Vibration Feature Evaluation of the Motor-Gear System with Gear Tooth Crack and Rotor Bar Error

The high speed and high power density electromechanical system for the electric vehicle is urgently required to meet stricter emission regulation and achieve higher performance. Therefore, the electromechanical coupling effect is becoming more strengthened and may significantly degrade the performance of the motor and gear system. When gear or motor failures like gear tooth crack or rotor bar breakage are present, the operation safety of the electric vehicle would be threatened. So the exploration of the fault features for the motor-gear system is crucial for prevention of disastrous consequences. In this paper, the fault vibration features of the motor-gear system with gear root crack and motor rotor error under various excitations from both motor and gear transmission system are investigated. The electromechanical dynamic model considering the nonlinear air-gap permeance and time-varying mesh stiffness is employed, and the gear tooth root crack fault and the rotor bar breakage are integrated into the dynamic model to acquire the dynamic characteristics with faults. Then, the angular-synchronous average technique is applied to strengthen the statistical characteristics of fault vibration signal and eliminate the effect of speed variation due to the external excitation. The statistical indicators extracted from the angular-synchronous average vibration signals can reveal the progression of gear faults for the gear transmission without motor rotor error. However, the analyzed results indicate that the popular statistical indicators would fail to detect the early tooth fault when the motor rotor error is coupled.