Axial piston pump and hydraulic system

Abstract

The present invention relates to the field of hydraulic pumps, and in particular, to an axial piston pump and a hydraulic system. The axial piston pump comprises a housing assembly, a driving assembly and a piston assembly. The housing assembly comprises a first end cover, an oil distributor cover, a housing and a second end cover, which are detachably connected in sequence. The first end cover is provided with an oil suction port and a first mounting cavity, the oil delivery port on the oil distributor cover is connected with the oil replenishment port, and the oil delivery port is connected with the first mounting cavity. The driving assembly comprises an impeller, an oil discharge pump and a transmission shaft; the oil inlet of the oil discharge pump is connected with the interior of the housing; the oil outlet of the oil discharge pump extends to the outside of the housing assembly. The piston assembly is located in the housing, and the piston assembly comprises a cylinder body and a plurality of piston rods. The piston assembly has an oil suction state and an oil discharge state. In the oil suction state, the piston cavity is connected with the oil delivery port, and the piston rod moves away from the oil distributor cover; in the oil discharge state, the piston cavity is connected with the oil discharge port, and the piston rod moves toward the oil distributor cover. In this way, the problem of poor heat dissipation performance of the axial piston pump is solved.

Description

Technical Field

[0001] The present invention relates to the field of hydraulic pumps, and in particular to an axial piston pump and a hydraulic system. Background Art

[0002] As the "heart" of the aircraft hydraulic system, the hydraulic pump is extremely important in the hydraulic system because of its high efficiency, reliability and stability. However, the internal structure of the hydraulic pump is precise and complex, and it often works under high temperature, high pressure and high speed. In particular, high temperature conditions will significantly reduce the viscosity of the hydraulic oil, making the working oil film of friction pairs, bearings and other components thinner, reducing the actual service life, and may even cause the hydraulic pump to wear and fail, causing aircraft safety accidents.

[0003] In order to meet the increasingly stringent requirements of the aerospace field for reliability and safety, the traditional technical path for heat dissipation is mainly to increase the internal leakage of the hydraulic pump, improve the friction and wear performance of the friction pair, or reduce the ambient temperature of the hydraulic pump. However, due to the high efficiency requirements of hydraulic pumps for aerospace, especially engine-driven pumps, the high power level of hydraulic pumps leads to the friction pair The effect of reducing friction and heat is not obvious, and the proximity to the engine compartment makes it impossible to reduce the ambient temperature. The heat dissipation design of hydraulic pumps has always been a technical difficulty for hydraulic pumps in aerospace. Therefore, the heat dissipation performance of plunger pumps still needs to be improved to better meet the heat dissipation needs of plunger pumps in high-intensity working environments. Summary of the invention

[0004] In order to solve the problem of poor heat dissipation performance of an axial piston pump, the present invention provides an axial piston pump and a hydraulic system.

[0005] In a first aspect, the present invention provides an axial piston pump, the axial piston pump comprising:

[0006] A shell assembly, the shell assembly comprising a first end cover, an oil separator cover, a shell and a second end cover; the first end cover, the oil separator cover, the shell and the second end cover are detachably connected in sequence; the first end cover is provided with an oil suction port and a first mounting cavity; the oil separator cover is provided with an oil delivery port, an oil discharge port and an oil replenishment port; the oil delivery port is communicated with the oil replenishment port; the oil delivery port is communicated with the first mounting cavity;

[0007] A drive assembly, the drive assembly comprising an impeller, an oil discharge pump and a transmission shaft; the impeller is rotatably arranged in the first mounting cavity; the oil discharge pump is installed in the housing assembly; the oil inlet of the oil discharge pump is communicated with the interior of the housing; the oil outlet of the oil discharge pump extends to the outside of the housing assembly; the transmission shaft is detachably connected to the rotating shaft of the impeller; the transmission shaft is detachably connected to the housing assembly;

[0008] A plunger assembly, wherein the plunger assembly is located in the housing; the plunger assembly comprises a cylinder body and a plurality of plunger rods; the cylinder body is coaxial with the transmission shaft and is detachably connected; a plunger cavity corresponding to the plunger on the cylinder body; the plunger rod is slidably inserted in the plunger cavity; the plunger assembly has an oil suction state and an oil discharge state; in the oil suction state, the plunger cavity is connected with the oil delivery port, and the plunger rod moves away from the oil distribution cover; in the oil discharge state, the plunger cavity is connected with the oil discharge port, and the plunger rod moves toward the oil distribution cover.

