Abstract: A mathematical model of EMU was established to analyze effects of suspension parameters on the suspension stiffness of the bogie. Then lab test was conducted to measure the actual suspension stiffness, which is used to verify the theoretical calculation results. The characteristics and distributions of the suspension stiffness under various conditions were summarized. Theoretical analysis shows that the rotation resistance factor of the bogie fluctuates greatly with the longitudinal stiffness of air springs and the lateral distance between two air springs, especially for small radius curves. Therefore, the rotation stiffness of the bogie and the anti-rolling stiffness of the vehicle should be considered simultaneously in the vehicle design stage. Test results of the primary suspension and second suspension stiffness are both a bit higher than the calculated stiffness with maximum error of 11%, which suggests that parameter verification after the assembling is essential and necessary. The test results also show that the greater are the rational angle and speed, the greater is rotation resistance factor. For a 300 m radius curve at inflated state, the rotation resistance factor is 0.023 with rotational speed of 0.05 °/s, and the resistance factor is 0.065 with rotational speed of 0.2 °/s, indicating that the higher is the speed, the greater is the rotation stiffness. However, at deflated state the corresponding resistance factor is 0.068 and 0.095, much greater than that at inflated state. We can be concluded that it is very dangerous when a vehicle passes small radius curve at high speed. The text results of rotation stiffness of the bogie are greater than calculated ones,and the dynamic characteristics of air spring stiffness and other suspension components should all be considered in theoretial calculations.

Key words: railway transportation, electric multi units(EMU), bogie, suspension stiffness, rotation resistance