The present competitive market scenario and customer requirements demand for improved NVH quality and to meet statutory norms without increased cost. When gears are used for power transmission, gear noise is of particular concern. The noise may be created due to harmonics of the rotating and meshing internal components. This has a significant effect on the overall vehicle sound quality. Various factors contribute to gearbox noise. Some of them include shaft misalignments, gear geometry, lubrication, bearings and loose mountings. Hence it is essential to study which factors contribute to the gearbox noise and to develop countermeasures for the same. Although a number of factors may contribute to gear noise as mentioned, the scope of this paper is limited to the effect of gear geometry alone on the gearbox noise.
This paper offers an experimental investigation of reducing the noise levels in Ashok Leyland gearbox by modifying the gear tooth profile on one of the gear trains in order to meet the futuristic noise statutory norms. The modification includes controlling the tip relief and introduction of lead-profile charts in the existing spur gear train as well as converting the existing spur gear train to helical gear train. The three gearboxes are tested on the vehicle and the same are validated in an acoustic enclosure and sound pressure levels at different dynamometer speed and torque are mapped. It is seen that by controlling the tip relief and introduction of lead-profile charts in the standard spur gear train leads to a reduction of around 3-3.5 dB in sound pressure level, whereas converting the same to helical gear train leads to an overall reduction of around 6-6.5dB in the sound pressure level.
