Abstract: A stirling engine or an internal combustion engine having one or more cylinders, each having a moveable piston which is coupled to a drive shaft to drive a load. The engine load coupling also includes a set of Class 1 elliptical gears of the first type which means each gear rotates about one of its focal points. The load and the engine are efficiently operated as a result of the operation of the coupling arrangement. In apparatus employing a Stirling engine, apparatus and engine efficiencies are enhanced through elliptical gear operation which enables the Stirling engine to operate very closely to the idealized Stirling cycle.