Assessment of Wheel-Rail Adhesion Coefficient from Anti-Slip Data of Operating Trains

To better understand the wheel-rail adhesion under actual operations, this study employs data collected from control systems of high-speed trains to assess the adhesion coefficient during traction at speeds up to 250 km/h. Based on the data, including train speed, temperature, wheel slip signals, sanding signals, as well as required and actual traction forces, the correlation of wheel slip occurrence with weather conditions is first analyzed. Afterwards, an approach is further proposed to assess adhesion coefficients, in which actual traction coefficients during slip are used to approximate adhesion coefficients. Combining assessed adhesion coefficients at different speeds, the relationship between adhesion coefficient and speed is fitted from the lower limit of scattered adhesion coefficients. It is found that wheel slip events occurred the most in snowy weather, followed by rainy weather, then in hazy weather, and the least in sunny/overcast/cloudy weather. Wheel slip durations reduced gradually from the leading to trailing cars in hazy, rainy weather as well as after snowfall, confirming the adhesion recovery phenomenon induced by the cleaning effect of passing wheels, and assessed adhesion coefficients across different axles further showed such a trend quantitatively. However, the recovery was not figured out during snowfall, possibly due to ice formation from snow particles through the pressure-melting mechanism. The fitted adhesion coefficients of typical axle positions in rainy and snowing weather are compared to those from Shinkansen and a full-scale rig, suggesting that the presented approach may be employed to assess wheel-rail adhesion coefficient under complicated operating conditions.