A hydraulic pump displacement secondary regulation device and control method

Abstract

The application discloses a hydraulic pump displacement secondary regulation device and a control method, and relates to the field of excavator hydraulic pump control. In the device, the oil inlet of a one-way valve is connected with an oil outlet A1; the oil inlet of an electric control reversing valve is connected with an oil outlet A2; the oil outlet of the electric control reversing valve and the oil outlet of the one-way valve are connected with the oil inlet of an electric proportional constant-difference pressure reducing valve; a first pressure sensor detects the pressure signal at the oil outlet A1; a second pressure sensor detects the pressure signal at an oil outlet B; a third pressure sensor detects the pressure signal at an oil outlet C; and a controller controls the opening or closing of the electric control reversing valve and the pressure difference of the electric proportional constant-difference pressure reducing valve according to the pressure signals at the oil outlet A1, the oil outlet B and the oil outlet C, thereby actively adjusting the pump control pressure signal and performing secondary regulation on the pump displacement. The application can improve the response speed and dynamic stability of the excavator hydraulic pump.

Description

Technical Field

[0001] This invention relates to the field of hydraulic pump control technology for excavators, and in particular to a secondary adjustment device and control method for hydraulic pump displacement. Background Technology

[0002] Excavator hydraulic pumps mainly have three flow control methods: positive flow control, negative flow control, and load-sensitive control. Most of them are hydraulically controlled variable pumps, which have problems such as the inability to actively adjust the pump displacement and poor dynamic stability and responsiveness.

[0003] In a positive flow control hydraulic pump, the pump displacement control signal is determined by the operator, handle stroke, and pilot pressure. Manual operation causes sawtooth wave components in the pump control signal, resulting in dynamic instability of the pump flow.

[0004] The negative flow control hydraulic pump takes its pump displacement control signal from the end of the bypass oil circuit of the multi-way valve-main valve. The change of the pump control signal occurs after the main valve is activated, which causes the hydraulic pump response to lag significantly behind the main valve operation.

[0005] The displacement control signal of a load-sensitive hydraulic pump is determined by the system pressure margin (the difference between the hydraulic pump outlet pressure and the maximum load pressure). When the pressure margin is large, the pump responds quickly, but the pressure shock is large and the stability is poor. When the pressure margin is small, the pump has good stability, but the response is slow. In addition, the load-sensitive pressure feedback system is transmitted through long pipelines, which are prone to oscillations in the pipeline, further deteriorating the pump stability.

[0006] Currently, hydraulic pumps integrating electronic control technology have simplified hydraulic feedback and control circuits and are maturely applied in excavators. However, in the field of electronic control of hydraulic pumps, there are few reports on secondary (auxiliary) pump displacement regulation devices that can improve the performance of hydraulic pumps by controlling positive / negative flow and load-sensitive control. Summary of the Invention

[0007] The purpose of this invention is to provide a secondary control device and method for hydraulic pump displacement, which is used to assist in controlling the displacement of a hydraulic variable pump, thereby improving the responsiveness and dynamic stability of the excavator system.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] A hydraulic pump displacement secondary control device includes: an electro-proportional differential pressure reducing valve, a check valve, a normally closed two-position two-way electrically controlled directional valve, a first pressure sensor, a second pressure sensor, a third pressure sensor, and a controller.

[0010] The inlet of the one-way valve is connected to the primary control pressure port A1 of the pump; the inlet of the electrically controlled directional valve is connected to the pressure oil source port A2; the outlet of the electrically controlled directional valve and the outlet of the one-way valve are both connected to the inlet of the electrically proportional differential pressure reducing valve.

[0011] The first pressure sensor is installed at the primary control pressure port A1 of the pump and is used to detect the pressure signal at the primary control pressure port A1 of the pump.

[0012] The second pressure sensor is installed at the secondary control pressure port B of the pump and is used to detect the pressure signal at the secondary control pressure port B of the pump.

[0013] The third pressure sensor is installed at the backup oil port C for operating condition detection; the third pressure sensor is used to detect the pressure signal at the backup oil port C for operating condition detection.

