Hydraulic pump/motor

Abstract

An axial-type hydraulic pump/motor in which a cylinder block with a plurality of cylinder bores formed around a rotation axis slides with respect to a valve plate that has a valve plate discharge port and a valve plate suction port, and controls the amount of reciprocation of a piston in each cylinder bore depending on the inclination of a swash plate. Based on the rotational direction of the cylinder block, an opening shape of an end portion on the front side in the rotational direction of a cylinder port and an opening shape of an end portion on the rear side in the rotational direction of the valve plate suction port PB1 have the same shape or partially have the same shape.

Claims

1. A hydraulic pump/motor in which a cylinder block with a plurality of cylinder bores formed around a rotation axis slides with respect to a valve plate including a high-pressure port and a low-pressure port, and which controls an amount of reciprocation of a piston in each of the cylinder bores depending on an inclination of a swash plate, wherein a first opening shape of the high-pressure port and a second opening shape of the low-pressure port extend circumferentially on a same arc centered around the rotation axis and are annular band shapes that do not include a top dead point and a bottom dead point, a third opening shape of a cylinder port in each of the cylinder bores extends circumferentially on a same arc where the high-pressure port and the low-pressure port are disposed, and is an annular band shape that does not communicate with the high-pressure port and the low-pressure port at least when positioned at the top dead point and the bottom dead point, a fourth opening shape of an end portion on a front side of the cylinder port and a fifth opening shape of an end portion of a rear side of the cylinder port with reference to a rotational direction of the cylinder block are circular convex shapes, a sixth opening shape of an end portion on a front side of the high-pressure port and a seventh opening shape of an end portion on a rear side of the high-pressure port in a rotational direction of the high-pressure port, and an eighth opening shape of an end portion on a front side of the low-pressure port in a rotational direction of the low-pressure port are circular convex shapes, a ninth opening shape of an end portion on a rear side of the low-pressure port in the rotational direction of the low-pressure port is a circular concave shape, and the fourth opening shape of the end portion on the front side of the cylinder port in a rotational direction of the cylinder port and the ninth opening shape of the end portion on the rear side of the low-pressure port in the rotational direction of the low-pressure port are a same shape.

2. A hydraulic pump in which a cylinder block with a plurality of cylinder bores formed around a rotation axis slides with respect to a valve plate including a high-pressure port and a low-pressure port, and which controls an amount of reciprocation of a piston in each of the cylinder bores depending on an inclination of a swash plate, wherein a first opening shape of the high-pressure port and a second opening shape of the low-pressure port extend circumferentially on a same arc centered around the rotation axis and are an annular band shape that does not include a top dead point and a bottom dead point, a third opening shape of a cylinder port in each of the cylinder bores extends circumferentially on the same arc where the high-pressure port and the low-pressure port are disposed, and is an annular band shape that does not communicate with the high-pressure port and the low-pressure port at the top dead point and the bottom dead point, a fourth opening shape of an end portion on a front side of the cylinder port and a fifth opening shape of an end portion of a rear side of the cylinder port with reference to a rotational direction of the cylinder block are circular convex shapes, a sixth opening shape of an end portion on a front side of the high-pressure port in a rotational direction of the high-pressure port is a circular concave shape, a seventh opening shape of an end portion on a rear side of the high-pressure port in the rotational direction of the high-pressure port is a circular convex shape, an eighth opening shape of an end portion on a front side of the low-pressure port and a ninth opening shape of an end portion of a rear side of the low-pressure port in a rotational direction of the low-pressure port are circular concave shapes, the fourth opening shape of the end portion on the front side of the cylinder port in a rotational direction of the cylinder port and the ninth opening shape of the end portion on the rear side of the low-pressure port in the rotational direction of the low-pressure port are a same shape, the fifth opening shape of the end portion on the rear side of the cylinder port in the rotational direction of the cylinder port, the eighth opening shape of the end portion on the front side of the low-pressure port in the rotational direction of the low-pressure port, and the sixth opening shape of the end portion on the front side of the high-pressure port in the rotational direction of the high-pressure port are a same shape, the valve plate further includes a residual pressure release port which communicates with each of the cylinder bores after each of the cylinder bores pass the top dead point and before each of the cylinder bores communicate with the low-pressure port, and a first opening portion of the end portion on the rear side of the low-pressure port in the rotational direction of the low-pressure port is separated from the top dead point so as to communicate with a second opening portion of an end portion on the front side of the cylinder port in the rotational direction of the cylinder port after passing a rotation assist region where rotation of the cylinder block is assisted by a pressure oil inside each of the cylinder bores from a top dead point position of the cylinder port and a residual pressure release region where a pressure inside each of the cylinder bores is decreased by a communication between the residual pressure release port and each of the cylinder bores and so as to shift to a suction process.

