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What Are the Reasons for Hub Motor Overheating?

Ⅰ. The characteristics of  hub motors

1. Hub motors have a simple structure, durability, low cost, reliable operation, small torque vibration, low noise, no need for position sensor, and high-speed limit.

2. Hub motors can use cylindrical radial magnetic field structure or disk axial magnetic field structure, with high power density and efficiency and broad speed range, and the development prospect is very broad. 

3. Hub motors have the characteristics of simple structure, low manufacturing cost, good speed/torque, suitable for electric bicycle drive.

Ⅱ. Reasons of hub motor overheating

1. Overload of hub motor: Because the motor load power is basically constant. When the voltage is more than 10% higher than the rated value, resulting in the increase of stator and rotor magnetic field strength, the motor overloads operation. Or the bearing of the motor is broken, so that the motor load increases, causing the motor temperature rise, wheel motor heating.

2. Problems of motor wiring system: The welding of the lead and line of wheel hub motors, wiring and terminal connection, wire core diameter, etc., may cause wiring system heating and directly affect the temperature of the wheel hub motor winding, thus affecting the motor heating. When this kind of problem gets serious, it will lead to local burning of the motor in a very short time and may also spread directly to the stator winding.

3. The heating caused by rotor defect: The problem mostly happens in the hub motor with relatively large power and relatively long rotor, as a result of casting defects of motor rotor itself, such as rotor article conducting bar with thin or broken defects. During the operation of the motor, the rotor will heat seriously, and the heat will naturally emit to the hub motor, resulting in the heating of the wheel hub motor.

4. Problems of Motor bearing system: Under normal circumstances, the temperature of hub motor bearing system with a relatively stable limit value to control, is generally at 95 ℃. The actual testing found that when the temperature of the bearing system is high, the heat will be conductive to the wheel hub motor, and when the winding temperature rises, the bearing system is adversely affected. The superposition of the two problems will lead to motor problems in a very short time.

5. Poor or ineffective grease: Poor or ineffective grease is also easy to lead to wheel hub motor heating. In addition to the motor operating in a specially high temperature environment, most of the operating temperature of the motor is below 70℃. The poor or ineffective grease will face the problem that the hub motor temperature is too high, and then the bearing is broken and locked.