Rotary swashplate type hydraulic pump

Abstract

To provide a rotary swash plate-type hydraulic pump capable of accurately adjusting a discharge capacity.SOLUTION: A rotary swash plate-type hydraulic pump includes: a casing; a cylinder block disposed in the casing in a manner of being not relatively rotatable and provided with a plurality of cylinder bores opened at one end face; a rotary swash plate rotatably housed in the casing in a manner of facing one end face of the cylinder block; a plurality of pistons each inserted to each of the cylinder bores and reciprocating in the cylinder bore by rotation of the rotary swash plate; and a variable capacity mechanism changing an effective stroke length of at least one piston among the plurality of pistons. The variable capacity mechanism includes: a shaft portion inserted to the cylinder block and interlocking with the rotary swash plate; and a swash plate portion disposed on the shaft portion in a manner that it can be advanced and retracted in an axial direction and cannot be relatively rotated. The shaft portion is journaled at an axially separating position in the cylinder block.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a swash plate type hydraulic pump that reciprocates a piston by rotating a swash plate.

Background Art

[0002] As a piston pump, for example, a swash plate type piston pump as disclosed in Patent Document 1 is known. In the piston pump of Patent Document 1, when the swash plate rotates, the piston reciprocates. As a result, pressurized oil is discharged from the piston pump.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the piston pump of Patent Document 1, the discharge capacity is constant. In a piston pump, it is desired that the discharge capacity can be changed according to the situation. Therefore, the inventor of the present application has developed a variable capacity mechanism. The variable capacity mechanism can change the effective stroke length of at least one of a plurality of pistons by rotating a swash plate rotation shaft interlocked with the swash plate. On the other hand, in a piston pump provided with a variable capacity mechanism, it is required to accurately adjust the discharge capacity.

[0005] Therefore, an object of the present invention is to provide a swash plate type hydraulic pump capable of accurately adjusting the discharge capacity.

Means for Solving the Problems

[0006] The rotary swashplate hydraulic pump of the present invention comprises a casing, a cylinder block disposed within the casing so as not to rotate relative to it and having a plurality of cylinder bores formed thereon with an opening at one end face, a rotary swashplate rotatably housed within the casing so as to face one end face of the cylinder block, a plurality of pistons inserted into each of the cylinder bores and reciprocating in the cylinder bores by the rotation of the rotary swashplate, and a variable displacement mechanism that changes the effective stroke length of at least one of the plurality of pistons, wherein the variable displacement mechanism includes a shaft portion inserted through the cylinder block and interlocked with the rotary swashplate, and a swashplate portion provided on the shaft portion so as to be able to move back and forth in the axial direction and not to rotate relative to it, and the shaft portion is pivotally supported in the cylinder block at positions separated in the axial direction.

[0007] According to the present invention, a shaft that rotates in conjunction with a rotating swash plate is pivotally supported in the cylinder block at a position axially separated from it. Therefore, the shaft rotates in a stable state. That is, the swash plate, which is non-rotatably mounted on the shaft, also rotates in a stable state. Since the swash plate moves back and forth in the axial direction while rotating in a stable state, the effective stroke length can be adjusted stably. Therefore, the discharge volume can be adjusted with high precision.

[0008] The rotary swashplate hydraulic pump of the present invention comprises a casing, a cylinder block disposed within the casing so as not to rotate relative to it and having a plurality of cylinder bores formed thereon with an opening at one end face, a rotary swashplate rotatably housed within the casing so as to face one end face of the cylinder block, a plurality of pistons inserted into each of the cylinder bores and reciprocating within the cylinder bores by the rotation of the rotary swashplate, the rotary swashplate including a shaft portion and a swashplate portion facing one end face of the cylinder block, the plurality of pistons reciprocating by the rotation of the swashplate portion, the shaft portion being rotatably supported by the casing via a first bearing externally mounted on the shaft portion, and the swashplate portion being rotatably supported by the casing via a second bearing externally mounted on the swashplate portion.

