Car buyers and bureaucrats are demanding better fuel economy, so automakers are hellbent on squeezing every last MPG from a tank of gas. The byproduct of this is more fuel-sipping powertrains, but there’s an unintended consequence: more unwanted noise in the cabin.
“Things are happening with powertrains that are good for fuel efficiency, but not necessarily good for the noise character inside the vehicle’s cabin,” John Pelliccio, manager of Technical Product Marketing for Bose, told Wired. That’s why Ford, Honda and other automaker are bringing new noise-cancellation technology into their vehicles – and in particular, hybrids – with the help of companies like Bose, amajor supplier to the automotive industry.
Automatic noise cancellation (ANC) in cars is nothing new. Automakers have been using it for over a decade to deliver a quieter cabin for drivers, primarily in luxury vehicles. But the technology is getting a second life now that fuel efficiency reigns supreme and automakers are looking to shed extraneous pounds from vehicles. The latest application of ANC is showing up in an unlikely place: on normally quiet hybrids when their gasoline engines kick in.
With hybrids’ powertrains that switch between electric and gasoline power, and traditional engines that deactivate banks of cylinders to save fuel, keeping noise out of the passenger compartment has become more of a challenge for automakers, Pelliccio adds. “Those types of power trains can produce noises that are not part of the sound character that the OEMs want their vehicle to have,” he says.
“Customers will come to us, saying, ‘Every time we switch from the gas powertrain to the electrical powertrain we get a bump in the [frequency] response and we don’t want that bump to be there.’ Or, ‘Every time we shut off a bank of cylinders, the resulting imbalance in the firing order creates a thrum that we want to reduce.’”
Pelliccio adds that past methods to quiet a car typically required “pounds of noise deadening material” or other mechanical means, such as “pieces of metal hung on various parts of the undercarriage or exhaust system to quiet noises that pop up in the drive train.” But these also usually reduce fuel efficiency. “We’ve been working for a few years with OEMs to try and find a more elegant solution,” Pelliccio adds. “And we’ve found a way to use the speakers and amplifiers that are already in the vehicle to acoustically reduce or cancel the noises that are being generated by the drive train – without adding a lot of weight or mechanical complexity to the car.
The process is much like Bose’s noise-cancelling headphones: Signals are generated at the same frequencies as the offending sound, but 180 degrees out of phase. “We broadcast sound waves from the speakers that will acoustically cancel the sound waves being generated by the engine,” explains Pelliccio. “It’s important to point out that the system we use is not a broadband noise cancellation system, like with our headphones. We’re not going after things like wind noise and tire noise. What we’re going after is very specific frequencies that are generated by the powertrain that make their way into the cabin and detract from the driving experience.”
The new 2103 Ford Fusion Hybrid is an example of this precision-targeted ANC application – and how increasing fuel efficiency can sometimes increase noise. Dr. Takeshi Abe, a Henry Ford Technical Fellow for Noise, Vibration and Harshness, told Wired that the firing order of the Ford Fusion Hybrid’s four-cylinder engine creates an “excessive booming noise that’s very unpleasant. By eliminating this booming noise [with ANC],” he adds, “the engine engineers can focus on the fuel economy.”
In the Fusion Hybrid, “the system reacts in milliseconds,” Ford spokesman Craig Daitch told Wired. “ANC responds to a noise input before a human notices.” A trio of microphones mounted in the Fusion Hybrid’s headliner – a pair over the first seat and one over the rear – detect and measure engine noise and then send a signal to the ANC control module. The module generates sound waves that cancel the “booming” engine noise feeds it to the car’s audio system. “ANC is always active and not tied to entertainment function,” Daitch adds.
The new all-new Honda Accord Hybrid also uses ANC to quite the cabin, but the feature is available on every model, not just the gas-electric version coming in 2013. (Neither Ford or Honda whether Bose is supplying ANC technology for their cars.) “It’s on all the Accords, down to the lowest trim,” says Chris Martin, a Honda spokesperson. “It appears on models with the four-cylinder and the V6s.”
Martin points out that active noise control has been used by Honda in the past on cars with V6 engines with variable-cylinder management. The latest version is not so much related to fuel economy but, similar to the Ford system, is primarily intended to get rid of harshness at certain RPMs. “What our system does is improve the engine sound quality by making the sound pressure level more linear, instead of having a kind of warbling effect,” Martin adds. “It’s basically a smoothing in the range of between 1,000 and 2,000 RPMs. It lowers sound pressure level by about three decibels.”
With a renewed emphasis on fuel economy – and weight reduction – by all automakers, Honda’s Martin predicts we’ll see more use of it. “Everything is a compromise in car design,” he says. “ANC is a very clean way to deal with noise, and you’re taking advantage of technology that’s becoming more and more available.”
Via Autopia