Detection of gear wear on the 757/767 internal drive generator using higher order spectral analysis and wavelets

The 757/767 internal drive generator (IDG), which provides 400 Hz/120 volt ac power to the aircraft cabin, experiences failures due to seizure of the scavenger drive pump and/or axial gears on the main drive shaft of the unit. These generators are an integral part of the aircraft's engines sitting outboard, inside the engine cowling. The seizure of gears represents a significant loss with gear replacement estimated at $17,000 and unit replacement costs at $250,000. One of the U.S. commercial airline companies engaged Oak Ridge National Laboratory in a brief study to determine if a methodology could be developed to interrogate and diagnose gear wear with the ultimate goal of deploying an instrument for test stand and flight line use. Through a structured analysis it was determined that accelerometers mapped with higher order spectral analysis (HOSA) and/or wavelets could provide an analytic approach and basis for a diagnostic sensor/system capable of assessing IDG gear wear on the aircraft or the test stand.