[0009] According to the above configuration, the rotating swash plate can be rotated stably by supporting it at two points: the shaft and the swash plate itself. This suppresses wobble of the rotating swash plate, and therefore improves the accuracy of the discharge volume. [Effects of the Invention]

[0010] According to the present invention, the discharge volume can be adjusted with high precision. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing a rotary swashplate type hydraulic pump according to an embodiment of the present invention. [Figure 2] This is an enlarged cross-sectional view showing an enlarged view of region X of the rotary swashplate type hydraulic pump shown in Figure 1. [Figure 3] Figure 2 is an enlarged cross-sectional view showing the swash plate portion of a rotary swash plate type hydraulic pump in a retracted position. [Modes for carrying out the invention]

[0012] Hereinafter, a rotary swashplate type hydraulic pump 1 according to an embodiment of the present invention will be described with reference to the aforementioned drawings. Note that the concept of direction used in the following description is for convenience of explanation and does not limit the orientation of the invention's configuration to that direction. Furthermore, the hydraulic pump 1 described below is merely one embodiment of the present invention. Therefore, the present invention is not limited to this embodiment, and additions, deletions, and modifications are possible without departing from the spirit of the invention.

[0013] <Rotating swashplate type hydraulic pump> The rotary swashplate hydraulic pump (hereinafter referred to as "hydraulic pump") 1 shown in Figure 1 is installed in various machines such as construction machinery like shovels and cranes, industrial machinery like forklifts, agricultural machinery like tractors, and hydraulic machinery like presses. In this embodiment, the hydraulic pump 1 is a rotary swashplate type and a variable displacement pump. The hydraulic pump 1 comprises a casing 11, a cylinder block 12, a rotary swashplate 13, a plurality of pistons 14, and a variable displacement mechanism 15. The hydraulic pump 1 also comprises a plurality of suction-side check valves 16, a plurality of discharge-side check valves 17, and a linear actuator 18. The hydraulic pump 1 discharges working fluid when driven by a drive source (e.g., an engine, an electric motor, or both).

[0014] <Casing> The casing 11 houses the cylinder block 12, the rotating swash plate 13, a plurality of pistons 14, and the variable displacement mechanism 15. The casing 11 includes an intake passage 11a and a discharge passage 11b. The casing 11 is a cylindrical member that extends along a predetermined axis L1. That is, the casing 11 is open at one end and the other end on the axial side and the other side, respectively.

[0015] The intake passage 11a is formed in the other end portion of the casing 11. The intake passage 11a is connected to a plurality of cylinder bores 12b of the cylinder block 12, which will be described in detail later. The intake passage 11a is also connected to the tank 19 via the intake port 11c. The discharge passage 11b is formed in the middle portion of the casing 11. The discharge passage 11b is connected to each of the cylinder bores 12b of the cylinder block 12, which will be described in detail later. More specifically, the discharge passage 11b branches into a plurality of passage sections 11e, which are connected to each side of the cylinder bore 12b. The passage sections 11e are also connected to the hydraulic actuator via the discharge port 11d.

[0016] <Cylinder Block> The cylinder block 12 is positioned within the casing 11 so as not to rotate relative to it. More specifically, the cylinder block 12 is fixed to the casing 11. In this embodiment, the cylinder block 12 is integrally formed in the axial intermediate portion of the casing 11. The cylinder block 12 also has a plurality of cylinder bores 12b that open at one end face 12a. The one end face 12a is the end face on one axial side of the cylinder block 12. Furthermore, the cylinder block 12 has a plurality of spool holes 12c, a plurality of communication passages 12d, and a shaft insertion hole 12e. The cylinder block 12 has an equal number of cylinder bores 12b and spool holes 12c. In this embodiment, nine cylinder bores 12b and nine spool holes 12c are formed in the cylinder block 12.

[0017] The nine cylinder bores 12b are arranged circumferentially at intervals around the axis L1. Each cylinder bore 12b extends axially from one end face 12a to the other end. Each cylinder bore 12b opens at one end face 12a and the other end face 12f of the cylinder block 12. Each cylinder bore 12b is connected to the intake passage 11a at the other end face 12f of the cylinder block 12. Each cylinder bore 12b is also connected to each of the passage portions 11e of the discharge passage 11b.

[0018] The nine spool holes 12c are arranged at circumferential intervals around the axis L1. The nine spool holes 12c are arranged radially inward of the nine cylinder bores 12b. More specifically, the cylinder block 12 has a protrusion 12g around the axis L1 on one end face 12a. The nine spool holes 12c are arranged at intervals around the protrusion 12g. Also, each of the spool holes 12c is associated with each of the cylinder bores 12b. The spool holes 12c are arranged radially inward with respect to the corresponding cylinder bores 12b. The nine spool holes 12c also penetrate the cylinder block 12 in the axial direction. And the nine spool holes 12c are connected to the suction passage 11a at the other end face 12f of the cylinder block 12.

