Rotating swash plate type hydraulic pump

Abstract

To provide a rotary swash plate-type hydraulic pump which is capable of changing a discharge capacity and can be formed in compact.SOLUTION: A rotary swash plate-type hydraulic pump includes: a casing; a cylinder block including a cylinder bore and disposed in the casing in a manner of being not relatively rotatable; a piston inserted to the cylinder bore; a rotary swash plate housed in the casing rotatably around an axis and reciprocating the piston; and a variable capacity mechanism for changing an effective stroke length of the piston. The variable capacity mechanism includes a spool for changing the effective stroke length of the piston by adjusting opening / closing of the corresponding cylinder bore, and the cylinder block includes a spool hole to which the spool is inserted.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rotating swash plate type hydraulic pump in which pistons are reciprocated by rotating a rotating swash plate. [Background technology]

[0002] Known piston pumps include a swash plate type piston pump as described in Patent Document 1. In the piston pump of Patent Document 1, the pistons reciprocate when the swash plate rotates, causing pressure oil to be discharged from the piston pump. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-205266 Summary of the Invention [Problem to be solved by the invention]

[0004] The piston pump in Patent Document 1 has a fixed discharge capacity. It is desirable for piston pumps to be able to change the discharge capacity according to the situation. In addition, it is desirable for a rotating swash plate type piston pump with a variable discharge capacity to be compact.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a rotating swash plate type hydraulic pump that is capable of changing the discharge capacity and that can be formed compactly. [Means for solving the problem]

[0006] The rotating swash plate type hydraulic pump of the present invention comprises a casing, a cylinder block including cylinder bores and arranged within the casing so as not to be rotatable relative to one another, pistons inserted into the cylinder bores, a rotating swash plate housed within the casing so as to be rotatable about an axis and causing the pistons to reciprocate, and a variable displacement mechanism for changing the effective stroke length of the pistons, wherein the variable displacement mechanism includes a spool that changes the effective stroke length of the pistons by adjusting the opening and closing of the corresponding cylinder bores, and the cylinder block includes a spool hole into which the spool is inserted.

[0007] According to the present invention, the variable displacement mechanism includes a spool that changes the effective stroke length of the piston. Therefore, the displacement of the swash plate hydraulic pump can be changed. The cylinder block includes a spool hole into which the spool is inserted. Therefore, the spool hole can be arranged more compactly than when the spool hole is arranged in a casing outside the cylinder block, allowing the swash plate hydraulic pump to be formed compactly. This allows the variable displacement swash plate hydraulic pump to be formed compactly.

[0008] The rotating swash plate type hydraulic pump of the present invention comprises a casing, a cylinder block including cylinder bores and arranged within the casing so as not to be rotatable relative to one another, pistons inserted into the cylinder bores, a rotating swash plate housed within the casing so as to be rotatable about an axis and causing the pistons to reciprocate, a variable displacement mechanism for changing the effective stroke length of the pistons, an intake check valve that allows working fluid to flow in one direction into the cylinder bores and prevents flow in the opposite direction, and a discharge check valve that allows working fluid to flow in one direction out of the cylinder bores and prevents flow in the opposite direction, wherein the pistons are inserted into one axial side of the cylinder bores, the cylinder bores are connected to an intake passage on the other axial side, the intake check valve is inserted into the other axial side of the cylinder bores, and the discharge check valve is arranged radially outward of the intake side check valve when viewed in the axial direction.

[0009] According to the present invention, the suction check valve is inserted into the other axial end of the cylinder bore. This connects the cylinder bore to the suction passage, eliminating the need for a cylinder port. The discharge check valve is positioned radially outward of the suction check valve as viewed in the axial direction, and extends radially outward. This allows the rotating swash plate type hydraulic pump to be more compact. [Effects of the Invention]

[0010] According to the present invention, a rotary swash plate type hydraulic pump can be formed in a compact size and with variable discharge capacity. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a rotating swash plate type hydraulic pump according to an embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of the rotating swash plate type hydraulic pump taken along line II-II in FIG. 1. FIG. [Figure 3] 3 is a cross-sectional view of the casing taken along line III-III in FIG. 1. FIG. [Figure 4] 2 is an enlarged cross-sectional view showing an area X shown in FIG. 1 in an enlarged manner. DETAILED DESCRIPTION OF THE INVENTION

[0012] A rotating swash plate type hydraulic pump 1 according to an embodiment of the present invention will be described below with reference to the drawings. Note that the concepts of directions used in the following description are used for convenience of explanation and do not limit the orientation of the configuration of the invention to those directions. Furthermore, the rotating swash plate type hydraulic pump 1 described below is merely one embodiment of the present invention. Therefore, the present invention is not limited to the embodiment, and additions, deletions, and modifications are possible within the scope of the spirit of the invention.

