Determination of Critical Speed of Railway Vehicles Using Measuring Technologies of Bench Tests

The paper is focused on the problem of increasing the reliability of determining the critical speed of railway vehicles during measurements in bench tests, due to the difference in the geometry of the contact interaction in the “wheel-roller” and “wheel-rail” systems. It is shown that existing approaches in dynamic stability analysis and the processing of measurement signals do not consider the systematic influence of equivalent conicity on the measurement results, which leads to a shift in the assessment of the threshold for loss of stability even with the high accuracy of the measuring equipment. An information-measuring approach is proposed, which is based on an analytical description of the relationship between the equivalent conicity of the wheel/rail contact and the critical speed. A generalized error model is developed integrating geometric, metrological and random components. A method for correcting the results of bench tests based on a coefficient considering the ratio of equivalent conicities is also proposed. It was found through the results of the research that neglecting the geometric mismatch of the contact interaction leads to an error in determining the critical speed at the level of 8 to 15%, while the application of the proposed approach reduces it to less than 1 to 2%. Additionally, frequency analysis of the oscillatory process was used. It allowed us to identify the critical mode of the frequency range of about 8 Hz and to establish its connection with the critical speed of movement. It was experimentally confirmed that the corrected results correspond with the calculated values within 1%. The obtained results provide an increase in the metrological consistency of bench and operational studies, expand the possibilities of interpreting test results and can be used in the development of methods for diagnostics, certification and prediction of the limit modes of operation of railway vehicles. The proposed approach provides increased reliability in determining the critical speed during bench tests and it can be used for analytical compensation of a systematic error without upgrading the test equipment.