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GM uses active noise cancellation technology to improve fuel economy

By

September 14, 2011

The 2011 Chevy Equinox comes with active noise cancelation technology to combat the noise ...

The 2011 Chevy Equinox comes with active noise cancelation technology to combat the noise of its engine

Charged with the task of getting the fuel economy of the 2011 Chevy Equinox down to 32 mpg on the highway and beat out the 28 mpg-rated Honda CR-V, Toyota RAV4 and Ford Escape, GM engineers employed some rather unconventional fuel efficiency technology - active noise cancellation (ANC). By using the same technique used in noise cancelling headphones, the team was able to let the Equinox's engine run at a more fuel efficient rpm without the associated low frequency noise and achieve what GM claims is segment-leading fuel economy.

Noise and vibration engineer at GM, Jim Valance, points out that most car engines typically idle at under 1,000 rpm and operate at over 1,500 rpm when in gear. In between that rpm range the engine is more fuel-efficient but produces a lot of vibration and low frequency noise.

"There's a boom, or very low frequency rumble that comes from the engine when it runs in that rpm range," said Vallance. "We knew if we could deaden those booms, we could run the engine at the lower rpm, which would provide a significant boost to fuel economy. So we started kicking around ideas and came up with noise cancellation like you see in some high-end stereo headphones."

The system Vallance and his team up with consists of an ANC module that kicks in when the engine is running in the 1,000 to 1,500 rpm range. Two microphones in the vehicle interior measure the amplitude and the phase of the engine noise sound waves and relay this information to the ANC module. To ensure it targets only the unwanted engine noise and not other noise inside the cabin, such as the stereo or passenger conversations, the module also takes into account the engine speed to calculate the target frequency that needs to be cancelled.

"We take a proactive approach and target only the unwanted sound in the vehicle, which in this case is linked with the engine firing frequency," says Vallance.

The ANC module then uses this information to generate a sound wave that has the same amplitude as the engine noise but with inverted phase. This inverted sound wave is directed through the speakers in the vehicle's front doors and the subwoofer in the rear so it combines with the original engine sound wave and the two cancel each other out.

GM provides the ANC system as standard on the 4-cylinder Equinox but it isn't the first time we've seen ANC technology employed in a car. Toyota used the same technique to reduce the interior engine noise of its Toyota Crown Hybrid when it was discovered that its engine, which also ran at a lower rotational frequency, was noisier than expected.

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
12 Comments

OK so they can cancel out the noise...but what about the vibration?

While clearly every engine model is different, I always thought that petrol engines reached maximum efficiency at higher revs (e.g. 4000 rpm) and diesel engines somewhat lower (perhaps 2500 rpm) so I must admit this article has confused me a little. Of course, that may be down to my ignorance. My own driving involves very little time between 700 and 1500 rpm. One is usually accelerating or decelerating through this range.

I should be happy if some expert wants to 'put me right' on this matter.

Alien
14th September, 2011 @ 07:00 am PDT

So we started kicking around ideas and came up with noise cancellation like you see in some high-end stereo headphones."

Or what Honda has been doing for years on their 6 cylinder deactivation Oddessy van. GM acts like they were the first to do this, but copied Honda.

Joseph J Shimandle
14th September, 2011 @ 11:19 am PDT

Comparing a 2 wheel drive vehicle (AWD is an option) and 4 wheel drive vehicles is clever marketing but only that. In general driving of the type most people will do the Ford Escape hybrid is going to provide the best fuel economy for an AWD vehicle. The lowest overall cost of ownership is the 27mpg highway $20,995 Subaru Forester which with AWD is $3,750 cheaper to buy than the $24,745 Equinox. $3,750 will buy the Subaru owner 1000 gallons of gas and that is enough to take them 27,000 miles.

Based on my own experience with two GM produced SUV vehicles I would expect the Subaru to be less likely to need repairs during its useful life than the Equinox as well.