3. A hydraulic pump in which a cylinder block with a plurality of cylinder bores formed around a rotation axis slides with respect to a valve plate including a high-pressure port and a low-pressure port, and which controls an amount of reciprocation of a piston in each of the cylinder bores depending on an inclination of a swash plate, wherein a first opening shape of the high-pressure port and a second opening shape of the low-pressure port extend circumferentially on a same arc centered around the rotation axis and are an annular band shape that does not include a top dead point and a bottom dead point, a third opening shape of a cylinder port in each of the cylinder bores extends circumferentially on the same arc where the high-pressure port and the low-pressure port are disposed, and is an annular band shape that does not communicate with the high-pressure port and the low-pressure port at the top dead point and the bottom dead point, a fourth opening shape of an end portion on a front side of the cylinder port and a fifth opening shape of an end portion of a rear side of the cylinder port with reference to a rotational direction of the cylinder block are circular convex shapes, a combination of eighth and ninth opening shapes of end portions on a front side and a rear side of the low-pressure port in a rotational direction of the low-pressure port differs from a combination of sixth and seventh opening shapes of end portions on a front side and a rear side of the high-pressure port in a rotational direction of the high-pressure port, at least one of the eighth opening shape of the end portion on the front side and the ninth opening shape of the end portion on the rear side of the low-pressure port is a circular concave shape, when the eighth opening shape of the end portion of the front side of the low-pressure port in the rotational direction of the low-pressure port is a circular concave shape, the fifth opening shape of the end portion of the rear side of the cylinder port in a rotational direction of the cylinder port and the eighth opening shape of the end portion of the front side of the low-pressure port in the rotational direction of the low-pressure port are a same shape, when the ninth opening shape of the end portion of the rear side of the low-pressure port in the rotational direction of the low-pressure port is a circular concave shape, the fourth opening shape of the end portion of the front side of the cylinder port in the rotational direction of the cylinder port and the ninth opening shape of the end portion of the rear side of the low-pressure port in the rotational direction of the low-pressure port are a same shape, the valve plate further includes a residual pressure release port which communicates with each of the cylinder bores after each of the cylinder bores pass the top dead point and before each of the cylinder bores communicate with the low-pressure port, and a first opening portion of the end portion of on the rear side of the low-pressure port in the rotational direction of the low-pressure port is separated from the top dead point so as to communicate with a second opening portion of the end portion on the front side of the cylinder port in the rotational direction of the cylinder port after passing a rotation assist region where rotation of the cylinder block is assisted by a pressure oil inside each of the cylinder bores from a top dead point position of the cylinder port and a residual pressure release region where a pressure inside each of the cylinder bores is decreased by a communication between the residual pressure release port and each of the cylinder bores and so as to shift to a suction process.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a sectional view illustrating a schematic configuration of a hydraulic pump according to an embodiment of the present invention.

(2) FIG. 2 is a line A-A cross-sectional view of the hydraulic pump illustrated in FIG. 1.

(3) FIG. 3 is a view illustrating a line B-B cross section of the hydraulic pump illustrated in FIG. 1 and a cross section of a working oil tank connected to the hydraulic pump.

(4) FIG. 4 is a view illustrating a configuration of a sliding surface of a cylinder block with respect to a valve plate when viewed in the X direction.

(5) FIG. 5 is a view illustrating opening shapes of a valve plate suction port and a valve plate discharge port of the valve plate with respect to a cylinder port illustrated in FIG. 3.

(6) FIG. 6 is a view illustrating opening shapes of a valve plate suction port and a valve plate discharge port of a valve plate, with respect to a cylinder port, according to a first modification of the embodiment in the present invention.

