Power plants – Pressure fluid source and motor – Pulsator
Patent
1997-06-11
1999-08-24
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Pulsator
60554, 60562, 60582, B60T 1320
Patent
active
059410710
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to boosted braking devices 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.
BACKGROUND OF THE INVENTION
In the conventional way, the master cylinder is full of brake fluid and equiped with a primary 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 a primary hydraulic circuit, and with a secondary hydraulic piston subjected to the hydraulic pressure in the primary hydraulic circuit and causing an increase in pressure in a secondary hydraulic circuit.
Also, in the conventional way, the pneumatic booster can be controlled by the application of the input force to a control rod controlling the opening of a valve in order to exert the actuating force on the primary 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, the input force being transmitted via a reaction disc against which the pneumatic piston also rests in order to impart 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.
In parallel, boosted braking devices have been developed in which the reaction exerted on the control rod is not supplied mechanically by a reaction disc, but by the hydraulic pressure prevailing in the master cylinder.
In these devices, she 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 secondary hydraulic piston which can receive at least the input force, elastic means exerting an elastic force between the secondary hydraulic piston and the moving cylinder and urging the secondary hydraulic piston towards the master cylinder, 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 FR-A-2,658,466.
These devices with hydraulic reaction have the main advantage that irrespective of the intensity of the braking action or the rate of application of the input force, their characteristic operating curve, namely the curve giving the pressure in the master cylinder as a function of the intensity of the input force on the booster, is unchanged.
However, in the event of failure in the hydraulic circuit between the master cylinder and the wheel brakes, the pressure inside the primary or secondary hydraulic circuit cannot be established. In both cases this results in an increase in the travel of the brake pedal in order to obtain an increase in the hydraulic pressure in the intact circuit. However, if this failure affects the primary hydraulic circuit, this additionally results in a complete loss of reaction felt by the driver on the brake pedal, which means that he can no longer gauge the braking force except by gauging the travel of the brake pedal, which travel is itself already disturbed.
Attempts have already been made to solve this problem, for example in documents FR-A-1,475,049 or U.S. Pat. No. 3,470,695. These documents envisage the use of the hydraulic pressure in the secondary circuit, assumed to be intact, to provide the desired reaction on the brake pedal. Aside from the fact that they result in complicated embodiments, they require the presence of a third piston sliding in leaktight fashion in the seco
REFERENCES:
patent: 3109287 (1963-11-01), Gardner
patent: 3470695 (1969-10-01), Kilb
patent: 3473329 (1969-10-01), Eggstein
patent: 4693083 (1987-09-01), Reinartz
patent: 5154056 (1992-10-01), Gautier et al.
Comstock Warren
Lopez F. Daniel
McCormick, Jr. Leo H
Robert Bosch Technology Corp
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