PISTON RING UNIT FOR STIRLING REFRIGERATOR

Disclosed is a piston ring unit for a Stirling-type refrigerator, including a compression unit operated by a driving force of an engine of a vehicle to compress a working fluid filled in the compression unit by reciprocation movement of a piston; an expansion unit for expanding the working fluid compressed by the compression unit by the reciprocating movement of the piston; and a regeneration unit for fluidically communicating the compression unit and the expansion unit. In the Stirling-type refrigerator in which the working fluid absorbs the heat in the expansion unit and radiates the heat in the compression unit through repetition of isothermal compression, constant-volume process, and isothermal expansion, the working efficiency is increased when the piston is reciprocated in a compression chamber and an expansion chamber provided in the compression unit and the expansion unit. A ring groove is formed on the outer peripheral surface of a front end of the piston, and two piston rings are mounted in the ring groove so that the piston rings are movable in a moving direction of the piston when the piston is reciprocated. The center of the ring groove is formed integrally with a protrusion, with each piston ring being interposed between the protrusions.