阅读说明：本技术 液压系统 (Hydraulic system ) 是由 汪云峰 欧坚冰 董广东 李峰 于 2019-04-30 设计创作，主要内容包括：本发明公开了一种液压系统,该液压系统能够在第一工作状态、第二工作状态和第三工作状态之间切换。在第一工作状态下,单个执行器以小于或等于预定速度的速度运行,供给单个执行器的流量由对应于该单个执行器的一个控制阀组件的开度确定,在第二工作状态下,单个执行器以大于预定速度的速度运行,供给单个执行器的流量由变量泵所提供的流量确定,以及在第三工作状态下,多个执行器中的至少两个执行器同时运行,基于至少两个执行器的期望流量来控制变量泵所提供的流量,并且控制器通过控制对应的控制阀组件的开度来控制供给至少两个执行器的流量。由此可以满足执行器在低速运行时的流量要求以及在高速运行时的流量要求。(The invention discloses a hydraulic system which can be switched among a first working state, a second working state and a third working state. In a first operating state, a single actuator is operated at a speed less than or equal to a predetermined speed, a flow rate supplied to the single actuator is determined by an opening degree of one control valve assembly corresponding to the single actuator, in a second operating state, the single actuator is operated at a speed greater than the predetermined speed, the flow rate supplied to the single actuator is determined by a flow rate supplied from a variable pump, and in a third operating state, at least two actuators of the plurality of actuators are operated simultaneously, the flow rate supplied from the variable pump is controlled based on desired flow rates of the at least two actuators, and a controller controls the flow rates supplied to the at least two actuators by controlling the opening degrees of the corresponding control valve assemblies. This makes it possible to meet the flow demand of the actuator at low speeds and at high speeds.)

1. A hydraulic system, comprising:

a variable displacement pump;

a plurality of actuators for performing different operations;

a plurality of control valve assemblies, each control valve assembly corresponding to a respective actuator; and

a controller that controls a displacement of the variable displacement pump and controls opening degrees of the plurality of control valve assemblies to enable the hydraulic system to switch between a first operating state, a second operating state, and a third operating state, wherein:

in a first operating state, the single actuator is operated at a speed less than or equal to a predetermined speed, the variable displacement pump provides a flow greater than that demanded by the single actuator, and the flow supplied to the single actuator is determined by the opening of a control valve assembly corresponding to the single actuator,

in a second operating state, the single actuator is operated at a speed greater than a predetermined speed, the flow rate to the single actuator is determined by the displacement of the variable displacement pump, the flow rate allowed by the opening of a control valve assembly corresponding to the single actuator is greater than or equal to the flow rate provided by the variable displacement pump, and

in a third operating state, at least two actuators of the plurality of actuators are simultaneously operated, the displacement of the variable displacement pump is controlled based on the desired flow rates of the at least two actuators, and the controller controls the flow rates to the at least two actuators by controlling the opening of the corresponding control valve assemblies.

2. The hydraulic system of claim 1, wherein:

each of the plurality of control valve assemblies comprises: the opening degree of the control valve component is determined by the opening degree of the reversing valve, and the opening degree of the reversing valve is controlled by the controller; and a pressure compensating valve that maintains a pressure differential between the inlet and the outlet of the reversing valve at a substantially constant value.

3. The hydraulic system of claim 1, wherein:

the pressure compensation valve is a front pressure compensation valve which is arranged at the upstream of an inlet of the reversing valve, one end of a valve core of the pressure compensation valve bears the pressure of the inlet of the reversing valve, and the other end of the valve core bears the pressure of an outlet of the reversing valve and the acting force of the pressure regulating spring, so that the pressure difference between the inlet and the outlet of the reversing valve is determined by the acting force of the pressure regulating spring.

4. The hydraulic system of claim 2 or 3, wherein:

in a third operating state, in the case that the flow provided by the variable displacement pump can meet the desired flow of the at least two actuators, the controller controls the opening of the corresponding control valve assembly to provide the desired flow to the at least two actuators.

