Fault detection on gearboxes operating under fluctuating load conditions

Gearboxes often operate under fluctuating load conditions during service. Conventional vibration monitoring techniques are based on the assumption that changes in the measured structural response are caused by the deterioration in the condition of the gearbox. However, this assumption is invalid under fluctuating load conditions. Experimental data were obtained from a test rig, which is able to apply fluctuating loads of up to 3 Hz on the system. Sinusoidal, step and chirp load fluctuations were considered. Conventional vibration monitoring techniques were applied to the test data in order to indicate the influence of the fluctuating load conditions and the severity of the problem. A vibration waveform normalisation approach is presented, which enables the use of the root mean square and variance statistical parameters to track the trend in the degradation of a gear under fluctuating load conditions.