Spring devices – Vehicle – Comprising compressible fluid
Reexamination Certificate
1999-06-22
2001-05-22
Schwartz, Christopher P. (Department: 3613)
Spring devices
Vehicle
Comprising compressible fluid
C267S064190, C267S064270, C267S123000
Reexamination Certificate
active
06234461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an adjustable length gas spring comprising a housing, which has a central longitudinal axis; a piston rod extended out of the housing concentrically of the central longitudinal axis; a piston, which is mounted on the piston rod and displaceable in the housing, and which divides the housing into a first partial volume and a second partial volume, the piston rod passing through the first partial volume; and a valve for connecting the partial volumes with each other.
1. Background Art
Adjustable length gas springs of the generic type are known for instance from U.S. Pat. No. 3,656,593 or U.S. Pat. No. 5,915,674 as so-called two-tube gas springs, the housings of which consist of an external cylinder and an internal cylinder, between which forms an annular space. A valve is provided at one end of the housing. A piston rod is extended out of the other end, a piston being disposed on its inside end, dividing the space in the interior cylinder into two partial volumes. Furthermore, adjustable length gas springs of the generic type are designed as so-called single-tube gas springs, in which a valve is formed in the piston and can be actuated from outside through the piston rod.
These known adjustable length gas springs are employed substantially as length adjustment elements in adjustable height chair columns. A problem resides in that when the piston rod is inserted to a large extent into the gas spring, with the valve being closed, the ease and convenience that springiness offers to a user sitting on the chair is low, because breakdown of the gas spring may occur in particular when heavyweight persons sit down on the chair.
To solve this problem, it has become known from U.S. Pat. No. 4,318,536, in a two-tube gas spring, to form a valve space in the partial volume turned towards the valve and to join to the piston a closing element which projects towards the valve space, moves sealingly into the valve space when the piston rod has a given position of insertion and separates the valve space from the partial volume. In this case, a marginal condition consists in that, when the valve space is closed by the closing element, the quotient of the cross-sectional surfaces of the piston ring surface and the surface of the closing element exceeds the quotient of the volume of a remaining space and the volume of the valve space. This helps obtain reliable terminal spring stiffening; however, the constructional requirements are considerable.
SUMMARY OF THE INVENTION
It is an object of the invention to embody an adjustable length gas spring of the generic type so that convenient springiness and terminal spring stiffening are attained by simple means.
According to the invention, this object is attained by the features which consist in that a device for closing the valve is disposed in the second partial volume, closing the valve when a predetermined minimum length of the second partial volume is reached by displacement of the piston. The device according to the invention for closing the valve can be inserted as an additional component into an otherwise unmodified adjustable length gas spring without the need of any special measures. The described breakdown of the gas spring does not occur any longer.
Further features, advantages and details of the invention will become apparent from the ensuing description of four exemplary embodiments, taken in conjunction with the drawing.
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Bohm Walter
Weisser Frank
Browdy and Neimark
Schwartz Christopher P.
Siconolfi Robert A.
Suspa Compart Aktiengesellschaft
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