The transmission will keep your motor in the proper power band at different speeds.
变速器将使电机在不同的功率范围内保持在适当的功率范围。
英语百科
Power band
The power band of an engine or electric motor refers to the range of operating speeds under which the engine or motor is able to operate efficiently. While engines and motors have a large range of operating speeds, the power band is usually a much smaller range of engine speed, only half or less of the total engine speed range (electric motors are an exception – see Electric Motors below).