[0013] <Rotating swash plate type hydraulic pump> A rotating swash plate type hydraulic pump (hereinafter referred to as "pump") 1 shown in FIGS. 1 and 2 is provided in various machines, such as construction machines such as excavators and cranes, industrial machines such as forklifts, agricultural machines such as tractors, and hydraulic machines such as presses. In this embodiment, the pump 1 is a rotating swash plate type variable displacement hydraulic pump. The pump 1 includes a casing 11, a cylinder block 12, a rotating swash plate 13, multiple pistons 21, and a variable displacement mechanism 15. The pump 1 also includes multiple suction check valves 16, multiple discharge check valves 17, multiple shoes 22, a pressure plate 23, a spherical bushing 24, and multiple biasing members 25. The multiple pistons 21, together with the multiple shoes 22, the pressure plate 23, the spherical bushing 24, and the multiple biasing members 25, form a piston mechanism 14. The pump 1 is driven by a drive source (e.g., an engine, an electric motor, or both). As a result, the pump 1 discharges hydraulic fluid.

[0014] <Casing> The casing 11 houses a cylinder block 12, a swash plate 13, a piston mechanism 14, and a variable displacement mechanism 15. The casing 11 includes an intake passage 19 and a discharge passage 20. The casing 11 is a cylindrical member that extends along a predetermined axis L1. The casing 11 is open at one end on one side in the axial direction along the axis L1 and at the other end on the other side.

[0015] The suction passage 19 is formed in the other end portion of the casing 11. More specifically, the suction passage 19 is disposed on the other axial side of the cylinder block 12. The suction passage 19 is connected to a plurality of cylinder bores 12a of the cylinder block 12, which will be described in detail later. The suction passage 19 is also connected to a tank 30 via a suction port 19a. The suction passage 19 draws working fluid from the tank 30 via the suction port 19a. The working fluid drawn from the tank 30 flows through the suction passage 19.

[0016] The discharge passage 20 has multiple branch portions 20a and an annular portion 20b. The discharge passage 20 is formed in the middle portion of the casing 11. The discharge passage 20 is connected to each of the cylinder bores 12a of the cylinder block 12, which will be described in detail later. Each of the branch portions 20a is connected to the corresponding cylinder bore 12a. More specifically, each of the branch portions 20a is connected to the side of the corresponding cylinder bore 12a. Each of the branch portions 20a rises radially outward from the cylinder bore 12a, then bends and extends in one axial direction. The annular portion 20b is arranged to surround the cylinder block 12, more specifically, the cylinder bores 12a of the cylinder block 12, from the outside. The annular portion 20b is connected to the branch portions 20a. Therefore, working fluid is guided to the annular portion 20b from the cylinder bores 12a via the branch portions 20a. The annular portion 20b is connected to, for example, a hydraulic actuator via a discharge port 20c. The hydraulic fluid guided to the annular portion 20b is discharged to the hydraulic actuator via the discharge port 20c.

[0017] <Cylinder block> As shown in FIG. 3, the cylinder block 12 includes a plurality of cylinder bores 12a and a plurality of spool holes 12b. The cylinder block 12 also includes a plurality of accommodating holes 12c, a plurality of communicating passages 12d, a shaft insertion hole 12e, and a plurality of communicating holes 12f. The cylinder block 12 is disposed within the casing 11 so as to be non-rotatable relative to the casing 11. More specifically, the cylinder block 12 is fixed to the casing 11. In this embodiment, the cylinder block 12 is integrally formed in the axially middle portion of the casing 11. However, the cylinder block 12 may be separate from the casing 11. If separate, the cylinder block 12 is fixed to the casing 11 by, for example, press fitting, spline connection, key connection, fastening, or bonding. A protrusion 12i is formed on one end face 12g of the cylinder block 12 around the axis L1 (see also FIGS. 1 and 2). The other end surface 12h of the cylinder block 12 faces the intake passage 19. The other end surface 12h is the end surface of the cylinder block 12 on the other side in the axial direction.

[0018] <Cylinder bore> Each of the cylinder bores 12a opens at one end face 12g of the cylinder block 12. The one end face 12g is an end face on one axial side of the cylinder block 12. In this embodiment, nine cylinder bores 12a open at the one end face 12g of the cylinder block 12. However, the number of cylinder bores 12a is not limited to nine.

