Temperature compensated gas spring

Claim 2

A temperature-compensated gas spring, comprising: a self-contained casing having a closed end wall and an apertured end wall; a piston rod extending from the interior to the exterior of said casing through said apertured end wall in sealed relation thereto; a piston mounted on the piston rod within the casing and dividing the interior of said casing into first and second sealed chambers adjacent said closed end wall and said apertured end wall, respectively, of said casing; a primary pressure source in said first chamber creating a primary pressure acting against the piston to urge the piston rod out of the casing; a secondary pressure source in said second chamber creating a secondary pressure acting against the piston to urge the piston rod into the casing; the magnitudes of said primary and secondary pressures relative to the respective piston areas on which they act being such that a new outward force is exerted on the piston rod; the primary pressure source comprising a pressurized gas characterized by (1) a first percent change of pressure with temperature and (2) a change of pressure with volume such that said net outward force varies with piston rod displacement; the secondary pressure source comprising a two-phase vapor-liquid system having a vapor pressure characterized by a second percent change in pressure with temperature at temperatures below the critical temperature of said system; the second percent change of pressure with temperature being greater than the first percent change of pressure with temperature; and the volume of said second chamber and the mass of said two-phase system in said second chamber being such that (1) the two-phase system does not fully condense into liquid at any point over the operating temperature range of the gas spring and at any point over the working stroke of the piston rod and (2) the liquid phase and the vapor phase of said two-phase system remain in equilibrium over at least a substantial portion of the temperature range over which temperature compensation is to be effected and over at least a portion of the working stroke of the piston rod, whereby the effect of temperature on the net outward force exerted on the piston rod is compensated for over part or all of the working stroke of the piston rod.

Claim 3

The gas spring of claim 1 wherein said primary pressure varies essentially proportionally with absolute temperature.

Claim 4

The gas spring of claim 2 wherein said secondary pressure varies approximately exponentially with absolute temperature.

Claim 5

The gas spring of claim 1 wherein said pressurized gas remains in the gas phase over the full operating temperature range of the gas spring.

Claim 6

The gas spring of claim 4 wherein said temperature range is -30° C. to 80° C.

Claim 7

The gas spring of claim 4 wherein said pressurized primary gas is nitrogen.

Claim 8

The gas spring of claim 1 wherein the liquid and vapor phases of the two-phase system remain in equilibrium over the full operating temperature range of the gas spring.

Claim 9

The gas spring of claim 7 wherein the two-phase system is selected from the group consisting of acetylene, ethane, FREON-12, FREON-13, FREON-114, propane, propadiene, perfluoropropane, dimethyl ether, N-butane, ammonia, hydrogen bromide and hydrogen iodide.

Claim 10

The gas spring of claim 7 wherein the two-phase system is ammonia.

Claim 11

The gas spring of claim 7 wherein the two-phase system is FREON-12.

Claim 12

The gas spring of claim 7 wherein the operating temperature range is -30° C. to 80° C.

Claim 13

The gas spring of claim 1 wherein the two-phase system is sulfur hexafluoride.

Claim 14

The gas spring of claim 1 wherein said primary pressure source is pressurized nitrogen gas, and said secondary pressure source is the vapor pressure of a two-phase system selected from the group consisting of ammonia, FREON-12, and sulfur hexafluoride.

Claim 15

The gas spring of claim 1 wherein said pressurized gas remains in the gas phase over the full working stroke of the piston rod.

Claim 16

The gas spring of claim 1 wherein the liquid and vapor phases of the two-phase system remain in equilibrium over the full working stroke of the piston rod.

Claim 17

A temperature-compensated gas spring, comprising: (a) a self-contained casing including an outer tube having a closed end wall at one end and a wall having an opening therethrough at the other end; (b) an inner tube disposed within the outer tube and having one end attached to said closed end wall; (c) a slidable piston disposed within said inner tube in sealed relation thereto and dividing said inner tube into a first inner volume between the piston and said closed end wall and a second inner volume in the remainder of the inner tube; (d) a rod secured to the piston and extending through the opening in said other end wall in sealed relation thereto; (e) means between said inner tube and said outer tube for dividing the casing volume exterior of said inner tube in a gas-tight manner into a first outer volume adjacent said closed end wall and a second outer volume adjacent said wall having an opening therethrough; (f) first conduit means connecting said first inner volume and said first outer volume; (g) second conduit means connecting said second inner volume and said second outer volume; (h) a primary pressure source in said first inner and outer volumes creating a primary pressure acting against said piston to urge said rod out of said casing, said primary pressure source comprising a pressurized gas characterized by (1) a first percent change of pressure with temperature and (2) a change of pressure with volume such that the magnitude of said primary pressure source varies with piston rod displacement; (i) a secondary pressure source in said second inner and outer volumes creating a secondary pressure acting against said piston to urge said rod into said casing, said secondary pressure source comprising a two-phase vapor-liquid system characterized by a second percent change of pressure with temperature at temperatures below the critical temperature of said system; (j) the magnitudes of said primary and secondary pressure sources relative to the respective piston areas on which they act being such that a net outward force is exerted on the piston rod which varies with piston rod displacement; (k) the second percent change of pressure with temperature being greater than the first percent change of pressure with temperature; and (l) the total volume of said secnd inner and outer volumes and the mass of said two-phase system in said second inner and outer volumes being such that (1) the two-phase system does not fully condense into liquid at any point over the operating temperature range of the gas spring and at any point of the working stroke of the piston rod and (2) the liquid phase and the vapor phase of said two-phase system remain in equilibrium over at least a substantial portion of the temperature range over which temperature compensation is to be effected and over at least a portion of the working stroke of the piston rod, whereby the effect of temperature on the net outward force exerted on the piston rod is compensated for over part or all of the working stroke of the piston rod.