[0019] Each of the communication passages 12d connects the corresponding cylinder bore 12b and the spool hole 12c. Each of the communication passages 12d is located on the side of the other end face 12f of the cylinder block 12. The communication passages 12d open to the circumferential surfaces of the corresponding cylinder bores 12b and the circumferential surfaces of the spool holes 12c, respectively. In the present embodiment, the communication passages 12d are arranged at positions radially opposed to the passage portion 11e of the discharge passage 11b. Therefore, the communication passages 12d are easy to form.

[0020] The shaft insertion hole 12e is formed along the axis L1 in the cylinder block 12. And the shaft insertion hole 12e penetrates the cylinder block 12 in the axial direction. More specifically, the shaft insertion hole 12e penetrates the cylinder block 12 in the axial direction from the tip end face of the protrusion 12g to the other end face 12f.

[0021] <Swash plate> The swash plate 13 includes a shaft portion 13a and a swash plate portion 13b. The swash plate 13 is rotatably accommodated in the casing 11 so as to face one end surface 12a of the cylinder block 12. The shaft portion 13a extends along the axis L1 and is rotatably supported by the casing 11. More specifically, a first bearing 13c is externally mounted on the shaft portion 13a. The shaft portion 13a is rotatably supported by the casing 11 via the first bearing 13c. Thereby, the shaft portion 13a rotates about the axis L1. The first bearing 13c is, for example, a radial bearing and is a cylindrical roller bearing in this embodiment. However, the first bearing 13c is not limited to a cylindrical roller bearing. Further, the shaft portion 13a protrudes from one end of the casing 11, that is, one end surface on the axial direction one side of the casing 11. The shaft portion 13a is connected to the above-described drive source at a portion on the axial direction one side. And the shaft portion 13a is rotationally driven by the drive source.

[0022] The swash plate portion 13b has a swash plate side inclined surface 13e. The swash plate portion 13b is arranged such that the swash plate side inclined surface 13e faces one end surface 12a of the cylinder block 12. The swash plate side inclined surface 13e is inclined toward the one end surface 12a. The swash plate portion 13b is rotatably supported by the casing 11. More specifically, a second bearing 13d is externally mounted on the swash plate portion 13b. The swash plate portion 13b is rotatably supported by the casing 11 via the second bearing 13d. Thereby, the swash plate portion 13b rotates about the axis L1. The second bearing 13d is, for example, a radial bearing and is a tapered roller bearing in this embodiment. However, the first bearing 13c is not limited to a cylindrical roller bearing.

[0023] <Piston> Multiple pistons 14 are inserted into each of the cylinder bores 12b of the cylinder block 12. That is, the cylinder block 12 has the same number of pistons 14 as the cylinder bore 12b (9 pistons in this embodiment). Each of the pistons 14 reciprocates within the cylinder bore 12b as the swash plate portion 13b of the rotating swash plate 13 rotates. More specifically, the 9 pistons 14 are in contact with the rotating swash plate side inclined surface 13e. Therefore, each of the 9 pistons 14 reciprocates within the cylinder bore 12b as the rotating swash plate 13 rotates. In this embodiment, each of the pistons 14 is in contact with the rotating swash plate side inclined surface 13e of the rotating swash plate 13 via a shoe 21. Furthermore, each of the shoes 21 is pressed against the rotating swash plate side inclined surface 13e by a retaining plate 22. As a result, when the rotating swash plate 13 rotates, the pistons 14 are reciprocated in one axial direction and the other via the shoes 21.

[0024] <Variable Capacitance Mechanism> The variable displacement mechanism 15 includes a plurality of spools 25, a plurality of springs 26, and a swash plate rotation shaft 27, as shown in Figure 2. In this embodiment, the variable displacement mechanism 15 includes the same number of spool holes 12c, i.e., nine spools 25 and springs 26. The variable displacement mechanism 15 adjusts the effective stroke length S of each of the nine pistons 14. This allows the variable displacement mechanism 15 to change the discharge capacity of the hydraulic pump 1. More specifically, the variable displacement mechanism 15 connects the cylinder bore 12b to the tank 19 via the spool holes 12c and the suction passage 11a when the piston 14 strokes at least from bottom dead center to top dead center (i.e., during the discharge stroke). This allows the variable displacement mechanism 15 to adjust the effective stroke length S of each of the pistons 14.