[0014] The pump primary control pressure port A1, pressure oil source port A2, pump secondary control pressure port B, and operating condition detection backup port C are all pressure ports of the pump displacement secondary regulation device.

[0015] The controller is connected to the electro-proportional differential pressure reducing valve, the check valve, the electro-controlled directional valve, the first pressure sensor, the second pressure sensor, and the third pressure sensor, respectively. The controller is used to control the opening or closing of the electro-controlled directional valve and adjust the inlet and outlet pressure difference of the electro-proportional differential pressure reducing valve according to the pressure signal at the pump primary control pressure port A1, the pressure signal at the pump secondary control pressure port B, and the pressure signal at the working condition detection standby port C.

[0016] Optionally, the primary control pressure port A1 of the pump is connected to the original hydraulic pump control pressure oil pipeline; the pressure oil source port A2 is connected to the pressure oil source; the secondary control pressure port B of the pump is connected to the control chamber of the hydraulic pump variable regulating valve; and the working condition detection backup port C is a backup port.

[0017] Optionally, the pressure signal at the pressure oil source port A2 is greater than the pressure signal at the pump primary control pressure port A1.

[0018] A secondary control method for hydraulic pump displacement, applied to the aforementioned secondary control device for hydraulic pump displacement, wherein the control method includes:

[0019] When the excavator's hydraulic system is running and the control pressure acting on the control chamber of the hydraulic pump's variable regulating valve is higher than the expected value, the controller controls the electronically controlled directional valve to close. Based on the pressure signals at the pump's primary control pressure port A1, the pump's secondary control pressure port B, and the working condition detection backup port C, the controller adjusts the inlet and outlet pressure difference of the electro-proportional differential pressure reducing valve to reduce the pressure at the pump's secondary control pressure port B and make it equal to the expected value.

[0020] A secondary regulation method for pump displacement, applied to the aforementioned secondary regulation device for hydraulic pump displacement, the control method further comprising:

[0021] When the excavator's hydraulic system is running and the control pressure acting on the control chamber of the hydraulic pump's variable regulating valve is lower than the expected value, the controller controls the electric directional valve to open. Based on the pressure signals at the pump's primary control pressure port A1, the pump's secondary control pressure port B, and the working condition detection backup port C, the controller adjusts the inlet and outlet pressure difference of the electro-proportional differential pressure reducing valve to increase the pressure at the pump's secondary control pressure port B and make it equal to the expected value.

[0022] According to specific embodiments provided by the present invention, the following technical effects are disclosed:

[0023] This invention, based on the collected pressure at the primary control pressure port A1, the secondary control pressure port B, and the operating condition detection port C, uses a controller to open or close an electrically controlled directional valve and adjust the inlet and outlet pressure difference of an electro-proportional constant-differential pressure reducing valve. This dynamically adjusts the pressure at the secondary control pressure port B (i.e., the control pressure acting on the control chamber of the hydraulic pump's variable displacement valve) to a desired value, ensuring the hydraulic pump flow dynamically meets control requirements. This invention improves the flow stability of existing positive flow control hydraulic pumps, the response speed of negative flow control hydraulic pumps, and the dynamic stability and responsiveness of load-sensitive control hydraulic pumps. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A schematic diagram of a secondary control device for hydraulic pump displacement provided by the present invention;

[0026] Figure 2 This is a schematic diagram of the secondary pump displacement control device provided in Embodiment 1 of the present invention applied to a positive flow control pump;

[0027] Figure 3 This is a schematic diagram of the secondary pump displacement control device provided in Embodiment 2 of the present invention applied to a negative flow control pump.

[0028] Figure 4 This is a schematic diagram of the secondary pump displacement control device provided in Embodiment 3 of the present invention applied to a load-sensitive control pump.

