Hydraulic system

Abstract

A hydraulic system includes: a hydraulic pump and a plurality of actuators; a hydraulic circuit for each actuator, wherein at least a first hydraulic circuit includes: a control valve having at least an inlet port, a first intermediate port, a second intermediate port, a first load port, and a second load port, the inlet port being connected to the output of the hydraulic pump, the first load port and the second load port being respectively connected to two working chambers of the corresponding actuator, the control valve having at least one working position, wherein the inlet port communicates with the first intermediate port, and the second intermediate port communicates with either the first load port or the second load port; and a pressure compensation valve configured to control the on / off connection between the first intermediate port and the second intermediate port. The pressure compensation valve integrates a first check valve oriented to allow hydraulic oil to flow from the pressure compensation valve toward the second intermediate port and to prevent hydraulic oil from flowing from the second intermediate port toward the pressure compensation valve.

Description

Technical Field

[0001] This application relates to an independent flow distribution hydraulic system with pressure compensation and anti-backflow function. Background Technology

[0002] Hydraulically powered machinery, such as excavators, aerial work platforms, cranes, and drilling rigs, typically utilizes a single hydraulic pump to supply hydraulic oil to multiple actuators via a multi-channel hydraulic system to achieve simultaneous operation. To facilitate coordination among these actuators, ensuring high controllability of the working device, improving operational efficiency and precise work trajectory, and reducing power source energy loss, the LUDV (Load Independent Flow Distribution) hydraulic system is employed. The LUDV system utilizes a pressure compensation valve to ensure that the pressure difference across the flow control valve of the multi-channel hydraulic system equals the pressure difference between the hydraulic pump outlet pressure and the highest pressure transmitted from the load. The flow allocated to each channel is controlled solely by the area of ​​the flow control valve for that channel, achieving independent flow distribution regardless of load size. When multiple actuators operate simultaneously with varying loads, to prevent preferential flow to the lower-load actuators, the pressure compensation valve increases the pressure downstream of the flow control valve of the lower-load actuator to match that of the highest-load actuator, ensuring that the flow allocated to each channel passes through essentially equally.

[0003] Although the LUDV hydraulic systems currently available on the market can provide good independent flow distribution capabilities, there is still room for improvement in their overall performance. Summary of the Invention

[0004] This application aims to provide a hydraulic system capable of independently distributing flow, which has comprehensively improved performance.

[0005] According to one aspect of this application, a hydraulic system is provided, comprising:

[0006] Hydraulic pump and multiple actuators; and

[0007] A hydraulic circuit is provided for each actuator, which supplies hydraulic oil to the corresponding actuator by the hydraulic pump;

[0008] Among them, at least the first hydraulic circuit in each hydraulic circuit includes:

[0009] A control valve having at least an inlet, a first intermediate port, a second intermediate port, a first load port, and a second load port, wherein the inlet is connected to the output of a hydraulic pump, and the first and second load ports are respectively connected to two working chambers of a corresponding actuator. The control valve has at least one working position, in which the inlet is connected to the first intermediate port, and the second intermediate port is connected to either the first or second load port.

[0010] A pressure compensation valve configured to control the on / off connection between the first intermediate port and the second intermediate port;

[0011] The pressure compensation valve integrates a first check valve, which is oriented to allow hydraulic oil to flow from the pressure compensation valve toward the second intermediate port and to prevent hydraulic oil from flowing from the second intermediate port toward the pressure compensation valve.

[0012] In one embodiment, the pressure compensation valve has a first port and a second port, the first port being connected to the first intermediate port via an upstream intermediate flow path, the second port being connected to the second intermediate port via a downstream intermediate flow path, and the first check valve being integrated into the second port.

[0013] In one embodiment, the pressure compensation valve further has a third port, a fourth port, a fifth port, and a sixth port, wherein the third port and the fifth port are connected to the upstream intermediate flow path, and the fourth port and the sixth port are connected to the pressure sensing oil path of the hydraulic system.

