Although the motor has a wide operating speed range, like the engine, the motor also has an optimal operating speed range. If it is higher or lower than this range, the efficiency will decrease. The efficiency of a 40kW motor is only 60%~70% when it is just started. As the speed increases, the efficiency gradually increases. When the speed is 3300~6000r/min, the efficiency can reach more than 94%. When approaching the limit speed of 100000r/min, the efficiency drops to about 70%. It can be seen that the rational use of the transmission to make the motor work in the optimal speed range is of great significance for improving efficiency. If a pure electric car uses a continuously variable transmission, the energy consumption per unit mileage will be reduced by 5% to 7% and the noise will be much reduced compared with the one-speed transmission.
Judging from the current development of electric cars, the biggest obstacle to the entry of pure electric cars into the market is the limitation of battery performance. Although battery technology has undergone a series of technological advancements from lead-acid batteries to hydrogen batteries and then to battery packs, the current pools cannot meet the requirements of large-scale commercialization in terms of energy density, unit capacity, and price. Every company that develops electric cars is doing its best to reduce battery costs and increase the range of cars on a single charge.
If the efficiency can be improved by using a suitable transmission and optimizing the calibration, this means that the battery consumption is less when driving the same mileage, the car’s own weight is lighter, the driving performance is higher, and the car cost is lower.
The transmission of pure electric cars only requires three gears, two gears and one gear, so the transmission is simplified to a certain extent, but pure electric cars have higher requirements for traditional systems. The optimized design of the transmission is beneficial to improve the efficiency of electric cars.
Most 1-speed transmissions have two-stage reduction ratios, that is, the transmission has only one transmission ratio, and the main reducer has one transmission ratio, and the total transmission ratio is the multiplication of the two transmission ratios. The motor-integrated transmission is shown in Figure 1, and is mostly used in low-end, small, and medium-sized vans.
The differential is a standard component of traditional cars, and single-axle, single-motor cars also use this technology. When a car turns, the turning radius of the outer wheels is larger than that of the inner wheels. Differentials must be used to adjust the speed of the wheels on both sides, otherwise the wheels will slip, which will cause increased tire wear, difficult steering, and poor road adhesion.
Due to the large low-speed torque and wide working speed range of the motor, the reverse gear is not designed, only the motor reverses.
2. 1-speed integrated power drive system
High-end electric cars mostly use the integrated electric drive system shown in Figure 2. The motor, reducer, differential, and power controller are integrated together, and there are only strong current, weak wire bundles and cooling water pipes outside. If each of the front and rear axles adopts such a power drive system, it is a good four-wheel drive.
3. multi-speed transmission
The pure electric passenger car transmission has undergone tremendous changes compared with the traditional fuel passenger car transmission. Traditional transmissions are gradually being replaced or weakened. For example, pure electric passenger cars exhibited by some domestic companies directly use motors to control speed. They use electronic torque control technology to directly control the wheel speed to achieve control of the car speed.
The main purpose of installing a transmission on a pure electric passenger car is to solve the problem of insufficient motor driving force. Setting the transmission can change the torque transmitted to the driving wheels and increase the power of the whole car. Compared with the transmission equipped on pure electric buses, the transmission on fuel cars has changed. The outstanding feature is that the transmission gears are simplified from the traditional 5 gears and 6 gears to 2 gears and 3 gears. The FAW bus CA6120VRBEV21 model is developed by FAW. The 2-speed automatic transmission. The KLQ6129GHV model of Suzhou King Long Haige is equipped with a 3-speed mechanical automatic transmission.
4. Multi-speed non-synchronized deep electronically controlled automatic transmission source
For pure electric passenger cars, in order to save cost and consider automatic shift without clutch, the electronically controlled automatic shift transmission without synchronizer becomes the first choice. The automatic shifting power assembly without synchronizer is shown in Figure 3.
The electronically controlled automatic transmission ECU receives the transmission output shaft speed sensor signal, and also receives the motor speed signal. Before shifting, adjust the motor speed to be the same as that of the driven gear. When the motor speed is reduced/increased to be synchronized with the driven gear to be shifted, three types of electro-pneumatic, hydraulic or electric can be used. One of the devices pushes the shift fork, and the shift fork pushes the engagement sleeve directly into the corresponding gear.