Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1993-09-07
1995-05-16
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
180197, 188181C, 303 96, 303103, B60T 832, B60K 2816
Patent
active
054154685
DESCRIPTION:
BRIEF SUMMARY
This application is the U.S. national-phase application of PCT International Application No. PCT/EP91/02108 filed Nov. 7, 1991.
BACKGROUND OF THE INVENTION
This invention relates to a circuit configuration and method for maintaining or improving the control function for a traction slip control system with brake and/or engine management for automotive vehicles when a smaller spare wheel has been mounted as a driven wheel instead of a normal size wheel. In the present invention, the rotating speed of the driven wheels is compared with the vehicle speed or with a corresponding measurement parameter for the purpose of detecting the traction slip. A correction factor is obtained from the rotating speeds measured with stable rotational behavior of the wheels. Traction slip control is triggered when wheel slip exceeds a predetermined limit value, namely the so-called slip threshold.
There are known circuit configurations for traction slip control systems. The information needed for control is obtained by means of wheel sensors, important information being developed from the comparison of the rotational behavior of the individual wheels and by distinguishing between the driven wheels and the non-driven wheels.
Replacing a normal wheel by an emergency wheel of the type in current use today, the dimensions of which often differ considerably from those of normal wheels, can lead to faulty information for traction slip control.
What, above all, is critical is the replacement of a driven wheel by an emergency wheel, the diameter of which is smaller than the diameter of the normal wheel. The traction slip control system identifies the higher rotating speed of the emergency wheel, caused by the smaller diameter, as "traction slip", with the control system responding and metering braking pressure into the wheel brake of the emergency wheel. This metering-in of braking pressure may completely prevent the car from starting in some situations such as in case of different right/left friction coefficients when the emergency wheel is located on the higher friction coefficient side. Up to now, in order to avoid this situation, it was necessary to turn off the traction slip control when an emergency wheel has been mounted.
SUMMARY OF THE INVENTION
It is thus an object of this invention to overcome these disadvantages linked with using emergency wheels in vehicles with a traction slip control system.
It has been found that this object can be achieved by a circuit configuration and method by which the correction factor is determined by axle-wise comparison of the rotating speeds of the two wheels of one axle and by comparing the speed differences measured on the driven axle and on the non-driven axle. The rotating speed measured at the spare wheel is evaluated by means of the correction factor and is thereby adapted to the measured value of the rotating speed of the second driven wheel of the same axle, so that the slip threshold, decisive for traction slip control, will become the same for the spare wheel as for a normal wheel.
Control will be improved in this way when, during the start or in a certain phase, traction slip control is not immediately activated. Thus the control system has sufficient time to determine the correction factor and effect a corresponding adaptation. If, however, traction slip control is activated at once when, for example, starting on a very slippery road surface, a variant of the inventive circuit configuration and method will become operative. In this arrangement of the invention, at first, the same slip threshold is decisive for the control of the two driven wheels upon the onset traction slip control whereupon the slip threshold is raised until pressure reduction comes about if, during a traction slip control operation, pressure reduction signals fail to appear after a predetermined period of time. If, during a period of time of the magnitude ranging from 200 to 500 msec, only braking pressure reduction takes place, this will be an indication of the completion of the traction slip control opera
REFERENCES:
patent: 4545623 (1985-10-01), Sato et al.
patent: 4844557 (1989-07-01), Giers
patent: 5015042 (1991-05-01), Yoshino
patent: 5200897 (1993-04-01), Makino et al.
Honus Klaus
Kolbe Alexander
Latarnik Michael
Alfred Teves GmbH
Butler Douglas C.
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