Design, Modeling And Shift Quality Optimize For The Wedge Clutch

Nowadays, there have been clear tendencies of fuel economy and environmental protection in the automotive industry. During the past several decades, hydraulic system with pistons is the most common configuration as the actuator, due to its high power density and flexible arrangement. Due to the significant proportion of the energy loss in hydraulic system, electrification technology is more and more popular in actuation system of modem vehicles. However, the main challenges for the electrification are large current demand for the electrical motor when using 12 V or 42 V on-board batteries. Especially for high force/torque applications like the clutch actuator, the large current demand leads to potential higher power loss and electro-circuit disturbance. Therefore, force enlargement mechanisms are necessary to reduce the current demands for the clutch actuation system.The wedge mechanism has the unique feature of “self-reinforcement”, which can apply a huge actuation force with a small driving force. The objective of this paper is to develop an electromechanical clutch actuation system by using the wedge mechanism, so as to reduce the force/torque requirement of the electric motor. However, the wedge mechanism also brings several issues need to be solved. Firstly, the self-reinforcement feature of the wedge mechanism is related with the specific situation and parameters. Therefore, besides the installation space of the target transmission, the different working conditions also need to be considered during the design of the wedge clutch actuator. Secondly, the self-reinforcement feature of wedge mechanism brings system stability problem, and by combining with its nonlinear factors, the dynamics of the wedge clutch actuation system is really complicated. The detailed and complete mathematical model needs to build and then study and analyze. Thirdly, the slip to stick state change of the clutch during the gear shift causes the abrupt change of the self-reinforcement ratio, which in turn brings the torque shock problem due to the variation of actuation force. So, suitable optimal control strategy needs to be proposed to improve the gear shift. Finally, considering the self-reinforcement feature also enlarges the errors, the system is more sensitive to the variation of the clutch parameters and working conditions. Thus, the high robustness of the wedge clutch controller is necessary. According to above issues, the following work has been finished in this paper.Therefore, through solving the above key issues during the development of wedge clutch actuation system, the following conclusions are obtained. 1) The designed wedge clutch actuator has compact structure, which can be integrated into AT and realize the basic functions; 2) The design rule of the key parameter is obtained through mathematical analysis, and the self-reinforcement feature is validated through simulation and experiments which contributes to reduce the required motor torque; 3) Although the wedge mechanism brings problem of torque shock, the integration control methods of motor torque and engine torque is proposed and the improvement of the torque shock, friction loss and temperature rising is realized by experiments; 4) finally, based on the conventional PID feedback controller, an self-tuning scheme is added to track the optimal referenced clutch slip speed. The robustness of the controller under time-vary clutch parameters and different working conditions is greatly improved, which solves the problem of system sensitivity to the input error.