Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1999-04-05
2000-10-31
Verdier, Christopher
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
91 35, F15B 910
Patent
active
061385484
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a pneumatic brake booster.
More specifically, the invention relates to a brake booster comprising: a rigid casing; a moving partition delimiting, in leaktight fashion, a front chamber and a rear chamber inside the casing, the front chamber in operation being permanently connected to a first pressure source delivering a first pressure; a pneumatic piston moving with the moving partition and having a hub slideably mounted in an opening of the casing; an operating rod that can move in the hub between a position of rest and an actuating position as a function of a resultant of forces which acts on it and which comprises an input force exerted in an axial actuating direction directed towards the front chamber and a main return force exerted by a main spring in an axial return direction, the opposite of the axial actuating direction; a plunger housed in a bore of the hub and driven by the operating rod; and a three-way valve itself comprising a fixed annular seat formed on an internal periphery of the hub, a moving annular seat, concentric with the fixed seat and borne by the plunger, and a tubular shutter, concentric with the plunger and with the hub, and exhibiting a frontal annular shut-off face, this frontal face interacting selectively with the moving seat to isolate the rear chamber from a second pressure source delivering a second pressure higher than the first, and this frontal face interacting selectively with the fixed seat to allow the rear chamber to be connected to the second pressure source.
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.
Recent research has shown that a great many drivers, when confronted with an emergency-braking situation, underestimate the actual risks involved and, having braked sharply, relax their braking under circumstances where sustaining heavy braking would, on the contrary, have been absolutely essential to avoid the accident.
This observation has led to the development of various solutions tending to alleviate any ill-advised behaviour of an inexperienced or panic-stricken driver.
The invention falls within this context and its purpose is to provide a simple solution to the problem of sustaining a heavy braking force following a violent braking action.
To this end, the booster of the invention, which in other respects conforms to the definition given in the preamble above, is essentially characterized in that the plunger comprises a cylindrical body secured to the operating rod and a collar of determined axial length, mounted to slide axially with respect to the cylindrical body between a front stop and a rear stop of the body, an anterior section of the collar being engaged between the cylindrical body and the bore of the hub, a posterior section of the collar forming a flange on which the moving seat is defined, and the front stop and rear stop being separated from one another by a distance that exceeds the axial length of the collar, in that a secondary spring exerts on the flange a secondary return force directed in the axial return direction and urging the flange towards the rear stop, and in that the bore in the hub and the collar comprise first and second respective reversible-retention means capable of keeping the collar stationary with respect to the bore in the hub in spite of the secondary return force exerted on the collar and consequently allowing the rear chamber to be connected to the second pressure source, these retention means being activated by the collar being pushed into the bore by an amount at least equal to a minimum determined travel, and being deactivated by the collar being driven along by the front stop when this front stop moves in the axial return direction under the effect of the main return force.
In a preferred embodiment of the invention, the retention means comprise an open elastic ring and an annular channel in which this ring can be housed temporarily, exerting an elastic compression force i
REFERENCES:
patent: 5647462 (1997-07-01), Tsubouchi et al.
Gautier Jean-Pierre
Leboisne Cedric
Michon Jean-Pierre
Verbo Ulysse
Bosch Systemes de Freinage
Comstock Warren
Lazo Thomas E.
McCormick, Jr. Leo H
Verdier Christopher
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