Dynamic modelling of planetary gear systems for gear tooth fault

Abstract

Geared systems have been widely used in mechanical applications for more than a hundred years. A large range of literature has been published especially for spur/helical gear systems and the investigations into technical areas of spur/helical gears have been very well developed, including understanding of condition monitoring systems, diagnostic and prognostic methods. However, there is a lack of understanding on the general dynamic behavior of planetary gear systems with tooth faults. Planetary gears are normally used as effective power transmission elements with high power to weight/volume ratios, large speed reductions in compact volume, and high reliability. They tend to have high efficiency and are used in many applications, such as automotive, heavy truck/tractor, helicopter, wind turbines and bucket wheel reclaimer gearboxes.The purpose of this research is to develop a vibration analysis system that simulates dynamic behavior of large low speed, high torque planetary spur gear systems such as used in bucket wheel reclaimer and wind turbine gearboxes, with and without gear element faults. This thesis investigates lumped mass modelling methods for planetary gearbox dynamic behavior based on previous gearbox modelling research including the use of the coupled torsional-transverse behavior of the gear body. The dynamic model of the planetary spur gear system includes effects such as: variable tooth mesh stiffness, dynamic transmission error effects, and pitch and profile excitation for gear fault detection purposes. Different tooth faults are simulated using the concept of combined torsional mesh stiffness. The dynamics of spur planetary gear systems with and without tooth faults are compared and analyzed to improve the understanding of fault detection in the present gear systems.Dynamic modelling of gear systems, such as outlined in this thesis can assist in understanding the consequence of large transient events, including the fluctuations in tooth loads which can reduce gear fatigue life and lead to further tooth damage. Early detection of faults on gear teeth can be used to initiate maintenance actions in order to reduce repair work and avoid catastrophic breakdown.