A hydraulic pump/motor includes: a cylinder block rotating about a rotation axis; a piston in a cylinder bore; and a valve plate facing a cylinder port. The valve plate includes: a high pressure port through which hydraulic oil discharged from the cylinder port flows; a low pressure port through which the oil to be sucked into the cylinder port flows; a region disposed between the high and low pressure ports in a circumferential direction of the rotation axis and including a top dead center position facing the cylinder port of the cylinder bore in which the piston moved to a top dead center is disposed; and a residual pressure release port between the top dead center position and the low pressure port in the region. The residual pressure release port includes first and second ports disposed at a positions different from each other in the radial direction of the rotation axis.

A hydraulic machine with oscillating axial cylinders includes a plurality of oscillating axial cylinders, put in synchronous rotation between a first rotating element, a rotating disc, which supports one end of the cylinder, bottom or piston, and a second rotating element, a rotating barrel, which supports the opposite end of the cylinder; each cylinder is connected to said rotating elements with a ball joint towards each of them; each ball joint is holed to allow for the passage and the feeding/discharge through it of the hydraulic liquid. At least the bottom or the piston is connected to the respective rotating element with a ball joint having a spherical surface with a diameter equal to or greater than the cylinder bore.

A hydrostatic axial piston machine includes a double-acting actuating cylinder configured to adjust the piston displacement. The actuating cylinder has two actuating chambers that are connected to two spatially separated cartridge valves. The two cartridge valves are inserted obliquely into a wall section of the axial piston machine. The wall section on the one hand forms a wall of the housing of the axial piston machine and on the other hand forms a wall of the actuating cylinder.

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 hydrostatic positive displacement machine has an adjustable swept volume, and has a lifting element, a rotor with positive displacement elements supported on the lifting element, and a hydraulic adjusting device that adjusts the swept volume and includes an adjusting piston that is mounted in or on a cylinder, is movable axially rectilinearly in relation to the cylinder, and is adjacent to a pressurizable adjusting chamber. A bearing gap is formed between a circular-cylindrical bearing surface of the adjusting piston and a circular-cylindrical bearing surface of the cylinder. The adjusting piston is mounted hydrostatically, wherein at least three pressure pockets are distributed uniformly in a row over the circumference of a bearing surface. Pressure fluid flows into each pressure pocket via a fixed throttle, which is assigned only to the respective pressure pocket, and flows out of each pressure pocket via the bearing gap.

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 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 hydraulic device comprises a shaft mounted in a housing rotatable about a first axis. A plurality of pistons are fixed to a flange rotatable about a first axis. A plurality of cylindrical sleeves sleeve bottoms and sleeve jackets that cooperate with the pistons to form compression chambers. Rotation of the shaft causes the volumes of the compression chambers. Each piston head forms a sealing line within the cooperating sleeve jacket. Each sleeve jacket has a thin wall and/or is elastically movable with respect to the sleeve bottom such that at a fixed pressure the radial deformation of the sleeve jacket at the sealing line is substantially constant at piston positions ranging from bottom dead center to a position where the distance between the sleeve bottom and the sealing line is less than 50% of the distance between the sleeve bottom and the sealing line at bottom dead center.

The present invention relates to a method of manufacturing a drum of an axial piston machine by machining a cylindrical round metal, with the machining comprising a forging and with at least one structural element of the drum being produced or prefabricated by the forging.

A cylinder block includes: a plurality of cylinder bores including respective openings formed on a piston insertion end surface of the cylinder block, pistons being inserted in the respective cylinder bores and being configured to reciprocate and slide in the respective cylinder bores when the cylinder block rotates; and a cooling portion, wherein the cooling portion includes a plurality of cooling holes each formed between the adjacent cylinder bores and extending from the piston insertion end surface in an axial direction of the cylinder block.