[0029] Explanation of symbols in the attached diagram: 1-Electro-proportional differential pressure reducing valve; 2-Check valve; 3-Normally closed 2-position 2-way electrically controlled directional valve; 4-First pressure sensor; 5-Third pressure sensor; 6-Controller; 7-Second pressure sensor; 8-Pump displacement secondary control device; 9-Oil tank; 10-Variable displacement hydraulic pump; 11-Variable displacement piston of hydraulic pump; 12-Variable displacement regulating valve of hydraulic pump; 13-Pressure oil source; 14-Excavator hydraulic system; 15-Pilot pump; 16-Relief valve; 17-Positive flow control main valve; 18-Operating handle; 19-Hydraulic actuator; 20-Negative flow control main valve; 21-Bypass damping valve; 22-Load-sensitive control main valve. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The purpose of this invention is to provide a secondary control device and method for hydraulic pump displacement, which is used to assist in controlling the displacement of a hydraulic variable pump, thereby improving the responsiveness and dynamic stability of the excavator system.

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 1 As shown, the hydraulic pump displacement secondary control device provided by the present invention includes: an electro-proportional differential pressure reducing valve 1, a check valve 2, a normally closed two-position two-way electrically controlled directional valve 3, a first pressure sensor 4, a second pressure sensor 7, a third pressure sensor 5, and a controller 6.

[0034] The inlet of the one-way valve 2 is connected to the primary control pressure port A1 of the pump displacement secondary regulation device 8; the inlet of the electrically controlled directional valve 3 is connected to the pressure oil source port A2 of the pump displacement secondary regulation device 8; the outlet of the electrically controlled directional valve 3 and the outlet of the one-way valve 2 are both connected to the inlet of the electrically proportional differential pressure reducing valve 1.

[0035] The first pressure sensor 4 is installed at the primary control pressure port A1 of the pump and is used to detect the pressure signal at the primary control pressure port A1 of the pump.

[0036] The second pressure sensor 7 is installed at the pressure oil source port A2 and is used to detect the pressure signal at the pressure oil source port A2.

[0037] The third pressure sensor 5 is installed at the pump secondary control pressure port C; the third pressure sensor 5 is used to detect the pressure signal at the standby port C under operating conditions.

[0038] The controller 6 is electrically connected to the electro-proportional differential pressure reducing valve 1, the electro-controlled directional valve 3, the first pressure sensor 4, the second pressure sensor 7, and the third pressure sensor 5, respectively; the others are connected via hydraulic oil pipes and hydraulic pipe joints; the controller 6 is used to control the opening or closing of the electro-controlled directional valve 3 and adjust the inlet and outlet pressure difference of the electro-proportional differential pressure reducing valve 1 based on the pressure signal at the pump primary control pressure port A1, the pressure signal at the pump secondary control pressure port B, and the pressure signal at the working condition detection backup port C.

[0039] The pump primary control pressure port A1 is connected to the hydraulic pump control pressure in the excavator hydraulic system 14. The pressure oil source port A2 is used to connect to the pressure oil source 13.

[0040] The pump secondary control pressure port B is used to connect to the control chamber of the variable displacement regulating valve 12. The working condition detection backup port C is a working condition detection backup port and is connected to the excavator hydraulic system 14. The variable displacement regulating valve 12 is connected to the oil tank 9, the hydraulic pump variable piston 11, and the variable hydraulic pump 10, and adjusts the displacement of the variable hydraulic pump 10 according to the control pressure of the control chamber of the variable displacement regulating valve 12.

[0041] Based on the above-mentioned secondary regulation device for excavator hydraulic pump displacement, the present invention also provides a secondary regulation method for pump displacement, the control method comprising:

[0042] S101, when the excavator hydraulic system is running and the control pressure acting on the control chamber of the hydraulic pump variable control valve is higher than the expected value, that is, when the controller needs to reduce the pressure at the pump secondary control pressure port B, the controller controls the electronic directional valve to close, and adjusts the inlet and outlet pressure difference of the electro-proportional constant differential pressure reducing valve according to the pressure signal at the pump primary control pressure port A1, the pressure signal at the pump secondary control pressure port B, and the pressure signal at the working condition detection standby port C, thereby reducing the pressure at the pump secondary control pressure port B (i.e., the control pressure acting on the control chamber of the hydraulic pump variable control valve) and making it equal to the expected value, so that the hydraulic pump flow dynamically meets the control requirements.

