Application acoustic emission techniques in helicopter main gearbox bearing defect identification

摘要

Helicopter transmission integrity is critical to the safety operation. Of all mechanical failures in helicopter transmission, the main gearbox (MGB) failures contribute approximately 16%. Great effort has been paid in early prevention and diagnosis of MGB failures. As a commonly employed monitoring technology, vibration analysis suffers from strong background noise due to variable transmission paths from the bearing to the receiving externally mounted vibration sensor. The background noise can mask the vibration signature of interest. This paper reports on an investigation to identify the presence of a bearing defect in a CS-29 'Category A' helicopter main gearbox with the acoustic emission (AE). This investigation involved performing the tests for fault-free condition, minor bearing damage and major bearing damage conditions within a helicopter gearbox under different power levels. The bearing faults were seeded on one of the planet gears of the second epicyclic stage. To overcome the issue of low signal to noise ratio (SNR), a AE sensor was directly attached on the dish of planet carrier. The AE signal was transferred wirelessly to avoid complex wiring inside MGB. The analysis results proved the feasibility of using AE sensor as in-suit bearing defect identification.