Method for optimizing the mechanical output of a fluid pressure free

Abstract

A fluid pressure, free piston engine, such as a centrifugal piston expander, provides a cyclically varying torque to a rotatable output shaft. A unidirectional or overrunning rotational clutch comprising two relatively rotatable elements has one element secured to a unidirectionally rotatable load and the other element driven by the output shaft of the centrifugal piston expander. The engine output shaft further drives, through appropriate gearing, a battery operated, starting motor-generator unit. The motor-generator is employed to initially rotate the expander to sufficient speed to ensure the centrifugal return of the free pistons of the centrifugal piston expander to their radially outermost positions. After start-up of the centrifugal piston expander, the starting motor functions as a generator to recharge the battery during the high torque portions of rotation of the engine output shaft, and during the low torque portions of the power output shaft, again functions as a motor to increase such speed. A plurality of fluid pressure engines may be connected to the same output shaft and selectively energized to further minimize the cyclical swing in speed of the power output shaft and to provide variable displacement operation by automatically varying the number of engines utilized to accommodate a varying load.