For many years axle plants have needed a practical testing method for rating the noise quality of rear axle assemblies before installation in cars. This report describes the development of such a test method. Creation of noise requires an energy source. The energy source of rear axle noise is the periodic variation in tooth meshing action of the gears. The frequency of axle noise is always related to tooth mesh frequency. A previous study of rear axle gear dynamics indicated the existence of a nearly vertical resonance of rear axle pinions excited by tooth meshing action. The dynamic resonant amplitude of the motion of the pinions related directly to the in-car noise quality of the gear sets.
In general, other resonances within the drive line-axle housing-suspension system can be excited by gear action and produce “axle” noise. An indication of the amplitude of the resonant member (or another responsive member within the system) directly relates to the relative noise quality of the gear set. To verify this relationship, the dynamic pinion response of a group of 30 axle assemblies was measured. The in-car noise ratings were obtained by using a jury of three experienced raters. The correlation between the dynamic pinion motion measured in a test stand and the in-car noise ratings was found to be very good, indicating the feasibility of using this method in axle plants. A statistical analysis was made of the data to determine the degree of correlation and the validity of the data. Details of the test stand operation, noise rating method and tests results are included in the report.