Radial piston type hydraulic pump or motor

Claim 1

A hydraulic machine operable as at least one of a pump and motor; said machine comprising a casing having a waved cam surface, a cylinder block mounted in the casing for relative movement with respect to said casing and having at least one cylinder, each of said cylinders having a piston arranged for reciprocating inward and outward movement therein, engagement means mounted on the inner end of each piston for engagement on the waved cam surface, hydraulic supply means for supplying hydraulic fluid to the cylinder against the outer end of said piston during inward movement of the piston, hydraulic fluid exhaust means for exhausting hydraulic fluid from the cylinder during outward movement of the piston, and pressurized lubricant feed means for feeding pressurized lubricant from a pressurized lubricant source into a space between the cylinder and the piston in a region of the cylinder where said cylinder is subjected to a side thrust force from the piston during at least portions of the reciprocating movement of said piston, wherein the inside dimensions of each cylinder are slightly greater than the corresponding outside dimensions of the associated piston along at least a portion of the length thereof such that a peripheral gap is formed between said cylinder and piston at each of respective opposite lateral sides of said piston when said piston is centrally positioned in and aligned with said cylinder, said piston and cylinder being configured such that relative lateral movement of said piston with respect to said cylinder resulting from said side thrust forces causes the width of the gap at one side of the piston tO be reduced and the width of the gap at the other side of the piston to be enlarged, and wherein said lubricant feed means includes at least one lubricant supply passage having an outlet end opening into one of said gaps and control means for controlling the supply of lubriccant to said outlet end, said control means being positioned upstream of said outlet end with respect to flow of lubricant through said supply passage and including means for varying said supply of lubricant to said outlet end as a direct function of the changes in lubricant back pressure in said passage resulting from changes in the width of said gap adjacent said outlet end.