Dynamic analysis of dry clutch engagement for hybrid electric vehicles

Clutch engagement plays a critical role in the driving comfort of hybrid electric vehicles (HEVs). In particular, the non-linearities of springs and the uncertainties of friction wear in dry-clutch systems significantly influence clutch torque transmissibility. As an accurate clutch torque model is essential for precise control, this study develops a detailed model of a normally-open, pull-type dry clutch that incorporates nonlinear component characteristics along with the dynamics of the pressure plate and actuator. The clutch model is integrated into a powertrain model to investigate the influences of these nonlinear characteristics on the entire system. A control strategy is proposed to ensure rapid clutch engagement, and modal analysis is conducted to analyze the dynamic characteristics of the powertrain. Vehicle startup from a standstill is simulated to assess performance based upon dry-clutch torque transmissibility, friction work, vehicle jerk, and engagement duration. Results from both the theoretical modal analysis and transient dynamic simulations demonstrate that vehicle body vibrations during clutch engagement are primarily governed by the first-order mode. Additionally, as friction wear increases, clutch torque declines while friction work and slipping duration increase significantly, which considerably degrades engagement performance. This research establishes a foundation for designing precise clutch controllers in HEVs, specifically by accounting for the impacts of frictional wear.