hydraulic pump

Abstract

To provide a hydraulic pump capable of moving a servo piston forward and backward by an electric actuator with small propulsion power.SOLUTION: A hydraulic pump 1 includes a casing 2 for housing a valve plate 3, a cylinder block 4 and a swash plate 5. An angle of the swash plate 5 is changed by a servo piston 7, and the servo piston 7 is slidably held by the casing. The servo piston 7 is driven by an electric actuator 8 mounted on the casing 2, and the electric actuator 8 includes the electric actuator including a screw shaft 84, a nut 83, and an electric motor 86. The casing 2 includes an auxiliary pressure chamber 91 for pressing the servo piston 7 toward the swash plate 5, and an introduction passage 2c for introducing a working fluid from a discharge passage of a first flow channel 2a or a second flow channel 2b of higher pressure to the auxiliary pressure chamber 91.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to hydraulic pumps. [Background technology]

[0002] BACKGROUND ART Conventionally, hydraulic pumps that are swash plate type axial piston pumps have been known. In such hydraulic pumps, a valve plate, a cylinder block, and a swash plate are housed in a casing (see, for example, Patent Document 1).

[0003] Specifically, the valve plate includes a first port and a second port, each arc-shaped and facing in opposite directions. When the hydraulic pump rotates in one direction, one of the first port and the second port is the suction port and the other is the discharge port. When the hydraulic pump rotates in both directions, one of the first port and the second port is the suction port and the other is the discharge port, depending on the direction of rotation.

[0004] Furthermore, multiple pistons are slidably held in the cylinder block, and shoes attached to the heads of the pistons slide against the swash plate. The angle of the swash plate is changed by a servo piston. Patent Document 2 discloses a hydraulic pump in which the servo piston is driven by an electric actuator. Patent Document 2 also describes a ball screw drive mechanism as a specific example of the electric actuator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-100759 [Patent Document 2] Special Publication No. 2011-522194 Summary of the Invention [Problem to be solved by the invention]

[0006] One method of driving a servo piston involves changing the hydraulic pressure acting on the servo piston. However, in this case, the drive of the servo piston may be affected by temperature changes in the hydraulic fluid. In contrast, if the servo piston is driven using a ball screw drive mechanism (i.e., an electric actuator including a screw shaft, a nut, and an electric motor), as in the specific example of Patent Document 2, such a problem does not occur.

[0007] However, the high pressure in the cylinder block exerts a large moment on the swash plate, pushing the servo piston forward. This increases the thrust when the electric actuator advances the servo piston. This leads to problems such as abnormal wear and shortened lifespan of the screw shaft and nut, as well as an increase in the size of the electric motor.

[0008] Therefore, an object of the present disclosure is to provide a hydraulic pump in which an electric actuator can move a servo piston forward and backward with a small propulsive force. [Means for solving the problem]

[0009] The present disclosure provides a hydraulic pump comprising: a cylinder block that slidably holds a plurality of pistons; a swash plate that slides against shoes attached to the heads of the plurality of pistons; a servo piston that changes the angle of the swash plate; a valve plate that slides against the cylinder block and includes first and second arc-shaped ports facing opposite to each other; a casing that houses the valve plate, the cylinder block, and the swash plate and slidably holds the servo piston; and an electric actuator that is attached to the casing and drives the servo piston, the electric actuator including a screw shaft extending along the axial direction of the servo piston, a nut that screws onto the screw shaft, and an electric motor that rotates the screw shaft, wherein the casing includes an auxiliary pressure chamber for pressing the servo piston toward the swash plate, a first flow path that communicates with the first port, a second flow path that communicates with the second port, and an inlet path that introduces hydraulic fluid from a discharge path that has a higher pressure than the first flow path or the second flow path to the auxiliary pressure chamber. [Effects of the Invention]

[0010] According to the present disclosure, a hydraulic pump is provided in which an electric actuator can move a servo piston forward and backward with a small thrust force. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a cross-sectional view of a hydraulic pump according to an embodiment. [Figure 2] FIG. 10 is a cross-sectional view of a modified hydraulic pump. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1 shows a hydraulic pump 1 according to one embodiment. The hydraulic pump 1 includes a casing 2 and a rotary shaft 11 extending from the inside to the outside of the casing 2. The hydraulic pump 1 further includes a valve plate 3, a cylinder block 4, and a swash plate 5 housed within the casing 2.

