Differential diagnosis of spall vs. cracks in the gear tooth fillet region: Experimental validation

This paper presents a technique to differentially diagnose two types of localized gear tooth faults: a spall and a crack in the gear tooth fillet region. These faults could have very different prognoses, but existing diagnostic techniques only detect the presence of localized tooth faults without being able to differentiate between a spall and a crack. The effects of spalls and cracks on the behaviour of gear assemblies were studied using static and dynamic simulation models. Changes in the kinematics of a pair of meshing gears due to a gear tooth fillet crack (TFC) and a tooth flank spall were compared using a static analysis model. The difference in the variation of the transmission error (TE) caused by the two faults reveals their characteristics. The effect of a tooth crack depends on the change in stiffness of the tooth while the effect of a spall is dominantly determined by the geometry of the fault. A technique has previously been proposed to detect spalls [M. EL Badaoui, J. Antoni, F. Guillet, J. Daniere, Use of the moving cepstrum integral to detect and localize tooth spalls in gears, Mechanical System and Signal Processing, 15 (5) (2001) 873-885; M. EL Badaoui, V. Cahouet, F. Guillet, J. Daniere R Velex, Modelling and detection of localized tooth defects in geared systems, Transaction of ASME, 123 (2001) 422-430], using the cepstrum to detect a negative echo in the signal (from entry into and exit from the spall) and successfully performed differential diagnosis on the simulated vibration signals. While the result of the experimental study showed some differences from the result of the simulation study, the differential diagnosis was successfully performed based on the technique presented in this paper. Further investigation revealed non-linear gearmesh behaviour which was causing differences in the experimental and simulation model results. (C) 2008 Elsevier Ltd. All rights reserved.