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Machining techniques that reduce the amplitude of low-speed radial uniformity measurements and their effects on smooth-road vehicle vibrations were investigated. The methods ranged from simple concentric and eccentric truing suited for service work to a servo-controlled tire-wheel assembly measuring and corrective machine installed at an auto assembly plant. These methods produce significant reduction of the measured low-speed radial uniformity. Corresponding vehicle evaluation showed significant reduction of smooth-road shake-a 1 per wheel revolution vibration-but little change of higher order vibrations. The simplicity of eccentric truing, combined with its predictable reduction of shake, provides a service fix for smooth-road shake.

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.

Automotive rear axle gear noise is characterized by a tonal peak of several mph bandwidth, usually in the 40-70 mph speed range. A study of the mass-elastic system of rear axle gears predicts the existence of a nearly vertical resonance of the pinion, relative to its supports near the frequency of the observed noise peak. Experimental studies of a variety of rear axles confirm the existence of this vibration peak and its coincidence with the observed noise. The magnitude of the various orders of gear meshing quality resultant from eccentricities, wobble, heat-treatment distortion and higher harmonics can be assessed by monitoring the amplitude of this resonance at specified gear meshing frequencies.

Rear axle tapered roller bearing wear has been studied in bench and car tests, using both commercial and experimental gear lubricants. In bench tests, magnitude of wear was affected by both lubricant additive treatment and lubricant viscosity; increased wear resulted from reduction in viscosity with lead soap-active sulfur and Pb-S-Cl lubricants but not with P-S and Zn-P-S-Cl lubricants. Substantial decreases in wear from one bearing lot to subsequent lots apparently resulted from mechanical improvement in the bearing manufacturing technique. These wear decreases, for a given bearing speed and load combination, were accompanied by decreased temperature and thickness of roller-end surface film formed from the lubricants. In rear axle car tests run as far as 94,000 miles, P-S additive package blends having viscosities as low as 4 cs at 210 F performed satisfactorily, although bearing wear was somewhat greater than that with P-S blends having viscosities of 9 cs at 210 F.