A constant pressure control system and control method for a variable displacement pump

Abstract

The present invention discloses a constant pressure control system for a variable pump, comprising a feedback control valve group and a multi-way valve group; the feedback control valve group includes a hydraulically controlled one-way valve; the multi-way valve group includes a three-position six-way reversing valve; in the present invention, by operating the reversing valve in a neutral position, the state of the variable pump can be switched to a low-pressure standby mode, thereby reducing energy consumption; and when the reversing valve is operated in an upper or lower position, the state of the variable pump can be switched to a constant pressure control mode, thereby improving response speed, that is, eliminating load response time. The present invention implements constant pressure control by applying a three-position six-way reversing valve without load feedback to the system, thereby reducing system construction costs and simultaneously achieving low-pressure, small-displacement standby and constant pressure mode operation. The present invention also discloses a constant pressure control method for a variable pump. The method of the present invention switches the operating mode of the variable pump and switches the output direction of the actuator by operating the reversing valve to switch between a neutral position, an upper position, and a lower position.

Description

Technical Field

[0001] The present invention relates to the technical field of pump control, and in particular to a constant pressure control system and a control method for a variable displacement pump. Background Art

[0002] In hydraulically driven mechanical equipment, its hydraulic circuit includes at least a hydraulic pump and a multi-way valve, wherein the hydraulic pump provides pressure oil to drive the mechanical equipment, and the multi-way valve is located between the hydraulic pump and the actuator to control the flow size and flow direction of the hydraulic oil, thereby realizing the control of the movement direction and speed of the actuator. According to whether the displacement of the variable pump used in the hydraulic system changes, the hydraulic system is divided into a fixed pump system and a variable pump system. The variable pump system is widely used because it can better adapt to load requirements and has better energy-saving effects. The multi-way valve is divided into a load-sensitive multi-way valve and a multi-way valve without load feedback according to whether it has load feedback. The two types of multi-way valves have their own applications in different usage scenarios.

[0003] According to the control strategy of the variable pump, the variable pump system has constant pressure control mode and load sensitive control mode; 1. Constant pressure control has the advantages of fast response and high stability, and load sensitive control mode has the advantages of high efficiency, small power loss and low energy consumption. When the actuator is far away from the control valve, the advantages of constant pressure control such as fast response and high stability are outstanding. At the same time, it can also avoid the operator's misjudgment of system failure due to a long waiting time; 2. In the quantitative pump system, the multi-way valve mostly adopts the open-center six-way multi-way valve, which has the advantages of compact structure and easy operation, but it does not have load feedback function, which is a defect in energy saving. If all four-way multi-way valves with load sensitive control function are used, the advantages of the six-way multi-way valve are lost and the cost is greatly increased.

[0004] Therefore, in the current variable pump control system, load-sensitive valves (i.e., four-way multi-way valves) are mostly used, which are relatively expensive. When using multi-way valves without load feedback (i.e., open-center six-way multi-way valves), shuttle valves are generally used to collect the working oil circuit pressure, or load feedback devices are added to the six-way multi-way valve, etc., which have complex structures and are inconvenient to operate.

[0005] In summary, there is an urgent need for a variable pump constant pressure control system and control method with a simple structure and low cost to enable the use of a multi-way valve without load feedback in a variable pump structure. Summary of the Invention

[0006] The present invention aims to provide a constant pressure control system and control method for a variable pump, so as to realize the use of a multi-way valve without load feedback in a variable pump structure. The specific technical solution is as follows:

[0007] A constant pressure control system for a variable pump, comprising a feedback control valve group and a multi-way valve group;

[0008] The feedback control valve group includes a hydraulically controlled one-way valve; the oil inlet of the hydraulically controlled one-way valve is connected to the oil outlet of the variable pump, and the oil outlet of the hydraulically controlled one-way valve is connected to the variable mechanism of the variable pump; the multi-way valve group includes a three-position six-way reversing valve; the three-position six-way reversing valve includes port A, port B, port P and a central oil circuit; port A and port B are respectively connected to the actuator; port P is connected to the oil outlet of the variable pump; the oil inlet of the central oil circuit is connected to the oil outlet of the variable pump, and the oil outlet of the central oil circuit is connected to the control chamber of the hydraulically controlled one-way valve.

