Rotary swashplate type hydraulic pump

Abstract

To provide a rotary swash plate-type hydraulic pump capable of suppressing variation in pressure loss generated in a hydraulic fluid, for each cylinder bore.SOLUTION: A rotary swash plate-type hydraulic pump includes: a casing provided with a suction passage; a cylinder block disposed in the casing in a manner of being not relatively rotatable and provided with a plurality of cylinder bores connected to the suction passage; a plurality of pistons each inserted to each of the plurality of cylinder bores; and a rotary swash plate housed in the casing rotatably around an axis and reciprocating each of the pistons. The suction passage has a plurality of suction ports to which a hydraulic fluid is sucked.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, a plurality of cylinder bores and a plurality of suction chambers are formed in a cylinder block. Each cylinder bore is connected to a discharge port via each suction chamber. The path of the working fluid guided from the discharge port to each suction chamber is different for each suction chamber. Therefore, the pressure loss generated in the working fluid is different for each cylinder bore. As a result, there is a variation in the suction pressure for each cylinder bore.

[0005] Therefore, an object of the present invention is to provide a swash plate type hydraulic pump that can suppress variations in pressure loss generated in the working fluid for each cylinder bore.

Means for Solving the Problems

[0006] The rotary swashplate hydraulic pump of the present invention comprises a casing in which an intake passage is formed; a cylinder block arranged within the casing so as not to rotate relative to it and having a plurality of cylinder bores connected to the intake passage; a plurality of pistons inserted into each of the plurality of cylinder bores; and a rotary swashplate housed within the casing so as to be rotatable about an axis and causing each of the pistons to reciprocate, wherein the intake passage has a plurality of intake ports into which working fluid is drawn.

[0007] According to the present invention, the intake passage has multiple intake ports through which the working fluid is drawn in. Therefore, the difference between cylinder bores in the path of the working fluid from the intake port to each cylinder bore can be reduced. This suppresses variations in pressure loss in the working fluid across cylinder bores. As a result, the intake pressure required to draw in the working fluid can be ensured in multiple cylinder bores. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress variations in pressure loss between cylinder bores with respect to the working fluid of a rotary swashplate type hydraulic pump. [Brief explanation of the drawing]

[0009] [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] Figure 1 shows a cross-sectional view of a rotary swashplate type hydraulic pump cut along the cutting line II-II. [Figure 3] Figure 1 is a right-hand side view of the rotary swashplate hydraulic pump as seen from the other side in the axial direction. [Figure 4] Figure 1 shows a cross-sectional view of a rotary swashplate type hydraulic pump cut along the cutting line IV-IV. [Figure 5] Figure 1 shows a cross-sectional view of a rotary swashplate type hydraulic pump cut along the cutting line VV. [Figure 6] Figure 1 shows a cross-sectional view of a rotary swashplate type hydraulic pump cut along the cutting line VI-VI. [Figure 7] Figure 1 shows a cross-sectional view of a rotary swashplate hydraulic pump cut along the cutting line VII-VII. [Modes for carrying out the invention]

[0010] 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 rotary swashplate type 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.

[0011] <Rotating swashplate type hydraulic pump> The rotary swashplate hydraulic pump (hereinafter referred to as "pump") 1 shown in Figures 1 and 2 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, pump 1 is a rotary swashplate type variable displacement hydraulic pump. Pump 1 comprises a casing 11, a cylinder block 12, a rotary swashplate 13, and a plurality of pistons 14. Pump 1 also comprises a variable displacement mechanism 15, a plurality of suction check valves 16, and a plurality of discharge check valves 17. Pump 1 is driven by a drive source (e.g., an engine, an electric motor, or both). As a result, pump 1 discharges working fluid.

[0012] <Casing> The casing 11 houses the cylinder block 12, the rotating swash plate 13, the piston 14, and the variable displacement mechanism 15. The casing 11 has an intake passage 19 and a discharge passage 20. The casing 11 is a cylindrical member that extends along a predetermined axis L1. More specifically, as shown in Figure 3, the casing 11 has a prismatic shape with its sides made up of multiple planes 11a. Therefore, the casing 11 is polygonal when viewed from the other side in the axial direction. In this embodiment, the casing 11 has a prismatic shape made up of the same number of planes 11a as the cylinder bore 12a described later, i.e., nine planes 11a. In other words, the casing 11 is 9-sided when viewed from the other side in the axial direction. Each of the planes 11a is flat and rectangular in shape. More specifically, the outer shape of the casing 11 is 9-sided from the middle portion in the axial direction to the other side portion. On the other hand, in the portion on one side in the axial direction to which the axis L1 extends, the outer shape of the casing 11 is circular. The casing 11 is open at one end on the axial direction to which the axis L1 extends and at the other end on the other side.

