Brakes – Internal-resistance motion retarder – Including seal or guide
Reexamination Certificate
2000-08-09
2001-11-06
Schwartz, Christopher P. (Department: 3613)
Brakes
Internal-resistance motion retarder
Including seal or guide
C188S322160
Reexamination Certificate
active
06311813
ABSTRACT:
BACKGROUND
1. Field of the Invention
The invention relates generally to an axially movable switching sealing ring within a groove, and more specifically to an improved form of such a switching ring for use in the piston of a piston-cylinder unit to control fluid flow across the piston.
2. Background
U.S. Pat. No. 4,595,182 discloses a piston-cylinder unit in the form of a gas spring, which has an axially movable switching sealing ring within a groove on the piston. The switching sealing ring is rectangular in transverse cross section. Owing to frictional force between the ring and the inner wall of the cylinder, the ring is able to move between the lateral faces of the groove, since the groove has an axial width greater than the axial width of the ring. Fluid flow through the piston is thereby controlled in both directions of axial movement of the piston.
The switching sealing ring is cut in sections from a cylindrical blank. In this cutting operation, it can hardly be avoided that the sections turn out to be more or less skewed, e.g., the axially opposed (upper and lower) sides are out of parallel. When the switching sealing ring is assembled, it cannot readily be checked how the surfaces of the opposite sides are positioned with respect to one another. Extensive testing has revealed that the described skewedness of the upper and lower sides of the ring significantly influences operating behavior. The upper and the lower sides of the switching sealing ring are acted upon by pressure within the gas spring. When the geometries of the upper and lower sides of the ring are undefined, it may happen that in an application according to U.S. Pat. No. 4,595,182 the switching sealing ring executes an axial motion more rapidly or more precisely in one direction than the other, which can be detected when the unit is tested.
To remedy the problem, it has been proposed to produce the switching sealing ring in an injection molding process. As a rule, switching sealing rings that are produced by this process clearly are more accurate in shape, but on the other hand are also much more costly to manufacture. In a mass-produced product such as, for example, a gas spring, such a higher price is unacceptable.
SUMMARY
An object of the present invention, therefore, is to provide a switching sealing ring which has uniform operating behavior under all operating conditions and which can be accommodated more easily than the prior art with regard to tolerances of shape and position.
According to the invention, this object is attained in that the upper and lower sides of the switching sealing ring have axially relieved sections adjacent the radially outer edge of the ring, so that the sealing surface on each axial side surface of the ring is formed optimally of a partial surface of the upper and lower sides.
The axially relieved section has the advantage that a small sealing surface is obtained, which minimizes the influence of any possible skewedness of the sealing ring. This results in more exact operating behavior of the unit provided with the switching sealing ring.
In another advantageous embodiment, it is provided that the axially relieved sections have their greatest depths at the outer diameter of the ring. The switching sealing ring and/or the sealing surface on the radially outer wall thereof are subject to a pressure-dependent prestress, since the operating pressure also acts on the radially inner wall of the ring. The resulting pressure-impacted surface is reduced by the relieved sections on the outer diameter, so that variations of the operating pressure within the groove for the switching sealing ring do not entail significant variations with regard to the prestress of the sealing ring.
Best results are obtained when the switching sealing ring has a substantially trapezoidal transverse cross section. In this connection, it should be taken into account that, although an exactly trapezoidal cross section represents the functional optimum, in terms of manufacture it is more difficult, since when the ring is manufactured the section must then exactly meet the corner between the covering sides and the inner or outer wall. For this reason, it is more appropriate for the upper and lower sidewall surfaces of the ring to be designed with a small parallel sealing surface in each instance.
With regard to favorable pressure equalization in the radial direction, the radially outer wall surface of the switching sealing ring preferably has a convex shape, so that the sealing surface on the outer wall has only a line contact when the ring seats.
Specifically, in very flat switching sealing rings, it is especially advantageous that the upper and lower sides of the ring be substantially symmetrical in shape. A flat switching ring permits only small relieved sections. However, when the upper and lower ring sides are substantially identical, differences in shape and position of the switching sealing ring can in practice no longer be detected by means of functional testing.
To permit greater independence with regard to the selection of material, particularly with respect to the permissible surface pressure and the elasticity occurring, a cover ring is preferably assigned to the switching sealing ring on at least one side.
REFERENCES:
patent: 3828897 (1974-08-01), Nandyal
patent: 4595182 (1986-06-01), Freitag et al.
patent: 5433452 (1995-07-01), Edlund et al.
patent: 6129358 (2000-10-01), Kiesel et al.
Lauderbach Leo
Stumm Rolf
Baker & Botts L.L.P.
Schwartz Christopher P.
Stabilus GmbH
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