid-Open Patent Publication No. 2004-27706 (Jan. 29, 2004)

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a hydraulic system for a construction machine that can improve the running performance of a construction machine and prevent deterioration of durability of a traveling system.

The present invention has been made in view of the above problems, and it is an object of the present invention to at least partially solve the problems in the conventional arts. There will be.

According to an aspect of the present invention, there is provided a hydraulic system for a construction machine, comprising: first and second main pumps (11, 12) through which high-pressure hydraulic oil is discharged; A sub-pump 70 through which the pilot hydraulic fluid 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 travel control valve unit (31) disposed on the second hydraulic line (22) for controlling the travel motor (80); A first relief valve (41) disposed on the first hydraulic line (21) to maintain the pressure of the first hydraulic line (21) at a relief pressure; A first control valve unit (51) which opens when the running mode is selected and allows the pilot hydraulic fluid to pass therethrough; A second control valve unit (52) which is operated by the pilot hydraulic oil passed through the first control valve unit (51) and connects the hydraulic oil discharged from the first main pump (11) to the second hydraulic line ); And a shuttle valve (60) connecting the pressure of the pilot hydraulic fluid to the first regulator (13) of the first main pump (11) with the pressure of the pilot hydraulic fluid colliding with the relief pressure at both ends.

In the hydraulic system of the construction machine according to the embodiment of the present invention, the relief pressure set in the first relief valve 41 and the pressure of the pilot hydraulic fluid discharged from the sub-pump 70 may be the same .

In the hydraulic system of the construction machine according to the embodiment of the present invention, when the pump pressure of any one of the first main pump 11 or the second main pump 12 is higher than the set pressure, the first regulator And a third control valve unit 53 for reducing the pressure of the operating oil supplied to the first and second control valves 13 and 13.

Further, in the hydraulic system of the construction machine according to the embodiment of the present invention, the third control valve unit 53 controls the hydraulic pressure of the hydraulic oil supplied to the first regulator 13 in proportion to the difference between the pump pressure and the set pressure It may be an electron proportional control valve that reduces the pressure.

In the hydraulic system of the construction machine according to the embodiment of the present invention, when the operation mode is selected, the first control valve unit 51 connects the spool pressure-receiving portion of the second control valve unit 52 with the drain tank, The second control valve unit 52 may disconnect the first hydraulic line 21 and the second hydraulic line 22 from each other.

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

In the hydraulic system of the construction machine according to the present invention as described above, the hydraulic oil discharged from the first main pump is joined to the hydraulic oil discharged from the second main pump in the traveling mode, Thereby improving the driving performance.

In the hydraulic system of the construction machine according to the embodiment of the present invention, even when a situation occurs in which the control of the first and third control valve units is not properly controlled due to an unknown reason, By limiting the discharge flow rate, traveling overspeed can be prevented, whereby the running stability can be ensured and the durability of the running system can be prevented from being lowered.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 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; FIG.
2 is a hydraulic circuit diagram for explaining a traveling mode in a 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 traveling mode in a hydraulic system of a construction machine according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent by reference to the embodiments described in detail below with reference to the accompanying drawings.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be understood that the embodiments described below are provided for illustrative purposes only, and that the present invention may be embodied with various modifications and alterations. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the subject matter of the present invention. The accompanying drawings are not necessarily drawn to scale to facilitate understanding of the invention, but may be exaggerated in size.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

Like reference numerals refer to like 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.

BRIEF DESCRIPTION OF DRAWINGS FIG. 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; FIG.

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 the power output from the engine 17 to discharge the high-pressure hydraulic oil, respectively.

The first and second main pumps 11 and 12 are provided with respective first and second regulators 13 and 14 for controlling the swash plate angle. That is, the flow rate and pressure of the operating fluid 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 can measure the respective pump pressures and provide them to the control unit. Each of the pump pressures can be detected by the first and second pressure sensors 15, 16. The first and second pressure sensors 15 and 16 may be disposed on the side where the hydraulic fluid is discharged from the first and second main pumps 11 and 12, respectively.

