FR2657136A2 - Piston cap - Google Patents

Abstract

The invention relates to a piston cap according to any one of the claims of the main patent application, the intermediate part of which, between the holding part and the bead (32) includes a fold capable of coming into contact with a wall. According to the invention, the external part of the fold is provided with a means (50) preventing the contact from being a sealing contact.

Description

PISTON HOOD
The present invention constitutes an addition to French patent application 88 17297 filed on 28.12.88 in the name of the applicant.

 The cap described in the main patent application is entirely satisfactory. However, it has a fold which is liable to come into contact with a wall of the brake thus equipped. This contact then determines two substantially sealed chambers with respect to each other. The vent provided to let air escape from the closed volume only acts on one of the two chambers. When two vents are provided, the air exhaust is not identical in both rooms.

 In all cases, therefore, this results in a difference between the pressures prevailing in the two chambers, a difference detrimental to the proper functioning of the brake.

 The object of the present invention is to obviate this drawback.

 According to the invention, the outer part of the fold is provided with a means preventing the sealing of the contact. This means can consist either of a plurality of notches made in the fold, or of a plurality of lugs projecting from the fold.

The invention and other objects, advantages and characteristics thereof will appear more clearly on reading the following description of preferred embodiments given without limitation and to which a drawing board is attached on which
the single figure shows in schematic section a cap according to the invention.

 With reference to this Figure, in which the numerical references have been taken from the main patent application, the person skilled in the art easily recognizes the metal insert 36 with the tongue 42 and the notches 44, the bead 32 being housed in a annular groove 34 formed on the head of the piston 24.

 The body of the cylinder 26 has a wall capable of being in contact with the fold 55 presented on the cap.

 In order to prevent the volume delimited by the cap, the piston 24 and the cylinder 26 from being divided into two sealed chambers with respect to each other, means 50 are provided to prevent any sealing between the two chambers at the level of the contact of the fold 55 with the wall of the cylinder 26. This means 50 may consist of notches made on the outside of the fold. I1 can also be constituted by lugs projecting from the fold at the level of the contact.

 Such a means therefore provides a passage for air to circulate from one room to another, thus avoiding any difference in pressure between the two rooms.

 Obviously, a person skilled in the art can make numerous modifications to the cap according to the invention without departing from the scope of the invention as defined by the appended claims.

Claims (3)

 1. Piston cap according to any one of the claims of the main patent application, the intermediate part between said retaining part and said bead (32) comprises a fold capable of coming into contact with a wall, characterized in that that the outer part of the fold is provided with means (50) preventing the sealing of said contact.  2. Piston cap according to claim 1, characterized in that said means consists of a plurality of notches made in the fold.  3. Piston cap according to claim I, characterized in that said means is constituted by a plurality of lugs projecting from the fold.