Calson
14th September, 2011 @ 11:24 am PDT

There is a basic construct here that is missing. 32mpg US is about 7.8l/100k. For a 4 cylinder AWD that's lousy. Using noise canceling technology means they can't get their basic design right in the first place.

Drsoar
14th September, 2011 @ 02:28 pm PDT

how on earth an active noise cancellation could contribute to fuel economy ?

Ilkin Alxasli
14th September, 2011 @ 03:27 pm PDT

Why not use an electric motor ? They seem to be noise-deficient if one listens to the latest talk around electric vehicles and safety !

icykel
14th September, 2011 @ 05:35 pm PDT

noise cancellation like that (using the vehicle speakers) will set up nodes and antinodes. So it will be quieter in some places in the car, and louder in others.

Unless you can put the cancelling signal at the same physical location as the source, you're always going to get spatial interference patterns.

Maybe the frequency is so low (wavelength so long) that this doesn't really matter. It might just be twice as loud for people you pass on the street.

Why not just fix the engine so it doesn't make so much noise in the first place?

Adrien
14th September, 2011 @ 06:16 pm PDT

They're saying the ANC improves economy because it will allow them to run the engine at 1000-1500 rpm, which they're saying is a very efficient range for fuel milage. Sounds too low to me, too, Alien. They'd have to choose some new gear ratios for the trans and/or the rear to get those rpms in play.

Vibration is probably already taken care of. Back 20 years or so (I guess) when Oldsmobile built the Aurora and marketed it as a step forward in luxury cars, or some such fanfare, I remember that one of the things they learned from studying Mercedes was that their chassis had a frequency of 25000kHz, which is beyond our human range. Which means - when it hit a bump, or even just rolling down the highway, the car wasn't pummeling you with a constant vibration background noise which, even though you'd get used to it, would still tire you out and irritate you. They built the Auroras to that new spec, and as I remember it was a first for the Big Three at the time. But I imagine that by now the noise and vibration guys have the low frequencies taken care of...I think our hearing runs out around 15-16000kHz, so they probably get close to that even on the less expensive cars. OK, I *hope* they have by now. I'm an optomist.

FastGuy
15th September, 2011 @ 12:59 am PDT

GM has a good approach. Lower engine RPM is possible even with existing gear ratios simply by requiring the automatic transmission to upshift earlier than now. How well GM has implemented the concept relies on their engineering skills. I agree that vibration cna be an issue. Engine mounts can be had in computer controlled hydraulic and GM's Magna-Matic form if that is required to absorb vibration.

Marvin McConoughey
15th September, 2011 @ 07:41 am PDT

Yeah, it's possible...good one.

So every time you go 0-30mph the transmission runs through all 4 or 5 or 7 gears, whatever you have. That would be pleasent.

FastGuy
17th September, 2011 @ 01:49 pm PDT

@alien

You are confusing power output and torque with efficiency. Most engines reach maximum horsepower at close to maximum RPM. It drops off quickly after attaining that maximum. Torque has a broader, flatter curve.

Efficiency of a car engine has a lot to do with gearing on the particular vehicle it is installed in, as well as wind and rolling tire resistance at a particular velocity. It is expressed strictly by distance covered vs fuel consumption. Unlike horsepower and torque, you cannot separate the engine from the vehicle to determine the efficiency of an engine installed in a particular vehicle. As the article states, the maximum efficiency is achieved at much lower engine speeds than maximum power and torque.

Facebook User
26th October, 2011 @ 05:55 pm PDT

I'm not a sound engineer, but do have the Equinox (2011). Around 1700 rpm, their is a loud boom that appears to come through the speaker system even it the stereo is off or not. It only started after 8 months and is very anoying. The dealer says that they are waiting on a software update that they have no time frame for from GM. Does this make sense? The way this vehicle is geared, you can be doing 55 and taching 1700-1800 and the boom is quite loud.

Jesse Huddleston
31st October, 2011 @ 12:00 pm PDT
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