Power plants – Pressure fluid source and motor – Pulsator
Patent
1998-07-24
2000-07-04
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Pulsator
B60T 1320
Patent
active
060821094
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a master cylinder with hydraulic reaction for a pneumatic brake booster, comprising: a body pierced with a main bore; a cylindrical main piston pierced with a stepped secondary bore, and of which one end, outside the body, can receive a boost force directed in a first direction, this main piston being mounted, without leaking, in the main bore in order therein to delimit a working chamber which during operation is subjected to a hydraulic pressure; and hydraulic reaction means including a reaction piston mounted with leaktight sliding in a cross section of a first diameter of the secondary bore which it closes off, and having an end outside the body, capable of receiving an actuating force directed in the first direction; relative to the actuating force, the boost force having a delay that increases with the rate of application of the actuating force.
BACKGROUND OF THE INVENTION
A master cylinder of this type is described, for example, in patent FR-2,724,354.
Devices of this type have been developed very recently for their ability to overcome the dynamic shortcomings of pneumatic brake boosters.
Now it is known that pneumatic brake boosters which are used to provide a force to assist with braking which is added to the actuating force exerted by the driver on the brake pedal and is in theory proportional to this force, have the shortcoming of being able to develop this boost force only after a certain delay from the application of the actuating force.
As the boost force is the result of the difference between the pneumatic pressures which there are on the one hand in a front chamber of the booster, this chamber being connected to a source of partial vacuum, and on the other hand in a rear chamber which is connected to atmosphere during braking, and as the delay in boost force compared with the actuating force is due to a limit on the rate at which atmospheric air is let into the rear chamber through the booster inlet valve at the time of braking, this delay is longer, the more abrupt the braking.
Now, the situations in which braking is rapid are generally emergency situations in which the driver would, by contrast, specifically need the greatest possible boost force as early as possible.
These considerations have quite recently led to the development of master cylinders with hydraulic reaction which, on the one hand, allow the booster inlet valve to open wider and therefore allow an increased air flow rate and, on the other hand, allow a dynamic modulation of the reaction force, that is to say a modulation as a function of the rate of brake application of the fraction of the boost force with which the reaction master cylinder opposes the actuating force in order to adjust the boost force as a function of this actuating force.
Using devices described in documents which have not been pre-published, it is thus possible considerably to reduce the reaction force in the event of emergency braking as compared with the value it would have for normal braking, and this allows a corresponding increase in the braking force available for emergency braking situations.
However, a problem still encountered in this development lies in the relative structural complexity of devices capable of fulfilling these functions, and especially the difficulty in obtaining a dynamic variation of the reaction force using a reaction piston made as just one part.
The object of the present invention is to propose a solution to this problem.
SUMMARY OF THE INVENTION
To this end, the master cylinder of the invention which in other respects is in accordance with the preamble above, is essentially characterized in that the hydraulic reaction means further comprise: a shut-off seat mounted on a front face of the reaction piston and pointing toward the working chamber; an annular wall arranged some distance from the reaction piston in the first direction, forming a fixed restriction for the secondary bore and delimiting a central passage which has a second diameter smaller than the first diameter and which m
REFERENCES:
patent: 2959011 (1960-11-01), Randol
patent: 3387455 (1968-06-01), Eggstein
patent: 5921084 (1999-07-01), Gautier et al.
Bosch Sistemas de Frenado S.L.
Comsbock Warren
Lopez F. Daniel
McCormick, Jr. Leo H
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