[0014] In one embodiment, the pressure compensation valve has:

[0015] The oil supply valve is in position where the third and fourth oil ports are in a cut-off state, the first and second oil ports are unobstructedly connected, and the fifth and sixth oil ports are unobstructedly connected; and

[0016] The valve is in a shut-off position, wherein the first oil port, the second oil port, the fifth oil port and the sixth oil port are in a shut-off state, and the third oil port and the fourth oil port are connected in a throttling manner.

[0017] In one embodiment, the pressure compensation valve has a transition valve position located between the oil supply valve position and the shut-off valve position, wherein the third oil port, the fourth oil port, the fifth oil port and the sixth oil port are in a shut-off state, and the first oil port and the second oil port are in throttling communication.

[0018] In one embodiment, the first-side control terminal of the pressure compensation valve is connected to the upstream intermediate flow path;

[0019] Furthermore, the first hydraulic circuit also includes a pressure selection valve configured to supply the higher of the pressure of the pressure sensing oil circuit and the pressure of the downstream intermediate flow path to the second control terminal of the pressure compensation valve.

[0020] In one embodiment, the pressure selection valve is a shuttle valve, with its first inlet connected to the pressure sensing oil circuit, its second inlet connected to the downstream intermediate flow path, and its outlet connected to the second control terminal of the pressure compensation valve.

[0021] In one embodiment, the pressure compensation valve is configured to be in the oil supply valve position when the control pressure at the first control terminal is higher than the control pressure at the second control terminal, and to be in the shut-off valve position when the control pressure at the second control terminal is higher than the control pressure at the first control terminal.

[0022] In one embodiment, a second check valve is provided between the upstream intermediate flow path and the third and fifth oil ports. The second check valve is oriented to allow hydraulic oil to flow from the upstream intermediate flow path to the third and fifth oil ports and to prevent hydraulic oil from flowing from the third and fifth oil ports to the upstream intermediate flow path.

[0023] In one embodiment, the displacement of the hydraulic pump is determined based on the difference between the output pressure of the hydraulic pump and the pressure in the pressure sensing oil circuit.

[0024] In one embodiment, at least the second hydraulic circuit in each hydraulic circuit of the hydraulic system has the same structure as the first hydraulic circuit, and the through area between the third and fourth ports of the pressure compensation valve in the first hydraulic circuit when the valve is shut off is smaller than the through area between the third and fourth ports of the pressure compensation valve in the second hydraulic circuit when the valve is shut off, so that the actuator supplied with oil by the first hydraulic circuit actuates before the actuator supplied with oil by the second hydraulic circuit.

[0025] The hydraulic system of this application provides pressure compensation by incorporating a pressure compensation valve between the intermediate oil passages of two or more working ports of the control valve, thereby enabling the hydraulic system to have independent flow distribution capabilities. By integrating a check valve into the pressure compensation valve to provide backflow prevention, the system structure is compact, thus reducing material and processing costs. Attached Figure Description

[0026] The foregoing and other aspects of this application will be more fully understood through the following detailed description with reference to the accompanying drawings, in which:

[0027] Figure 1 This is a schematic diagram of a hydraulic system according to one embodiment of this application;

[0028] Figure 2 , Figure 3 These are the graphic symbols for the main control valve and pressure compensation valve used in the hydraulic system. Detailed Implementation

[0029] This application generally relates to a LUDV hydraulic system with pressure compensation and anti-backflow function. Figure 1 An exemplary layout of the hydraulic system is shown in the figure.

[0030] like Figure 1 As shown, the hydraulic system of this application includes a common hydraulic pump (main pump) 1 for supplying hydraulic oil to multiple actuators 2. The displacement of the hydraulic pump 1 is controlled by a hydraulic variable displacement mechanism 3, such as the variable piston shown in the figure. One side of the variable displacement mechanism 3 is connected to a pressure sensing oil circuit L0 (as described below), and the other side is connected to a high-pressure oil circuit L1 at the output end of the hydraulic pump 1. The variable displacement mechanism 3 is actuated by the pressure difference between the output end of the hydraulic pump 1 and the pressure sensing oil circuit L0 to control the displacement of the hydraulic pump 1.

