Currently the fatigue testing of bevel gears are being done by using non rotating type of fixtures that applies fatigue load on a single tooth, which does not resemble the actual loading condition in an automotive differential gear box. This paper discusses the experimental setup with the noise and vibration analysis approach to determine the signature of failures of spiral bevel gears. The proposed experimental setup seems promising for further research and development in the fatigue testing of spiral bevel gears. The Crown pinion and wheel assembly is used for the testing. The pinion is connected to the electric 3 phase AC motor of 75HP with a suitable coupling and the crown wheel is mounted on the half axle shaft, which in turn is connected to an electric dynamometer. The speed/torque of electric motor and the load applied by the dynamometer can be varied. The acoustic sensor is mounted near the differential gear box and the accelerometers are mounted on the Pinion bearing, Crown wheel bearing and the half axle bearing. A four channel data acquisition system is used to log data in time domain (raw data) by three accelerometers and an acoustic sensor. The variations of sound pressure(dB) v/s time, sound Pressure(FFT-(RMS)) amplitude v/s Frequency, Acceleration v/s Time, Octave analysis i.e., Band power v/s Frequency, Noise spectrum Power v/s Frequency, Histogram, Power density v/s Time can be obtained. These data are then used to plot vibration and SPP levels in frequency domain to develop the noise and vibration signature of that crown pinion for given cycles of operation. The tests on Bevel pinion and gear set were performed in the BEC, Bagalkot NVH lab facility. The gear set run successfully at double the rated torque for 30 million pinion cycles. And the signature of pinion failure was obtained. The results demonstrated the suitability of using the given bevel crown pinion and gears set for specified speed, high load application in differential gear box of an automobile.

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This paper describes the experimental destructive testing of spiral bevel gears used in automotive differential gear box. The experimental testing is aimed at early detection of failure of spiral bevel gears during operation by continuously recording and comparing the sound and vibration characteristics during testing. For this purpose, a special fatigue test rig has been developed which can apply dynamic rotational loads with the help of a three phase AC electric motor. The accelerometers located on the drive side (crown pinion) and the slave side (crown wheel) measures the vibration characteristics and an acoustic sensor place near the gears in mesh measures noise levels. The acquired data in time domain are then converted to frequency domain by using a FFT. The signature of failure of pinion was obtained. Three pairs of gears were tested a new gear pair, a used gear pair and a gear pair after breakage of one teeth of pinion. The results obtained show that there is a significant increase in sound and vibration level for used and damaged gear pair. By comparing the results, it is possible for early prediction of point of failure which can be a significant finding in early detection of failure of spiral bevel gears.

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