Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Patent
1995-08-23
1998-01-27
Richter, Sheldon
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
F15B 910
Patent
active
057112037
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pneumatic boosters of the type used to boost the braking in motor vehicles.
Such boosters are well known and commonly employed in the automobile field. They include a casing fixed to the bulkhead separating the engine compartment from the passenger compartment, so that they can be actuated by a brake pedal situated in the passenger compartment and can actuate the primary piston of a master cylinder situated in the engine compartment and connected to the brakes of the vehicle by a hydraulic circuit.
For the purpose of optimizing the operation of these boosters, and also the "feel" experienced by the driver when he presses on the brake pedal, it has for a long time been sought to decrease what is termed the effort of attack, that is to say the force necessary to actuate the booster.
Now, it has been noted that there is a lower physical limit below which this effort of attack cannot drop. In effect, after having been actuated, a booster restores a certain force, termed return force, when it resumes its position of rest. It can easily be understood that the effort of attack cannot be less than the return force.
For example, document WO 94/04403 makes known a booster corresponding to the preamble of the main claim, in which the effort of attack is reduced by providing means for causing the pressure prevailing in the rear chamber of the booster to act on the rear face of the shut-off element constituting the three-way valve of a booster.
This known booster includes a casing having an axis of symmetry divided in leaktight fashion by a movable wall structure into a front chamber permanently connected to a source of low pressure, and a rear chamber connected selectively to the front chamber or to a source of high pressure by a three-way valve means actuated by a control rod capable of pressing, via the front face of a plunger, on the rear face of a push rod, the plunger sliding in a bore of the movable wall, the three-way valve including a valve element located in a tubular rear part of the movable wall and interacting via an annular front face with a first annular valve seat formed on the plunger and with a second annular valve seat formed on the movable wall, the first valve seat being concentric with the second valve seat and of smaller diameter, the annular front face of the valve element being able to move in the tubular rear part of the movable wall and being sealed in the latter via its outer edge and via its inner edge, the annular front face of the valve including at least one opening causing a chamber situated behind the annular front face of the valve to communicate with the space situated between the first valve seat and second valve seat.
Such an arrangement makes it possible to distribute the pressure differences over the various elements making up the three-way valve, and thus reduce the stresses at rest and in the operating position of the various return springs used for the operation of the three-way valve. It follows that the effort of attack required to compress these springs to begin with may be decreased.
However, this known booster still has quite a substantial effort of attack with regard to the current requirements of motor manufacturers, which effort it would therefore be appropriate to decrease.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide a booster in which the effort of attack is as small as possible, and to this end it proposes to reduce still further the return force thereof.
To this end, according to the present invention, the resultant of the forces generated by the low pressure and by the high pressure exerted on the plunger is permanently zero or negligible.
Other objects, features and advantages of the present invention will emerge more clearly from the description which follows of one embodiment given by way of illustration with reference to the appended drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
The single FIGURE is a side view in longitudinal section representing the rear central part of a
REFERENCES:
patent: 4898073 (1990-02-01), Seip et al.
patent: 5546846 (1996-08-01), Bauer
patent: 5651300 (1997-07-01), Ikeda et al.
Gautier Jean Pierre
Perez Revilla Miguel
Verbo Ulysse
Bosch Systems de Freinage
McCormick Leo H.
Richter Sheldon
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