Abstract: In a compression piston, the wrist pin clearance bearing is lubricated by gas from the volume of working gas. The clearance bearing is formed by a wrist pin positioned within a pinhole of the piston. During reciprocation of the piston, the wrist pin oscillates in the piston pinhole and compresses the gas therein. The compression produces a squeeze film which prevents contact between the wrist pin and piston. The stroke time of the piston is not long enough during a cycle to collapse the squeeze film. The gas squeeze film thus lubricates the wrist pin clearance bearing. A clearance seal is formed between the piston and a cylinder of the piston housing. The clearance seal is of small clearance relative to the clearance bearing so that it limits leakage by the wrist pin. The small clearance seal also enables the requisite pressure buildup within the pinhole to generate an adequate squeeze film about the clearance bearing.

Abstract: A cryocooler 8 is described which has a low magnetic signature in which a ceramic displacer 10 reciprocates within a helium impenetrable cold finger cylinder 12. A cyrogenic refrigerator formed by the displacer and the cold finger cylinder cools a cold space 22 to cryogenic temperature. The cold space 22 is magnetically shielded from a drive motor 18 which both drives the displacer 10 and compressor pistons 14, 15, 16. The motor is magnetically shielded by means of magnetic shields 70, 72, 74, 90, 76, 78, 80, 82.

Abstract: A cermet piston 36 is positioned to reciprocate within a ceramic sleeve 58 of a cryogenic refrigerator 12. The sleeve 58 forms a very tight clearance seal 67 with the piston 36 yet is allowed to float within a large gap 66 between piston housing 35 and the sleeve. The gap 66 allows the sleeve 66 to compensate for misalignment or distortions of the piston housing 35. Elastic seals 68, 70 prevent gas blow-by between the working space 18 of the piston 36 and the piston's dead space 19. The piston is connected to a motor drive mechanism through connecting rod 44 and helium lubricated wrist pin 48.

Abstract: In an integral Stirling cryogenic refrigerator the compressor piston is several times heavier than the displacer. In order to counterbalance both the displacer and compressor piston with a rotating counterweight, the displacer connecting rod is formed of a high density material. Specifically, the connecting rod is formed of a tungsten alloy and is several times heavier than the displacer.

Abstract: In a split Stirling refrigerator, the dynamic seals about the displacer are virtually dragless clearance seals. The displacer is driven by pressure differential between a working gas and a gas in a spring volume, but the displacer movement is retarded until about peak pressure by forces resulting from fluid friction of gas flowing through the regenerative matrix. The fluid friction results in pressure differentials across the displacer, and the retarding effects of those pressure differentials can be increased to eliminate the need for any Coulomb friction to retard the displacer movement.