Abstract: A long-term tracking test on a high-speed EMU train is conducted, and it is found that when the vehicle runs more than 180 000 km after wheel tread repaired, an abnormal shaking phenomenon of the car body occurs, meanwhile, the lateral and vertical vibrations of the car body are abnormally amplified at around 10 Hz. Based on wheel tread test analysis, car body and frame vibration test analysis and modal analysis of the car body, the mechanism of the abnormal car body shaking is studied. Results show that when the running distance of the EMU reaches more than 180 000 km after wheel tread repaired, the equivalent conicity exceeds 0.501, and the wheel tread has concave grinding, the contact position of the wheel and rail is scattered, and there is a jump phenomenon. When the running vehicle is subjected to a relatively large lateral disturbance from the track, the wheel will have a large amount of lateral movement and the contact position between the wheel and rail will change suddenly. As a result, the frequency of the bogie hunting motion suddenly rises to be close to the frequency of the diamond-shaped deformation mode of the car body, which triggers the synchronous movement of them. This causes the amplification of the diamond-shaped deformation modal vibrations, which is the cause of abnormal car body shaking. To suppress the phenomenon of the car body shaking, with the aim of improving the vehicle’s running stability and ride quality, an optimization method of multi-target vehicle system suspension parameters based on orthogonal experiments is proposed, the lateral and the longitudinal of primary positioning stiffness, the stiffness of the bush and the damping of the yaw damper are simultaneously optimized. Simulation results show with the optimized suspension parameters, the critical speed, running safety and ride quality of the vehicle under different tread wear states have been significantly improved. An in-situ test is conducted to verify the suspension parameter optimization scheme. Results show that after using the optimized suspension parameters, the energy of the car body shaking is significantly reduced, and the shaking problem is significantly improved.

Key words: electric multiple unit trains, car body shaking, wheel wear, orthogonal test, suspension parameter optimization