Page - 27 - in Maximum Tire-Road Friction Coefficient Estimation

2 Estimation of the friction potential 0 0.2 0.4 0.6 0.8 1 1.2 0 100 0 0.2 0.4 0.6 0.8 1 1.2 Slip s x in % asphalt, dry asphalt, wet cobblestone, dry cobblestone, dry ice snow *scattered Figure 2.6.: Left: Range for the longitudinal friction potentialsµmaxx for different road condition categories used in ZEDATU, [Urd12, p.51]. The representation is basedona literature reviewbyBarace, [Urd12, p.50-51]; seeAppendixAfor additional information. Right: Qualitative representation of the coefficient of friction µx displayed versus the longitudinal slip sx for different road conditions based on Bachmann, [Bac98, p.60]. friction potentialµmax is the quotient of the maximum horizontal force and the tire load (see also Equation 2.2),µmax decreases with increasing tire loadFz due to its behaviour, as described in Section 2.1.3. Figure 2.7 shows the declining dependence of the friction potential on the tire load Fz. The influence of the longitudinal speed vx is shown in Figure 2.8. On dry asphalt, the influence on the friction potentialµmaxx may be excluded within a certain velocity range vx≤ 40 m/s2. However, for increasing longitudinal slip values sx, the coefficient of friction µx decreases significantly with vx. On wet roads, the friction potential shows dependence on vx. Other than on wet roads, µx decreases evenly for allvx for increasingvaluesofsx. Also, it has tobe considered that the friction potential decreases when both longitudinal and lateral tire forces are acting on the tire, see Section 2.1.2. Most of the tire-dependent parameters are influenced by the tire design and do not change during driving. The exceptions are ageing and abrasion effects on a long-term scale, and inflation pressure and tire tread temperature on a shorter time scale. The 27