Seal for a joint or juncture – Seal between relatively movable parts – Piston ring or piston ring expander or seat therefor
Reexamination Certificate
1998-08-07
2001-04-17
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Piston ring or piston ring expander or seat therefor
C277S377000, C277S377000, C277S377000
Reexamination Certificate
active
06217029
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a seal arrangement for a piston rod, particularly for a shock absorber of a motor vehicle wherein the piston rod is arranged in a cylinder so as to be axially movable therein and at least two seal elements are provided between the piston rod and the inner wall of the cylinder.
Such an arrangement is known, for example, from EP-A 00 32 988. The seal arrangement shown in this publication comprises a first seal ring in the form of a sleeve which includes a sealing lip in contact with the outer surface of the piston rod. A part of the sleeve extends around a second seal ring which is axially spaced from the first seal ring and is also in contact with the piston rod.
This arrangement has a disadvantage in that the first seal ring has an irregular cross-sectional shape and its manufacture is therefore relatively expensive. Because of the irregular shape, also the tensions in the seal ring material are not uniform; there is the danger of rupture in areas which are subjected to high tensions. Also, it is not insured that the pressure required for an effective seal is always present at the seal lip over a long period of operation.
It is furthermore disadvantageous that the second seal ring, although improving the sealing effect, increases the friction at the surface of the piston rod so that a greater force is required for moving the piston rod. Because of the greater force required for moving the piston, the material wear is also increased.
It is the object of the present invention to provide with simple means a seal arrangement which has little wear and operates reliably.
SUMMARY OF THE INVENTION
In a seal arrangement for sealing a piston rod, particularly for a shock absorber of a motor vehicle, where the piston rod is supported in a cylinder so as to be axially movable therein and a slide seal ring is supported in the cylinder in engagement with the piston rod for sealing the piston rod, at least two seal elements are supported in the cylinder so as to be arranged around, and adjacent to, the slide seal ring and all are disposed in a common radial plane extending normal to the axis of the piston rod for pressing the slide seal ring into sealing engagement with the piston rod.
The single slide ring disposed immediately adjacent the piston rod reduces the friction forces between the piston rod and the seal arrangement and consequently, also the wear of the seal ring sealing edge.
It is furthermore advantageous that, with the arrangement of several seal rings and elements in a radial array adjacent one another, the spring performance graph of the whole seal arrangement is relatively flat. This indicates that even relatively large spring travel distances within the seal arrangement result in only small changes of the contact pressure of the seal ring arrangement with respect to the piston rod. This also means that relatively large assembly tolerances, temperature differences and wear can be accommodated without large changes of the seal force or, respectively, the friction force in axial direction of the piston rod.
The seal arrangement can be manufactured inexpensively using standard components. Seal rings of complicated cross-sectional geometry are not needed.
The slide seal preferably consists of Teflon® which has a low friction coefficient so that the friction forces are relatively low.
Preferably, the common radial plane is at the same time the symmetry plane of each seal element or ring. With this arrangement, a symmetrical and uniform force distribution within the seal arrangement is achieved and the pressure on the outer surface of the piston rod remains constant whereby the chances of material fatigue are greatly reduced and a uniform sealing effect is obtained over a long period of operation.
The seal elements are preferably O-rings with circular cross-sections. The slide seal ring has preferably an essentially rectangular cross-section with a radially inner projection which is disposed adjacent the piston rod so that the contact pressure of the slide seal ring on the piston rod is increased and the seal effect is improved. Because of the small friction coefficient of the slide seal ring, the friction forces generated by movement of the piston rod in axial direction are relatively small inspite of a high contact pressure. In place of two O-rings, elements with other than circular cross-section can be used.
The seal elements and the slide seal ring are preferably supported in a seal support structure such that the radial arrangement of the rings can be provided and maintained in a simple manner and the direction of the engagement pressure normal to the axis of the piston rod can be accurately established.
Further advantages and suitable embodiments will become more readily apparent from the following description of the invention on the basis of the accompanying drawings.
REFERENCES:
patent: 3860250 (1975-01-01), Lundquist
patent: 4179131 (1979-12-01), Nussbaumer
patent: 4364573 (1982-12-01), Gautier et al.
patent: 5149107 (1992-09-01), Maringer et al.
patent: 5291974 (1994-03-01), Bianchi
patent: 5433452 (1995-07-01), Edlund et al.
patent: 5820130 (1998-10-01), Zakharov
patent: 0 032 988 (1981-08-01), None
patent: 0 408 177 (1991-01-01), None
patent: 0 434 908 (1991-07-01), None
patent: 2 371 618 (1987-06-01), None
patent: WO 90/00693 (1990-01-01), None
patent: WO 91/19920 (1991-12-01), None
“Kolbendichtungen SIMKO 300”, Antriebstechnik 33, (1994) Nr. 1-2, p. 67.
Bach Klaus J.
Daimler-Chrysler AG
Knight Anthony
Williams Mark
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