Four models of tribological wear of turbine jet engine bearings based on methods of electrical generator signal analysis
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Instytut Techniczny Wojsk Lotniczych
Andrzej Jan Gębura   

Instytut Techniczny Wojsk Lotniczych, ul. Księcia Bolesława 6, 01-494 Warszawa, Polska
Submission date: 2016-12-20
Final revision date: 2017-02-24
Acceptance date: 2017-02-24
Publication date: 2017-03-23
Diagnostyka 2017;18(1):59–66
The article describes test results of rolling bearings conducted on turbojets, with the simultaneous use of two diagnostics methods: FAM-C and FDM-A [7]. For these methods, no installation of additional sensors on the aircraft is needed – the on-board electric generators are used as sensors. The „FAM-C” method uses the aircraft’s alternating current (AC) tachometer generator, whereas the “FDM-A” method uses the direct current (DC) commutator-type generator. Spectrum of angular velocity of individual bearings manifests itself in high frequency ranges (60-240 Hz for the tachometer generator, 3-10 kHz for the DC generator), making the oscillation signal resistant to noise. This frequency modulated signal can be picked up by measuring instruments in any point of the aircraft electrical system. After detection the initial signal is obtained. Measurement analysis can be easily automated [10]. During detection, the carrier frequency is filtered off. Currently, with the simultaneous use of correlated FAM-C and FDM-A methods, four models of rolling bearings wear can be detected: increase of aggregate friction, seizure of rolling elements, increase of radial clearances, increase of axial clearance. This division was made on the basis of observing the technical condition of rolling bearings on many (around 30) turbojets during its normal operation