Automatically controlled boosted braking system with monitored r

Details Automatically controlled boosted braking system with monitored r Automatically controlled boosted braking system with monitored r

1994-09-30

1997-08-05

Young, Lee W.

Fluid-pressure and analogous brake systems

Speed-controlled

Having a valve system responsive to a wheel lock signal

3031143, 91 6, 1376275, B60T 844

Patent

active

056535147

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to an automatically controlled braking system for a motor vehicle, comprising: a pneumatic vacuum servo provided with at least a first adjustable-pressure chamber; first and second pressure sources respectively delivering a relatively low pressure and a relatively high pressure; a pneumatic solenoid valve connected to the two sources of pressure and to the first chamber of the servo and comprising an electromagnet capable of transmitting an actuating force to a flap valve capable of isolating, on the one hand, the first pressure source from the second permanently, and, on the other hand, the first chamber from one or other of the two sources depending on a control current selectively supplied to the electromagnet; and a switchable current generator capable of powering the electromagnet selectively.
Systems of this type, well known in the prior art especially by virtue of the American U.S. Pat. No. 4,667,471, make it possible to provide braking of the wheels of the vehicle without voluntary intervention from the driver of the vehicle, when circumstances require it.
These systems, which may, in particular, be used to prevent the wheels from spinning upon startup or during acceleration, when the drive torque is excessive taking account of the adherence of the vehicle to the ground, exhibit a major benefit and their application is more and more widespread.
However, under certain conditions of excessive stress, these systems risk giving rise to relative exhausting of the low pressure reserve which the first pressure source constitutes, and risks no longer being able subsequently to provide voluntary braking under optimal conditions.
Indeed, the low pressure source, which in general essentially consists of the induction pipes of the engine, represents a limited volume into which the air utilized by the servo is delivered after each activation of the latter, which tends to cause this source to be exhausted and to degrade the boost offered by the servo.
This situation is particularly unfavourable in the case of a wheel antilock system providing no control over the engine, insofar as acceleration of the latter already naturally tends to degrade performance of the low pressure source.
The present invention lies within this context and aims to guarantee constant effectiveness of voluntary braking, by preventing the low pressure reserve from being exhausted.
To this end, the braking system of the invention, moreover in accordance with the abovementioned preamble, and in which the flap valve of the solenoid valve is subject, over a pressure cross section to a suction force, the intensity of which is proportional to a pressure difference between the first and second sources and in the same direction as the actuating force, is essentially characterized in that the solenoid valve comprises elastic means capable of applying to the flap valve an elastic force of given value greater than that of the suction force and in the opposite direction, and in that the actuating force is limited to a value less than that of the elastic force.
In the simplest embodiment of the invention, the value of the actuating force is limited by making provision for the current generator to deliver a current, the mean intensity of which is less than a given threshold.
By virtue of these arrangements, the solenoid valve in some way acts as a differential pressure sensor and responds to the stresses of a control current only if the sum of the suction force and of the actuating force corresponding to this current is capable of overcoming the elastic force, which happens only if the suction force is greater than a threshold above which the first pressure source is under no risk of being exhausted.
Other characteristics and advantages of the invention will emerge clearly from the description thereof which is given hereafter, by way of nonlimiting indication, with reference to the appended drawings in which:
FIG. 1 is a diagrammatic view of a braking system in accordance with the invention; and
FIG. 2 is an enlarged view fo

REFERENCES:
patent: 3364818 (1968-01-01), Hager et al.
patent: 4208872 (1980-06-01), Shimizu et al.
patent: 4667471 (1987-05-01), Fulmer et al.
patent: 5046314 (1991-09-01), Levrai
patent: 5067524 (1991-11-01), Pickenhahn

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