[0019] The cylinder bores 12a are arranged at intervals (equally spaced apart in this embodiment) in the circumferential direction around the axis L1. The cylinder bores 12a extend in the other axial direction from one end face 12g to the other end face 12h. The other end face 12h is the end face on the other axial side of the cylinder block 12. The cylinder bores 12a are connected to an intake passage 19 on the other axial side. More specifically, the cylinder bores 12a have intake-side ports 12j that open at the other end face 12h of the cylinder block 12, as shown in FIGS. 1 and 2. The cylinder bores 12a are connected to the intake passage 19 via the intake-side ports 12j.

[0020] <Spool hole> Each spool hole 12b is formed in the cylinder block 12. More specifically, the cylinder block 12 has the same number of spool holes 12b as the number of cylinder bores 12a (nine in this embodiment). Each spool hole 12b is connected to the tank 30. More specifically, the spool holes 12b are connected to the tank 30 via an intake passage 19. The spool holes 12b are also arranged at intervals (equally spaced in this embodiment) in the circumferential direction around the axis L1. More specifically, the spool holes 12b extend from the other end face 12h to the one end face 12g of the cylinder block 12. As shown in FIG. 3, the spool holes 12b are also open at the one end face 12g. The spool holes 12b are arranged at equal intervals around the protrusion 12i. The spool holes 12b are arranged inside the cylinder bores 12a (radially inside in this embodiment). Here, each spool hole 12b corresponds to a corresponding cylinder bore 12a. The spool holes 12b are arranged radially inward relative to the corresponding cylinder bore 12a. That is, the corresponding spool holes 12b and cylinder bores 12a are arranged in line with each other in the radial direction. The spool holes 12b are intended to release part of the capacity of the cylinder bores 12a. For example, the diameter of the spool holes 12b is smaller than the diameter of the cylinder bores 12a.

[0021] <Housing Cavity> Each of the accommodating holes 12c accommodates a corresponding one of the biasing members 25, which will be described in detail later. Each of the accommodating holes 12c opens to one end face 12g of the cylinder block 12. In this embodiment, nine accommodating holes 12c open to the one end face 12g of the cylinder block 12. However, the number of accommodating holes 12c is not limited to nine. The accommodating holes 12c are also arranged at intervals (equally spaced in this embodiment) circumferentially around the axis L1. More specifically, the accommodating holes 12c are arranged at equal intervals around the spool hole 12b. The accommodating holes 12c are arranged radially between the spool hole 12b and the cylinder bore 12a. More specifically, the central axis of each of the accommodating holes 12c is located between the spool hole 12b and the cylinder bore 12a. More specifically, the accommodating holes 12c are arranged in a staggered pattern with respect to the cylinder bore 12a and the spool hole 12b. This prevents the outer diameter of the cylinder block 12 and the outer diameter of the casing 11 from increasing.

[0022] <Communication path> 1 and 2, each of the communication passages 12d connects the corresponding cylinder bore 12a and spool hole 12b. That is, the cylinder block 12 is formed with the same number of communication passages 12d as the number of cylinder bores 12a and spool holes 12b (nine in this embodiment). The communication passages 12d extend radially. The communication passages 12d are located on the other end face 12h side of the cylinder block 12.

[0023] <Shaft insertion hole> The shaft insertion hole 12e is formed along the axis L1 in the cylinder block 12. The shaft insertion hole 12e passes through the cylinder block 12 in the axial direction from the tip end surface of the protrusion 12i to the other end surface 12h.

[0024] <Communication hole> Each of the communication holes 12f penetrates the cylinder block 12 from one end face 12g to the other end face 12h. In this embodiment, three communication holes 12f are formed in the cylinder block 12 as shown in FIG. 3. However, the number of communication holes 12f is not limited to three. Each of the communication holes 12f is disposed radially outward from the cylinder bore 12a. The communication holes 12f are disposed at intervals (equidistant in this embodiment) in the circumferential direction. The communication holes 12f are connected to the suction passage 19 and guide the working fluid in the suction passage 19 to the swash plate-side inclined surface 13a of the swash plate 13, which will be described later. This cools the swash plate-side inclined surface 13a.

[0025] <Rotating swash plate> As shown in FIGS. 1 and 2 , the swash plate 13 includes a swash-plate-side inclined surface 13a. The swash plate 13 is accommodated in the casing 11 and is rotatable about the axis L1. More specifically, the swash plate 13 is accommodated on one axial side of the casing 11. The swash plate 13 extends along the axis L1. The swash plate 13 is supported by the casing 11 and is rotatable about the axis L1. The swash plate 13 faces one end surface 12g of the cylinder block 12. One end of the swash plate 13 protrudes from one end of the casing 11. The one axial end of the swash plate 13 is connected to the drive source. The swash plate 13 is rotated by the drive source. The rotation of the swash plate 13 reciprocates pistons 21, which will be described later in detail. In this embodiment, the swash plate 13 is formed integrally with a disk portion having the swash plate-side inclined surface 13a and a rotatably supported shaft portion, but may be formed as separate bodies.