[0009] In some embodiments, the oil separator cover has a second installation cavity; the oil drain pump is located in the second installation cavity; and the oil drain pump is detachably connected to the oil separator cover.

[0010] In some embodiments, the oil drain pump is detachably connected to the second end cover, and the oil drain pump is located inside the second end cover.

[0011] In some embodiments, the rotating shaft of the oil discharge pump is coaxial with the transmission shaft and is detachably connected thereto.

[0012] In some embodiments, the axial piston pump also includes a positioning assembly; the positioning assembly includes a limit plate; the second mounting cavity is located on the side of the oil separator cover away from the plunger assembly; the limit plate is detachably connected to the oil separator cover; the limit plate abuts the oil drain pump; the limit plate is located on the side of the oil separator cover away from the plunger assembly; a limit ring is integrally formed on the oil separator cover; the oil drain pump abuts the side of the limit ring away from the plunger assembly; an abutment ring is fixedly connected to the rotating shaft of the impeller; the abutment ring abuts the side of the limit ring facing the plunger assembly.

[0013] In some embodiments, the driving assembly further includes a spring and a bearing; a third mounting cavity is formed on a side of the oil separation cover facing the plunger assembly, and the abutment ring is separated between the second mounting cavity and the third mounting cavity; the bearing is located in the third mounting cavity; the transmission shaft is rotatably connected to the oil separation cover through the bearing; the spring is sleeved on the outside of the transmission shaft; a fourth mounting cavity is formed between the cylinder body and the transmission shaft; the spring is located in the fourth mounting cavity;

[0014] The cylinder body is provided with a first oil return port, which is located at one end of the cylinder body close to the second end cover; the fourth installation cavity is connected with the inner cavity of the outer shell through the first oil return port; the third installation cavity is connected with the fourth installation cavity; and the oil inlet of the oil discharge pump is connected with the third installation cavity.

[0015] In some embodiments, a plurality of the first oil return ports are provided, and the plurality of the first oil return ports are evenly distributed around the axis of the cylinder body.

[0016] In some embodiments, an extending direction of the oil replenishing port is perpendicular to an axial direction of the oil separator cover.

[0017] In some embodiments, a second oil return port is provided on the oil separator cover, and the oil inlet of the oil drain pump is connected with the inner cavity of the outer shell through the second oil return port; a line connecting one end of the second oil return port connected with the inner cavity of the outer shell to the center of the oil separator cover is a first reference line; a line connecting the oil replenishing port to the center of the oil separator cover is a second reference line; and an angle between the first reference line and the second reference line is greater than 90°.

[0018] In a second aspect, the present invention provides a hydraulic system, the hydraulic system comprising the axial piston pump according to any one of the first aspects, the hydraulic system further comprising:

[0019] The oil tank; the oil suction port is connected to the oil tank; the oil outlet of the oil discharge pump is connected to the oil tank.

[0020] In order to solve the problem of poor heat dissipation performance of the axial piston pump, the present invention has the following advantages:

[0021] The present invention has built an integrated circulation heat dissipation device in the axial piston pump. The low-temperature hydraulic oil sucked in by the impeller circulates inside the housing assembly. The circulation path passes through the cylinder body and the plunger rod, which are the parts with the highest temperature, and can take away the heat to the greatest extent, with a significant heat dissipation effect. The use of an oil discharge pump can prevent oil backflow under high return oil pressure conditions and improve the heat dissipation effect. In addition, the integrated integrated structure of the present invention is compact, and the weight and volume of the axial piston pump can be controlled within a smaller range while enhancing the heat dissipation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic cross-sectional view of an axial piston pump according to an embodiment is shown;

[0023] Figure 2 Shows Figure 1 A partial enlarged view of the axial piston pump shown at point A;

[0024] Figure 3 A partial schematic diagram of an axial piston pump according to an embodiment is shown;

[0025] Figure 4 Shows Figure 3 A top view of a partial schematic diagram of an axial piston pump is shown.

[0026] Figure numerals: 10 shell assembly; 11 first end cover; 111 oil suction port; 112 first installation cavity; 12 oil distributor cap; 121 oil delivery port; 122 oil discharge port; 123 oil replenishing port; 124 second installation cavity; 125 third installation cavity; 126 second oil return port; 13 outer shell; 14 second end cover; 15 limit ring; 20 drive assembly; 21 impeller; 22 oil discharge pump; 23 transmission shaft; 24 abutment ring; 25 bearing; 26 spring; 30 plunger assembly; 31 cylinder body; 32 plunger rod; 33 fourth installation cavity; 40 positioning assembly; 41 limit plate; 42 adjusting washer. DETAILED DESCRIPTION

[0027] The present disclosure will now be discussed with reference to several exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and thus implement the present disclosure, rather than implying any limitation on the scope of the present disclosure.