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

On the other hand, a first hydraulic line 21 is connected to the first main pump 11. Likewise, a 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 main control valve 30 described above. The main control valve 30 may have a plurality of control valves therein. In addition, a plurality of control valves may be arranged in series on the first hydraulic line 21, and a plurality of control valves may be arranged in series on the second hydraulic line 22. [ Each control valve is operated by the pilot oil in which the control signal is generated, and the pilot oil is applied to the spool of the corresponding control valve, whereby the spool of the corresponding control valve is moved and the corresponding actuator is operated.

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

The first relief valve 41 may be disposed on the first hydraulic line 21 and the second relief valve 42 may be disposed on the second hydraulic line 22 in the same manner. More specifically, the first hydraulic line 21 is provided with a plurality of control valves, and the above-mentioned first relief valve 41 is disposed at the most downstream. Similarly, 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.

Relief pressures can be set for the first and second relief valves 41 and 42 described above. Thus, when an abnormally 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 abnormally high pressure is formed in the second hydraulic line 22, the second relief valve 42 is opened and the second hydraulic line 22 maintains the relief pressure. The relief pressure may be, for example, 40 kgf / cm ² .

In addition, the 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 to the first relief valve 41 and the pressure pc of the pilot hydraulic fluid discharged from the sub-pump 70 can be set to the same value.

Thus, since the discharge flow rate of the hydraulic pump at the pressure pc of the pilot hydraulic oil is the minimum value, when the hydraulic oil discharged from the first and second main pumps 11 and 12 is merged, the discharge flow rate of the first main pump 11 becomes minimum And can be discharged at a flow rate. The stability of running is improved by keeping the discharge flow rate of the first main pump 11 at a minimum.

On the first hydraulic line 21, a second control valve unit 52 is provided.

The third hydraulic line 23 connects the pressure control portion of the first control valve unit 51 and the pressure control portion of the second control valve unit 52. The first control valve unit 51 is connected to the pressure receiving portion of the second control valve unit 52 and the drain tank when the first current signal is not inputted, The hydraulic pressure portion and the sub-pump 70 are disconnected.

On the contrary, when the first current signal is input, the first control valve unit 51 is connected to the sub-pump 70 and the pressure receiving portion of the second control valve unit 52. That is, when the first control valve unit 51 is opened, the pilot hydraulic oil is passed through and the pilot hydraulic oil is applied to the hydraulic pressure portion of the second control valve unit 52. The first current signal described above is a signal for determining whether or not the hydraulic oil is merged.

The fourth hydraulic line 24 connects the second control valve unit 52 and the second hydraulic line 22 to each other.

The second control valve unit 52 is operated by the pilot hydraulic oil passed through the first control valve unit 51 described above. That is, when the pilot hydraulic oil is not supplied to the second control valve unit 52, the hydraulic oil discharged from the first main pump 11 flows toward the first relieve valve 41 along the first hydraulic line 21. [ On the contrary, when the pilot hydraulic oil is supplied to the second control valve unit 52, the flow path from the first hydraulic line 21 to the main control valve 30 is disconnected, and the hydraulic oil discharged from the first main pump 11 And is joined to 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 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.

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

Therefore, the pressure of the pilot hydraulic oil and the relief pressure are contested at both ends of the shuttle valve 60, the hydraulic oil of a relatively larger pressure is selected, and the selected hydraulic oil is applied to the first regulator 13.

On the other hand, an 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 control unit determines whether the pump pressure is high or low, and the second current signal is applied to the third control valve unit 53 according to the judged result.

When the third control valve unit 53 is opened, the hydraulic fluid in the seventh hydraulic line 27 is drained. When the third control valve unit 53 is opened, the pressure of the seventh hydraulic line 27 is reduced.