[0013] For ease of explanation, the axial direction of the rotating shaft 11 will be referred to as the front-to-rear direction (one end located outside the casing 2 will be referred to as the front, and the other end will be referred to as the rear), and the two directions perpendicular to the axial direction of the rotating shaft 11 will be referred to as the up-down direction (the upper side of Figure 1 will be referred to as the upside, and the lower side will be referred to as the downside) and the left-to-right direction.

[0014] The casing 2 includes a container-shaped casing main body 22 that opens rearward, and a valve cover 21 that closes the opening of the casing main body 22. The casing main body 22 includes a front wall 23 through which the rotating shaft 11 passes, and a bottom wall 24, a top wall 25, and a pair of side walls that surround an internal space. The front wall 23 and the valve cover 21 of the casing main body 22 each hold bearings 12 and 13 that rotatably support the rotating shaft 11.

[0015] The valve plate 3 is attached to the front surface of the valve cover 21. The valve plate 3 is provided with a first port 31 and a second port 32, which are arc-shaped and face opposite each other. In FIG. 1, the first port 31 is drawn at the top dead center on the lower side (the position where a piston 61, which will be described later, is moved farthest back), and the second port 32 is drawn at the bottom dead center on the upper side (the position where the piston 61 is moved farthest forward), but the actual positions of the first port 31 and the second port 32 are on both sides of the rotation shaft 11 in the left-right direction (the direction perpendicular to the direction of separation between 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 open to the outer peripheral surface or rear surface of the valve cover 21, and these openings form external connection ports. As described above, the hydraulic pump 1 rotates in one direction, so the first flow path 2a is the intake path and the second flow path 2b is the discharge path. In other words, the pressure in the second flow path 2b is higher than the pressure in the first flow path 2a.

[0018] The cylinder block 4 is fixed to the rotary shaft 11 and rotates together with the rotary shaft 11 to slide against the valve plate 3. The cylinder block 4 has a plurality of cylinder bores 41 that open forward around the periphery of the rotary shaft 11. A plurality of pistons 61 are inserted into each of the cylinder bores 41. This allows the pistons 61 to be slidably held in the cylinder block 4.

[0019] The cylinder block 4 is also provided with cylinder ports 42 that extend from each cylinder bore 41 to the valve plate 3. Some of these cylinder ports 42 communicate with the first ports 31, and some communicate with the second ports 32. For example, if there are nine cylinder bores 41 and nine cylinder ports 42, four or five of the cylinder ports 42 communicate with the first ports 31 or the second ports 32, depending on the rotational position of the cylinder block 4.

[0020] A plurality of shoes 62 are attached to the heads of the pistons 61. In this embodiment, the shoes 62 slide on the swash plate 5 via annular shoe plates 63 attached to the swash plate 5. However, the shoe plates 63 may be omitted and the shoes 62 may slide directly on the swash plate 5. The shoes 62 are held down by a holding plate 64 so as to maintain contact with the shoe plates 63.

[0021] The swash plate 5 is supported by a support base 14 provided on the front wall 23 of the casing body 22 so as to be swingable about a swing axis extending in the left-right direction. The angle of the swash plate 5 is changed by a servo piston 7, which is slidably supported on the ceiling wall 25 of the casing body 22.

[0022] More specifically, the swash plate 5 includes a main body 50 through which the rotary shaft 11 passes and an operating portion 51 that protrudes upward from the main body 50. In this embodiment, a tip end 71 of the servo piston 7 is connected to the operating portion 51 via a pin 52.

[0023] However, the servo piston 7 does not necessarily have to be connected to the operating portion 51 of the swash plate 5. For example, the servo piston 7 may abut against the operating portion 51 of the swash plate 5 from the rear, and the operating portion 51 may be biased rearward by a spring disposed between the operating portion 51 and the front wall 23 of the casing body 22.

[0024] A retaining hole 26 into which the servo piston 7 is inserted is provided in the ceiling wall 25 of the casing body 22. In this embodiment, the retaining hole 26 includes a first guide portion 27 that forms an opening to the internal space of the casing 2, and a second guide portion 28 that is located on the opposite side of the first guide portion 27 from the swash plate 5. 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 tip portion 71 and slidably held in the first guide portion 27, and a second sliding portion 73 slidably held in the second guide portion 28. In other words, the diameter of the first sliding portion 72 is approximately equal to the diameter of the first guide portion 27, and the diameter of the second sliding portion 73 is approximately equal to the diameter of the second guide portion 28.