[0028] As used herein, the term "including" and its variants are to be interpreted as open-ended terms meaning "including but not limited to". The term "based on" is to be interpreted as "based at least in part on". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment". The term "another embodiment" is to be interpreted as "at least one other embodiment". The orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal" and the like is based on the orientation or position relationship shown in the accompanying drawings. These terms are mainly for better describing the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation. In addition, in addition to being used to indicate an orientation or position relationship, some of the above terms may also be used to indicate other meanings, such as the term "upper" may also be used to indicate a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to the specific circumstances. In addition, the terms "install", "set", "provided with", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be an internal connection between two devices, elements or components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances. In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, "plurality" means two or more.

[0029] The hydraulic pump in the aircraft hydraulic system works intensively and often operates under high temperature, high pressure and high speed. The high temperature condition will significantly reduce the viscosity of the hydraulic oil, resulting in insufficient lubrication of the components in the hydraulic pump, reducing the actual service life, and may even cause the hydraulic pump to wear and fail, causing aircraft safety accidents. Traditional heat dissipation methods mainly increase the internal leakage of the hydraulic pump, improve the friction and wear performance of the friction pair, or reduce the ambient temperature of the hydraulic pump. However, the oil in the existing plunger pump housing cavity relies on the leakage of the friction pair oil and slow oil return. The circulation of the oil in the housing cavity is poor, and the heat dissipation effect is not good. In this embodiment, an axial piston pump is provided, such as Figure 1 and Figure 3As shown, the axial piston pump includes a housing assembly 10, a drive assembly 20 and a piston assembly 30. The housing assembly 10 includes a first end cover 11, an oil separator cover 12, a housing 13 and a second end cover 14. The first end cover 11, the oil separator cover 12, the housing 13 and the second end cover 14 are detachably connected in sequence. The first end cover 11 has an oil suction port 111 and a first mounting cavity 112, and the oil separator cover 12 has an oil delivery port 121, an oil discharge port 122 and an oil replenishment port 123. The oil delivery port 121 is connected to the oil replenishment port 123, and the oil delivery port 121 is connected to the first mounting cavity 112. The inner cavity of the housing 13 is a housing cavity.

[0030] The driving assembly 20 includes an impeller 21, an oil discharge pump 22 and a transmission shaft 23. The impeller 21 is rotatably arranged in the first installation cavity 112. The oil discharge pump 22 is installed in the housing assembly 10. The oil inlet of the oil discharge pump 22 is connected to the interior of the housing 13, and the oil outlet of the oil discharge pump 22 extends to the outside of the housing assembly 10. The transmission shaft 23 is detachably connected to the rotating shaft of the impeller 21, and the transmission shaft 23 is detachably connected to the housing assembly 10. When the transmission shaft 23 rotates, it drives the impeller 21 to rotate, and the impeller 21 continuously sucks the oil into the first installation cavity 112 through the oil suction port 111. The oil flowing into the first installation cavity 112 can flow into the inner cavity of the housing 13, that is, the housing cavity, through the oil delivery port 121 and the oil replenishment port 123 on the oil distributor cover 12 in turn, thereby playing a role in supplying oil to the housing cavity. In addition, the oil discharge pump 22 disposed in the housing assembly 10 can extract the oil in the housing cavity and discharge it into the oil return line of the axial piston pump, thereby dissipating heat and cooling the plunger assembly 30 in the housing cavity. Since the oil discharge pump 22 acts as a pressurizer on the oil, the oil flow rate can be accelerated, and the circulation amount of the oil in the inner cavity of the housing 13 can be increased, thereby improving the heat dissipation efficiency, and at the same time, it can also prevent the oil from flowing back into the housing cavity.

