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 hydraulic drive device includes a running surface having a pair of arcuate kidney ports formed thereon. The running surface also includes a plurality of pressure gradient grooves formed on the running surface, each pressure gradient groove having a proximal end adjacent to a respective one of the ends of one of the kidney ports and a distal end. The distal end of one of the pressure gradient grooves associated with one kidney port may overlap the distal end of a pressure gradient groove associated with the other kidney port. The distal end of at least one of the pressure gradient grooves is located outside the circumference of a pitch circle that passes through the center of each kidney port. The distal end of at least one of the other pressure gradient grooves is located inside the pitch circle circumference.

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 valve plate or end cap includes a running surface having a pair of arcuate kidney ports formed thereon. The running surface also includes a plurality of pressure gradient grooves formed on the running surface, each pressure gradient groove having a proximal end adjacent to a respective one of the ends of one of the kidney ports and a distal end. The distal end of one of the pressure gradient grooves associated with one kidney port may overlap the distal end of a pressure gradient groove associated with the other kidney port. The distal end of at least one of the pressure gradient grooves is located outside the circumference of a pitch circle that passes through the center of each kidney port. The distal end of at least one of the other pressure gradient grooves is located inside the pitch circle circumference.

A mounting member for a hydraulic pump or other rotating kit for a hydraulic drive device includes a running surface having a pair of arcuate kidney ports formed thereon. The running surface also includes a plurality of pressure gradient grooves formed on the running surface, each pressure gradient groove having a proximal end adjacent to a respective one of the ends of one of the kidney ports and a distal end. The distal end of one of the pressure gradient grooves associated with one kidney port may overlap the distal end of a pressure gradient groove associated with the other kidney port. The distal end of at least one of the pressure gradient grooves is located outside the circumference of a pitch circle that passes through the center of each of the kidney ports. The distal end of at least one of the other pressure gradient grooves is located inside the circumference of the pitch circle.