Axial piston type liquid pressure rotary machine

Abstract

To provide an axial piston type liquid pressure rotary machine capable of reducing a leakage flow amount and mitigating a contact surface pressure.SOLUTION: A hydraulic pump 1, which is an axial piston liquid pressure rotary machine, comprises a cylinder block 5, a plurality of pistons 7, and a valve plate 8. The cylinder block 5 has an annular first sliding contact surface 5C where a cylinder port 6A is open. The valve plate 8 has an annular second sliding contact surface 8C that comes into sliding contact with the first sliding contact surface 5C of the cylinder block 5. An outer peripheral edge of the second sliding contact surface 8C of the valve plate 8 is provided with an outer diameter side tapered surface 21 that is inclined away from the cylinder block 5 as the distance from the outer peripheral edge increases radially. Also, an inner peripheral edge of the second sliding contact surface 8C of the valve plate 8 is provided with an inner diameter side tapered surface 22 that is inclined away from the cylinder block 5 as the distance from the inner peripheral edge increases radially.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an axial piston hydraulic rotary machine that is mounted on construction machinery such as hydraulic excavators, hydraulic cranes, and wheel loaders and used as a hydraulic pump or hydraulic motor. [Background technology]

[0002] For example, Patent Documents 1 and 2 describe hydraulic rotating machines including a cylinder block, pistons, a swash plate, and a valve plate. In the hydraulic rotating machine of Patent Document 1, the radius of curvature of the concave spherical sliding surface provided on the cylinder block is larger than the radius of curvature of the convex spherical sliding surface provided on the valve plate. This creates a minute gap between the outer peripheral edge of the sliding surface of the cylinder block and the outer peripheral edge of the sliding surface of the valve plate. In the hydraulic rotating machine of Patent Document 2, an annular shallow groove is formed on the sliding surface of the cylinder block or the sliding surface of the valve plate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-037783 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-094912 Summary of the Invention [Problem to be solved by the invention]

[0004] The hydraulic rotating machine of Patent Document 1 has a small gap between the cylinder block and the valve plate, which may increase the flow rate of hydraulic oil leaking from between the cylinder block and the valve plate (leakage flow rate). The hydraulic rotating machine of Patent Document 2 also has shallow grooves on the sliding contact surface, which may increase the flow rate of hydraulic oil leaking. In response to this, for example, the leakage flow rate can be reduced by making the radius of curvature of the sliding contact surface of the cylinder block closer to the radius of curvature of the sliding contact surface of the valve plate. However, if this is left as is, there is a possibility that the contact surface pressure between the cylinder block and the valve plate will increase when the cylinder block and the valve plate come into partial contact. This increased surface pressure may then lead to excessive wear and seizure.

[0005] An object of the present invention is to provide an axial piston type hydraulic rotary machine that can achieve both a reduction in leakage flow rate and a reduction in contact surface pressure. [Means for solving the problem]

[0006] The present invention preferably relates to an axial piston hydraulic rotary machine comprising: a cylinder block having a plurality of cylinders extending in the axial direction and spaced apart circumferentially, and an annular first sliding contact surface into which cylinder ports of each of the plurality of cylinders open; a plurality of pistons inserted so as to be able to reciprocate within the plurality of cylinders of the cylinder block; and a valve plate having an annular second sliding contact surface in sliding contact with the first sliding contact surface of the cylinder block, and suction ports and discharge ports that open on the second sliding contact surface and intermittently communicate with the plurality of cylinders via the cylinder ports; wherein at least one of the outer and inner peripheral edges of the first sliding contact surface and the outer and inner peripheral edges of the second sliding contact surface is provided with an annular tapered surface that is connected to the first peripheral edge over the entire circumference and that inclines in a direction that increases radially away from the first peripheral edge, thereby increasing the distance from a mating member with which the first peripheral edge slides. [Effects of the Invention]

[0007] According to the present invention, it is possible to achieve both a reduction in leakage flow rate and a reduction in contact surface pressure. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a longitudinal sectional view showing an axial piston type hydraulic rotary machine according to an embodiment. [Figure 2] FIG. 2 is a vertical cross-sectional view showing a cylinder block and a valve plate. [Figure 3] FIG. 3 is an enlarged cross-sectional view showing part (III) in FIG. 2. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing part (IV) in FIG. [Figure 5] FIG. 4 is an enlarged cross-sectional view showing the boundary between the sliding contact surface and the tapered surface of the valve plate. [Figure 6] FIG. 2 is a front view showing a valve plate according to an embodiment. [Figure 7] FIG. 10 is a front view showing a valve plate according to a first modified example. [Figure 8] FIG. 10 is a front view showing a valve plate according to a second modified example. [Figure 9] FIG. 4 is a longitudinal cross-sectional view showing, in an exaggerated manner, a state in which the cylinder block is inclined relative to the valve plate. [Figure 10] FIG. 10 is an enlarged cross-sectional view showing the portion (X) in FIG. [Figure 11] FIG. 11 is an enlarged cross-sectional view taken at the same position as in FIG. 10, illustrating a state in which the cylinder block is not inclined relative to the valve plate. [Figure 12] FIG. 10 is an explanatory diagram showing the difference in efficiency between the embodiment and a reference example. [Figure 13] FIG. 10 is a front view showing a valve plate of a reference example (a valve plate without a tapered surface). DETAILED DESCRIPTION OF THE INVENTION

[0009] Axial piston type hydraulic rotary machines according to the embodiments and modifications will be described in detail below with reference to the accompanying drawings, taking as an example a case where they are used as a hydraulic pump (variable displacement swash plate type hydraulic pump).

[0010] 1 to 6 show an embodiment. In Fig. 1, a variable displacement swash plate type hydraulic pump 1 (hereinafter referred to as hydraulic pump 1) includes a casing 2, a rotating shaft 4, a cylinder block 5, a plurality of cylinders 6, a plurality of pistons 7, a valve plate 8, a plurality of shoes 9, a swash plate 10, a cradle 11, a retainer 12, a retainer guide 13, a spring 14, and a tilting actuator 15. The hydraulic pump 1 is configured such that the rotating shaft 4 connected to a prime mover (an engine or electric motor serving as a drive source) of a hydraulic excavator, for example, is driven to rotate, and the hydraulic pump 1 discharges hydraulic oil drawn from a tank into the plurality of cylinders 6 as high-pressure oil.

[0011] The casing 2 is formed in a cylindrical (hollow) shape and constitutes the outer shell of the hydraulic pump 1. The casing 2 includes a cylindrical casing main body 2A, a one-side closing section 2B that closes the opening on one axial side (left side in FIG. 1) of the casing main body 2A, and an other-side closing section 2C that closes the opening on the other axial side (right side in FIG. 1) of the casing main body 2A. A cradle 11 is provided in the one-side closing section 2B facing the rear surface of the swash plate 10.

