Wet clutches are widely used in vehicle transmission systems to start and shift. The temperature field of the wet clutch components is influenced by friction and is closely related to the vehicle performance and service life. This work improves the numerical modelling of the temperature field by taking into account the groove cooling, the local heat dissipation and the time-varying friction coefficient on the contact surface. An equivalent convection heat transfer coefficient and an equivalent gain coefficient are introduced. The proposed model is more accurate than the traditional model, and its accuracy is verified by bench experiments. The influence of the rotational speed difference, the oil pressure and the lubrication flow on the temperature field is analyzed. Moreover, the temperature rise characteristics during deformation are measured, which also confirms the abnormal radial and circumferential change of temperature field. These results can guide the accurate simulation of interface temperature and the appropriate control operation of the friction components in the wet clutch.

The hydro-viscous drive (HVD) performance is crucial for the long-term stable operation of the heavy equipment cooling system. To accurately evaluate the HVD performance degradation, a fuzzy comprehensive evaluation method is proposed. This method first conducts an accelerated life test to obtain the HVD performance degradation data and establish a factor and evaluation set for the HVD performance degradation evaluation. The index subjective and objective weights are combined using an improved game theory combination weighting method, and the reliability of the combination weight is verified. The trapezoidal membership degree function is introduced to visualize the performance degradation process of HVD. The results indicate that the average relative errors of the fuzzy comprehensive and linear fitting evaluation models are 19.5% and 40.7%, and the fuzzy comprehensive model using Gaussian membership function and triangular membership function are 25.9% and 31.4% in HVD performance degradation evaluation. These results verify the accuracy and superiority of the fuzzy comprehensive evaluation model.

Proposing an appropriate control strategy is an effective and practical way to address the overheat problems of the wet multi-plate clutches in Direct Shift Gearbox under the long-time creeping condition. To do so, the temperature variation of the wet multi-plate clutch is investigated first by establishing a thermal resistance model for the gearbox cooling system. To calculate the generated heat flux and predict the clutch temperature precisely, the friction torque model is optimized by introducing an improved friction coefficient, which is related to the pressure, the relative speed and the temperature, before being demonstrated experimentally using a full scale powertrain test. After that, the verified heat transfer model and the reasonable friction torque model are employed by the vehicle powertrain model to construct a comprehensive co-simulation model for the Direct Shift Gearbox vehicle, capable of simulating the dynamic responses and predicting the temperature variations of two clutches. A creeping control strategy is then proposed and, to evaluate the vehicle performance, the safety temperature (250°C) is particularly adopted as an important metric. From the variations in torque and speed obtained from the simulation results, the vehicle can track the desired speed (1.5 km/h) satisfactorily, with only 3% fluctuation, and have good longitudinal dynamic performance (8.5 m/s³). But above all, during the entire 174 s creeping process, the temperature of two clutches is always under the safety value (250°C), which demonstrates the effectiveness of the proposed control strategy in avoiding the thermal failures of clutches.