Traction motor suspension-induced frequency veering in high-speed rail vehicles: mechanisms and optimisation

As a crucial component of the powered bogie in high-speed rail vehicles, the traction motor significantly affects bogie hunting stability due to its large mass and elastic suspension. Initially, the frequency veering mechanism of the 3-degree-of-freedom (DOF) motor suspension system was investigated, and the frequency veering point as well as the analytical solution of the mode shapes were derived. Subsequently, based on the 8-DOF bogie model, the coupling characteristics between the motor lateral mode and the bogie hunting mode were further explored, and two quantitative criteria were adopted to evaluate the similarity of mode shapes. Finally, an overall optimisation rate, defined as the enclosed area of the minimum damping ratio curves of the vehicle system, was proposed, on the basis of which the motor suspension parameters were optimised. The theoretical analysis and numerical simulation show that: In the frequency veering zone, a notable mode shape interchange occurs between the motor lateral mode and in-phase hunting mode, while the two mode shapes exhibit the same amplitudes but opposite phases in motor lateral motion. It is recommended that the motor suspension parameters should be determined at the critical state between frequency veering and crossing, as this approach can enhance hunting stability.