5. The hydraulic system of claim 2 or 3, wherein:

in a third working state, the controller controls the opening degree of the corresponding control valve component under the condition that the flow provided by the variable displacement pump cannot meet the expected flow of the at least two actuators, and provides the flow smaller than the expected flow to the at least two actuators under the condition that the proportion of the expected flow of the at least two actuators is kept unchanged.

6. The hydraulic system of claim 1, wherein:

in the first operating condition, the displacement of the variable displacement pump is maintained substantially constant.

7. The hydraulic system of claim 1, wherein:

the variable pump is integrated with an electric proportional variable control valve, and the controller controls the variable pump to supply the flow rate in an electric proportional variable manner in the second and third operating states.

8. The hydraulic system of claim 1, wherein:

the variable pump is integrated with an electric proportional variable control valve and a load sensing variable control valve, and in a third operating state, the variable pump supplies flow in a pilot controlled load sensing variable manner, or the controller controls the variable pump to supply flow in an electric proportional variable manner.

9. The hydraulic system of claim 1, wherein:

In the second operating state, the opening degree of the control valve assembly is maintained at the maximum opening degree.

10. The hydraulic system of claim 1, further comprising:

an oil tank; and

the differential pressure valve is installed between an outlet of the variable pump and an oil tank, one end of a valve core of the differential pressure valve bears the pressure of an operating actuator and the acting force of a pressure regulating spring, the other end of the valve core bears the pressure of the outlet of the variable pump, when the acting force of the pressure of the outlet of the variable pump on the valve core is larger than the total acting force of the pressure of the operating actuator and the acting force of the pressure regulating spring on the valve core, the differential pressure valve is opened, part of fluid of the outlet of the variable pump flows into the oil tank through the differential pressure valve, and when the acting force of the pressure of the outlet of the variable pump on the valve core is smaller than or equal to the total acting force of the pressure of the.

11. The hydraulic system of claim 1, wherein:

the reversing valve is an analog quantity control reversing valve or a digital quantity control reversing valve.

Technical Field

Embodiments of the present invention relate to a hydraulic system.

Background

The hydraulic system needs to meet the flow requirements of the actuator at low speed operation as well as at high speed operation.

Disclosure of Invention

It is an object of embodiments of the present invention to provide a hydraulic system whereby, for example, flow requirements of an actuator at low speed and flow requirements at high speed may be met.

An embodiment of the present invention provides a hydraulic system including: a variable displacement pump; a plurality of actuators for performing different operations; a plurality of control valve assemblies, each control valve assembly corresponding to a respective actuator; and a controller that controls a displacement of the variable displacement pump and controls opening degrees of the plurality of control valve assemblies to enable the hydraulic system to switch between a first operating state, a second operating state, and a third operating state, wherein: in a first operating state, the single actuator is operated at a speed less than or equal to a predetermined speed, the variable displacement pump provides a flow greater than that demanded by the single actuator, and the flow rate to a single actuator is determined by the opening of a control valve assembly corresponding to that single actuator, in a second operating state, the single actuator is operated at a speed greater than a predetermined speed, the flow rate to the single actuator is determined by the displacement of the variable displacement pump, the flow permitted by the opening of a control valve assembly corresponding to the single actuator is greater than or equal to the flow provided by the variable displacement pump, and in a third operating state, at least two actuators of the plurality of actuators are simultaneously operated, the displacement of the variable displacement pump is controlled based on the desired flow rates of the at least two actuators, and the controller controls the flow to the at least two actuators by controlling the opening of the corresponding control valve assembly.

Thus, the flow rate requirement of the actuator at low speed operation and the flow rate requirement at high speed operation can be satisfied.