A higher pump pressure means that more work flow is needed because the workload is greater. On the other hand, when the pressure of the seventh hydraulic line 27 is reduced, the pressure acting on the first regulator 13 is reduced, and the first regulator 13 forms a large swash plate 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 is reduced, the second regulator 13 increases the swash plate angle of the second main pump 12 to increase the discharge flow rate, ).

On the other hand, the third control valve unit 53 may be an electron proportional control valve. More specifically, the third control valve unit 53 is connected to the first regulator 13 in proportion to the difference between the pump pressure ps1 of the first main pump 11 and the set pressure of the first relief valve 41, The pressure of the working oil supplied to the working fluid is reduced proportionally. As a result, when the minimum flow rate is discharged by the first main pump 11, the discharge flow rate can be increased gradually as the load is increased.

 <Operation mode>

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

When the work mode is selected by the operator's choice, the pilot hydraulic oil is disconnected by the first control valve unit 51, so that the second control valve unit 52 does not operate.

As a result, the hydraulic fluid 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.

On the other hand, the hydraulic fluid 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. The pressure formed in the sixth hydraulic line 26 and the pressure formed in the fifth hydraulic line 25 compete with each other in the shuttle valve 60. Since the fifth hydraulic line 25 is connected to the drain tank, have. However, in the sixth hydraulic line 26, a pressure equal to the relief pressure or a pressure lower than the relief pressure is formed. Therefore, the pressure of the sixth hydraulic line 26 of the shuttle valve 60 is selected.

The sixth hydraulic line 26 thus has a maximum pressure relief pressure which 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 supplied to each control control unit provided in the second hydraulic line 22 including the travel control valve unit 31. [ That is, in the operation mode, the spool of the control valve unit corresponding to the adjustment of the joystick is operated to perform the desired operation while supplying the high-pressure hydraulic fluid to the actuator.

 &Lt; Running mode >

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

The running mode can be selected by the operator's choice. When the running mode is selected, the first current signal is input to the first control valve unit 51. Thus, the first control valve unit 51 provides the pilot hydraulic fluid to the hydraulic pressure portion of the second control valve unit 52 and the shuttle valve 60.

The second control valve unit 52 is switched by the supplied pilot operating 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 And is joined to the second hydraulic line 22 along the fourth hydraulic line 24.

In other words, since the traveling motor 80 can be supplied with a greater amount of operating fluid, the running performance is improved.

On the other hand, the shuttle valve 60 compares the relief pressure with the pilot pressure. As described above, since the first hydraulic line 21 is disconnected, no pressure is formed in the sixth hydraulic line 26, do. On the other hand, since the fifth hydraulic line is provided with the pilot hydraulic oil, the pressure of the pilot hydraulic oil is formed.

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

The pilot hydraulic fluid is transferred 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 the pressure of the hydraulic oil discharged from the first and second main pumps 11, 12. As a more specific example, the pressure of the pilot hydraulic fluid may be 40 kgf / 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. The first control valve 51 is controlled by the current value. Even if any unknown error occurs in the first control valve 51, the pressure for controlling the first regulator 13 is controlled by the pilot hydraulic pressure The running speed of the construction machine is prevented from being abnormally overspeed, thereby improving the running stability.

Further, by preventing abnormal overspeed, the durability of the components related to the traveling system can be prevented from abnormally deteriorated.

 <Travel mode - Overload>

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

When the construction machine is running, it can travel uphill. At this time, a larger amount of hydraulic fluid may be required in the traveling 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 is increased. The pump pressure can be detected at the pressure ps1 at the first pressure sensor 15 and detected at the pressure ps2 at the second pressure sensor 16. [

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

When the third control valve unit 53 is opened, the hydraulic fluid in the seventh and eighth hydraulic lines 27 and 28 is drained, so that the pressure in the seventh and eighth hydraulic lines 27 and 28 is lowered. In other words, the pressure applied to the first regulator 13 means that a pressure lower than the pressure of the pilot hydraulic oil is applied.