(7) FIG. 7 is a view illustrating opening shapes of a valve plate suction port and a valve plate discharge port of a valve plate, with respect to a cylinder port, according to a second modification of the embodiment in the present invention.

(8) FIG. 8 is a view illustrating opening shapes of a valve plate suction port and a valve plate discharge port of a valve plate, with respect to a cylinder port, according to a third modification of the embodiment in the present invention.

(9) FIG. 9 is a view illustrating opening shapes of a valve plate suction port and a valve plate discharge port of a valve plate, with respect to a cylinder port, according to a fourth modification of the embodiment in the present invention.

(10) FIG. 10 is a view illustrating an example of an opening shape of a valve plate suction port with respect to a cylinder port according to a fifth modification of the embodiment in the present invention.

(11) FIG. 11 is a view illustrating an example of an opening shape of the valve plate suction port with respect to the cylinder port according to the fifth modification of the embodiment in the present invention.

DESCRIPTION OF EMBODIMENTS

(12) In the following, a hydraulic pump/motor which is an embodiment of the present invention will be described with reference to the drawings.

Embodiment

(13) [Entire Configuration of Hydraulic Pump]

(14) FIG. 1 is a sectional view illustrating a schematic configuration of a hydraulic pump according to a first embodiment of the present invention. FIG. 2 is a line A-A cross-sectional view of the hydraulic pump illustrated in FIG. 1. The hydraulic pump illustrated in FIGS. 1 and 2 converts the engine speed and the torque transmitted to a shaft 1 to hydraulic pressure and then, discharges oil, sucked in from a suction port P1, through a discharge port P2 as a high-pressure working oil. Furthermore, the hydraulic pump is a variable displacement hydraulic pump that can vary the discharge amount of the working oil from the pump by changing an inclination angle a of a swash plate 3.

(15) Hereinafter, an axis along an axis C of the shaft 1 is referred to as an X-axis, an axis along an inclined central axis which is a line that connects fulcrums for the swash plate 3 to incline is referred to as a Z-axis, and an axis perpendicular to the X-axis and the Z-axis is referred to as a Y-axis. In addition, the direction from an end portion on an input side of the shaft 1 to an end portion on the opposite side is referred to as the X direction.

(16) The hydraulic pump includes the shaft 1, a cylinder block 6, and the swash plate 3. The shaft 1 is rotatably and pivotally supported by a case 2 and an end cap 8 via bearings 9a, 9b, respectively. The cylinder block 6 is connected to the shaft 1 via a spline structure 11, and is driven to rotate integrally with the shaft 1 inside the case 2 and the end cap 8. The swash plate 3 is provided between a side wall of the case 2 and the cylinder block 6. The cylinder block 6 is provided with a plurality of piston cylinders (cylinder bores 25) disposed at equal intervals circumferentially about the axis C of the shaft 1 and in parallel to the axis C of the shaft 1. A piston 5 capable of reciprocating in parallel to the axis C of the shaft 1 is inserted into each of the plurality of cylinder bores 25.

(17) The piston 5 that projects from each of the cylinder bores 25 has a spherical concave portion at the tip end thereof. A spherical convex portion of a shoe 4 fits into the spherical concave portion, and the piston 5 and the shoe 4 form a spherical shaft bearing. The spherical concave portion of the piston 5 is caulked and thus, the separation from the shoe 4 is prevented.

(18) The swash plate 3 includes a flat sliding surface S on the side facing the cylinder block 6. The shoe 4, in accordance with the rotation of the cylinder block 6 interlocked with the rotation of the shaft 1, slides circularly or elliptically while being pressed against the sliding surface S. A spring 15, a movable ring 16, a needle 17, and a ring-shaped pressing member 18 are provided around the axis C of the shaft 1. The spring 15 is supported by a ring 14 provided on the inner periphery of the X direction side of the cylinder block 6. The movable ring 16 and the needle 17 are pressed by the spring 15. The pressing member 18 abuts on the needle 17. The shoe 4 is pressed against the sliding surface S by the pressing member 18.

