Abstract: Reciprocating apparatuses such as a displacer in a Stirling engine or Vuilleumier (thermally-driven) heat pump and such as a poppet valve in an internal combustion engine have been known to be built with a mechatronic actuator. The reciprocating element has two springs in compression biased against each other. It has been found that conventional springs in compression introduce losses. A spring is disclosed in which a portion of the coil is wound in a clockwise direction and a portion is wound in a clockwise direction. Also, in reciprocation, the spring is in compression at one end of travel and in tension at the other end of travel.

Abstract: Regenerators for Stirling engines and Vuilleumier heat pumps are difficult to reliably manufacture. A regenerator is disclosed in which edges of the regenerator wire meshes are coated with a stabilizing material. The regenerator wire meshes are then sufficiently stable to be machined to the dimensions of the housing. In some embodiments, the material on the outer surface of the edges of the regenerator is relatively thermally insulating to limit heat transfer to the housing.