According to an embodiment of the invention, each of the plurality of control valve assemblies comprises: the opening degree of the control valve component is determined by the opening degree of the reversing valve, and the opening degree of the reversing valve is controlled by the controller; and a pressure compensating valve that maintains a pressure differential between the inlet and the outlet of the reversing valve at a substantially constant value.

Thereby, the flow supplied to the actuator through the control valve assembly can be kept substantially constant.

According to an embodiment of the invention, the pressure compensation valve is a pre-pressure compensation valve which is arranged upstream of the inlet of the reversing valve, one end of a valve core of the pressure compensation valve is used for bearing the pressure of the inlet of the reversing valve, and the other end of the valve core of the pressure compensation valve is used for bearing the pressure of the outlet of the reversing valve and the acting force of the pressure regulating spring, so that the pressure difference between the inlet and the outlet of the reversing valve is determined by the acting force of the pressure regulating spring.

Therefore, the pressure difference between the inlet and the outlet of the reversing valve can be controlled more accurately, and the pressure difference between the inlet and the outlet of the reversing valve is not influenced by load change and feedback pressure between the variable displacement pump and the reversing valve.

According to an embodiment of the invention, in the third operating state, in case the flow rate provided by the variable displacement pump is able to meet the desired flow rates of the at least two actuators, the controller controls the opening of the corresponding control valve assembly to provide the desired flow rates to the at least two actuators.

Thereby, the flow rates to the at least two actuators can be accurately controlled.

According to an embodiment of the invention, in the third operating state, in the case where the flow rate provided by the variable displacement pump cannot meet the desired flow rates of the at least two actuators, the controller controls the opening degree of the corresponding control valve assembly, and in the case where the ratio of the desired flow rates of the at least two actuators is kept unchanged, the controller provides a flow rate smaller than the desired flow rate to the at least two actuators.

Therefore, the flow rate accurate distribution among the actions of the multiple mechanisms is realized without changing the cooperative work among the actuators.

According to an embodiment of the invention, in the first operating state the displacement of the variable displacement pump is kept substantially constant.

Therefore, the variable pump is operated in a stable state, and the hydraulic system is operated stably.

According to an embodiment of the present invention, the variable displacement pump is integrated with an electrically proportional variable control valve, and the controller controls the variable displacement pump to supply the flow rate in an electrically proportional variable manner in the second and third operation states.

Thereby, the variable displacement pump can be controlled to supply a desired flow rate.

According to an embodiment of the present invention, the variable displacement pump is integrated with an electric proportional variable control valve and a load sensing variable control valve, and in the third operation state, the variable displacement pump supplies the flow rate in a pilot controlled load sensing variable manner, or the controller controls the variable displacement pump to supply the flow rate in an electric proportional variable manner.

Thereby, the variable displacement pump can be made to supply flow in different ways, making the hydraulic system more adaptable.

According to an embodiment of the invention, in the second operating state, the opening degree of the control valve assembly is maintained at the maximum opening degree.

Thereby, the control of the control valve assembly is made simpler.

According to an embodiment of the invention, the hydraulic system further comprises: an oil tank; and the differential pressure valve is arranged between the outlet of the variable pump and the oil tank, one end of a valve core of the differential pressure valve bears the pressure of the operating actuator and the acting force of the pressure regulating spring, the other end of the valve core bears the pressure of the outlet of the variable pump, when the acting force of the pressure of the outlet of the variable pump on the valve core is greater than the total acting force of the pressure of the operating actuator and the acting force of the pressure regulating spring on the valve core, the differential pressure valve is opened, part of fluid of the outlet of the variable pump flows into the oil tank through the differential pressure valve, and when the acting force of the pressure of the outlet of the variable pump on the valve core is smaller than or equal to the total acting force of the pressure of the operating actuator and.

The excess flow provided by the variable displacement pump is thereby relieved through the differential pressure valve.

According to an embodiment of the invention, the reversing valve is an analog quantity control reversing valve, or a digital quantity control reversing valve.

