Wheel motor classification
The hub motor power system usually consists of an electric motor, a speed reduction mechanism, a brake and a heat dissipation system. The power system is divided into two types according to the rotor type of the motor: an inner rotor type and an outer rotor type.
Inner rotor type: In general, the inner rotor type uses a high-speed inner rotor motor and is equipped with a fixed gear ratio reducer. In order to achieve a higher power density, the speed of the motor is typically as high as 10,000 r/min. The deceleration structure usually adopts a planetary gear reduction device with a transmission ratio of about 10:1, and the rotation speed of the wheel is about 1000r/min.
The high-speed inner rotor hub motor has the following advantages: high specific power, light weight, small volume, high efficiency, low noise and low cost; its disadvantage is that a reduction gear must be used to reduce the efficiency and increase the unsprung mass. The maximum speed of the motor is limited by factors such as coil loss, friction loss, and the ability of the shifting mechanism to withstand.
Since the inner wheel hub motor has an integrated reducer, the front wheel of the passenger car must be placed in a narrow and limited space to lower the motor, reducer, brake, steering system, etc., so the inner rotor hub motor is less used. On the passenger car. The scheme of the inner rotor accelerating device is theoretically high in power density and compact in structure, but due to the complicated manufacturing process, the current products have not yet been mass-produced.
Outer rotor type: Usually, the outer rotor type uses a low-speed external sub-motor. The maximum speed of the motor is about 1000-1500r/min. There is no deceleration device. The outer rotor of the motor is fixed or integrated with the wheel rim. The motor is the same.
The low-speed outer rotor motor has the advantages of simple structure, small axial dimension, high specific power, control of torque over a wide speed range, fast response, and the outer rotor is directly connected to the wheel without a speed reduction mechanism, so the efficiency is high. The disadvantage is that if a large torque is to be obtained, the engine volume and quality must be increased, so that the cost is high, the efficiency is low during acceleration, and the noise is large.
The outer rotor hub motor saves half shaft and reducer, etc., but its volume is huge. Without the speed reducer, if you want to get the torque that meets the demand, you must reduce the speed. It is well known that when the torque is constant, the power and the rotational speed are proportional, the rotational speed is not high, and the power density cannot be increased, resulting in a large volume and a high weight. Even if the outer rotor hub motor is bulky and heavy, its structure is relatively simple compared to the inner rotor hub motor, the transmission chain is small, and the efficiency is high. At present, some enterprises have entered mass production.