[0012] On the other hand, the other-side blocking section 2C is provided with a pair of supply and discharge passages, i.e., an inflow passage 3A serving as a supply passage and an outflow passage 3B serving as a discharge passage, as shown by dashed lines in Fig. 1. One of the pair of supply and discharge passages, i.e., the inflow passage 3A, serves as a low-pressure side suction passage and is connected to a tank (not shown). The other of the pair of supply and discharge passages, i.e., the outflow passage 3B, serves as a discharge passage and is connected to a high-pressure side discharge pipe (not shown).

[0013] The rotating shaft 4 is rotatably mounted in the casing 2. That is, the rotating shaft 4 extends in the axial direction within the casing 2 and is rotatably supported by a cradle 11 fixed to the one-side closing part 2B and the other-side closing part 2C via bearings 16, 16, respectively. In addition, a seal member 17 is provided between the rotating shaft 4 and the one-side closing part 2B.

[0014] One end side (the left end side in FIG. 1) of the rotating shaft 4 forms a protruding end 4A that protrudes in the axial direction from one side closing portion 2B of the casing 2. A prime mover such as an engine is connected to the protruding end 4A of the rotating shaft 4 via a power transmission mechanism (neither of which is shown) or the like. Furthermore, a male spline 4B is formed on the outer circumferential surface of the rotating shaft 4 at a portion that faces radially opposite the cylinder block 5. The male spline 4B is splined to a female spline 5A of the cylinder block 5.

[0015] The cylinder block 5 is disposed within the casing 2 so as to rotate integrally with the rotary shaft 4. To this end, the inner circumferential surface of the cylinder block 5 is formed with female splines 5A that are splined to male splines 4B of the rotary shaft 4. One end of the cylinder block 5, i.e., the left end facing the swash plate 10, is provided with a small-diameter end 5B that is smaller in diameter than the other portions. A retainer guide 13 is inserted into the small-diameter end 5B.

[0016] The cylinder block 5 has a plurality of cylinders 6 that are circumferentially spaced apart and extend in the axial direction. Each cylinder 6 of the cylinder block 5 is formed with a cylinder port 6A that intermittently communicates with an intake port 8A and a discharge port 8B of the valve plate 8. The cylinder port 6A opens to a first sliding contact surface 5C that comes into sliding contact with the valve plate 8. The first sliding contact surface 5C is a concave spherical surface that comes into sliding contact with a second sliding contact surface 8C of the valve plate 8.

[0017] The multiple pistons 7 are inserted and fitted so as to be able to reciprocate (slide) within each cylinder 6 of the cylinder block 5. As the cylinder block 5 rotates, the pistons 7 reciprocate within the cylinder 6 between top dead center and bottom dead center, repeating intake and discharge strokes. Therefore, the pressure within each cylinder 6, which is connected to the high-pressure discharge port 8B, acts on the swash plate 10 via the pistons 7.

[0018] The piston 7 is formed as a cylindrical (or columnar) rod (rod body) overall. The tip end (right end in FIG. 1) of the piston 7 forms a flat surface 7A. Meanwhile, the base end (left end in FIG. 1) of the piston 7 forms a spherical recess 7B to which the spherical portion 9A of the shoe 9 is attached. The piston 7 is provided with an oil supply hole 7C that extends axially between the flat surface 7A and the spherical recess 7B. The engagement portion between the spherical portion 9A of the shoe 9 and the spherical recess 7B of the piston 7, as well as the sliding portion between the shoe 9 and the swash plate 10, are lubricated by hydraulic oil supplied through the oil supply hole 7C.

[0019] The valve plate 8 is located inside the casing 2 and fixed to the other-side closing part 2C. That is, the valve plate 8 is provided between the side surface of the other-side closing part 2C, which is the inner surface of the casing 2, and the cylinder block 5. The valve plate 8 supports the cylinder block 5, which rotates integrally with the rotary shaft 4, so that the valve plate 8 can rotate together with the casing 2. In this state, the valve plate 8 is in sliding contact with the end face of the cylinder block 5. That is, the valve plate 8 has a second sliding contact surface 8C that is in sliding contact with the cylinder block 5. The second sliding contact surface 8C is a convex spherical surface and is in sliding contact with the first sliding contact surface 5C of the cylinder block 5.

[0020] The valve plate 8 is formed with a pair of eyebrow-shaped supply and discharge ports, i.e., a suction port 8A and a discharge port 8B. That is, the suction port 8A and the discharge port 8B open on the second sliding contact surface 8C. The suction port 8A communicates with the inlet passage 3A of the casing 2 (the other-side closing portion 2C). The discharge port 8B communicates with the outlet passage 3B of the casing 2 (the other-side closing portion 2C). The suction port 8A and the discharge port 8B of the valve plate 8 intermittently communicate with the cylinder ports 6A of each cylinder 6 as the cylinder block 5 rotates. During this time, the pistons 7 reciprocating within each cylinder 6 draw hydraulic oil into each cylinder 6 from the inlet passage 3A through the suction port 8A during their suction stroke. During their discharge stroke, the pressurized oil in each cylinder 6 is discharged to the outlet passage 3B through the discharge port 8B.

[0021] A plurality of shoes 9 are attached to the protruding ends of the pistons 7 protruding from the cylinders 6 so as to be able to swing. Each shoe 9 has a spherical portion 9A that forms a spherical bearing, and the spherical portion 9A of each shoe 9 is attached to the spherical recess 7B of the piston 7. The shoes 9 are pressed against the smooth surface 10A of the swash plate 10 by the pressing force (hydraulic force) from the pistons 7 and are held in this state via a retainer 12 or the like. In this state, each shoe 9 rotates together with the rotating shaft 4, cylinder block 5, and pistons 7, sliding and displacing on the smooth surface 10A of the swash plate 10 to trace a ring-shaped circular locus.

[0022] The swash plate 10 is tiltably mounted within the casing 2 via a cradle 11. The front surface of the swash plate 10 is a smooth surface 10A that slidably guides each shoe 9. On the other hand, the rear surface of the swash plate 10 is tiltably supported by the cradle 11 on the casing 2 side. For this purpose, the rear surface of the swash plate 10 is provided with a pair of left and right swash plate sliding surfaces (not shown) that protrude convexly toward the cradle sliding surface (not shown) of the cradle 11.

[0023] The swash plate 10 has sliding surfaces spaced apart from each other across the rotary shaft 4, and is slidably inserted into the cradle sliding surface of the cradle 11. The swash plate 10 has a through-hole 10B extending through its thickness. The through-hole 10B is located between the sliding surfaces of the swash plate, and the rotary shaft 4 is inserted through the through-hole 10B with a gap therebetween. The swash plate 10 is tilted in the directions of arrows A and B shown in FIG. 1 by a tilt actuator 15. The discharge capacity (flow rate of pressure oil discharged) of the hydraulic pump 1 is variably controlled according to the tilt angle of the swash plate 10.

