Displacement adjusting hydraulic unit and traveling hydraulic system

Abstract

This invention relates to the field of hydraulic technology, specifically to a displacement-adjusting hydraulic unit and a travel hydraulic system. The displacement-adjusting hydraulic unit acts on a hydraulic pump, which is a variable displacement pump driven by a speed-adjustable engine. It includes: a variable displacement piston configured to adjust the displacement of the hydraulic pump; a control valve configured to control the oil inlet and outlet of the variable displacement piston; and a DA valve, whose inlet X is connected to a replenishment oil source M, and whose outlet Y generates an actuation pressure proportional to the engine speed. The pilot pressure of the control valve comes from the actuation pressure generated by the DA valve, and the hydraulic oil source controlled by the control valve to be output to the variable displacement piston comes from the replenishment oil source M. This invention solves the technical problem in the prior art where the series closed-loop pump uses a combination of hydraulic direct control and a DA valve, resulting in different swing forces between the front and rear pumps due to differences in internal components, leading to a large difference in the output flow rate between the front and rear pumps, and causing high deviation in the travel machinery.

Description

Technical Field

[0001] This invention relates to the field of hydraulic technology, specifically to a displacement regulating hydraulic unit and a walking hydraulic system. Background Technology

[0002] In many closed-loop systems, series closed-loop pumps are commonly used to control the left and right travel motors separately to achieve the best travel performance. The series closed-loop pump adopts a control method of hydraulic direct control + DA valve combination. This control method can match the engine power well, making the whole machine compact and making reasonable use of engine power. However, due to the consistency of the flow of the front and rear pumps, this control method causes the mechanical movement to deviate, which is unavoidable. It can only minimize the deviation, but the consistency requirements of the internal parts of the plunger pump are too high, and the pass rate is too low to meet the high deviation requirements of the whole vehicle.

[0003] like Figure 1 As shown, the series closed-loop pump adopts a control method combining hydraulic direct control and a DA valve. The displacement of the front pump 11' is controlled by the front variable piston 21', and the displacement of the rear pump 12' is controlled by the rear variable piston 22'. The pressure at the Y' port of the DA valve 3' is controlled to enter the two side chambers of the front variable piston 21' through the X1' and X2' ports to control the movement of the front variable piston 21'; similarly, the pressure at the Y' port of the DA valve 3' is controlled to enter the two side chambers of the rear variable piston 22' through the X3' and X4' ports to control the movement of the rear variable piston 22'. The hydraulic direct-push + DA valve combination control method is mainly used when the flow difference between the front and rear pumps is large at low engine speeds. At low speeds, the pressure of the DA valve is low and insufficient to maintain the pump at its maximum displacement. Due to the large variable piston spring force, the positions of the variable pistons of the front and rear pumps differ under no-load conditions. When under load, the load pressure acts on the swashplate through the distribution plate, causing the swashplate to swing back. The swing forces generated by the differences in internal parts of the front and rear pumps are different, resulting in a large difference in the output flow of the front and rear pumps. Summary of the Invention

[0004] To address the technical problem in existing series closed-loop pumps that use a combination of hydraulic direct control and DA valves, where the different swing forces generated by the internal components of the front and rear pumps result in significant differences in output flow rates and cause high deviation of the traveling machinery, this invention provides a displacement regulating hydraulic unit and a traveling hydraulic system, thus solving the aforementioned technical problem.

[0005] The technical solution of the present invention is as follows:

[0006] This invention provides a displacement-adjusting hydraulic unit that acts on a hydraulic pump, wherein the hydraulic pump is a variable displacement pump driven by a speed-adjustable engine, comprising:

[0007] A variable piston is configured for the hydraulic pump to adjust the pump's displacement.

[0008] A control valve, designed for variable pistons, is used to control the inflow and outflow of oil from the variable piston.

[0009] The DA valve has its inlet X connected to the replenishing oil source M, and its outlet Y generates an actuation pressure proportional to the engine speed.

[0010] The pilot pressure of the control valve comes from the actuation pressure generated by the DA valve, and the hydraulic oil source controlled by the control valve to output to the variable piston comes from the replenishment oil source M.

[0011] According to one embodiment of the present invention, the control valve is a hydraulically controlled proportional control valve.