(19) On the side wall of the case 2, two hemispherical shaft bearings 20, 21 each projecting to face the side of the swash plate 3 are provided in symmetrical positions with respect to the axial center of the shaft 1. On the side of the side wall of the case 2 of the swash plate 3, two concave spheres are each formed on the portion corresponding to the positions where the shaft bearings 20, 21 have been disposed. A shaft bearing of the swash plate 3 is formed when the shaft bearings 20, 21 and two concave spheres of the swash plate 3 abut on each other. The shaft bearings 20, 21 are disposed in the Z-axis direction.

(20) As illustrated in FIG. 2, the swash plate 3 inclines in a plane perpendicular to an X-Y plane using a line that connects the shaft bearings 20, 21 as an axis (parallel to the Z-axis). The inclination of the swash plate 3 is determined by a piston 10 that reciprocates while pressing one end of the swash plate 3 along the

(21) X direction from the side of the side wall of the case 2. The swash plate 3 inclines, by the reciprocation of the piston 10, using the line that connects the shaft bearings 20, 21 as a fulcrum. The sliding surface S also inclines due to the inclination of the swash plate 3 and thus, the cylinder block 6 rotates in accordance with the rotation of the shaft 1. For example, as illustrated in FIGS. 1 and 2, in a case where the inclination angle from an X-Z plane is a, when the cylinder block 6 rotates counterclockwise as viewed in the X direction, the shoe 4 slides circularly or elliptically along the sliding surface S and accordingly, the piston 5 inside each of the cylinder bores 25 reciprocates.

(22) When the piston 5 moves to the side of the swash plate 3, the oil is sucked from a suction port P1 into each of the cylinder bores 25 via a valve plate 7. When the piston 5 moves to the side of the valve plate 7, the oil inside each of the cylinder bores 25 is discharged, via the valve plate 7, from the discharge port P2 as a high-pressure working oil. The amount of the working oil discharged from the discharge port P2 is variably controlled by adjusting the inclination of the swash plate 3.

(23) [Configuration of Valve Plate and Cylinder Block]

(24) The valve plate 7 fixed to the side of the end cap 8 and the cylinder block 6 which rotates are in contact with each other via a sliding surface Sa. FIG. 3 is a line B-B cross-sectional view of the hydraulic pump illustrated in FIG. 1. FIG. 4 is a view illustrating a configuration of the sliding surface Sa of the cylinder block 6 with respect to the valve plate 7 when viewed in the X direction. An end surface on the side of the sliding surface Sa of the valve plate 7 and an end surface on the side of the sliding surface Sa of the cylinder block 6 illustrated in FIGS. 3 and 4 slide over each other by the rotation of the cylinder block 6.

(25) As illustrated in FIG. 3, the valve plate 7 includes a valve plate suction port PB1 that communicates with the suction port P1, and a valve plate discharge port PB2 that communicates with the discharge port P2. Opening shapes of the valve plate suction port PB1 and the valve plate discharge port PB2 extend circumferentially on the same arc centered around the rotation axis C, and are annular band shapes that do not include a top dead point and a bottom dead point. As illustrated in FIG. 4, the ports of the nine cylinder bores 25 (cylinder ports 25P) where the piston 5 reciprocates are provided on the side of the sliding surface Sa of the cylinder block 6 at equal intervals and on the same arc where the valve plate suction port PB1 and the valve plate discharge port PB2 are disposed. An opening shape of the cylinder port 25P extends circumferentially on the same arc where the valve plate suction port PB1 and the valve plate discharge port PB2 are disposed, and is an annular band shape that does not communicate with the valve plate suction port PB1 and the valve plate discharge port PB2 when positioned at the top dead point and the bottom dead point.

(26) In FIGS. 3 and 4, when the cylinder block 6 rotates clockwise as viewed in a direction toward the X direction, as in FIG. 3, the discharging process is performed on the side of the valve plate discharge port PB2 which is at the upper side of the drawing, and the suction process is performed on the side of the valve plate suction port PB1 which is at the lower side of the drawing. Accordingly, in such case, the right end side of the drawing in FIG. 3 becomes the top dead point where the discharging process has switched to the suction process and where the piston 5 has entered maximally to the side of the sliding surface Sa inside the cylinder bore 25. The high-pressure state inside the cylinder bore 25 shifts to the low-pressure state. On the other hand, the left end side of the drawing in FIG. 3 becomes the bottom dead point where the suction process has switched to the discharging process and where the piston 5 has moved furthest away from the side of the sliding surface Sa inside the cylinder bore 25. When the cylinder port 25P passes the bottom dead point, the low-pressure state shifts to the high-pressure state.

