Detection and diagnosis of incipient bearing failure in helicopter gearboxes

Abstract In most machines, the vibration signature of bearing faults extends into a higher frequency range than most other components, and this allows separation. In the case of helicopter gearboxes, there is a very wide range of shaft frequencies between input and output, and the associated gearmesh frequencies cover the whole audio frequency range. Techniques have thus been developed to separate the gear signals from the bearing signals, based on their different statistical properties. Other techniques have been developed to separate gear and bearing effects even when they are combined multiplicatively rather than additively. The techniques are illustrated using case history data obtained from the US Navy, from faults in three helicopter gearboxes.