[0031] Figure 1 Two actuators 2 are shown, but it is understood that the hydraulic system may include more actuators 2 supplied with hydraulic oil by a common hydraulic pump 1. The actuator 2 may be a hydraulic cylinder, a hydraulic motor, or other type of actuator. Each actuator 2 is equipped with a corresponding hydraulic circuit, which is described below for one such hydraulic circuit (which may be referred to as the first hydraulic circuit).

[0032] First, the hydraulic circuit uses a control main valve V1 and a pressure compensation valve V2.

[0033] like Figure 2 As shown, the main control valve V1 is a three-position six-way valve, including three valve positions and six ports. The main control valve V1 can be switched between positions via hydraulic control, electro-hydraulic control, or a combination of both. The six ports are P (inlet), A (first intermediate port), B (second intermediate port), C (first load port), D (second load port), and T (drain port). In the neutral position, ports P, A, B, C, D, and T are all disconnected. In the first operating position, ports P and A are connected, ports B and C are connected, and ports D and T are connected. In the second operating position, ports P and A are connected, ports B and D are connected, and ports C and T are connected.

[0034] like Figure 3As shown, the pressure compensation valve V2 is a three-position six-way valve, including three valve positions and six ports. The pressure compensation valve V2 switches positions via two hydraulic control terminals. The six ports are U (first port), V (third port), W (fifth port), X (second port), Y (fourth port), and Z (sixth port). Port X integrates a check valve (first check valve) V3, which is oriented to prevent any flow of hydraulic oil from port X into the pressure compensation valve V2, while allowing hydraulic oil to flow out of port X. In the first valve position (supply valve position), ports Y and V are shut off, and ports U and X are connected without throttling, as are ports W and Z. In the second valve position (transition valve position), ports V, W, Y, and Z are all shut off, and ports U and X are connected with throttling (pressure reduction). In the third valve position (shutdown valve position), ports U, W, X, and Z are all shut off, and ports V and Y are throttled (pressure reduced) connected. The flow area between ports V and Y (referred to as Ls cavity area) determines the pressure drop between ports V and Y (referred to as Ls cavity pressure drop).

[0035] Reference Figures 1-3 Oil circuit L2 is connected between high-pressure oil circuit L1 and the P port of control main valve V1; oil circuit (upstream side intermediate flow path) L3 is connected between the A port of control main valve V1 and the U port of pressure compensation valve V2; oil circuit (downstream side intermediate flow path) L4 is connected between the X port of pressure compensation valve V2 and the B port of control main valve V1; oil circuit L5 is connected between the C port of control main valve V1 and one side oil chamber of actuator 2; oil circuit L6 is connected between the D port of control main valve V1 and the other side oil chamber of actuator 2; and oil circuit L7 is connected between the T port of control main valve V1 and the oil tank.

[0036] Oil circuit L8 connects to oil circuit L3 and the first control terminal of pressure compensation valve V2. Oil circuit (upstream sensing flow path) L9 connects to oil circuit L3 and the V and W ports of pressure compensation valve V2. Oil circuit L9 has a check valve (second check valve) V4 in its upstream section, and a branch in its downstream section leads to the V and W ports of pressure compensation valve V2. Check valve V4 is configured to allow hydraulic oil to flow from oil circuit L3 through oil circuit L9 to the V and W ports, and to prevent hydraulic oil from flowing from the V and W ports back to oil circuit L9.

[0037] The oil circuit (downstream sensing flow path) L10 is connected between the pressure sensing oil circuit L0 and the Z port and Y port of the pressure compensation valve V2. The upstream branch of the oil circuit L9 is connected to the Z port and the Y port, and the downstream branch is connected to the pressure sensing oil circuit L0.

[0038] The hydraulic circuit also includes a shuttle valve V5 (pressure selection valve), which has two inlets and one outlet. Oil circuit L11 is connected between the first inlet of the shuttle valve V5 and the pressure sensing oil circuit L0. Oil circuit L12 is connected between the second inlet of the shuttle valve V5 and oil circuit L4. Oil circuit L13 is connected between the outlet of the shuttle valve V5 and the second control end of the pressure compensation valve V2.

