Hydraulic pump

Abstract

A hydraulic pump (1) of one embodiment includes a housing (2) that accommodates a valve plate (3), a cylinder block (4), and a swash plate (5). The angle of the swash plate (5) is changed by a servo piston (7) that is slidably held to the housing. The servo piston (7) is driven by an electric actuator (8) that is mounted to the housing (2). The electric actuator (8) includes a threaded shaft (84), a nut (83), and an electric motor (86). The housing (2) includes an auxiliary pressure chamber (91) for urging the servo piston (7) against the swash plate (5), and a lead passage (2c) for introducing working fluid from a side where the pressure is higher of a first flow passage (2a) and a second flow passage (2b), that is, a discharge passage, to the auxiliary pressure chamber (91).

Description

Technical Field

[0001] This disclosure relates to hydraulic pumps. Background Technology

[0002] Currently, hydraulic pumps that are swashplate-type axial piston pumps are known. In such hydraulic pumps, a valve plate, cylinder, and swashplate are housed within a casing (see, for example, Patent Document 1).

[0003] Specifically, the valve plate includes a first port and a second port in opposite directions of arc shape. When the hydraulic pump rotates in one direction, one of the first port and the second port becomes the suction port, and the other becomes the discharge port. When the hydraulic pump rotates in both directions, depending on the direction of rotation, either the first port or the second port becomes the suction port, and the other becomes the discharge port.

[0004] Furthermore, multiple pistons are slidably held on the cylinder body, and slippers mounted on the heads of these pistons slide against a swashplate. The angle of the swashplate is changed by a servo piston. Patent Document 2 discloses a hydraulic pump that drives the servo piston via an electric actuator. Patent Document 2 describes a ball screw drive mechanism as a specific example of an electric actuator.

[0005] Existing technical documents: Patent documents: Patent Document 1: Japanese Patent Application Publication No. 8-100759; Patent Document 2: Japanese Patent Publication No. 2011-522194. Summary of the Invention

[0006] The problem the invention aims to solve: Another method of driving a servo piston is to change the hydraulic pressure acting on it. However, in this case, the driving of the servo piston may be affected by changes in the temperature of the working fluid. In contrast, as illustrated in the specific example of Patent Document 2, if a ball screw drive mechanism (i.e., an electric actuator including a threaded shaft, a nut, and an electric motor) is used to drive the servo piston, this problem does not occur.

[0007] However, the swashplate experiences a strong torque, similar to that exerted on the servo piston, due to the high pressure within the cylinder. Therefore, the thrust required to advance the servo piston via the electric actuator is increased. Consequently, issues arise such as abnormal wear or reduced lifespan of the threaded shaft and nut, and the need for larger electric motors.

[0008] Therefore, the purpose of this disclosure is to provide a hydraulic pump with an electric actuator that can move a servo piston forward and backward with a small thrust.

[0009] Solution methods: This disclosure provides a hydraulic pump comprising: a cylinder body slidably holding a plurality of pistons; a swashplate sliding with a slipper mounted on the heads of the plurality of pistons; a servo piston changing the angle of the swashplate; a valve plate sliding with the cylinder body and including a first port and a second port in opposite arcuate shapes; a housing housing the valve plate, the cylinder body, and the swashplate, and slidably holding the servo piston; and an electric actuator mounted on the housing and driving the servo piston, including a threaded shaft extending axially along the servo piston, a nut threaded with the threaded shaft, and an electric motor for rotating the threaded shaft; the housing comprising: an auxiliary pressure chamber for pushing the servo piston against the swashplate; a first flow path communicating with the first port; a second flow path communicating with the second port; and an inlet path for introducing working fluid into the auxiliary pressure chamber from the higher pressure of the first flow path and the second flow path, i.e., an outlet path.

[0010] Invention effects: According to this disclosure, a hydraulic pump with an electric actuator that can move a servo piston forward and backward with a small thrust can be provided. Attached Figure Description

[0011] Figure 1 This is a cross-sectional view of a hydraulic pump according to one embodiment; Figure 2 This is a cross-sectional view of a modified hydraulic pump. Detailed Implementation

[0012] Figure 1 A hydraulic pump 1 according to one embodiment is shown. The hydraulic pump 1 includes a housing 2 and a rotating shaft 11 extending from the inside of the housing 2 to the outside. In addition, the hydraulic pump 1 includes a valve plate 3, a cylinder 4 and a swashplate 5 housed within the housing 2.

