Design of optimized tread profile for high-speed EMUs

To address two significant issues in high-speed electric multiple units (EMU), i.e. degraded vehicle dynamic performance under existing wheel-rail interactions and increased wheel tread wear at elevated operating speeds, this paper proposes an optimized tread profile design that balances wheel-rail interactions, dynamic performance, and wear resistance. The aim is to mitigate hunting instability induced by excessively low equivalent conicities in the interactions between the LMA tread profile and 60N rails and further reduce wheel wear. Through wheel-rail contact analysis, the underlying reason for low equivalent conicities in the interactions of the LMA tread profile with 60N and over-ground rails was identified. A reverse design method was then employed to enhance the nominal equivalent conicity while preserving the existing wheel-rail contact characteristics, resulting in the first-stage tread profile optimization, LMA_opt1. Subsequently, a dual verification framework combining a vehicle dynamics model and an Archard theory-based wear prediction model was developed. Verification results revealed that the first-stage optimization, while improving dynamic performance, led to increased wear. To resolve this compromise, a second-stage optimization was conducted nonlinearly using an equivalent conicity curve. This process reconstructed the wheel-rail contact relationship while retaining the nominal equivalent conicity attained in LMA_opt1, yielding the final optimized tread profile, LMA_opt2. The resulting dynamic performance and wear characteristics were then verified through simulations. The results demonstrate that the tread profile in LMA_opt2 facilitates a more refined wheel-rail contact relationship, increasing the nominal equivalent conicity in interactions with 60N rails to 0.04 and expanding the wheel-rail contact band by 15% in width. In terms of dynamic performance, this optimization proves effective in eliminating primary hunting instability at speeds from 100 to 200 km/h, thereby enhancing the vehicle running stability. Regarding wear resistance, LMA_opt2 helps reduce wheel flange wear, alleviate pitting-type wear in the frequent contact zone, and slow the growth rate of the tread profile nominal equivalent conicity after wear.