[0009] Preferably, the above technical solution comprises the feedback control valve group further comprising a first relief valve; the oil inlet of the first relief valve is connected to the oil outlet of the hydraulically controlled one-way valve, and the oil outlet of the first relief valve is connected to the oil tank.

[0010] Preferably, the above technical solution comprises the feedback control valve group further comprising a first damper; the first damper is arranged between the oil inlet of the hydraulically controlled one-way valve and the oil outlet of the variable pump.

[0011] Preferably, the above technical solution comprises the feedback control valve group further comprising a second damper; the oil outlet of the hydraulically controlled one-way valve is connected to the oil tank, and the second damper is arranged between the oil outlet of the hydraulically controlled one-way valve and the oil tank.

[0012] Preferably, the above technical solution comprises the feedback control valve group further comprising a third damper; the control chamber of the hydraulically controlled one-way valve is connected to the oil tank, and the third damper is arranged between the control chamber of the hydraulically controlled one-way valve and the oil tank.

[0013] The above technical solution is preferred, wherein the multi-way valve group includes multiple groups of three-position six-way directional valves; the central oil circuits of the multiple groups of three-position six-way directional valves are connected in series, the oil inlet of the first group of three-position six-way directional valves is connected to the oil outlet of the variable pump, and the oil outlet of the last group of three-position six-way directional valves is connected to the control chamber of the hydraulically controlled one-way valve; the actuators correspond one-to-one to the three-position six-way directional valves.

[0014] The above technical solution is preferably that the three-position six-way directional valve is an open-center three-position six-way directional valve.

[0015] Preferably, the above technical solution has a T port of the three-position six-way directional valve connected to the oil tank.

[0016] Preferably, the multi-way valve group further comprises a second relief valve; the oil inlet of the second relief valve is connected to the oil outlet of the variable pump, and the oil outlet of the second relief valve is connected to the oil tank.

[0017] A constant pressure control method for a variable pump, using the constant pressure control system of the variable pump, is specifically as follows:

[0018] When all three-position six-way directional valves of the multi-way valve group are in the middle position:

[0019] The central oil circuit of the three-position six-way reversing valve is connected, and the outlet oil of the variable pump is divided into two paths. One path reaches the oil inlet of the hydraulically controlled one-way valve, and the other path enters the control chamber of the hydraulically controlled one-way valve along the central oil circuit of multiple groups of three-position six-way reversing valves, causing the hydraulically controlled one-way valve to close. At this time, the outlet oil of the variable pump cannot be fed back to the variable mechanism of the variable pump, and the variable pump is in a low-pressure standby state;

[0020] When at least one of the three-position six-way directional valves in the multi-way valve group is in the upper or lower position:

[0021] The working state of the three-position six-way reversing valve is in the upper or lower position, the hydraulically controlled one-way valve is in the on state, the outlet oil of the variable pump passes through the hydraulically controlled one-way valve and is fed back to the variable mechanism of the variable pump, and the variable pump is in a constant pressure control state.

[0022] The application of the technical solution of the present invention has the following beneficial effects:

[0023] (1) The constant pressure control system of the variable pump of the present invention includes a feedback control valve group and a multi-way valve group; the feedback control valve group includes a hydraulically controlled one-way valve; the multi-way valve group includes a three-position six-way reversing valve (hereinafter referred to as the reversing valve); the reversing valve includes an A port, a B port, a P port and a central oil circuit; in the present invention, by operating the reversing valve in the middle position, the state of the variable pump can be switched to a low-pressure standby mode, thereby reducing energy consumption, and when the reversing valve is operated in the upper or lower position, the state of the variable pump can be switched to a constant pressure control mode, thereby improving the response speed, that is, eliminating the load response time, which has obvious advantages in long-distance control systems, and the present invention realizes constant pressure control by applying a three-position six-way reversing valve without load feedback to the system, thereby reducing the construction cost of the system, and can also realize low-pressure small-displacement standby and constant pressure mode operation at the same time.