[0039] In the above hydraulic circuit, when the pressure compensation valve V2 is in the first valve position, oil circuit L3 is connected to oil circuit L4 without throttling through the U port and X port of the pressure compensation valve V2. At the same time, oil circuit L3 is connected to oil circuit L10 without throttling through the W port and Z port of the pressure compensation valve V2.

[0040] When the pressure compensation valve V2 is in the second valve position, oil circuit L3 is throttled and connected to oil circuit L4 through the U port and X port of the pressure compensation valve V2, and oil circuit L3 is disconnected from oil circuit L10.

[0041] When the pressure compensation valve V2 is in the third valve position, the oil circuit L3 and oil circuit L4 are disconnected. Oil circuit L3 is throttled (pressure reduced) to oil circuit L10 via oil circuit L9 and the V and Y ports of the pressure compensation valve V2.

[0042] The first inlet of shuttle valve V5 is connected to pressure sensing oil circuit L0 via oil circuit L11, and the second inlet is connected to oil circuit L4 via oil circuit L12. Shuttle valve V5 connects the outlet of the pressure sensing oil circuit L0 and oil circuit L4 with the higher pressure, and applies oil pressure to the second control terminal of pressure compensation valve V2 via oil circuit L13 connected to the outlet, serving as the control pressure for the second control terminal. The control pressure of the first control terminal of pressure compensation valve V2 is taken from oil circuit L3 via oil circuit L8, meaning the control pressure of the first control terminal is the output pressure of port A of main valve 1.

[0043] The valve position of pressure compensation valve V2 is determined by the control pressure at the first and second control terminals.

[0044] When the pressure compensation valve V2 is in the first valve position, it establishes a non-throttling connection between oil circuits L3 and L4 via ports U and X, allowing the hydraulic oil in oil circuit L3 to be delivered to oil circuit L4 without obstruction. At the same time, the oil pressure in oil circuit L3 is transmitted to the pressure sensing oil circuit L0 via ports W and Z.

[0045] When the pressure compensation valve V2 is in the second position, it establishes a throttling connection between oil circuits L3 and L4, allowing the hydraulic oil in oil circuit L3 to be delivered to oil circuit L4 in a throttling manner. At the same time, the oil pressure in oil circuit L3 is no longer transmitted to the pressure sensing oil circuit L0.

[0046] When the pressure compensation valve V2 is in the third position, the connection between oil circuits L3 and L4 is cut off, and the check valve V3 prevents the hydraulic oil in oil circuit L4 from flowing back to oil circuit L3. At the same time, the oil pressure in oil circuit L3 is throttled (reduced) through the V and Y ports and transmitted to the pressure sensing oil circuit L0.

[0047] The second valve position of the pressure compensation valve V2 is a transition valve position between the first valve position and the third valve position.

[0048] When the main control valve V1 is in the neutral position, ports P, A, B, C, D, and T are all cut off, and the hydraulic oil output by hydraulic pump 1 cannot reach actuator 2, so actuator 2 does not operate.

[0049] When the main control valve V1 is switched to the first working position, oil circuit L2 connects to oil circuit L3 via ports P and A of the main control valve V1. The pressure in oil circuit L3 acts on the first control end of the pressure compensation valve V2 via oil circuit L8, making the control pressure at the first control end of the pressure compensation valve V2 higher than the control pressure at the second control end, thus switching the pressure compensation valve V2 to the first valve position. In this state, oil circuit L3 connects to oil circuit L4 via ports U and X of the pressure compensation valve V2. Oil circuit L4 then connects to oil circuit L5 via ports B and C of the main control valve V1, and oil circuit L6 connects to oil circuit L7 via ports D and T of the main control valve V1. In this way, the hydraulic oil output by the hydraulic pump 1 through the high-pressure oil circuit L1 is supplied to one side of the oil chamber of the actuator 2, causing the actuator 2 to move in the first direction.

