Acceleration Sound Preference from a CVT Perspective

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.

For this paper, a NVH driving simulator was employed to create several acceleration sounds with varying engine RPM versus vehicle speed characteristics. These sounds included conventional and modified CVT ramp ups as well as simulated Automatic Transmission (A/T) type shifts. Jury evaluations were conducted on the NVH driving simulator using a large sample of random participants from the general driving population in mid-west USA. The jurors rated the sounds on a semantic difference scale. Even though the jury rated the CVT sounds as smoother & quieter, they showed a clear preference for the AT-like shift sounds during hard acceleration over the conventional CVT sound. The AT-type shift sounds were perceived to be faster, stronger and more exciting than the CVT sounds. The study concluded that in order to gain better customer satisfaction from CVTs, it is necessary to employ some form of simulated shift patterns during the acceleration scenes. Linearizing the CVT ramp also provides a clear improvement in customer acceptance. The study also identified differences in acceleration sound preference for several groups of jurors based on gender, age and type of transmission driven.