A Study on Gearbox Noise with Induced Tooth Defects

Abstract

Rotating machinery plays an important role in industrial applications. When these machines recently are getting more complicated, fault diagnosis techniques have become more and more significant. Gears are used extensively in drive systems. Effective gear fault detection is crucial to ensure safety. In addition, tremendous economic benefits can result from condition based maintenance practices, for which gear fault detection plays an important role. Over the past 25 years, much research has been devoted to the development of Health and Usage Monitoring systems for gearbox and drivetrain components. In order to keep the machine performing at its best, the principal tools for the diagnosis of rotating machinery problems is the vibration analysis & noise analysis, which can be used to extract the fault features and then identify the fault patterns. In the majority of cases the source of noise and vibrations is transmission errors introduced during manufacture. These errors can e.g. be geometry inaccuracies and eccentricities which both results in impact noises. Other sources of impact noises can be gear rattle. Gear rattle is caused by a combination of backlash and unloaded gears. Friction, wear, crack and pitting due to gear fatigue are also sources of noise. Most modern techniques for gear diagnostics are based on the vibration signal picked up by an accelerometer from the gearbox casing. The vibration signal is normally filtered by time synchronous averaging (TSA) and analysed in the frequency domain with methods such as the Wavelet Transform (WT) or the FFT. A similar approach is to use a microphone instead of an accelerometer and record the noise from the gearbox. This method was used to detect faults in industrial gears. The expected noise spectrum from a gearbox would contain the gear meshing frequencies and integer multiples of it. A different method for measuring the noise from the gearbox with seeded fault is used. Sound level meter is used to measure the SPL of gearbox with different imposed faults (cracks and decrease in tooth height) in the tooth of gear. The results have been compared with the sound pressure of normal gear to extract the fault information.