[0024] The cradle 11 is located around the rotating shaft 4 and fixed to the casing 2 (more specifically, the one-side closing portion 2B). The cradle 11 serves as a swash plate support (swash plate support) for the casing 2. The cradle 11 supports the swash plate 10 so that it can tilt (slide) in the directions indicated by arrows A and B in FIG. 1. The cradle 11 has a shaft insertion hole 11A through which the rotating shaft 4 is inserted. The rotating shaft 4 is rotatably supported within the shaft insertion hole 11A via a bearing 16. The cradle 11 is integrally formed with a pair of cradle sliding surfaces on the left and right sides of the shaft insertion hole 11A (i.e., the rotating shaft 4). The cradle sliding surfaces of the cradle 11 support the swash plate 10 so that it can tilt.

[0025] The retainer 12 is positioned between the protruding end of each piston 7 and each shoe 9, and the rotating shaft 4 is inserted through it. The retainer 12 abuts each shoe 9 against the smooth surface 10A of the swash plate 10. The retainer 12 is an annular plate as a whole, and has a through hole 12A formed in the center. The inner circumferential surface 12B of the through hole 12A is formed, for example, in a concave spherical or tapered shape. The inner circumferential surface 12B of the retainer 12 abuts against the outer circumferential surface 13A of a retainer guide 13, which is inserted onto the rotating shaft 4.

[0026] The retainer 12 holds each shoe 9 relative to the swash plate 10. To this end, the retainer 12 has a plurality of retaining holes 12C spaced apart in the circumferential direction for holding each shoe 9. The retainer 12 presses and holds each shoe 9 against the smooth surface 10A of the swash plate 10, thereby compensating for the sliding displacement of each shoe 9 along a circular path on the smooth surface 10A of the swash plate 10. In this case, the retainer 12 is biased toward the swash plate 10 (smooth surface 10A) by a spring 14 via a retainer guide 13.

[0027] The retainer guide 13 is provided between the retainer 12 and the cylinder block 5. That is, the retainer guide 13 is positioned between the cylinder block 5 and the retainer 12 and is inserted onto the rotary shaft 4. The outer peripheral surface 13A of the retainer guide 13 is formed into a convex spherical shape. The inner peripheral surface 12B of the retainer 12 abuts against the outer peripheral surface 13A of the retainer guide 13. The outer peripheral surface 13A of the retainer guide 13 presses the retainer 12 toward the swash plate 10. The retainer guide 13 has a flange portion 13B with which the spring 14 abuts.

[0028] The spring 14 is provided between the retainer guide 13 and the cylinder block 5. The spring 14 is inserted into a spring hole 5D provided in the cylinder block 5. The retainer guide 13 constantly presses the retainer 12 toward the swash plate 10 by the spring force of the spring 14. In other words, the spring 14 applies an elastic force between the cylinder block 5 (bottom surface of the spring hole 5D) and the retainer guide 13 (flange portion 13B) to the retainer guide 13 and the cylinder block 5 in directions that move them away from each other.

[0029] The tilt actuator 15 drives the swash plate 10 to tilt. The tilt actuator 15 is provided in the casing 2. The tilt actuator 15 includes, for example, a cylinder and a piston (neither of which are shown). The piston of the tilt actuator 15 is connected to the swash plate 10 via a connecting pin 15A fixed to the piston and a tilt lever 10C provided on the swash plate 10. The tilt actuator 15 drives the swash plate 10 to tilt in the directions of arrows A and B using the piston.

[0030] That is, a tilt control pressure is supplied from the outside to a hydraulic chamber (not shown) between the cylinder and piston of the tilt actuator 15. When the piston of the tilt actuator 15 is displaced axially to one side (left side in FIG. 1), the swash plate 10 is tilted in the direction of arrow A (i.e., in the direction that decreases the tilt angle) by this tilt control pressure. On the other hand, when the piston of the tilt actuator 15 is displaced axially to the other side (right side in FIG. 1), the swash plate 10 is tilted in the direction of arrow B (i.e., in the direction that increases the tilt angle).

[0031] In the hydraulic rotary machine of Patent Document 1, when the cylinder block is tilted relative to the valve plate, a small gap between the cylinder block and the valve plate reduces the contact pressure between the cylinder block and the valve plate. However, because a small gap is provided between the outer peripheral edge of the sliding surface of the cylinder block and the outer peripheral edge of the sliding surface of the valve plate, the flow rate (leakage flow rate) of hydraulic oil leaking from between the cylinder block and the valve plate may increase. That is, in the hydraulic rotary machine of Patent Document 1, the radius of curvature of the sliding surface of the cylinder block is made larger than the radius of curvature of the sliding surface of the valve plate to provide the small gap. This hydraulic rotary machine of Patent Document 1 may have a larger leakage flow rate than a configuration in which the radius of curvature of the sliding surface of the cylinder block and the radius of curvature of the sliding surface of the valve plate are closer (for example, a configuration in which the radii of curvature are the same).

[0032] Furthermore, the hydraulic rotating machine of Patent Document 2 also has shallow grooves on the sliding contact surface, which may increase the leakage flow rate of hydraulic oil. That is, the hydraulic rotating machine of Patent Document 2 may also have a higher leakage flow rate compared to a configuration in which the radius of curvature of the sliding contact surface of the cylinder block and the radius of curvature of the sliding contact surface of the valve plate are closer (e.g., the radii of curvature are identical). On the other hand, if the radius of curvature of the sliding contact surface of the cylinder block and the radius of curvature of the sliding contact surface of the valve plate are closer (e.g., identical), the leakage flow rate can be reduced. However, if this is left as is, the contact surface pressure between the cylinder block and the valve plate may increase when uneven contact occurs between the cylinder block and the valve plate. This increased surface pressure may then lead to excessive wear and seizure.

[0033] Therefore, in the embodiment, the radius of curvature of the sliding surface of the cylinder block and the radius of curvature of the sliding surface of the valve plate are made closer (for example, the spherical diameters of the sliding surfaces are made the same), and a tapered surface at a slight angle to the spherical surface is provided on the outer periphery, inner periphery, or both the outer periphery and inner periphery adjacent to the sealing surface (sliding surface) of the valve plate. As a result, when uneven contact occurs between the cylinder block and the valve plate, i.e., when the cylinder block comes into contact with the edge of the valve plate, the tapered surface can increase the contact area and reduce the contact pressure. In other words, in the embodiment, by providing a continuous tapered surface on the sealing surface (sliding surface) of the valve plate, the contact area near the edge of the sealing surface is increased and the contact pressure is reduced. These points will be explained in detail below.

[0034] As shown in Figure 1, hydraulic pump 1, which is an axial piston type hydraulic rotary machine, includes a cylinder block 5, multiple pistons 7, and a valve plate 8. The cylinder block 5 has multiple cylinders 6 that are circumferentially spaced apart and extend in the axial direction, and an annular first sliding surface 5C on which cylinder ports 6A of each of the multiple cylinders 6 open. The multiple pistons 7 are respectively inserted into the multiple cylinders 6 of the cylinder block 5 so as to be able to reciprocate. Ends of each of the multiple pistons 7 slide against a swash plate 10 via shoes 9. In other words, the hydraulic pump 1 is a swash plate type hydraulic pump that includes the swash plate 10.

