Fluid-pressure and analogous brake systems – Speed-controlled – And traction control
Patent
1994-04-29
1996-02-27
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
And traction control
303147, B60T 824
Patent
active
054943442
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a cornering identification method provided, in particular, for automotive vehicles with anti-lock and/or traction slip control. This method involves (a) continuously detecting a correction value which depends on the difference in the rolling circumferences of the tires, (b) with this correction value being taken into account, detecting the velocity difference of the two wheels, and (c) evaluating the velocity difference for cornering identification.
Cornering identification is useful, for example, for improvement of an anti-lock or traction slip control system. In such control systems, the information required for control is generally derived solely from the rotational behavior of the individual wheels. However, situations arise where the wheel signals are not absolutely clear. There are very similar wheel variations in case of controlled braking operations on .mu.-split roads (meaning different friction coefficients on the right and left sides) and in case of braking during cornering when the centrifugal force on the wheel load differences on the inside and on the outside of the bend increase. However, while on .mu.-split roads, the pressure build-up gradient on the side of the higher friction coefficient should be flattened to prevent high yawing moments. Such a measure, taken during a braking operation in a bend, can cause the vehicle to oversteer and lead to a lengthening of the stopping distance. Consequently, yawing moment management should be switched off or changed during braking operations when cornering.
German Patent Application (DE) No. 37 18 421 A1 discloses a circuit configuration where the velocity difference of the two wheels of one axle is evaluated for cornering identification. Moreover, this circuit configuration has circuits for generating a system-induced error correction signal which is independent of the momentary cornering situation and which essentially is obtained by filtering the scaled velocity difference signal with different time constants; when identifying a cornering situation, the time constant of approximately 30-120 seconds, which is valid for straight-line driving, will be raised to a time constant of approximately 150-300 seconds.
A cornering identification device for a traction control circuitry is described in German Patent Application (DE) No. 31 27 302 C2. Cornering identification is based solely on measuring the speed difference between the two non-driven wheels. In this known circuitry, speed differences due to different rolling circumferences or the like can automatically lead to a faulty shift in the response thresholds.
SUMMARY OF THE INVENTION
It is, thus, an object of the present invention to develop a method by means of which, in evaluating the signals representative of the rotational behavior of the wheels, it will be possible to differentiate between a cornering situation and a situation of straight-line driving reliably and independently of any differences in the rolling circumferences of the tires.
The particular feature of the present inventive method is that: (a) a reference value is developed which is representative of a straight-line course, (b) this reference value is continuously corrected in dependence on the corrected and rated velocity difference between the two wheels of one axle in accordance with a predetermined time pattern or time grid, and (c) for cornering identification, this velocity difference or difference value is compared with the momentary value of the reference value.
Due to the continuous correction, there will be a permanent increase in the correctness or, rather, in the measure of coincidence of this reference value with a value actually characteristic of a straight-line course. This is also true in case of considerable differences in the rolling circumferences of the tires caused, for example, by unilateral wear, by the mounting of an emergency wheel or the like. As travelling time becomes longer, identification of the rolling differences of the tires will become
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Buschmann Gunther
Gronau Ralph
Heyn Harald
Striegel Thomas
ITT Automotive Europe GmbH
Muratori Alfred
Oberleitner Robert J.
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