[0013] The intake passage 19 has multiple intake ports 19a. The intake passage 19 also has an intake-side annular portion 19b, a communication chamber 19c, and multiple communication portions 19d. The intake passage 19 is formed in the other end portion of the casing 11. More specifically, the intake passage 19 is formed axially to the other of the cylinder block 12 housed in the casing 11. The intake passage 19 is connected to multiple cylinder bores 12a of the cylinder block 12, which will be described in detail later. As shown in Figure 4, the intake passage 19 is formed in an annular shape when viewed axially. As shown in Figure 5, the intake passage 19 is arranged to overlap each of the cylinder bores 12a when viewed axially. The intake passage 19 is connected to the tank 30 and also to the cylinder bores 12a. Working fluid is drawn in from the tank 30 through the intake passage 19.

[0014] Each of the intake ports 19a is connected to the tank 30 (see Figure 1). In this embodiment, two intake ports 19a are formed in the casing 11 as shown in Figure 4. Note that the number of intake ports 19a formed in the casing 11 is not limited to two, but may be one or three or more. The intake ports 19a are formed on the outer circumferential surface of the casing 11, on the other end in the axial direction. The intake ports 19a are arranged at equal intervals in the circumferential direction when viewed in the axial direction. In this embodiment, the two intake ports 19a are arranged at a 180-degree interval.

[0015] The intake-side annular portion 19b is formed in an annular shape (circular in this embodiment) around the axis L1. Here, the intake-side annular portion 19b is formed in an annular shape centered on the axis L1. The outer and inner diameters of the intake-side annular portion 19b decrease radially inward as one side moves along the axial direction (see also Figure 1). The other end face 12h of the cylinder block 12 faces the intake-side annular portion 19b. As shown in Figure 5, the intake-side annular portion 19b overlaps with a plurality of cylinder bores 12a when viewed in the axial direction and is connected to the plurality of cylinder bores 12a. The intake-side annular portion 19b is connected to each of the intake ports 19a at its outer circumference. More specifically, the intake ports 19a are connected at circumferentially spaced positions on the outer surface of the intake-side annular portion 19b. In this embodiment, each of the intake ports 19a is connected to the outer circumferential surface of the intake-side annular portion 19b at positions spaced 180 degrees apart in the circumferential direction.

[0016] More specifically, each of the intake ports 19a is connected to the outer circumferential portion of the intake-side annular portion 19b via each of the passage portions 19e. The passage portions 19e are arranged at circumferential intervals on the outer circumferential surface of the intake-side annular portion 19b. In this embodiment, the passage portions 19e are formed on the outer circumferential surface of the intake-side annular portion 19b at 180-degree intervals in the circumferential direction.

[0017] The communication chamber 19c is arranged inside the suction-side annular portion 19b. The communication chamber 19c is also formed in an annular shape around the axis L1. The communication chamber 19c communicates with the suction-side annular portion 19b through a plurality of communication portions 19d.

[0018] As shown in FIGS. 6 and 7, the discharge passage 20 has a discharge port 20a. The discharge passage 20 also has a plurality of discharge-side branch portions 20b and a discharge-side annular portion 20c. The discharge passage 20 is formed in an intermediate portion in the casing 11. The discharge passage 20 is formed in an annular shape as shown in FIGS. 6 and 7. More specifically, the discharge passage 20 is formed in an annular shape in the casing 11 and surrounds each of the cylinder bores 12a from the outside. The discharge passage 20 is connected to the cylinder bore 12a. The discharge passage 20 is connected to, for example, a hydraulic actuator (not shown). The pump 1 discharges the working fluid led from the cylinder bore 12a from the discharge passage 20.

[0019] The discharge port 20a is formed on the outer peripheral surface of the casing 11. The discharge port 20a is arranged at a different phase from the plurality of suction ports 19a in the circumferential direction. More specifically, the discharge port 20a is arranged with a 90-degree shift with respect to each of the suction ports 19a in the circumferential direction. That is, in the circumferential direction centered on the axis L1, the positions of the discharge port 20a and the suction port 19a are different. The discharge port 20a is formed at an intermediate portion in the axial direction on the outer peripheral surface of the casing 11 (see FIG. 1). The pump 1 discharges the working fluid from the discharge port 20a.

[0020] As shown in FIG. 6, each of the discharge-side branch portions 20b extends radially outward from the corresponding cylinder bore 12a. The discharge-side branch portion 20b extends in the radial direction, further bends, and extends in one axial direction.