[0025] <Spool> The nine spools 25 are arranged to correspond to each of the cylinder bores 12b. The nine spools 25 open and close the space between the corresponding cylinder bore 12b and the tank 19 (see Figure 1) by reciprocating motion. In this embodiment, the nine spools 25 open and close the space between the corresponding cylinder bore 12b and the intake passage 11a by reciprocating motion. The nine spools 25 connect the corresponding cylinder bore 12b to the tank 19 via the intake passage 11a. The spools 25 are synchronized with the reciprocating motion of the piston 14 (hereinafter referred to as the "corresponding piston") located in the corresponding cylinder bore 12b. For example, when each spool 25 moves toward the bottom dead center of the piston 14, it eventually opens the space between the corresponding cylinder bore 12b and the intake passage 11a. On the other hand, when each spool 25 moves toward the top dead center of the piston 14, it eventually closes the space between the corresponding cylinder bore 12b and the intake passage 11a. Therefore, the spool 25 connects the cylinder bore 12b to the tank 19 during the discharge process. Each of the spools 25 is also provided with a spring 26. Each of the spools 25 is biased toward the swash plate section 32, which will be described later, by the spring 26.

[0026] <Swashplate rotation axis> The swash plate rotation shaft 27 has a shaft portion 31 and a swash plate portion 32. The swash plate rotation shaft 27 rotates in conjunction with the rotating swash plate 13. The rotation of the swash plate rotation shaft 27 causes each of the spools 25 to reciprocate. The swash plate rotation shaft 27 can also change the open and closed positions of each of the spools 25. The open and closed positions of each of the spools 25 are the positions in which each of the spools 25 begins to open the communication passage 12d and the closed positions.

[0027] The shaft portion 31 is inserted through the cylinder block 12. More specifically, the shaft portion 31 extends along the axis L1. The shaft portion 31 is inserted through the shaft insertion hole 12e of the cylinder block 12. The shaft portion 31 is supported at axially separated positions within the shaft insertion hole 12e. More specifically, the shaft portion 31 is fitted with a third bearing 33 and a fourth bearing 34. The third bearing 33 and the fourth bearing 34 are axially separated from each other within the shaft portion 31.

[0028] The third bearing 33 is positioned axially in pairs on the tip end of the shaft portion 31 and is not relative to it in the axial direction. The third bearing 33 is fitted into the projection 12g of the cylinder block 12. As a result, the shaft portion 31 is pivotally supported by the cylinder block 12 via the third bearing 33 at its tip end. The fourth bearing 34 is positioned in the middle portion of the shaft portion 31 so as to be relative to it in the axial direction. More specifically, the fourth bearing 34 is positioned on the shaft portion 31 so as to be relative to it in the axial direction on one side of the swash plate portion 32, which will be described in detail later. The fourth bearing 34 is also positioned on the other end face 12f side of the cylinder block 12. As a result, the shaft portion 31 is pivotally supported by the cylinder block 12 in the middle portion via the fourth bearing 34.

[0029] Furthermore, the shaft portion 31 is linked to the rotating swash plate 13. More specifically, one axial end portion 31a of the shaft portion 31 protrudes from the shaft insertion hole 12e toward the rotating swash plate 13. The axial end portion 31a of the shaft portion 31 is detachably and non-rotatably connected to the rotating swash plate 13. Therefore, the shaft portion 31 rotates around the axis L1 in conjunction with the rotating swash plate 13. In this embodiment, the shaft portion 31 is spline-coupled or key-coupled to the rotating swash plate 13. The shaft portion 31 may also be connected to the rotating swash plate 13 by a joint member, or it may be integrally formed with the rotating swash plate 13. The other axial end portion of the shaft portion 31 protrudes from the shaft insertion hole 12e toward the suction passage 11a.