(27) As illustrated in FIG. 3, a notch 26 is provided in the valve plate 7. The notch 26 is provided so as to extend from the end portion of the valve plate discharge port PB2 on the side of the bottom dead point to the side of the bottom dead point. The notch 26 has a function of regulating the self-pressure of the cylinder bore 25 before the cylinder bore 25 communicates with the valve plate discharge port PB2. By providing the notch 26, the pressure inside the cylinder bore 25 gradually gets close to the pressure inside the valve plate discharge port PB2 right before the cylinder bore 25 communicates with the valve plate discharge port PB2. Consequently, the erosion and noise of the cylinder bore 25 caused when the cylinder bore 25 communicates with the valve plate discharge port PB2 are suppressed.

(28) As illustrated in FIG. 3, a residual pressure release port 30 is provided in the valve plate 7. The residual pressure release port 30 is provided in a region within a rotational movement region E of the cylinder port 25P and from the vicinity of the top dead point to the valve plate suction port PB1. The residual pressure release port 30 is provided at a position being able to communicate with the cylinder bore 25 before the cylinder bore 25 communicates with the valve plate suction port PB1. The residual pressure release port 30 is connected to a working oil tank T via a flow path L1. The working oil tank T is connected to the valve plate suction port PB1 via a flow path L.

(29) The working oil tank T is provided with a partition plate 50 that partitions the working oil into regions E1, E2 in the horizontal direction. The working oil, inside the cylinder bore 25, which contains a large amount of air flows into the region E1 via the flow path L1. The working oil is supplied from the region E2 to the valve plate suction port PB1 via the flow path L. The air in the working oil that has flowed into the region E1 is removed in the region E1. The clean working oil with the air reduced in the region E1 flows into the region E2 via the upper portion of the partition plate 50. In the region E2, a shielding plate 51 that extends horizontally is provided at the upper portion of an outlet port for the working oil. By providing the shielding plate 51, the clean working oil that does not contain settled dust or the like is supplied to the side of the valve plate suction port PB1.

(30) From a position where the cylinder port 25P is at the top dead point, that is, a position where the circumferential tip end of the cylinder port 25P in the rotation direction is at an angle 0, to a position where the cylinder bore 25 communicates with the residual pressure release port 30 (rotation assist region 1), the rotation of the cylinder block 6 is assisted by the compressed working oil inside the cylinder bore 25. Conventionally, the working oil in the suction port P1 is assisted using an impeller (not illustrated) that uses the rotational force of the shaft 1; however, depending on the types of devices, there is a case where the impeller does not have to be used by performing the rotation assist. Therefore, by performing the rotation assist as much as possible, energy efficiency can be improved while the structure becomes simple.

(31) Thereafter, until the circumferential tip end of the cylinder port 25P passes an angle 1 and the cylinder bore 25 communicates with the residual pressure release port 30, and the cylinder bore 25 communicates with the valve plate suction port PB1 when the circumferential tip end of the cylinder port 25P is at an angle 2 (residual pressure release region 2), the compressed working oil inside the cylinder bore 25 flows into the working oil tank T via the residual pressure release port 30 and the flow path L1. As a result, a residual pressure inside the cylinder bore 25 is decreased.

(32) [Opening Shapes of Cylinder Port and Valve Plate Suction Port]

(33) As illustrated in FIG. 5, an opening shape PB1b of an end portion on the rear side in the rotational direction of a conventional valve plate suction port PB1 has an arc projecting toward the rear end side. Similarly, an opening shape S1a of an end portion on the front side in the rotational direction of the cylinder port 25P has an arc projecting toward the tip end side. Therefore, when the cylinder port 25P communicates with the valve plate suction port PB1 at the angle 2, they contact each other at a point and the communicating area has been enlarged gradually in accordance with the rotation of the cylinder block 6.