[0021] The discharge-side annular section 20c is positioned to surround the cylinder block 12, more specifically, the multiple cylinder bores 12a from the outside. The discharge-side annular section 20c is connected to multiple discharge-side branch sections 20b. Therefore, the working fluid is guided to the discharge-side annular section 20c from the cylinder bores 12a via the discharge-side branch sections 20b. The discharge-side annular section 20c is connected to the discharge port 20a. The working fluid guided to the discharge-side annular section 20c is discharged from the discharge port 20a.

[0022] As shown in Figures 1 and 2, the casing 11 includes a casing body 21, a first cover 22, and a second cover 23. The casing 11 is formed by combining the casing body 21, the first cover 22, and the second cover 23. The casing body 21 houses the cylinder block 12 in a manner that prevents relative rotation. The casing body 21 is a cylindrical member extending along a predetermined axis L1. More specifically, the casing body 21 has a prismatic shape with its side surface consisting of nine planes 11a. That is, the casing body 21 is a 9-sided polygon when viewed from the other side in the axial direction. An intake passage 19 is formed at the other end of the casing body 21. A discharge passage 20 is formed in the axial middle portion of the casing body 21. A flange 21a is formed on the outer circumferential surface of one end of the casing body 21 on one side in the axial direction.

[0023] The first cover 22 houses the swash plate 13, which will be described in detail later. More specifically, the first cover 22 houses the swash plate 13 in the portion on the other side in the axial direction. The first cover 22 is placed over the casing body 21 so that the swash plate 13 faces the cylinder block 12. The first cover 22 is formed in a cylindrical shape. The first cover 22 is placed over the opening on one side in the axial direction of the casing body 21. This allows the swash plate 13 to face the cylinder block 12. A flange 22a is formed on the outer circumferential surface of the other end of the first cover 22 on the other side in the axial direction. The first cover 22 is placed over the casing body 21 so that the flange 22a abuts against the flange 21a of the casing body 21. The first cover 22 is fixed to the casing body 21 by fastening the flanges 21a and 22a together.

[0024] The second cover 23 is provided at the other axial end of the casing body 21 so as to block the intake passage 19. The second cover 23 is formed in an annular shape. The second cover 23 is provided at the other axial end of the casing body 21. More specifically, the second cover 23 is fitted into the opening on the other axial side of the casing body 21. A linear actuator 18, which will be described later, is attached to the second cover 23 so as to block the inner hole 23a. Therefore, the intake passage 19 is blocked by providing the second cover 23 at the other axial end of the casing body 21.

[0025] <Cylinder Block> The cylinder block 12 includes a plurality of cylinder bores 12a, as shown in Figure 5. Furthermore, the cylinder block 12 includes a plurality of spool holes 12b, a plurality of communication passages 12c, and a shaft insertion hole 12d, as shown in Figure 1. The cylinder block 12 is positioned within the casing 11 so as to be non-rotatable relative to it. More specifically, the cylinder block 12 is positioned within the casing body 21 so as to be non-rotatable relative to it. The cylinder block 12 is fixed to the axially intermediate portion within the casing 11. In this embodiment, the cylinder block 12 is integrally formed with the casing 11 (more specifically, the casing body 21). However, the cylinder block 12 may be a separate component from the casing 11. If it is a separate component, the cylinder block 12 is fixed to the casing 11 by, for example, press-fitting, spline coupling, key coupling, fastening, or joining. A cylinder bore 12a is formed on one end face 12g of the cylinder block 12. The other end face 12h of the cylinder block 12 faces the intake passage 19. One end face 12g is the end face on one side of the cylinder block 12 in the axial direction, and the other end face 12h is the end face on the other side of the cylinder block 12 in the axial direction.

[0026] <Cylinder bore> Each of the cylinder bores 12a is connected to an intake passage 19. In this embodiment, the cylinder block 12 includes nine cylinder bores 12a, however, the number of cylinder bores 12a is not limited to nine. The cylinder bores 12a are arranged circumferentially at intervals (equally spaced in this embodiment) around the axis L1. The cylinder bores 12a extend from one end face 12g to the other axially. The cylinder bores 12a penetrate the cylinder block 12 to the other end face 12h. Thus, the cylinder bores 12a are connected to the intake passage 19 on the other axial side.

