Proposal for the Diagnosis of Railway Engines

This article contains a proposal of another kind of analysis than the traditional time-frequency analysis (see Lee and White, 1999; Mallat, 1989; Uchikawa et all, 2002; Wang and McFadden, 1993). The proposed method increases the resolution of the spectral analysis on the frequency scale down to values lower than can be obtained while using the Fourier transform in a situation when it is not possible to obtain samples with sufficient duration, e. g. in not fully stationary motion (when slowly changing disturbance of rotational speed occurs). During many years of research on railway engines, the authors often came across the problem of maintaining over a longer period (for the time required for the registration of signals) of constant speeds. Failure to fulfit this requirement either hinders or makes the use of simple methods of digital analysis of stationary signals in a diagnostic task impossible. In such a situation we can choose from among two ways to proceed: - for a long time of averaging we have insufficient mapping of main spectral vibrations (spectral line broadening), - for a very short time sample (limited to the part of run registered for a constant rotational speed) we get insufficient analytical resolution. A good example of such problems is the research related to the power units of vehicles. Since the length of the registered signal does not always allow the obtaining the relevant analytical resolution, the authors decided to use some of the properties of the ordinary coherence function to increase the digital precision of the signal analysis. As an example of applying the proposed method we present the results of vibration measurements of the casing of a bearing in a power unit of an electrical locomotive (EZT) of EN-57 type. The power unit consists of an electrical, direct current motor and of a one-stage helical reduction gear, whose slow speed shaft serves at the same time as the axle of the driving wheels. For the digital registration of acceleration of vibration at various points of the EZT locomotive we used the ROADRUNNER analyser from LMS. The numerical analysis was performed no MATLAB software.