[0026] The swash plate-side inclined surface 13a is formed on the other end of the swash plate 13. The swash plate-side inclined surface 13a faces the end surface 12g of the cylinder block 12. The swash plate-side inclined surface 13a is inclined toward the end surface 12g of the cylinder block 12 about a first orthogonal axis L2. The first orthogonal axis L2 is an axis perpendicular to the axis L1. In this embodiment, the inclination angle of the swash plate-side inclined surface 13a is fixed. For ease of explanation, the inclination of the swash plate-side inclined surface 13a in FIG. 2 is shown differently from that of the swash plate-side inclined surface 13a in FIG. 1.

[0027] <Piston mechanism> 2, the piston mechanism 14 includes a plurality of pistons 21, a plurality of shoes 22, a presser plate 23, a spherical bushing 24, and a plurality of biasing members 25. Each of the pistons 21 is inserted into one axial side of each of the cylinder bores 12a of the cylinder block 12. That is, the same number of pistons 21 as the number of cylinder bores 12a (nine pistons in this embodiment) are inserted into the cylinder block 12. Each of the pistons 21 reciprocates in the cylinder bore 12a as the swash plate 13 rotates.

[0028] Each shoe 22 is rotatably connected to a corresponding piston 21. More specifically, each shoe 22 is rotatably connected to the tip of each piston 21. In this embodiment, the piston mechanism 14 is provided with nine shoes 22, the same number as the pistons 21. Each shoe 22 abuts against the swash plate 13. Like the pistons 21, the shoes 22 are arranged at equal intervals around the axis L1 and abut against the swash plate-side inclined surface 13a of the swash plate 13. The swash plate-side inclined surface 13a slides against the shoes 22.

[0029] The presser plate 23 is attached to the shoes 22. More specifically, the presser plate 23 is a circular plate-shaped member. The presser plate 23 has shoe insertion holes 23a. In this embodiment, the presser plate 23 has the same number of shoe insertion holes 23a as the number of shoes 22 (i.e., nine). One of the shoes 22 is inserted into each of the shoe insertion holes 23a.

[0030] The spherical bushing 24 supports the pressure plate 23 in a rollable manner. More specifically, the spherical bushing 24 is fitted to the protrusion 12i. The tip end portion of the spherical bushing 24, i.e., the axial end portion, of the spherical bushing 24, is a partially spherical portion 24a, which is formed in a partially spherical shape. The pressure plate 23 is rollably fitted to the partially spherical portion 24a of the spherical bushing 24. This allows the pressure plate 23 to roll on the partially spherical portion 24a of the spherical bushing 24 in accordance with the movement of the swash plate-side inclined surface 13a.

[0031] Each of the biasing members 25 is accommodated in the corresponding one of the accommodation holes 12c. Each of the biasing members 25 biases the pressure plate 23 toward the swash plate 13. As a result, the biasing members 25 press each of the shoes 22 against the swash plate 13 via the pressure plate 23. More specifically, the biasing members 25 bias the pressure plate 23 toward the swash plate 13 via the spherical bushings 24. As a result, the shoes 22 are pressed against the swash plate 13. In this embodiment, the piston mechanism 14 includes nine biasing members 25, the same number as the number of accommodation holes 12c. However, the number of biasing members 25 included in the piston mechanism 14 is not limited to nine. Here, each of the biasing members 25 is a compression coil spring. The biasing members 25 are inserted into the accommodation holes 12c in a compressed state.

[0032] <Variable capacity mechanism> As shown in FIG. 1 , 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 nine spools 26 and springs 27, the same number as the number of spool holes 12b. The variable displacement mechanism 15 adjusts the effective stroke length S of each of the nine pistons 21. In this embodiment, the variable displacement mechanism 15 opens and closes the cylinder bore 12a to change the effective stroke length S of the pistons 21. Changing the effective stroke length S changes the discharge capacity of the pump 1.

[0033] More specifically, the variable displacement mechanism 15 adjusts the opening and closing of the cylinder bore 12a and the tank 30 when the piston 21 strokes from the bottom dead center toward the top dead center (i.e., during the discharge stroke of the pump 1). In this embodiment, the variable displacement mechanism 15 adjusts the opening and closing of the communication passage 11d. In this way, the variable displacement mechanism 15 adjusts the effective stroke length S of each of the pistons 21. However, the variable displacement mechanism 15 is not limited to adjusting the effective stroke length S of all nine pistons 21. Note that the top dead center is the point where the piston 21 is located furthest to one side, and the bottom dead center is the point where the piston 21 is located furthest to one side.

