Resilient column of adjustable length

Claim 1

A column of adjustable length comprising: (a) an elongated guide tube having a longitudinal axis and formed with a longitudinal bore, (1) said tube having an apertured end wall transverse to said axis, (2) said end wall having an axially inner face and an axially outer face directed in axially opposite directions; (b) a pneumatic spring at least partly received in said bore for axial movement therein and including (1) a cylinder member defining a sealed cavity therein, (2) a piston axially movable in said cavity and normally sealing two compartments of said cavity from each other, (3) a piston rod member fastened to said piston and projecting axially outward of said cavity, and (4) fluid in said cavity under a pressure higher than atmospheric pressure for elastically supporting said piston rod member within said cylinder member so as to resist a load transmitted to the end of the pneumatic spring remote from said apertured end wall; (c) a bar member axially elongated and fixedly fastened to one of said members of the pneumatic spring, said bar member axially extending from said one member through said bore and through the aperture in said end wall for movement inward and outward of said bore; (d) spring seat means on said one member in said bore; (e) yieldably resilient means located entirely within said bore between said spring seat means and the axially inner face of said end wall for biasing said bar member inward of said bore in the direction of said remote end and for resiliently permitting substantial axial displacement of said bar member outward of said bore in response to a load applied to the remote end of said pneumatic spring, thereby to afford additional resilience in the column in series with the resilience afforded by the pneumatic spring; said resilient means surrounding said bar member and being axially prestressed between said seat means and said inner face in all positions of said one member within said bore; and (f) an abutment member carried by said bar member outside said bore and dimensioned for abutting engagement with said outer face of said end wall to limit movement of said bar member inward of said bore, said abutment member being urged into abutting engagement with said outer face in the absence of an external load on said pneumatic spring compressing said resilient means.