Why do pure electric vehicles use single-speed gearboxes?

2021-03-23 15:12

People who are accustomed to fuel cars generally know that for a car, the more gears, the higher the price of the body. For example, most ordinary models are equipped with 6-speed or lower gearboxes, while luxury models generally have It is an 8-speed, 9-speed or even 10-speed gearbox. However, if this logic is obtained in the field of pure electric vehicles, it will not work. The actual situation is that from tens of thousands of pedestal cars to more than one million Teslas, almost all pure electric vehicles use single speed. Gearbox, a fixed name is "electric vehicle single-speed gearbox", also known as "single-speed fixed gear ratio gearbox".

is this gearbox. In fact, many people in the industry don't think this is a gearbox. To put it bluntly, it is a reducer. For example, Tesla is equipped with a reducer with a fixed gear ratio of 9.73 and does not provide gear shifting.

Why don’t pure electric vehicles use multi-speed gearboxes? This is determined by the characteristics of the electric motor itself. Unlike the engine, the electric motor can output full power from 0 speed without the problem of idling. Moreover, the speed range of the motor is wider and higher than that of the engine, and it can generally reach Above 7000-10000 revolutions, the function of the reducer is to reduce the speed of the motor and transfer the power to the wheels. At the same time, the maximum output power of the motor can maintain a wide range of speeds, which can basically cover various operating conditions encountered by the vehicle, so it only needs a fixed gear ratio reducer is enough, and does not need to be too complicated. Multi-speed gearbox.

The high-speed motors used in electric vehicles are adjusted by an electronic control system. The fixed gear ratio gearbox can change the vehicle speed through different gear ratios. The shortcomings of this structure make the electric vehicle consume large starting energy, the motor speed is large, and the gearbox has a single speed regulation function. In the high-speed driving state, it is impossible to pass the gearbox overspeed gear ratio less than one gear, reduce the motor speed, and single-stage transmission. The box also makes the speed of the vehicle not high.

In addition, the motor itself has an automatic transmission function. As long as the input power of the motor is kept constant, it can automatically find the best balance point between the output power and the output torque without you having to control the speed. This is determined by the inherent circuit characteristics of the motor, so there is no need to use a gearbox to control it.


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