[0035] The valve plate 8 has an annular second sliding contact surface 8C that is in sliding contact with the first sliding contact surface 5C of the cylinder block 5, and suction ports 8A and discharge ports 8B that open to the second sliding contact surface 8C and intermittently communicate with the multiple cylinders 6 via cylinder ports 6A. The first sliding contact surface 5C of the cylinder block 5 is a concave spherical surface. The second sliding contact surface 8C of the valve plate 8 is a convex spherical surface. The radius of curvature of the concave spherical surface of the first sliding contact surface 5C and the radius of curvature of the convex spherical surface of the second sliding contact surface 8C are the same.

[0036] Note that "matching" includes not only perfect matching but also "substantially matching." That is, "matching" includes the case where the radius of curvature of the first sliding contact surface 5C and the radius of curvature of the second sliding contact surface 8C are slightly different due to, for example, manufacturing errors, processing errors, etc. That is, "matching" includes unavoidable deviations due to manufacturing errors, processing errors, etc. Furthermore, "matching" also includes the case where the deviation is within a range that can suppress the flow rate (leakage flow rate) of hydraulic oil leaking from between the first sliding contact surface 5C and the second sliding contact surface 8C, in other words, the deviation is within a range that can limit the leakage flow rate to a desired level. Note that the first sliding contact surface 5C and the second sliding contact surface 8C may be flat.

[0037] Here, Figure 9 exaggerates the state in which the cylinder block 5 is tilted with respect to the valve plate 8. Note that Figures 9 to 11 are reference examples. That is, the valve plate 8 in Figures 9 to 11 does not have tapered surfaces 21, 22 (the tapered surfaces 21, 22 shown in Figures 2 to 8) described below. The cylinder block 5 may be tilted and eccentric with respect to the valve plate 8, for example, based on the gap between the bearings 16, 16 that hold the rotating shaft 4. In addition, the cylinder block 5 may be tilted and eccentric with respect to the valve plate 8, for example, based on the gap between the spline coupling portion (male spline 4B, female spline 5A) between the cylinder block 5 and the rotating shaft 4.

[0038] Furthermore, the cylinder block 5 may become tilted or eccentric with respect to the valve plate 8, for example, due to deflection of the rotary shaft 4. Furthermore, since the cylinder block 5 is pressed against and supported by the axial elastic force (spring force) of the spring 14, it may also move away (float) from the valve plate 8. As a result, as shown in Figure 9, the cylinder block 5 may become tilted or eccentric with respect to the valve plate 8. The arrow in Figure 9 indicates the direction in which the cylinder block 5 moves relative to the valve plate 8.

[0039] If the cylinder block 5 is tilted or eccentric relative to the valve plate 8, uneven contact may occur at the outer peripheral edge of the second sliding contact surface 8C of the valve plate 8, as indicated by the black dots in FIG. 10 . That is, the outer peripheral edge of the second sliding contact surface 8C of the valve plate 8 may come into uneven contact with the first sliding contact surface 5C of the cylinder block 5, which is the mating member. This increases the contact pressure between the cylinder block 5 and the valve plate 8, which may result in excessive wear and seizure. On the other hand, FIG. 11 shows a state in which the cylinder block 5 is not tilted relative to the valve plate 8. As indicated by the black dots in FIG. 11 , if the cylinder block 5 is not tilted relative to the valve plate 8, uneven contact may occur at the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8 due to the slight difference in spherical diameter between the first sliding contact surface 5C and the second sliding contact surface 8C. That is, the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8 may come into uneven contact with the first sliding contact surface 5C of the cylinder block 5, which is the mating member. This may increase the contact surface pressure between the cylinder block 5 and the valve plate 8.

[0040] In contrast, in this embodiment, as shown in FIGS. 2 to 6, annular tapered surfaces 21, 22 are provided on both the outer and inner peripheral edges of the second sliding contact surface 8C of the valve plate 8. The tapered surfaces 21, 22 incline in a direction away from the cylinder block 5, which is the mating member, as the distance from the outer peripheral edge increases. That is, as shown in FIGS. 2 to 6, an annular outer diameter side tapered surface 21 is provided on the outer peripheral edge of the second sliding contact surface 8C of the valve plate 8. The outer diameter side tapered surface 21 is connected to the outer peripheral edge of the second sliding contact surface 8C over the entire circumference. The outer diameter side tapered surface 21 inclines in a direction away from the cylinder block 5 with which the outer peripheral edge slides, as the distance from the outer peripheral edge of the second sliding contact surface 8C increases radially outward. In this way, in this embodiment, the outer diameter side tapered surface 21 extending radially outward from the outer peripheral edge is provided on the outer peripheral edge of the second sliding contact surface 8C. Therefore, even if the outer peripheral edge of the second sliding contact surface 8C of the valve plate 8 comes into contact with the inclined or eccentric cylinder block 5, the first sliding contact surface 5C of the cylinder block 5 comes into contact with the outer diameter side tapered surface 21. This increases the contact area and reduces the contact surface pressure.

[0041] As shown in FIGS. 2, 3, and 6, an annular inner diameter tapered surface 22 is provided on the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8. The inner diameter tapered surface 22 is connected to the inner peripheral edge of the second sliding contact surface 8C along the entire circumference. The inner diameter tapered surface 22 is inclined in a direction away from the cylinder block 5 with which the inner peripheral edge slides, as the inner diameter tapered surface 22 moves radially inward from the inner peripheral edge of the second sliding contact surface 8C. Thus, in this embodiment, the inner diameter tapered surface 22 extends radially inward from the inner peripheral edge of the second sliding contact surface 8C. Therefore, even if a partial contact occurs at the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8 due to a slight difference in spherical diameter between the first sliding contact surface 5C and the second sliding contact surface 8C, the first sliding contact surface 5C of the cylinder block 5 will contact the inner diameter tapered surface 22. This increases the contact area and reduces the contact pressure.

[0042] 3 to 5, the angle α (inclination angle α) of the outer diameter side tapered surface 21 is regulated as follows. That is, as shown in Fig. 5, at the peripheral edge that forms the boundary between the outer diameter side tapered surface 21 and the second sliding contact surface 8C connected to this outer diameter side tapered surface 21 (i.e., the outer peripheral edge of the second sliding contact surface 8C and the inner peripheral edge of the outer diameter side tapered surface 21), an imaginary line that is tangent to the second sliding contact surface 8C and extends in the radial direction of the second sliding contact surface 8C is defined as an imaginary tangent line K. The dashed line in Fig. 5 is an extension line L of the tapered surface that extends from the outer peripheral edge of the outer diameter side tapered surface 21 at the same angle as this outer diameter side tapered surface 21. The dashed line in Fig. 5 is an extension line M of the sliding contact surface that extends from the outer peripheral edge of the second sliding contact surface 8C with the same curvature as this second sliding contact surface 8C. 5 is an imaginary tangent K that contacts the second sliding contact surface 8C at the outer circumferential edge of the second sliding contact surface 8C. In this case, the angle α (inclination angle α) formed between the imaginary tangent K and the outer diameter side tapered surface 21 is 10° or less (α≦10°), preferably 7° or less (α≦7°), and more preferably 5° or less (α≦5°).

