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This paper describes the results of a study carried out in Renault about the effects of variation of flywheel bending stiffness on powertrain vibrations in the range of acceleration noise (250 Hz and 500 Hz octave bands). The flywheels used covered a wide range of stiffness, from a standard rigid flywheel to a very flexible one. On the one hand, NVH tests have been carried out on a Diesel common rail injection engine with 4 flywheels of different bending stiffness, from a rigid flywheel to a flexible one. On the other hand, simulations have been carried out by Excite on a whole Diesel powertrain model. Both test and calculation results have shown that the vibrations at powertrain mounting points in the 250 Hz octave band decrease continuously with the reduction of flywheel bending stiffness, and there is a nearly linear relationship between the vibration amplitudes and the first bending frequency of the cranktrain.

The recent use of electric motors for vehicle propulsion has stimulated the development of numerical methodologies to predict their noise and vibration behavior. These simulations generally use models based on an ideal electric motor. But sometimes acceleration and noise measurements on electric motors show unexpected harmonics that can generate acoustic issues. These harmonics are mainly due to the deviation of the manufactured parts from the nominal dimensions of the ideal machine. The rotor eccentricities are one of these deviations with an impact on acoustics of electric motors. Thus, the measurement of the rotor eccentricity becomes relevant to understand the phenomenon, quantify the deviation and then to use this data as an input in the numerical models. An innovative measurement method of rotor eccentricities using fiber optic displacement sensors is proposed.