[0050] When the main control valve V1 is switched to the second working position, oil circuit L2 connects to oil circuit L3 via ports P and A of the main control valve V1. Pressure compensation valve V2 is also in the first position, and oil circuit L3 connects to oil circuit L4 via ports U and X of the pressure compensation valve V2. Oil circuit L4 connects to oil circuit L6 via ports B and D of the main control valve V1, and oil circuit L5 connects to oil circuit L7 via ports C and T of the main control valve V1. In this way, the hydraulic oil output from hydraulic pump 1 via high-pressure oil circuit L1 is supplied to the other side of the oil chamber of actuator 2, causing actuator 2 to actuate in the second direction.

[0051] During hydraulic system operation, when the pressure in pressure sensing circuit L0 is higher than or equal to the pressure in circuit L4 (representing the load of actuator 2), the pressure in pressure sensing circuit L0 acts on the second control terminal of pressure compensation valve V2 through the action of shuttle valve V5. Simultaneously, the pressure in circuit L3 acts on the first control terminal of pressure compensation valve V2. Because check valve V4 has a certain opening pressure, the pressure in pressure sensing circuit L0 is lower than the pressure in circuit L3. That is, the control pressure at the second control terminal of pressure compensation valve V2 is lower than the control pressure at the first control terminal. Pressure compensation valve V2 is in the first valve position and operates normally. The flow rate allocated to actuator 2 is controlled solely by the main control valve V1 and is independent of the load on actuator 2.

[0052] If the load pressure of actuator 2 suddenly increases (e.g., due to inertia), causing a sharp increase in pressure in oil circuit L4 (exceeding the pressure in oil circuit L3), resulting in the pressure in pressure sensing oil circuit L0 being lower than the pressure in oil circuit L4, the pressure in oil circuit L4 will act on the second control end of pressure compensation valve V2 through the action of shuttle valve V5, pushing pressure compensation valve V2 to the third valve position, cutting off the connection between oil circuit L3 and oil circuit L4. At the same time, the check valve V3 in pressure compensation valve V2 prevents hydraulic oil from actuator 2 from flowing backward through pressure compensation valve V2 to control main valve 1, thereby protecting the hydraulic system, especially hydraulic pump 1.

[0053] Furthermore, when the main control valve V1 is in the first or second working position and the hydraulic pump 1 starts operating, causing the oil pressure supplied to the actuator 2 to rise from zero to the load pressure, the pressure compensation valve V2 is in the third position. During this period, the check valve V3 can also prevent the actuator 2 from backflowing oil under load.

[0054] In the third valve position of the pressure compensation valve V2, since the pressure sensing oil circuit L0 remains connected to the oil circuit L3, even though the oil circuit L3 and the oil circuit L4 are disconnected, the pressure sensing oil circuit L0 is not closed, and the hydraulic variable displacement mechanism 3 can still receive the load sensing pressure from the pressure sensing oil circuit L0 and maintain normal operation.

[0055] For the other actuators 2 in the hydraulic system, their hydraulic circuits can be the same as or similar to those described above. The hydraulic circuits are connected in parallel, and their oil passages L10 are unobstructedly connected to the common pressure sensing oil passage L0. Therefore, the sensed pressure in the pressure sensing oil passage L0 is the highest pressure in the oil passage L10 of each hydraulic circuit, which represents the highest load pressure.

[0056] In the first position of the pressure compensation valve V2, oil circuit L3 is connected to the pressure sensing oil circuit L0 via the check valve V4. Therefore, the pressure in oil circuit L3 is essentially equal to the load pressure sensed in the pressure sensing oil circuit L0 plus the pressure reduction pressure in the pressure compensation valve V2. This maintains the pressure in oil circuit L3 across multiple hydraulic circuits at approximately equal levels. This achieves load-independent flow control, where the flow rate delivered to each actuator depends only on the flow area of ​​the corresponding control valve.

