Clearance seals and piston for cryogenic refrigerator compressors

Claim 2

In a cryogenic refrigerator, an assembly comprising: a piston housing; a sleeve positioned to float within said housing and having a flexible seal between the sleeve and housing to permit transverse movement relative to the housing, the sleeve comprising ceramic and being a substantial peak to peak pressure variation at one end of the sleeve and a relatively constant pressure at the other end of the sleeve; and a piston comprising ceramic positioned within said sleeve for axial reciprocation.

Claim 3

The cryogenic refrigerator of claim 1 wherein the sleeve is retained in the piston housing by means of a snap ring.

Claim 4

The cryogenic refrigerator assembly of claim 1 wherein the piston housing is comprised of two pieces and the sleeve is trapped in position by the assembly of the two piece piston housing.

Claim 5

The cryogenic refrigerator of claim 1 wherein said piston positioned within said sleeve has an outer diameter within 0.005 inches of the inner diameter of the sleeve.

Claim 6

The cryogenic refrigerator of claim 1 wherein the ceramic material of the piston is cermet.

Claim 7

The cryogenic refrigerator of claim 1 wherein the piston is driven by a rotary drive motor.

Claim 8

In a cryogenic refrigerator, a compressor piston assembly comprising: a two piece housing with a seal between the two pieces of the housing; a sleeve comprising ceramic, loosely retained in positioned by the assembly of the two pieces of the housing; a piston comprising ceramic for axial reciprocation within said sleeve, wherein the piston forms with one of said pieces of the housing a substantially closed work space for the compression of gas and wherein the other piece of the housing is open to allow connection of drive means to the piston; a clearance seal between said piston and said sleeve; and an elastic seal to prevent gas leakage between said sleeve and housing from said work space.

Claim 9

In a cryogenic refrigerator, a compressor piston assembly comprising: a two piece housing with a seal between the two pieces of the housing; a sleeve comprising ceramic, loosely retained in positioned by the assembly of the two pieces of the housing; a piston comprising ceramic for axial reciprocation within said sleeve, wherein the piston forms with one of said pieces of the housing a substantially closed work space for the compression of gas and wherein the other piece of the housing is open to allow connection of drive means to the piston; a clearance seal between said piston and said sleeve; and an elastic seal to prevent gas leakage between said sleeve and housing from said work space.

Claim 10

A helium cryogenic refrigerator of the type comprising a reciprocating displacer within a refrigerator cylinder, the displacer being driven in a reciprocating motion by the pressure differential between helium gas in the refrigerator cylinder and gas in a gas spring volume, the refrigerator cylinder being in fluid communication with a compressor space in a compressor cylinder, the compressor space and the refrigerator cylinder defining a closed working volume of helium gas which is compressed and expanded by a piston in the compressor housing; the refrigerator further comprising a fluid seal between the ends of the compressor piston which is a low friction clearance seal between a hard, smooth wall of a floating sleeve loosely positioned within the compressor housing and a hard, smooth piston wall to permit transverse movement relative to the housing.

Claim 11

A helium cryogenic refrigerator of the type comprising a reciprocating displacer within a refrigerator cylinder, the displacer being driven in a reciprocating motion by the pressure differential between helium gas in the refrigerator cylinder and gas in a gas spring volume, the refrigerator cylinder being in fluid communication with a compressor space in a compressor cylinder, the compressor space and the refrigerator cylinder defining a closed working volume of helium gas which is compressed and expanded by a piston in the compressor housing; the refrigerator further comprising a fluid seal between the ends of the compressor piston which is a low friction clearance seal between a hard, smooth wall of a floating sleeve loosely positioned within the compressor housing and a hard, smooth piston wall to permit transverse movement relative to the housing.

Claim 12

A refrigerator as claimed in claim 8 wherein the radial clearance between the sleeve and piston is less than 1×10 -4 inches.

Claim 13

A refrigerator as claimed in claim 8 wherein the sleeve comprises ceramic material.

Claim 14

A refrigerator as claimed in claim 10 wherein the piston is comprised of cermet.

Claim 15

The cryogenic refrigerator of claim 8 wherein a crank mechanism is connected to the piston for oscillatory movement by means of a ceramic wrist pin, said pin forming a sleeve bearing and being lubricated by helium gas.