Thus, the opening degree of the reversing valve can be more accurately controlled by the controller.

Drawings

FIG. 1 is a schematic illustration of a hydraulic system according to an embodiment of the present disclosure; and

FIG. 2 is an enlarged partial schematic view of a hydraulic system according to an embodiment of the present invention.

Detailed Description

As shown in fig. 1, referring to fig. 1, a hydraulic system 100 according to an embodiment of the present invention includes: a variable displacement pump 10; a plurality of actuators 70 for performing different operations; a plurality of control valve assemblies 60, each control valve assembly 60 corresponding to a respective one of the actuators 70; and a controller 30, the controller 30 controlling a displacement of the variable displacement pump 10 and controlling opening degrees of the plurality of control valve assemblies 60 to enable the hydraulic system 100 to be switched among the first, second, and third operating states. In a first operating state, the single actuator 70 is operating at a speed less than or equal to a predetermined speed, the variable displacement pump 10 provides a flow greater than that demanded by the single actuator 70, and the flow supplied to the single actuator 70 is determined by the opening of a control valve assembly 60 corresponding to the single actuator 70. In the second operating state, in which the single actuator 70 is operated at a speed greater than the predetermined speed, the flow rate supplied to the single actuator 70 is determined by the displacement of the variable displacement pump 10, and the flow rate allowed by the opening degree of one control valve assembly 60 corresponding to the single actuator 70 is greater than or equal to the flow rate supplied by the variable displacement pump 10, for example, the opening degree of the control valve assembly 60 is maintained at the maximum opening degree. In the third operating state, at least two actuators 70A and 70B of the plurality of actuators 70 are simultaneously operated, the displacement of the variable displacement pump 10 is controlled based on the desired flow rates of the at least two actuators 70A and 70B, and the controller 30 controls the flow rates to the at least two actuators 70A and 70B by controlling the opening degrees of the corresponding control valve assemblies 60A and 60B.

In some embodiments of the present invention, the predetermined speed may be any suitable threshold and, in the first operating state, actuator 70 may be operating at the lowest steady speed. In the second operating state, actuator 70 may be operating at a speed above its minimum stable speed. The operating speed of the actuator 70 in the first operating state is lower than the operating speed of the actuator 70 in the second operating state.

Referring to fig. 1 and 2, in some embodiments of the present invention, each of the plurality of control valve assemblies 60 comprises: a direction change valve 61, an opening degree of the control valve assembly 60 is determined by an opening degree of the direction change valve 61, and the opening degree of the direction change valve 61 is controlled by the controller 30; and a pressure compensation valve 62, the pressure compensation valve 62 maintaining a pressure difference between the inlet 611 and the outlet 612 of the directional valve 61 at a substantially constant value. The direction valve 61 may be an analog quantity control direction valve 61, or a digital quantity control direction valve 61. According to an example of the present invention, the pressure compensation valve 62 is a pre-pressure compensation valve 62, the pre-pressure compensation valve 62 is disposed upstream of the inlet 611 of the direction valve 61, one end of a valve core of the pressure compensation valve 62 receives the pressure of the inlet 611 of the direction valve 61, and the other end receives the pressure of the outlet 612 of the direction valve 61 and the force of the pressure regulating spring 621, so that the pressure difference between the inlet 611 and the outlet 612 of the direction valve 61 is determined by the force of the pressure regulating spring 621. According to an embodiment of the invention, hydraulic fluid from the variable displacement pump 10 enters the inlet 611 of the reversing valve 61 via the pressure compensating valve 62. As can be seen from fig. 1 and 2, when the spool of the direction valve 61 is in one of the other two positions different from the position shown in the drawing, the hydraulic fluid enters the direction valve 61 via the inlet 611 of the direction valve 61 and then flows out of the direction valve 61 from one of the two outlets 612 of the direction valve 61 into the actuator 70.

