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|Title:||Process and system for determination of friction/slip characteristics of road vehicle tires|
|Abstract:||For the determination of the friction/slip characteristics of the tires of a road vehicle which is equipped with an antilock system designed for an individual wheel control, in an initial phase of a controlled braking, only the wheel brake of an individual vehicle wheel is acted upon by brake pressure and the latter is dimensioned so that the result is the initial retardation in accordance with the driver's wish. During this initial test phase of the braking, the absolute brake slip .lambda..sub.B as well as the friction utilization .mu..sub.B linked therewith is continuously determined as soon as, as a result of just the braking of the test wheel, the vehicle retardation z increases no further and/or the braked vehicle wheel is more strongly retarded than corresponds to a predetermined threshold value, the test braking is interrupted and the braking is continued by pressure action on the further vehicle wheels; corresponding test braking phases are carried out in cyclic sequence for all guidance wheels.|
|Inventor(s):||Burckhardt; Manfred (Waiblingen, DE), Eilert; Gerd (Schwaikheim, DE), Freitag; Rainer (Nuertingen, DE), Mueller; Armin (Backnang, DE), Schoeb; Reinhold (Filderstadt, DE), Spiecker; Rainer (Kernen, DE), Kazan; Sinan (Esslingen, DE), Zimmer; Richard (Fellbach, DE)|
|Assignee:||Mercedes-Benz AG (DE)|
1. A process for determining friction/slip characteristics of tires of a road vehicle having an individual wheel control antilock system such that in a traction mode of the vehicle,
comprising the steps of (a) concluding, in an initial braking test phase, a course of the respective tire characteristic in an entire friction coefficient to slip, or .mu./.lambda., field from pairs of measured values of the slip, .lambda., and of the
friction coefficient, .mu., at a given slip, (b) during the initial test braking phase, continuously determining the absolute brake slip, .lambda..sub.B, according to the relationship ##EQU7## and the friction, .mu..sub.B, coefficient in braking of a
rear wheel linked with the respective value of the absolute brake slip .lambda..sub.B is determined according to the relationship ##EQU8## and, in braking of a front wheel, according to the relationship ##EQU9## wherein v.sub.F designates vehicle speed,
v.sub.R designates braked vehicle wheel speed, .psi. designates the rear axle load component, .chi. designates the wheel base-related height of the center of gravity of the vehicle, and z designates the measured braking vehicle retardation, (c) using a
value obtained from wheel circumference speeds of the unbraked vehicle wheels, to an approximation, as the vehicle speed v.sub.F, (d) in an initial phase of a controlled braking linked with moderate vehicle retardation, using brake pressure on only a
wheel brake of an individual vehicle wheel and dimensioning the brake pressure in an initial rising phase so that increasing initial retardation in accordance with the driver's wish is at least approximately obtained; (e) as soon as, as a result of just
the braking of the test wheel, at least one of the vehicle retardation, z, no longer increases and the braked vehicle wheel is retarded more strongly than corresponds to a predetermined threshold value, interrupting the test braking and continuing the
braking by pressure action on other vehicle wheels; and (f) carrying out test braking phases according to steps (d) and (e) in cyclic sequence for all remaining vehicle wheels.
2. The process according to claim 1 wherein the test braking phase is carried out on a rear wheel when a vehicle driver seeks braking with moderate vehicle retardation between 0.1 g and 0.2 g, and on a front wheel when the vehicle driver seeks a somewhat higher vehicle retardation between 0.2 g and 0.4 g.
3. The process according to claim 1, wherein two diagonally opposite vehicle wheels are braked during the test braking phase, if the driver seeks a braking retardation of more than 0.4 g.
4. The process according to claim 3, wherein the test braking phase is carried out on a rear wheel when a vehicle driver seeks braking with moderate vehicle retardation between 0.1 g and 0.2 g and on a front wheel when the vehicle driver seeks a somewhat higher vehicle retardation between 0.2 g and 0.4 g.
5. The process according to claim 3, wherein the test braking phase is carried out first on the rear wheel and thereafter on the front wheel.
6. The process according to claim 1, wherein the test braking phase step occurs on a driven vehicle wheel, the driven vehicle wheel is decoupled from the drive train of the vehicle.
7. The process according to claim 1, wherein a controlled braking of the vehicle is recognized as an operational situation in which the driver actuates the brake pedal of the braking system with a force, K.sub.p, which is smaller than a selectively predetermined threshold value.
8. The process according to claim 1, wherein a controlled braking of the vehicle is recognized as an operational situation in which the vehicle retardation is smaller than a selectively predetermined threshold value z.sub.min.
9. The process according to claim 1, wherein a controlled braking of the vehicle is recognized as an operational situation in which the brake pressure which the driver feeds into a braking system of the vehicle by actuation of a braking device is smaller than a selectively predetermined threshold value, P.sub.min.
10. The process according to claim 1, wherein for the friction coefficient/slip interrelationship which is determined with reference to at least slip and retardation and which is applicable to a respective vehicle wheel, an algorithm is obtained by interpolation or matching of an approximation relation which can be evaluated by an electronic control unit to characteristic base points of stored .mu..sub.B /.lambda..sub.B value pairs obtained by measurement and stored for a continuous processing of measured .lambda..sub.B data in units of friction coefficient currently utilized.
11. The process according to claim 10, wherein determination of the currently utilized friction coefficient, .mu..sub.B, occurs by evaluating the relation
in which C.sub.1, C.sub.2 and C.sub.3 are constants obtained by matching the relation to measured .lambda..sub.B and .mu..sub.B values and are stored as parameters of the relation used for the continuous evaluation and continuously updated.
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