[0012] According to one embodiment of the present invention, it further includes a reversing valve, wherein the actuation pressure provides pilot pressure to the control valve under the control of the reversing valve.

[0013] According to one embodiment of the present invention, the variable piston includes a piston body, cavities are formed on both sides of the piston body, elastic elements acting on the piston body are disposed in the cavities, the piston body slides to control the displacement of the hydraulic pump, the control valve controls the oil inlet and outlet of the cavities on both sides of the piston body, and the piston body acts on the control valve through a feedback element.

[0014] According to one embodiment of the present invention, the control valve is a three-position four-way valve, which includes a pressure port, a return port, and two working ports. The pressure port is connected to the replenishing oil source M, and the two working ports are respectively connected to the cavities on both sides of the piston body. In the neutral position, the control valve controls the pressure port and the two working ports to be throttled and connected to the return port. In the two working positions, the control valve controls the pressure port to be connected to one working port and the other working port to be connected to the return port.

[0015] The present invention also provides a walking hydraulic system, comprising:

[0016] There are two hydraulic pumps, one for driving the left and one for driving the right movement.

[0017] The displacement regulating hydraulic unit has two variable pistons, each designed for one of the two hydraulic pumps; and two control valves, each designed for one of the two variable pistons.

[0018] An engine is used to drive two hydraulic pumps, the speed of which is adjustable.

[0019] According to one embodiment of the present invention, two hydraulic pumps are connected in series via a coupling, and the engine directly drives one of the hydraulic pumps. One of the hydraulic pumps forms a closed loop with the left travel motor, and the other hydraulic pump forms a closed loop with the right travel motor.

[0020] According to one embodiment of the invention, it further includes a reversing valve, wherein the actuation pressure, under the control of the reversing valve, provides pilot pressure to two control valves, the reversing valve including a handle valve and / or a foot valve.

[0021] According to one embodiment of the present invention, the replenishing oil source M comes from the replenishing oil pump.

[0022] According to one embodiment of the present invention, the hydraulic pump is a piston pump, and a swashplate is provided inside the hydraulic pump, and the variable piston acts on the swashplate.

[0023] Based on the above technical solution, the technical effects that the present invention can achieve are as follows:

[0024] 1. The displacement regulating hydraulic unit of the present invention uses a combination of a DA valve and a control valve to regulate the displacement of the hydraulic pump. The inlet pressure of the control valve is provided by a stable and high-pressure replenishment oil source M. By using a higher replenishment oil pressure, the swashplate backlash force generated by internal components can be overcome, accurately controlling the swashplate angle, i.e., the hydraulic pump displacement. This avoids the problem in the prior art where, when the DA valve pressure is low, it is insufficient to overcome the swashplate backlash force inherent in the hydraulic pump itself. Especially when the hydraulic pump load pressure is high, the backlash force is even greater, causing the hydraulic pump to automatically change to a smaller displacement. This backlash force is greatly affected by the consistency of the pump's internal components. The pump displacement depends entirely on the control pressures on both sides of the control valve, i.e., the actuation pressure generated by the DA valve. In other words, the displacement regulating hydraulic unit of the present invention combines the function of the DA valve in making the pump displacement positively correlated with the engine speed, and the function of overcoming the swashplate backlash force generated by internal components, making the hydraulic pump displacement regulation accurate. When this displacement regulating hydraulic unit is used in the walking hydraulic system, it solves the problem of uncontrollable deviation that exists in the existing technology without changing the customer's original configuration (it is still a hydraulic control system, the DA valve is still used, and the whole vehicle except for the pump is still retained) and without changing the excellent performance of the whole vehicle (it matches the engine power very well, making the whole machine compact and making reasonable use of the engine power, i.e. the function of the DA valve).

[0025] 2. In the hydraulic unit for adjusting the displacement of the present invention, cavities are formed on both sides of the piston body. The position of the piston body can be adjusted by controlling the oil inlet and outlet of the two cavities through the control valve, thereby adjusting the displacement of the hydraulic pump. Elastic elements are respectively provided in the two cavities to provide a reset force for the piston body. The piston body acts on the control valve through the feedback element, which can realize the dynamic adjustment of the displacement of the hydraulic pump.

