Tire road friction estimation for improvements to traction control during drive off maneuvers in vehicles

During drive off maneuvers from stand still with high torque unpleasant longitudinal oscillations of the vehicle occur, commonly referred to as the power hop phenomenon. This effect especially arises in vehicles with manual transmission in a maneuver with abrupt release of the clutch, also known as snap start. Traction control on the engine control unit provides a cheap and easy way to reduce power hop and thus to improve the comfort for the passengers. In this paper two methods for estimation of tire road friction coefficient during snap start are presented with regard to road condition dependent parametrization of a Sliding Mode traction control. Since the road conditions can change in every maneuver, a fast but also accurate estimation algorithm is necessary. The first method is based on a vehicle model and uses an Extended Kalman Filter to estimate the current maximum friction coefficient. The second method uses only wheel speed measurements to deduce information about the road condition. These methods can be used to adapt the parameters of the control algorithm to different road surfaces and thus improve the performance. Experimental results on different road surfaces are presented.