[0043] S102, when the excavator hydraulic system is running and the control pressure acting on the control chamber of the hydraulic pump variable control valve is lower than the expected value, that is, when the controller needs to increase the pressure at the pump secondary control pressure port B, the controller controls the electric directional valve to open, and adjusts the inlet and outlet pressure difference of the electro-proportional constant differential pressure reducing valve according to the pressure signal at the pump primary control pressure port A1, the pressure signal at the pump secondary control pressure port B, and the pressure signal at the working condition detection standby port C, thereby increasing the pressure at the pump secondary control pressure port B (i.e., the control pressure acting on the control chamber of the hydraulic pump variable control valve) and making it equal to the expected value, so that the hydraulic pump flow dynamically meets the control requirements.

[0044] The effects of the present invention are illustrated in detail below through three embodiments:

[0045] Example 1: The secondary pump displacement control device 8 is applied to a positive flow control pump.

[0046] like Figure 2 As shown, the variable hydraulic pump 10 using positive flow control has its pump displacement control signal determined by the operator-handle stroke-pilot pressure, and the pump displacement increases with the increase of its control signal. Manual operation causes the pump control signal (the pressure of the pump primary control pressure port A1 and the pump secondary control pressure port B) to have sawtooth wave components, which can easily cause the hydraulic pump flow to be unstable.

[0047] To improve the dynamic stability of the flow rate of the positive flow control hydraulic pump, a secondary pump displacement adjustment device 8 is configured for the original positive flow control pump, such as... Figure 2 As shown, the pressure oil source port A2 is connected to the pilot pump 15, and the primary control pressure oil port A1 is connected to the operating handle 18-pilot pressure. The pressure of the pressure oil source port A2 is set to be greater than the pressure of port A1.

[0048] When the operating handle 18 is activated, the controller 6 controls the electronically controlled directional valve 3 to open. The pressure sensor 4 collects the pressure at the primary control pressure port A1 of the pump, and a filtering algorithm is used to filter out the sawtooth wave component in the pressure signal at port A1. Simultaneously, the controller 6 uses the filtered pressure signal from the primary control pressure port A1 as the control target value, and dynamically adjusts the pressure difference between the inlet and outlet of the electro-proportional differential pressure reducing valve 1 to make the pressure at the secondary control pressure port B of the pump equal to the control target value. Compared to the previous method of secondary pump displacement control, the control pressure in the left control chamber of the hydraulic pump variable control valve 12 is smoother due to the elimination of the sawtooth wave component, thus improving the stability of the hydraulic pump flow.

[0049] Example 2: The secondary pump displacement control device is applied to a negative flow control pump.

[0050] like Figure 3As shown, the variable hydraulic pump 10 using negative flow control increases its pump displacement as the pump displacement control signal decreases. The pump displacement control signal is taken from the end of the bypass oil circuit of the multi-way valve-main valve. The change in the pump displacement control signal occurs after the main valve is activated, causing the hydraulic pump response to lag significantly behind the main valve operation.

[0051] To improve the response speed of the negative flow control hydraulic pump, a secondary pump displacement adjustment device 8 is configured for the original negative flow control pump, such as... Figure 3 As shown, the pressure oil source port A2 of the secondary pump displacement control device 8 is connected to the pilot pump 15, and the primary control pressure port A1 of the pump is connected to the upstream pressure of the negative feedback pressure-bypass damping valve 21, and the pressure of the pressure oil source port A2 is set to be greater than the pressure of port A1.

[0052] Preferred solution: When pressure sensor 5 detects the action of operating handle 18 and the opening of negative flow control main valve 20, the electronically controlled directional valve 3 is closed; controller 6 generates control commands based on the pressure signals collected by first pressure sensor 4, third pressure sensor 5, and second pressure sensor 7, and sends them to electro-proportional differential pressure reducing valve 1 to adjust its inlet and outlet pressure difference, thereby adjusting the negative feedback pressure at pump primary control pressure port A1, and outputting the reduced control pressure to pump secondary control pressure port B, reducing the control pressure acting on the control chamber of hydraulic pump variable regulating valve 12, and the flow rate of variable hydraulic pump 10 increases accordingly, and the response speed of variable hydraulic pump 10 becomes relatively faster.