[0043] The angle α between the imaginary tangent K and the outer diameter side tapered surface 21 is A -S A is the central axis S of the valve plate 8 B -S B9, the angle β is set to be larger than the maximum angle βmax of the inclination relative to the central axis S of the cylinder block 5. A -S A is the central axis S of the valve plate 8 B -S B The angle of inclination relative to the imaginary tangent K is defined as β. The maximum angle of this angle β is defined as βmax. In this case, the angle α formed by the imaginary tangent K and the outer diameter side tapered surface 21 is set to be larger than the maximum angle βmax (βmax<α). The maximum angle βmax is, for example, about 1° (less than 1°). Although not shown in the drawings, the angle (inclination angle) of the inner diameter side tapered surface 22 can also be set in the same way as the angle α (inclination angle α) formed by the outer diameter side tapered surface 21.

[0044] The outer diameter side tapered surface 21 and the inner diameter side tapered surface 22 are both conical surfaces and are separate from the second sliding contact surface 8C, which is a spherical surface. In other words, the outer diameter side tapered surface 21 and the inner diameter side tapered surface 22 are in contact with the second sliding contact surface 8C, but the second sliding contact surface 8C is provided in a separate position. The radial lengths (widths) of the outer diameter side tapered surface 21 and the inner diameter side tapered surface 22 are not particularly specified. The radial lengths (widths) of the outer diameter side tapered surface 21 and the inner diameter side tapered surface 22 may be short (for example, approximately 1 mm). The radial lengths (widths) of the outer diameter side tapered surface 21 and the inner diameter side tapered surface 22 can be set, for example, taking into consideration ease of processing, etc.

[0045] As described above, according to the embodiment, the hydraulic pump 1 includes the rotating shaft 4 serving as the shaft, the swash plate 10, the cylinder block 5 serving as the rotor, the valve plate 8 serving as the valve plate, the pistons 7, the shoes 9, the springs 14, the retainer guides 13 serving as bushings, the retainer 12, and the casing 2. The rotational power of the prime mover is transmitted to the rotating shaft 4 and then to the cylinder block 5. The cylinder block 5 is provided with a plurality of cylinders 6, and the pistons 7 are inserted into the cylinders 6 in a state in which they are movable in the axial direction.

[0046] The pistons 7 are connected to shoes 9 via ball joints. The shoes 9 are pressed against a swash plate 10 by the force of springs 14 via retainer guides 13 and retainers 12. The swash plate 10 forms a plane at an angle with respect to the central axis of rotation of the rotary shaft 4. The shoes 9 move along the plane of the swash plate 10 (smooth surface 10A). In other words, when the cylinder block 5 rotates, the pistons 7 reciprocate within the cylinders 6. The cylinder block 5 is also pressed against a valve plate 8 by the force of springs 14.

[0047] The volume inside the cylinder 6 changes with the reciprocating motion of the piston 7. At this time, hydraulic oil is sucked into the cylinder 6 through the suction port 8A of the valve plate 8, and is discharged from the cylinder 6 through the discharge port 8B of the valve plate 8. Through this series of operations, the hydraulic pump 1 sucks in and discharges hydraulic oil. While the hydraulic pump 1 is operating, the pressure inside the cylinder 6 increases along with the discharge pressure. This generates hydraulic thrust on the bottom surface of the piston 7. The hydraulic thrust is transmitted from the piston 7 to the swash plate 10 via the shoe 9.

[0048] Here, because the swash plate 10 is tilted relative to the direction of the hydraulic thrust, a radial force (lateral force) is generated. The radial force is transmitted from the shoes 9 via the pistons 7 to the cylinder block 5, tending to tilt the cylinder block 5. Furthermore, because the pressure inside the cylinder 6 differs between the suction side and the discharge side, the resultant force of the hydraulic thrust acting on the bottom surface of the cylinder 6 acts closer to the high-pressure port than the center of the rotary shaft 4. This resultant force of the hydraulic thrust also acts to tilt the cylinder block 5.

[0049] If the contact surface between the cylinder block 5 and the valve plate 8 were flat, tilting the cylinder block 5 would widen the gap on one side, increasing leakage flow. In addition, the cylinder block 5 would come into uneven contact with the outer periphery of the valve plate 8, resulting in significant wear and seizure. To prevent this uneven contact due to tilting the cylinder block 5, the contact surface (sliding surface) between the cylinder block 5 and the valve plate 8 is generally spherical, providing self-alignment. However, in an actual cylinder block 5, eccentricity occurs due to deflection of the rotating shaft 4, gaps between the various components, and the like. Therefore, even if the contact surface (sliding surface) between the cylinder block 5 and the valve plate 8 is spherical, there is a possibility that it will not be fully aligned and uneven contact will occur.

[0050] If the pressure inside the cylinder 6 is low or if the tilt angle of the swash plate 10 is small, the radial force (lateral force) described above will be small, and the thrust load will become dominant. The spherical contact area between the cylinder block 5 and the valve plate 8 is designed so that the spherical diameter on the valve plate 8 side is slightly smaller to prevent uneven contact on the outer periphery. However, in this case, uneven contact will mechanically occur on the inside of the valve plate 8 even if the cylinder block 5 is not tilted.

[0051] The contact surface between the cylinder block 5 and the valve plate 8 is designed based on the balance ratio between the hydraulic thrust acting on the bottom surface of the cylinder of the cylinder block 5 in a direction pressing the cylinder block 5 against the valve plate 8, and the hydraulic thrust acting on the gap between the valve plate 8 and the cylinder block 5 in a direction separating the cylinder block 5 and the valve plate 8. When the balance ratio is calculated as the separating force / pressing force, the balance ratio is designed to be less than 1 to prevent the cylinder block 5 from floating too far above the valve plate 8 and thereby failing to function as a pump / motor. Each thrust can be calculated from the applied pressure and pressure-receiving area, but because the pressure acting inside the cylinder 6 and the pressure acting at the entrance to the gap between the cylinder block 5 and the valve plate 8 (around the suction port 8A and discharge port 8B) are the same, the balance ratio can also be calculated from the ratio of the pressure-receiving areas.