[0057] Furthermore, as mentioned earlier, the area of ​​the Ls chamber of the pressure compensation valve V2 determines the pressure drop of the Ls chamber. If the area of ​​the Ls chamber of the pressure compensation valve V2 in a certain hydraulic circuit is designed to be smaller than that of the pressure compensation valve V2 in other hydraulic circuits, then the pressure drop of the Ls chamber of the pressure compensation valve V2 in this hydraulic circuit will be greater than that of the pressure compensation valve V2 in other hydraulic circuits. After the hydraulic pump 1 starts, the pressure build-up rate of oil circuits L3 and L8 in this hydraulic circuit will be greater than that of oil circuits L3 and L8 in other hydraulic circuits, causing the pressure compensation valve V2 in this hydraulic circuit to switch to the first valve position slightly earlier than the pressure compensation valve V2 in other hydraulic circuits. Consequently, the actuator 2 corresponding to this hydraulic circuit will actuate before other actuators 2. This function is not achievable in existing LUDV hydraulic systems.

[0058] Based on this principle, the Ls chamber area of ​​the pressure compensation valve V2 in one or more hydraulic circuits can be designed to be smaller than the Ls chamber area of ​​the pressure compensation valve V2 in other hydraulic circuits, so that the corresponding actuator 2 can obtain a slightly superior performance compared to other actuators 2.

[0059] Based on the principles of this application, those skilled in the art can make various adaptive modifications to the hydraulic system of this application. For example, the control valves and compensation valves (especially the number of ports, the number of valve positions, etc.) need not be limited to the examples shown in the figure, as long as they can achieve the various functions described above.

[0060] The hydraulic system of this application provides pressure compensation by setting a pressure compensation valve V2 between the intermediate oil passages (oil passages L3 and L4) connecting the two working ports of the control valve V1, thereby enabling the hydraulic system to have independent flow distribution capability. By integrating a check valve V3 into the pressure compensation valve V2 to provide anti-backflow function, the system structure space is reduced, thereby reducing material and processing costs.

[0061] In addition, a check valve V4 (or other type of pressure reducing valve) is installed between oil circuit L3 and pressure sensing oil circuit L0 to provide pressure reduction for pressure sensing oil circuit L0 relative to oil circuit L3, so that pressure compensation valve V2 can achieve correct switching between the three valve positions.

[0062] In addition, the sensed pressure in the pressure sensing oil circuit L0 is used to control the displacement of the hydraulic pump 1. Even when the pressure compensation valve V2 is switched to the third valve position and the check valve V3 is used to achieve the anti-backflow function, the hydraulic pump 1 can still sense the load pressure and work normally.

[0063] Furthermore, although in the example described above the pressure compensation valve is located between the intermediate oil passages connecting the two working ports of the control valve, it is also feasible to install pressure compensation valves between the intermediate oil passages connecting more working ports of the control valve.

[0064] While this application has been described herein with reference to specific embodiments, the scope of this application is not limited to the details shown. Various modifications may be made to these details without departing from the basic principles of this application.

Claims

1. A hydraulic system comprising: a hydraulic pump (1) and a plurality of actuators (2); and a hydraulic circuit equipped for each actuator (2) for supplying hydraulic oil from the hydraulic pump (1) to the corresponding actuator (2); wherein at least a first hydraulic circuit among the hydraulic circuits comprises: a control valve (V1) having at least an oil inlet port (P), a first intermediate oil port (A), a second intermediate oil port (B), a first load oil port (C) and a second load oil port (D), wherein the oil inlet port (P) is connected to an output of the hydraulic pump (1), the first and second load oil ports (C, D) are connected to two working chambers of the corresponding actuator (2), respectively, the control valve (V1) has at least one working valve position in which the oil inlet port (P) is in communication with the first intermediate oil port (A) and the second intermediate oil port (B) is in communication with the first or second load oil port (C, D); and a pressure compensation valve (V2) configured to control the communication between the first and second intermediate oil ports (A, B); wherein a first check valve (V3) is integrated in the pressure compensation valve (V2) and oriented to allow the flow of hydraulic oil from the pressure compensation valve (V2) towards the second intermediate oil port (B) and to prevent the flow of hydraulic oil from the second intermediate oil port (B) towards the pressure compensation valve (V2). The pressure compensation valve (V2) has a first oil port (U) connected to the first intermediate oil port (A) via an upstream-side intermediate flow path (L3) and a second oil port (X) connected to the second intermediate oil port (B) via a downstream-side intermediate flow path (L4), and the first check valve (V3) is integrated in the second oil port (X).

