Piston Sealing Arrangement for Pressure-Fluid-Operated Systems

The present invention relates to a piston sealing arrangement for pressure-fluid-operated systems of the type to be gathered from the preamble of claim 1.

Piston sealing arrangements, e.g. in brake force regulators, are known. For example, ring seals of different profile are rigidly fitted in an annular recess of the piston or its housing. Depending on the piston's cross-section and on the force which presses the piston against its stop, for instance by a preloaded spring, a specific initial pressure is required to move the piston in opposition to this force. In the presence of great initial pressure, the ring seal deforms elastically before the piston starts to move. The axial thickness of the ring seal, that is viewed in relation to the piston axis, decreases while the radial thickness thereof increases. Due to this, the ring seal is pressed tightly against the walls to be sealed relative to one another, and upon attainment of the initial pressure the piston first has to overcome a high amount of static friction before it yields the pressure. This has as a result a jerky initial movement of the piston afflicted with a hysteresis (stick-slip effect).

Attempts have been made to avoid this by reducing the friction values and by optimizing the sealing edge. However, these attempts met with only little success. Moreover, a precisely machined sealing edge is susceptible wear.

The present invention has for its object to safeguard a movement of the piston that is uniform to the largest possible extent by means of a simple and wear-resistant arrangement.

This object is achieved by the features set forth in claim 1. The essence of the present invention is that an annular sealing element moves in opposition to an associated elastic element that counteracts the pressure force, already at a preload pressure which is less than the initial pressure required to initiate piston movement. A thin pressure fluid film is formed thereby between the sealing element and the walls to be sealed in relation to each other so that once the initial pressure is reached the piston itself will have to over-come only an amount of friction force much smaller than the static friction of the sealing arrangement. It is sufficient to give the piston and housing cross-sections normal dimensions in order to have the pressure act on the sealing arrangement, thereby obviating the need for additional modifications of the piston or the housing. Moreover, a like sealing arrangement is wear-resistant in comparison to an exact sealing edge.

The present invention permits various forms of embodiments. The piston sealing arrangement can be placed in an annular recess of the piston or in the mating housing.

A spring element is suitable as an elastic element of this sealing arrangement. It is favorable to use a cup spring or an undulating or wave washer owing to their small axial extension. In account of the piston resetting force and the ratio of the application surfaces, the spring rate or constant is to be chosen such that the sealing element starts to move against its compression spring so short a time before the piston that the pressure fluid film between the sealing element and the walls still exists when the initial pressure is reached. This avoids a jerky start of the piston and hence a hysteresis of the initial movement of the piston. This advantage recommends in particular to use the sealing arrangement for the regulating piston of a brake force regulator.

The annular sealing element can be a ring seal having a profile towards the pressure side which is customary and suits its purpose, the rear side whereof is shaped such as to ensure proper seating of the elastic element.

Two of the various embodiments possible are shown in the drawings.

In the drawings,

FIG. 1A, is a piston sealing arrangement with cup spring column in the housing wall;

FIG. 1B, is a side view of a cup spring;

FIG. 2A, is a piston sealing arrangement with an undulating washer in the piston; and

FIG. 2b, is a side view of the undulating washer.

The piston sealing arrangement 1a, 2 is placed in an annular recess 4 of the housing wall in FIG. 1A. The ring seal 1a exhibits a roughly V-shaped profile, and a cup spring 2 serves as an elastic element (see FIG. 1B). Piston 6 in FIG. 2A is furnished with an annular recess 5 in which the sealing arrangement 1b, 3 is placed. Herein an undulating washer 3 serves as an elastic element of the sealing arrangement (see FIG. 2B).

The illustrations show the piston assembly in its stop position. The pressure increasing from the direction A via pressure passage 9, the ring seal 1a and 1b will be displaced to the right in opposition to its compression spring 2 and 3, respectively, shortly before the initial pressure for the piston movement is reached so that its contact surfaces towards the piston 6 and towards the housing wall are covered with a thin film of the pressure fluid encompassing the ring seal. Once the pressure has risen up to the initial pressure, the piston 6 will start to move in opposition to an associated compression spring 8 in drain passage 10.

1 seal

2 cup spring

3 ondular washer

4 annular housing recess

5 annular recess of the piston

6 piston

7 housing

8 compression spring

9 pressure passage

10 drain passage

A direction of the pressure force