Spring devices – Resilient shock or vibration absorber
Reexamination Certificate
1998-12-18
2001-03-20
Oberleitner, Robert J. (Department: 3613)
Spring devices
Resilient shock or vibration absorber
Reexamination Certificate
active
06202993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a self-pumping hydropneumatic spring strut or shock strut with internal level regulation for use with motor vehicles. The shock strut includes a working cylinder which is filled with oil and acted upon with pressure from at least one gas cushion arranged in a high-pressure chamber and acting as a spring. The work cylinder is divided into two work spaces by a work piston having a hollow piston rod and a piston pump which is driven by the spring movements. One of the work spaces is connected to the high-pressure chamber. The piston pump has a pump cylinder formed by the hollow piston rod and delivers oil from a low-pressure chamber to the work space connected with the high-pressure chamber. A hollow pump rod which is fastened to the work cylinder and has a suction valve at its front end penetrates into the hollow piston rod. The bore of the hollow pump rod is connected with the low-pressure chamber. The hollow pump rod also has a regulating opening which is closable as a function of the position of the piston rod in the working cylinder and which connects the work space connected with the high-pressure chamber with the bore of the hollow pump rod.
2. Description of the Related Art
In shock struts of the type mentioned above which are already known, for example, from DE-PS 33 06 393, the work cylinder is divided into two work spaces by a work piston carried by a hollow piston rod and a pump cylinder is formed by the hollow piston rod. A pump rod penetrates into this pump cylinder to form a piston pump. The hydraulic piston pump is constantly in operation during driving operation, so that movements of the vehicle axle and of the piston rod fastened thereto which are brought about by uneven roadways constantly deliver oil to the working cylinder. The piston rod is displaced outward until a regulating opening of the pump rod releases a connection between the work cylinder acted upon by high pressure and the low-pressure space. In this position, the piston pump which continues active does not cause any further outward movement of the piston rod relative to the work cylinder. A disadvantage of this invention is that a pressure compensation takes place between the high pressure and the low pressure space when the regulating opening is released, so that the piston rod dips back into the work cylinder. Therefore, the height or level of the vehicle must then be achieved anew by means of the piston pump.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a simple, reliable functioning and sensitive level regulation device in which any overpressure that might occur does not lead directly to regulation of the shock strut.
This object is met according to the invention in that the piston pump is provided with a relief or overload valve.
The advantage herein consists in that a maximum operating pressure cannot be exceeded, so that overloading of the vehicle will not lead to a failure of the level regulation system.
The pressure increase is already prevented at the pump, so that the volume flows to be managed by the overload valve are small in contrast to overload valves which let out directly from the high-pressure space into the low-pressure space. In these overload valves between high-pressure space and low-pressure space, the piston rod volume must be displaced, whereas in the described overload valves of the invention, only the pump rod volume must be displaced.
In one arrangement of the present invention, the overload valve is formed of a valve seat and a spring-loaded adapter. According to another feature, the adapter of the overload valve is simultaneously constructed as a valve seat for the suction valve.
It is further provided that the end face of the adapter cooperates with a stationary stop arranged at the pump rod and that a bore arranged in the adapter forms the valve seat for a valve body of the suction valve.
In one embodiment, a spring, an adapter, a valve body and an additional spring are arranged axially in succession in a stepped bore of the pump rod proceeding from the bore step and are held by a closure part having an opening to the pump space for forming both a suction valve and an overload valve.
In an essential feature, the closure part is held relative to the pump rod in a positive and/or frictional engagement.
The closure part may also be constructed integral with the adapter. Operation is carried out in such a way that oil is drawn in from the low pressure chamber when the pump begins to operate. After a determined pressure difference between high pressure (pump pressure space) and low pressure space, the drawn in oil is pushed back through the opening overload valve into the pump space. The opening pressure can be freely selected by the spring pretensioning.
In this construction, the valve is not pressed against a stationary wall in the stepped bore, but rather is held in a floating or suspended manner by a spring. This version is pretensioned in a force-dependent manner and is then fastened in the stepped bore by frictional or positive engagement.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
REFERENCES:
patent: 4577840 (1986-03-01), Meller
patent: 5564680 (1996-10-01), Sano
Kirchner Holger
Meier Achim
Wilms Bernd
Bartz C. T.
Cohen & Pontani, Lieberman & Pavane
Mannesmann Sachs AG
Oberleitner Robert J.
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