Process for determining wheel speed signal correction factors

Details Process for determining wheel speed signal correction factors Process for determining wheel speed signal correction factors

1997-04-28

1999-07-27

Noori, Max H.

Measuring and testing

Tire, tread or roadway

Tire inflation testing installation

73488, 73 137, E01C 2300

Patent

active

059293292

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method of determining correction factors by which the differences of the tire-tread circumferences are ascertained in the evaluation of wheel speed signals, which are input signals for automotive vehicle control systems, wherein, in the absence of control operations, the wheel speeds are measured, a reference speed is determined and the wheel speed is compared to the reference speed for producing the correction factors.
International application WO 89/04783 discloses a process of the above-mentioned type, wherein the wheel speed is measured during wheel slip free periods, correction values are determined from the deviations of the wheels from this vehicle speed and, subsequently, the wheel speed of the individual vehicle wheels is corrected by using the correction values.
All wheels are compared in pairs in this known process. The wheel pair having the lowest speed difference is identified, and the average speed of this wheel pair is assessed as the vehicle speed. An average value of consecutive measurements is then produced. Thereafter, a relation is established between the speed of the individual wheels and the average value to determine the respective correction factor.
Difficulties are involved in thereby achieving the accuracy required for an anti-lock system (ABS) or a traction slip control system (TCS), for example, and in additionally preventing false and misleading correction values due to cornering, or the like.
German patent application No. 39 15 879 discloses a method, wherein a base speed is derived from the speed signals of the individual wheels and a wheel factor or correction factor is developed for each wheel according to a predetermined algorithm. The correction factor multiplied with the actual wheel speed results in the base speed. The wheel speed multiplied with the correction factor, determined this way, is made the basis of further signal processing instead of the actual wheel speed. The method is used to evaluate the wheel speed signals of a brake system with anti-lock or traction slip control.
Further, German patent application No. 40 36 742 discloses a circuitry for a traction slip control system with brake management or engine management which is used to improve the control function when a smaller spare wheel instead of a driven normal wheel is mounted. This circuitry is used to evaluate the rotational speed measured on the spare wheel by a correction factor measured when the wheel rotational behavior is stable. The rotational speed is then conformed to the measured speed value of the second driven wheel of the same axle so that the same slip control threshold applies for the (smaller) spare wheel as for a normal wheel. In this case, the correction factor is also determined during normal travel and when the traction slip control system is not activated.
An object of the present invention is to develop a method which involves a particularly high degree of accuracy of adjustment of the different tire-tread circumferences. The degree of accuracy should even render possible electronic control of brake force distribution on the basis of the wheel speed signals. Compared to an anti-lock system (ABS), the electronic control of brake force distribution necessitates an adjustment of much greater accuracy, i.e. an adjustment ten times more accurate, of the tire-tread circumferences.
It has been found that this object can be achieved by a preferred aspect of the method of the present invention including that developed for each wheel (n), correction factor is determined, signals representative of the deviation below a bottom speed threshold and above a top speed threshold, low-pass filter, and of the driving condition, for the correction or adaption of the long-time correction factor.
Anti-lock control, traction slip control and the electronic control of brake force distribution is achieved by the high-precision correction of the wheel speeds according to the present invention. The variations of the wheel speed signals due to mounting of an emergency wheel,

REFERENCES:
patent: 5415468 (1995-05-01), Latarnik et al.
patent: 5479811 (1996-01-01), Baumann et al.
German Search Report for Application P4426960.9.
English Translation of the International Preliminary Examination Report for PCT/EP95/02630 filed Jul. 6, 1995.

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