[0030] The swash plate portion 32 has a base portion 32a and a contact portion 32b. The swash plate portion 32 is mounted on the shaft portion 13a so as not to rotate relative to it. More specifically, the swash plate portion 32 is externally mounted on the other axial end portion of the shaft portion 31 so as not to rotate relative to it. Therefore, the swash plate portion 32 is positioned on the shaft portion 31 so as to face the other end face 12f of the cylinder bore 12b in the intake passage 11a. The spool 25, biased by a spring 26, is in contact with the swash plate portion 32. The swash plate portion 32 has a swash plate rotation axis side inclined surface 32c, which will be described in detail later. Therefore, the swash plate portion 32 causes each of the spools 25 to reciprocate by the rotation of the swash plate rotation axis 27. In this embodiment, the swash plate portion 32 causes the spools 25 to reciprocate in synchronization with the reciprocating motion of the corresponding piston 14. The swash plate portion 32 is also mounted on the shaft portion 13a so as to be able to move back and forth in the axial direction. The swashplate portion 32 adjusts the opening and closing position of the spool 25 by moving back and forth in the axial direction.

[0031] The base portion 32a is mounted on the shaft portion 31 so as to be able to move back and forth in the axial direction but not to rotate relative to it. More specifically, the base portion 32a is mounted on the other axial end portion of the shaft portion 31 and is key-coupled so as to be able to move back and forth but not to rotate relative to it. The axial intermediate portion of the base portion 32a is formed to be large in diameter. The outer circumferential surface of the axial intermediate portion of the base portion 32a is formed to be cylindrical and its axis is inclined clockwise with respect to the rotation axis of the shaft portion 31. In this embodiment, the rotation axis of the shaft portion 31 coincides with axis L1.

[0032] The contact portion 32b has an inclined surface 32c on the swash plate rotation axis side. The contact portion 32b is provided on the base portion 32a. More specifically, the contact portion 32b is externally mounted on the axial intermediate portion of the base portion 32a via a fifth bearing 32d. The fifth bearing 32d is a radial bearing, and in this embodiment, it is a ball bearing. However, the fifth bearing 32d is not limited to a radial bearing and may be a thrust bearing. The intermediate portion of the base portion 32a is fitted to the inner circumferential surface of the fifth bearing 32d. As a result, the fifth bearing 32d is externally mounted on the intermediate portion of the shaft portion 31 such that its axis is tilted clockwise with respect to the rotation axis of the shaft portion 31. Furthermore, the fifth bearing 32d is positioned so that one axial end portion faces the other end face 12f of the valve block 12. The contact portion 32b is attached to the axial end portion of the outer ring of the fifth bearing 32d. More specifically, the contact portion 32b is formed in an annular shape with an L-shaped cross-section. The contact portion 32b is fitted onto one axial end of the outer ring of the fifth bearing 32d.

[0033] The swash plate rotation axis side inclined surface 32c is the portion that faces the other end surface 12f of the cylinder block 12 at the contact portion 32b. The swash plate rotation axis side inclined surface 32c is inclined with respect to the rotation axis of the shaft portion 31. More specifically, the swash plate rotation axis side inclined surface 32c is inclined with respect to the rotation axis of the shaft portion 31 because the contact portion 32b is externally mounted on the axial intermediate portion of the base portion 32a via the fifth bearing 32d. In this embodiment, the swash plate rotation axis side inclined surface 32c is tilted in the same direction as the rotation swash plate side inclined surface 13e, that is, clockwise around an orthogonal axis L2 perpendicular to the rotation axis of the shaft portion 31. Nine spools 25 are in contact with the swash plate rotation axis side inclined surface 32c. More specifically, the other axial ends of the nine spools 25, which are biased by the spring 26, are in contact with the swash plate rotation axis side inclined surface 32c.

[0034] The swash plate section 32 causes the spool 25 to reciprocate in synchronization with the corresponding piston 14 as the swash plate rotation shaft 27 rotates. More specifically, the swash plate rotation shaft 27 synchronizes the timing of when the spool 25 and the corresponding piston 14 are positioned at each dead center. This allows the swash plate rotation shaft 27 to connect the cylinder bore 12b to the intake passage 11a at the bottom dead center of the corresponding piston 14. On the other hand, the swash plate rotation shaft 27 can narrow the opening of the cylinder bore 12b between the intake passage 11a and the corresponding piston 14 as it moves from the bottom dead center to the top dead center, and eventually close it.

[0035] Furthermore, the swash plate portion 32 adjusts the opening and closing position of the spool 25 by moving forward and backward. More specifically, the swash plate portion 32 moves forward and backward relative to the other end face 12f of the cylinder block 12 by moving the base portion 32a relative to the shaft portion 31. This allows the dead center position of the spool 25 in the cylinder bore 12b to be changed. For example, when the swash plate portion 32 moves forward in one axial direction, the dead center position of the spool 25 in the cylinder bore 12b shifts to one axial side. On the other hand, when the swash plate portion 32 moves backward in the other axial direction, the dead center position of the spool 25 in the cylinder bore 12b shifts to the other axial side. Therefore, the opening and closing position of the spool 25 in the cylinder bore 12b can be shifted in the axial direction.

