Affiliations: Dynamics of Mechanical Systems Research Unit, National
School of Engineers of Sfax, University of Sfax, Sfax, Tunisia | Diagnostics and Vibro-Acoustic Laboratory, Wroclaw
University of Technology, Poland
Note: [] Corresponding author: Fakher Chaari, Dynamics of Mechanical
Systems Research Unit, National School of Engineers of Sfax, University of
Sfax, BP 1173-3038, Sfax, Tunisia. Tel.: +216 98637156; Fax: +216 74 275595;
E-mail: fakher.chaari@gmail.com
Abstract: Gearboxes usually run under fluctuating load conditions during
service, however most of papers available in the literature describe models of
gearboxes under stationary load conditions. Main task of published papers is
fault modeling for their detection. Considering real situation from industry,
the assumption of stationarity of load conditions cannot be longer kept.
Vibration signals issued from monitoring in maintenance operations differ from
mentioned models (due to load non-stationarity) and may be difficult to analyze
which lead to erroneous diagnosis of the system. The objective of this paper is
to study the influence of time varying load conditions on a gearbox dynamic
behavior. To investigate this, a simple spur gear system without defects is
modeled. It is subjected to a time varying load. The speed-torque
characteristic of the driving motor is considered. The load variation induces
speed variation, which causes a variation in the gearmesh stiffness period.
Computer simulation shows deep amplitude modulations with sidebands that don't
differ from those obtained when there is a defective tooth. In order to put in
evidence the time varying load effects, Short Time Fourier Transform and then
Smoothed Wigner-Ville distribution are used. Results show that the last one is
well suited for the studied case. The experimental validation presented at the end of the paper
confirms the obtained results. Such results offer useful information when
diagnosing gear transmissions by avoiding confusing conclusions from vibration
signals.
Keywords: Gear transmission, varying load, gearmesh stiffness, amplitude modulation, frequency modulation, time frequency analysis
