How to mantenance and repair the electric bike motor

 

 

 

The technical requirements

They have different special requirements in terms of load requirements, technical performance and working environment:

1.The drive motor of electric vehicle needs to be 4-5 times of overload to meet the requirements of short-term acceleration or hill climbing; Industrial motors require only twice as much overload.

2.The maximum speed of electric vehicles is required to reach 4-5 times of the basic speed when cruising on the highway, while industrial motors only need to reach the constant power of 2 times of the basic speed.

3.The driving motor of electric vehicle needs to be designed according to the model and driver’s driving habits, while the industrial motor only needs to be designed according to the typical working mode.

4.Electric vehicles are required to have a high power density (generally within 1kg/kw) and a good efficiency chart (with high efficiency within a wide range of rotation speed and torque) to reduce vehicle weight and extend driving mileage; However, industrial motors generally take power density, efficiency and cost into consideration, and optimize the efficiency near the rated working point.

5.Electric vehicle drive motor requires high controllability, high steady-state precision and good dynamic performance; The industrial motor has only a specific performance requirements.

6.Electric vehicle driving motor is installed on the motor vehicle, with small space, and works in high temperature, bad weather, frequent vibration and other adverse environment. Industrial motors usually work in a fixed position.

 

 

Common faults

Common faults with brushless dc motors are usually examined from their three components.

When the fault location is not clear, the motor body should be checked first, followed by the position sensor, and finally check the drive control circuit. In the motor body, the possible problems are:

1.Bad contact of motor winding, broken wire or short circuit. Will cause the motor not to turn; The motor can start in some positions, but cannot start in some positions; The motor is out of balance.

2.Demagnetization of the main magnetic pole of the electric motor will make the torque of the motor obviously small, while the no-load speed is high and the current is large. In the position sensor, the common problems are hall element damage, poor contact, position change, will make the motor output torque smaller, serious will make the motor does not move or vibration back and forth at a certain point. The power transistor is the most prone to failure in the drive control circuit, that is, the power transistor is damaged due to long-term overload, overvoltage or short circuit. The above is a simple analysis of the common faults of brushless motor, in the actual operation of the motor will be a variety of problems, inspectors should pay attention to not exactly grasp the situation, not at random power, so as not to cause damage to other components of the motor.

 

 

Maintenance and repair methods

There are two kinds of motor faults: mechanical faults and electrical faults. Mechanical faults are easy to find, while electrical faults are analyzed and judged by measuring their voltage or current. The following are the detection and troubleshooting methods of common motor faults.

High no-load current of the motor

When the no-load current of the motor exceeds the limit data, it indicates that the motor has a fault. The reasons for the large no-load current of the motor include: large mechanical friction inside the motor, local short-circuit of the coil, magnetic steel demagnetization. We continue to do the relevant test and inspection items, can further determine the fault cause or fault location.

The no-load/load speed ratio of the motor is greater than 1.5. Turn on the power and turn the handle to make the motor rotate at a high speed and no load for more than 10s. When the motor speed is stable, measure the maximum no-load speed N1 of the motor at this time. Under standard test conditions, drive beyond 200m to measure the maximum load speed N2 of the motor. No-load/load ratio =N2÷N1.

When the no-load/load speed ratio of the motor is greater than 1.5, it indicates that the magnetic steel demagnetization of the motor is quite severe, and the whole set of magnetic steel inside the motor should be replaced. In the actual maintenance process of electric vehicles, the entire motor is usually replaced.

Motor heating

The direct cause of the motor heating is caused by the large current. The relationship between the motor current I, the input electromotive force E1 of the motor, and the induced electromotive force E2 of the motor rotation (also called inverse electromotive force) and the motor coil resistance R is: I= (e1-e2) ÷R, the increase of I indicates that R decreases or E2 decreases. R decrease is generally caused by coil short circuit or open circuit, E2 decrease is generally caused by magnetic steel demagnetization or coil short circuit or open circuit. In the whole vehicle maintenance practice of electric bicycle, the method to deal with the motor heat release barrier is generally to replace the motor.

 

 

There is mechanical collision or mechanical noise inside the motor during operation

No matter the high speed motor or the low speed motor, there should be no mechanical collision or irregular mechanical noise when the load is running. Different types of motors can be repaired in different ways.

The vehicle mileage is shortened, motor fatigue

The reasons for short driving range and motor fatigue (commonly known as motor fatigue) are complicated. However, when the above four motor faults are eliminated, generally speaking, the fault with short driving range of the vehicle is not caused by the motor, which is related to the attenuation of battery capacity, the charger charging with insufficient power, the controller parameter drift (PWM signal does not reach 100%) and so on.

Brushless motor phase

Brushless motor phase loss is usually due to the brushless motor hall element damage. By measuring the resistance of the output lead of hall element to the ground lead of hall and to the lead of hall power supply, we can determine which hall element fails by comparison.

It is generally recommended to replace all three hall components at the same time to ensure the accurate position of motor commutation. Before replacing the hall element, it must be clear whether the phase algebraic Angle of the motor is 120° or 60°. Generally, the position of the three hall elements of the 120° phase Angle motor is parallel. For the 60° phase Angle motor, the hall element in the middle of the three hall elements is placed in a 180° position.

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