Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1995-11-13
1998-08-04
Denion, Thomas E.
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
913691, 913692, F15B 910
Patent
active
057877882
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pneumatic brake booster using first and second sources of air pressure delivering first and second respective and different pressures, this booster comprising a rigid casing divided by at least one leaktight movable partition into at least two chambers, the first of which is connected to the first source, and the second of which is capable of being connected selectively, by means of a valve, to either one of the two sources, the movable partition being capable of being urged by the difference between the pressures established in the chambers so as to entrain an essentially cylindrical pneumatic piston which slides in leaktight fashion inside the casing and carries the valve, the inside of this piston and especially the valve being separated from the second source by an impurities filter.
Devices of this type, which are well known in the prior art, are used on a very great number of motor vehicles nowadays.
Despite the conventional nature of the techniques involved, boosters continue to form the subject of considerable research, aiming to optimize their operating characteristics.
Included in this research there feature, in particular, attempts to reduce both the level of noise of boosters in operation, and their response time when acted upon, a simultaneous reduction in these two parameters being made very tricky by the fact that a booster is quieter if the air it takes into the rear chamber is more filtered, while it exhibits a shorter response time if the air which it takes in is less filtered.
The invention falls within this context and its object is to provide a booster which meets the expectations of the public as regards the reduction in the level of noise in operation, while offering a response time which is at least as satisfactory as those of the boosters of the prior art, in all cases where the need for a short response time is felt.
To this end, the booster of the invention is essentially characterized in that it includes closing-off means, the opening of which is controlled, installed between the second pressure source and the inside of the piston and controlling an air inlet path which avoids passing through the filter, and elastic means, which are sensitive to a difference in pressure between the inside of the piston and the second source of pressure, in order to allow the closing-off means to be opened selectively when this pressure difference exceeds a given threshold.
According to a first possible embodiment, in which the valve is controlled by a control rod, the booster of the invention is characterized in that the filter adopts the shape of a cylinder surrounding the control rod, in that the closing-off means comprise a valve seat formed at the internal periphery of the piston and a flexible annular seal closing off a gap between the filter and the valve seat and bearing on the latter, and in that the elastic means comprise a spring pressing the seal onto the valve seat, against a force which may be exerted on this seal by the difference in pressure between the inside of the piston and the second source of pressure.
According to a second possible embodiment, in which the pneumatic piston is housed, outside the casing, in a protective tubular gaiter made at least partially from a porous elastomeric material and acting as a filter, the booster of the invention is characterized in that the closing-off means comprise at least one lip produced in the form of a slit made in the porous gaiter, and in that the elastic means comprise at least one elongate spur formed in the gaiter and exhibiting edges which converge towards the said slit and keep it elastically closed for as long as the pressure difference between the inside of the piston and the second pressure source is below the said given threshold.
Other features and advantages of the invention will emerge clearly from the description thereof which is given below, by way of non-limiting indication, with reference to the appended drawings, in which:
FIG. 1 is a diagrammatic view in section of a pneumatically
REFERENCES:
patent: 5249504 (1993-10-01), Gautier et al.
patent: 5279203 (1994-01-01), Gautier et al.
Gautier Jean Pierre
Verbo Ulysse
Bosch Systems de Freinage
Comstock Warren
Denion Thomas E.
Karimi Bujan N.
McCormick Jr. Leo H.
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