Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1995-07-31
1996-10-01
Denion, Thomas E.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
913692, 92 98D, F15B 910
Patent
active
055602762
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters of the vacuum type comprising a casing formed from a cylinder and from a cover and divided into two chambers by a moving wall structure, consisting of a plate and of a flexible membrane fixed by a bead formed on its outer peripheral edge to the casing, and forming a fold in the space located between the plate and the casing, the plate being secured centrally to a hub structure housing a valve means, the plate comprising a forwards extension at its outer edge.
BACKGROUND OF THE INVENTION
Such a booster can be used particularly for boosting the braking of motor vehicles. In this application, the operation of such a booster is well known and can therefore be explained briefly as follows: in the rest phase, the two chambers are connected to a vacuum source; in the braking phase, air at atmospheric pressure is admitted into one of the chambers; the difference in pressure between the two chambers then gives rise to the displacement of the moving wall and consequently boosts the braking.
Document FR-B-2,334,862 describes a pneumatic booster in which a membrane is supported by a rigid plate comprising a cylindrical forwards extension at its outer edge for preventing the membrane, under the effect of the difference in pressure, from deforming towards the center of the booster and from hindering the movement of the plate. With such a design, the diameter of the plate remains limited by the diameter of the rear part of the casing. It follows that the active surface of the moving wall, that is to say the one on which the difference in pressure is exerted, is itself also limited by the rear part of the casing.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome this drawback and to provide a booster in which the active surface of the moving wall is as large as possible.
In order to achieve this goal, according to one characteristic of the invention, the extension comprises a radial shoulder, and the radial distance between the rear part of the extension and the cover is substantially equal to the radial distance between the front part of the extension and the cylinder.
The invention will be better understood and other objects, features and advantages will emerge more clearly from the following description of one embodiment given by way of nonlimiting example with reference to the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial view in half-section of a pneumatic booster of the prior art;
FIG. 2 is a partial view in half-section of a booster produced in accordance with the present invention; and
FIG. 3 is an enlarged view of the part III of the booster of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
By convention, the parts of the booster pointing towards the master cylinder are termed the "front" and the parts pointing towards the brake pedal are termed the "rear". Thus, in the figures, the front is to the left and the rear is to the right.
FIG. 1 shows, in half-section, a pneumatic brake booster whose main constituent elements and operation are assumed to be known to the person skilled in the art. A moving wall structure 10 formed from an assembly of a metal plate 12 located substantially in a radial plane and of a flexible membrane 14 separates a casing 16 into two chambers 18, 20 inside which different pressures are set up during a braking action so as to bring about the forward displacement of the moving wall 10 and thereby to create the assistance to braking.
In a known fashion, the plate 12 is secured to a hub 22, generally made from plastic, which is combined with an actuating member 24. This actuating member 24 further determines the state of a distribution valve means 26 making it possible to obtain different pressures in the chambers 18 and 20. The hub is also secured to a push rod 28 whose end bears on the input piston of a master cylinder (not shown).
The flexible membrane 14 is fixed by its inner peripheral edge to the metal plate 12 and by its outer peripheral edge to the casing 16, and has a
REFERENCES:
patent: 3037487 (1962-06-01), Brooks
patent: 5154106 (1992-10-01), Castel et al.
AlliedSignal Europe Services Techniques
Denion Thomas E.
McCormick Jr. Leo H.
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