Cryogenic refrigerator

Abstract

A cryogenic refrigerator includes a cylinder, a displacer configured to be moved back and forth in the cylinder by a drive unit, an inlet valve configured to be opened in supplying a refrigerant gas into the cylinder, an exhaust valve configured to be opened in exhausting the refrigerant gas from the cylinder, and an expansion space formed in the cylinder and configured to generate a cooling by expanding the refrigerant gas caused by back and forth movement of the displacer. A moving speed of the displacer in the vicinity of a bottom dead center is set to be faster than the moving speed of the displacer in the vicinity of a top dead center.

What is claimed is: 
     
         1 . A cryogenic refrigerator comprising:
 a cylinder;   a displacer configured to be moved back and forth in the cylinder by a drive unit;   an inlet valve configured to be opened in supplying a refrigerant gas into the cylinder;   an exhaust valve configured to be opened in exhausting the refrigerant gas from the cylinder; and   an expansion space formed in the cylinder and configured to generate a cooling by expanding the refrigerant gas caused by back and forth movement of the displacer,   wherein a moving speed of the displacer in the vicinity of a bottom dead center is set to be faster than the moving speed of the displacer in the vicinity of a top dead center.   
     
     
         2 . The cryogenic refrigerator as claimed in  claim 1 ,
 wherein the moving speed of the displacer is increased since the inlet valve is opened until the displacer reaches the bottom dead center.   
     
     
         3 . The cryogenic refrigerator as claimed in  claim 1 ,
 wherein a part of the movement of the displacer centering the bottom dead center is symmetric.   
     
     
         4 . The cryogenic refrigerator as claimed in  claim 1 ,
 wherein the drive unit further includes a Scotch-yoke mechanism, the Scotch-yoke including a bearing and a Scotch-yoke, the Scotch-yoke including a slide groove with which the bearing engages movably, and   a convex part is provided at a position corresponding to the bottom dead center of the slide groove.   
     
     
         5 . The cryogenic refrigerator as claimed in  claim 4 ,
 wherein the convex part includes a circular shape part at the center thereof.   
     
     
         6 . The cryogenic refrigerator as claimed in  claim 5 ,
 wherein a straight line part is provided on both sides of the circular shape part.   
     
     
         7 . The cryogenic refrigerator as claimed in  claim 1 ,
 the drive unit further includes a drive chamber to allow a driver gas for driving the displacer,   a high-pressure valve for supplying the driver gas to the drive chamber, and   a low-pressure valve for exhausting the driver gas in the drive chamber.   
     
     
         8 . The cryogenic refrigerator as claimed in  claim 7 ,
 wherein an opened period of the low-pressure valve is set to be longer than that of the high-pressure valve.   
     
     
         9 . The cryogenic refrigerator as claimed in  claim 8 ,
 wherein a flow passage resistance is provided between the high-pressure valve and the drive chamber.   
     
     
         10 . The cryogenic refrigerator as claimed in  claim 1 ,
 wherein the drive unit is a linear motor connected to the displacer.