(34) In the present embodiment, the opening shape PB1b of the end portion on the rear side in the rotational direction of the valve plate suction port PB1 is an opening shape B1b of an end portion on the rear side in the rotational direction thereof. In addition, the opening shape B1b of the end portion on the rear side in the rotational direction and the opening shape S1a of the end portion on the front side in the rotational direction have the same shape. That is, when the cylinder port 25P communicates with the valve plate suction port PB1 in accordance with the rotation of the cylinder block 6, the opening shape S1a of the end portion on the front side in the rotational direction of the cylinder port 25P and the opening shape B1b of the end portion on the rear side in the rotational direction of the valve plate suction port PB1 overlap. As a result, in comparison with the past, the suction capacity in the suction process can be increased by the area of regions E10, E11 illustrated by diagonal lines. That is, it is possible to suppress the reduction in suction capacity even if the rotation assist region 1 is set larger in comparison with the past.

(35) When the cylinder port 25P communicates with the valve plate suction port PB1, the opening shape B1b of the end portion on the rear side in the rotational direction of the valve plate suction port PB1 and the opening shape S1a of the end portion on the front side in the rotational direction of the cylinder port 25P may partially have the same shape and partially overlap.

(36) Both end portions in the radial direction of the opening shape B1b of the end portion on the rear side in the rotational direction of the valve plate suction port PB1 are chamfered by the end mill processing.

(37) (First Modification)

(38) In the embodiment described above, the opening shape Bib of the end portion on the rear side in the rotational direction of the valve plate suction port PB1 and the opening shape S1a of the end portion on the front side in the rotational direction of the cylinder port 25P have the same shape. As illustrated in FIG. 6, in a first modification, an opening shape B1a of an end portion on the front side in the rotational direction of a valve plate suction port PB1 and an opening shape H1a of an end portion on the front side in the rotational direction of a valve plate discharge port PB2 each have the same shape as an opening shape Sib of an end portion on the rear side in the rotational direction of a cylinder port 25P. That is, when the communication between the cylinder port 25P and the valve plate suction port PB1 is cut off in accordance with the rotation of the cylinder block 6, and when the communication between the cylinder port 25P and the valve plate discharge port PB2 is cut off, the opening shape S1b of the end portion on the rear side in the rotational direction of the cylinder port 25P overlaps an opening shape B1a of am end portion on the front side in the rotational direction of the valve plate suction port PB1 and an opening shape H1a of an end portion on the front side in the rotational direction of the valve plate discharge port PB2. As a result, the suction area and the discharge area can be larger than in the past.

(39) When the communication between the cylinder port 25P and the valve plate suction port PB1 is cut off, the opening shape B1a of the end portion on the front side in the rotational direction, the opening shape H1a of the end portion on the front side in the rotational direction, and the opening shape S1b of the end portion on the rear side in the rotational direction may partially be the same, and the opening shape B1a and the opening shape H1a may each partially overlap the opening shape S1b. The opening shape B1a of the end portion on the front side in the rotational direction or the opening shape H1a of the end portion on the front side in the rotational direction may be the same or partially be the same as the opening shape S1b of the end portion on the rear side in the rotational direction.

(40) As illustrated in FIG. 6, in order to enlarge the suction area and the discharge area as described above, it is preferable that the opening areas of the valve plate suction port PB1 and the valve plate discharge port PB2 be widened as much as possible so that the cylinder port 25P does not communicate with the valve plate suction port PB1 and the valve plate discharge port PB2 only when the cylinder port 25P is positioned at a top dead point and a bottom dead point. However, a circumferential rear end opening position of the valve plate suction port PB1 that includes a rotation assist region 1 where a discharging process is shifted to a suction process is not limited to this. In a case where a notch 26 is provided on the valve plate discharge port PB2, the cylinder port 25P does not communicate with the tip end portion of the notch 26 only when the cylinder port 25P is positioned at the bottom dead point. The opening areas of the valve plate suction port PB1 and the valve plate discharge port PB2 are widened as much as possible so that the cylinder port 25P does not communicate with the valve plate suction port PB1 and the valve plate discharge port PB2 only when the cylinder port 25P is positioned at the top dead point and the bottom dead point; however, in consideration of manufacturing errors, it is preferable to separately position the ports PB1 and PB2 at a predetermined margin.