[0034] <Spool> Each spool 26 is disposed corresponding to a corresponding cylinder bore 12a. More specifically, the spool 26 is inserted into each spool hole 12b of the cylinder block 12 so as to be able to reciprocate. The spool 26 opens and closes the corresponding cylinder bore 12a. More specifically, the spool 26 opens and closes the connection between the corresponding cylinder bore 12a and the tank 30 by reciprocating. In this embodiment, the spool 26 connects the corresponding cylinder bore 12a to the suction passage 19 by opening and closing. This connects the cylinder bore 12a to the tank 30 via the suction passage 19. The spool 26 adjusts the effective stroke length S of each piston 21 by adjusting the opening and closing of the connection between the cylinder bore 12a and the tank 30 during the discharge stroke.

[0035] <Spring> Each spring 27 is inserted in a compressed state into each spool hole 12b. More specifically, each spring 27 is disposed in each spool hole 12b on one axial side of the spool 26. The spring 27 biases the spool 26 toward a swash plate rotation shaft 28, which will be described later.

[0036] <Swash plate rotating shaft> The swash plate rotating shaft 28 rotates in conjunction with the rotating swash plate 13. The rotation of the swash plate rotating shaft 28 causes each of the spools 26 to reciprocate. As a result, the swash plate rotating shaft 28 causes the spools 26 to open and close the space between the cylinder bore 12a and the tank 30. Here, the swash plate rotating shaft 28 causes the spools 26 to open and close the communication passage 12d. The swash plate rotating shaft 28 can also change the open and closed positions of each of the spools 26. The open and closed positions of the spools 26 are the positions where the spools 26 begin to open and close the communication passage 12d.

[0037] More specifically, the swash plate rotation shaft 28 has a swash plate rotation shaft-side inclined surface 28a. The swash plate rotation shaft 28 is inserted through the shaft insertion hole 12e 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 12e toward the swash plate 13. This one axial end of the swash plate rotation shaft 28 is non-rotatably connected to the swash plate 13. Therefore, the swash plate rotation shaft 28 rotates about the axis L1 in conjunction with the swash plate 13. The other axial end of the swash plate rotation shaft 28 also protrudes from the shaft insertion hole 12e into the suction passage 19.

[0038] The swash plate rotation shaft-side inclined surface 28a is located in the axially intermediate portion of the swash plate rotation shaft 28. The swash plate rotation shaft-side inclined surface 28a faces the other end face 12h of the cylinder block 12. More specifically, the swash plate rotation shaft-side inclined surface 28a faces the other axial opening of the spool bore 12b. The swash plate rotation shaft-side inclined surface 28a is inclined about a second orthogonal axis L3 parallel to the first orthogonal axis L2. The second orthogonal axis L3 is also an axis perpendicular to the axis L1. In this embodiment, the swash plate rotation shaft-side inclined surface 28a is inclined in the same direction as the swash plate rotation shaft-side inclined surface 13a, and the inclination angle is fixed. The other axial end of the spool 26, which is biased by the spring 27, abuts against the swash plate rotation shaft-side inclined surface 28a. The swash plate rotation shaft-side inclined surface 28a slides and rotates relative to the spool 26. Therefore, when the swash plate rotation shaft 28 rotates, the spool 26 reciprocates in the spool hole 12b with a stroke corresponding to the inclination angle of the swash plate rotation shaft side inclined surface 28a.

[0039] The swash plate shaft-side inclined surface 28a can move axially. This movement adjusts the opening and closing of the gap between the cylinder bore 12a and the tank 30. More specifically, this movement adjusts the opening and closing position of the spool 26. A linear actuator 18 is connected to the other axial end of the swash plate shaft 28. The linear actuator 18 may be either an electric or hydraulic linear actuator. The linear actuator 18 can move the swash plate shaft-side inclined surface 28a toward and away from the other end face 12h of the cylinder block 12. This allows the dead center position of the spool 26 in the cylinder bore 12a (more specifically, the axial position of the dead center) to be changed. For example, the axial movement of the swash plate shaft-side inclined surface 28a shifts the dead center position of the spool 26 in the cylinder bore 12a toward one side. On the other hand, by retracting the swash plate shaft-side inclined surface 28a in the other axial direction, the dead center position of the spool 26 in the cylinder bore 12a is shifted in the other axial direction, so that the opening and closing position of the spool 26 in the cylinder bore 12a can be shifted in the axial direction.

