Gas spring suitable as a lifting aid for hatchbacks or trunk lids of motor vehicles

Claim 1

A gas spring, especially suitable as a lifting aid for hatchbacks or trunk lids of motor vehicles, comprising a housing formed by a cylindrical tube, a piston rod disposed coaxially displaceably in said housing, a guide piston supported on said piston rod and guided in a sealed manner against the inside wall of the housing, said piston rod extending from one end of said housing in a gas-tight manner and serving as a compressing piston, gas under pressure within said housing, and means for holding the piston rod in the extended position against a predetermined retracting force, the improvement wherein said means for holding the piston rod in the extended position comprises at least one connecting passage extending through said guide piston and valve means for said at least one connecting passage to prevent gas from flowing past said guide piston and permit gas to flow in only one direction at any one time through said at least one connecting passage, said valve means comprising at least one first check valve for said connecting passage, said valve being openable when said piston rod is pushed into said housing and tightly closable when said piston rod is withdrawn from said housing, and a second check valve for said passageway, said second check valve sealing tightly when said piston rod is pushed into said housing and opening when said piston rod is withdrawn from said housing, said first check valve being tensioned in the closed position with a holding means exerting a holding force which counteracts opening, said holding force being substantially greater than the force exerted by the absolute gas pressure at the start of retraction.