[0036] The effective stroke length S of each piston 14 is the range of stroke from which the working fluid can be discharged from the cylinder bore 12b. That is, the effective stroke length S is the actual stroke length S1 minus the open stroke length S2. The actual stroke length S1 is the actual operating stroke length of the piston 14 (i.e., the distance from bottom dead center to top dead center). The open stroke length S2 is the stroke length of the piston 14 from bottom dead center until the communication passage 12d is closed, and it changes as the open and closed positions change. Therefore, the effective stroke length S of each piston 14 can be adjusted by moving the swashplate 32 forward and backward. This makes it possible to change the discharge capacity in each of the cylinder bores 12b.

[0037] <Intake side check valve> Each of the intake-side check valves 16 is provided in each of the cylinder bores 12b. That is, in this embodiment, there are nine intake-side check valves 16, the same number as the cylinder bores 12b. The intake-side check valves 16 open and close the gap between the cylinder bore 12b and the intake passage 11a. More specifically, the intake-side check valves 16 allow the flow of working fluid from the intake passage 11a to the cylinder bore 12b and block the flow in the reverse direction. That is, during the intake process when the piston 14 moves from top dead center to bottom dead center, working fluid flows from the intake passage 11a to the cylinder bore 12b. On the other hand, during the discharge process when the piston 14 is discharged, the flow of working fluid from the intake passage 11a to the cylinder bore 12b is stopped.

[0038] <Discharge side check valve> Each of the multiple discharge-side check valves 17 is provided in each of the cylinder bores 12b. In this embodiment, each of the discharge-side check valves 17 is provided in each of the passage portions 11e of the discharge passage 11b. That is, in this embodiment, there are nine discharge-side check valves 17, the same number as the passage portions 11e, or in other words, the same number as the cylinder bore 12b. The discharge-side check valves 17 open and close the gap between the cylinder bore 12b and the discharge port 11d. More specifically, the discharge-side check valves 17 allow the flow of working fluid from the cylinder bore 12b to the discharge port 11d and prevent flow in the reverse direction. Furthermore, the discharge-side check valves 17 allow the flow of working fluid from the cylinder bore 12b to the discharge port 11d when the fluid pressure in the cylinder bore 12b exceeds a predetermined set pressure. That is, during the suction process, the flow of working fluid from the cylinder bore 12b to the discharge port 11d is stopped. On the other hand, in the discharge process, the working fluid is flowed from the cylinder bore 12b to the discharge port 11d.

[0039] <Linear Actuator> The linear actuator 18 moves the swash plate portion 32 forward and backward relative to the shaft portion 31. The linear actuator 18 is connected to the swash plate portion 32 via a thrust bearing 35. More specifically, the linear actuator 18 has a movable portion 18a that moves in the axial direction. The base portion 32a of the swash plate portion 32 is provided on the movable portion 18a via the thrust bearing 35. Therefore, the thrust bearing 35 suppresses the transmission of the rotation of the swash plate portion 32 to the movable portion 18a. Note that the linear actuator 18 is not limited to an electrically driven actuator, but may also be a hydraulically driven actuator such as a hydraulic cylinder. Furthermore, the bearing connecting the linear actuator 18 and the swash plate portion 32 may also be an angular contact ball bearing or a tapered roller bearing, as long as it can suppress the transmission of the rotational force of the swash plate portion 32 to the linear actuator 18.

[0040] <Operation of a hydraulic pump> In the hydraulic pump 1, when the rotating swash plate 13 is driven by the drive source, it operates as follows: When the rotating swash plate 13 is driven, each piston 14 reciprocates in the cylinder bore 12b accordingly. As a result, in the suction phase, each piston 14 draws working fluid from the suction port 11c through the suction passage 11a and into the cylinder bore 12b via the suction-side check valve 16. On the other hand, in the discharge phase, each piston 14 discharges working fluid from the cylinder bore 12b to the discharge port 11d via the discharge-side check valve 17.

