How Do You Keep Fuel Economy Quiet?

Edward Niedermeyer
by Edward Niedermeyer
how do you keep fuel economy quiet

A GM NVH engineer brags:

[GMC] Terrain measured quieter than the Honda CR-V and Toyota RAV4 in our on-road interior noise tests. At 70 miles per hour, Terrain’s interior is quiet enough to allow conversation in normal tones of voice.

How did they manage that? Hours of engine tuning, right? Wrong.

When GM engineers set out to deliver segment-leading fuel economy on Terrain they chose to lower the 6-speed transmission’s gear shift points to enable the Ecotec 2.4L four-cylinder engine to run at lower rpm torque. In this “Eco” mode, which the driver can activate with a click of a button on the console, the torque converter clutch engages at lower engine speeds to help save gas. While the engineering action improved fuel efficiency by up to one mpg, it also created an objectionable low-end frequency boom. To counteract that boom the engineers turned to active noise cancellation technology.

Terrain’s noise cancellation system relies on two microphones embedded in the headliner to detect the hum and prompt an onboard frequency generator to create counteracting sound waves through the audio system’s speakers and sub-woofer. The system also reduces higher rpm engine noise at highway cruising speeds to help keep the vehicle interior quiet.

OK, that solution may not satisfy our desire to imagine engineers slaving over the details of engine tuning, but hey, it’s a solution. Too bad GM’s Theta CUVs have yet to live up to their MPG ratings in real-world testing.

Join the conversation
4 of 31 comments
  • Bridge2farr Bridge2farr on Feb 28, 2011

    I've seen noise cancellation in the Ecotec motors for at least the past 6 years. Hardly anything new from GM as they have had this technology in place for some time now.

  • Jerseydevil Jerseydevil on Feb 28, 2011

    I wonder how it works? One of the things that I like about my DTS is how wonderfully quiet it is. Both inside and outside noises are almost not there, its awesome. I wonder if these technologies can quiet down my Golf, which is way more fun, but way more noisy.

  • Accs Accs on Feb 28, 2011

    Ya could just put some sound deadening under the hood, thicker / laminated glass... Wouldn't know the difference. On the other hand.. If the motor doesnt sound right... well people in these damn things wouldnt know any better anyway.

  • Carve Carve on Feb 28, 2011

    It's about time. This technique has great potential to reduce vehicle weight. Sound deadener, insulation, thick glass, etc. all weigh a lot, and can be thinned out with active cancelation.