Spring and resonant system for free-piston stirling engines

Abstract

A free-piston Stirling engine having a double acting, gas spring system for applying bi-directional, resilient spring forces to the displacer piston rod and also a free-piston Stirling engine having a displacer and power piston which are mechanically resonant at the operating frequency of the engine. The springing system is a gas containing compartment which is formed in communication with the effective end of the displacer rod. An adjustable spool valve arrangement may be formed in the mating walls of the displacer rod and its cylinder for connecting the gas containing compartment with the bounce space during a relatively minor interval of the displacer rod stroke intermediate its extremes for adjustably maintaining the mean position of the displacer at the position at which the interconnection occurs. The resonant system comprises the combination of a displacer and associated spring with the displacer mass and the spring force constant being such that the combination is resonant at the engine operating frequency. Similarly, the power piston may be linked to a gas or mechanically deformable spring wherein that combination is also resonant at the same operating frequency. Preferably, the displacer spring is a gas spring linked to the engine cylinder block. A balanced, multi-piston engine is described which has a power piston spring which comprises a mass of gas in a passage communicating with an end of each of the power piston cylinders.