Reduction of Gearbox noise by optimizing Gear micro geometry

Vehicle noise level has to be maintained within the limit specified by Pass By Noise (PBN) standards to meet the regulatory requirements. Gearboxes and engines are the main sources of noise in a vehicle, owing to the mechanical and physical processes involved. The noise problem in transmission system is characterized by high amplitude acoustic signals, and the gear mesh noise can be indirectly estimated using the Transmission error parameter. Transmission error is defined as the difference between the actual position of the output gear and the position it would occupy if the gear drive were perfect, which can be attributed to various factors such as tooth profile errors, misalignment, and tooth deflections. A six-speed manual transmission commercial vehicle is observed to exhibit higher noise levels during the vehicle PBN test. The gearbox is modelled in Romax gearbox simulation software and the transmission error value is identified to be high. The micro geometry parameters lead crowning, lead slope, tip relief, and profile barreling of the gear pair is studied in Romax and optimized using design of experiments, resulting in a considerable reduction in Transmission Error from 10.27 µm to 2.98 µm. An improved gearbox with the modified gear pair is assembled and the fitted vehicle is tested for the noise levels for validating the improvement. A significant reduction of 2 dB is observed in the vehicle noise compared to the baseline value obtained during initial PBN test. This improvement ensures the vehicle noise level to fall below the PBN regulatory requirement, essentially eliminating the need for an additional noise shield for the gearbox.