According to an embodiment of the invention, in the second operating state, the directional control valve 61 is used only for the movement direction control of the actuator.

According to the embodiment of the invention, the valve core of the pressure compensation valve is controlled by load pressure, inlet pressure of the reversing valve and the pressure regulating spring together, the pressure compensation valve limits the pressure difference between the inlet and the outlet of the reversing valve to correspond to the pressure regulating spring of the pressure compensation valve, once the pressure regulating spring is regulated, the pressure difference between the inlet and the outlet of the reversing valve is a fixed value, so that the flow passing through the reversing valve is in a direct proportional relation with the opening area of the valve core. The controller controls the displacement of the variable pump, the flow output to each actuator by the reversing valve corresponds to the opening area of the reversing valve one by one, and the flow is accurately and controllably output without being influenced by load change and feedback pressure between the variable pump and the reversing valve.

Referring to fig. 1 and 2, in some embodiments of the present invention, in a third operating state, where the flow provided by the variable displacement pump 10 is sufficient to meet the desired flow of the at least two actuators 70A and 70B, the controller 30 controls the opening of the corresponding control valve assemblies 60A and 60B to provide the desired flow to the at least two actuators 70A and 70B. In a third operating state, in the event that the flow provided by the variable displacement pump 10 fails to meet the desired flow of the at least two actuators 70A and 70B, the controller 30 controls the opening of the corresponding control valve assemblies 60A and 60B to provide a flow to the at least two actuators 70A and 70B that is less than the desired flow while maintaining the ratio of the desired flows of the at least two actuators 70A and 70B unchanged.

Referring to fig. 1 and 2, in some embodiments of the present invention, the displacement of the variable displacement pump 10 remains substantially constant in the first operating condition.

In some embodiments of the present invention, the variable displacement pump 10 is an electrically proportional variable displacement pump 10 (i.e., integrated with an electrically proportional variable control valve), and the controller 30 controls the variable displacement pump 10 to supply flow in an electrically proportional variable manner in the second and third operating states. That is, the controller 30 controls the displacement of the variable displacement pump 10 by sending a control signal to the variable displacement pump 10.

In some embodiments of the present invention, the variable displacement pump 10 is integrated with an electric proportional variable control valve and a load sensing variable control valve, and in the third operating state, the variable displacement pump 10 supplies the flow rate in a pilot controlled load sensing variable manner, or the controller 30 controls the variable displacement pump 10 to supply the flow rate in an electric proportional variable manner.

In some embodiments of the present invention, referring to fig. 1, hydraulic system 100 further comprises: a fuel tank 50; and a differential pressure valve 20, the differential pressure valve 20 is installed between the outlet 11 of the variable displacement pump 10 and the oil tank 50, one end of a valve core of the differential pressure valve 20 bears the pressure of the operating actuator 70 and the acting force of the pressure regulating spring 21, the other end bears the pressure of the outlet 11 of the variable displacement pump 10, when the acting force of the pressure of the outlet 11 of the variable displacement pump 10 on the valve core is larger than the total acting force of the pressure of the operating actuator 70 and the acting force of the pressure regulating spring 21 on the valve core, the differential pressure valve 20 is opened, part of the fluid of the outlet 11 of the variable displacement pump 10 flows into the oil tank 50 through the differential pressure valve 20, and when the acting force of the pressure of the outlet 11 of the variable displacement pump 10 on the valve core is smaller than or equal to the total acting force of the pressure of the operating actuator 70 and the acting force of the. The excess flow provided by the variable displacement pump 10 is bled off through the differential pressure valve 20. Referring to fig. 1, one end of the spool of the differential pressure valve 20 receives the maximum actuator 70 pressure collected by the shuttle valve 81.

