Spring devices – Vehicle – Comprising compressible fluid
Reexamination Certificate
1998-10-21
2001-01-09
Schwartz, Christopher P. (Department: 3613)
Spring devices
Vehicle
Comprising compressible fluid
C267S124000
Reexamination Certificate
active
06170806
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns piston/cylinder assemblies.
As a rule, a piston/cylinder assembly consists of a cylinder and a piston that is received for sliding movement along the cylinder and is affixed to a piston rod that extends out of the cylinder. Connecting members on the cylinder and on the outer end of the piston rod serve to connect the piston/cylinder to elements that are axially movable relative to one another.
A vibration damper for a motor vehicle chassis is an example of a piston/cylinder assembly. A fundamental problem with vibration dampers is the production of a large damping force with small cylinder diameters. One possibility is to use relatively thick piston rods whose displacing volume figures significantly in the calculation of damping forces. However, doing so is associated with a requirement for considerable radial installation space since the piston rod also requires a piston rod guide and piston rod seal. Moreover, an equalization chamber must also be present for the displacing volume, which further increases the space requirement.
A similar problem exists for gas springs. The principal structure is comparable to a vibration damper. Rather than a damping force, a compression or tension force is intended to be available for use, which is calculated from the area of the piston rod cross section exposed to pressure multiplied by the operating pressure in the cylinder. In this application, too, a large piston rod diameter is desirable on the one hand, but is limited by the installation space generally available.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a piston/cylinder assembly that makes possible maximum utilization of operating force with as little installation space as possible.
The object is attained, in accordance with the invention, by a piston/cylinder assembly that includes a cylinder and a piston received in the cylinder for axial movement and dividing the cylinder into two working chambers. A first connecting member is affixed to the cylinder and is adapted to connect the cylinder to one of two elements that are movable relative to each other. At least one second connecting member is operatively coupled to the piston, extends through an opening in the cylinder, and is adapted to connect the piston to the other of the two elements. The opening in the cylinder has a length axially of the cylinder that is not less than the length of the stroke of the piston.
As a consequence of the principle of the invention, the piston has a relatively long guideway in the cylinder. In order to avoid the effect of undesired transverse forces, several connecting members can be arranged in circumferentially spaced-apart relation on the piston. When there are several connecting members, particularly when they are arranged symmetrically, the transverse forces counterbalance one another, thus reducing or eliminating transverse (lateral) loads on the piston.
In another embodiment, the opening has offset sections in the circumferential direction that form a guide frame for the connecting member on the piston. By this means, a rotary motion of the piston can also be effected via the piston stroke and thus a rotary motion of the components attached to the piston/cylinder assembly.
With a view to good guidance of the piston in its movements along the cylinder and to low weight, the piston is designed as a tubular body with a base.
When the piston/cylinder assembly is used as a locking element, the piston has at least one flow connection between the working chambers, of which at least one can be at least partially closed via a control unit in conjunction with a valve. The control unit can be actuated radially in the piston from outside of the cylinder. In comparison to a design with a hollow piston rod, the control unit can be made much shorter. As a result, there are also smaller inaccuracies in the guidance of the control unit.
Even though the control unit acts radially, the flow connection that can be closed by the control unit is designed to be essentially axial to the longitudinal axis of the piston. Thus, the shortest connection between the working chambers is available. Moreover, the flow connections are arranged in the base of the piston and open to the space within the tubular body. The intent of this measure is to reduce the throttling effect originating from the length of the flow connection. This feature is important, especially in piston/cylinder assemblies that must always be equally ready for operation even at low temperatures in winter.
When the piston/cylinder assembly is used as a gas spring, one working chamber is filled with a pressure medium, specifically gas, and the other working chamber has a vent open to the outside of the cylinder.
To modify the operating characteristic curves, for example, the damping force characteristic curve in a vibration damper or the spring force characteristic curve in a gas spring, a spring is arranged in at least one working chamber and exerts a force that acts upon the piston as a function of the ratio of the spring length to the stroke length. To be especially compact, the spring can be arranged within the tubular body of the piston.
REFERENCES:
patent: 1027288 (1912-05-01), Sherman
patent: 2520406 (1950-08-01), Hollingsworth
patent: 4373599 (1983-02-01), Walter et al.
patent: 4406215 (1983-09-01), Lacasse
patent: 4685383 (1987-08-01), Ruchser
patent: 5299489 (1994-04-01), Obrecht et al.
patent: 6945901 U (1969-11-01), None
patent: 34 29 783 (1986-02-01), None
patent: 34 35 027 (1986-04-01), None
Fuhrmann Castor
Greb Oliver
Mintgen Rolf
Baker & Botts L.L.P.
King Bradley
Schwartz Christopher P.
Stabilus GmbH
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