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GMC Terrain uses active noise cancellation to improve gas mileage

Who knew there was a connection between noise and gas mileage? Obviously there is, because the GMC Terrain uses active-noise cancellation to help deliver a segment-leading EPA-rated 32 mpg in highway driving, as well as one of the most quiet interiors in its segment.

The GMC Terrain uses the same technology that makes high-end noise-cancelling headphones coveted by frequent flyers and iPod audiophiles.

Active noise cancellation (ANC) in the case of the GMC Terrain does double duty: One, it creates one of the quietest interiors in its segment; two, it covers up noise from the lower rpm shift points.

“The use of active noise cancellation for fuel economy benefit on Terrain is among the first at GM,” said Paul Beaker, program engineering manager for GMC Terrain via the news release. “It has strong potential for implementation on other four-cylinder vehicle programs.”

On the highway, Terrain’s 32-mpg easily tops the 28-mpg rating of Honda CR-V, Toyota RAV4 and Ford Escape.

Behind the Technology

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. This is called “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.

By working on clay models in GM’s state-of-the-art wind tunnel, the engineers were also able to reduce its wind noise to ensure quiet driving. In this manner, program engineers even improved Terrain’s highway fuel economy up to one mpg by reducing aerodynamic drag through the refinement of the front air dam, rocker panel, roof line, outside rear view mirrors and front bumper.

Other Key Vehicle Management Areas

GM engineers also worked closely with tire suppliers to develop low-rolling resistance tires, which typically require less effort to roll forward and minimize wasted energy. Terrain’s tires, unlike some low drag tires, was designed to provide good grip on snow and wet pavement while improving fuel economy by more than 1 mpg.

The use of direct injection and variable valve timing more directly help maximize Terrain’s fuel efficiency. In a direct injection engine, fuel is fed straight to the engine's combustion chamber, allowing it to burn more evenly and thoroughly. For the driver, that can translate to better mileage and greater power to the wheels.

Variable valve timing eliminates the compromise inherent in conventional fixed valve timing and allows a previously unattainable mix of low-rpm torque – even torque delivery over a broad range of engine speeds – and free-breathing, high-rpm horsepower. Variable valve timing literally allows the engine to take advantage of late intake valve closing for greater efficiency.

“Whether we’re lowering gear shift points, reducing wind drag or eliminating engine-driven power steering pumps, it takes laser-like focus on every detail to deliver segment leading fuel economy to our customers,” said Dave Poniatowski, product marketing manager for Terrain.

For the record, the Terrain recently earned “Best Buy” recommendations from both Consumer Guide and Consumer Digest.

About the Author: After 39 years in the auto industry as a design engineer, Frank Sherosky now trades stocks and writes articles, books and ebooks via, but may be contacted here by email: [email protected]

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