Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1999-06-01
2001-02-13
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06186042
ABSTRACT:
The present invention relates to a pneumatic brake booster.
More specifically, the invention relates to a pneumatic brake booster comprising: a rigid casing; a moving partition delimiting, in leaktight manner, a front chamber and a rear chamber inside the casing, the front chamber in operation being subject to a first pressure and the rear chamber being connected selectively to the front chamber or subject to a second pressure higher than the first; a pneumatic piston moving with the moving partition; an axial operating rod moving in the piston as a function of an input force selectively exerted against a return force and oriented in an axial actuating direction pointing towards the front chamber, the return force urging the operating rod towards a return position, and the input force urging the operating rod towards an actuating position which depends on the input force; a plunger made to slide in the piston by the operating rod; a three-way valve connecting the rear chamber to the front chamber when the operating rod is in the position of rest, and subjecting the rear chamber to the second pressure when actuated by a movement of the operating rod towards its actuating position; and force-transmission means capable of receiving and of passing on at least part of the input force transmitted by a front face of the plunger, and a boost force exerted by a front face of the piston when the valve is actuated, these force-transmission means themselves comprising a pushrod of which one end adjacent to the plunger is capped by a cup in which a reaction disc is housed, a first face of the reaction disc receiving the input force and the boost force, and a second face of the reaction disc bearing against the cup; and stop means for limiting the sliding of the plunger with respect to the cup to a predetermined travel.
BACKGROUND OF THE INVENTION
Devices of this type are well known in the prior art, as illustrated, for example, in patent documents U.S. Pat. No. 3,470,697, FR-2,532,084 and FR-2,658,466.
The continuing preoccupation with reducing braking distances has recently led to the development of various arrangements aimed at reducing booster response times, particularly during emergency braking.
The invention falls within this context and its purpose is to provide a simple solution to this problem, at the same time allowing optimum and immediate use of the braking force exerted by the driver, wider opening of the booster inlet valve, and better air flow towards the rear chamber of the booster.
SUMMARY OF THE INVENTION
To this end, the booster of the invention, which in other respects is in accordance with the definition in the above preamble, is essentially characterized in that the force-transmission means comprise an intermediate member mounted to slide axially with respect to the plunger and with respect to the piston, and capable of being driven by the plunger, with respect to the piston, over a driven distance that exceeds the determined travel, and in that this intermediate member is at least partially inserted between the front face of the piston and the first face of the reaction disc so as to be able to pass on to the reaction disc the boost force when it occurs, and in that the stop means are borne by the plunger and the intermediate member and define a maximum excursion of the plunger with respect to the intermediate member.
According to a preferred embodiment of the invention, the intermediate member is at least partially arranged radially between the plunger and a stepped axial bore of the piston, and at least partially arranged radially between the cup and the stepped axial bore of the piston.
The stop means may, for example, comprise a snap ring secured to the plunger and mounted to slide in a groove of the intermediate member, and a step of the plunger capable of coming to bear against a rear face of the intermediate member.
By virtue of the layout given to the booster of the invention, it is possible to contrive for the piston to be urged towards its position of rest by a spring which exerts no force on the intermediate member itself.
Furthermore, it is possible to contrive for the booster of the invention, once actuated by a sudden application of the brakes, to continue to apply a strong braking force even if the driver partially releases his own braking force.
To this end, provision is preferably made for the moving partition to comprise a rigid skirt mounted so that it can slide with respect to the piston so that it can adopt, with respect to the piston, a forward position in the axial actuating direction, and for the booster to comprise means of firmly securing the cup to the piston, these securing means being placed in an operational state by the intermediate member when this intermediate member reaches a predetermined driven position with respect to the piston, and being locked in their operational state by the rigid skirt when this rigid skirt adopts its forward position.
According to one possible embodiment, the means of firmly securing attaching the cup to the piston comprise a sharp-edged radial drilling made in the axial bore of the piston, a tapering-edged radial drilling made in the intermediate member, an external housing defined in the cup, and a ball engaged in the sharp-edged drilling, this ball passing through the tapering-edged drilling to engage in the housing when the intermediate member has reached its predetermined driven position.
In this case, the rigid skirt hasp for example, an internal locking edge capable of pressing the ball into the housing when this rigid skirt adopts its forward position while the intermediate member has reached its predetermined driven position.
Other features and advantages of the invention will emerge clearly from the description thereof given hereafter by way of non-limiting indication with reference to the appended drawings:
REFERENCES:
patent: 4173172 (1979-11-01), Ohmi
patent: 4242943 (1981-01-01), Nakamura et al.
patent: 4577548 (1986-03-01), Gautier
Boisseau Jean-Pierre
Levrai Roland
Pujol Herve
Comstock Warren
McCormick Jr. Leo H.
Robert & Bosch GmbH
Ryznic John E.
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