Real-time static unbalance evaluation of the Cardan shaft equipped in high-speed train based on nonzero frequency filter.

To reduce the upsprung weight, cardan shafts are equipped in high-speed train to transmit torque from motor to gearbox. The driving safety and stability of the train are closely related to the condition of the cardan shaft, which may experience unbalance during operation. Therefore, vibration sensors are installed on the train to monitor the condition of the cardan shaft. In this study, a mechanical model of the cardan shaft was developed to elucidate the unbalance force characteristics of the cardan shaft with static unbalance. Based on the analysis of the unbalance force, a narrow bandpass filter constructed using the nonzero frequency filter (NZFF) was employed to extract unbalance signals from the measured signals. A double integration in time is applied to the extracted signal to eliminate the effect of circular frequency on the signal amplitude and mitigate signal noises caused by track irregularities. Efficient value of the extracted signal was used as an index to evaluate the static unbalance of the cardan shaft. Effects of mechanical suspension structures on value of the index were considered. Kalman filter was utilized to enhance the stability of the evaluated static unbalances. According to the experimental results, the static unbalances were accurately evaluated by the NZFF method.