A pump barrel (70) for use in a hydrostatic pump assembly includes a barrel body (88) defining a plurality of piston bores (84) that receive a plurality of pistons moveable within the bores, and a porting face (74) that defines a plurality of ports (72) in fluid communication with the piston bores and providing fluid flow paths into and out from the barrel body. Each port (72) has a leading edge surface and a trailing edge surface relative to a direction of rotation of the pump barrel, said leading and trailing edge surfaces being oriented in a first direction (along line 6-6) at non-right angles relative to the porting face (74). Each port (72) has an inner edge surface (80) and an outer edge surface (82) relative to a radial direction of the pump barrel, said inner and outer edge surfaces (80,82) being oriented in a second direction (along line 9-9) comprising a tilt angle (90,92) relative to the porting face (74) that is different from the angles in the first direction. A hydrostatic pump assembly incorporating such a pump barrel (70) is also disclosed.

A piston and cylinder assembly of an axial piston machine is disclosed which includes a cylinder having a uniform internal diameter, a cylindrical bushing press-fit against the inner surface of the cylinder and extending at least partially therein, the bushing comprising at least one circumferential groove formed on an outer surface of the bushing against the inner surface of the cylinder, a piston reciprocably disposed within the cylindrical bushing, generating a piston-bushing-interface, the piston and the bushing defining a diametrical clearance therebetween, the diametrical clearance defining a lubrication gap and a fluid-dynamic seal between the piston and the cylindrical bushing.

A piston and cylinder assembly of an axial piston machine is disclosed which includes a cylinder having a uniform internal diameter, a cylindrical bushing press-fit against the inner surface of the cylinder and extending at least partially therein, the bushing comprising at least one circumferential groove formed on an outer surface of the bushing against the inner surface of the cylinder, a piston reciprocably disposed within the cylindrical bushing, generating a piston-bushing-interface, the piston and the bushing defining a diametrical clearance therebetween, the diametrical clearance defining a lubrication gap and a fluid-dynamic seal between the piston and the cylindrical bushing.

A pump barrel (70) for use in a hydrostatic pump assembly includes a barrel body (88) defining a plurality of piston bores (84) that receive a plurality of pistons moveable within the bores, and a porting face (74) that defines a plurality of ports (72) in fluid communication with the piston bores and providing fluid flow paths into and out from the barrel body. Each port (72) has a leading edge surface and a trailing edge surface relative to a direction of rotation of the pump barrel, said leading and trailing edge surfaces being oriented in a first direction (along line 6-6) at non-right angles relative to the porting face (74). Each port (72) has an inner edge surface (80) and an outer edge surface (82) relative to a radial direction of the pump barrel, said inner and outer edge surfaces (80,82) being oriented in a second direction (along line 9-9) comprising a tilt angle (90,92) relative to the porting face (74) that is different from the angles in the first direction. A hydrostatic pump assembly incorporating such a pump barrel (70) is also disclosed.

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 cylinder block (1) for a compressor has a central opening (3) for accommodating a drive shaft of a drive unit and defines a central axis of the cylinder block (1) with a plurality of cylinder bores (2) arranged around the central opening and each of the cylinder bores (2) adapted for accommodating a piston (14).The cylinder block (1) also has at least one stop (10) on a drive side of the cylinder block (1) with the stop (10) arranged within a triangular area which is delimited by the central opening (3) and the two adjacent cylinder bores (2).

A variable displacement compressor includes a swash plate, a housing and a displacement control valve. The housing has a crank chamber where the swash plate is disposed, a discharge chamber and a suction chamber. The housing has plural bolt holes and is formed by separate members fastened together by plural bolts inserted through the bolt holes. The displacement control valve has a first valve member movable to connect the crank chamber and the discharge chamber, controlling the position of the first valve member to vary compressor displacement. The displacement control valve has a valve chamber and a second valve member serving to connect the crank chamber and the suction chamber in the valve chamber. The valve chamber is connected to the crank chamber by a drain passage part of which serves as the bolt hole located at the lowest of the plural bolt holes when the compressor is installed.

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.