Experimental study of failing differential gears and introduction of a new condition indicator for ultra low speed applications

Detecting gear cracks in ultra low speed, high load planetary gears plays an important role in engineering praxis and in the development of differential gearboxes for vehicles. The analysis of the acceleration signals for condition monitoring purposes, which is widely used in the industry, cannot be applied for this use case. The aim of this paper and experimental study is to develop a new condition monitoring method, which makes it possible to detect cracks and follow the crack propagation in differential gears under realistic test conditions without any artificially seeded faults. The variation of the Locking Factor (LF) and its vibration spectrum over the complete testing time (14–81 h) is analysed with the new method. The successive change of the spectrum of the LF and the Condition Indicator (CI) is presented in this paper. Due to the complex structure of the test bed and the complex modulation phenomenon, a new approach was needed for detecting the cracks.