[0027] <Spool hole> Each of the spool holes 12b is formed in the cylinder block 12. More specifically, the cylinder block 12 has the same number of spool holes 12b as the cylinder bore 12a (nine in this embodiment). The spool holes 12b are connected to the intake passage 19. More specifically, the spool holes 12b are connected to the tank 30 via the intake passage 19. The spool holes 12b are also spaced circumferentially around the axis L1 (equally spaced in this embodiment). More specifically, the spool holes 12b extend in one axial direction from the other end face 12h of the cylinder block 12. On the other end face 12h, the spool holes 12b are spaced equally around the shaft insertion hole 12d, which will be described in detail later. The spool holes 12b are located inside the cylinder bore 12a (radially inward in this embodiment).

[0028] <Communication passages and shaft insertion holes> As shown in Figures 1 and 2, each of the connecting passages 12c connects the corresponding cylinder bore 12a and spool hole 12b. That is, the cylinder block 12 has the same number of connecting passages 12c as the cylinder bore 12a and spool hole 12b (9 in this embodiment). Each of the connecting passages 12c is located on the other end face 12h side of the cylinder block 12.

[0029] <Shaft insertion hole> The shaft insertion hole 12d is formed in the cylinder block 12 along the axis L1. More specifically, the shaft insertion hole 12d penetrates the cylinder block 12 axially from one end face 12g to the other end face 12h.

[0030] <Rotating swashplate> As shown in Figures 1 and 2, the swash plate 13 includes a swash plate-side inclined surface 13a. The swash plate 13 is housed within the casing 11 so as to be rotatable around axis L1. More specifically, the swash plate 13 is housed within the casing 11 on one side in the axial direction. In this embodiment, the swash plate 13 is housed within the first cover 22. The swash plate 13 extends along axis L1. The swash plate 13 is supported by the casing 11 so as to be rotatable about axis L1. The swash plate 13 is positioned to face one end face 12g of the cylinder block 12. One end portion of the swash plate 13 protrudes from one end of the casing 11. One end portion of the swash plate 13 is connected to the aforementioned drive source on the axial side. The swash plate 13 is rotationally driven by the drive source. The rotation of the swash plate 13 causes the piston 14, which will be described in detail later, to reciprocate. In this embodiment, the rotating swash plate 13 is integrally formed with a disc portion having a rotating swash plate-side inclined surface 13a and a rotatably supported shaft portion; however, the disc portion and the shaft portion may be formed separately.

[0031] The swash plate-side inclined surface 13a is formed on the other end side of the swash plate 13. The swash plate-side inclined surface 13a faces one end face 12g of the cylinder block 12. The swash plate-side inclined surface 13a is tilted toward one end face 12g of the cylinder block 12 around a first orthogonal axis L2. The first orthogonal axis L2 is an axis perpendicular to axis L1. In this embodiment, the tilt angle of the swash plate-side inclined surface 13a is fixed. For the sake of explanation, the inclination of the swash plate-side inclined surface 13a shown in Figure 2 is shown differently from the inclination of the swash plate-side inclined surface 13a shown in Figure 1.

[0032] <Piston> Multiple pistons 14 are inserted into each of the cylinder bores 12a of the cylinder block 12. That is, the cylinder block 12 has the same number of pistons (9 pistons in this embodiment) 14 as the cylinder bore 12a. Each of the pistons 14 reciprocates within the cylinder bore 12a as the rotating swash plate 13 rotates. More specifically, the pistons 14 are in contact with the rotating swash plate side inclined surface 13a. The rotating swash plate side inclined surface 13a slides relative to the pistons 14. As the rotating swash plate 13 rotates, each of the pistons 14 reciprocates within the cylinder bore 12a with a stroke amount corresponding to the tilt angle. In this embodiment, the pistons 14 are in contact with the rotating swash plate side inclined surface 13a of the rotating swash plate 13 via shoes 24. Each of the shoes 24 is pressed against the rotating swash plate side inclined surface 13a by a retaining plate 25. As a result, when the rotating swash plate 13 rotates, the piston 14 is made to reciprocate in one axial direction and the other via the shoe 24.

[0033] <Variable Capacitance Mechanism> As shown in Figures 1 and 2, the variable displacement mechanism 15 includes a plurality of spools 26, a plurality of springs 27, and a swash plate rotation shaft 28. In this embodiment, the variable displacement mechanism 15 includes the same number of spools 26 and springs 27 as the spool holes 12b, i.e., nine spools 26 and springs 27. The variable displacement mechanism 15 adjusts the effective stroke length S of the piston 14. In this embodiment, the variable displacement mechanism 15 changes the effective stroke length S of the piston 14 by adjusting the opening and closing of the cylinder bore 12a. By changing the effective stroke length S of the piston 14, the variable displacement mechanism 15 changes the discharge capacity of the pump 1.

