Fluid-pressure and analogous brake systems – Speed-controlled – Front-rear axle apportioning or speed difference
Reexamination Certificate
1996-09-30
2001-10-16
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Front-rear axle apportioning or speed difference
C303S113500
Reexamination Certificate
active
06302501
ABSTRACT:
STATE OF THE ART
The invention pertains to a method and to an apparatus for controlling the brake system of a vehicle wherein a control unit builds up and release pressure at least at the rear wheel brakes.
A brake pressure control system for a vehicle is known from DE 41 12 388 A1 (U.S. Pat. No. 5,281,012), in which, in addition to an antilock control, the braking force distribution between the front and rear axle brakes is adjusted electronically. The pressure reducer normally used is replaced by the known electronic control of the braking force distribution. If this controller fails for some reason, the rear wheels can lock before the front wheels in certain braking situations as a result of the overbraking of the rear axle. This can lead to undesirable driving situations.
SUMMARY OF THE INVENTION
It is therefore the task of the present invention to provide for the failure-proof braking force distribution between the front and rear axles without hydraulic or pneumatic pressure reducers. This failure-proof braking force distribution should preferably serve to distribute the braking forces on an emergency basis after the failure of the electronic controller.
This is achieved by the alternating buildup and release of pressure at the rear wheel brakes, until a saturation pressure value is reached, which is below the primary pressure specified by the driver.
It is known from the publication SAE 89078 “Electronic Control Unit of the Sumitomo Electronic Anti-Lock System” that it is possible to check the working order of the electronic control unit and of the components of a brake system of a motor vehicle.
The method according to the invention ensures that the rear wheels do not lock before the front wheels even in cases where no electronic controller for the braking force distribution is present. The method according to the invention therefore offers particular advantages in cases where the electronic braking force distribution controller has failed.
This has the advantage that, even in the presence of a defect, the stability of the vehicle remains preserved during the braking process. It is possible to eliminate the supplemental pressure reducers provided for emergency situations.
It is especially advantageous that the method for distributing the braking forces according to the invention makes it possible to control the braking force distribution between the front and rear axles without any additional information.
The method according to the invention offers particular advantages when the so-called “double defect” case occurs, when, for example, all of the speed sensors of one axle fail.
The method according to the invention can also be used advantageously in cases not characterized by a defect.
It is especially advantageous that the pressure being reached at the rear axle is adjusted independently of the primary pressure specified by the driver through his actuation of the brake pedal.
In an exemplary embodiment, the dependence of the adjustment of the rear axle brake pressure as a function of the voltage of the vehicle's electrical system, of the primary pressure, or of the brake pressure level already present at the rear axle brakes is especially advantageous.
A further advantageous increase in the availability of the brake system is achieved in that the strategy according to the invention for distributing the braking force is calculated not in to the main computer, which implements the electronic control, but rather in a separate component, which works independently of the main computer element.
Another advantage is achieved by limiting the time during which the method according to the invention is applied. As a result, the components are protected from thermal overloads during prolonged periods of braking. Here it is advantageous that the pressure level in the rear wheel brakes is raised in accordance with a predetermined “ramp” to the primary pressure level after the expiration of a specified time.
REFERENCES:
patent: 4850650 (1989-07-01), Eckert et al.
patent: 5219210 (1993-06-01), Maehara
patent: 5281012 (1994-01-01), Binder et al.
patent: 5284385 (1994-02-01), Müller et al.
patent: 5632535 (1997-05-01), Luckevich et al.
patent: 4208581 (1993-05-01), None
patent: 4226646 (1994-02-01), None
patent: 2539687 (1984-07-01), None
Dominke Peter
Gottwick Ulrich
Fulbright & Jaworski LLP
Graham Matthew C.
Robert & Bosch GmbH
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