[0031] The plunger assembly 30 is located in the housing 13, and the plunger assembly 30 includes a cylinder body 31 and a plurality of plunger rods 32. The cylinder body 31 is coaxial with the transmission shaft 23 and is detachably connected. The cylinder body 31 has a plunger cavity corresponding to the plunger one by one, and one end of the plunger rod 32 is slidably arranged in the plunger cavity. The plunger assembly 30 has an oil suction state and an oil discharge state. In the oil suction state, the plunger cavity is connected to the oil delivery port 121, the plunger rod 32 moves away from the oil distribution cover 12, and the plunger cavity absorbs oil from the oil delivery port 121; in the oil discharge state, the plunger cavity is connected to the oil discharge port 122, the plunger rod 32 moves toward the oil distribution cover 12, and the plunger cavity discharges oil into the oil discharge port 122. The heat generated by the plunger rod 32 during the movement can be absorbed by the oil in the housing 13, thereby achieving the effect of cooling the plunger assembly 30. The oil circulation path passes through the surface of the cylinder body 31 and the plunger rod 32, and at the same time, the oil replenishment and oil discharge efficiency is increased through the oil replenishment port 123 and the oil discharge pump 22, thereby improving the heat dissipation effect.

[0032] In this embodiment, if Figure 2 As shown, the oil separator cover 12 has a second installation cavity 124, and the oil drain pump 22 can be located in the second installation cavity 124. The oil drain pump 22 is detachably connected to the oil separator cover 12. Since the oil separator cover 12 needs to be provided with an oil delivery port 121 and an oil drain port 122, which is usually thick, the oil drain pump 22 is integrated into the oil separator cover 12, so that the space occupied by the oil separator cover 12 can be effectively utilized, and the integration of the efficient circulation function of the cooling oil is realized without increasing the volume of the plunger pump.

[0033] In this embodiment, the oil drain pump 22 can be detachably connected to the second end cover 14, and the oil drain pump 22 is located inside the second end cover 14, so that the distance between the oil drain pump 22 and the impeller 21 can be relatively large to avoid mutual influence of vibrations generated during operation.

[0034] Specifically, the oil drain pump 22 may be disposed in the oil separation cover 12 or the second end cover 14 according to actual needs.

[0035] In this embodiment, if Figure 2 As shown, the rotating shaft of the oil discharge pump 22 is coaxial with the transmission shaft 23 and is detachably connected, so that the oil discharge pump 22 and the impeller 21 share the same transmission shaft 23. The direction of oil suction by the oil discharge pump 22 is the flow direction of the oil in the inner cavity of the housing 13 toward the oil discharge pump 22. When the oil discharge pump 22 is arranged on the oil separation cover 12, since the oil flow direction of the oil suction port 111 is opposite to the oil suction direction of the oil discharge pump 22, the impeller 21 and the oil discharge pump 22 can be regarded as a whole, and the impact force generated by the oil suctioned by the impeller 21 and the oil suctioned by the oil discharge pump 22 can offset each other to a certain extent, thereby improving the overall stability of the axial piston pump. And the rotating shaft of the oil discharge pump 22 and the rotating shaft of the impeller 21 are all arranged coaxially with the transmission shaft 23, which can simplify the shaft system design and is conducive to bearing the load. When the oil discharge pump 22 is arranged on the second end cover 14, making the rotating shaft of the oil discharge pump 22 coaxial with the transmission shaft 23 can also simplify the shaft system design.

[0036] In this embodiment, if Figure 2 As shown, the axial piston pump also includes a positioning assembly 40, and the positioning assembly 40 includes a limit plate 41 and an adjusting washer 42. The second mounting cavity 124 is located on the side of the oil separator cover 12 away from the plunger assembly 30. The limit plate 41 is detachably connected to the oil separator cover 12, and one side of the limit plate 41 abuts against the oil discharge pump 22. The limit plate 41 is located on the side of the oil separator cover 12 away from the plunger assembly 30. One side of the adjusting washer 42 abuts against the impeller 21, and the other side abuts against the limit plate 41, so that the gap between the impeller 21 and the limit plate 41 can be adjusted to avoid a large friction force when the impeller 21 rotates. At the same time, the oil can also flow into the gap through the first mounting cavity 112 to facilitate lubrication and heat dissipation of the rotating shaft of the impeller 21.

[0037] The oil separation cover 12 is integrally formed with a limit ring 15, and the oil discharge pump 22 abuts against the side of the limit ring 15 away from the plunger assembly 30. The impeller 21 is fixedly connected to the rotating shaft with an abutment ring 24, which abuts against the side of the limit ring 15 facing the plunger assembly 30.

[0038] The impeller 21 will bear an axial load toward the oil suction port 111 during operation. Through the limiting effect of the limit ring 15 on the abutment ring 24, the limit ring 15 can be used to bear a part of the axial load toward the oil suction port 111 borne by the operation of the impeller 21. At the same time, the limit plate 41, the oil separation cover 12 and the abutment ring 24 can bear a part of the radial load and axial load borne by the oil discharge pump 22. Therefore, the impeller 21 and the oil discharge pump 22 can be divided and positioned according to the different load-bearing positions, which can avoid the interference of loads between the two as much as possible and improve the stability of equipment operation.

