Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1995-09-19
1998-05-05
Richter, Sheldon
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
F15B 910
Patent
active
057461074
DESCRIPTION:
BRIEF SUMMARY
The present invention relates, in general, to pneumatic brake boosters.
More precisely, the invention relates to a pneumatic brake booster of the type of those which comprise: a rigid casing in which a movable partition delimits a front chamber and a rear chamber; a hollow piston into which there emerge a first inlet connected to a first source of pressure delivering a relatively high pressure, a second inlet connected to the front chamber of the booster and to a second source of pressure delivering a relatively low pressure and an outlet connected to the rear chamber whose pressure is to be controlled, this piston being capable of being entrained by the movable wall; and a valve incorporated into the piston in order to establish selectively a communication between either one of the inlets and the outlet, this valve itself comprising: a first annular seat formed by an internal crown of the piston on the outside of which the second inlet emerges; a second annular seat, closed off axially, mounted in the first seat with clearance defining a passage connected to the outlet, and sliding axially inside this first seat between a position of rest, in which it is further from the front chamber than the first annular seat, and an actuating position, in which it is at least as close to the front chamber as the first annular seat; and a shut-off member of tubular shape exhibiting, on the one hand, a posterior part mounted in leaktight fashion in the piston some distance from the first seat, and the inside of which is connected to the first source and, on the other hand, an annular active face which can move along an axis of the piston, urged by an elastic force in a first axial direction pointing towards the front chamber and able to interact with the second seat in the position of rest of the latter in order to connect the outlet to the second source through the passage, and with the first seat in the position of actuation of the second seat in order to connect the outlet to the first source through this passage, while preventing communication between the two inlets in all cases, the annular active face of the shut-off member being coupled to the posterior part by its internal diameter and pierced with at least one orifice communicating with the passage formed between the two seats, and the internal perimeter of the piston and the edge of the active face of the shut-off member both being shaped in order to exert on one another a contact pressure which is sufficient to guarantee that one of them shuts off the other in leaktight fashion for at least one position of the second seat.
A booster of this type is described in the international patent document published under the number WO 94/04403, and invented in parallel and independently by the Applicant.
A problem conventionally encountered with known boosters, and even also with the booster described in this document, lies in the fact that the forces to be overcome to actuate the booster are not applied with the same intensity or in the same direction when the booster returns to its position of rest, which causes undesirable hysteresis to arise in the operation of these boosters.
The invention falls within this context and aims to reduce this undesirable hysteresis. To this end, the booster of the invention which, moreover, conforms to the generic definition thereof given in the preamble above, is essentially characterized in that the internal perimeter of the piston and the edge of the active face of the shut-off member are shaped in order to exert on one another when the second seat is some distance from its actuating position, a contact pressure which is less than the one which they exert when the second seat is in its actuating position.
According to a first possible embodiment of the invention, the edge of the active face of the shut-off member bears a sealing lip, and the internal perimeter of the piston, in a plane close to the first seat and perpendicular to the first axial direction, widens out as this plane gets further away from this seat and from the front
REFERENCES:
patent: 5263398 (1993-11-01), Kobayashi et al.
patent: 5546846 (1996-08-01), Bauer
patent: 5579675 (1996-12-01), Gautier et al.
Gautier Jean Pierre
Verbo Ulysse
Bosch Systems de Freinage
McCormick Jr. Leo H.
Richter Sheldon
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