[0034] More specifically, the variable displacement mechanism 15 adjusts the opening and closing of the cylinder bore 12a as the piston 14 strokes from bottom dead center to top dead center (i.e., during the discharge stroke). The top dead center is the point where the piston 14 is furthest to the other axial direction, and the bottom dead center is the point where the piston 14 is furthest to the one axial direction. By adjusting the opening and closing of the cylinder bore 12a, the variable displacement mechanism 15 adjusts the effective stroke length S of each piston 14. However, the variable displacement mechanism 15 is not limited to adjusting the effective stroke length S of all pistons 14. The variable displacement mechanism 15 is located radially inward of the nine cylinder bores 12a in the cylinder block 12.

[0035] <Spool> Each of the spools 26 is positioned corresponding to each of the cylinder bores 12a. The spools 26 are reciprocally inserted into the spool holes 12b of the cylinder block 12. Thus, the spools 26 are positioned radially inward of the cylinder bores 12a. The spools 26 open and close the corresponding cylinder bores 12a. More specifically, the spools 26 open and close the connection between the corresponding cylinder bores 12a and the tank 30 by reciprocating motion. In this embodiment, the spools 26 connect the corresponding cylinder bores 12a and the intake passage 19 by opening. This connects the cylinder bores 12a to the tank 30 via the intake passage 19. The spools 26 adjust the effective stroke length S of each piston 14 by adjusting the opening and closing of the connection between the cylinder bores 12a and the tank 30 during the discharge process.

[0036] <spring> Each of the springs 27 is inserted in a compressed state into each of the spool holes 12b. More specifically, the springs 27 are positioned in the spool holes 12b on one side in the axial direction relative to the spool 26. The springs 27 bias the spool 26 toward the swash plate rotation axis 28, which will be described later.

[0037] <Rotating swashplate axis> The swash plate rotation shaft 28 has a swash plate rotation shaft side inclined surface 28a. The swash plate rotation shaft 28 rotates in conjunction with the rotating swash plate 13. By rotating, the swash plate rotation shaft 28 causes each of the spools 26 to reciprocate. This causes the swash plate rotation shaft 28 to open and close the gap between the cylinder bore 12a and the tank 30. More specifically, the swash plate rotation shaft 28 opens and closes the communication passage 12c by causing the spools 26 to reciprocate. The swash plate rotation shaft 28 can change the open and closed positions of each of the spools 26. The open and closed positions of each of the spools 26 are the position where each of the spools 26 begins to open the communication passage 12c and the position where it closes.

[0038] More specifically, the swash plate rotation shaft 28 is inserted through the shaft insertion hole 12d of the cylinder block 12 and extends along the axis L1. One axial end of the swash plate rotation shaft 28 protrudes from the shaft insertion hole 12d toward the rotating swash plate 13. This axial end of the swash plate rotation shaft 28 is connected to the rotating swash plate 13 in a manner that prevents relative rotation. Therefore, the swash plate rotation shaft 28 rotates around the axis L1 in conjunction with the rotating swash plate 13. The other axial end of the swash plate rotation shaft 28 also protrudes from the shaft insertion hole 12d toward the intake passage 19.

[0039] The swash plate rotation axis side inclined surface 28a is located in the axial middle portion of the swash plate rotation axis 28. The swash plate rotation axis side inclined surface 28a faces the other end face 12h of the cylinder block 12. More specifically, the swash plate rotation axis side inclined surface 28a faces the other axial opening of each spool hole 12b. The swash plate rotation axis side inclined surface 28a is tilted about a second orthogonal axis L3 which is parallel to the first orthogonal axis L2. The second orthogonal axis L3 is also an axis perpendicular to axis L1. In this embodiment, the swash plate rotation axis side inclined surface 28a is tilted in the same direction as the rotation swash plate side inclined surface 13a. The tilt angle of the swash plate rotation axis side inclined surface 28a is fixed. The other axial end of the spool 26, which is biased by the spring 27, abuts against the swash plate rotation axis side inclined surface 28a. The inclined surface 28a on the swash plate rotation axis side slides and rotates relative to the spool 26. Therefore, when the swash plate rotation axis 28 rotates, the spool 26 reciprocates in the spool hole 12b with a stroke corresponding to the tilt angle of the inclined surface 28a on the swash plate rotation axis side.

