A data processing method for noise measurements of snowmobiles and their sub-systems on test bench

Résumé

A new method for processing and analyzing noise data from a snowmobile on a test bench is proposed and applied to compare the sound levels of two different CVT models. Because of the important dependency of the noise to the engine speed, the signal is analyzed through a relatively simple algorithm so as to be automatically associated to the engine speed, resulting in comparable noise levels at the same mean speed for both CVT models. Two indicators calculated from the unbiased variance are provided by this method and allow to conclude on noise differences between different CVT models. Those indicators are the confidence intervals (using Student's law) and the significance of differences coefficient (SD-coefficient), the latter being introduced and detailed for the first time in this study. The method is applied to test bench measurements and compared to pass-by noise measurements. As time averaging does not give good results on test bench, particularly as engine speed control is difficult, hence this approach to data processing is necessary to obtain results comparable to a pass-by test. Even if the absolute values on test bench are not exactly the same as pass-by values, the use of the data processing method is advantageous for comparing several CVT models and making predictions on the CVT pass-by noise reduction. Thereby the proposed methodology saves time (test bench measurements are faster than setting up and executing pass-by tests) and avoids problems and discrepancies caused by environmental conditions (snow quality/quantity, wind, piloting).