[0040] The effective stroke length S of the piston 21 is the stroke range within which hydraulic fluid can be discharged from the cylinder bore 12a. Therefore, the effective stroke length S of the piston 21 can be changed by axially shifting the opening / closing position of the spool 26. Therefore, the discharge capacity of the cylinder bore 12a can be changed by axially advancing and retracting the swash plate rotation shaft side inclined surface 28a.

[0041] <Suction check valve> Each suction check valve 16 allows hydraulic fluid to flow in one direction from the suction passage 19 to the cylinder bore 12a and prevents flow in the opposite direction. The suction check valves 16 are provided in the cylinder bores 12a. In this embodiment, there are nine suction check valves 16, the same number as the cylinder bores 12a. Each suction check valve 16 is inserted into the other axial side of the cylinder bore 12a. As shown in FIG. 4, one end of each suction check valve 16 is inserted into the suction-side port 12j. The other end of each suction check valve 16 protrudes from the cylinder bore 12a into the suction passage 19. Each suction check valve 16 is positioned to face the piston 21 on the other axial side. The suction check valves 16 have a smaller diameter than the cylinder bore 12a when viewed axially. The suction check valves 16 are positioned in the cylinder bores 12a so that their axes are aligned.

[0042] More specifically, each of the suction check valves 16 includes a sleeve 16a, a valve element 16b, and a spring 16c. The sleeve 16a is cylindrical. One end of the sleeve 16a is inserted into the cylinder bore 12a, and one end of the sleeve 16a forms a valve seat 16d. An internal passage 16e is formed in the sleeve 16a. The internal passage 16e connects the suction passage 19 and the cylinder bore 12a.

[0043] The valve element 16b has an umbrella portion 16f and a valve stem portion 16g. The valve element 16b is a poppet type valve element. The valve element 16b is seated on a valve seat 16d and is also spaced away from the valve seat 16d toward the piston 21. This allows the valve element 16b to open and close the space between the suction passage 19 and the cylinder bore 12a. The valve element 16b protrudes from the suction-side port 12j in the other axial direction.

[0044] The head portion 16f is formed on the cylinder bore 12a side of the valve body 16b. The head portion 16f is seated on the valve seat 16d. The head portion 16f is separated from the valve seat 16d toward the piston 21. The valve stem 16g is inserted through the sleeve 16a and extends from the head portion 16f in the other axial direction.

[0045] Spring 16c biases valve element 16b so that valve element 16b seats on valve seat 16d. More specifically, spring 16c biases valve element 16b against the pressure of hydraulic fluid introduced from suction passage 19 into suction check valve 16 (more specifically, sleeve 16a). Therefore, suction check valve 16 opens communication between cylinder bore 12a and suction passage 19 during the suction stroke in which piston 21 moves from top dead center to bottom dead center, and closes communication between cylinder bore 12a and suction passage 19 during the discharge stroke. Spring 16c is located upstream of valve seat 16d. More specifically, spring 16c is located on the other axial side of valve element 16b (the portion protruding from suction-side port 12j).

[0046] <Discharge check valve> Each discharge check valve 17 shown in FIG. 1 allows hydraulic fluid to flow in one direction, from the cylinder bore 12a to the discharge port 20c, and prevents reverse flow. One discharge check valve 17 is provided for each cylinder bore 12a. In this embodiment, there are nine discharge check valves 17, the same number as the cylinder bores 12a. The discharge check valves 17 are located radially outward of the suction check valves 16 when viewed in the axial direction. More specifically, the radially outermost portion of the valve body 17a of each discharge check valve 17 is located further outward than the radially outermost portion of the valve body 16b of each suction check valve 16. The valve seat 20d of each discharge check valve 17 is located further outward than the axial center of the suction check valve 16. The discharge check valve 17 extends radially outward. The discharge check valve 17 is provided at the branch portion 20a of the discharge passage 20. In this embodiment, discharge check valve 17 is inserted into a portion of branch portion 20a that extends radially from the outer peripheral surface of casing 11. This allows discharge check valve 17 to open and close discharge passage 20 at a position away from annular portion 20b. Therefore, the opening and closing operation of discharge check valve 17 is less affected by hydraulic fluid introduced into annular portion 20b from other cylinder bores 12a.

