直升机信息_直升机_直升飞机_旋翼机_Helicopter

where xper f ect (t) is some idealized vibration signal, Pn and φn are the amplitude and phase of the nth harmonic respec-tively, fm is the gear mesh frequency, and w(t) is the noise which is assumed to have a normal distribution.
Errors in manufacturing, tooth spacing, tooth pro.le, alignment, and installation, as well as damage have been shown to manifest as modulating signals, thus producing sidebands in the measured signal. These modulating func-tions are also periodic with the shaft frequency and can be divided into two components: amplitude modulation, a(t) and phase modulation, b(t). These can be written as
∞
a(t)= ∑ An cos(2π fsnt + αn) (2) n=0

and
∞
b(t)= ∑ Bn cos(2π fsnt + βn) (3) n=0

where An and Bn are the amplitudes of the nth harmonic and αn and βn are the phase. The shaft frequency is given by fs. For amplitude modulation, the sidebands represent scaled versions of the modulating function’s frequency spectrum.
The equation representing the vibration signal is ob-tained by modulating xper f ect with a(t) and b(t):
∞
x(t)= ∑ Pn(1 + an(t)) cos(2π fmnt + φn + bn(t)) + w(t) n=0

(4) Equation 4 demonstrates that detecting errors in the trans-mission system is possible by analyzing the sideband ac-tivity of the signal. For example, an eccentric shaft gives a slight change in center distance between gears every cy-cle. This manifests as a once-per-revolution .uctuation in mesh force producing an AM signal that results in side-bands spaced at the shaft frequency. Other contributors to amplitude modulation are tooth pro.le errors, tooth pitting, and spalling. In addition, the relative relationship between the gears and sensors also creates sidebands. The modula-tion can often be seen as a lobe pattern in the data associated with a planetary gear system.
　
直升机网 www.helicopter.cn
直升机翻译 www.aviation.cn
本文链接地址：Sun Gear Fault Detection on an OH-58C Helicopter Transmission(4)