① Brush disc winding motor. The brushed disc winding motor is bonded to a cylinder body with rare earth materials, and the disc winding made of enameled copper wire is placed inside the cylinder body to form the rotor. The motor phase is adjusted by a mechanical inverter. Mechanical inverters adjust voltage phase by friction between fixed carbon brushes and rotating copper commutation surfaces. The electric brushes of this motor are constantly worn out during use, and the lifespan of the motor is difficult to exceed 2000 hours. At the same time, due to the high speed of the motor, two-stage gear reduction must be adopted, which brings two problems: first, high noise, and second, large efficiency loss. The rated efficiency of the motor after reduction often only reaches 68% to 72%. The capacity of the battery used in electric bicycles is limited, usually 36V/12Ah. If the motor efficiency is not high, it will increase power consumption and affect the driving range.
② Brush printed winding motor. The brushed printed winding motor uses copper foil board as the winding, which reduces the weight of the motor. Due to the fact that all of these motors are produced on automatic production lines with reliable processes, the lifespan of the motor has been extended to 3000 hours, noise has been significantly reduced, and efficiency has been increased to 72% to 76%. But this type of motor has a "buzzing" high-frequency noise, and the efficiency is still not ideal even after gear reduction. The use of brushed inverters makes it impossible to further improve the service life of the motor.
③ Brush pressed winding motor. This type of motor can increase its efficiency to 74% to 78% by compressing the wound copper wire into a new type of winding. This type of motor is still widely used by electric bicycle manufacturers, but its efficiency, noise, and lifespan defects are still issues that must be improved.
The wheel type brushed DC motor with gear transmission consists of a disc-shaped armature brushed motor and a gear reduction and transmission system. A disc-shaped armature is a high-speed rotating rotor. The structure of a brushed DC motor with wheel type gear transmission is shown in Figure 2-2. The torque of the motor is transmitted to the first stage gear through the shaft, and is then reduced by the gear to drive the hub shell to rotate.
The disc-shaped armature of the brushed and toothed wheel hub motor is thin, small in size, lightweight, and easy to install. After the winding is prepared, it is hot pressed into a mold with resin and glass fiber. During operation, due to the friction between the electric brush and commutator, as well as the gear meshing reduction, the operating sound of the brushed motor is louder than that of the brushless motor.
In order to adapt to the wheel hub structure, the brushed motor is designed with the armature placed on the outside as the rotor, the magnetic steel placed inside the motor as the stator, multiple pieces of magnetic steel with multiple windings, and a low-speed motor with a design speed of around 180r/min. Figure 2-3 (a) shows the armature winding in the outer rotor of the motor that has not undergone pressure shaping. Inside the winding, there are commutator segments arranged in a flat circular pattern. Figure 2-3 (b) shows a stator with 10 magnetic steel bars arranged at intervals inside the outer rotor. There are two holes on the hub plate in the middle, and the brush holder of the electric brush is located on the back side of the holes. The electric brush carries the wire and is ejected from the brush holder by a spring.
The stator shaft end of the brushed motor has a nut that prevents damage to the threads on the shaft during processing. Arrange the electric brush and insert it into the brush holder. Then, insert this end into the hole shown in Figure 2-3 (a), and the electric brush can contact the plane of the commutator. With the help of the spring's elasticity, the commutator is pressed tightly, and the magnetic steel just enters the outer rotor winding, leaving only a small annular air gap. The larger the diameter of this annular air gap, the greater the torque generated by the motor.
Due to the improvement in the design of brushed motors, there is no need for gear reduction, which can achieve low noise and low cost. Many low-priced electric bicycles widely use this type of motor. However, this type of motor has low torque, low load capacity, poor climbing ability, and consumes a lot of electricity during use. Mechanical brush inverters are still used, and the problem of motor life has not been solved. Therefore, this type of motor is not used in mid to high end electric bicycles.