Claim 18

A temperature-compensated gas spring, comprising: (a) a self-contained casing including an outer tube having a closed end wall at one end and a wall having an opening therethrough at the other end; (b) an inner tube disposed within the outer tube and having one end attached to said closed end wall; (c) a slidable piston disposed within said inner tube in sealed relation thereto and dividing said inner tube into a first inner volume between the piston and said closed end wall and a second inner volume in the remainder of the inner tube; (d) a rod secured to the piston and extending through the opening in said other end wall in sealed relation thereto; (e) means between said inner tube and said outer tube for dividing the casing volume exterior of said inner tube in a gas-tight manner into a first outer volume adjacent said closed end wall and a second outer volume adjacent said wall having an opening therethrough; (f) first conduit means connecting said first inner volume and said first outer volume; (g) second conduit means connecting said second inner volume and said second outer volume; (h) a primary pressure source in said first inner and outer volumes creating a primary pressure acting against said piston to urge said rod out of said casing, said primary pressure source comprising a pressurized gas characterized by (1) a first percent change of pressure with temperature and (2) a change of pressure with volume such that the magnitude of said primary pressure source varies with piston rod displacement; (i) a secondary pressure source in said second inner and outer volumes creating a secondary pressure acting against said piston to urge said rod into said casing, said secondary pressure source comprising a two-phase vapor-liquid system characterized by a second percent change of pressure with temperature at temperatures below the critical temperature of said system; (j) the magnitudes of said primary and secondary pressure sources relative to the respective piston areas on which they act being such that a net outward force is exerted on the piston rod which varies with piston rod displacement; (k) the second percent change of pressure with temperature being greater than the first percent change of pressure with temperature; and (l) the total volume of said secnd inner and outer volumes and the mass of said two-phase system in said second inner and outer volumes being such that (1) the two-phase system does not fully condense into liquid at any point over the operating temperature range of the gas spring and at any point of the working stroke of the piston rod and (2) the liquid phase and the vapor phase of said two-phase system remain in equilibrium over at least a substantial portion of the temperature range over which temperature compensation is to be effected and over at least a portion of the working stroke of the piston rod, whereby the effect of temperature on the net outward force exerted on the piston rod is compensated for over part or all of the working stroke of the piston rod.

Claim 19

The gas spring of claim 16 wherein said first conduit means comprises at least one hole through said inner tube beyond the extent of travel of said piston toward said closed end wall, wherein said inner tube extends toward but stops short of said wall having an opening therethrough, and wherein said inner tube is open between said second inner volume and second outer volume to form second connecting means.

Claim 20

The gas spring of claims 17 including a stop which limits the travel of said piston away from said closed end wall.

Claim 21

The gas spring of claim 18 wherein said first conduit means comprises at least one hole through said inner tube beyond the extent of travel of said piston toward said closed wall, wherein said inner tube extends to and is attached to said wall having an opening therethrough, and wherein said second conduit means comprises at least one hole through said inner tube beyond the extent of travel of said piston away from said closed end wall.

Claim 22

The gas spring of claims 16, 17, or 19 wherein said primary pressure varies essentially proportionally with absolute temperature.

Claim 23

The gas spring of claim 20 wherein said pressurized gas remains in the gas phase over the full operating temperature range of the gas spring.

Claim 24

The gas spring of claim 21 wherein said operating temperature range is -30° C. to 80° C.

Claim 25

The gas spring of claim 21 wherein said pressurized gas is nitrogen gas.

Claim 26

The gas spring of claim 20 wherein said secondary pressure varies approximately exponentially with absolute temperature.

Claim 27

The gas spring of claim 16 wherein the liquid and vapor phases of said two-phase system remain in equilibrium over the full operating temperature range of the gas spring.

Claim 28

The gas spring of claim 25 wherein said two-phase system is selected from the group consisting of acetylene, ethane, FREON-12, FREON-13, FREON-114, propane, propadiene, perfluoropropane, dimethyl ether, N-butane, ammonia, hydrogen bromide, and hydrogen iodide.

Claim 29

The gas spring of claim 25 wherein said two-phase system is ammonia.

Claim 30

The gas spring of claim 25 wherein said two-phase system is FREON-12.

Claim 31

The gas spring of claim 16 wherein said two-phase system is sulfur hexafluoride.

Claim 32

The gas spring of claims 16, 17, or 19 wherein said primary pressure source is pressurized nitrogen gas, and said secondary pressure source is the vapor pressure of a two-phase system selected from the group consisting of ammonia, FREON-12, and sulfur hexafluoride.

Claim 33

The gas spring of claims 16, 17, or 19 wherein said inner tube, said outer tube, and said piston are cylindrical in cross section.