In accordance with at least one aspect of this disclosure, a system includes, a cylinder barrel configured to rotate within a pump housing of a pump operatively connected to a driving member of the pump via a first shaft. A piston is seated within a bore defined in the cylinder barrel. The piston is operatively connected to the driving member of the pump via a second shaft. The first shaft and the second shaft each include a ball end configured to seat within the driving member. In embodiments, the ball end of at least the second shaft is of silicon nitride.

A hydrostatic axial piston machine (1) utilizing a bent-axis construction has a driveshaft (4) with a drive flange (3) rotatable around an axis of rotation (R.sub.t) inside a housing (2). A cylinder barrel (7) has pistons (10) fastened in an articulated manner to the drive flange (3). The drive flange (3) is supported on a housing-side slide face (101) by an axial bearing (100) in the form of a hydrostatically relieved sliding bearing (102) having a plurality of slippers (105). Each of the slippers (105) is mounted in an articulated manner in the drive flange (3) so that when the drive flange (3) rotates, a compensating force (F.sub.FR) acts on the slipper (105) which is in the opposite direction to the centrifugal force (F.sub.F) acting on the slipper (105). The point of application (AP) of the compensating force (F.sub.FR) on the slipper (105) is selected so that there is no tipping moment on the slipper (105) or to compensate for some or all of any tipping moment that does occur.

Hydraulic axial piston unit (1) of the swashplate construction type having a drive shaft (2) adapted to drive or be driven by a cylinder block (4). The cylinder block comprises a plurality of cylinder bores (6), in which several pistons (8) are moveable in general along the rotational axis (10) of the drive shaft (2) and relative to the cylinder bores (6). First ends of the pistons (8) protrude outside of the cylinder bores (6) and are slidable fixed by means of slippers (14) to a swashplate (16). The slippers (14) are hold down in a sliding manner on a sliding surface (18) of the swashplate (16) by means of a slipper hold down ring (20) arranged parallel to the sliding surface (18). The slipper hold down ring (20) is in a sliding contact with its radial inner surface (22) with a matching surface (26) on a guide ball (24) rotationally fixed on the drive shaft (2) and axially moveable in direction of the rotational axis (10) relative to the cylinder block (4) against resilient forces of springs (28) characterized in that a mounting ring (30) is attached to the cylinder block (4) in order to limit the axial movement of the guide ball (24) towards the cylinder block (4).

A piston is cylindrical and includes: a concave spherical portion formed at one of end portions of the piston and having a partially spherical shape; a cylindrical hollow portion formed at the other end portion of the piston; and an oil passage formed between the concave spherical portion and the hollow portion, the concave spherical portion and the hollow portion communicating with each other through the oil passage. The concave spherical portion includes a concave spherical surface formed by forging and having a partially spherical shape. A convex spherical portion of a shoe is supported by the concave spherical surface so as to be slidable and rotatable. An area of contact between the concave spherical surface and a predetermined master ball corresponding to the convex spherical portion is 40% or more of an entire area of the concave spherical surface.

An axial piston machine (1) is shown, comprising: a shaft (2) having an axis (3) of rotation, a cylinder drum (4) connected to said shaft (2) and having at least a cylinder (5) parallel to said axis (3) of rotation, a piston (6) movable in said cylinder (5), a swash plate (13), a slide shoe (11) pivotally mounted to said piston (6), and holding means holding said slide shoe (11) against said swash plate (13), said holding means having a pressure plate (14) and a number of coil springs (15) arranged between said cylinder drum (4) and said pressure plate (14). The object is to have a reliable operation of said machine with a simple construction. To this end each coil spring (15) is at least at one end fixed by a protrusion (20) extending into said coil spring (15).

An axial piston machine is shown comprising a cylinder drum rotatable around an axis of rotation and having at least a cylinder, a piston arranged in said cylinder, a swash plate arranged in front of said cylinder drum, said piston being provided with a slipper (11) resting against said swash plate and having a pressure area (17) on a side facing said swash plate, wherein a cylinder axis of said cylinder is arranged on a circle line (27) around said axis of rotation (16). Such a machine should be made compact. To this end said pressure area (17) deviates from a circular form.

A bent-axis hydrostatic axial piston machine (1) has a drive shaft (4) with a drive flange (3) rotatable around an axis of rotation (R.sub.t) and a cylinder drum (7) rotatable around an axis of rotation (R.sub.z). The cylinder drum (7) has a plurality of piston bores (8) concentric to the axis of rotation (R.sub.z) of the cylinder drum (7) and having longitudinally displaceable pistons (10) fastened in an articulated manner to the drive flange (3). Between the drive shaft (4) and the cylinder drum (7) there is a drive joint (30) (constant velocity joint) for rotationally synchronous rotation of the cylinder drum (7) and the drive shaft (4). The drive joint (30) and the cylinder drum (7) include a longitudinal bore (11) concentric to the axis of rotation (R.sub.z) of the cylinder drum, through which bore (11) the drive shaft (4) extends such that in the vicinity of the drive shaft (4) there is a torque transfer to a cylinder-drum-side end of the axial piston machine (1).

A slipper retainer of a hydraulic unit having a circular body having a back surface and an outer edge, the circular body defining a diameter of about 2.240 inches (5.629 cm), a central aperture through a center of the circular body, the circular body having a curved surface defining an edge of the central aperture, wherein the curved surface is defined by a sphere that is centered at a point located a distance of about 0.209 inches (0.531 cm) from the back surface of the body, and a plurality of slipper apertures located between the curved surface of the circular body and the outer edge of the circular body, wherein each slipper aperture of the plurality of slipper apertures has a diameter of about 0.464 inches (1.179 cm).

A slipper retainer ball of a hydraulic unit having an aperture passing through a body, the body having a flat bottom surface, a flat top surface, an external curved surface, and an interior profiled surface that extends in an axial direction from the bottom surface to the top surface. The interior profiled surface includes a first surface extending parallel to the axis from the bottom surface in the axial direction, a second surface extending perpendicular to the axis from the first surface and outward toward the external curved surface, a third surface extending from the second surface axially at a first angle, a fourth surface extending from the third surface in the axial direction, and a fifth surface extending from the fourth surface to the top surface at a second angle that is skew from the axis. The axial thickness of the body is about 0.471 inches.

It is an object of the present invention to provide a semispherical shoe which can be prevented from being subjected to seizure even in a dry lubrication state in which there is no lubricating oil at the start time of an operation of a swash plate compressor, is excellent in its sliding contact property and load resistance, does not deteriorate in its lubricating property due to generated frictional heat, does not subject a resin layer to peeling from a base material, and ensures sufficient durability. It is another object of the present invention to provide a swash plate compressor in which a lubricating film is not formed on a sliding contact surface of the swash plate and that of a piston owing to the use of the semispherical shoe. A semispherical shoe (4) is subjected to sliding contact with the swash plate of the swash plate compressor and the piston thereof. Abase material (5) consists of a metallic member. A resin layer (6b) is formed on a surface of a planar part (4b) to be subjected to sliding contact with the swash plate. A resin layer (6a) is formed on a surface of a spherical part (4a) to be subjected to sliding contact with the piston. The resin layer (6a) and the resin layer (6b) are integral with each other. At least one portion of the base material (5) is not covered with the resin layer (6) and is exposed.