[0047] More specifically, as shown in FIG. 4, the discharge check valve 17 has a valve element 17a. The valve element 17a is seated on a valve seat 20d in the branch portion 20a. The valve element 17a is biased toward the cylinder bore 12a by a spring 17c. Here, the spring 17c is located downstream of the valve seat 20d. The valve element 17a has an internal passage 17b. The valve element 17a directs downstream pressure of the valve element 17a to the back pressure chamber 17d through the internal passage 17b. This causes pressures before and after the valve element 17a to act on the valve element 17a. Therefore, the valve element 17a moves away from the valve seat 20d during the discharge stroke. This opens the discharge passage 20 (more specifically, the branch portion 20a). This allows hydraulic fluid to flow in one direction, from the cylinder bore 12a to the discharge port 20c. That is, during the discharge stroke, hydraulic fluid flows from the cylinder bore 12a to the discharge port 20c. On the other hand, the discharge check valve 17 prevents flow in the reverse direction. Therefore, during the suction stroke, the flow of hydraulic fluid from the cylinder bore 12a to the discharge port 20c is stopped.

[0048] <Pump operation> The operation of the pump 1 will now be described. When the swash plate 13 is rotated by the drive source, each piston 21 reciprocates in its cylinder bore 12a. As a result, during the suction stroke, each piston 21 draws hydraulic fluid into the cylinder bore 12a from the suction passage 19 via the suction check valve 16. On the other hand, during the discharge stroke, each piston 21 discharges hydraulic fluid from the cylinder bore 12a via the discharge check valve 17 and the discharge passage 20. More specifically, when the hydraulic fluid in the cylinder bore 12a is pressurized by the piston 21 during the discharge stroke, the discharge check valve 17 eventually opens the discharge passage 20. This allows hydraulic fluid to flow from the cylinder bore 12a through the branch portion 20a to the annular portion 20b. The hydraulic fluid is then discharged from the discharge port 20c.

[0049] In the pump 1, the swash plate shaft 28 rotates in conjunction with the rotation of the swash plate 13, causing each spool 26 to reciprocate in synchronization with the corresponding piston 21 in the spool bore 12b. This causes the communication passage 12d to open during the suction stroke of each piston 21 and close during the discharge stroke of each piston 21. This establishes communication between the cylinder bore 12a and the communication passage 12d until the communication passage 12d closes during the discharge stroke (i.e., until the piston 21 moves the opening stroke length S2). Until the communication passage 12d closes, the discharge of hydraulic fluid from the cylinder bore 12a to the discharge port 20c is restricted. Therefore, the effective stroke length S of each piston 21 is shorter than the actual stroke length S1 by the opening stroke length S2, and the pump 1 discharges hydraulic fluid at a discharge capacity corresponding to the effective stroke length S. In the pump 1, the open / close position of the spool 26 is changed by moving the inclined surface 28a of the swash plate rotation shaft side in the axial direction by the linear motion actuator 18. This changes the effective stroke length S of each piston 21, thereby increasing or decreasing the discharge capacity of the pump 1.

[0050] In the pump 1 of this embodiment, the variable displacement mechanism 15 includes a spool 26 that changes the effective stroke length S of the piston 21. This allows the displacement of the pump 1 to be changed. The cylinder block 12 includes spool holes 12b into which each of the spools 26 is inserted so that they can reciprocate. This allows the spool holes 12b to be arranged more compactly than if the spool holes 12b were arranged in the casing 11 outside the cylinder block 12, thereby allowing the pump 1 to be made compact. This allows the pump 1 with a variable displacement to be made compact.

[0051] Furthermore, in the pump 1 of this embodiment, the spool hole 12b is disposed inside the cylinder bore 12a, which allows the pump 1 to be made even more compact.

[0052] Furthermore, in the pump 1 of this embodiment, the accommodating hole 12c is disposed radially between the spool hole 12b and the cylinder bore 12a, eliminating the need to secure additional space for forming the accommodating hole 12c in the cylinder block 12, thereby enabling the pump 1 to be made even more compact.

[0053] Furthermore, in the pump 1 of this embodiment, the suction check valve 16 is inserted into the other axial end of the cylinder bore 12a. This allows the suction check valve 16 to connect the cylinder bore 12a to the suction passage 19, eliminating the need for a cylinder port connecting the cylinder bore 12a to the suction passage 19. This allows the pump 1 to be made even more compact.

[0054] Furthermore, in the pump 1 of this embodiment, the suction check valve 16 is disposed so as to face the other axial side of the piston 21. Therefore, the space in the pump 1 can be used effectively.

[0055] Furthermore, in the pump 1 of this embodiment, the discharge check valve 17 is disposed radially outward of the suction check valve 16 as viewed in the axial direction. This allows the discharge check valve 17 and the suction check valve 16 to be disposed close to each other in the axial direction. This allows the pump 1 to be formed compactly in the axial direction.

[0056] Furthermore, in the pump 1 of this embodiment, the discharge check valve 17 extends radially outward, which allows the pump 1 to be made compact in the axial direction.

