Patent ID: 6983680

Claim:
In a hydraulic machine having a plurality of pistons reciprocally mounted in respective cylinders formed in a cylinder block and positioned circumferentially at a first radial distance about the rotational axis of a drive element, each said piston having an axially cylindrical body portion and a head end and each respective cylinder having a valve end and an open head portion beyond which said head end of each said piston extends at all times, and said pistons also having a stroke varying up to a predetermined maximum for receiving and delivering pressurized fluid, the improvement comprising: a respective lubricating channel formed in the cylindrical wall of each said cylinder in said cylinder block for retaining said pressurized fluid; all of said lubricating channels being interconnected to form a continuous lubricating passageway in said cylinder block; said pressurized fluid being retained in said continuous lubricating passageway by the substantial closure of each said respective lubricating channel by the outer surface of the axially cylindrical body of each respective piston during the entire stroke of each said piston, the only source of pressurized fluid received by said continuous lubricating passageway is being a minimal flow of said fluid between each said respective cylindrical wall of each said cylinder and said axial cylindrical body of each respective piston; and said closed continuous lubricating passageway being formed entirely within said cylinder block, transecting each said cylinder and being centered circumferentially at substantially the same radial distance as said cylinders are centered about the rotational axis of the drive element.