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In a traditional NVH development process, the realization of the targeted vehicle acceleration sound quality can be a highly laborious and costly process involving the creation and evaluation of multiple iterations of prototype parts. Consequently, development engineers are limited by long prototype part fabrication times while key product decision makers have to often accept the “in-process” sound quality due to aggressive program timing milestones and escalating program costs. The NVH simulator provides an alternative approach that is potentially more efficient in terms of reducing program timing, reducing development and prototype costs and improving the end-product sound quality. This paper presents the case of a V6 vehicle under development whose acceleration sound quality needed improvement. The NVH simulator was used to determine the key contributors that lead to the sound quality of the targeted vehicle.

In recent years, Continuously Variable Transmissions (CVTs) have made significant inroads into passenger cars because of advantages over traditional Automatic Transmissions (ATs) such as improved efficiency, reduced weight and smoother operation. However, from an acceleration sound quality perspective, drivers generally seem to prefer the AT sound over the CVT sound, especially in sub-compact/compact vehicle segment with small displacement engines and cost-conscious sound packaging. Vehicles equipped with ATs maintain a linear relationship between vehicle speed and engine RPM during wide-open throttle (WOT) acceleration that is dictated by fixed gear ratios. Vehicles with CVTs typically rise rapidly to a high engine RPM (near peak engine torque) and then dwell at a constant engine RPM as the vehicle speed continues to increase by varying CVT pulley ratios.

The fuel economy benefits of Continuously Variable Transmission (CVT) technology have led to a steady growth in their adoption since the 1990's that is likely to continue despite the competition from Dual Clutch Transmission (DCT) & Automated Manual Transmission (AMT) technology. Even though CVTs provide a smoother driving experience due to their “shift-free” operation, general market feedback indicates some level of consumer dissatisfaction in the area of acceleration sound quality. This is particularly evident in the sub-compact and compact vehicle segments that feature small four cylinder engines with cost/weight limited sound packaging. The dissatisfaction with the acceleration sound quality is primarily linked to the non-linear relationship between engine RPM and vehicle speed that is inherent to CVTs and is often referred to as “rubber-band” feel.