Power plants – Pressure fluid source and motor – Pulsator
Patent
1996-01-16
1998-03-03
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Pulsator
B60T 11224
Patent
active
057222401
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a boosted braking device of the type used for the braking of motor vehicles.
BACKGROUND OF THE INVENTION
Such braking devices have been known for a long time and conventionally comprise, on the one hand, a master cylinder filled with a brake fluid and equipped with a main hydraulic piston designed to receive an actuation force composed of an input force and of a boost force, both acting in an axial direction and, on the other hand, a pneumatic booster capable of being operated through the application of the input force to an operating rod controlling the opening of a valve, in order to exert the actuation force on the main hydraulic piston, the booster including a rigid casing divided in leaktight fashion into two chambers by means of a moving partition capable of being urged by a difference in pressure, between the two chambers, resulting from the opening of the valve and of driving a pneumatic piston which can move relative to the casing and which carries the valve, the input force being transmitted via a reaction disk against which the pneumatic piston also bears in order to supply at least some of the boost force to it.
A device of this type is well known in the prior art and is described, for example, in document U.S. Pat. No. 4,491,058.
For a long time it has been sought to improve these devices so that the total travel of the operating rod, and therefore the total travel available for the brake pedal, will be the result of a compromise between two contradictory parameters, so as to obtain what has become known in the art as good pedal feel.
In fact, the travel of the operating rod has to be just sufficient for the driver to be able to control the deceleration of the vehicle during braking in an optimum fashion. However, the total travel of the operating rod is necessarily extended by a relatively significant initial travel during which the hydraulic pressure in the braking circuit reaches a minimum value, beyond which any increase in pressure will result in an effective braking action.
SUMMARY OF THE INVENTION
In order to solve this problem, a solution has already been proposed, for example in document FR-A-2,696,141, (U.S. Pat. No. 5,475,978) corresponding to the preamble of the main claim and according to which the main hydraulic piston of the master cylinder itself includes a hollow moving cylinder communicating with the master cylinder, which receives at least some of the boost force and inside which a secondary hydraulic piston capable of receiving at least the input force slides, over an axial distance L, in a leaktight fashion and in the axial direction, the moving partition being slidably mounted on the pneumatic piston so as to be able to slide over the axial distance L relative to it in the direction of the master cylinder, from an initial relative position in which it is in abutment toward the rear against the pneumatic piston and bearing at least indirectly on the moving cylinder toward the front, when it is urged by a pressure difference.
Such a solution makes it possible to obtain the minimum braking pressure in response to a very small initial travel of the operating rod, which initial travel may even be imperceptible to the driver of the vehicle.
This solution does, however, involve an increase in the travel of the main piston of the master cylinder, and correspondingly an increase in the axial length of the latter, and consequently an increase in the length of the braking device, whose total overall size may prevent it from being fitted in the engine compartment of some vehicles.
The object of the present invention is therefore to provide a boosted braking device whose effectiveness comes into play right at the beginning of braking, that is to say after a very short initial travel of the brake pedal, and the overall size of which is not greater than that of a conventional braking device as illustrated, for example, by the first above mentioned document.
To this end, the invention provides a boosted braking device of the type defined above, in w
REFERENCES:
patent: 2587023 (1952-02-01), Allyn
patent: 2820346 (1958-01-01), Cook
patent: 5475978 (1995-12-01), Gautier et al.
Bosch Systems de Freinage
Lopez F. Daniel
McCormick Jr. Leo H.
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