[0026] An auxiliary pressure chamber 91 is formed between the annular end face of the first sliding portion 72 on the second sliding portion 73 side and the step portion between the first guide portion 27 and the second guide portion 28 in the retaining hole 26. This auxiliary pressure chamber 91 presses the servo piston 7 toward the swash plate 5.

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

[0028] An electromagnetic proportional valve 92 that sets the pressure in the auxiliary pressure chamber 91 is provided in the introduction path 2c. In this embodiment, the electromagnetic proportional valve 92 functions as a pressure reducing valve that reduces the pump discharge pressure to the set pressure. In the illustrated example, the electromagnetic proportional valve 92 is an inverse proportional type in which the command current and the secondary pressure show a negative correlation, but the electromagnetic proportional valve 92 may also be a direct proportional type in which the command current and the secondary pressure show a positive correlation.

[0029] An electric actuator 8 that drives the servo piston 7 is attached to the ceiling wall 25 of the casing body 22. The electric actuator 8 includes a screw shaft 84 that extends along the axial direction of the servo piston 7, a nut 83 that screws onto the screw shaft 84, and an electric motor 86 that rotates the screw shaft 84.

[0030] Furthermore, the electric actuator 8 includes a hollow rod 82 that is connected to the servo piston 7 and has a nut 83 fixed thereto, and a cylindrical housing 85 that holds the rod 82 slidably in the axial direction of the servo piston 7. The housing 85 is fixed to the ceiling wall 25 of the casing main body 22, and an electric motor 86 is attached to this housing 85.

[0031] In this embodiment, the rod 82 is connected to the servo piston 7 via a universal joint. Specifically, a slot is provided at the front end of the rod 82, and a ball 81 is held in this slot. Meanwhile, the second sliding portion 73 of the servo piston 7 is provided with a plate-shaped protrusion 74 that is inserted into the slot, and this protrusion 74 is provided with a hole that fits over the ball 81.

[0032] However, contrary to this embodiment, a slot for holding the ball 81 may be provided in the second sliding portion 73 of the servo piston 7, and a protrusion 74 to be inserted into the slot may be provided at the front end of the rod 82. Alternatively, the rod 82 may be connected to the servo piston 7 by a joint other than a universal joint (for example, a ball joint or a spherical joint).

[0033] As described above, in the hydraulic pump 1 of this embodiment, a relatively high-pressure hydraulic fluid is introduced into the auxiliary pressure chamber 91, and this pressure presses the servo piston 7 toward the swash plate 5. This reduces the thrust required by the electric actuator 8 to move the servo piston 7 forward. Therefore, the electric actuator 8 can move the servo piston 7 forward and backward with a small thrust.

[0034] That is, it is possible to use a small electric actuator 8, thereby reducing the manufacturing costs of the hydraulic pump 1. Also, the propulsive force required for the electric actuator 8 is reduced, which reduces power consumption. Moreover, since the rotation angle of the output shaft of the electric actuator 8 is usually detected by a rotation angle sensor such as a resolver or rotary encoder, the discharge capacity, which is the capacity per rotation of the hydraulic pump 1, can be controlled with high precision using the rotation angle sensor.

[0035] Furthermore, in this embodiment, since the electromagnetic proportional valve 92 is provided in the introduction passage 2c, the pressure in the auxiliary pressure chamber 91 can be changed electrically.

[0036] (Variation) The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0037] For example, the hydraulic pump 1 may rotate in both directions. In this case, as in the modified hydraulic pump 1A shown in Fig. 2, the inlet passage 2c is connected to both the first flow path 2a and the second flow path 2b via the high-pressure selection valve 93. Even in this configuration, the inlet passage 2c introduces hydraulic fluid into the auxiliary pressure chamber 91 from the discharge path, whichever has the higher pressure, of the first flow path 2a and the second flow path 2b.

[0038] Furthermore, it is not necessary to provide a pressure reducing valve such as an electromagnetic proportional valve 92 in the inlet passage 2c, and depending on the area of ​​the auxiliary pressure chamber 91 (i.e., the area of ​​the annular end face of the first sliding portion 72 of the servo piston 7 on the second sliding portion 73 side), the inlet passage 2c may directly guide the pump discharge pressure to the auxiliary pressure chamber 91.