Referring to FIG. 1, in one example of the present invention, a hydraulic system 100 includes: the variable displacement pump 10, the differential pressure valve 20, the controller 30, the handle 40, the pressure compensating valve 62A, the reversing valve 61A, the actuator 70B, the reversing valve 61B, the pressure compensating valve 62B, the expansion link 80, the shuttle valve 81 and the hydraulic oil tank 50. The handle 40 sends a control signal to the controller 30, the controller 30 controls the variable displacement pump 10 to vary, the output flow passes through the pressure compensation valves 62A and 62B and the reversing valves 61A and 61B and then enters the actuators 70A and 70B, and the excess flow provided by the variable displacement pump 10 overflows through the differential pressure valve 20. For example, the handle 40 is a biaxial handle, and the operation control actuator 70A in the left-right direction of the handle and the operation control actuator 70B in the front-rear direction of the handle are provided. Extension block 80 is identical to the hydraulic control components (pressure compensating valves, directional control valves, shuttle valves) of each of the corresponding units of actuators 70A, 70B, which may be identical or different.

The handle 40 controls the operation of the hydraulic system and inputs signals to the controller 30 to control the operation of the hydraulic system in different flow supply states. The three operating states corresponding to the handle respectively correspond to the three working states of the hydraulic system.

In a first operating state, handle 40 is operated at a relatively small angle in the left-right direction, controller 30 is instructed to actuate actuator 70A at a relatively small speed, and controller 30 controls variable displacement pump 10 to supply a sufficient amount of flow (more flow than is required by actuator 70A) to the hydraulic system in an electrically proportional variable manner, e.g., variable displacement pump 10 may provide a substantially constant displacement. The hydraulic fluid provided by the variable displacement pump 10 passes through the pressure compensating valve 62A, passes through the open passage of the reversing valve 61A, and enters the actuator 70A to drive the actuator to act. The pressure difference across the passage in which the direction change valve 61A opens is limited by the pressure compensating valve 62A so that the flow through the direction change valve 61A is controlled only by the area of its opening passage, which area of the opening passage of the direction change valve 61A is proportional to the operating angle of the handle 40. The control pressure for opening the pressure compensation valve 62A is taken from the inlet and the outlet of the reversing valve 61A, the outlet pressure (i.e. the load pressure) of the reversing valve 61A is selected (high pressure is passed) through the shuttle valve 81 and acts on the spring cavity of the differential pressure valve 20, so that the flow output by the variable displacement pump 10 can be preferentially supplied to the reversing valve 61A, and the surplus flow is overflowed through the differential pressure valve 20.

In the second operating state, the angle of the left-right operation of the handle 40 is further increased, a command for the actuator 70A to operate at a high speed is transmitted to the controller 30, the controller 30 controls the variable pump 10 to supply a flow rate corresponding to the speed of the actuator 70A to the hydraulic system in an electrically proportional variable manner, the selector valve 61A is opened to an opening degree larger than the speed demand flow rate of the actuator 70A, and all the flow rate (except for the leakage of the control valve itself) output by the variable pump 10 is used to drive the actuator 70A to operate at a high speed. The opening degree of the direction valve 61A may be kept substantially constant, for example, to its maximum opening degree.

In the third operating state, the handle 40 is added with the front and rear operating angles on the premise of the original left and right operating angles, the controller 30 is transmitted with the command of the actuators 70A and 70B, the controller 30 can control the variable pump 10 to supply oil in an electric proportional variable mode, the pressure compensation valves 62A and 62B limit the flow corresponding to the arbitrary opening channel areas of the reversing valves 61A and 61B, and the opening channel areas of the reversing valves 61A and 61B are respectively controlled by the left and right and front and rear operating angles of the handle 40 in a proportional manner. When the flow provided by the variable displacement pump 10 can meet the sum of the flows required by the actuators 70A and 70B, the opening channel areas of the reversing valves 61A and 61B are opened according to the preset corresponding relation with the operating angle of the handle 40, and when the flow is insufficient, the opening channel areas of the reversing valves 61A and 61B are reduced in the same proportion with the preset corresponding relation with the operating angle of the handle 40.

