Analysis and simulation of clutch engagement judder and stick-slip in automotive powertrain systems

Clutch engagement judder and stick-slip are investigated analytically and numerically to examine the influencing factors on these phenomena. Models are developed for a four degree-of-freedom (4DOF) torsional system with slipping clutch and for a powertrain with automatic transmission system. Stability analysis is performed to demonstrate that clutch judder is dependent on the slope of the friction coefficient and the analysis is verified with numerical simulations. An algorithm for modelling stick-slip is developed and is used in numerical simulations which show that the likelihood of stick-slip is increased by clutch pressure fluctuations, judder approaching engagement, and external torque fluctuations. Numerical simulations for second to third gear up shifts demonstrate that the likelihood of stick-slip to occur from clutch engagernent is increased by clutch applied pressure fluctuations, judder approaching engagement, and external torque fluctuations and that the likelihood of stick-slip occurring is decreased dramatically by applied pressure ramps proximus to the engagement point.