[0026] 3. The walking hydraulic system of the present invention includes two hydraulic pumps and adopts the aforementioned displacement regulating hydraulic unit. The pilot pressure of the two control valves comes from the DA valve, ensuring that the vehicle can be well matched with the engine power. The two control valves respectively control the hydraulic oil source output to the variable piston to come from the replenishment oil source M, which solves the problem of uncontrollable deviation in the prior art.

[0027] 4. In the walking hydraulic system of the present invention, two hydraulic pumps are connected in series and driven by the engine, and the hydraulic pumps and the corresponding walking motors form a closed loop. The walking hydraulic system adopts a series closed pump structure design, which is compact, occupies a small area, and is easy to install and arrange in a limited space, and is easy to install and maintain.

[0028] 5. In the walking hydraulic system of the present invention, the setting of the reversing valve can facilitate the control of the actuation pressure to provide pilot pressure to the two control valves. The reversing valve includes a handle valve and / or a foot valve, that is, the operator can control the state of the reversing valve by using a handle or foot operation. The setting of the replenishing pump can ensure the supply of a stable replenishing oil source M with a high pressure value. Attached Figure Description

[0029] Figure 1 The hydraulic schematic diagram is shown below for the control method of the series closed pump using a combination of hydraulic direct control and DA valve in the existing technology.

[0030] Figure 2 This is a hydraulic schematic diagram of the walking hydraulic system of the present invention;

[0031] Figure 3 for Figure 2 Enlarged view of part D;

[0032] In the diagram: 1-Variable piston; 11-First variable piston; 111-First piston body; 112-First cavity; 113-First elastic element; 114-First linkage rod; 12-Second variable piston; 2-Control valve; 21-First control valve; 22-Second control valve; 3-DA valve; 4-Directional control valve; 5-Feedback rod; 51-First feedback rod; 52-Second feedback rod; 20-Hydraulic pump; 201-First hydraulic pump; 202-Second hydraulic pump; 30-Coupling; 11'-Front pump; 12'-Rear pump; 21'-Front variable piston; 22'-Rear variable piston; 3'-DA valve. Detailed Implementation

[0033] 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. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. 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.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0036] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0037] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0038] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0039] like Figure 2-3 As shown, this embodiment provides a displacement regulating hydraulic unit that acts on a hydraulic pump 20 to regulate the displacement of the hydraulic pump 20. The hydraulic pump 20 is a variable displacement pump driven by a speed-adjustable engine. The displacement regulating hydraulic unit includes a variable piston 1, a control valve 2, a DA valve 3, and a replenishing oil source M. The variable piston 1 is configured for the hydraulic pump 20 to regulate its displacement. The control valve 2 is configured for the variable piston 1 to control the oil flow into and out of the variable piston, thereby controlling its movement. The DA valve 3 generates an actuation pressure proportional to the engine speed. The control valve 2 is a hydraulically controlled proportional control valve. The pilot pressure of the control valve 2 comes from the actuation pressure generated by the DA valve 3. The hydraulic oil source controlled by the control valve 2 and output to the variable piston 1 comes from the replenishing oil source M.

[0040] like Figure 2 As shown, the variable piston 1 is configured for the hydraulic pump 20. The variable piston 1 acts on the swashplate of the hydraulic pump 20, and the displacement of the hydraulic pump 20 is adjusted by adjusting the tilt angle of the swashplate. The variable piston 1 includes a piston body, and cavities are formed on both sides of the piston body. The piston body moves under the pressure of the cavities on both sides. The piston body acts on the swashplate through a linkage rod to adjust the displacement of the hydraulic pump 20.

[0041] As a preferred technical solution in this embodiment, such as Figure 3 As shown, elastic elements acting on the piston body are provided in the cavities on both sides of the piston body.

[0042] like Figure 2-3As shown, control valve 2 is used to control the inflow and outflow of oil to the variable piston 1, specifically controlling the inflow and outflow of oil to the two cavities on both sides of the piston body. Control valve 2 is a hydraulic proportional control valve, which can be a three-position four-way valve. Control valve 2 has a pressure port, a return port, and two working ports. The pressure port introduces hydraulic oil, the return port connects to the return oil tank, and the two working ports connect to the cavities on both sides of the piston body. Control valve 2 has a neutral position and two working positions. When control valve 2 is in the neutral position, the pressure port and both working ports are connected to the return port, and the cavities on both sides of the piston body are in a low-pressure state. When control valve 2 is in both working positions, the pressure port is connected to one working port, and the other working port is connected to the return port; that is, control valve 2 controls oil inflow to one working port and oil return to the other working port.