[0024] (2) In the present invention, the first relief valve is used to limit the control oil pressure fed back to the variable pump, ensuring that the control oil pressure fed back to the variable pump does not exceed the set value, and at the same time has the function of remote pressure regulation.

[0025] (3) In the present invention, the function of the first damper is to reduce the flow rate of the control oil circuit, reduce the risk of system leakage, and at the same time ensure that the pressure of the control oil circuit will not fluctuate greatly when the system pressure fluctuates.

[0026] (4) In the present invention, after all the reversing valves in the multi-way valve group are switched from the upper and lower positions to the middle position, the outlet oil of the hydraulically controlled one-way valve is discharged into the oil tank through the second damper, and the small displacement mode is restored, which can avoid the next load start-up. In addition, the second damper can ensure that the pressure oil passing through the hydraulically controlled one-way valve will not be discharged in the constant pressure mode.

[0027] (5) In the present invention, when at least one group of reversing valves is operating in the upper or lower position, the oil in the control chamber of the hydraulically controlled one-way valve is discharged through the third damper, causing the hydraulically controlled one-way valve to be conductive, thereby switching the variable pump to a constant pressure control mode. Moreover, due to the presence of the third damper, when switching to a small displacement mode, the pressure in the control chamber of the hydraulically controlled one-way valve can be established.

[0028] (6) The multiple groups of reversing valves of the present invention can control different actuators respectively, and by operating the corresponding reversing valves to switch between the upper position and the lower position, the oil inlet and outlet directions of the actuators can be changed to change their output direction. Moreover, only when all the reversing valves in the multi-way valve group are in the middle position can the low-pressure and small-displacement mode be switched, which has good practicality.

[0029] (7) The present invention adopts an open-center three-position six-way directional valve, which makes the system of the present invention have the advantages of compact structure and easy operation. In addition, the open-center three-position six-way directional valve cooperates with the feedback control valve group in the present invention, so that the directional valve of the present invention can achieve constant pressure control; the three-position six-way directional valve in the present invention adopts a self-resetting three-position six-way directional valve, which can automatically return to the middle position. After all the directional valves return to the middle position, the small displacement mode is started.

[0030] (8) In the present invention, the actuator returns oil to the oil tank through the T port, which is a reasonable structure.

[0031] (9) In the present invention, the second overflow valve is used to limit the maximum working pressure of the system to ensure system stability.

[0032] (10) The constant pressure control method of the variable pump of the present invention uses the constant pressure control system of the variable pump. The method of the present invention switches between the middle position, the upper position and the lower position by operating the reversing valve, and can switch the working mode of the variable pump and the output direction of the actuator. It is easy to operate and has high reliability.

[0033] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] In the attached figure:

[0036] Figure 1 is a schematic diagram of the constant pressure control system of this embodiment;

[0037] Figure 2 yes Figure 1Schematic diagram of the feedback control valve group;

[0038] Figure 3 yes Figure 1 Schematic diagram of the multi-way valve group;

[0039] Figure 4 yes Figure 3 Schematic diagram of the reversing valve in;

[0040] Among them, 1. Feedback control valve group; 1.1. Hydraulic-controlled one-way valve; 1.2. First overflow valve; 1.3. First damping; 1.4. Second damping; 1.5. Third damping; 2. Multi-way valve group; 2.1. Reversing valve; 2.2. Second overflow valve; 3. Variable pump; 3.1. Variable mechanism of variable pump; P3, oil outlet of variable pump; LS, control oil port of variable mechanism. DETAILED DESCRIPTION

[0041] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0042] Example:

[0043] The present embodiment discloses a constant pressure control system for a variable pump, which includes a feedback control valve group 1 and a multi-way valve group 2. The feedback control valve group 1 and the multi-way valve group 2 of the present embodiment cooperate to switch the variable pump 3 (load-sensitive variable pump) between a low-pressure standby mode and a constant pressure control mode. The constant pressure control system in the present embodiment is mainly divided into two parts for description. The first part mainly describes the structures and connection relationships of the feedback control valve group 1 and the multi-way valve group 2. The second part mainly describes the structural functions of the feedback control valve group 1 and the multi-way valve group 2, such as Figures 1 to 4 As shown, the details are as follows:

