A phenomenological model for torque transmissibility during dry clutch engagement

In this paper, a phenomenological model of clutch torque transmissibility is proposed. This model applies to clutch engagement during vehicle start-up in both manual and automated-manual configurations. The proposed model can be identified through on board measurements available in most production vehicles. The model is based on the identification of a nonlinear characteristic that relates the transmissibility of engine torque to the mainshaft to the clutch actuator position and the clutch slip speed. To smooth the effect of neglected dependencies on torque transmissibility and obtain a non-linear characteristic with very low dispersion, the engine torque setpoint is also included in the model. An empirical estimation of load torque during start-up, dependent on slip speed and engine torque set-point, completes the model and improves its accuracy. The model has been identified and validated on two prototype vehicles with very different features: a small city car with an electrically-actuated automated manual transmission and a big executive car with a hydraulic-actuated manual transmission. An application example is given at the end of the paper to show the usefulness of the model: an alternative analysis, based on power computation, of the conditions that have to be respected to avoid oscillations at clutch engagement.