[0043] As a preferred embodiment, the hydraulic oil source controlled by the control valve 2 to the variable piston 1 comes from the replenishment oil source M. That is, the pressure port is connected to the replenishment oil source M. Preferably, a filter is provided in the oil line connecting the pressure port and the replenishment oil source M to facilitate oil filtration; filters are also provided in the oil lines connecting the two working ports to the cavity of the variable piston 1.

[0044] As a preferred embodiment, the control valve core of the control valve 2 moves under the action of pilot pressure at both ends. Pilot chambers are formed at both ends of the control valve core of the control valve 2, and the pilot pressure comes from the actuation pressure generated by the DA valve.

[0045] As a preferred embodiment, the variable piston 1 acts on the control valve 2 via the feedback rod 5. Specifically, the feedback rod 5 can be hinged, with the piston body of the variable piston 1 movably engaged with one end of the feedback rod 5, and the other end of the feedback rod 5 acting on the control valve 2 to feed back the motion state of the variable piston 1 to the control valve 2, thereby achieving dynamic balance.

[0046] like Figure 2 As shown, the inlet X of DA valve 3 is connected to the replenishing oil source M to introduce hydraulic oil from the replenishing oil source M. The outlet Y of DA valve 3 can be used as pilot oil for control valve 2. Hydraulic oil enters through the inlet X of DA valve 3. One path of hydraulic oil flows directly to one end of DA valve 3, while the other path flows through a throttle orifice to the other end of DA valve 3. Due to the presence of the throttle orifice, there is a pressure difference between the two ends of DA valve 3, which can push the valve core of DA valve 3 to slide. The oil at inlet X can flow to outlet Y, forming an actuating pressure. Spring elements are respectively provided at both ends of DA valve 3.

[0047] like Figure 2As shown, the actuation pressure generated by DA valve 3 is provided as pilot pressure to control valve 2 under the control of directional valve 4. Specifically, the outlet Y of DA valve 3 is connected to the input port of directional valve 4, and the two output ports of directional valve 4 are respectively connected to the pilot chambers on both sides of control valve 2 via oil passages, which facilitates the control of the oil inlet and outlet of the two pilot chambers of control valve 2.

[0048] The replenishing oil source M can provide a stable and high replenishing pressure. Preferably, the replenishing oil source M provides a replenishing pressure of not less than 2 MPa.

[0049] like Figure 2 As shown, this embodiment also provides a walking hydraulic system, including a hydraulic pump 20, the aforementioned displacement regulating hydraulic unit, and an engine. There are two hydraulic pumps 20, which control left walking and right walking respectively. There are two variable pistons 1, which are respectively set for the two hydraulic pumps 20 and are used to adjust the displacement of the corresponding hydraulic pumps 20. There are two control valves 2, which are respectively set for the two variable pistons 1 and are used to control the oil inlet and outlet of the two variable pistons 1. There is one DA valve 3 and one directional valve 4. The outlet Y of the DA valve 3 is supplied as pilot oil to the two control valves 2 under the control of the directional valve 4. The hydraulic oil source of the two control valves 2 is from the replenishment oil source M.

[0050] There are two hydraulic pumps 20, namely the first hydraulic pump 201 and the second hydraulic pump 202, which drive the left travel and the right travel respectively.

[0051] As a preferred embodiment, both the first hydraulic pump 201 and the second hydraulic pump 202 are variable displacement pumps, specifically variable displacement piston pumps. Both the first hydraulic pump 201 and the second hydraulic pump 202 have swashplates, and the variable displacement piston 1 acts on the swashplates. The displacement of the hydraulic pumps is adjusted by adjusting the tilt angle of the swashplates.

[0052] As a preferred embodiment, the first hydraulic pump 201 and the second hydraulic pump 202 are driven by an engine, and the engine speed is adjustable. Specifically, the first hydraulic pump 201 and the second hydraulic pump 202 can be connected in series via a coupling 30, and the engine can directly drive one of the first hydraulic pump 201 and the second hydraulic pump 202. The coupling 30 is optional, but not limited to, a coupling sleeve.

