Cryogenic refrigerator

Abstract

A cryogenic refrigerator includes : a axially extending cylinder; an axially reciprocating displacer provided inside the cylinder, at a gap between an inner circumferential surface of the cylinder and an outer circumferential surface of the displacer, the displacer shifting to create an expansion space between the displacer and a first axial end portion of the cylinder; a regenerator built in the displacer; and a sleeve disposed along the inner circumferential surface of the first axial end portion of the cylinder, encompassing the expansion space. A first passage for guiding the refrigerant gas from the regenerator to the gap is provided in the displacer, and a second passage for guiding the refrigerant gas from the gap to the expansion space is provided between the first axial end of the cylinder and the sleeve, and/or is provided between the outer surface and the inner surface of the sleeve.

What is claimed is: 
     
         1 . A cryogenic refrigerator comprising:
 an axially extending cylinder;   an axially reciprocating displacer provided inside the cylinder, at a gap between an inner circumferential surface of the cylinder and an outer circumferential surface of the displacer, for shifting to create an expansion space for refrigerant gas between the displacer and an axial end portion of the cylinder;   a regenerator built into the displacer; and   a sleeve disposed along the inner circumferential surface of the axial end portion of the cylinder, encompassing the expansion space; wherein   a first passage for guiding the refrigerant gas from the regenerator to the gap is provided in the displacer, and   a second passage for guiding the refrigerant gas from the gap to the expansion space is provided between the axial end portion of the cylinder and the sleeve, and/or is provided between the outer surface and the inner surface of the sleeve.   
     
     
         2 . The cryogenic refrigerator according to  claim 1 , wherein:
 the sleeve includes a cylindrical portion opposing the inner circumferential surface of the cylinder, and a bottom plate opposing a bottom portion of the cylinder; and   the second passage includes a lateral gap formed between the cylindrical portion of the sleeve and the inner circumferential surface of the cylinder, and a bottom gap, connecting with the lateral gap, formed between the bottom plate of the sleeve and the bottom portion of the cylinder.   
     
     
         3 . The cryogenic refrigerator according to  claim 2 , wherein the bottom plate of the sleeve is centrally perforated by a through-hole communicating the bottom gap with the expansion space. 
     
     
         4 . The cryogenic refrigerator according to  claim 1 , wherein the cryogenic refrigerator is a single-stage refrigerator.