(41) (Second Modification)

(42) According to a second modification, as illustrated in FIG. 7, the convex opening shape S1a of the end portion on the front side in the rotational direction of the cylinder port 25P is changed to a concave opening shape S2a of an end portion on the front side in the rotational direction, and the concave opening shape B1b of the end portion on the rear side in the rotational direction of the valve plate suction port PB1 is changed to a convex opening shape B2b of an end portion on the rear side in the rotational direction of a valve plate suction port PB1; therefore, the opening shape S2a of the end portion on the front side in the rotational direction and the opening shape B2b of the end portion on the rear side in the rotational direction have the same shape. That is, when a cylinder port 25P communicates with the valve plate suction port PB1 in accordance with the rotation of a cylinder block 6, the opening shape S2a of the end portion on the front side in the rotational direction of the cylinder port 25P and the opening shape B2b of the end portion on the rear side in the rotational direction of the valve plate suction port PB1 overlap. Similar to the first modification, when the communication between the cylinder port 25P and the valve plate suction port PB1 is cut off, and when the communication between the cylinder port 25P and the valve plate discharge port PB2 is cut off, an opening shape S1b of an end portion on the rear side in the rotational direction of the cylinder port 25P overlaps an opening shape B1a of an end portion on the front side in the rotational direction of the valve plate suction port PB1 and an opening shape H1a of an end portion on the front side in the rotational direction of the valve plate discharge port PB2. Also in this case, the opening shape S2a of the end portion on the front side in the rotational direction and the opening shape B2b of the end portion on the rear side in the rotational direction may partially be the same.

(43) (Third Modification)

(44) According to a third modification, as illustrated in FIG. 8, an opening shape of an end portion on the front side in the rotational direction of a cylinder port 25P is a convex opening shape S1a of the end portion on the front side in the rotational direction, and an opening shape of an end portion on the rear side in the rotational direction of the cylinder port 25P is a concave opening shape S2b of the end portion on the rear side in the rotational direction. Accordingly, an opening shape of an end portion on the rear side in the rotational direction of a valve plate suction port PB1 is a concave opening shape B1b of the end portion on the rear side in the rotational direction, an opening shape of an end portion on the front side in the rotational direction of the valve plate suction port PB1 is a convex opening shape B2a of the end portion on the front side in the rotational direction, and an opening shape of an end portion on the front side in the rotational direction of a valve plate discharge port PB2 is a convex opening shape H2a of the end portion on the front side in the rotational direction. Furthermore, the opening shape S1a of the end portion on the front side in the rotational direction and the opening shape B1b of the end portion on the rear side in the rotational direction have the same shape. The opening shape S2b of the end portion on the rear side in the rotational direction and the opening shape B2a of the end portion on the front side in the rotational direction have the same shape. The opening shape S2b of the end portion on the rear side in the rotational direction and the opening shape H2a of the end portion on the front side in the rotational direction have the same shape. That is, when the cylinder port 25P communicates with the valve plate suction port PB1 and when the communication therebetween is cut off, and when the communication between the cylinder port 25P and the valve plate discharge port PB2 is cut off, one opening shape of the end portion in the port overlaps the other. Also in this case, the opening shapes may not have completely the same shape, but may partially have the same shape.

(45) (Fourth Modification)

(46) According to a fourth modification, as illustrated in FIG. 9, an opening shape of an end portion on the front side in the rotational direction of a cylinder port 25P and an opening shape of an end portion on the rear side in the rotational direction of the cylinder port 25P are a concave opening shape S2a of the end portion on the front side in the rotational direction and a concave opening shape S2b of the end portion on the rear side in the rotational direction, respectively. Accordingly, an opening shape B2b of an end portion on the rear side in the rotational direction of a valve plate suction port PB1 has a convex shape, an opening shape B2a of an end portion on the front side in the rotational direction of the valve plate suction port PB1 has a convex shape, and an opening shape H2a of an end portion on the front side in the rotational direction of a valve plate discharge port PB2 has a convex shape. Furthermore, the opening shape S2a of the end portion on the front side in the rotational direction and the opening shape B2b of the end portion on the rear side in the rotational direction have the same shape. The opening shape S2b of the end portion on the rear side in the rotational direction and the opening shape B2a of the end portion on the front side in the rotational direction have the same shape. The opening shape S2b of the end portion on the rear side in the rotational direction and the opening shape H2a of the end portion on the front side in the rotational direction have the same shape. That is, when the cylinder port 25P communicates with the valve plate suction port PB1 and when the communication therebetween is cut off, and when the communication between the cylinder port 25P and the valve plate discharge port PB2 is cut off, one opening shape of the end portion in the port overlaps the other. Also in this case, the opening shapes may not have completely the same shape, but may partially have the same shape