[0040] The swash plate rotation axis side inclined surface 28a can move forward and backward in the axial direction. By moving forward and backward, the swash plate rotation axis side inclined surface 28a adjusts the opening and closing of the space between the cylinder bore 12a and the tank 30. More specifically, by moving forward and backward, the swash plate rotation axis side inclined surface 28a adjusts the opening and closing position of the spool 26. A linear actuator 18 is connected to the other end of the swash plate rotation axis 28 in the axial direction. The linear actuator 18 may be either an electric or hydraulic linear actuator. As described above, the linear actuator 18 is attached to the second cover 23. More specifically, the linear actuator 18 is attached to the second cover 23 from the outside of the casing 11 so as to close the inner hole 23a of the second cover 23. The linear actuator 18 moves the swash plate rotation axis side inclined surface 28a forward and backward so as to approach and move away from the other end face 12h of the cylinder block 12. This adjusts the opening and closing of the space between the cylinder bore 12a. More specifically, the dead center position of the spool 26 in the cylinder bore 12a (more precisely, the axial position of the dead center) can be changed. For example, when the swash plate rotation axis side inclined surface 28a advances in one axial direction, the dead center position of the spool 26 in the cylinder bore 12a shifts to one side in the axial direction. Conversely, when the swash plate rotation axis side inclined surface 28a retracts in the other axial direction, the dead center position of the spool 26 in the cylinder bore 12a shifts to the other side in the axial direction. Therefore, the opening and closing position of the spool 26 in the cylinder bore 12a can be shifted in the axial direction.

[0041] The effective stroke length S of the piston 14 is the range of stroke from which the working fluid can be discharged from the cylinder bore 12a. Therefore, the effective stroke length S of the piston 14 can be changed by shifting the opening and closing position of the spool 26 in the axial direction. Consequently, the discharge capacity in the cylinder bore 12a can be changed by moving the swash plate rotation axis side inclined surface 28a in the axial direction.

[0042] <Intake check valve> Each of the intake check valves 16 allows a unidirectional flow of working fluid from the intake passage 19 to the cylinder bore 12a and prevents flow in the reverse direction. Each intake check valve 16 is provided in each of the cylinder bores 12a. In this embodiment, there are nine intake check valves 16, the same number as the cylinder bore 12a. As shown in Figure 5, the intake check valves 16 are inserted into the cylinder bore 12a from one side in the axial direction. The other end portion of the intake check valve 16 protrudes from the cylinder bore 12a into the intake passage 19 (more specifically, the intake-side annular portion 19b). As shown in Figure 1, the intake check valves 16 open and close the cylinder bore 12a. More specifically, the intake check valve 16 has a check valve body 16a and an inner passage 16b. The inner passage 16b connects the intake-side annular portion 19b and the cylinder bore 12a. The check valve body 16a opens and closes the space between the intake-side annular portion 19b and the cylinder bore 12a by opening and closing the internal passage 16b. This allows a unidirectional flow of working fluid from the intake passage 19 to the cylinder bore 12a, while preventing reverse flow. More specifically, each of the multiple intake check valves 16 allows working fluid to flow from the intake passage 19 to the cylinder bore 12a during the intake process when the piston 14 moves from top dead center to bottom dead center. On the other hand, during the discharge process when the piston 14 is discharged, the intake check valve 16 stops the flow of working fluid from the intake passage 19 to the cylinder bore 12a. The internal passage 16b opens to the communication portion 19d. Therefore, the intake-side annular portion 19b is always connected to the spool hole 12b.

[0043] <Discharge check valve> Each of the multiple discharge check valves 17 shown in Figure 1 allows a unidirectional flow of working fluid from the cylinder bore 12a to the discharge port 20a and prevents reverse flow. Each of the multiple discharge check valves 17 is provided for each of the cylinder bore 12a, as shown in Figure 6. Therefore, in this embodiment, there are nine discharge check valves 17, the same number as the discharge-side branch sections 20b. Each of the discharge check valves 17 is provided for each of the discharge-side branch sections 20b of the discharge passage 20. More specifically, the discharge check valves 17 are inserted into the portion of the discharge-side branch section 20b that extends radially from the outer circumferential surface of the casing 11.

[0044] More specifically, each of the planes 11a on the outer circumferential surface of the casing 11 has an insertion hole 11b formed therein. The insertion holes 11b extend toward the radially extending portion of the discharge-side branch 20b. In this embodiment, the insertion holes 11b are formed coaxially with the radially extending portion of the discharge-side branch 20b. Each of the discharge check valves 17 is inserted through the insertion hole 11b into the radially extending portion of each discharge-side branch 20b.

[0045] Each of the discharge check valves 17 opens and closes the discharge passage 20. More specifically, the discharge check valve 17 opens and closes the discharge-side branch portion 20b (more precisely, the radially extending portion) by the check valve body 17a. The check valve body 17a opens the discharge passage 20 during the discharge process. Therefore, the discharge check valve 17 allows a unidirectional flow of working fluid from the cylinder bore 12a to the discharge-side annular portion 20c (or discharge port 20a) during the discharge process. On the other hand, the nine discharge check valves 17 block the flow in the reverse direction. Therefore, during the suction process, the flow of working fluid from the cylinder bore 12a to the discharge port 20a is stopped.

