Document Type


Publication Date



Describes a pump that has a fixed gear axis eccentricity and varies displacement by moving controlling elements linearly along the drive shaft. A pressure compensator may be employed to displace the controlling elements. It includes a housing penetrated by a drive shaft rotating internal elements. The internal components slide along the longitudinal axis established by the drive shaft to vary the fluid displacement. The axially-moving elements include the drive shaft, inner gerotor element, port plug, thrust bearing and retainer sleeve. The drive shaft includes an internal flanged forming a piston. The outward face of the piston is in contact with fluid at system pressure. The internal gerotor element and port plug are retained against the piston by a thrust bearing that slides over the drive shaft and is held in place by a retainer sleeve. The port plug has a rear face that also functions as a piston and this face is the same size as the flanged piston. Thus, the outward piston face and rear face of the port plug can push the assembly in the housing along the longitudinal axis established by the driveshaft. A pressure compensator senses the system pressure and then displaces the axially-moving elements to produce the required displacement. The compensator is controlled by pressure operating against a return spring. The pressure compensator may either be external or integral with the pump.


Mechanical Engineering

Patent Number


Application Filed



University of Arkansas (Little Rock, AR)


Jack H. Cole, Department of Mechanical Engineering, University of Arkansas, Fayetteville, AR