The transmission system of automobile is one of the core competitiveness of automobile. The transmission system of traditional fuel vehicle (Fig. 1 (a)) is generally composed of engine, clutch,, main reducer and differential. Although the technology of the transmission scheme is very mature, the system has many transmission links and complex structure. At present, there are three schemes: centralized motor drive (Fig. 1 (b)), wheel motor drive (Fig. 1 (c)) and hub motor drive (Fig. 1 (d)).
The three pure electric vehicle transmission schemes shown in Figure 1 have their own advantages and disadvantages. Although the wheel side motor drive scheme can reduce the unsprung mass of the vehicle, make the bearing capacity strong and improve the vehicle comfort, its cost is high and the technology is difficult, so the scheme is only used in a small number of commercial vehicles and some special occasions. The wheel motor drive scheme can accurately control the wheel torque, and because the motor is highly integrated in the wheel hub, it can greatly save the space of other parts of the vehicle. However, due to the layout and heat dissipation difficulties, high cost and many other reasons, the hub motor has not been put into the market on a large scale. The technology of centralized motor drive is mature, high reliability and low cost, and the current motor technology can meet the technical requirements of the scheme in terms of volume, quality, integration and power. On the other hand, the chassis layout of the power transmission scheme with centralized motor drive is the closest to that of traditional fuel vehicles. It can apply the chassis and other related technologies of traditional fuel vehicles to electric vehicles, which is conducive to reducing the cost and cycle of research and development. Therefore, most pure electric vehicles adopt this transmission scheme, especially in pure electric passenger vehicles. Figure 2 shows the chassis structure of Tesla electric vehicle, and the front and rear electric drives are all centralized motor drive schemes.
The specific form of the centralized drive transmission system of pure electric vehicle is that the motor, fixed gear reducer and differential are integrated into a whole structure, which saves space in the vehicle and is easy to be arranged. For example, Tesla Model s, Weilai es8 and other pure electric vehicles at home and abroad widely use this layout structure.
In addition, as the power source of electric vehicles, in order to achieve the purpose of motor miniaturization and lightweight, electric vehicle motors have been developing in the direction of high power density, which is more conducive to the improvement of other aspects of the performance of electric vehicles. At present, the most commonly used motor types of electric vehicles are AC asynchronous motor (Tesla, Weilai and other brands), permanent magnet synchronous motor (Changan, BYD and other brands).
The motor and reducer assembly manufacturers for electric vehicles at home and abroad mainly include GKN, bergwarner, Schaeffler, etc., which are widely used in the electric vehicle models promoted by domestic and foreign automobile enterprises, and the peak speed of the motor is generally above 10000 rpm.