Dynamic Behavior of Back to Back Planetary Gear in Presence of Pitting Defects

The diagnosis of rotating machinery such as planetary gearbox running under operating condition is a complex task. Depending on their nature, the defects can be classified into teeth, geometrical or bearing defects. This paper studies the dynamic behavior of a back-to-back spur planetary gear running in stationary condition in the presence of teeth defects. This damage is the pitting and it is located in one tooth of the sun gear. An experimental test is performed by the measurement of the instantaneous accelerations on a test gear. The tests are carried out under a fixed load and speed. The presence of the tooth pitting defect activates repeated-like transient in ring’s vibration displacement because of phase change and amplitude reduction of the mesh stiffness when the damage tooth comes into contact. The Fast Fourier Transform (FFT) is used to transform the time signal into the frequency domain for signature analysis. The acceleration spectra show the influence of damage both in frequency and amplitude. The frequency of pitting which is the frequency of rotation of the test sun and the frequency of rotation of the motor appears along of frequency bandwidth. Moreover, the impulses of the defect tooth with the planets become important in amplitude.