Positive displacement machines and methods therefor capable of increasing a load-carrying capacity of a piston-cylinder lubrication interface of positive displacement machines having a cylinder block, a cylindrical bore defined in the cylinder block, a piston reciprocably disposed within the cylindrical bore, and a working fluid within the piston-cylinder lubrication interface to provide a load-bearing function between the piston and the bore wall of the cylinder bore. The method includes providing at least one circumferential groove on a bore wall of the cylindrical bore within the piston-cylinder lubrication interface having an opening facing the piston and that is in fluidic communication with the piston-cylinder lubrication interface so as to contain a portion of the working fluid, and operating the positive displacement machine such that the working fluid enters the cylindrical groove and promotes hydrostatic balancing of pressure of the working fluid within the piston-cylinder lubrication interface.

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 hydrostatic positive-displacement machine, in particular a hydrostatic axial piston machine, having a cylinder drum with at least one cylinder, in which a longitudinally displaceable piston is received, which is supported directly or indirectly by a support portion on an inclined plane of the positive-displacement machine. An outer circumferential surface portion of the piston is in bearing contact with an inner circumferential surface portion of the cylinder.

A hydraulic machine includes radial cylinders including, oscillating radial cylinders arranged in a crown or star of cylinder-piston units, the pistons of the groups are made slidable on a crankshaft or with a cam, or on interposed members concentric to it, and realizing the reciprocating motion in the oscillating cylinders. The oscillating cylinders are placed in contact with a surface of distribution concentric or corresponding to the surface of oscillation of the respective cylinder on which a distributor body is placed separate from the machine body and housed in a seat in the body, or part fixed to the body, of the hydraulic machine, and each distributor body is mobile in its seat under the action of the pressure of liquid in connection on the back surface of the distributor body against the surface of distribution of the oscillating radial cylinder subject to the distribution.

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 piston motor includes a bush in the form of a curved plate held in sliding contact with a back surface of a tiltable swash plate, a supply/discharge passage formed on the casing including a swash plate port formed on the swash plate and open on the back surface of the swash plate and a bush port penetrating through the bush and provided from a piston to the swash plate, and an elastic ring interposed between the casing and the bush and surrounding an opening end of the bush port.

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.

An axial piston machine may include a rotor rotatably mounted in a housing. A plurality of cylinders may be arranged in a ring around the rotor. A plurality of pistons may each be arranged within each of the plurality of cylinders and may be constructed and arranged to selectively translate within the plurality of cylinders. A plurality of inlet openings may be defined in a cylinder head and at least one outlet opening may be defined in the housing. The plurality of cylinders may be in operative communication with the plurality of inlet openings and the at least one outlet opening. An inlet channel may be defined in the cylinder head and may extend to each of the plurality of inlet openings. An outlet channel may be defined in the housing and may be in operative communication with the at least one outlet opening. A bypass channel may be defined in the housing and may extend from the cylinder head into one of the outlet channel or a swashplate space. A bypass valve may be connected to the cylinder head or may be integrated with the cylinder head. The bypass valve may be constructed and arranged to selectively apportion a working medium to the inlet channel and the bypass channel based on a switching position of the bypass valve.

An axial piston machine may include a rotor with a shaft. A plurality of cylinders may be arranged in an annular manner about the shaft. A plurality of pistons may each be positioned within each of the plurality of cylinders and may be constructed and arranged to move translationally within the plurality of cylinders. A cylinder head may include a plurality of inlet openings and may be in operative communication with the plurality of cylinders. A sealing washer having a plurality of passage openings may be disposed on the cylinder head so that the plurality of passage openings and the plurality of inlet openings may be flush with one another. A number of the plurality of inlet openings may correspond to a number of the plurality of passage openings. A valve plate may be connected to the shaft in a rotationally fixed manner and may be constructed and arranged to be brought into congruence with the plurality of passage openings of the sealing washer based on a rotary angle. The sealing washer may be disposed between the plurality of inlet openings and the valve plate and may be prestressed against the cylinder head and onto the inlet openings.

An opposed swash plate type fluid pressure rotating machine in which a first piston and a second piston projecting from opposite ends of a cylinder block reciprocate in a cylinder, respectively following a first swash plate and a second swash plate includes a center spring for biasing the cylinder block toward the second swash plate. A housing hole (biasing force receiving part) for receiving a biasing force of the center spring is formed on one end part of the cylinder block. The tip of a second neck (reaction force receiving part) for receiving a reaction force from the second swash plate is formed on the other end part of the cylinder block. The cylinder block is biased only toward the second swash plate by the center spring.