Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1996-12-11
1998-12-15
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
913691, 91376R, 188356, B60T 1357
Patent
active
058488278
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters or servo actuators, of the kind which are used to provide braking assistance for automobile vehicles.
BACKGROUND OF THE INVENTION
Such boosters are well known in automobile technology and comprise in general an envelope within which is disposed a piston formed from a hub and a skirt. The piston defines a front chamber connected permanently to a source of low pressure and a rear chamber connected selectively to the front chamber or to a source of high pressure by a valve means. This valve means is actuated by a control rod which is capable of bearing, through the intermediary of the front face of a plunger, on the rear face of a reaction disc which is solid with a thrust rod, the thrust rod actuating a master cylinder. The valve means usually comprises a valve member whose annular front face co-operates with a first circular valve seat formed on the plunger and a second circular valve seat formed on the piston and of diameter greater than that of the first valve seat. The valve member is formed from a flexible membrane fixed seatingly by its outer peripheral edge to the piston, the annular front face of the valve member being urged forwards by a valve spring.
Such boosters present several disadvantages. In particular, to avoid having too long a dead stroke for the control rod, it is necessary to design the valve means in such a way that the "valve lift" between the valve member and the first valve seat is as small as possible. It follows that, during an actuation, the passage opened to the flow of air under high pressure towards the rear chamber is reduced, as well as the passage opened to the flow of air from the rear chamber towards the front chamber during brake release.
A disadvantage due to these reduced and turbulent air flow passages is based on the fact that the different movements of the air between the atmosphere, the rear chamber and the front chamber become considerably slowed down, and so known boosters present response times which are long.
Another result is that the operation of these boosters is accompanied by air intake noises which can become troublesome, all the more so as the structure of the hub of the piston, which presents a single radial passage towards the rear chamber and a single axial passage towards the front chamber, induces considerable turbulence in the moving air.
Moreover, because of the concentric and substantially coplanar disposition of the two valve seats, the flexible membrane of the valve member is subjected to a variable pressure differential between the high pressure which is substantially constant prevailing permanently within the tubular hub around the input rod, and the variable pressure prevailing in the annular chamber surrounding this part of the flexible membrane of the valve member, on one part of which is exerted the pressure prevailing in the front chamber of the booster and on another part of which is exerted the variable pressure prevailing in the rear chamber of the booster.
This pressure differential, which exists in the rest condition and in the phase of brake release, applies an axial force to the annular front face of the valve member which adds to the valve spring force and which the plunger of the valve must overcome during each phase of brake release to disengage the annular front face of the valve member from the first valve seat formed in the hub and re-establish the communication between the rear working chamber of the booster and the vacuum chamber, which requires the return spring of the input rod to be oversize and in particular results in the driver having to apply a high force to bring the booster into operation, this force being known in the art under the term of "step-in force".
The document FR-A-2 537 524 attempts to find a solution by providing air passages of increased cross section, but it still comprises a conventional valve means mounted in the tubular central part formed at the rear of the booster envelope, cooperating with a modified plunger, which presents a substantial sur
REFERENCES:
patent: 4667471 (1987-05-01), Fulwer et al.
patent: 4828337 (1989-05-01), Wagner et al.
patent: 5437217 (1995-08-01), Castel et al.
patent: 5483866 (1996-01-01), Schlutter
patent: 5518305 (1996-05-01), Jakobi et al.
Bosch Systems de Freinage
McCormick Jr. Leo H.
Oberleitner Robert J.
Schwartz Chris
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