Page - 26 - in Maximum Tire-Road Friction Coefficient Estimation

2 Estimation of the friction potential Intermediary layers Type Dry friction Water Ice Snow Mud Oil Dirt Depth of water film Temperature Density Vehicle Speed Tire forces & moments Vertical tire load Wheel inclination Camber Slip angle Toe-In Operating point of wheel Tire deflection Combined slip (long. + lat.) Superposition Long. and lateral tire forces According to Roth, the road condition has by far the largest influence on the friction potential, which thus canbeusedasameasureof the roadcondition, [Rot92, p.50], Sim- ilarly, Bachmann mentions the road textureandthepresenceofwater as theparameters with the highest influence on the friction potential, [Bac98, p.13]. Figure 2.6 shows the range of the friction potential for different road conditions shown in a literature research by Barace, [Urd12, p.50-51]. In critical driving states, it is not only the road condition that is of interest, but also the ability of a vehicle to accelerate, decelerate and/or corner. Important vehicle- dependent parameters that influence the friction potential are the vertical tire load and the vehicle’s longitudinal speed. For a given slip, the horizontal tire force increases in a degressive way with the vertical tire load. This means that doubling the vertical tire load results in a lower horizontal force than twice the horizontal tire force atFz,i. As the 26