Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1993-09-13
1996-12-03
Nguyen, Hoang
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
91376R, F15B 910
Patent
active
055796753
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters, and more particularly of the type which are used for boosting the braking of motor vehicles.
Boosters of this type conventionally comprise a casing inside which there is a piston formed from a hub and from a skirt to define a front chamber permanently connected to a vacuum source and a back or rear chamber selectively connected to either the front chamber or to the atmosphere by a valve means. The valve means being actuated by a control rod capable of pressing, by means of the front face of a plunger on the back face of a reaction disk securely fastened to a thrust rod. A return spring for the control rod is being arranged between the piston and the plunger. The valve means comprising a shutter interacting with a first circular valve seat formed on the plunger and a second circular valve seat formed on the piston. The shutter is formed from a flexible membrane fixed in a leaktight manner by its outer peripheral edge to the piston.
An example of such booster is illustrated in the document EP-A-0,004,477boosters, exhibit several drawbacks such as the following: in order to prevent the control rod from having too long an idle travel, the valve means must be designed so that the "shutter lift" between the shutter and the first valve seat is as small as possible. It therefore follows that, on braking, the passage offered to the atmospheric air towards the back chamber is reduced, and likewise the passage offered to the air of the back chamber towards the front chamber during brake release is also reduced.
Another drawback due to these reduced and turbulent air passages resides in the fact that the air is greatly slowed down in its various movements between the atmosphere, the back chamber and as a the front chamber, and the boosters have long response times.
In addition, the operation of these boosters can be accompanied by air suction noises, which may become troublesome as the structure of the hub of the piston has a single radial passage towards the back chamber and a single axial passage towards the front chamber may induce a high degree of turbulence in the moving air.
Another major drawback of the known boosters resides in the fact that the annular shutter element has a general frustoconical shape with an external mounting bead, associated with the element support of the shutter, in the tubular hub of the piston assembly. The active part of the shutter element is connected to the mounting bead by a thin web which flaring out towards the outside for its connection with the mounting bead. In such an arrangement, the intermediate web element of the shutter element is subjected, during the useful life of the booster, to numerous flexural and compressive stresses which can, after a period of time, induce weakening at this point, of the elastomer material making up the shutter element.
In addition, in operation, this intermediate web part of the shutter element is subjected to a pressure differential between the atmosphere prevailing permanently inside the tubular hub, around the input rod, and the vacuum permanently prevailing in the annular chamber surrounding this intermediate web part of the shutter element and permanently connected to the front chamber, or vacuum chamber of the booster. This pressure differential, aside from contributing to fatigue of the intermediate web part, induces an axial force on the active part of the shutter element, which axial force adds to the force of the valve spring. The valve plunger must overcome such axial forces during each brake release phase to free the active part of the shutter element from the first shutter seat formed in the hub and to re-establish communication between the back working chamber of the booster and the vacuum chamber. Because all such forces imposes an oversizing of the return spring for the input rod resulting especially in a high force to be supplied by the driver in order to implement the booster, this force being known in the art by the term "attack force".
Likewise, the plunger has a surface,
REFERENCES:
patent: 4598548 (1986-07-01), Wagner
patent: 4641568 (1987-02-01), Boehm et al.
patent: 4821623 (1989-04-01), Shinohara
patent: 5367941 (1994-11-01), Gautier et al.
Gautier Jean Pierre
Perez Revilla Miguel
Verbo Ulysse
AlliedSignal Europe Services Techniques
McCormick Jr. Leo H.
Nguyen Hoang
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