[0039] In this embodiment, if Figure 1 As shown, the drive assembly 20 also includes a spring 26 and a bearing 25. A third mounting cavity 125 is provided on the side of the oil separator 12 facing the plunger assembly 30, and the abutment ring 24 is separated between the second mounting cavity 124 and the third mounting cavity 125. The bearing 25 is located in the third mounting cavity 125, and the transmission shaft 23 is rotatably connected to the oil separator 12 through the bearing 25. The spring 26 is sleeved on the outside of the transmission shaft 23. A fourth mounting cavity 33 is formed between the cylinder body 31 and the transmission shaft 23, and the spring 26 is located in the fourth mounting cavity 33. The bearing 25 can be a needle bearing 25.

[0040] The cylinder body 31 is provided with a first oil return port, which is located at one end of the cylinder body 31 close to the second end cover 14. The fourth installation cavity 33 is connected to the inner cavity of the housing 13 through the first oil return port. The third installation cavity 125 is connected to the fourth installation cavity 33, and the oil inlet of the oil discharge pump 22 is connected to the third installation cavity 125. The cooling circulation path of the oil can be sucked into the first installation cavity 112 by the impeller 21 through the oil suction port 111, and then flow into the gap between the cylinder body 31 and the housing 13 through the oil delivery port 121 and the oil replenishment port 123 on the oil separation cover 12. Then the oil absorbs the heat of the cylinder body 31 and the plunger rod 32, and then flows into the fourth installation cavity 33 and the third installation cavity 125 through the first oil return port on the cylinder body 31, so as to achieve the effect of cooling the spring 26 and the bearing 25. Finally, the oil discharge pump 22 extracts the oil in the inner cavity of the housing 13 through the first oil return port. Through the design of the first oil return port and the oil replenishment port 123, the circulation path of the oil is extended, so that the cooling area on the cylinder body 31 with the highest temperature is increased, thereby enhancing the heat dissipation effect.

[0041] In this embodiment, if Figure 1As shown, a plurality of first oil return ports may be provided, and the plurality of first oil return ports are evenly distributed around the axis of the cylinder body 31. Thus, the circulation path of the oil is smoother, and at the same time, the cooling area on the cylinder body 31 is larger and the cooling is more uniform, thereby obtaining a stronger heat dissipation effect.

[0042] In this embodiment, if Figure 2 As shown, the extension direction of the oil replenishing port 123 is perpendicular to the axial direction of the oil separation cover 12, which makes the structure simpler and easier to process without changing the oil circuit.

[0043] In this embodiment, if Figure 4 As shown, the oil separator 12 may be provided with a second oil return port 126, and the oil inlet of the oil discharge pump 22 is connected to the inner cavity of the housing 13 through the second oil return port 126. The line connecting one end of the second oil return port 126 connected to the inner cavity of the housing 13 to the center of the oil separator 12 is the first reference line, and the line connecting the oil replenishment port 123 to the center of the oil separator 12 is the second reference line. The angle between the first reference line and the second reference line is greater than 90°, which increases the oil return path, thereby making the oil circulation path smoother and the heat dissipation effect better.

[0044] In this embodiment, a hydraulic system is provided, and the hydraulic system includes the axial piston pump in any of the above embodiments, and the hydraulic system also includes an oil tank. The oil suction port 111 can be connected to the oil tank, and the first oil return port is also connected to the oil tank. Thus, the oil enters the first installation cavity 112 from the oil suction port 111, and then flows into the gap between the cylinder body 31 and the outer shell 13 through the oil delivery port 121 and the oil replenishment port 123 on the oil distribution cover 12, so that the oil in the inner cavity of the outer shell 13 can efficiently dissipate heat for the cylinder body 31 and the plunger rod 32, and then the oil in the inner cavity of the outer shell 13 flows into the fourth installation cavity 33 and the third installation cavity 125 through the first oil return port on the cylinder body 31, and finally flows back to the oil tank through the oil discharge port 122, realizing the circulation function of the cooling oil.

[0045] The present invention is an integrated structure with compact structure, small size and light weight. It integrates the functions of fastening, sealing, transmission, oil self-pressurization, oil self-circulation and oil return forced discharge, etc. It conforms to the requirements of aerospace hydraulic pumps for high-reliability integrated design and weight reduction of hydraulic pumps, and has broad market prospects.