[0044] Part 1 (connection between parts):

[0045] The feedback control valve group 1 includes a hydraulically controlled one-way valve 1.1, a first relief valve 1.2, a first damper 1.3, a second damper 1.4 and a third damper 1.5. Figure 1 and Figure 2 As shown:

[0046] The oil inlet of the hydraulically controlled one-way valve 1.1 is connected to the oil outlet P3 of the variable pump. The oil outlet of the hydraulically controlled one-way valve 1.1 is respectively connected to the variable mechanism 3.1 of the variable pump, the oil tank, and the first relief valve 1.2. When the hydraulically controlled one-way valve 1.1 is open, oil at the oil outlet P3 of the variable pump is fed back to the variable mechanism through the hydraulically controlled one-way valve 1.1. The variable mechanism then operates based on the fed-back oil (i.e., the LS signal). (The operation herein refers to the prior art and will not be described in detail in this embodiment.) At this point, the variable pump 3 is in constant pressure control mode. In this embodiment, when oil flows into the control chamber of the hydraulically controlled one-way valve 1.1, the hydraulically controlled one-way valve 1.1 is closed (i.e., closed). Conversely, after the oil in the control chamber of the hydraulically controlled one-way valve 1.1 is released, the hydraulically controlled one-way valve 1.1 is opened. In this embodiment, the control chamber of the hydraulically controlled one-way valve 1.1 is connected to the multi-way valve assembly 2 (specifically, port P2 of the three-position, six-way reversing valve 2.1).

[0047] The oil inlet of the first relief valve 1.2 is connected to the oil outlet of the hydraulically controlled one-way valve 1.1, and the oil outlet of the first relief valve 1.2 is connected to the oil tank; the relief pressure of the first relief valve 1.2 is selected according to actual conditions.

[0048] The first damper 1.3 is provided between the oil inlet of the hydraulically controlled one-way valve 1.1 and the oil outlet P3 of the variable displacement pump.

[0049] The second damper 1.4 is arranged between the oil outlet of the hydraulically controlled one-way valve 1.1 and the oil tank. In this embodiment, the input end of the second damper 1.4 is specifically connected between the oil outlet of the hydraulically controlled one-way valve 1.1 and the variable mechanism (specifically the control oil port LS of the variable mechanism).

[0050] The control chamber of the hydraulically controlled one-way valve 1.1 is connected to the oil tank, and the third damper 1.5 is arranged between the control chamber of the hydraulically controlled one-way valve 1.1 and the oil tank. In this embodiment, the input end of the third damper 1.5 is specifically connected between the control chamber of the hydraulically controlled one-way valve 1.1 and the P2 port of the three-position six-way reversing valve 2.1.

[0051] In this embodiment, the damping forces of the second damper 1.4 and the third damper 1.5 are greater than the damping force of the first damper 1.3, that is, the inner diameters of the damping openings of the second damper 1.4 and the third damper 1.5 are smaller than the inner diameter of the damping opening of the first damper 1.3.

[0052] The multi-way valve group 2 includes a three-position six-way reversing valve 2.1 and a second relief valve 2.2. Figure 1 and Figure 3 As shown:

[0053] The three-position, six-way directional valve 2.1 in this embodiment is an open-center, three-position, six-way directional valve 2.1 (hereinafter referred to as the directional valve). The directional valve 2.1 specifically includes port A, port B, port P, port T, and a central oil circuit. The oil ports at both ends of the central oil circuit are port P1 (oil inlet) and port P2 (oil outlet). The three-position, six-way directional valve 2.1 can be provided in one or more groups, as follows:

[0054] When the number of reversing valves 2.1 is one group: port P1 of reversing valve 2.1 is connected to the oil outlet P3 of the variable pump, port P2 of reversing valve 2.1 is connected to the control chamber of hydraulically controlled check valve 1.1, port A is connected to the second oil port of the actuator, port B is connected to the first oil port of the actuator, port P is connected to the oil outlet P3 of the variable pump, and port T is connected to the oil tank.

