Fluid-pressure and analogous brake systems – Speed-controlled – Specific mu determination
Patent
1994-05-10
1997-02-04
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Specific mu determination
303148, 303155, B60T 800
Patent
active
055990762
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a process for determination of the friction/slip characteristics of a road vehicle tires, in which the vehicle which is equipped with an antilock system configured on the basis of an individual wheel control, according to which, in the traction mode of the vehicle, the course of the respective tire characteristic in the entire .mu./.lambda. field is concluded from pairs of measured values of the slip and of the coefficient of friction utilized at a given slip.
German Patent Application P 41 02 301.3 describes a process which in the traction mode of the vehicle, the tire characteristics of the driven vehicle wheels are determined and, on account of the equivalence of drive slip and brake slip, the thus determined tire characteristics are also used for the determination of brake slip thresholds which when exceeded cause the antilock system of the vehicle to respond. The maximum utilizable coefficients of friction (the .mu.-maximum of the respective tire characteristic are concluded from the spin behavior of the driven vehicle wheels, the speed of rotation of which drastically increases when a slip value corresponding to the maximum of the characteristic is exceeded. A precise determination of the tire characteristics in the braking mode is not possible in accordance with this known process.
Further, WO 85/02592 (PCT/EP84/00402) discloses a process for the determination of an optimal slip value .lambda. at at least one wheel of a vehicle for controlling the brake force with the use of the wheel speed V.sub.R and of the vehicle speed V.sub.F of at least approximate signals. During the journey, the slip .lambda. is varied by altering the basic pressure P.sub.B and at individual instants of measurement (k, k+1, . . .) signal value combinations of the wheel speed V.sub.R * (K), of the vehicle speed V.sub.F * (K), of the brake pressure P.sub.B * (K) and of the normal reaction force F.sub.A * (K) effective at the wheel are determined; following the availability of a plurality of such signal value combinations, determined respectively one following the other by a measurement time interval .DELTA.t, for various values of the slip .lambda., a function V.sub.R (K+1)=f is determined. This function represents the solution of a system of equations with unknown coefficients .alpha..sub.n, the coefficients of which can be determined with the aid of this system of equations. From these coefficients .alpha..sub.n there are then determined coefficients .alpha..sub.n, which are coefficients of a general description of the .mu. slip curve .mu.=f(V.sub.R,V.sub.F), from the course of which the position of the optimal slip value .DELTA..sub.opt is then determined.
This known process requires, during a braking, measurement of parameters which are fundamentally affected by a high error. For example, the wheel normal reaction force F.sub.A, which can be "measured" only indirectly or, in the case of a more direct measurement (e.g. with the aid of strain gauges) by which the spring strain of wheel springs can be picked up, is exposed to considerable disturbance variables as a result of the resilient spring movements. Also the value of the vehicle speed V.sub.F is determinable only very imprecisely, during a braking in which all vehicle wheels are affected by a brake slip, this being at all events the case where the vehicle speed is obtained from an averageing of individual wheel speeds which are picked up by wheel speed-of-rotation sensors individually allocated to the vehicle wheels. Consequently, the known process, which requires the performance of a multiplicity of computation steps, converges only very slowly. That is, a reasonably reliable course--one which is close to reality --of the thus determinable .mu. slip curves can be achieved only after a multiplicity of brakings, but this multiplicity is not carried out in the course of a normal journey.
Accordingly, an object of the present invention is to provide an improved process which permits, in the braking
REFERENCES:
patent: 3967862 (1976-07-01), Hunter et al.
patent: 4111496 (1978-09-01), Leiber
patent: 4645272 (1987-02-01), Leiber
patent: 4755008 (1988-07-01), Imoto et al.
patent: 5096267 (1992-03-01), Volz
Burckhardt Manfred
Eilert Gerd
Freitag Rainer
Kazan Sinan
Mueller Armin
Graham Matthew C.
Mercedes-Benz AG
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