[0013] For ease of explanation, the axial direction of the rotating shaft 11 will be referred to as the front-rear direction (the side located outside the housing 2 is the front, and the other side is the rear), and the two directions orthogonal to the axial direction of the rotating shaft 11 will be referred to as the up-down direction. Figure 1 (The top side is above, the bottom side is below) and the left and right directions.

[0014] The outer casing 2 includes a container-shaped outer casing body 22 that opens rearward and a valve cover 21 that closes the opening of the outer casing body 22. The outer casing body 22 includes a front wall 23 through which the rotation shaft 11 passes, a bottom wall 24 surrounding the internal space, a top wall 25, and a pair of side walls. Bearings 12 and 13 that rotatably support the rotation shaft 11 are respectively held on the front wall 23 of the outer casing body 22 and the valve cover 21.

[0015] The valve plate 3 is mounted on the front surface of the valve cover 21. The valve plate 3 is provided with a first port 31 and a second port 32 in opposite directions. Figure 1In the diagram, the first port 31 is drawn at the top dead center on the lower side (the last retraction position of the piston 61, which will be described later), and the second port 32 is drawn at the bottom dead center on the upper side (the forwardmost position of the piston 61). However, the actual positions of the first port 31 and the second port 32 are on both sides of the rotation axis 11 in the left-right direction (the direction orthogonal to the separation direction of the top dead center and the bottom dead center).

[0016] In this embodiment, the hydraulic pump 1 rotates in one direction. Therefore, the first port 31 is the suction port, and the second port 32 is the discharge port. That is, in the rotation direction of the rotating shaft 11, the first port 31, which is the suction port, is located downstream of the top dead center and upstream of the bottom dead center, and the second port 32, which is the discharge port, is located downstream of the bottom dead center and upstream of the top dead center.

[0017] The valve cover 21 is provided with a first flow path 2a communicating with the first port 31 and a second flow path 2b communicating with the second port 32. The first flow path 2a and the second flow path 2b have openings on the outer peripheral surface or rear surface of the valve cover 21, forming external connection ports. As described above, the hydraulic pump 1 rotates in one direction, so the first flow path 2a is the suction path and the second flow path 2b is the discharge path. That is, the pressure in the second flow path 2b is higher than the pressure in the first flow path 2a.

[0018] The cylinder body 4 is fixed to the rotating shaft 11 and slides against the valve plate 3 by rotating together with the rotating shaft 11. Multiple forward-opening cylinder holes 41 are provided on the cylinder body 4 around the rotating shaft 11. Multiple pistons 61 are inserted into these cylinder holes 41 respectively. Thus, the pistons 61 are slidably held in the cylinder body 4.

[0019] Furthermore, the cylinder body 4 is provided with cylinder ports 42 extending from each cylinder bore 41 to the valve plate 3. Some of these cylinder ports 42 communicate with the first port 31, while others communicate with the second port 32. For example, when there are nine cylinder bores 41 and cylinder ports 42, depending on the rotational position of the cylinder body 4, four or five cylinder ports 42 communicate with either the first port 31 or the second port 32.

[0020] Multiple sliding shoes 62 are mounted on the head of the piston 61. In this embodiment, the sliding shoes 62 slide on the swashplate 5 via an annular support plate 63 mounted on the swashplate 5. However, the support plate 63 can be omitted, and the sliding shoes 62 slide directly on the swashplate 5. The sliding shoes 62 are pushed by the push plate 64 to maintain contact with the support plate 63.

[0021] The swashplate 5 is sway-supported about a swing axis extending in the left-right direction by a support platform 14 provided on the front wall 23 of the housing body 22. The angle of the swashplate 5 is changed by a servo piston 7, which is slidably held against the top wall 25 of the housing body 22.

[0022] More specifically, the swashplate 5 includes a main body 50 through which the rotation shaft 11 passes and an operating part 51 protruding upward from the main body 50. In this embodiment, the tip 71 of the servo piston 7 is connected to the operating part 51 via a pin 52.

[0023] However, the servo piston 7 does not necessarily need to be connected to the operating part 51 of the swashplate 5. For example, the servo piston 7 can also abut against the operating part 51 of the swashplate 5 from the rear, with the operating part 51 being spring-loaded between the operating part 51 and the front wall 23 of the housing body 22.