[0041] In addition, in the hydraulic pump 1, the swash plate rotation shaft 27 rotates in conjunction with the rotation of the rotating swash plate 13. As a result, each of the spools 25 reciprocates in sync with the corresponding piston 14 in the spool hole 12c. Consequently, the communication passage 12d is opened during the suction stroke of each piston 14, and the communication passage 12d is closed during the discharge stroke of each piston 14 (see the dotted-dash lines on the pistons 14 in Figure 2) (see the dotted-dash lines on the spools 25 in Figure 2). As a result, communication exists between the cylinder bore 12b and the communication passage 12d until the communication passage 12d is closed during the discharge stroke (i.e., until the piston 14 moves the open stroke length S2). As a result, the discharge of working fluid from the cylinder bore 12b to the discharge port 11d is restricted until the communication passage 12d is closed. Therefore, the effective stroke length S of each piston 14 is shorter than the actual stroke length S1 by the amount of the open stroke length S2, and the hydraulic pump 1 discharges working fluid with a discharge capacity corresponding to the effective stroke length S.

[0042] In the hydraulic pump 1, the swash plate 32 is moved axially by the linear actuator 18. This changes the effective stroke length S. That is, when the linear actuator 18 moves the swash plate 32 forward and backward (see the dashed and solid lines in Figure 3), the contact position between each spool 25 and the swash plate 32 shifts axially to one side or the other. This changes the opening and closing position of each spool 25, and changes the open stroke length S2 of each piston 14. This allows the effective stroke length S of each piston 14 to be changed. Therefore, the discharge capacity of the hydraulic pump 1 increases or decreases. Note that when the swash plate 32 is moved to its furthest position as shown in Figure 3, the open stroke length S2 of each piston 14 becomes 0. Therefore, the discharge capacity of the hydraulic pump 1 is maximized.

[0043] In the hydraulic pump 1 of this embodiment, the shaft portion 31 is pivotally supported in the cylinder block 12 at a position separated in the axial direction. Therefore, the shaft portion 31 can rotate in a stable state. That is, the swash plate portion 32, which is non-rotatably mounted on the shaft portion 31, can also rotate in a stable state. Since the swash plate portion 32 moves back and forth in the axial direction while rotating in a stable state, the effective stroke length S can be adjusted stably. Therefore, the discharge capacity can be adjusted with high precision.

[0044] In the hydraulic pump 1 of this embodiment, the shaft portion 31 is detachably connected to the rotating swash plate 13 and is not capable of relative rotation. Therefore, it is easy to link the swash plate rotation shaft 27 to the rotation of the rotating swash plate 13. In addition, since the shaft portion 31 is detachable from the rotating swash plate 13, the assembly and disassembly of the hydraulic pump 1 are easy.

[0045] In the hydraulic pump 1 of this embodiment, the shaft portion 31 is spline-coupled or key-coupled to the rotating swash plate 13. Therefore, it is easy to attach and detach the shaft portion 31 to the rotating swash plate 13.

[0046] In the hydraulic pump 1 of this embodiment, the contact portion 32b can rotate relative to the base portion 32a. This suppresses the transmission of rotational force from the base portion 32a to the contact portion 32b. Therefore, when the spool 25 reciprocates, the rotation of the contact portion 32b relative to the spool 25 can be suppressed. As a result, the sliding of the spool 25 on the contact portion 32b can be suppressed, and thus wear of the contact portion 32b can be suppressed.

[0047] In the hydraulic pump 1 of this embodiment, the swash plate 32 is connected to the linear actuator 18 via a thrust bearing 35. Therefore, the transmission of the rotation of the swash plate 32 to the linear actuator 18 can be suppressed. As a result, the rotating swash plate 32 can be moved forward and backward by the linear actuator 18.

[0048] In the hydraulic pump 1 of this embodiment, the rotating swash plate 13 is supported at two points, the shaft portion 13a and the swash plate portion 13b, allowing the rotating swash plate 13 to rotate in a stable state. This suppresses wobble of the rotating swash plate 13. Therefore, the accuracy of the discharge volume can be improved.

