ABSTRACT A wedge clutch with a wedge ramp transfers the tangential force to an axial force. It has unique features of self- reinforcement and small actuation force, and can be packaged into tight spaces. This wedge clutch can be developed to apply to an automatic transmission (AT) or a hybrid transmission. This paper focuses on the simulation of one wedge clutch in AT during shifting. A mathematical formula is given to describe the self-reinforcement principle of the wedge. The dynamic model of a motor actuated wedge clutch during shifting is built to simulate and develop the control algorithm. The model is implemented in Matlab/Simulink, which includes a DC motor model, a dynamic model of the wedge mechanism and clutch pack, and a driveline model of AT which can simulate a gear shift process. The key characteristics such as variation of normal pressure, response time and energy consumption are evaluated, and the results show a favorable comparison with the traditional hydraulic clutch. INTRODUCTION With the rapid development of electronic technology, electromechanical systems (drive-by-wire) with high efficiency are in high demand. Compared with conventional hydraulic and pneumatic systems, electromechanical systems have many merits, such as, rapid response, energy-efficiency, and compatibility with intelligent control. Generally, driving force of the actuator is supplied by a motor in an electromechanical system. However, a motor with largepower and high energy consumption is needed for directly driving the shift clutch in an automatic transmission (AT). Furthermore the on-board 12V power supply in a conventional passenger car cannot meet the power demand. So the challenge is to transmit and increase torque efficiently while keeping compact mechanical structure in the actuator design of electromechanical system. In many ways similar to the mechanism design of torque reinforcement in an AT, modern wheel braking systems can be referred. Bosch has developed a set of actuator, which adopts electromagnetic clutch to control a two-planetary gear of achieving torque reinforcement [ 1]; Siemens launched a set of actuator using a pressure pan and a reinforcement lever [2]; and Continental AG developed a set of actuator with a double reduction gearbox for reinforcement function [ 3]. All three mechanisms work but have some drawbacks, such as, complicated structure, lots of mechanical parts and inconvenience of installation. However, a simple and reliable mechanism is more applicable in an AT. The above three mechanisms are too complicated to be used in actuating the clutch plates. Wedge mechanism has a simple structure, and is not a novel idea. It has been quoted in several mechanisms. The limited slip differential, with a wedge mechanism to limit slip but not prevent it completely, is widely used in 4×4 such as hummer H2. VDO has developed a braking system with the wedge mechanism [ 4]. However, it has not been applied to the clutch in AT. With accurate arrangement and intelligent control, the wedge mechanism can fully transfer kinetic energy of the vehicle propulsion system into friction energy in clutch engagement, which is called “self-reinforcement”. Furthermore, compared with conventional hydraulic clutch, Modeling of a Wedge Clutch in an Automatic Transmission2010-01-0186 Published 04/12/2010 Jian Yao, Li Chen, Cheng-Liang Yin, Jie Shu and Xin Zheng Shanghai Jiao Tong University Chunhao J. Lee , Yu Dong, Chi-Kuan Kao, Kumar Hebbale and Farzad Samie General Motors LLC Copyright © 2010 SAE InternationalDownloaded from SAE International by University of British Columbia, Wednesday, August 01, 2018wedge mechanism actuated by DC motor has characteristics, such as, rapid response, energy-efficiency and accurate control. Considering the characteristics of the wedge mechanism mentioned above and combining with the worm gear mechanism, a new-type of wedge clutch using the wedge mechanism has been proposed in this paper. It can b