Estimation of tire-road friction coefficient for improving the engagement control of automotive dry clutch

An adaptive sliding mode controller (ASMC) based on estimation of tireroad friction coefficient is proposed for engagement control of automotive dry clutch. The control of clutch engagement is one of the most important parts of gear-shift process for automated manual transmission. Accurate amount of drive shaft torque in modelling of powertrain system is essential to guarantee smooth engagement of the clutch and rapid response of the control system. As the tire-road friction coefficient has significant influence on drive shaft torque, an estimator is designed to calculate this parameter. The ASMC is proposed for the clutch control to overcome the system uncertainties and a proportional integral (PI) controller is adopted to engine speed control. In addition, an estimator based on an unscented Kalman filter is used to observe the states hardly measured like wheel slip ratio and longitudinal vehicle velocity. The simulation results show the significant capability of the combined use of the designed control system and road friction coefficient estimator for improving the smooth clutch engagement in comparison to the control system without estimator.