[0055] When there are multiple sets of reversing valves 2.1, the number of actuators corresponds to the number of sets of reversing valves 2.1. The multiple sets of actuators are driven by the multiple sets of reversing valves 2.1. The central oil circuits of the multiple sets of reversing valves 2.1 are connected in series. Specifically, port P1 of the first set of reversing valves 2.1 is connected to the oil outlet P3 of the variable pump, port P2 of the first set of reversing valves 2.1 is connected to port P1 of the second set of reversing valves 2.1, and port P2 of the second set of reversing valves 2.1 is connected to port P1 of the third set of reversing valves 2.1 (only two sets of reversing valves 2.1 are shown in this embodiment). In this manner, the multiple sets of reversing valves 2.1 are connected in series, and port P2 of the last set of reversing valves 2.1 is connected to the control chamber of the hydraulically piloted check valve 1.1. The connection relationship between ports A, B, P, and T of the multiple sets of reversing valves 2.1 is the same as described above (i.e., the same as when there is only one set of reversing valves 2.1).

[0056] The reversing valve 2.1 in this embodiment is a reversing valve with a self-resetting function, which can automatically return to the middle position.

[0057] In this embodiment, it is necessary to explain the reversing valve 2.1. Figure 4 As shown:

[0058] When the reversing valve 2.1 is in the middle position: the central oil circuit is connected (i.e., port P1 is connected to port P2), ports A and B are both connected to port T, and port A is not connected to port P;

[0059] When the reversing valve 2.1 is in the upper position: the central oil circuit is not connected, port A is connected to port T, and port B is connected to port P;

[0060] When the reversing valve 2.1 is in the lower position: the central oil circuit is not connected, port A is connected to port P, and port B is connected to port T.

[0061] The oil inlet of the second relief valve 2.2 is connected to the oil outlet P3 of the variable pump, and the oil outlet of the second relief valve 2.2 is connected to the oil tank. The relief pressure of the second relief valve 2.2 is set according to actual conditions.

[0062] Part II (Main functions of each part):

[0063] Hydraulic control one-way valve 1.1: The function of the hydraulic control one-way valve 1.1 is to ensure that when all the reversing valves 2.1 are working in the middle position, it is in the closed state, so that the pressure oil at the outlet of the variable pump 3 will not be fed back to the variable mechanism. When at least one group of reversing valves 2.1 is working in the upper or lower position, the hydraulic control one-way valve 1.1 is in the open state so that the pressure oil at the outlet of the variable pump 3 can be fed back to the variable mechanism 3.1 of the variable pump, specifically entering the variable mechanism from the control oil port of the variable mechanism.

[0064] First relief valve 1.2: The function of the first relief valve 1.2 is to limit the control oil pressure fed back to the variable pump 3, to ensure that the control oil pressure fed back to the variable pump 3 does not exceed the set value, and at the same time has the function of remote pressure regulation.

[0065] First damping 1.3: The function of the first damping 1.3 is to reduce the flow rate of the control oil circuit, reduce the risk of system leakage, and ensure that the pressure of the control oil circuit will not fluctuate greatly when the system pressure fluctuates.

[0066] Second damping 1.4: The function of the second damping 1.4 is to ensure that when all the reversing valves 2.1 are switched to the middle position, the pressure oil fed back to the variable mechanism can be released, so that the variable pump 3 can return to a small displacement.

[0067] The third damper 1.5: The function of the third damper 1.5 is to ensure that when all the reversing valves 2.1 are switched to the middle position, the pressure oil in the control chamber of the hydraulically controlled one-way valve 1.1 can be drained to ensure that the hydraulically controlled one-way valve 1.1 can open normally.

[0068] Directional valve 2.1: The function of the directional valve 2.1 is to connect or close the oil circuit and the load, or to change the direction of oil flow, so as to start, stop or change the output direction of the actuator.

[0069] Second relief valve 2.2: The second relief valve 2.2 is connected to the main oil circuit of the system to limit the maximum working pressure of the system.

