Dynamics and control of gearshifts in wet-type dual clutch transmission for BEVs 2020-01-0767
In recent years, electric vehicles (EVs) have been an attractive and promising solution to the environmental pollution and fuel shortages faced by the traditional automotive industry. Although in current electric vehicle, the fixed speed ratio transmission system still dominates due to cost considerations. But the researchers found that the multi-speed transmission such as Automatic Manual Transmission (AMT), Dual Clutch Transmission (DCT), Continuously Variable Transmission (CVT), or Automatic Transmission (AT) etc. is integrated into an electric vehicle (EV), the working efficiency of the motor can be improved, the cruising range can be extended, and the dynamic performance can be enhanced. Among them, the dual clutch automatic transmission has the advantages of simple structure, high transmission efficiency and good shift smoothness.
The dynamic process analysis of the shifting needs to establish a dynamic model, and the shifting characteristics of the wet dual clutch transmission are obtained through dynamics simulation. The dynamics modeling combines the Patir-Cheng Average Reynolds equation of the fluid with the statistically based micro-convex contact model to express the clutch extrusion process, the transfer torque of the mixed friction process and the rough contact process with time and the change of the clutch control signal. In addition, the stiffness, damping and moment of inertia of the components in the motor, gearbox, drive shaft and differential are considered in the model to complete the construction of the transmission system.
Considering that the torque is difficult to collect in the actual application of the vehicle, the three algorithms of PID control, rule-based open-loop control and a modified open-loop control are compared, and three kinds of algorithms are obtained for the clutch action of the shifting process. By comparing these algorithms, the change of the transmission torque and the speed difference in the two phases of the inertia phase and the torque phase are analyzed. The parameters such as the shifting jerk are used to evaluate the shift quality. According to the simulation results, the DCT shifting strategy based on the wet clutch engagement characteristics can obtain better ride comfort, and has a faster shifting process.
Through the simulation of the dynamic characteristics of the wet clutch, it provides guiding significance for the wet DCT shift strategy, and integrates the longitudinal dynamics model of the vehicle, and builds a shift controller to simulate the shift strategy under different working conditions. The simulation results show that the shifting quality has obvious improvement comparing to the original strategy.