[0052] An example of how to calculate the balance ratio is explained below. The method for calculating the balance ratio is described, for example, in "(b) Between the cylinder block and the valve plate" under "Basic calculation formulas for hydraulic balance" on page 159 of "Practical Hydraulics Pocket Book (2020 edition), published by the Japan Fluid Power Industry Association." For example, it is as follows:

[0053] As shown in FIG. 13, the inner diameter of the inner contact surface of the valve plate 8, which is a valve, is defined as "R1", the outer diameter of the inner contact surface is defined as "R2", the inner diameter of the outer contact surface is defined as "R3", and the outer diameter of the outer contact surface is defined as "R4". In addition, the pressing force that presses the cylinder block 5, which is a rotor, against the valve plate 8 is defined as "F p " and the pressure-receiving area on the cylinder block 5 side is "A p ” and the opening force between the cylinder block 5 and the valve plate 8 is “F b " and the pressure-receiving area on the valve plate 8 side is "A b ", the pressure inside the cylinder is "P", the cylinder diameter is "d", and the number of high-pressure cylinders is "z". Then, the balance ratio (hydraulic thrust ratio) is "η", and the balance ratio (area ratio) is "η3".

[0054] In this case, the pressing force F p is expressed as the following equation.

[0055]

number

[0056] The pressure receiving area Ap on the cylinder block 5 side is given by the following formula 2.

[0057]

number

[0058] The opening force F between the cylinder block 5 and the valve plate 8 b is expressed as the following equation 3.

[0059]

number

[0060] Pressure-receiving area A on the valve plate 8 side b is expressed as the following equation 4.

[0061]

number

[0062] The balance ratio (hydraulic thrust ratio) η is expressed by the following equation (5).

[0063]

number

[0064] The balance ratio (area ratio) η3 is given by the following equation (6).

[0065]

number

[0066] A reference value for the balance ratio η3 is "η3 = 0.95 to 0.98." If the balance ratio η3 is 1 or more, the cylinder block 5 will rise significantly above the valve plate 8, and may not function as a pump.

[0067] Although the above explanation uses a swash plate type hydraulic pump as an example, similar uneven contact can occur in a swash plate type hydraulic motor, in which the input power and output power are reversed compared to a hydraulic pump. Furthermore, similar uneven contact can occur in a bent-axis type hydraulic pump or hydraulic motor, in which the volume inside the cylinder is changed by tilting the cylinder block relative to the rotation axis, rather than using a swash plate.

[0068] In contrast, according to the embodiment, the second sliding contact surface 8C of the valve plate 8 has an outer diameter side tapered surface 21 and an inner diameter side tapered surface 22 that are slightly angled on the outer and inner circumferences. Therefore, even if uneven contact occurs between the cylinder block 5 and the valve plate 8, the tapered surfaces 21 and 22 near the boundary with the second sliding contact surface 8C also come into contact with the first sliding contact surface 5C of the cylinder block 5. This increases the contact area and reduces the contact surface pressure. This reduces the risk of excessive wear and seizure due to uneven contact between the cylinder block 5 and the valve plate 8.

[0069] FIG. 12 shows a comparison of the measurement results of pump efficiency with and without tapered surfaces 21, 22. That is, FIG. 12 shows the difference in pump efficiency (efficiency difference) between "an embodiment having tapered surfaces 21, 22 on both the outer peripheral edge and the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8" and "a reference example having no tapered surfaces." As is clear from FIG. 12, the embodiment having tapered surfaces 21, 22 has improved pump efficiency compared to the reference example having no tapered surfaces. That is, since the embodiment has improved pump efficiency compared to the reference example, it is thought that providing tapered surfaces 21, 22 reduces contact surface pressure, thereby reducing sliding resistance (sliding resistance) and friction loss.

[0070] Although not shown, even when a tapered surface is provided on either the outer peripheral edge or the inner peripheral edge of the second sliding contact surface of the valve plate, the pump efficiency can be improved compared to the reference example without a tapered surface. The best effect (improved pump efficiency) can be obtained when tapered surfaces 21, 22 are provided on both the outer peripheral edge and the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8.

[0071] The hydraulic pump 1 according to the embodiment has the above-described configuration, and its operation will now be described.

[0072] The hydraulic pump 1 converts the rotational motion of the rotating shaft 4 (cylinder block 5) into the motion of oil. When the rotating shaft 4 is driven to rotate by a prime mover such as an engine, the cylinder block 5 rotates integrally with the rotating shaft 4 within the casing 2. This causes multiple shoes 9 to slide and displace along the surface (smooth surface 10A) of the swash plate 10, tracing a ring-shaped trajectory, and in response, each piston 7 repeatedly reciprocates within each cylinder 6.

[0073] During one rotation of the cylinder block 5, each piston 7 repeatedly undergoes an intake stroke in which it slides from top dead center to bottom dead center within the cylinder 6, and a discharge stroke in which it slides from bottom dead center to top dead center. During the intake stroke of the piston 7, for example, hydraulic oil is drawn into the cylinder 6 from the inlet passage 3A side through the intake port 8A of the valve plate 8 and the cylinder port 6A. During the discharge stroke of the piston 7, the piston 7 converts the hydraulic fluid in each cylinder 6 into high-pressure oil and discharges it from the outlet passage 3B side through the cylinder port 6A and the discharge port 8B of the valve plate 8.

[0074] According to this embodiment, the outer and inner peripheral edges of the second sliding contact surface 8C of the valve plate 8 are provided with outer diameter side tapered surfaces 21 and inner diameter side tapered surfaces 22 that slope in a direction away from the mating member, the cylinder block 5, the further radially away from the peripheral edges. Therefore, even if the outer or inner peripheral edge of the second sliding contact surface 8C comes into uneven contact with the first sliding contact surface 5C of the cylinder block 5, the first sliding contact surface 5C comes into contact with the tapered surfaces 21, 22, thereby increasing the contact area. This reduces the contact surface pressure and reduces excessive wear and seizure caused by uneven contact between the cylinder block 5 and the valve plate 8.

[0075] Furthermore, even if there is no minute gap between the first sliding contact surface 5C of the cylinder block 5 and the second sliding contact surface 8C of the valve plate 8, i.e., even if the radii of curvature of the first sliding contact surface 5C and the second sliding contact surface 8C are made close to each other, the first sliding contact surface 5C will come into contact with the tapered surfaces 21 and 22 when partial contact occurs. This increases the contact area and reduces the contact surface pressure. This makes it possible to achieve both a reduction in leakage flow rate and a reduction in contact surface pressure.

[0076] According to the embodiment, the angle α formed by the imaginary tangent K at the boundary between the second sliding contact surface 8C and the tapered surfaces 21, 22 and the tapered surfaces 21, 22 is 10° or less (preferably 7° or less, more preferably 5° or less). Therefore, the gently inclined tapered surfaces 21, 22 can ensure a sufficient contact area between the tapered surfaces 21, 22 and the first sliding contact surface 5C when partial contact occurs, and can reduce the contact surface pressure. Note that if the angle α formed by the imaginary tangent K and the tapered surfaces 21, 22 is greater than 10°, the contact surface pressure increases, and it may not be possible to fully achieve the effect of reducing the surface pressure.

