Fluid-pressure and analogous brake systems – Multiple fluid-receiving devices – Multiple motors
Patent
1996-10-09
1999-11-02
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Multiple fluid-receiving devices
Multiple motors
303186, B60T 826, B60T 832
Patent
active
059756500
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention pertains to a method and to an apparatus for controlling the brake system of a vehicle according to the introductory clauses of the independent claims.
A method and an apparatus for controlling the brake system of a motor vehicle are known from WO-A 94/13517, in which, to ensure the optimum distribution of the braking force between the front and rear axles, the difference between the wheel rpm's of the front axle and the wheel rpm's of the rear axle is determined. This slip between the front and the rear axle is compared with a predetermined limit, the absolute value of which is larger when the vehicle is driving straight ahead than when it is driving around a curve. When the detected slip exceeds this defined limit, any further pressure increase in the rear-axle brakes is prevented. Even though two different threshold values are specified to deal with two different actual driving situations, it is still possible for the pressure level at the rear axle to be too high. This is especially the case when the vehicle is traveling straight ahead, the driver brakes, the brake system stabilizes at close to the ideal braking force distribution, and the vehicle then enters a curve. Because the pressure level in this case is too high, the rear wheels tend to lock, which is reduced by an antilock protective function. When the antilock protective function is activated, pressure is reduced in the rear-wheel brakes; because of the associated startup of the return pump at this point, a strong reaction is produced at the brake pedal. This sudden reaction at the brake pedal can confuse the driver and thus lead to unwanted situations.
It is therefore the task of the present invention to provide measures for ensuring the almost complete stability of the vehicle in the partial braking range even without any intervention by the antilock protection. At the same time, the driver should experience little or no reaction at the pedal.
SUMMARY OF THE INVENTION
According to the invention, the brake pressure at the rear axle brakes is released when the difference between the speed of a front wheel and the speed of a rear wheel exceeds a predetermined threshold.
The method according to the invention ensures, during the braking process, the almost complete stability of the vehicle in the partial braking range without the need to actuate the antilock controller.
It is especially advantageous that the antilock controller is called upon to intervene less often, which has the effect of prolonging the service life of the components.
It is also advantageous that two velocity difference thresholds (slip thresholds) are specified; when the first threshold is exceeded, pressure is maintained in the rear-axle brakes; when the second difference threshold is exceeded, pressure is released in the rear-axle brakes. As a result, it is possible for the pressure to be released in the rear-axle brakes without any additional sensor signals.
Because the second velocity difference threshold is more sensitive than the slip threshold which activates the antilock controller, the advantageous result is obtained that the pressure is released at the rear axle before the antilock controller intervenes.
It is especially advantageous that, during the release of pressure at the rear axle, the motor of the return pump is not driven, and thus there is no perceptible reaction at all or only a very weak one at the brake pedal.
By turning on the motor of the return pump for a predetermined length of time upon conclusion of the braking process, the storage chamber which allows the pressure to be equalized during the release of pressure is emptied.
It is advantageous in this regard for the actuation time to be specified as a function of the quantity of operating medium to be pumped out.
Additional advantages can be derived from the following description of exemplary embodiments and also from the dependent claims.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows a general circuit diagram of a control system for the brake system of
REFERENCES:
patent: 3764182 (1973-10-01), Andreyko et al.
patent: 4943922 (1990-07-01), Tanaka
patent: 5415469 (1995-05-01), Poggenburg et al.
patent: 5632535 (1997-05-01), Luckevich et al.
patent: 5700074 (1997-12-01), Sugimoto et al.
Dressler Norbert
Meier Thomas
Strehle Alfred
Graham Matthew C.
Robert & Bosch GmbH
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