[0053] As a preferred technical solution in this embodiment, the first hydraulic pump 201 can be used to drive left travel, and the first hydraulic pump 201 can form a closed loop with the left travel motor; the second hydraulic pump 202 can be used to drive right travel, and the second hydraulic pump 202 can form a closed loop with the right travel motor.

[0054] like Figure 2As shown, there are two variable pistons 1, namely a first variable piston 11 and a second variable piston 12. The first variable piston 11 is set for the first hydraulic pump 201 and is used to adjust the displacement of the first hydraulic pump 201. The second variable piston 12 is set for the second hydraulic pump 202 and is used to adjust the displacement of the second hydraulic pump 202.

[0055] As a preferred technical solution in this embodiment, the first variable piston 11 and the second variable piston 12 have the same structure. Figure 3 As shown, the first variable piston 11 includes a first piston body 111, with first cavities 112 formed on both sides of the first piston body 111. The first piston body 111 acts on the swashplate of the first hydraulic pump 201 via a first linkage rod 114. First elastic elements 113 are disposed within the two first cavities 112, and the first elastic elements 113 act on the first piston body 111. The second variable piston 12 includes a second piston body, with second cavities formed on both sides of the second piston body. The second piston body acts on the swashplate of the second hydraulic pump via a second linkage rod. Second elastic elements are disposed within the two second cavities, and the second elastic elements act on the second piston body. The first elastic elements 113 and the second elastic elements can be, but are not limited to, springs.

[0056] like Figure 2 As shown, there are two control valves 2, namely a first control valve 21 and a second control valve 22. The first control valve 21 is set for the first variable piston 11 and is used to control the oil inlet and outlet of the first variable piston 11. The second control valve 22 is set for the second variable piston 12 and is used to control the oil inlet and outlet of the second variable piston 12.

[0057] As a preferred technical solution in this embodiment, the first control valve 21 and the second control valve 22 have the same structure, such as Figure 2-3 As shown, taking the first control valve 21 as an example, the first control valve 21 has a pressure port p, a return port t, a working port a, and a working port b. The pressure port p is connected to the replenishing oil source M, the return port t is connected to the return oil tank, and the working ports a and b are respectively connected to the two first chambers 112 of the first variable piston 11. The two ends of the first control valve 21 form ports Y1 and Y2, respectively, which can be connected to the actuation pressure of the outlet Y of the DA valve as the driving force of the valve core of the first control valve 21. Correspondingly, the two ends of the second control valve 22 form ports Y3 and Y4, respectively, which can be connected to the actuation pressure of the outlet Y of the DA valve as the driving force of the valve core of the second control valve 22.

[0058] As a preferred technical solution in this embodiment, the first variable piston 11 acts on the first control valve 21 via the first feedback rod 51, and the second variable piston 12 acts on the second control valve 22 via the second feedback rod 52.

[0059] The directional control valve 4 is used to control the actuation pressure of the outlet Y of the DA valve to be connected to ports Y1, Y2, Y3, and Y4. The directional control valve 4 can be configured to include a handle valve and / or a foot valve. When the directional control valve 4 includes a handle valve, its position can be manually switched to control the direction of the actuation pressure at the outlet Y of the DA valve; when the directional control valve 4 includes a foot valve, its position can be switched by foot to control the direction of the actuation pressure at the outlet Y of the DA valve; when the directional control valve 4 includes both a handle valve and a foot valve, it combines both manual and foot adjustment methods.

[0060] The replenishing oil source M comes from the replenishing pump, which can be a fixed displacement pump or a variable displacement pump combined with a pressure reducing valve, etc., as long as it can provide a stable replenishing oil source M with a high pressure value. The fixed displacement pump can be selected from, but is not limited to, a gear pump. In this embodiment, a fixed displacement pump is used as the replenishing pump, which is connected in series with the second hydraulic pump 202 through a coupling.