(47) (Fifth Modification)

(48) In the embodiment and first to fourth modifications described above, the opening shapes of the end portions on the front side and/or the rear side in the rotational direction have been circular convex shapes or circular concave shapes; however, the opening shapes of the end portions are not limited to these, and may be of any shape. For example, each opening shape may have the same shape with a straight line shape as an opening shape S3a of an end portion on the front side in the rotational direction of a cylinder port 25P and an opening shape B3b of an end portion on the rear side in the rotational direction of a valve plate suction port PB1 illustrated in FIG. 10. In addition, each opening shape may have the same shape with a wave shape having a convex/concave shape as an opening shape S4a of an end portion on the front side in the rotational direction of the cylinder port 25P and an opening shape B4b of an end portion on the rear side in the rotational direction of the valve plate suction port PB1 illustrated in FIG. 11. Also in these cases, the shapes may not have completely the same shape, but may partially have the same shape.

(49) The convex shape or concave shape of the opening shape in the embodiment and first to fourth modifications described above includes an inverted U-shape or a U-shape, respectively.

(50) The components of the embodiment and first to fifth modifications described above can be combined as appropriate.

(51) In the embodiment and first to fifth modifications described above, the hydraulic pump has been described as an example; however, the invention is not limited to this, and can also be applied to a hydraulic motor. In the case of the hydraulic motor, a high-pressure side corresponds to a discharge side of the hydraulic pump, and a low-pressure side corresponds to a suction side of the hydraulic pump.

(52) Also in this case, in accordance with the rotation of a cylinder block 6, when a cylinder port 25P communicates with a low-pressure port or when the communication therebetween is cut off, or when the communication between the cylinder port 25P and a high-pressure port is cut off, each opening shape of the end portion in the rotational direction in the port completely or partially overlaps.

(53) Furthermore, in the embodiment and first to fifth modifications, the swash plate-type hydraulic pump/motor has been described as an example; however, the invention is not limited to this, and can also be applied to an inclined shaft-type hydraulic pump/motor.

REFERENCE SIGNS LIST

(54) 1 Shaft

(55) 2 Case

(56) 3 Swash plate

(57) 4 Shoe

(58) 5, 10 Piston

(59) 6 Cylinder block

(60) 7 Valve plate

(61) 8 End cap

(62) 9a, 9b Bearing

(63) 11 Spline structure

(64) 14 Ring

(65) 15 Spring

(66) 16 Movable ring

(67) 17 Needle

(68) 18 Pressing Member

(69) 20, 21 Shaft bearing

(70) 25 Cylinder bore

(71) 25P Cylinder port

(72) 26 Notch

(73) 30 Residual pressure release port

(74) 50 Partition plate

(75) 51 Shielding plate

(76) L, L1 Flow path

(77) P1 Suction port

(78) P2 Discharge port

(79) PB1 Valve plate suction port

(80) PB2 Valve plate discharge port

(81) S, Sa Sliding surface

(82) S1a, S2a, S3a, S4a Opening shape of end portion on rear side in rotational direction of cylinder port

(83) S1b, S2b Opening shape of end portion on rear side in rotational direction of cylinder port

(84) B1a, B2a Opening shape of end portion on front side in rotational direction of valve plate suction port

(85) B1b, B2b, B3b, B4b Opening shape of end portion on rear side in rotational direction of valve plate suction port

(86) H1a, H2a Opening shape of end portion on front side in rotational direction of valve plate discharge port

(87) T Working oil tank