An improvement is provided to a pressurized close-cycle machine that has a cold-end pressure vessel and is of the type having a piston undergoing reciprocating linear motion within a cylinder containing a working fluid heated by conduction through a heater head by heat from an external thermal source. The improvement includes a heat exchanger for cooling the working fluid, where the heat exchanger is disposed within the cold-end pressure vessel. The heater head may be directly coupled to the cold-end pressure vessel by welding or other methods. A coolant tube is used to convey coolant through the heat exchanger.

A hot fluid expansion engine has a plurality of actuator modules arranged in a star configuration around a central shaft. Each module includes a drive piston defining a working chamber of variable volume in the first enclosure; a movable displacement piston subdividing a second enclosure into a low temperature chamber of variable volume and a high temperature chamber of variable volume with the high temperature chamber communicating with a unit of a fluid heater device and the low temperature chamber communicating with the working chamber; and a fluid circulation circuit extending between the fluid heater device and the working chamber. The drive piston and the displacement piston of each actuator module are connected to the central shaft via respective first and second eccentric transmission devices suitable for imparting reciprocating motion in translation to each of the pistons with a phase lag of 90.

Provided is a thermally efficient Stirling cycle engine including: a casing; a cylinder housed within the casing; a piston reciprocatable inside said cylinder; a displacer reciprocatable with a phase difference relative to the piston; a compression chamber defined between the piston and the displacer; an expansion chamber arranged on a first side of the displacer with a second side thereof opposite to the compression chamber; a heat exhausting unit arranged in the neighborhood of the compression chamber; a heat absorbing unit arranged in the neighborhood of the expansion chamber; a regenerator arranged between the heat exhausting unit and the heat absorbing unit; and a heat exhausting chamber defined between an outer surface of the casing and an inner surface of the heat exhausting unit, said heat exhausting chamber in communication with the compression chamber and the regenerator respectively through a first passage and a second passage provided in the casing.