Power plants – Pressure fluid source and motor – Pulsator
Patent
1997-09-03
2000-06-20
Look, Edward K.
Power plants
Pressure fluid source and motor
Pulsator
91371, B60T 1320
Patent
active
060763515
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to boosted braking systems for motor vehicles, comprising a master cylinder controlling the hydraulic pressure in the brake circuit connected to the brakes of the vehicle, it being possible for this master cylinder to be actuated by a pneumatic booster when the driver of the vehicle depresses the brake pedal, the reaction force being transmitted hydraulically to this pedal.
BACKGROUND OF THE INVENTION
In the conventional way, the master cylinder is full of brake fluid and equipped with a main hydraulic piston intended to receive an actuating force composed of an input force and of a boost force both acting in an axial direction.
Also, the pneumatic booster can be controlled by the application of the input force to a control rod controlling the opening of a valve by means of a plunger in order to exert the actuating force on the main hydraulic piston of the master cylinder, the booster including a rigid casing divided in leaktight fashion into two chambers by means of a moving partition which can be acted upon by a difference in pressure between the two chambers resulting from the opening of the valve and can drive a pneumatic piston, which can move with respect to the casing, carrying the valve, and contributing at least to transmitting the boost force.
In braking systems with hydraulic reaction, the main hydraulic piston of the master cylinder itself includes a hollow moving cylinder communicating with the master cylinder and receiving at least some of the boost force, and inside which there slides, in leaktight fashion and in the axial direction, a reaction piston which can receive at least the input force, at least one opening being made in the moving cylinder to make the inside of the latter communicate with the inside of the master cylinder.
Such a device is described, for example, in document EP-B-0,443,886.
These devices with hydraulic reaction have as their advantages optimum control of the pressure of the brake fluid by the force exerted on the brake pedal and a characteristic operating curve giving the pressure prevailing in the master cylinder as a function of the input force exerted on the brake pedal, which is constant irrespective of the conditions of operation.
However, they have the drawback that when the reaction piston comes into contact with the plunger in order to transmit the reaction force to it, this contact is somewhat abrupt depending on the rate of application of the input force, and is transmitted to the control rod integral with the plunger and to the brake pedal articulated to the control rod and is felt as a rather unpleasant sensation by the driver of the vehicle. What is more, these impacts between the plunger and the reaction piston may damage the plunger and/or the reaction piston and detract from the correct operation of the braking system, or in any case reduce its life.
SUMMARY OF THE INVENTION
The present invention falls within this context and its object is to propose a boosted braking system in which the sensation felt by the driver when he depresses the brake pedal is improved, it furthermore being necessary for such a braking system to be of low cost while having an operation which is reliable under all circumstances.
To this end, the present invention proposes a boosted braking system for a motor vehicle, comprising on the one hand a master cylinder full of brake fluid and equipped with a main hydraulic piston intended to receive an actuating force composed of an input force and of a boost force both acting in an axial direction, so as to cause an increase in pressure in the brake fluid and on the other hand a pneumatic booster which can be controlled by the application of the input force to a control rod integral with a plunger controlling the opening of a three-way valve in order to exert the actuating force on the main hydraulic piston, the booster including a rigid casing divided in leaktight fashion into at least two chambers by means of at least one moving partition which can be acted upon by a difference in pressure betwe
REFERENCES:
patent: 3470695 (1969-10-01), Kilb
patent: 3910046 (1975-10-01), Gardner et al.
Bosch Systemes de Freinage
Comstock Warren
Lazo Thomas E.
Look Edward K.
McCormick Jr. Leo H.
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