2. The hydraulic system of claim 1, wherein, The pressure compensation valve (V2) further has a third oil port (V), a fourth oil port (Y), a fifth oil port (W) and a sixth oil port (Z), the third and fifth oil ports (V, W) being connected to the upstream-side intermediate flow path (L3) and the fourth and sixth oil ports (Y, Z) being connected to a pressure sensing oil path (L0) of the hydraulic system.

3. The hydraulic system of claim 2, wherein, The pressure compensation valve (V2) has:

4. The hydraulic system of claim 3, wherein, a supply valve position in which the third and fourth oil ports (V, Y) are in a blocked state, the first and second oil ports (U, X) are in an unobstructed communication, and the fifth and sixth oil ports (W, Z) are in an unobstructed communication; and a blocked valve position in which the first and second oil ports (U, X), the fifth and sixth oil ports (W, Z) are in a blocked state, and the third and fourth oil ports (V, Y) are in a throttling communication. The pressure compensation valve (V2) has a transition valve position between the supply valve position and the blocked valve position, in which the third and fourth oil ports (V, Y), the fifth and sixth oil ports (W, Z) are in a blocked state, and the first and second oil ports (U, X) are in a throttling communication.

5. The hydraulic system of claim 4, wherein, ​ 6. The hydraulic system of claim 4, wherein, The first side control port of the pressure compensating valve (V2) is connected to the upstream-side intermediate flow path (L3); The first hydraulic circuit further includes a pressure selection valve (V5) configured to supply the higher of the pressure of the pressure sensing oil path (L0) and the pressure of the downstream-side intermediate flow path (L4) to the second side control port of the pressure compensating valve (V2).

7. The hydraulic system of claim 6, wherein, The pressure selection valve (V5) is a shuttle valve (V5) having a first oil inlet connected to the pressure sensing oil path (L0), a second oil inlet connected to the downstream-side intermediate flow path (L4), and an oil outlet connected to the second side control port of the pressure compensating valve (V2).

8. The hydraulic system of claim 6, wherein, The pressure compensating valve (V2) is configured to be in the oil supply valve position when the control pressure of the first side control port is higher than the control pressure of the second side control port, and to be in the shut-off valve position when the control pressure of the second side control port is higher than the control pressure of the first side control port.

9. The hydraulic system of any of claims 3-8, wherein, A second check valve (V4) is provided between the upstream-side intermediate flow path (L3) and the third oil port (V) and the fifth oil port (W), and is oriented to allow hydraulic oil to flow from the upstream-side intermediate flow path (L3) to the third oil port (V) and the fifth oil port (W), and to prevent hydraulic oil from flowing from the third oil port (V) and the fifth oil port (W) to the upstream-side intermediate flow path (L3).

10. The hydraulic system of any one of claims 3-8, wherein, The displacement of the hydraulic pump (1) is determined based on the difference between the output port pressure of the hydraulic pump (1) and the pressure in the pressure sensing oil path (L0).

11. The hydraulic system of any one of claims 3-8, wherein, At least a second hydraulic circuit of the hydraulic system has the same configuration as the first hydraulic circuit, and the through area between the third oil port (V) and the fourth oil port (Y) when the pressure compensating valve (V2) in the first hydraulic circuit is in the shut-off valve position is smaller than the through area between the third oil port (V) and the fourth oil port (Y) when the pressure compensating valve (V2) in the second hydraulic circuit is in the shut-off valve position, so that the actuation of an actuator (2) supplied with oil by the first hydraulic circuit precedes the actuation of an actuator (2) supplied with oil by the second hydraulic circuit.

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