[0024] The top wall 25 of the outer casing 22 is provided with a retaining hole 26 for inserting the servo piston 7. In this embodiment, the retaining hole 26 includes: a first guide portion 27 having an opening relative to the internal space of the outer casing 2; and a second guide portion 28 located on the opposite side of the swashplate 5 relative to the first guide portion 27. The diameter of the second guide portion 28 is smaller than the diameter of the first guide portion 27.

[0025] On the other hand, the servo piston 7 includes: a first sliding portion 72 adjacent to the aforementioned tip 71 and slidably held in the first guide portion 27; and a second sliding portion 73 slidably held in the second guide portion 28. That is, the diameter of the first sliding portion 72 is substantially equal to the diameter of the first guide portion 27, and the diameter of the second sliding portion 73 is substantially equal to the diameter of the second guide portion 28.

[0026] Furthermore, an auxiliary pressure chamber 91 is formed between the annular end face of the first sliding portion 72 on the side of the second sliding portion 73 and the stepped portion between the first guide portion 27 and the second guide portion 28 in the retaining hole 26. This auxiliary pressure chamber 91 is used to push the servo piston 7 against the swashplate 5.

[0027] The outer casing 22 and valve cover 21 are provided with an inlet path 2c that branches off from the second flow path 2b to the auxiliary pressure chamber 91. In this embodiment, as described above, the second flow path 2b is a discharge path, so the inlet path 2c introduces working fluid from the discharge path into the auxiliary pressure chamber 91.

[0028] An electromagnetic proportional valve 92 is provided on the inlet path 2c to set the pressure of the auxiliary pressure chamber 91. In this embodiment, the electromagnetic proportional valve 92 functions as a pressure reducing valve to reduce the pump discharge pressure to the set pressure. In the illustration, the electromagnetic proportional valve 92 is an inverse proportional type where the command current is negatively correlated with the secondary pressure, but the electromagnetic proportional valve 92 can also be a direct proportional type where the command current is positively correlated with the secondary pressure.

[0029] An electric actuator 8 for driving the servo piston 7 is mounted on the top wall 25 of the housing body 22. The electric actuator 8 includes a threaded shaft 84 extending axially along the servo piston 7, a nut 83 engaging with the threaded shaft 84, and an electric motor 86 that rotates the threaded shaft 84.

[0030] Furthermore, the electric actuator 8 includes: a hollow rod 82 connected to the servo piston 7 and fixed with a nut 83; and a cylindrical housing 85 that slidably holds the rod 82 in the axial direction of the servo piston 7. The housing 85 is fixed to the top wall 25 of the outer casing 22, and an electric motor 86 is mounted on the housing 85.

[0031] In this embodiment, rod 82 is connected to servo piston 7 via a universal joint. Specifically, the front end of rod 82 is provided with a groove, in which ball 81 is held. On the other hand, the second sliding part 73 of servo piston 7 is provided with a plate-shaped protrusion 74 that inserts into the groove, and the protrusion 74 is provided with a hole that fits into ball 81.

[0032] However, contrary to this embodiment, a groove for retaining ball 81 can be provided on the second sliding part 73 of the servo piston 7, and a protrusion 74 inserted into the groove can be provided at the front end of the rod 82. Alternatively, the rod 82 can also be connected to the servo piston 7 through a connector other than a universal joint (e.g., a ball joint or spherical joint).

[0033] As explained above, in the hydraulic pump 1 of this embodiment, a working fluid with a relatively high pressure is introduced into the auxiliary pressure chamber 91, and this pressure pushes the servo piston 7 against the swashplate 5. Therefore, the thrust required by the electric actuator 8 to advance the servo piston 7 is reduced. Thus, the electric actuator 8 can advance and retract the servo piston 7 with a smaller thrust.

[0034] That is, since a small electric actuator 8 can be used, the manufacturing cost of the hydraulic pump 1 can be reduced. Furthermore, the thrust required by the electric actuator 8 is reduced, thus reducing power consumption. Moreover, the rotation angle of the output shaft of the electric actuator 8 is generally detected by a rotation angle sensor such as a resolver or rotary encoder, so this rotation angle sensor can be used to precisely control the capacity per revolution of the hydraulic pump 1, i.e., the output capacity.

[0035] Furthermore, in this embodiment, an electromagnetic proportional valve 92 is provided on the inlet path 2c, so that the pressure of the auxiliary pressure chamber 91 can be electrically changed.

[0036] (Modified Example) This disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of this disclosure.

