An axial piston pump may comprise a valve plate assembly including a plurality of valve plates rotatably disposed adjacent to each other and configured to control the flow of fluid between a piston chamber and inlet and outlet port passages. The piston pump may also comprise a swashplate arrangement that is capable of being angled in two different directions to be used in combination with the valve plate assembly. A fixed displacement axial piston pump may also comprise the valve plate assembly disclosed herein in which pressure transitions are facilitated in the same fashion, but without the variable of changing swashplate angles which control pump flow.

A nitriding layer (13) is formed on the front surface side of a base material of a cylinder block (7) including an opening side end surface (7B) and each cylinder hole (12). Then, a piston sliding surface (12A) of each cylinder hole (12) is formed as a compound layer-removed hole (17) by removing a compound layer (16) that is located on the front surface side of the nitriding layer (13) by using polishing means such as, for example, honing and so forth. Further, a compound layer-removed surface (18) is formed on a part (A) where a compound layer-removed hole (17) and a cylinder inlet side tapered surface (12B) of each cylinder hole (12) intersect by using the polishing means such as, for example, the honing and so forth. This compound layer-removed surface (18) is formed as a tapered-state inclined surface of an angle α.

A nitriding layer (13) is formed on the front surface side of a base material of a cylinder block (7) including an opening side end surface (7B) and each cylinder hole (12). Then, a piston sliding surface (12A) of each cylinder hole (12) is formed as a compound layer-removed hole (17) by removing a compound layer (16) that is located on the front surface side of the nitriding layer (13) by using polishing means such as, for example, honing and so forth. Further, a compound layer-removed surface (18) is formed on a part (A) where a compound layer-removed hole (17) and a cylinder inlet side tapered surface (12B) of each cylinder hole (12) intersect by using the polishing means such as, for example, the honing and so forth. This compound layer-removed surface (18) is formed as a tapered-state inclined surface of an angle α.

A valve plate for a fluid pump includes a body having a first surface and an oppositely disposed second surface. The body defines a first kidney slot that extends through the first and second surfaces and a second kidney slot that extends through the first and second surfaces. A first notch is disposed in the first surface of the body and extends outwardly from the first kidney slot in a direction toward the second kidney slot. A second notch is disposed in the first surface and extends outwardly from the first kidney slot in a direction toward the second kidney slot. The second notch is separated from the first notch.

A valve plate for a fluid pump includes a body having a first surface and an oppositely disposed second surface. The body defines a first kidney slot that extends through the first and second surfaces and a second kidney slot that extends through the first and second surfaces. A first notch is disposed in the first surface of the body and extends outwardly from the first kidney slot in a direction toward the second kidney slot. A second notch is disposed in the first surface and extends outwardly from the first kidney slot in a direction toward the second kidney slot. The second notch is separated from the first notch.

A swashplate-type axial piston machine includes a housing, a first pivot bearing received in the housing, a drive shaft rotatably mounted in respect of an axis of rotation, a cylinder drum, a control plate, a third control aperture in the plate, and a first channel arranged in the housing. The first pivot bearing delimits a first and second housing space from one another. The drum and the plate are arranged in the first housing space. The plate has at least a first and at least a second control aperture. The first aperture is in fluidic exchange connection with a first fluid connection on the housing. The second aperture is in fluidic exchange connection with a second fluid connection on the housing. The third aperture is arranged in the peripheral direction between a first and a second aperture. The first channel fluidically connects the third aperture to the second housing space.

A swashplate-type axial piston machine includes a housing, a first pivot bearing received in the housing, a drive shaft rotatably mounted in respect of an axis of rotation, a cylinder drum, a control plate, a third control aperture in the plate, and a first channel arranged in the housing. The first pivot bearing delimits a first and second housing space from one another. The drum and the plate are arranged in the first housing space. The plate has at least a first and at least a second control aperture. The first aperture is in fluidic exchange connection with a first fluid connection on the housing. The second aperture is in fluidic exchange connection with a second fluid connection on the housing. The third aperture is arranged in the peripheral direction between a first and a second aperture. The first channel fluidically connects the third aperture to the second housing space.

A hydrostatic axial piston machine includes a cylinder drum that rotates during operation and has a plurality of cylinder bores in which displacement pistons are arranged, each of which opens out in a control opening in one end face of the cylinder drum, and having a control part against which the cylinder drum bears with the end face and on which two kidney-shaped control ports in the form of circular arcs are provided. Between the two kidney-shaped control ports, a first changeover web and a second changeover web are formed, wherein two sets of compensating openings that are able to be overlapped by control openings are located in the changeover webs with one compensating opening of each set located in each changeover web, and the compensating openings in the two sets of compensating openings are connected together via respective compensating fluid paths.

A hydraulic pump motor includes: a cylinder block; a plurality of cylinder bores; a port block and a valve plate, the valve plate being provided with a high pressure port and a low pressure port, the port block being provided with a discharge oil passage and a suction oil passage, a piston disposed in each cylinder bore, and oil flowing through the discharge oil passage and the suction oil passage. Further, the valve plate is provided with a reproduction port at a bottom dead center side position, the port block is internally provided with a reproduction oil passage, and the reproduction oil passage passes through a first region on a side of the high pressure port of the virtual plane and passes through a second region on a side of the low pressure port of the virtual plane in the port block.

A hydrostatic axial piston machine includes a cylinder drum that rotates during operation and has a plurality of cylinder bores in which displacement pistons are arranged, each of which opens out in a control opening in one end face of the cylinder drum, and having a control part against which the cylinder drum bears with the end face and on which two kidney-shaped control ports in the form of circular arcs are provided. Between the two kidney-shaped control ports, a first changeover web and a second changeover web are formed, wherein two sets of compensating openings that are able to be overlapped by control openings are located in the changeover webs with one compensating opening of each set located in each changeover web, and the compensating openings in the two sets of compensating openings are connected together via respective compensating fluid paths.