[0070] This embodiment also discloses a constant pressure control method for the variable pump 3, which uses the constant pressure control system of the variable pump, as follows:

[0071] When all three-position six-way directional valves 2.1 of the multi-way valve group 2 are in the middle position, the variable pump 3 is in the low-pressure standby state. Specifically:

[0072] Since all the reversing valves 2.1 in the multi-way valve group 2 are in the middle position, the central oil circuits of all the reversing valves 2.1 are connected. The outlet oil of the variable pump 3 is divided into two paths. One path reaches the oil inlet of the hydraulically controlled non-return valve 1.1, and the other path enters the control chamber of the hydraulically controlled non-return valve 1.1 along the central oil circuit of the multiple groups of reversing valves 2.1. Due to the presence of the third damper 1.5, the pressure in the control chamber can be built up, causing the hydraulically controlled non-return valve 1.1 to close (i.e., not conduct). At this time, the outlet oil of the variable pump 3 cannot pass through the hydraulically controlled non-return valve 1.1 and cannot be fed back to the variable mechanism 3.1 of the variable pump. In other words, the variable pump 3 is in a low-pressure standby state.

[0073] When at least one of the three-position six-way directional valves 2.1 in the multi-way valve group 2 is in the upper or lower position, the variable pump 3 is in a constant pressure control state. Specifically:

[0074] When reversing valve 2.1 is in the upper or lower working state, the central oil circuit of reversing valve 2.1 is cut off. That is, since the central oil circuit of reversing valve 2.1 is blocked, the outlet oil of variable pump 3 cannot enter the control chamber of hydraulically piloted check valve 1.1 along the central oil circuit of multiple sets of reversing valves 2.1. In addition, the pressure in the control chamber of hydraulically piloted check valve 1.1 is released through third damper 1.5, causing hydraulically piloted check valve 1.1 to be in the open state. Second damper 1.4 builds up the pressure in the feedback control oil circuit. At this time, the outlet oil of variable pump 3 passes through the oil outlet of hydraulically piloted check valve 1.1 and is fed back to the variable mechanism 3.1 of the variable pump (i.e., the LS signal is fed back to the variable mechanism), indicating that variable pump 3 is in a constant pressure control state.

[0075] When a set of reversing valves 2.1 switches between the upper and lower positions, the oil circuit direction of the actuator corresponding to the reversing valve 2.1 can change, thereby changing the output direction of the actuator. The oil flow direction of the actuator is as follows:

[0076] When the reversing valve 2.1 is in the middle position, the oil in the P port cannot enter the actuator, so the actuator does not operate.

[0077] When the reversing valve 2.1 is in the up position, the oil in port P enters the actuator through port B, and the actuator returns oil to the tank through ports A and T;

[0078] When the reversing valve 2.1 is in the lower position, the oil in port P enters the actuator through port A, and the actuator returns oil to the tank through ports B and T.

[0079] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A constant pressure control system for a variable displacement pump, characterized in that: It comprises a feedback control valve group (1) and a multi-way valve group (2); The feedback control valve group (1) includes a hydraulically controlled one-way valve (1.1); an oil inlet of the hydraulically controlled one-way valve (1.1) is connected to an oil outlet (P3) of a variable pump, and an oil outlet of the hydraulically controlled one-way valve (1.1) is connected to a variable mechanism (3.1) of the variable pump; The multi-way valve group (2) includes a three-position six-way directional control valve (2.1); the three-position six-way directional control valve (2.1) includes an A port, a B port, a P port and a central oil circuit; Port A and port B are respectively connected to the actuator; port P is connected to the oil outlet (P3) of the variable pump; the oil inlet (P1) of the central oil circuit is connected to the oil outlet (P3) of the variable pump, and the oil outlet (P2) of the central oil circuit is connected to the control chamber of the hydraulically controlled one-way valve (1.1).

2. The constant pressure control system of a variable displacement pump according to claim 1, characterized in that: The feedback control valve group (1) further comprises a first overflow valve (1.2); the oil inlet of the first overflow valve (1.2) is connected to the oil outlet of the hydraulically controlled one-way valve (1.1), and the oil outlet of the first overflow valve (1.2) is connected to the oil tank.

