Gear Design for Low Whine Noise in a Supercharger Application

Supercharger gear whine noise has been a NVH concern for many years, especially around idle rpm. The engine masking noise is very low at idle and the supercharger is sensitive to transmitted gear whine noise from the timing gears. The low loads and desire to use spur gears for ease in timing the rotors have caused the need to make very accurate profiles for minimizing gear whine noise. Over the past several years there has been an effort to better understand gear whine noise source and transmission path. Based on understanding the shaft bending mode frequencies and better gear design optimization tools, the gear design was modified to increase the number of teeth in order to move out of the frequency range of the shaft bending modes at idle speed and to lower the transmission error of the gear design through optimization using the RMC (Run Many Cases) software from the OSU gear laboratory. RMC is a design tool that allows the user to investigate a wide design space involving all the gear design parameters to optimize the design for the features desired, such as low bending stress, contact stress, low noise, etc. New gear designs greatly increase the contact ratio for spur gearing with minimal increase tooth bending stresses and a nominal decrease in contact stress. A procedure for developing new gear designs has been developed and is being implemented for new supercharger designs.