Abstract: In a hot gas engine, for example, of the Stirling cycle type, having a displacer member and associated working piston member, normally moving in respective cylinder spaces with a selected phase relation and having controllable torque output in magnitude and direction, or a plurality of associated displacer piston pairs, the displacer drive affords changeable control of displacer stroke length between a zero or minimum stroke length and a maximum and phase reversal, with or corresponding to a torque requirement of direction and magnitude between a minimum and maximum, thereby to minimize windage type energy losses due to displacer motion at times of low power or low torque demand, and also with displacer stroke length control, controlling torque and output direction.

Abstract: A multi-cylinder self-starting hot gas engine according to the present invention consists of two parallel pairs of opposed displacer cylinders with respective displacer members mounted for movement therein and two parallel pairs of opposed work cylinders disposed parallel to the displacer cylinders and having respective pistons arranged to reciprocate therein; each work cylinder communicating with a respective displacer cylinder to provide a cold end chamber. First transmission connects the displacers for synchronized movement offset in phase within the cylinders and a second transmission interconnects the pistons for synchronized movement offset in phase within the cylinders. An output drive is connected to the pistons.