[0037] For example, hydraulic pump 1 can rotate in both directions. At this time, as... Figure 2In the modified hydraulic pump 1A shown, the inlet path 2c is connected to both the first flow path 2a and the second flow path 2b via a high-pressure selector valve 93. In this configuration, the inlet path 2c also introduces working fluid into the auxiliary pressure chamber 91 from the discharge path, which is the one with the higher pressure in the first flow path 2a and the second flow path 2b.

[0038] Furthermore, it is not necessary to install a pressure reducing valve such as an electromagnetic proportional valve 92 on the feed path 2c. The feed path 2c can also guide the pump discharge pressure to the auxiliary pressure chamber 91 according to the area of ​​the auxiliary pressure chamber 91 (i.e., the area of ​​the annular end face on the side of the second sliding part 73 of the first sliding part 72 of the servo piston 7).

[0039] (Summarize) This disclosure provides a hydraulic pump comprising: a cylinder body slidably holding a plurality of pistons; a swashplate sliding with a slipper mounted on the heads of the plurality of pistons; a servo piston changing the angle of the swashplate; a valve plate sliding with the cylinder body and including a first port and a second port in opposite arcuate shapes; a housing housing the valve plate, the cylinder body, and the swashplate, and slidably holding the servo piston; and an electric actuator mounted on the housing and driving the servo piston, including a threaded shaft extending axially along the servo piston, a nut threaded with the threaded shaft, and an electric motor for rotating the threaded shaft; the housing comprising: an auxiliary pressure chamber for pushing the servo piston against the swashplate; a first flow path communicating with the first port; a second flow path communicating with the second port; and an inlet path for introducing working fluid into the auxiliary pressure chamber from the higher pressure of the first flow path and the second flow path, i.e., an outlet path.

[0040] Based on the above structure, since a high-pressure working fluid is introduced into the auxiliary pressure chamber, and this pressure pushes the servo piston against the swashplate, the thrust required by the electric actuator to advance the servo piston is reduced. Therefore, the electric actuator can move the servo piston forward and backward with a smaller thrust.

[0041] Alternatively, the feed line may be equipped with an electromagnetic proportional valve for setting the pressure of the auxiliary pressure chamber. With this configuration, the pressure of the auxiliary pressure chamber can be electrically changed.

[0042] For example, the housing may include a retaining hole for inserting the servo piston, the retaining hole including: a first guide portion; and a second guide portion located on the opposite side of the swashplate relative to the first guide portion and having a smaller diameter than the first guide portion, the servo piston including: a first sliding portion slidably held in the first guide portion; and a second sliding portion slidably held in the second guide portion, the auxiliary pressure chamber being formed between the end face of the second sliding portion side of the first sliding portion and the stepped portion between the first guide portion and the second guide portion in the retaining hole.

Claims

1. A hydraulic pump, characterized in that, have: The cylinder block can slidably hold multiple pistons; The swashplate slides with a slipper mounted on the head of the plurality of pistons; A servo piston changes the angle of the swashplate. The valve plate slides with the cylinder body and includes a first port and a second port in opposite directions of each other in an arc shape; The housing accommodates the valve plate, the cylinder, and the swashplate, and slidably holds the servo piston. as well as An electric actuator, mounted on the housing and driving the servo piston, includes a threaded shaft extending axially along the servo piston, a nut threaded to the threaded shaft, and an electric motor for rotating the threaded shaft. The housing includes: an auxiliary pressure chamber for pushing the servo piston onto the swashplate; a first flow path communicating with the first port; a second flow path communicating with the second port; and an inlet path for introducing working fluid into the auxiliary pressure chamber from the higher pressure side of the first flow path and the second flow path, i.e., the discharge path. The electric actuator includes: a hollow rod with the nut fixed to it, the rod being connected to the servo piston; The housing includes a retaining hole for insertion of the servo piston, the retaining hole including: a first guide portion; and a second guide portion located on the opposite side of the swashplate relative to the first guide portion and having a smaller diameter than the first guide portion; The servo piston includes: a first sliding portion slidably held in the first guide portion; and a second sliding portion slidably held in the second guide portion; An auxiliary pressure chamber is formed between the end face of the first sliding portion on the second sliding portion side and the stepped portion between the first guide portion and the second guide portion in the retaining hole.

2. The hydraulic pump according to claim 1, characterized in that, The inlet path is equipped with an electromagnetic proportional valve for setting the pressure of the auxiliary pressure chamber.

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