Downloaded from https://www.everyspec.com ADS-79D-HDBK BPFI is the frequency at which rolling elements pass over a point on the inner race. It is designed to capture the frequency of vibrations produced by defects of the inner race. d N BPFI cos 1 2 [1] contact pitch RE shaft d D.7.3 MSPU Bearing Energy CI Creation. To capture these frequencies and their first few harmonics, a CI that calculates the energy from 100 Hz to 1100 Hz, excluding the band from 152 Hz to 172 Hz, was created. The reject band centered at 162 Hz is used to exclude the second harmonic of the tail rotor drive shaft rotational speed.
This shaft harmonic can be a valuable indicator of drive shaft alignment, but it is captured by a different CI and does not provide useful information about the condition of the bearing itself. The reject band centered at 685 Hz is used to exclude the gear mesh of the planetary gears in the main transmission. The frequencies that are captured by this bearing energy CI are highlighted in Table D-II. D.7.4 MSPU High Frequency Energy CI Creation. Not all bearing faults produce detectable or separable vibrations at the fundamental bearing fault frequencies or their first few harmonics so additional CIs are needed.
The simplest approach that is often effective is to select a higher frequency energy band and calculate the energy in that band. The determination of the band to use for such a CI is usually experimentally determined through seeded fault testing or from data associated with a component that has been torn down and found to be faulted. The band should maximize the separability between the known faulted components and the known/assumed healthy components. However, the band should not be so specific to the individual faulted components that it is really identifying unique features of those components rather than features that are likely to occur in other components with similar faults.
Based on the known faulted case of a corroded aft hanger bearing removed from AH-64D 01- 05270 in October 2004, a CI was developed that calculates the energy in the band from 12.5 to 17.5 kHz. D.7.5 Effectiveness. The HIs for AH-64 hanger bearings apply limits of 7 and 14 to the Bearing Energy CI and 20 and 40 to the High Frequency Energy CI. This results in an overall confirmed true positive (TP) rate of 100% and an overall confirmed true negative (TN) rate of 86.7%. Out of a total of five TDAs, the Bearing Energy CI contributes to four TPs and one false positive (FP), and the High Frequency Energy contributes to two TPs and one FP. 95 TABLE D-II.
AH-64D aft hanger bearing fault frequencies and harmonics Harmonic CFF (Hz) BSF (Hz) BPFO (Hz) BPFI (Hz) 1 31.95 2 63.90 3 95.85 4 127.80 182.9 287.6 442.0 365.8 575.1 883.9 95.85 548.7 862.6 127.80 731.6