The swash plate angle of the first main pump 11 is increased by lowering the pressure applied to the first regulator 13, whereby the discharge flow rate of the hydraulic oil in the first main pump 11 is increased.

Further, the operating fluid increased by the increase in the hydraulic fluid flow rate discharged from the first main pump 11 is merged into the second hydraulic line 22 from the first hydraulic line 21 and supplied to the traveling motor 80. Therefore, even if the running load is increased, such as climbing uphill, more running oil can be supplied to the running motor 80, so that the running performance can be kept good.

On the other hand, the third control valve 53 is controlled by the current value. Even if any unknown error occurs in the third control valve 53, the pressure for controlling the first regulator 13 is controlled by the pilot hydraulic pressure The running speed of the construction machine is prevented from being abnormally overspeed, thereby improving the running stability.

Further, by preventing abnormal overspeed, the durability of the components related to the traveling system can be prevented from abnormally deteriorated.

As described above, in the hydraulic system of the construction machine according to the embodiment of the present invention, the hydraulic oil discharged from the first main pump 11 in the traveling mode is joined to the hydraulic oil discharged from the second main pump 12, And the running performance of the running motor 80 can be improved.

In the hydraulic system of the construction machine according to the present invention, even if a situation occurs in which the control of the first and third control valve units 51 and 53 is not properly controlled due to an unknown reason, the first main pump 11 It is possible to prevent the traveling overspeed, thereby securing the running stability and preventing the durability of the running system from deteriorating.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. will be.

Therefore, it should be understood that the above-described embodiments are to be considered in all respects as illustrative and not restrictive, and the scope of the present invention is indicated by the appended claims. The scope of the claims and their equivalents It is to be understood that all changes or modifications that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

The hydraulic system of the 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: first and second regulators
15, 16: first and second pressure sensors
17: engine
21, 22, 23, 24, 25, 26, 27, 28: 1st to 8th hydraulic lines
30: Main control valve (MCV)
31: Driving control valve unit
41, 42: first and second relief valves
51, 52, 53: first, second and third control valve units
60: Shuttle valve
70: Sub pump
80: Traveling motor

Claims (5)

First and second main pumps (11, 12) through which high-pressure hydraulic oil is discharged, respectively;
A sub-pump 70 through which the pilot hydraulic fluid 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 travel control valve unit (31) disposed on the second hydraulic line (22) for controlling the travel motor (80);
A first relief valve (41) disposed on the first hydraulic line (21) to maintain the pressure of the first hydraulic line (21) at a relief pressure;
A first control valve unit (51) which opens when the running mode is selected and allows the pilot hydraulic fluid to pass therethrough;
A second control valve unit (52) which is operated by the pilot hydraulic oil passed through the first control valve unit (51) and connects the hydraulic oil discharged from the first main pump (11) to the second hydraulic line ); And
A shuttle valve (60) connecting both the pressure of the pilot hydraulic fluid and the relief pressure at both ends to connect a relatively large pressure hydraulic fluid to the first regulator (13) of the first main pump (11);
The hydraulic system of the construction machine.
The method of claim 1, wherein
The relief pressure set in the first relief valve (41)
And the pressure of the pilot hydraulic fluid discharged from the sub-pump (70) is set to be the same.
The method according to claim 1,
A third control valve unit for decreasing the pressure of the operating oil supplied to the first regulator (13) when the pump pressure of either the first main pump (11) or the second main pump (12) (53);
The hydraulic system of the construction machine.
The method of claim 3,
Wherein the third control valve unit (53) is an electron proportional control valve which reduces the pressure of the operating oil supplied to the first regulator (13) in proportion to the difference between the pump pressure and the set pressure. Hydraulic system
The method according to claim 1,
When the work mode is selected,
The first control valve unit 51 connects the spool pressure-receiving portion of the second control valve unit 52 to the drain tank,
The second control valve unit 52 is provided for disconnecting the connection between the first hydraulic line 21 and the second hydraulic line 22
The hydraulic system of the construction machine.

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