Amplitude Demodulation of Instantaneous Angular Speed for Fault Detection in Multistage Gearbox

Traditional fault detection processes in gearbox are mostly based on vibration signal analysis. However, many a times extraction of fault features by the vibration signal analysis becomes difficult as the signal carries structure-borne noise. Moreover, position of the vibration sensor affects the signal to noise ratio of the signal. The presence of a fault in a gearbox changes the rotating dynamics of the system which varies the speed of the output shaft. Therefore, aim of this paper is to analyse the varying speed of the output shaft for detection of fault in a multistage automobile gearbox. Here, the varying speed is measured as instantaneous angular speed (IAS). Besides carrying information related to the fault, this IAS signal carries less structure borne noise due to direct response of rotating dynamics. Furthermore, in presence of fault, this varying speed signal or IAS signal is frequency modulated signal. Besides frequency modulation, the IAS signal becomes amplitude modulated under the application of load. Demodulation is a well known technique in the area of signal processing, which extracts the modulating part from a signal. Hence, the amplitude demodulation technique has been applied to the IAS signal which reveals various important frequencies related to the gearbox. Thus the technique helps to detect the fault in a multistage automobile gearbox under different load conditions.