A New Model for Studying Nonlinear Vibration Behaviors of Gear-Bearing System

A new model for nonlinear vibration behaviors of gear-bearing system is proposed in this work. For presenting the nonlinear excitation from bearing compliance, the enhanced bearing force excitation model containing two kinds of bearing stiffnesses, which are mean stiffness for the load transfer capacity and alternating stiffness for the disturbance resisting ability, is developed. Considering other dynamic excitations including mesh stiffness, contact pressure angle, center distance, unbalance force caused by static and dynamic eccentricity, an advanced iterative numerical method is introduced, which can timely and accurately update the excitations caused by load-dependent and time-varying nonlinearities inside of the system. The constant bearing stiffness and time-varying bearing alternating stiffness models are introduced and compared with the enhanced bearing excitation force model. The parametric resonant regions and system nonlinear periodic motion states are studied and compared for different bearing supporting models. The effects from internal and external excitations on the system nonlinear vibration behaviors are investigated.

Diagnostically Oriented Experiments and Modelling of Switched Reluctance Motor Dynamic Eccentricity

The article compares the results of experimental and modelling research of switched reluctance motor at two different operational states: one proper and one with mechanical fault, i.e., with dynamic eccentricity of the rotor. The experiments were carried out on a test bench and then the results were compared with mathematical modelling of quasi-static and dynamic analysis of 2D geometry model. Finally, it was examined how the operation with dynamic eccentricity fault of the motor affected its main physical parameter—the phase current. The analysis was presented in the frequency domain using the Fast Fourier Transform (FFT); however, individual current waveforms in the time domain are also shown for comparison. Applying results of the research could increase reliability of the maintenance of SRM and enhance its application in vehicles for special purposes as well as its military and industrial applications.

Eccentricity in Induction Machines—A Useful Tool for Assessing Its Level

In the condition monitoring of induction machines operating in various industry sectors, the assessment of eccentricity is as important as the assessment of the condition of windings, bearings, mechanical vibrations or noise. The reasons for the eccentricity can be various; for example, rotor imbalance, damage or wear of the bearings, improper alignment of the rotor and the load machine and finally, assembly errors after overhaul. Disregard of this phenomenon during routine tests may result in the development of vibrations transmitted to the stator windings, faster wear of the bearings and even, in extreme cases, rubbing of the rotor against the stator surface and damage to the windings and local overheating of the machine core. On the basis of years of experience in the diagnosis of large induction machines operating in various industries, the article deals with the problem of developing reliable indicators for assessing the levels of commonly accepted types of eccentricity. Starting from field calculations and analyzing various cases of eccentricity, the methodology for determining the indicators for evaluation from the stator current spectrum is shown. The changes in the values of these indices for various cases of simultaneous occurrence of static and dynamic eccentricity are shown. The calculation results were verified in the laboratory. Also shown are three interesting cases from diagnostic practice in the evaluation of high-power machines in the industry. It has been shown that the proposed indicators are useful and enable an accurate diagnosis of levels of eccentricity.