Abstract: Problems with out-of-round wheels are widespread in subway trains. They can result in impact loads between wheels and rails, increase vehicle vibrations and noise, and cause fatigue fractures of vehicle/track components, which has a significant effect on ride comfort, operational safety, and wheel maintenance. The out-of-roundness test data of more than 9,000 wheels from 21 subway lines in China are statistically analyzed, covering four types of subway trains with maximum speeds of 80, 90, 100, and 120 km/h. The characteristics of wheel out-of-roundness such as radial run-out, orders, and wavelengths are determined. Welch’s method is used to estimate the spectra of all measured out-of-roundness data of the wheels. Then, the two-segment power function is used to obtain the roughness spectra, which are compared with the roughness spectra of high-speed wheels. The results show that the subway wheels have out-of-round problems to varying degrees, with about 10% of the wheels having radial run-out greater than 0.5 mm. The order of wheel polygonal wear is mainly 1st order (eccentric), 5th to 9th, and 12th to 16th order. The dominant wavelength of high-order polygonal wear (more than 10th order) is in the range of 160-200 mm in the 1/3 octave band. Compared with the roughness spectra of high-speed wheels, the roughness spectra of subway wheels are higher. The results of this paper can be helpful in the evaluation, maintenance, and repair of subway wheels in out-of-round conditions, as well as provide important information for dynamic wheel-rail interaction and wheel-rail noise simulation.

Key words: metro wheel, wheel out-of-roundness, wheel roughness spectra, wheel polygonal wear, statistical analysis