[0039] (summary) The present disclosure provides a hydraulic pump comprising: a cylinder block that slidably holds a plurality of pistons; a swash plate that slides against shoes attached to the heads of the plurality of pistons; a servo piston that changes the angle of the swash plate; a valve plate that slides against the cylinder block and includes first and second arc-shaped ports facing opposite to each other; a casing that houses the valve plate, the cylinder block, and the swash plate and slidably holds the servo piston; and an electric actuator that is attached to the casing and drives the servo piston, the electric actuator including a screw shaft extending along the axial direction of the servo piston, a nut that screws onto the screw shaft, and an electric motor that rotates the screw shaft, wherein the casing includes an auxiliary pressure chamber for pressing the servo piston toward the swash plate, a first flow path that communicates with the first port, a second flow path that communicates with the second port, and an inlet path that introduces hydraulic fluid from a discharge path that has a higher pressure than the first flow path or the second flow path to the auxiliary pressure chamber.

[0040] With the above configuration, hydraulic fluid with a relatively high pressure is introduced into the auxiliary pressure chamber, and this pressure presses the servo piston toward the swash plate, so that the thrust force required by the electric actuator to move the servo piston forward is small, and therefore the electric actuator can move the servo piston forward and backward with a small thrust force.

[0041] The introduction passage may be provided with an electromagnetic proportional valve that sets the pressure in the auxiliary pressure chamber. With this configuration, the pressure in the auxiliary pressure chamber can be changed electrically.

[0042] For example, the casing may include a retaining hole into which the servo piston is inserted, the retaining hole having a first guide portion and a second guide portion located on the opposite side of the swash plate from the first guide portion and having a smaller diameter than the first guide portion, the servo piston may include a first sliding portion slidably held in the first guide portion and a second sliding portion slidably held in the second guide portion, and the auxiliary pressure chamber may be formed between the end face of the first sliding portion facing the second sliding portion and a step portion in the retaining hole between the first guide portion and the second guide portion. [Explanation of symbols]

[0043] 1,1A hydraulic pump 2 Casing 2a First flow path 2b Second flow path 2c Introductory path 26 retaining hole 27 First guide section 28 Second guide section 3 Valve Plate 31 Port 1 32 Second Port 4 Cylinder block 5 Swash plate 61 Piston 62 Shoe 7 Servo Piston 72 First sliding part 73 Second sliding part 8 Electric Actuators 83 Nut 84 Screw shaft 86 Electric Motor 91 Auxiliary pressure chamber 92 Solenoid proportional valve 93 High pressure selection valve

Claims

1. a cylinder block that slidably holds a plurality of pistons; a swash plate that slides on shoes attached to the heads of the pistons; a servo piston for changing the angle of the swash plate; a valve plate that slides on the cylinder block and includes a first port and a second port that are arc-shaped and face opposite to each other; a casing that houses the valve plate, the cylinder block, and the swash plate and slidably holds the servo piston; an electric actuator attached to the casing to drive the servo piston, the electric actuator including a threaded shaft extending along the axial direction of the servo piston, a nut threadedly engaging with the threaded shaft, and an electric motor that rotates the threaded shaft; the casing includes a retaining hole into which the servo piston is inserted, an auxiliary pressure chamber for pressing the servo piston toward the swash plate, a first flow path communicating with the first port, a second flow path communicating with the second port, and an introduction path for introducing hydraulic fluid from a discharge path having a higher pressure of the first flow path or the second flow path to the auxiliary pressure chamber, the retaining hole having a first guide portion and a second guide portion having a smaller diameter than the first guide portion and located on the opposite side of the swash plate with respect to the first guide portion, the servo piston includes a first sliding portion slidably held by the first guide portion and a second sliding portion slidably held by the second guide portion, a hydraulic pump, wherein the auxiliary pressure chamber is formed between an end face of the first sliding portion on the second sliding portion side and a step portion between the first guide portion and the second guide portion in the retaining hole.

2. 2. The hydraulic pump according to claim 1, wherein the inlet passage is provided with an electromagnetic proportional valve for setting the pressure of the auxiliary pressure chamber.

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