In the third operating state, the variable displacement pump 10 may also be supplied with pilot-controlled load sensing variable. The differential pressure of the hydraulic control load sensing variable of the variable pump 10 is larger than the differential pressure limited by the pressure compensation valves 62A and 62B, the pressure compensation valves 62A and 62B limit the flow corresponding to the arbitrary opening channel areas of the reversing valves 61A and 61B, and the opening channel areas of the reversing valves 61A and 61B are respectively controlled by the left and right and front and back operation angles of the handle 40 in proportion. When the flow rate provided by the variable displacement pump 10 can meet the sum of the flow rates of the actuators 70A and 70B, the opening channel areas of the reversing valves 61A and 61B are opened according to the preset corresponding relation with the operating angle of the handle 40, and when the flow rate is insufficient, the opening channel areas of the reversing valves 61A and 61B are reduced in the same proportion with the preset corresponding relation with the operating angle of the handle 40.

In the first operating state, when the front and rear operating angles of the handle 40 are added, the system directly enters the third operating state.

In the course of small increase in the operating angle of the handle 40, the system operating state goes through the first to third operating states. During the large reduction of the operating angle of the handle 40, the system operating state goes from the third to the first operating state.

According to the embodiment of the invention, in the first working state of the hydraulic system, the pressure compensation valve limits the pressure difference of the opening channel of the proportional reversing valve, so that the flow passing through the proportional reversing valve is accurately controlled in the multi-way valve and is not influenced by the change of the feedback pressure difference between the variable pump and the multi-way valve. And the variable pump provides sufficient flow, so that the flow of the system is only controlled by the area of the opening channel of the proportional reversing valve, and the control of the micro speed of the actuator is convenient to realize. In the second working state of the hydraulic system, the variable pump electric proportional variable provides flow corresponding to the speed of the actuator, the proportional reversing valve is opened to an opening passage area larger than the speed demand flow of the actuator, the proportional reversing valve only controls the action direction of the actuator, and the speed is controlled by the variable pump proportional variable, so that the pressure loss in the multi-way valve can be reduced. Under the third working state, the hydraulic system realizes the accurate flow distribution among the actions of the multiple mechanisms by reducing the area of the opening channel of the proportional valve in the same proportion without changing the cooperative work among the actuators. The hydraulic system provided by the embodiment of the invention can be automatically switched among the first working state, the second working state and the third working state, so that seamless connection is realized.

According to an embodiment of the present invention, referring to fig. 1, when the handle corresponding to the actuator 70A is operated, the system is operated in the first operating state when the handle is small, and the actuator 70A is operated at a speed close to the lowest stable rotational speed. When the handle corresponding to the actuator 70A is continuously operated to a large opening, the controller control system is switched from the first operating state to the second operating state, and the actuator 70A is operated at a speed greater than the lowest stable rotation speed. When the actuator 70B or more actuators are added to the actuation of the actuator 70A on the premise that the actuator 70A is already actuated, the controller controls the system to switch from the second operating state to the third operating state. When the added actuators 70B or more actuators stop working and only the actuator 70A acts, the controller control system switches from the third working state to the first or second working state, and the working state of the actuator 70A is related to the size of the operating angle of the handle corresponding to the actuator 70A.

It will be appreciated that the above-mentioned handles are merely examples and that the hydraulic system may have signal input devices other than handles, such as a steering wheel, foot pedals, etc.

It CAN be understood that although fig. 1 shows that the controller 30 and the handle 40 and the controller 30 and the reversing valve are connected through the CAN bus to transmit digital quantity signals, the present invention is not limited to this, and may also transmit analog quantity signals or pwm (pulse width modulation) signals by using current input, voltage input, etc. In addition, although fig. 1 illustrates PWM signal communication between the controller 30 and the variable displacement pump 10, current signal, voltage signal communication, or communication via a CAN bus may be used.