[0049] <Other Embodiments> In the hydraulic pump 1 of this embodiment, the spool 25 of the variable displacement mechanism 15 may be composed of a valve body. In the case of a valve body, for example, the communication passage 12d is opened and closed by the valve body. Although all spools 25 are formed to be the same shape, the spools 25 may have different shapes. For example, the length of the round portion of the spool 25 may be different. The number of pistons 14 and spools 25 may be 8 or less, or 10 or more. Also, some of the spools 25 may be fully closed spools that do not open the communication passage 12d. For example, 3 or 9 of the 9 spools 25 may be fully closed spools. Furthermore, the number of spools 25 does not need to be the same as the number of pistons 14, and may be less than the number of pistons 14. In this case, it is preferable that the number of spool holes 12c is also the same as the number of spools 25.

[0050] In the hydraulic pump 1 of this embodiment, the effective stroke length S of all pistons 14 is adjusted, but it is sufficient if the effective stroke length S of at least one piston 14 is adjusted. Furthermore, in the hydraulic pump 1 of this embodiment, the communication passage 12d is connected to the tank 19 via the suction passage 11a, but it may also be directly connected to the tank 19, or it may be connected to the tank 19 via another passage or the like.

[0051] In the hydraulic pump 1 of this embodiment, the contact portion 32b is provided so as to be rotatable relative to the base portion 32a, but the contact portion 32b may be provided so as not to be rotatable relative to the base portion 32a. That is, the contact portion 32b may be fixed to the base portion 32a or integrally formed with it. Also, the contact portion 32b may be the outer ring portion of the fifth bearing 32d. Furthermore, the swash plate portion 32 may not contact the spool 25, but instead hook onto the spool 25 and cause it to reciprocate. [Explanation of symbols]

[0052] 1. Hydraulic pump (rotary swashplate type hydraulic pump) 11 Casing 12 Cylinder Block 12a One end face 12b Cylinder bore 13. Rotating swashplate 13a Shaft part 13b Swash plate part 13c First bearing 13d Second bearing 14 pistons 15 Variable Capacitance Mechanism 18 Linear Actuator 19 tanks 25 spools 27 Swashplate rotation axis 31 Shaft 32 Swash plate section 32a Base part 32b Contact part 32c Inclined surface on the rotation axis side of the swashplate 35 Thrust bearing S Effective stroke length

Claims

1. Casing and, A cylinder block having multiple cylinder bores formed within the casing, which are arranged so as not to rotate relative to each other and have openings at one end face, A rotating swash plate is rotatably housed within the casing so as to face one end face of the cylinder block, A plurality of pistons are inserted into each of the cylinder bores and reciprocate within the cylinder bores by the rotation of the rotating swash plate, The system includes a variable displacement mechanism that changes the effective stroke length of at least one of the plurality of pistons, The variable displacement mechanism includes a shaft portion inserted through the cylinder block and interlocked with the rotating swash plate, and a swash plate portion provided on the shaft portion so as to be able to move back and forth in the axial direction and not be able to rotate relative to it. The shaft portion is supported at an axially separated position in the cylinder block, and is a rotary swashplate type hydraulic pump.

2. The rotary swash plate type hydraulic pump according to claim 1, wherein the shaft portion is detachably and non-rotatably connected to the rotary swash plate.

3. The rotary swash plate type hydraulic pump according to claim 2, wherein the shaft portion is spline-coupled or key-coupled to the rotary swash plate.

4. The variable capacity mechanism includes a plurality of spools arranged in correspondence with each of the cylinder bores and which reciprocate to open and close the corresponding cylinder bore and tank, The swash plate portion has a base portion that is movable in the axial direction and not rotatable relative to the shaft portion, and a contact portion that is provided on the base portion and contacts the plurality of spools. The rotary swash plate type hydraulic pump according to any one of claims 1 to 3, wherein the contact portion has a swash plate rotation axis side inclined surface that is inclined with respect to the rotation axis of the shaft portion and into contact with the plurality of spools, and is provided so as to be rotatable relative to the base portion.

5. The system further comprises a linear actuator that moves the swash plate portion forward and backward relative to the shaft portion, The rotary swash plate type hydraulic pump according to any one of claims 1 to 4, wherein the linear actuator is connected to the swash plate portion via a thrust bearing.

6. The rotating swash plate includes a shaft portion and a swash plate portion that faces one end face of the cylinder block and rotates to cause the plurality of pistons to reciprocate. The aforementioned shaft portion is rotatably supported by the casing via a first bearing that is externally mounted on the shaft portion. The rotary swash plate hydraulic pump according to any one of claims 1 to 5, wherein the swash plate portion is rotatably supported in the casing via a second bearing externally mounted on the swash plate portion.

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