Cryogenic refrigerator

Abstract

A cryogenic refrigerator includes a cylinder; a displacer configured to reciprocate in the cylinder; a driving unit configured to drive a rotational shaft having an axial direction oriented in a direction of reciprocating movement of the displacer; and a movement conversion unit configured to convert rotational movement of the rotational shaft into the reciprocating movement of the displacer. The movement conversion unit is a screw unit including a male thread and a female thread one of which is a part of the displacer.

What is claimed is: 
     
         1 . A cryogenic refrigerator, comprising:
 a cylinder;   a displacer configured to reciprocate in the cylinder;   a driving unit configured to drive a rotational shaft having an axial direction oriented in a direction of reciprocating movement of the displacer; and   a movement conversion unit configured to convert rotational movement of the rotational shaft into the reciprocating movement of the displacer,   wherein the movement conversion unit is a screw unit including a male thread and a female thread one of which is a part of the displacer.   
     
     
         2 . The cryogenic refrigerator as claimed in  claim 1 , wherein the male thread is formed on an outer circumferential surface of the displacer and the female thread is formed on an inner circumferential surface of the cylinder. 
     
     
         3 . The cryogenic refrigerator as claimed in  claim 1 , wherein the female thread is formed on an inner circumferential surface of a hole extending from a hot-end surface toward a cold-end surface of the displacer. 
     
     
         4 . The cryogenic refrigerator as claimed in  claim 3 , further comprising:
 a cylindrical part that is drivably coupled to the rotational shaft such that the cylindrical part is movable in the axial direction relative to the rotational shaft,   wherein the male thread is formed on an outer circumferential surface of the cylindrical part.   
     
     
         5 . The cryogenic refrigerator as claimed in  claim 2 , further comprising:
 a seal disposed in a clearance formed between the displacer and the cylinder,   wherein the seal includes an intermediate layer containing a lubricant and sandwich layers sandwiching the intermediate layer in the axial direction.   
     
     
         6 . The cryogenic refrigerator as claimed in  claim 1 , further comprising:
 a rotary valve configured to control intake and exhaust of gas into and from an expansion space formed by the cylinder and the displacer,   wherein the driving unit is configured to drive the rotary valve.