Hybrid cryogenic refrigerator

Claim 1

In a cryogenic refrigerator in which a movable displacer means defines within an enclosure first and second chambers of variable volume, and in which a refrigerant fluid is circulated in a fluid flow path between said first chamber and said second chamber by the movement of said displacer means controlled in part through the introduction of high-pressure fluid and the discharge of low-pressure fluid, the improvement comprising chamber means for guiding a slide connected to the displacer means, said slide having an axial passage communicating with one end of said chamber means remote from the displacer means, a motor coupled to said slide for controlling movement of the displacer means adjacent top dead center and bottom dead center positions thereof, a fluid reaction surface on said slide intermediate its ends, means for applying pressure to said surface for overriding said motor when the slide is spaced from top dead center, said passage in said slide having a restriction, a valve having a spool valve member for controlling flow of the high and low pressure fluid, means including a conduit communicating one end of said spool valve member with said one end of said chamber means for introducing high fluid pressure into the conduit to shift the spool valve member when the displacer means is at one of the extremities of its movement.