Patent ID: 7677871

Claim:
A variable displacement hydraulic pump/motor comprising: a yoke comprising a pair of axially-aligned shafts defining a pivot axis for said yoke and a valve plate connected to and intermediate said shafts and axially offset relative to said shafts, said valve plate presenting a valve plate surface having a discharge aperture and an arc-shaped intake aperture; a cylinder barrel rotatable about a longitudinal axis and having a plurality of piston cylinders formed therein in a circle centered on said longitudinal axis, each piston cylinder being open at one end of said cylinder barrel to receive a piston reciprocably mounted therein and opening at a second end of said cylinder barrel through a fluid port, said second end of said cylinder barrel mating with said valve plate surface for intake of fluid from the arc-shaped intake aperture to a fluid port in communication with one of said piston cylinders and discharge of fluid from another of said piston cylinders through its fluid port and the arc-shaped discharge aperture; a drive block mounted on an end of an input/output shaft for rotation about a central axis of rotation inclined at an angle of inclination relative to said longitudinal axis; a plurality of piston rods, each piston rod connected at a first end to one of said pistons and pivotally connected at a second end to said drive block, said second ends being connected to said drive block in a circular array centered on said axis of rotation; and a raised annular grid extending from said second end of said cylinder barrel, said fluid ports being surrounded and separated by said grid; and a second raised annular area extending from said second end of said cylinder barrel coextensive with and spaced radially outward from said annular grid.