Application of no-tachometer time synchronous averaging (TSA) and relative signal strengths to localize gear and bearing faults in a helicopter gearbox

Health and Usage Monitoring Systems (HUMS) installed on helicopters monitor a wide variety of input signals to track system conditions. Improving fault detection on existing platforms precludes installation of additional hardware such as shaft speed sensors and additional accelerometers. The application of no-tachometer TSA and bearing fault harmonic energy techniques can be used to improve HUMS detection ability. In this presentation I will present a case study of gear tooth and bearing fault detection for a helicopter intermediate gearbox (IGB). Gear-mesh frequency demodulation is used to determine angular zero-crossing to synthesize a tachometer signal for gear fault detection, allowing for TSA techniques to readily identify gear tooth faults. The methods presented in "Autonomous Bearing Fault Diagnosis Method based on Envelope Spectrum" (2017 Klausen et al.) are then applied to determine the presence of bearing faults inside the IGB. Due to overlapping fault frequencies from multiple bearings a detected fault could be attributed to several bearings, the use of two accelerometer signals to spatially localize faults is developed and presented.