Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
1999-08-16
2001-03-06
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
Reexamination Certificate
active
06195993
ABSTRACT:
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 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 so that it can slide, without leaking, in the main bore in order therein to delimit a working chamber which during operation is subjected to a hydraulic pressure; and a reaction piston of which a first end, outside the body, is capable of receiving an actuating force directed in the first direction, and of which a second end is mounted so that it can slide, without leaking, by virtue of a first annular seal, in the secondary bore in order therein to delimit at least a first reaction chamber that communicates with the working chamber, the reaction piston being capable of moving, with respect to the main piston, through a travel of non-zero minimum amplitude for an actuation force gradient that exceeds a given threshold.
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 compared with the actuating force.
As the boost force is the result of the difference between the pneumatic pressures prevailing, 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 the atmosphere during braking, and as the delay in the 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 the 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, 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 developing these devices lies in the fact that most drivers, caught out by the deceleration, tend to release their braking effort far too early in a panic situation, which means that it is advisable, after a sharp application of the brakes, for the drop in braking effort to be compensated for, in order to reduce or cancel the negative effects of this dangerous reflex.
The object of the present invention is to put forward a solution to this problem.
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 it further comprises: a first shut-off seat formed on a front face of the second end of the reaction piston; a second shut-off seat mounted at a first end of a seat support placed in the first reaction chamber, at a distance from the first shut-off seat that is at most equal to the said minimum-amplitude travel; and at least a first spring urging the reaction piston in a direction likely to move the first shut-off seat away from the second shut-off seat, in that the seat support has a second end sliding, without leaking, in the main piston by virtue of a second annular seal, this seat support being, via its first end, subjected to a pressure prevailing in the first reaction chamber and, via its second end, subjected to a pressure lower than the pressure prevailing in the first reaction chamber, and in that the reaction piston and the seat support constitute, by contact between the first and second seats, a stepped assembly which, from the first end of the reaction piston towards the second end of the seat support, has an increase in section forming an annular surface subjected to the pressure of the first reaction chamber.
In a first possible embodiment of the invention, the annular surface at least partially consists of a difference in diameters of sliding of the first and second annular seals.
In a second possible embodiment of the invention, the reaction piston delimits in the secondary bore, between its first and second ends, a second reaction chamber which communicates with the first reaction chamber and that the reaction piston shuts off in a sealed manner by virtue of third and fourth annular seals which follow one another in this order in the first direction, this reaction piston also delimiting in the secondary bore, between the fourth and first annular seals, an empty chamber subjected to a pressure lower than the pressure prevailing in the first reaction chamber, and the annular surface at least partially consisting of a difference in diameters of sliding of the third and fourth annular seals.
In a third possible embodiment of the invention, the annular surface at least partially consists of a difference between the diameter of sliding of the first annular seal and the shut-off diameter between the reaction piston and the seat support.
The shut-off seats may then be formed on radial shoulders extending outwards from the reaction piston and from the seat support respectively.
A volume-compensation device will then advantageously be arranged in the space defined between the reaction piston and the seat support, it being possible for this volume-compensation device to consist of a diaphragm made of a flexible material defining a sealed compensation chamber filled with a compressible material.
The feeler, which is used to transmit the actuating force to the reaction piston, may be mounted to slide between two axial stops on the first end of the reaction piston, a return spring urging this feeler in the first direction with respect to the reaction piston.
It is also possible to contrive for the response curve of the booster equipped with the master cylinder of the invention to have, as is conventionally the case, an initial jump, by envisaging for the master cylinder with hydraulic reaction to comprise a second spring urging a moving ring in a first direction against an internal rest of the secondary bore, and for the reaction piston to comprise means for carrying along the moving ring, when this piston is moved, from a position of rest, in a direction which is the opposite direction to the first direction.
REFERENCES:
patent: 2862366 (1958-12-01), Ingres et al.
patent: 4091619 (1978-05-01), Carre et al.
patent: 4172364 (1979-10-01), Young
patent: 4179980 (1979-12-01), Kito et al.
patent: 4660381 (1987-04-01), Kuromitu
patent: 5921084 (1999-07-01), Gautier et al.
patent: 5941071 (1999-08-01), Simon Bacardit
patent: 6079208 (2000-06-01), Verbo et al.
patent: 6082109 (2000-07-01), Simon Bacardit
patent: 6085522 (2000-07-01), Simon Bacardit
Bacardit Juan Simon
Bentz Jean-Paul
Berthomieu Bruno
Leboisne Cedric
Sacristan Fernando
Comstock Warren
McCormick Jr Lee H
Robert & Bosch GmbH
Ryznic John E.
LandOfFree
Master cylinder with hydraulic reaction and selective... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Master cylinder with hydraulic reaction and selective..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Master cylinder with hydraulic reaction and selective... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2452664