[0053] Optional solution: When pressure sensor 5 detects the action of operating handle 18 and the opening of negative flow control main valve 20, controller 6 controls the opening of the electronically controlled directional valve 3. At this time, the pressure of pressure oil source port A2 is greater than the pressure of pump primary control pressure port A1, and check valve 2 is in the closed state. At the same time, controller 6 generates control commands based on the pressure signals collected by pressure sensors 4, 5, and 7, and sends them to the electro-proportional differential pressure reducing valve 1 to adjust its inlet and outlet pressure difference, thereby adjusting the negative feedback pressure of pump primary control pressure port A1, and outputting the reduced control pressure to pump secondary control pressure port B, reducing the control pressure acting on the control chamber of hydraulic pump variable regulating valve 12, and the flow rate of variable hydraulic pump 10 increases accordingly, and the response speed of variable hydraulic pump 10 becomes relatively faster.

[0054] The two schemes described above enable the operating handle signal to directly affect the pump displacement control signal, similar to a positive flow control method, thus avoiding the phenomenon of the pump lagging behind the valve caused by a negative flow control method.

[0055] Example 3: The secondary pump displacement control device is applied to a load-sensitive control pump.

[0056] like Figure 4As shown, the variable displacement hydraulic pump 10, which adopts load-sensitive control, has its displacement control signal determined by the system pressure margin (the difference between the hydraulic pump outlet pressure and the maximum load pressure). The system uses pressure margin control to ensure that the pump outlet pressure is higher than the maximum load pressure by a constant value. When the preset pressure margin is large, the pump responds quickly but experiences significant impact and poor dynamic stability; when the preset pressure margin is small, the pump exhibits good dynamic stability but a slow response.

[0057] Configure a secondary pump displacement control device 8 for the original load-sensitive control pump, such as Figure 4 As shown, connect the pressure oil source port A2 to the main pump pressure and connect the pump primary control pressure port A1 to the load pressure. At this time, the pressure of the pressure oil source port A2 is greater than the pressure of the pump primary control pressure port A1.

[0058] To improve the dynamic stability of the load-sensitive hydraulic pump, when the operating handle 18 is actuated, the controller 6 controls the electric directional valve 3 to open, and the pressure sensor 4 collects the pressure at the primary control pressure port A1 of the pump. A filtering algorithm is used to filter out high-frequency oscillation waves and oscillation waves with the same frequency as the system's natural frequency in the pressure signal of the primary control pressure port A1 of the pump. At the same time, the controller 6 uses the filtered pressure signal value of the primary control pressure port A1 of the pump as the control target value, and dynamically adjusts the inlet and outlet pressure difference of the electro-proportional differential pressure reducing valve 1 to make the pressure at the secondary control pressure port B of the pump equal to the control target value, thereby reducing the oscillation of the pump control signal.

[0059] Optionally, to improve the dynamic stability of the load-sensitive hydraulic pump, when the operating handle 18 is actuated, the controller 6 controls the electric directional valve 3 to open. The controller 6 adjusts the inlet and outlet pressure difference of the electro-proportional differential pressure reducing valve 1 according to the pressure signal of the pump's secondary control pressure port B, thereby adjusting the pressure of the pump's primary control pressure port A1 and outputting the increased control pressure to the pump's secondary control pressure port B, so that the pressure of the pump's secondary control pressure port B increases relatively, thereby reducing the system pressure margin. Under a lower system pressure margin, the dynamic stability of the variable hydraulic pump is better.

[0060] To improve the response speed of the load-sensitive hydraulic pump, when the operating handle 18 is activated and the rate of change of the pressure signal at the standby port C detected by the third pressure sensor 5 exceeds a certain value, it is determined that the operator requires a fast system response. At this time, the controller 6 generates a control command based on the pressure signals collected by the first pressure sensor 4, the third pressure sensor 5, and the second pressure sensor 7, and sends it to the electro-proportional differential pressure reducing valve 1 to adjust its inlet and outlet pressure difference. This adjusts the pressure at the primary control pressure port A1 of the pump and outputs the reduced control pressure to the secondary control pressure port B of the pump, thereby increasing the system pressure margin. With a higher system pressure margin, the response speed of the variable hydraulic pump becomes faster.

