Fluid-pressure and analogous brake systems – Electric control
Reexamination Certificate
1999-06-07
2001-05-29
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Electric control
C188S071700
Reexamination Certificate
active
06238011
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for controlling a wheel brake in open loop.
BACKGROUND INFORMATION
When controlling a wheel brake, in some applications, it is important to know when the brake pads (or linings) lift off from the brake disc or drum. This holds true, for example, in connection with the adjustment of the clearance (air gap). Another application can be seen in the control of the wheel brake when the brake releases, it being possible to ensure that the vehicle wheel brakes are released essentially simultaneously. In the following, the problem of adjusting the clearance is discussed as the preferred field of application.
The adjustment of the clearance at a wheel brake is desirable with a view to the continually existing wear and tear of the brake pad, as well as changes in the marginal conditions such as the brake temperature. This holds true in particular for motor-vehicle wheel-brake systems operated using electric motors, in which the wheel brakes are controlled by driving brake actuators having electric motors. Motor-vehicle wheel brakes operated by electric motors are known, for example, from PCT Publication No. 94/24453 or German Published Patent Application No. 19 526 645, where the application force is produced by an electric motor. In an electrically controlled braking system, a required clearance (distance between the brake pad and the brake disc) should be maintained in all working points in the unbraked state. For example, in the event of a lateral runout of the brake disc, a clearance which is too small leads to friction losses between the brake disc and the brake pad even in the unbraked state. If there is no compensation for the continually existing wear and tear of the brake pad, then a clearance which is too large will occur. This will result in a reduction of the dynamic response of the braking process, since after initiating the braking process, the electric motor would first of all have to run through the clearance before any braking action would come about at the brake disc. In addition, the goal should be for the clearance to be adjusted approximately equally at both wheels of a vehicle axle. A different clearance leads to a different response characteristic of the two wheel brakes of a vehicle axle during a braking process. In this context, one must expect a quicker braking action at the wheel having the smaller clearance than at the wheel having a larger clearance. Accordingly, the clearance has a not inconsiderable influence on the comfort and safety during the braking process of a motor vehicle.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to specify measures which make it possible to determine the release of a wheel brake, in particular, to adjust a predefined clearance at the wheel brake.
The following described design approach makes it possible to determine exactly and simply when the wheel brake has released, i.e., the wheel pads have lifted off from the disc or the drum, even when the sensors employed at the wheel brake exhibit drifts.
It is particularly advantageous that it allows a defined adjustment of a clearance after the termination of a braking. In so doing, appearances of drift in the sensor signals used for adjusting the clearance are taken into account. In this manner, a zero shift of the sensors used, e.g., of braking-force, braking-torque, and/or angular-position sensors, as the result of temperature influences, etc., are rectified, it being possible to always adjust the same clearance, irrespective of the respective zero shift.
Used in particularly advantageous manner to ascertain the clearance is not the absolute value of the braking-force or braking-torque sensor, but rather a relative value of such a sensor. From this relative value can be determined the offset of an angular-position sensor, according to whose signal the optimum clearance is adjusted.
The adjustment of the clearance is particularly accurate if the offset determination is repeated at brief time intervals, until the temperature equilibrium between the wheel brake and the ambient temperature has settled. Therefore, to adjust the clearance, in advantageous manner the brake pads are applied for a short period and released again outside of the braking process, as well.
Particularly advantageous, particularly because of low costs, is the determination of an angle in the region of a brake actuator having an electric motor, e.g., the rotational angle of the electric motor or a rotational angle of the gear output of the brake actuator using Hall-effect sensors which emit several pulses per revolution.
REFERENCES:
patent: 5522269 (1996-06-01), Takeda et al.
patent: 5549371 (1996-08-01), Konaga et al.
patent: 6000507 (1999-12-01), Bohm et al.
patent: 6003640 (1999-12-01), Ralea
patent: 6008604 (1999-12-01), Maisch
patent: 6015194 (2000-01-01), Decker
patent: 6059379 (2000-05-01), Deml et al.
patent: 195 26 645 (1997-01-01), None
patent: 0795463 (1997-09-01), None
patent: 2305988 (1997-04-01), None
patent: 94/24453 (1994-10-01), None
Burch Melody M.
Kenyon & Kenyon
Oberleitner Robert J.
Robert & Bosch GmbH
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