[0046] <Pump operation> The operation of pump 1 is now described. When the rotating swash plate 13 is driven by the drive source, each piston 14 reciprocates in the cylinder bore 12a accordingly. As a result, each piston 14 draws working fluid into the cylinder bore 12a from the intake passage 19 via the intake check valve 16 during the intake process. On the other hand, during the discharge process, each piston 14 discharges working fluid from the cylinder bore 12a via the discharge check valve 17 and the discharge passage 20. More specifically, during the discharge process, when the working fluid in the cylinder bore 12a is pressurized by the piston 14, the discharge check valve 17 eventually opens the discharge passage 20. As a result, the working fluid is guided from the cylinder bore 12a to the discharge annular section 20c via the discharge branch section 20b. Furthermore, the working fluid is discharged from the discharge port 20a.

[0047] Furthermore, in pump 1, the swash plate rotation shaft 28 rotates in conjunction with the rotation of the rotating swash plate 13, causing each of the spools 26 to reciprocate in sync with the corresponding piston 14 in the spool hole 12b. As a result, the communication passage 12c opens during the suction stroke of each piston 14, and closes during the discharge stroke of each piston 14. This allows communication between the cylinder bore 12a and the communication passage 12c until the communication passage 12c is closed during the discharge stroke (i.e., until the piston 14 moves the open stroke length S2). Until the communication passage 12c is closed, the discharge of working fluid from the cylinder bore 12a to the discharge port 20a is restricted. 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 pump 1 discharges working fluid with a discharge volume corresponding to the effective stroke length S. In pump 1, the inclined surface 28a on the swash plate rotation axis side is moved axially by the linear actuator 18, thereby changing the opening and closing position of the spool 26. This changes the effective stroke length S of each piston 14, so that the discharge capacity of pump 1 increases or decreases.

[0048] In the pump 1 of this embodiment, the intake passage 19 has multiple intake ports 19a. Therefore, the difference between each cylinder bore 12a in the path through which the working fluid flows from the intake port 19a to each cylinder bore 12a can be reduced. This suppresses variations in pressure loss in the working fluid across each cylinder bore 12a. As a result, the intake pressure required to draw in the working fluid can be secured in multiple cylinder bores 12a.

[0049] Furthermore, in the pump 1 of this embodiment, the intake-side annular portion 19b is formed in an annular shape. Therefore, the difference between each cylinder bore 12a in the path through which the working fluid flows from the intake port 19a to each cylinder bore 12a can be made smaller. This further reduces the variation between each cylinder bore 12a in terms of the pressure loss generated in the working fluid.

[0050] Furthermore, in the pump 1 of this embodiment, the multiple suction ports 19a and discharge ports 20a are formed on the outer circumferential surface of the casing 11 at different phases in the circumferential direction when viewed in the axial direction. Therefore, interference between piping (not shown) connected to each port 19a, 20a is suppressed. Thus, the degree of freedom in piping arrangement can be improved.

[0051] Furthermore, in the pump 1 of this embodiment, since multiple intake ports 19a and discharge ports 20a are formed on the outer circumferential surface of the casing 11, the cylinder bore 12a can be used more widely compared to when they are formed on the end face of the casing 11. Therefore, the variable displacement mechanism 15 can be positioned inside the multiple cylinder bores 12a in the cylinder block 12. This suppresses the increase in size of the pump 1.

[0052] Furthermore, in the pump 1 of this embodiment, each of the multiple discharge check valves 17 is inserted from the outer circumferential surface of the casing 11 toward the corresponding cylinder bore 12a. Therefore, each of the discharge check valves 17 is easily installed.

[0053] Furthermore, in the pump 1 of this embodiment, each of the multiple discharge check valves 17 is inserted from each of the multiple planes 11a of the casing 11 toward the corresponding cylinder bore 12a. Therefore, it is easy to form insertion holes 11b in the casing 11 for inserting the discharge check valves 17.

[0054] Furthermore, in the pump 1 of this embodiment, the first cover 22 is placed over the casing body 21 so that the rotating swash plate 13 faces the cylinder block 12. Therefore, since the rotating swash plate 13 and the cylinder block 12 can be housed and assembled in separate parts, it is easy to house the rotating swash plate 13 and the cylinder block 12 inside the casing.

[0055] Furthermore, in the pump 1 of this embodiment, the suction passage 19 is formed at the other axial end of the casing body 21, and the second cover 23 is provided at the other axial end of the casing body 21 so as to close the suction passage 19. Therefore, it is easy to form the suction passage 19.

