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Vehicle noise emission requirements are becoming more stringent each passing year. Pass-by noise requirement for passenger vehicles is now 74 dB (A) in some parts of the world. The common focus areas for noise treatment in the vehicle are primarily on three sub-systems i.e., engine compartment, exhaust systems and power train systems. Down- sizing and down- speeding of engines, without compromising on power output, has meant use of boosting technologies that have produced challenges in order to design low-noise intake systems which minimize losses and also meet today’s vehicle emission regulations. In a boosted system, there are a variety of potential noise sources in the intake system. Thus an understanding of the noise source strength in each component of the intake system is needed. One such boosting system consists of Turbo-Super configuration with various components, including an air box, supercharger, an outlet manifold, and an intercooler.

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.

Extensive experimental and numerical investigations were done to improve the vibration and acoustic performance due to excitation at the timing gears of automotive supercharger. Gear excitation, system response, and covers have been studied to find the most cost efficient method for reducing gear whine noise. Initially, gear excitation was studied where it was found that transmission error due to profile quality was the dominant source parameter for gear whine noise. To investigate the system effects on gear noise, a parametric study was carried using FEM model of the supercharger, with special interests in optimizing dynamic characteristics of internal components and the coupling to supercharger housing. The BEM model of the corresponding supercharger was built to predict the noise improvement after dynamic optimization of the system. Good correlations were observed between experimental and numerical results in both dynamic and acoustic parameters.

Supercharger timing gears have been a source of rattle noise due to torsional vibration from the engine and sometimes have required torsional isolators to reduce the rattle noise significantly. Supercharger gear rattle is studied analytically and experimentally in this paper in order to understand to what extent basic design parameters could impact gear rattle noise to eliminate the need for isolators. A 3 DOF (degree of freedom) discrete model is used to represent a geared rotor system in the supercharger. A mathematical dynamic model is established in Matlab handling the non-linearity due to gear backlash. The fluctuation of input torque is used as source of excitation. A real time simulation technique is used for the analysis. Good correlation has been obtained between the experimental and analytical results. An index for comparing analytical results to gear noise and vibration level has been proposed.

The spur timing gears in Eaton superchargers operate at low torque loads and the supercharger system is especially sensitive to gear whine noise created by minute differences in the spur gear tooth profile quality. This has necessitated the grinding of very high quality profiles on high-contact-ratio spur gears. The manufacturing operation has used subjective evaluation of profile and lead measurements to qualify grinder diamonds and audit gear quality related to noise. They have also relied on supercharger end-of-line-testers to provide a direct measurement of gear noise as the primary quality feedback to the gear manufacturing process. Since the difference in the inspection plots of very high quality profiles is difficult to determine subjectively, the inspection process assessments have been difficult to correlate to the resultant gear noise measurements.

A simulation methodology for dynamic modeling of geared rotor systems such as superchargers was used for determining the housing vibration response. The approach provides an ability to make quick parametric design modifications to the model for evaluation of relative noise response with the assumption that the averaged housing vibration level correlates approximately to the noise radiating from the surface. The housing in some cases was modeled as a lumped mass representation for efficiency, and when higher accuracy of housing modes was needed, a detailed flexible Finite Element Analysis (FEA) representation was used. The interesting features of the methodology were the use of constraint equations to model the gear mesh response per unit Transmission Error (TE) input, along with summarizing the component kinetic and strain energy for each mode and the mesh compliance for fast evaluation of opportunities for noise reduction.