Expansible chamber devices – Piston with rigid axially extending hollow stem
Reexamination Certificate
1999-10-22
2001-05-01
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Piston with rigid axially extending hollow stem
C092S129000
Reexamination Certificate
active
06223649
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a piston/cylinder unit comprising a working cylinder, a piston attached to a piston rod and arranged in the working cylinder so that it is axially displaceable in the working cylinder, and a fastening element screwed into a threaded bore of the piston rod.
2. Description of the Related Art
Prior art piston/cylinder units, e.g. self-pumping hydropneumatic spring struts with internal leveling, are disclosed, for example, in German reference DE 33 16 069A1 in which a tubular piston rod is closed at its outer end by a screw-in bolt. The screw-in bolt has an offset which is pressed onto the end of the piston rod by the torque applied to the threaded joint. This type of piston-rod closure offers the advantage of allowing different screw-in bolts to be threaded into the piston rod so that the same piston rod can be used with many different screw-in bolts. This threaded joint is designed principally for transmitting forces in the axial direction, that is to say for elements constructed as axle dampers (shock absorbers).
The disadvantage with these embodiments is that, when these piston/cylinder units are used in spring struts, the screw-in bolts of the piston rod are exposed to bending loads at different wheel locations. Therefore, the screw-in bolts must accept the bending loads. The bending strength of a spring strut of this kind is dependent on the contact pressure on the end of the piston rod, said contact pressure being generated by the torque. Tests in the field have shown that, because the contact-pressure surface is at right angles to the center line, the threaded joint either loosens or, the screw-in bolt may shear off at this point.
SUMMARY OF THE INVENTION
It is the object of the invention to attach fastening elements to a piston rod of a piston/cylinder unit such that axial forces and dynamic bending loads may be transmitted by the joint with sufficient reliability.
According to the invention, this object is achieved by a bore in the piston rod which widens from the diameter of the thread to a first outer diameter thereby creating a first tapered surface and a corresponding collar on the fastening element which diminishes from a second outer diameter to the diameter of the thread thereby creating a second tapered surface.
The advantage with this design is that the first and second tapered surfaces enable the joint to be made with a high pressure per unit area, thus allowing the two parts to be connected firmly to one another.
According to a further refinement, the widening bore of the piston rod is of conical design.
According to another feature, the tapering collar of the fastening element is also conical.
According to a particularly preferred embodiment, the fastening element, the collar and the bolt having the thread are of one-piece design.
To obtain satisfactory sealing of the cavity in the piston rod when a hollow piston rod is used, a further embodiment includes a fastening element which closes the cavity in the piston rod in a pressure-tight manner. It is advantageous here if at least one optional seal is arranged between the cavity in the piston rod and the fastening element.
According to a particularly preferred embodiment, the widening tapered surface of the piston rod and the diminishing tapered surface of the collar are provided with angles of different sizes. The collar of the fastening element and the end region of the piston rod both have a conically shaped contact-pressure surface, wherein the angle of taper of the collar being slightly greater than the angle of taper of the piston rod. This facilitates automatic centering of the fastening element and the piston rod. Furthermore, the difference in angle ensures a high pressure per unit area at the end of the piston rod at all times and thus provides a rigid connection between the two parts.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and formiing 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: 1390078 (1921-09-01), Blain
patent: 3424062 (1969-01-01), Gummer et al.
patent: 3951046 (1976-04-01), Lochmann et al.
patent: 4628795 (1986-12-01), Pickard et al.
patent: 677900 (1952-08-01), None
Beck Hubert
Molitor Matthias
Cohen & Pontani, Lieberman & Pavane
Mannesmann Sachs AG
Ryznic John E.
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