[0061] The secondary displacement control device for excavator hydraulic pumps provided by this invention is installed in the control oil circuit of the hydraulic pump to assist in adjusting the control pressure of the variable displacement hydraulic pump, thereby improving the dynamic stability and dynamic responsiveness of the hydraulic pump. This invention is applicable to excavator positive flow control pumps, negative flow control pumps, and load-sensitive control pumps.

[0062] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0063] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A hydraulic pump displacement secondary control device, characterized by, The hydraulic pump displacement secondary regulation device comprises an electric proportional constant-difference pressure reducing valve, a check valve, a normally closed two-position two-way electric control reversing valve, a first pressure sensor, a second pressure sensor, a third pressure sensor, and a controller. The oil inlet of the check valve is connected with a pump primary control pressure oil port A1; the oil inlet of the electric control reversing valve is connected with a pressure oil source oil port A2; the oil outlet of the electric control reversing valve and the oil outlet of the check valve are both connected with the oil inlet of the electric proportional constant-difference pressure reducing valve. The first pressure sensor is arranged at the pump primary control pressure oil port A1 and is used for detecting the pressure at the pump primary control pressure oil port A1. The second pressure sensor is arranged at a pump secondary control pressure oil port B and is used for detecting the pressure at the pump secondary control pressure oil port B. The third pressure sensor is arranged at a working condition detection standby oil port C and is used for detecting the pressure at the working condition detection standby oil port C. The pump primary control pressure oil port A1, the pressure oil source oil port A2, the pump secondary control pressure oil port B, and the working condition detection standby oil port C are all pressure oil ports of the pump displacement secondary regulation device. The controller is connected with the electric proportional constant-difference pressure reducing valve, the check valve, the electric control reversing valve, the first pressure sensor, the second pressure sensor, and the third pressure sensor respectively; the controller is used for controlling the electric control reversing valve to be opened or closed and adjusting the inlet and outlet pressure difference of the electric proportional constant-difference pressure reducing valve according to the pressure signal at the pump primary control pressure oil port A1, the pressure signal at the pump secondary control pressure oil port B, and the pressure signal at the working condition detection standby oil port C. The pump primary control pressure oil port A1 is connected with an original hydraulic pump control pressure oil pipeline; the pressure oil source oil port A2 is connected with a pressure oil source; the pump secondary control pressure oil port B is connected with a control cavity of a hydraulic pump variable adjusting valve; and the working condition detection standby oil port C is a standby oil port. The hydraulic pump displacement secondary regulation method comprises the following steps. When the excavator hydraulic system is running and the control pressure acting on the control cavity of the hydraulic pump variable adjusting valve is higher than an expected value, the controller controls the electric control reversing valve to be closed, adjusts the inlet and outlet pressure difference of the electric proportional constant-difference pressure reducing valve according to the pressure signal at the pump primary control pressure oil port A1, the pressure signal at the pump secondary control pressure oil port B, and the pressure signal at the working condition detection standby oil port C, reduces the pressure at the pump secondary control pressure oil port B, and makes the pressure equal to the expected value. Or when the excavator hydraulic system is running and the control pressure acting on the control cavity of the hydraulic pump variable adjusting valve is lower than the expected value, the controller controls the electric control reversing valve to be opened, adjusts the inlet and outlet pressure difference of the electric proportional constant-difference pressure reducing valve according to the pressure signal at the pump primary control pressure oil port A1, the pressure signal at the pump secondary control pressure oil port B, and the pressure signal at the working condition detection standby oil port C, increases the pressure at the pump secondary control pressure oil port B, and makes the pressure equal to the expected value. The pressure at the pressure oil source oil port A2 is greater than the pressure at the pump primary control pressure oil port A1.

2. The hydraulic pump displacement secondary control device of claim 1, wherein ​

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