3. The constant pressure control system of a variable displacement pump according to claim 1, characterized in that: The feedback control valve group (1) further comprises a first damper (1.3); the first damper (1.3) is arranged between the oil inlet of the hydraulically controlled one-way valve (1.1) and the oil outlet (P3) of the variable pump.

4. The constant pressure control system of a variable displacement pump according to claim 1, characterized in that: The feedback control valve group (1) also includes a second damper (1.4); the oil outlet of the hydraulically controlled one-way valve (1.1) is connected to the oil tank, and the second damper (1.4) is arranged between the oil outlet of the hydraulically controlled one-way valve (1.1) and the oil tank.

5. The constant pressure control system of a variable displacement pump according to any one of claims 1 to 4, characterized in that: The feedback control valve group (1) also includes a third damper (1.5); the control chamber of the hydraulically controlled one-way valve (1.1) is connected to the oil tank, and the third damper (1.5) is arranged between the control chamber of the hydraulically controlled one-way valve (1.1) and the oil tank.

6. The constant pressure control system of a variable displacement pump according to any one of claims 1 to 4, characterized in that: The multi-way valve group (2) comprises multiple groups of three-position six-way directional valves (2.1); the central oil circuits of the multiple groups of three-position six-way directional valves (2.1) are connected in series, the oil inlet (P1) of the first group of three-position six-way directional valves (2.1) is connected to the oil outlet (P3) of the variable pump, and the oil outlet (P2) of the last group of three-position six-way directional valves (2.1) is connected to the control chamber of the hydraulically controlled one-way valve (1.1); and the actuators correspond one to one with the three-position six-way directional valves (2.1).

7. The constant pressure control system of a variable displacement pump according to claim 6, characterized in that: The three-position six-way directional control valve (2.1) is an open-center three-position six-way directional control valve (2.1).

8. The constant pressure control system of a variable displacement pump according to claim 6, characterized in that: The T port of the three-position six-way reversing valve (2.1) is connected to the oil tank.

9. The constant pressure control system of a variable displacement pump according to claim 1, characterized in that: The multi-way valve assembly (2) further comprises a second overflow valve (2.2); the oil inlet of the second overflow valve (2.2) is connected to the oil outlet (P3) of the variable pump, and the oil outlet of the second overflow valve (2.2) is connected to the oil tank.

10. A constant pressure control method for a variable displacement pump, characterized in that: The constant pressure control system using the variable pump as claimed in claim 6 is specifically as follows: When all three-position six-way directional valves (2.1) of the multi-way valve group (2) are in the middle position: The central oil circuit of the three-position six-way directional valve (2.1) is connected, and the outlet oil of the variable pump (3) is divided into two paths. One path reaches the oil inlet of the hydraulically controlled one-way valve (1.1), and the other path enters the control chamber of the hydraulically controlled one-way valve (1.1) along the central oil circuit of the multiple groups of three-position six-way directional valves (2.1), so that the hydraulically controlled one-way valve (1.1) is closed. At this time, the outlet oil of the variable pump (3) cannot be fed back to the variable mechanism (3.1) of the variable pump, and the variable pump (3) is in a low-pressure standby state; When at least one set of three-position six-way directional valves (2.1) of the multi-way valve group (2) is in the upper or lower position: When the three-position six-way directional valve (2.1) is in the upper or lower working state, the central oil circuit of the three-position six-way directional valve (2.1) is cut off. That is, since the central oil circuit of the three-position six-way directional valve (2.1) is not conductive, the outlet oil of the variable pump (3) cannot enter the control chamber of the hydraulically controlled one-way valve (1.1) along the central oil circuit of the multiple groups of three-position six-way directional valves (2.1), and the pressure of the control chamber of the hydraulically controlled one-way valve (1.1) can be released through the third damper (1.5), so that the hydraulically controlled one-way valve (1.1) is in the conductive state, and the outlet oil of the variable pump (3) is fed back to the variable mechanism (3.1) of the variable pump after passing through the hydraulically controlled one-way valve (1.1), and the variable pump (3) is in the constant pressure control state.

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