[0057] Furthermore, in the pump 1 of this embodiment, the valve element 16b of the suction check valve 16 protrudes from the suction passage 19 in the other axial direction, and the spring 16c is located on the other axial side of the valve element 16b. This allows the suction check valve 16 to be located outside the cylinder bore 12a. This prevents the cylinder bore 12a from becoming too long, allowing the pump 1 to be compact in the axial direction.

[0058] Furthermore, in the pump 1 of this embodiment, the suction check valve 16 is inserted into the other axial end of the cylinder bore 12a. This connects the cylinder bore 12a to the suction passage 19, eliminating the need for a cylinder port. Furthermore, the discharge check valve 17 is positioned radially outward of the suction check valve as viewed in the axial direction, and extends radially outward. This allows the pump 1 to be made even more compact.

[0059] <Other embodiments> In the pump 1 of this embodiment, multiple spool holes 12b may be disposed outside the multiple cylinder bores 12a. Each of the spool holes 12b may be disposed at a position offset circumferentially from the radially inward position relative to the corresponding cylinder bore 12a. The pump 1 of this embodiment does not necessarily require the multiple shoes 22, the retaining plate 23, the spherical bushing 24, and the multiple biasing members 25. The piston 21 may directly abut against the swash plate 13. The suction check valve 16 does not necessarily need to be inserted into the suction port 12j of the cylinder bore 12a. It may be attached to a separately formed cylinder port or the like. The shape of the discharge passage 20 is not limited to the above-described shape. For example, the branch portion 20a may extend radially inward from the annular portion 20b and connect to the cylinder bore 12a. In this case, each of the discharge check valves 17 is disposed in the branch portion 20a so as to penetrate the annular portion 20b. [Explanation of symbols]

[0060] 1 Rotating swash plate type hydraulic pump 11 Casing 12 Cylinder block 12a Cylinder bore 12b spool hole 12c Receiving hole 13 Rotating swash plate 14 Piston mechanism 15 Variable capacity mechanism 16 Intake check valve 16b Valve body 16c spring 16d valve seat 17 Discharge check valve 17c spring 19 Suction passage 21 Piston 22 Shoe 23 Presser plate 25 biasing member 26 spools 27 Spring 30 Tank

Claims

1. A casing; a cylinder block including a cylinder bore and disposed within the casing so as to be non-rotatable relative to the cylinder block; a piston inserted into the cylinder bore; a swash plate that is accommodated in the casing and is rotatable about an axis, and that causes the pistons to reciprocate; a variable displacement mechanism that changes the effective stroke length of the piston, the variable displacement mechanism includes a spool that adjusts the opening and closing of the corresponding cylinder bore to change the effective stroke length of the piston; The cylinder block includes a spool hole into which the spool is inserted.

2. The rotating swash plate type hydraulic pump according to claim 1 , wherein the spool hole is disposed inside the cylinder bore.

3. a shoe rotatably connected to the piston and slidably contacting the swash plate; a presser plate attached to the shoe; a biasing member that biases the presser plate toward the swash plate, thereby pressing the shoes against the swash plate; the cylinder block includes a receiving hole in which each of the biasing members is received, The rotating swash plate type hydraulic pump according to claim 1 or 2, wherein the accommodation hole is disposed between the cylinder bore and the spool hole in the radial direction.

4. an intake check valve that allows hydraulic fluid to flow in one direction into the cylinder bore and prevents hydraulic fluid from flowing in the reverse direction; the casing includes an intake passage through which hydraulic fluid flows; The piston is inserted into one side of the cylinder bore in the axial direction, The cylinder bore is connected to the intake passage on the other axial side, 4. The rotating swash plate type hydraulic pump according to claim 1, wherein the suction check valve is inserted into the other axial side portion of the cylinder bore.

5. The cylinder bore extends in an axial direction, 5. The rotating swash plate type hydraulic pump according to claim 4, wherein the suction check valve is disposed opposite to the other side of the piston in the axial direction.

6. a discharge check valve that allows hydraulic fluid to flow in one direction from the cylinder bore and prevents hydraulic fluid from flowing in the opposite direction; 6. The rotating swash plate type hydraulic pump according to claim 4, wherein the discharge check valve is disposed radially outward of the suction check valve as viewed in the axial direction.

7. 7. The rotating swash plate hydraulic pump of claim 6, wherein the discharge check valve extends radially.

8. The intake check valve has a valve body that seats on a valve seat in the cylinder bore, and a spring that biases the valve body so that the valve body seats on the valve seat, The valve body protrudes from the cylinder bore into the intake passage, 8. The rotating swash plate type hydraulic pump according to claim 4, wherein the spring is disposed on the other axial side of the valve body.

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