Reasons, models and experiments for unsteady friction of vehicle tires

Vehicle tires are exposed to high loads under strong driving maneuvers and under braking and acceleration conditions. Control interventions of ABS- and ESP-systems lead to short-time fluctuations of the local slip and varying local contact pressure. In contrast to a pure sliding process appearing under a braking condition with locked wheels, for the ABS-braking the tire tread block passes the contact zone periodically whereas a vehicle velocity of 100 km/h leads to a single contact duration of about 5 ms. Under a rolling condition of the tire, the contact between tread block and road surface is characterized by a high dynamic sequence of loading and unloading with alternating local stick and slip phases particularly at thetrailing area of the tire. The contact of an individual tread block of a rolling tire can be seen as a chronology of recurring single contact events. Within this report unsteady friction processes caused by wear procedures, local heating and also alternations of load and slip are regarded and models are built to describe such contact phenomena.