[0046] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present disclosure, and in actual applications, various changes may be made thereto in form and detail without departing from the scope of the present disclosure.

Claims

1. An axial piston pump, characterized in that: The axial piston pump comprises: A shell assembly, the shell assembly comprising a first end cover, an oil separator cover, a shell and a second end cover; the first end cover, the oil separator cover, the shell and the second end cover are detachably connected in sequence; the first end cover is provided with an oil suction port and a first mounting cavity; the oil separator cover is provided with an oil delivery port, an oil discharge port and an oil replenishment port; the oil delivery port is communicated with the oil replenishment port; the oil delivery port is communicated with the first mounting cavity; A drive assembly, the drive assembly comprising an impeller, an oil discharge pump and a transmission shaft; the impeller is rotatably arranged in the first mounting cavity; the oil discharge pump is installed in the housing assembly; the oil inlet of the oil discharge pump is communicated with the interior of the housing; the oil outlet of the oil discharge pump extends to the outside of the housing assembly; the transmission shaft is detachably connected to the rotating shaft of the impeller; the transmission shaft is detachably connected to the housing assembly; A plunger assembly, wherein the plunger assembly is located in the housing; the plunger assembly comprises a cylinder body and a plurality of plunger rods; the cylinder body is coaxial with the transmission shaft and is detachably connected; the cylinder body is provided with a plunger cavity corresponding to the plunger rods one by one; the plunger rod is slidably arranged in the plunger cavity; the plunger assembly has an oil suction state and an oil discharge state; in the oil suction state, the plunger cavity is communicated with the oil delivery port, and the plunger rod moves away from the oil distribution cover; in the oil discharge state, the plunger cavity is communicated with the oil discharge port, and the plunger rod moves toward the oil distribution cover; The oil separator cover is provided with a second installation cavity; the oil drain pump is located in the second installation cavity; the oil drain pump is detachably connected to the oil separator cover; The axial piston pump also includes a positioning assembly; the positioning assembly includes a limit plate; the second mounting cavity is located on the side of the oil separation cover away from the plunger assembly; the limit plate is detachably connected to the oil separation cover; the limit plate abuts the oil discharge pump; the limit plate is located on the side of the oil separation cover away from the plunger assembly; a limit ring is integrally formed on the oil separation cover; the oil discharge pump abuts the side of the limit ring away from the plunger assembly; an abutment ring is fixedly connected to the rotating shaft of the impeller; the abutment ring abuts the side of the limit ring facing the plunger assembly; The driving assembly further includes a spring and a bearing; a third mounting cavity is formed on the side of the oil separation cover facing the plunger assembly, and the abutment ring is separated between the second mounting cavity and the third mounting cavity; the bearing is located in the third mounting cavity; the transmission shaft is rotatably connected to the oil separation cover through the bearing; the spring is sleeved on the outside of the transmission shaft; a fourth mounting cavity is formed between the cylinder body and the transmission shaft; the spring is located in the fourth mounting cavity; The cylinder body is provided with a first oil return port, which is located at one end of the cylinder body close to the second end cover; the fourth installation cavity is connected with the inner cavity of the outer shell through the first oil return port; the third installation cavity is connected with the fourth installation cavity; and the oil inlet of the oil discharge pump is connected with the third installation cavity.

2. An axial piston pump according to claim 1, characterized in that: The rotating shaft of the oil discharge pump is coaxial with the transmission shaft and is detachably connected.

3. An axial piston pump according to claim 1, characterized in that: A plurality of the first oil return ports are provided, and the plurality of the first oil return ports are evenly distributed around the axis of the cylinder body.

4. An axial piston pump according to claim 1, characterized in that: The extending direction of the oil replenishing port is perpendicular to the axial direction of the oil separation cover.

5. The axial piston pump according to claim 1, characterized in that: A second oil return port is provided on the oil separator cover, and the oil inlet of the oil drain pump is connected with the inner cavity of the outer shell through the second oil return port; a line connecting one end of the second oil return port connected with the inner cavity of the outer shell to the center of the oil separator cover is a first reference line; a line connecting the oil replenishing port to the center of the oil separator cover is a second reference line; an angle between the first reference line and the second reference line is greater than 90°.

6. A hydraulic system, characterized in that: The hydraulic system comprises: The axial piston pump according to any one of claims 1 to 5; The oil tank; the oil suction port is connected to the oil tank; the oil outlet of the oil discharge pump is connected to the oil tank.

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