[0077] According to the embodiment, the angle α formed by the imaginary tangent K of the boundary between the second sliding contact surface 8C and the tapered surfaces 21, 2 ... is the angle α between the central axis S of the cylinder block 5 and the imaginary tangent K of the boundary between the second sliding contact surface 8C and the tapered surfaces 21, 22. A -S A is the central axis S of the valve plate 8 B -S B Therefore, the central axis S of the cylinder block 5 is larger than the maximum angle βmax of inclination relative to A -S A is the central axis S of the valve plate 8 B -S B When the imaginary tangent K is inclined relative to the tapered surface 21, the first sliding contact surface 5C can be prevented from contacting the outer peripheral edge of the outer diameter side tapered surface 21. When the angle α between the imaginary tangent K and the tapered surfaces 21, 22 is equal to or smaller than the maximum angle βmax, the first sliding contact surface 5C can be prevented from contacting the outer peripheral edge of the outer diameter side tapered surface 21. A -S A is the central axis S of the valve plate 8 B -S B When the outer diameter side tapered surface 21 is inclined relative to the outer diameter side tapered surface 21, the first sliding contact surface 5C may come into contact with the outer peripheral edge of the outer diameter side tapered surface 21. This may increase the contact surface pressure, making it impossible to fully obtain the effect of reducing the surface pressure.

[0078] According to this embodiment, the radius of curvature of the first sliding contact surface 5C, which is a concave spherical surface, is the same as the radius of curvature of the second sliding contact surface 8C, which is a convex spherical surface. This makes it possible to reduce the gap between the first sliding contact surface 5C of the cylinder block 5 and the second sliding contact surface 8C of the valve plate 8. In other words, it is possible to reduce the gap between the sealing surfaces of the cylinder block 5 and the valve plate 8. This makes it possible to reduce the amount of hydraulic oil leaking from between the cylinder block 5 and the valve plate 8 (leakage flow rate).

[0079] According to this embodiment, the ends of the pistons 7 slide on the swash plate 10 via the shoes 9. Therefore, the swash plate type hydraulic pump 1 can achieve both a reduction in leakage flow rate and a reduction in contact surface pressure.

[0080] In the embodiment, the tapered surfaces 21, 22 are provided on both the outer and inner peripheral edges of the second sliding contact surface 8C of the valve plate 8. However, the present invention is not limited to this. For example, as in a first modified example shown in FIG. 7, the tapered surface 22 may be provided on the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8, but no tapered surface may be provided on the outer peripheral edge of the second sliding contact surface 8C of the valve plate 8. In this manner, in the first modified example, the inner diameter-side tapered surface 22 is provided on the inner peripheral edge of the second sliding contact surface 8C. In this case, even if a partial contact occurs on the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8 due to a slight difference in spherical diameter between the first sliding contact surface 5C and the second sliding contact surface 8C, the first sliding contact surface 5C of the cylinder block 5 contacts the inner diameter-side tapered surface 22. This increases the contact area and reduces the contact surface pressure.

[0081] In the embodiment, the case where the tapered surfaces 21, 22 are provided on both the outer and inner peripheral edges of the second sliding contact surface 8C of the valve plate 8 has been described as an example. However, this is not limiting. For example, as in a second modified example shown in FIG. 8 , the tapered surface 21 may be provided on the outer peripheral edge of the second sliding contact surface 8C of the valve plate 8, but the inner peripheral edge of the second sliding contact surface 8C of the valve plate 8 may not be provided with a tapered surface. In this way, in the second modified example, the outer diameter side tapered surface 21 is provided on the outer peripheral edge of the second sliding contact surface 8C. In this case, even if the outer peripheral edge of the second sliding contact surface 8C of the valve plate 8 comes into contact with the outer diameter side tapered surface 21 due to tilt or eccentricity of the cylinder block 5, the first sliding contact surface 5C of the cylinder block 5 will contact the outer diameter side tapered surface 21. This increases the contact area and reduces the contact surface pressure.

[0082] In the embodiment, the case where the tapered surfaces 21, 22 are provided on the periphery of the second sliding contact surface 8C of the valve plate 8 has been described as an example. However, this is not limiting, and for example, a tapered surface may be provided on the periphery of the first sliding contact surface of the cylinder block. Also, tapered surfaces may be provided on both the outer peripheral edge and the inner peripheral edge of the first sliding contact surface, or on one of the outer peripheral edge and the inner peripheral edge of the first sliding contact surface. Furthermore, tapered surfaces may be provided on both the periphery of the first sliding contact surface and the periphery of the second sliding contact surface, or on one of the periphery of the first sliding contact surface and the periphery of the second sliding contact surface. Furthermore, the angle formed by the tapered surface and the imaginary tangent of the tapered surface provided on the periphery of the first sliding contact surface can be set in the same way as the tapered surfaces 21, 22 provided on the periphery of the second sliding contact surface 8C.

[0083] In summary, the tapered surface can be provided on at least one of the outer peripheral edge and inner peripheral edge of the first sliding contact surface and the outer peripheral edge and inner peripheral edge of the second sliding contact surface. The tapered surface can be connected to the peripheral edge over the entire circumference and inclined in a direction away from the counter member with which the peripheral edge slides, as it moves away from the peripheral edge in the radial direction. In other words, at least one of the outer peripheral edge and inner peripheral edge of the first sliding contact surface and the outer peripheral edge and inner peripheral edge of the second sliding contact surface is provided with an annular tapered surface that is connected to the peripheral edge over the entire circumference and inclined in a direction away from the counter member with which the peripheral edge slides, as it moves away from the peripheral edge in the radial direction.

[0084] With this configuration, even if the peripheral edge of the sliding surface provided with the tapered surface comes into contact with the mating member, the contact area between the cylinder block and the valve plate can be increased by the mating member coming into contact with the tapered surface. This reduces the contact pressure between the cylinder block and the valve plate, and reduces excessive wear and seizure caused by the uneven contact between the cylinder block and the valve plate. Furthermore, even without providing a minute gap between the sliding surface of the cylinder block and the sliding surface of the valve plate (for example, by making the radii of curvature of the sliding surface of the cylinder block and the sliding surface of the valve plate closer), when uneven contact occurs, the contact area can be increased by the mating member coming into contact with the tapered surface, thereby reducing the contact pressure. This allows for both a reduction in leakage flow rate and a reduction in contact pressure.

[0085] Furthermore, at the peripheral edge that forms the boundary between the tapered surface and the sliding contact surface connected to this tapered surface, if an imaginary line that is tangent to the sliding contact surface and extends radially from the sliding contact surface is taken as an imaginary tangent, the angle between this imaginary tangent and the tapered surface can be 10° or less. This allows the gently sloping tapered surface to ensure a sufficient contact area between the tapered surface and the sliding contact surface when partial contact occurs, thereby reducing contact surface pressure. Furthermore, the angle between the imaginary tangent and the tapered surface can be greater than the maximum angle of inclination of the central axis of the cylinder block relative to the central axis of the valve plate. This prevents the sliding contact surface from contacting the peripheral edge of the tapered surface when the central axis of the cylinder block is inclined relative to the central axis of the valve plate.