[0056] <Other Embodiments> The pump 1 in this embodiment may be a fixed-displacement hydraulic pump. That is, the pump 1 does not necessarily have to be equipped with a variable displacement mechanism 15. The variable displacement mechanism 15 is also not limited to the configuration described above, and may be any mechanism that changes the effective stroke length S of the piston 14 by adjusting the opening and closing of the cylinder bore 12a. The two suction ports 19a do not necessarily have to be 180 degrees apart in the circumferential direction. The discharge port 20a does not need to be 90 degrees apart in the circumferential direction from the two suction ports 19a, and may be formed in the same phase as either of the two suction ports 19a. Furthermore, the two ports 19a and 20a do not necessarily have to be formed on the outer circumferential surface of the casing 11, and may be formed on one end face or the other end face in the axial direction of the casing 11.

[0057] In the pump 1 of this embodiment, multiple discharge check valves 17 are inserted from the outer circumferential surface of the casing 11 toward the cylinder bore 12a, but they may also be inserted from the first cover 22 or the second cover 23. The casing 11 is not limited to a prismatic shape, but may also be cylindrical. That is, the outer shape of the casing 11 may be round instead of polygonal. In this case, counterbores corresponding to the number of cylinder bores 12a are formed on the outer circumferential surface of the casing 11. The insertion holes 11b are formed from the counterbores toward the cylinder bore 12a (in this embodiment, the portion extending radially).

[0058] In the pump 1 of this embodiment, the casing 11 does not necessarily have to be configured to be divisible into a casing body 21, a first cover 22, and a second cover 23, and may be configured to be divisible into more than one component. The first cover 22 does not necessarily have to house the rotating swash plate 13, and the rotating swash plate 13 may be housed in the casing body 21. [Explanation of Symbols]

[0059] 1. Rotary swashplate hydraulic pump 11 Casing 11a plane 12 Cylinder Block 12a Cylinder bore 13. Rotating swashplate 14 pistons 15 Variable Capacitance Mechanism 17 Discharge check valve 19 Suction passage 19a Inhalation port 20 Discharge passage 20a Discharge port 21 Casing body 22 First Lid 23. Second Lid L1 axis

Claims

1. A casing in which an intake passage is formed, A cylinder block is provided, which is arranged within the casing in a manner that prevents relative rotation and has a plurality of cylinder bores formed therein that connect to the intake passage. Multiple pistons inserted into each of the aforementioned multiple cylinder bores, A rotating swash plate is housed within the casing so as to be rotatable around its axis and causes each of the pistons to reciprocate, The system includes a variable displacement mechanism that changes the effective stroke length of the piston by adjusting the opening and closing of the cylinder bore, The aforementioned suction passage has a plurality of suction ports through which the working fluid is drawn in. A discharge passage having a discharge port for discharging working fluid is formed on the outer circumferential surface of the casing. The plurality of cylinder bores are each arranged around the axis in the cylinder block, The variable displacement mechanism is a rotary swashplate type hydraulic pump located inside the plurality of cylinder bores in the cylinder block.

2. The intake passage has an intake-side annular portion connected to the intake port and the cylinder bore, respectively. The rotary swashplate type hydraulic pump according to claim 1, wherein the suction-side annular portion is formed in an annular shape.

3. The rotary swashplate type hydraulic pump according to claim 1 or 2, wherein the discharge port is formed on the outer circumferential surface of the casing at a different phase from the plurality of suction ports in the circumferential direction.

4. Each of the aforementioned multiple cylinder bores is provided with a plurality of discharge check valves that open and close the respective discharge passages, The rotary swashplate type hydraulic pump according to claim 3, wherein each of the plurality of discharge check valves is inserted toward each of the plurality of cylinder bores on the outer circumferential surface of the casing.

5. The casing has a prismatic shape with its sides consisting of multiple planes, The rotary swashplate hydraulic pump according to claim 4, wherein each of the plurality of discharge check valves is inserted toward each of the plurality of cylinder bores in each of the plurality of planes.

6. The casing includes a casing body that houses the cylinder block so that it cannot rotate relative to it, and a first cover that houses the rotating swash plate. The rotary swash plate type hydraulic pump according to any one of claims 1 to 5, wherein the first cover is placed over the casing body such that the rotary swash plate faces the cylinder block.

7. The casing further includes a second lid, The intake passage is formed at the other end of the casing body in the axial direction, The rotary swashplate type hydraulic pump according to claim 6, wherein the second cover is provided at the other axial end of the casing body so as to block the suction passage.

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