Piston with piston rod being latchable through a retaining membe

Details Piston with piston rod being latchable through a retaining membe Piston with piston rod being latchable through a retaining membe

1994-11-17

1996-03-19

Ryznic, John E.

Expansible chamber devices

Resilient means interposed between working member and...

403133, 92128, F16J 110, F01B 2900, F16C 1100

Patent

active

054995701

DESCRIPTION:

BRIEF SUMMARY
This application is a Rule 371 of PCT/EP93/00306 filed Feb. 9, 1993.


TECHNICAL FIELD

The invention relates to pistons and more particularly relates to pistons used in the master cylinder of a vehicle brake system.


BACKGROUND OF THE INVENTION

Push rods of pistons used in vehicle brake applications are pushed into the cylinder by the actuating force of the operating person and returned into their starting position by return springs. In this context, two return springs are provided, one of which is positioned within the piston and acts directly on the piston while the other one is fixed outside the piston and returns the brake pedal into its starting position.
In master cylinders it may happen that the external spring extracts the piston rod out of the piston. To prevent separation of the rod and piston various approaches have been taken such as clips. All of these known solutions share a common drawback in of steel, retaining members in the shape of rubber rings, and undercuts in the piston in respect of the piston rod, which are formed, for example, by caulking that the known securing means do not suffice in many cases to prevent the piston rod from being moved out in the event of a sudden release of the actuating pedal. In many cases the solutions which have become state of the art are, furthermore, difficult to assemble insofar as they require additional operations when the piston rod is attached to the piston. Many times the prior-art solutions are, moreover, dependent in their securing action on the angular position the piston rod assumes at each moment in respect of the longitudinal axis of the piston.
An object of the present invention is to create an inexpensive securing means which reliably latches the rod within the piston and resists sizable extracting forces (independent of the angular position of the piston rod).


SUMMARY OF THE INVENTION

The present invention consists of a retaining member which seats on the piston rod and which is formed with latching noses which grip behind matching undercuts within the interior space of the piston when the piston rod is introduced into the piston. The retaining member is configurated such that in the latched condition the latching noses remain largely compressed, as a result the projections in the piston-rod opening of the retaining member are held with a position shifted radially inwardly and thus retain a matching attachment at the piston rod. In this way, a double function of the latching noses of the retaining member is realized insofar as, on one hand, they prevent a moving-out of the retaining member itself with the piston rod in axial direction while simultaneously by the radial abutment of the latching noses against the inside wall of the piston the securing projections of the retaining member are stably maintained in engagement with the matching attachment at the piston rod.
The retaining member is preferably made of plastic material because such sophisticated shapes easily lend themselves to be manufactured at low cost and because such plastics offer the necessary elasticity for the retaining noses and for the projections moving against one another. Accordingly, in the course of the assembly first of all the latching retaining member must be pushed over the end of the push rod or piston rod, respectively, whereby the projections are swivelled in the open direction due to the penetrating attachment of the piston rod. Subsequently, said projections will return radially inwardly into their starting position because of the elasticity of the latching noses. Due to the subsequent pushing-in into the piston of the retaining member (including the end of the push rod seated within member), the latching noses will be compressed still further in the radial direction within the piston opening as they pass through the blind-end bore. After having passed the undercuts they will move back outwardly into their starting position sufficiently so as to abut against the internal generated surface of the piston which is disposed radially within the unstressed s

REFERENCES:
patent: 3013537 (1961-12-01), Schultz
patent: 4878346 (1989-11-01), Metzelfeld et al.
patent: 4904106 (1990-02-01), Love
patent: 5143469 (1992-09-01), Cadeddu
patent: 5163773 (1992-11-01), Denney et al.
patent: 5290120 (1994-03-01), Osterfeld et al.

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