[0061] Based on the above technical solution, the walking hydraulic system of this embodiment uses a control valve to solve the problem caused by the swashplate backlash while ensuring that the DA valve is still in use. The inlet pressure of the control valve must be provided by a stable and high-pressure replenishment pressure (above 2MPa). By using a higher replenishment pressure to overcome the swashplate backlash generated by the internal parts, the pump displacement depends entirely on the control pressure on both sides of the control valve (i.e., the control pressure provided by the output pressure of the DA valve). This solves the problem of uncontrollable deviation in the prior art: The prior art directly introduces the DA valve pressure into the variable piston chamber to control the swashplate tilt angle, i.e., to control the pump displacement. However, when the DA valve pressure is low, it is insufficient to overcome the swashplate backlash of the pump itself. Especially when the pump load pressure is high, the backlash is even greater, and the pump will automatically change to a smaller displacement. This backlash is greatly affected by the consistency of the internal parts of the pump. The front and rear pumps will be at different displacements due to the difference in backlash, and the difference in output flow will cause the left and right motors to rotate at different speeds, which will cause the whole vehicle to deviate. The current processing and manufacturing level basically cannot guarantee the consistency of parts required for slight deviation.

[0062] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A displacement-adjusting hydraulic unit, acting on a hydraulic pump (20), said hydraulic pump (20) being a variable displacement pump driven by a speed-adjustable engine, characterized in that, include: A variable piston (1) is set for the hydraulic pump (20) to adjust the displacement of the hydraulic pump (20); Control valve (2), which is set for variable piston (1), is used to control the oil inlet and outlet of variable piston (1); The DA valve (3) has its inlet X connected to the replenishing oil source M, and its outlet Y generates an actuation pressure proportional to the engine speed. The pilot pressure of the control valve (2) comes from the actuation pressure generated by the DA valve (3), and the hydraulic oil source controlled by the control valve (2) to the variable piston (1) comes from the replenishment oil source M.

2. The displacement regulating hydraulic unit according to claim 1, characterized in that, The control valve (2) is a hydraulic proportional control valve.

3. The displacement regulating hydraulic unit according to claim 1, characterized in that, It also includes a reversing valve (4), the actuation pressure of which provides pilot pressure to the control valve (2) under the control of the reversing valve (4).

4. The displacement regulating hydraulic unit according to claim 1, characterized in that, The variable piston (1) includes a piston body, and cavities are formed on both sides of the piston body. An elastic element acting on the piston body is provided in the cavity. The piston body slides to control the displacement of the hydraulic pump (20). The control valve (2) controls the oil inlet and outlet of the cavities on both sides of the piston body. The piston body acts on the control valve (2) through a feedback element (5).

5. The displacement regulating hydraulic unit according to claim 4, characterized in that, The control valve (2) is a three-position four-way valve. The control valve (2) includes a pressure port, a return port and two working ports. The pressure port is connected to the replenishing oil source M. The two working ports are connected to the cavities on both sides of the piston body. In the middle position, the control valve (2) controls the pressure port and the two working ports to be throttled and connected to the return port. In the two working positions, the control valve (2) controls the pressure port to be connected to one working port and the other working port to be connected to the return port.

6. A walking hydraulic system, characterized in that, include: There are two hydraulic pumps (20), which drive the left and right travel respectively; The displacement regulating hydraulic unit according to any one of claims 1-5, wherein there are two variable pistons (1), each for a different hydraulic pump (20); and two control valves (2), each for a different variable piston (1). An engine is used to drive two hydraulic pumps (20), the speed of which is adjustable.

7. A walking hydraulic system according to claim 6, characterized in that, Two hydraulic pumps (20) are connected in series via a coupling (30), and the engine directly drives one of the hydraulic pumps (20). One of the hydraulic pumps (20) forms a closed loop with the left travel motor, and the other hydraulic pump (20) forms a closed loop with the right travel motor.

8. A walking hydraulic system according to claim 6, characterized in that, It also includes a reversing valve (4), under the control of the reversing valve (4), which provides pilot pressure to two control valves (2), the reversing valve (4) including a handle valve and / or a foot valve.

9. A walking hydraulic system according to claim 6, characterized in that, The replenishment oil source M comes from the replenishment pump.

10. A walking hydraulic system according to claim 6, characterized in that, The hydraulic pump (20) is a plunger pump, and a swashplate is provided inside the hydraulic pump (20). The variable piston (1) acts on the swashplate.

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