Electric Motor Mechanical Fault of Electric Vehicles
Mechanical failures are as important as electrical failures and need to be detected in a timely manner. The most important mechanical errors are bearing errors and air gap eccentricity. Other mechanical failures include bent shafts, damaged magnets, loose screws, etc.
1) Bearing errors
Bearing failure is the most common failure among all possible engine failures, accounting for about 40-50%. Bearing failures can occur in the inner ring, outer ring, cage or ball bearings. The main causes of bearing failure, even under normal conditions, are poor lubrication, mechanical vibration, shaft misalignment, overload, corrosion, and ultimately fatigue.
If bearing defects go undetected and not repaired, other types of failures can occur, such as air gap eccentricity, ITSF, and even complete motor failure.
2) Air Gap Eccentricity Error
Some mechanical problems, such as uneven loading, shaft misalignment, rotor imbalance, missing bolts, and bearing failure, will cause rotor eccentricity error in motors. In reality, this is an uneven air gap between the stator and rotor, which is classified into three types: static eccentricity (SE), dynamic eccentricity (DE), and mixed eccentricity (ME).
SE refers to a state in which the minimum air gap has a constant value and changes very little over time, and it mainly occurs during the manufacturing stage. DE occurs when the minimum air gap point rotates with the rotor and is caused by rotor failure, bearing wear, and bent shaft. ME is the simultaneous presence of SE and DE defects.
3) Sensor Errors
Various types of sensors, such as current, voltage, speed, and position sensors, are required to provide various feedback signals to the motor drive control system. Sensor failure refers to sensor defects or failures that may be caused by vibration, temperature, humidity, etc. Sensor errors may include open circuits, gain mismatch, or high noise.
If any of these sensors fail, erroneous information will be sent to the engine monitoring and control system, resulting in poor performance and even complete engine failure. Therefore, fault detection and diagnosis are essential to avoid such failures and reduced reliability.
4) Current Sensor Anomaly
At least two current sensors are used to measure the phase currents in a three-phase PMSM. Current sensor errors can occur in three types: zero output, false gain, and DC offset. None of these faults require immediate identification and repair, but they can cause efficiency loss and overheating.
5) Voltage Sensor Error
If a voltage sensor error causes a sudden increase in the measured DC voltage, it can cause a system failure in a short period of time. In this situation, rapid error detection and resolution is important. In some cases, the error may cause a slight change or deviation in the readings, which may cause the engine to operate at reduced power for some time.
6) Speed ​​or position sensor error
The rotor position and speed are measured by position and speed sensors in the motor drive and fed to the control system. Photoelectric incremental encoders are usually used for this object. If this sensor fails, it can affect the functioning of the engine.
This can result in rotation in the wrong direction, a drop in speed from the required speed to zero, engine stalling, or, most dangerously, a rise in speed higher than required to reach the maximum possible engine speed. The latter can lead to prolonged overloads and even fatal accidents. Therefore, the FDD plays a key role in preventing such conditions.
