Most hybrid electric vehicles employ a Retarder braking system or a regenerative braking system to provide enhanced braking performance and energy regeneration. The electro-mechanical braking system studied in this paper is composed of a mechanical brake, an eddy current brake and a regenerative braking system. This paper investigates the optimal parameter matching for the electro-mechanical braking system. In addition, a hybrid energy storage system comprising electrochemical batteries and ultracapacitors is proposed for this application. An optimal matching of three brake systems has been done as a reference indicator in the high regenerative efficiency , good braking performance, life and cost of the system. The simulation shows the matched program can achieve its desired performance.Keywords: electro-mechanical braking system; parameter matching; optimization; hybrid electric vehicle(HEV); regenerative braking; hybrid energy storage system Ⅰ INTRODUCTIONEnergy regeneration during braking is important for hybrid electric vehicle (HEV) ,because it allows the vehicle to improve its fuel economy and extend its driving range. During braking, the electric motor applies a negative torque to the wheels to convert a part of the vehicle's kinetic energy into electrical energy for recharging the battery to improve the utilization of energy. [1][2][3][4][5] The energy regeneration technique is widely used in electric vehicles. In order to ensure appropriate braking performance and energy regeneration, most HEVs equip a conventional hydraulic braking system, a mechanical braking system and a regenerative braking system. In this kind of HEV, the cooperation among the three braking systems is an important issue to study. Generally, the regenerative braking torque cannot be made large enough to provide all the required braking torque of the vehicle. In addition, the regenerative braking system may not be used under many conditions, such as with a high state of charge (SOC) or a high temperature of the battery. In these cases, the conventional hydraulic braking system works to cover the required total braking torque. Thus, cooperation among the hydraulic braking system, the mechanical braking system and the regenerative braking system is a main part of the design of the HEV braking system. [6][7][8][9][10] Based on the analysis and comparison of various types of regenerative braking systems, a research on optimal parameter matching for HEVs is presented in this paper. The paper is for the heavy-duty vehicle which has the Characteristics of high speed, high maneuverability and compound transmissions. According to the driver's braking needs and the requirements for vehicle high-pressure electrical systems safety, distribute the braking energy among the mechanical braking, regenerative braking and hydraulic braking, and achieve some brake energy recovery. According to the energy recovery, brake life , the basic allocation target and other factors, match the paramete of each braking system to meet the design requirements. The sys...