Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1999-05-19
2001-08-07
Ryznic, John E. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06269731
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 fashion, a front chamber and a rear chamber inside the casing, the front chamber in operation being subjected to a first pressure and the rear chamber being selectively connected to the front chamber or subjected to a second pressure higher than the first; a pneumatic piston moving with the moving partition; an operating rod moving in the piston as a function of an input force selectively exerted in an axial actuating direction orientated towards the front chamber, and of a return force exerted by a main spring in an axial return direction which is the opposite of the axial actuating direction, the return force urging the operating rod into a return position, and the input force urging the operating rod into an intermediate actuating position or into an extreme actuating position, depending on whether the input force is applied at a rate that is lower or higher than a determined limiting rate; a plunger housed in the piston and driven along by the operating rod; a three-way valve itself comprising an annular seat borne by a rear section of the plunger, this 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 the operating rod is in one of its actuating positions; force-transmission means capable of receiving and of transmitting at least a boost force exerted by a front face of the piston when the valve subjects the rear chamber to the second pressure, these force-transmission means themselves comprising reaction means capable of reacting against the input force with a reaction force that depends on the boost force.
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.
Recent research has shown that a good many drivers, when confronted with an emergency braking situation, underestimate the risks actually involved and, having braked sharply, release their braking effort under circumstances in which, on the contrary, it is absolutely essential that they maintain a substantial braking effort in order to avoid the accident.
This observation has led to the development of various solutions in an attempt to alleviate any possible shortcomings in the behaviour of an inexperienced or panic-stricken driver.
SUMMARY OF THE INVENTION
The invention falls within this context and is intended to provide a simple solution to the problem of maintaining a substantial braking force after a violent braking action.
To this end, the booster of the invention which in other respects is in accordance with the definition given in the above preamble, is essentially characterized in that the plunger comprises a front section connected to the rear section by a secondary spring exerting, between the front and rear sections, a mutual-contact force that is lower than the return force, and in that the front section and the force-transmission means comprise respective reversible retention means capable of securing the front section to the piston when the boost force exceeds a determined threshold while the operating rod is in its extreme actuating position.
In one possible embodiment of the invention, the retention means comprise an elastic annular layer axially subjected to the boost force, this layer having an axial thickness and an inside diameter which are smaller, the higher the boost force.
For example, reaction means comprise a reaction disc made of elastomeric material, the retention means comprise a rigid disc constituting a front face of the front section of the plunger, and the annular layer consists of a thickening of the reaction disc which delimits, in the reaction disc, a housing capable of trapping the rigid disc when the boost force exceeds the determined threshold while the operating rod is in its extreme actuating position.
In this case, the housing and the rigid disc preferably have complementary frustoconical shapes.
The retention means may also comprise a shoulder with the external shape, for example at least partially cylindrical, of the front section.
In this case, the retention means advantageously comprise a rigid insert located in the elastic annular layer and interacting with the shoulder with the external shape of the front section in order to combine the front section with the piston when the boost force exceeds the determined threshold while the operating rod is in its extreme actuating position.
In other embodiment of the invention, the retaining means comprise a rigid sleeve arranged inside an elastic sleeve wich delimits a housing capable of trapping the rigid sleeve when the boost force exceeds the determined theshold while the operating rod is in its extreme actuating position.
REFERENCES:
patent: 5884548 (1999-03-01), Ando et al.
patent: 5893316 (1999-04-01), Inoue et al.
patent: 5907990 (1999-06-01), Satoh
patent: 5943937 (1999-08-01), Endo
patent: 2092251 (1982-08-01), None
patent: 4-257760 (1992-09-01), None
Gautier Jean-Pierre
Leboisne Cedric
Medina Raphael
Richard Philippe
Verbo Ulysse
Comstock Warren
McCormick Jr. Leo H
Robert & Bosch GmbH
Ryznic John E.
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