Types and structures of motors for electric bicycles
There are two categories and five varieties of motors for electric bicycles.
The two categories are: brush motors and brushless motors; five types are brush motors with gear transmission and gearless transmission, brushless motors with sensors, sensorless and disc-shaped armature gear reduction brushless motors.
1.Hub-type geared DC motor with brush. Half of the motor is a disc-shaped armature brush motor, and the other half is a gear reduction and transmission system. The disk armature is a rotor that rotates at a high speed. The torque of the motor is transmitted to the first-stage gear through the shaft, and the hub shell is driven to rotate by the gear reduction. The disk-shaped armature of a brushed geared hub motoris thin, small in size, light in weight, and easy to install. After the winding is prepared, it is thermoformed with resin and glass fiber in the mold, and then rotated at a high speed at a speed of 5000r/min, and tested for 2 minutes. The deflection, runout and strength of the armature should be qualified. When the motoris running, due to the friction between the brushes and the commutator, and the gear meshing and decelerating, the sound of the brushed motor is louder than that of the brushless motor.
2.In order to adapt to the hub structure and simplify the ebike motor, the hub-type gearless drive brushed DC motor is designed as the armature on the outside to make the rotor, and the magnet is placed inside the motor to make the stator, and multiple magnets are equipped with multiple windings. It is composed of a low-speed motor with a rotation speed of about 180r/min. In the outer rotor of the motor, the armature winding that has not been pressure-shaped, there are flat and ring-shaped commutating segments neatly arranged inside the winding. There are 10 magnetic steel stators arranged at intervals on the outer rotor. Two holes are opened in the middle hub plate. The brush holder of the brush is set on the back side of the hole, and the brush carries the wire from the brush holder by the spring. pop up. It can be seen from the figure that the shaft end of the stator is covered with a nut to prevent the thread of the shaft from being damaged during processing. The brush is arranged in the brush holder, and this end is fed into the hole. The brush can be contacted and replaced. On the plane of the commutator, the commutator is compressed by the elastic force of the spring, 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 produced by the motor.
3.The brushless DC motor reverses the stator and rotor of a gearless brushed DC motor. The winding is changed to three phases as the stator. The magnet is installed in the ebike motor casing, and the brush and commutator are eliminated. It is in the middle of the armature winding. With three Hall sensors installed, this becomes a brushless DC motor. Its appearance is the same as Figure 4-4. In the stator of the armature, you can see the shape of the windings embedded in the stator core. After the three-phase winding leads are fixed by the pressure plate, they are drawn out from one end of the shaft hollow, and two corresponding planes are milled from both ends of the shaft, which can be installed in the car. Tighten the nut in the front* or back* mouth of the machine to generate a reaction torque during operation. For armatures with sensors, 3 Hall sensors are installed evenly at 120° where the lead end of the winding is close to the magnetic steel of the outer rotor. Each sensor has 3 leads, of which the power line and the ground wire are shared. After the combination, they become 5 total leads, which are led out from the shaft hole with the winding leads. The outer rotor of the brushless DC motor consists of 7-20 pairs or more of NdFeB magnets with alternating n and s poles. The magnetic field strength is high and the relative price is low. The NdFeB magnet has a low Curie point, but the heat dissipation condition of the shell is good. On the contrary, the inner magnetic rotor or inner magnetic stator adopts magnets with higher Curie temperature, such as samarium-cobalt alloy or other magnets with magnetic field strength that meet the requirements, and the Curie temperature should not be lower than 400℃.
4.The brushless geared motor has basically the same structure as the brushed disk-shaped armature and geared ebike motor. It also has a smart disk-shaped armature, and even the arrangement of the magnets is the same. The essential difference is that it does not have a commutator. Ear position detection device. The bigger difference between them lies in the controller. There is a power commutation circuit to provide current for each phase of the armature, and there is Hall signal decoding and encoding to determine the power supply phase or direction based on the detected n-pole position of the magnet. Simply put, it has the structure of a brushed and geared motor, but it has the principle of a brushless motor.
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