[0086] In the above embodiment, the swash plate 10 is tilted by one tilt actuator 15 via the connecting pin 15A and the tilt lever 15C of the swash plate 10. However, the present invention is not limited to this configuration, and the swash plate may be tilted by two tilt actuators. This also applies to the first and second modifications.

[0087] In the embodiment, the hydraulic pump 1 is described as a single-tilt hydraulic pump in which the swash plate 10 is tilted to one side. However, the present invention is not limited to this, and may be applied to a double-tilt hydraulic pump in which the swash plate is tilted to both sides of the tilt angle of 0. This also applies to the first and second modified examples.

[0088] In the embodiment, a swash plate-type hydraulic pump 1 in which each end of a plurality of pistons 7 slides against a swash plate 10 via shoes 9 has been described as an example. However, the present invention is not limited to this. For example, the present invention may be applied to a bent-axis hydraulic pump in which each end of a plurality of pistons is swingably supported on a drive disk. A bent-axis hydraulic pump may include, for example, a rotating shaft rotatably mounted within a casing and having a drive disk at its tip, a cylinder block that rotates with the rotating shaft, multiple pistons inserted into multiple cylinders of the cylinder block and each having a protruding end swingably supported on the drive disk of the rotating shaft, and a valve plate with which the cylinder block slides. Even in such a bent-axis hydraulic pump, providing a tapered surface on the periphery of the sliding contact surface can both reduce leakage flow and alleviate contact surface pressure. This also applies to the first and second modifications.

[0089] In the embodiment, a variable displacement hydraulic pump 1 in which the tilt angle of the swash plate 10 is variable has been described as an example. However, the present invention is not limited to this, and may be used, for example, in a fixed displacement hydraulic pump in which the tilt angle of the swash plate is constant (fixed). The same applies to a bent-axis hydraulic pump, and may be used regardless of whether it is a variable displacement or fixed displacement type. This also applies to the first and second modified examples.

[0090] In the embodiment, the hydraulic pump 1 that converts the rotational motion of a cylinder block 5 into the motion of oil has been described as an example of a hydraulic rotating machine. However, the present invention is not limited to this, and may be used as other hydraulic rotating machines, such as a hydraulic motor that converts the motion of oil into the rotation of a cylinder block. For example, in the case of a hydraulic motor, hydraulic oil flows into and out of the cylinder block from a hydraulic source such as a hydraulic pump via a valve plate. This causes the pistons to reciprocate along a swash plate, converting the oil motion into the rotational motion of the cylinder block, thereby converting the oil motion into the rotational motion of a rotating shaft. This also applies to the first and second modifications.

[0091] In the embodiment, the hydraulic pump 1 has been described as being applied to a hydraulic excavator. However, the invention is not limited to this, and may be applied to construction machinery other than hydraulic excavators, such as hydraulic cranes and wheel loaders. Furthermore, the invention is not limited to construction machinery, and may be widely applied as an axial piston hydraulic rotating machine used in various machinery, such as hydraulic pumps and hydraulic motors incorporated in industrial machinery and general machinery.

[0092] The above-described embodiment, first modified example, and second modified example are merely examples, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments and modified examples is possible. [Explanation of symbols]

[0093] 1 Hydraulic pump (axial piston type hydraulic rotary machine) 5 Cylinder block 5C 1st sliding surface 6 cylinders 6A cylinder port 7 Pistons 8 Valve plate 8A intake port 8B Discharge port 8C 2nd sliding surface 9. Shoe 10 Swash plate 21 Outer diameter tapered surface (tapered surface) 22 Inner diameter tapered surface (tapered surface) K Virtual tangent

Claims

1. a cylinder block having a plurality of cylinders extending in an axial direction and spaced apart in a circumferential direction, and an annular first sliding surface on which each cylinder port of the plurality of cylinders opens; a plurality of pistons reciprocally inserted into the plurality of cylinders of the cylinder block; a valve plate having an annular second sliding contact surface that is in sliding contact with the first sliding contact surface of the cylinder block, and an intake port and a discharge port that open to the second sliding contact surface and intermittently communicate with the plurality of cylinders via the cylinder ports; In an axial piston type hydraulic rotary machine equipped with At least one of the outer peripheral edge and inner peripheral edge of the first sliding contact surface and the outer peripheral edge and inner peripheral edge of the second sliding contact surface is provided with an annular tapered surface that is connected to the entire circumference of the outer peripheral edge and that is inclined in a direction away from the mating member with which the outer peripheral edge slides as it moves away from the outer peripheral edge in the radial direction. An axial piston type hydraulic rotary machine characterized by:

2. At the periphery that is the boundary between the tapered surface and the sliding surface connected to this tapered surface, when an imaginary line that is in contact with the sliding surface and extends in the radial direction of the sliding surface is defined as an imaginary tangent line, The angle between the virtual tangent and the tapered surface is 10° or less.

2. The axial piston type hydraulic rotary machine according to claim 1, wherein the hydraulic rotary machine comprises:

3. At the periphery that is the boundary between the tapered surface and the sliding surface connected to this tapered surface, when an imaginary line that is in contact with the sliding surface and extends in the radial direction of the sliding surface is defined as an imaginary tangent line, an angle formed by the imaginary tangent line and the tapered surface is larger than a maximum angle of inclination of the central axis of the cylinder block relative to the central axis of the valve plate; 2. The axial piston type hydraulic rotary machine according to claim 1, wherein the hydraulic rotary machine comprises:

4. the first sliding contact surface of the cylinder block is a concave spherical surface, the second sliding contact surface of the valve plate is a convex spherical surface, The radius of curvature of the first sliding contact surface and the radius of curvature of the second sliding contact surface are the same.

2. The axial piston type hydraulic rotary machine according to claim 1, wherein the hydraulic rotary machine comprises:

5. an outer peripheral edge of the second sliding contact surface is provided with an annular outer diameter side tapered surface that is connected to the outer peripheral edge over the entire circumference and that inclines in a direction away from the cylinder block as it moves radially away from the outer peripheral edge; 2. The axial piston type hydraulic rotary machine according to claim 1, wherein the hydraulic rotary machine comprises:

6. The inner peripheral edge of the second sliding contact surface is provided with an annular inner diameter side tapered surface that is connected to the inner peripheral edge over the entire circumference and that inclines in a direction away from the cylinder block as it moves radially away from the inner peripheral edge.

2. The axial piston type hydraulic rotary machine according to claim 1, wherein the hydraulic rotary machine comprises:

7. The ends of the pistons slide against a swash plate via shoes.

2. The axial piston type hydraulic rotary machine according to claim 1, wherein the hydraulic rotary machine comprises:

8. an end of each of the plurality of pistons being supported by a drive disk so as to be able to swing; 2. The axial piston type hydraulic rotary machine according to claim 1, wherein the hydraulic rotary machine comprises:

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