Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1996-09-12
1998-04-07
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
188356, B60T 1366, B60T 1357, F15B 912, F15B 13044
Patent
active
057355819
DESCRIPTION:
BRIEF SUMMARY
This application is a continuation of PCT Application PCT/EP95/00954 filed Mar. 14, 1995 which in turn is based on German Application No P4410769.2 filed Mar. 28, 1994.
The invention relates to a valve assembly for controlling a pneumatic brake booster, which comprises the characteristics of the preamble of claim 1.
A valve assembly of such a type is known from EP-0 405 603 A2.
With this state of the art the valve assembly which controls the brake booster is designed in such a manner that the brake booster assists emergency braking operations very effectively but, under "normal" braking conditions, does not behave in a manner which is considerably different from the usual manner. The term "emergency braking operation" is defined as a very strong, abruptly starting pedal actuation on the part of the driver, whereas a "normal" braking operation takes place when the driver actuates the brake pedal gently. An emergency braking operation is sometimes also referred to as "panic braking". It is known that most drivers actuate the pedal too timidly when carrying out panic braking operations such as these and do not dare to fully press down the pedal. The initially mentioned state of the art according to EP-0 405 603 A2 provides a remedy for this problem in that the brake booster is equipped with a special valve assembly to provide for additional and increased brake boosting which becomes effective upon a heavy braking operation.
With this state of the art, an additional valve is provided in addition to the usual two valve seats, which comprises a sleeve which encompasses the control housing at a radial distance and which is axially movable with respect to the control housing. The sleeve is biased towards the valve seat of the additional valve, and an additional ventilation duct is formed between the sleeve and the control housing via which the overpressure chamber of the brake booster is supplied with air.
This state of the art involves a purely mechanical actuation of the valve assembly in response to an actuation of the brake pedal (by the driver).
From the state of the art it is also already known to provide an electromagnetic actuation for brake boosters in addition to the mechanical actuation, by means of which under certain braking situations a higher air pressure than under "normal" braking situations is generated very rapidly in the over-pressure chamber of the brake booster (the term "overpressure" means that a higher air pressure prevails in said chamber than in the evacuated chamber). Such electromagnetically operated auxiliary air control systems are known from DE 4 217 409 A1, DE 4 309 850 A1 and DE-GM 9 202 154. From EP 0 478 396 A1 a pneumatic brake booster with a housing is known which is divided into a vacuum chamber and a working chamber, with a double valve arrangement with a first valve between the vacuum chamber and the working chamber and a second valve between the atmosphere and the working chamber being arranged at the housing. In a rest position, the valve arrangement enables a pressure level in the vacuum chamber and in the working chamber which is isolated from atmosphere; in a working position, it keeps the vacuum chamber closed and enables a connection between the atmosphere and the working chamber. Under normal operating conditions, this brake booster can be actuated by means of an actuation rod. However, this arrangement is disadvantageous in that when the pedal is not actuated, automatic braking as a result of activation of the solenoid is not possible because the large axial movability of the valve housing relative to the actuation rod and the comparatively smaller possible opening stroke of the valve between the working chamber and the atmosphere makes effective closing of the working chamber against the vacuum chamber unachievable over the entire stroke of the valve housing.
From DE 42 11 849 A1 a brake booster is known which can be controlled in a particularly sensitive manner by means of small movements of the actuation member. To this end, this arrangement is provided with a s
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Butler Douglas C.
Lucas Industries public
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