Smaller engines, lightweighting, and even connectivity are a few of the trends that dominate the drive to reduce fuel consumption and emissions. Those developments are making life harder for those tasked with reducing NVH.
Even the growth of telematics and smartphone connections are working against design engineers. The NVH environment is rapidly evolving as consumers expect quieter cabins.
“Connectivity will continue to grow, and customers will demand hands-free devices at all price classes, which requires quiet cabins,” said Bernie Swanson Jr., Senior Manager, NVH, for Chrysler Group.
The sources of noise and vibration have changed significantly over the past decade, according to speakers on the “The New Art of Quiet—NVH Powertrain Advancements and the Future of Quiet” panel at SAE 2014 World Congress. Powertrain noise remains a key contributor, though traits have changed as smaller engines moved to the fore.
“Today, engine vibration is the largest factor,” said Mark Stickler, Powertrain NVH Manager, Ford. “In 2000, we spent most of our time on engine radiant noise. When you fast-forward to 2020, engine vibration will continue to dominate.”
While design teams look toward the future, they can also benefit from the past. For example, pendulums have been used to reduce noise and vibration since World War II, but they haven’t been efficient in cars until recently. Schaeffler deployed the concept in a dual mass flywheel to reduce vibration from downsized engines.
“You need to keep older ideas in mind; there may be a time when it’s effective to implement them,” said Jeff Hemphill, Chief Technology Officer of Schaeffler Group USA.
Panelists agreed that modeling and simulation are critical tools in all aspects of designing for noise reduction. Some of these tools are being developed in-house to augment commercial offerings. These tools let engineers try many alternatives and explore the impact of minor changes.
Many of these changes come from the frantic drive to reduce weight. Shaving a bit of metal in specific areas is among the tweaks that are being examined.
“You want to put the thickness of gauge where you need it to be and not put thickness where you don’t need it,” Swanson said.
He added that Chrysler is currently using glass fiber as a noise barrier. Other options such as polyurethane foam and acoustic windows can reduce noise, but they are expensive.
As factors such as noise generation and materials evolve, ownership of solutions is also changing. Components such as alternators that come from external suppliers are coming under closer scrutiny.
“NVH solutions are moving from being under OEM control to supplier control,” Stickler said. “We need to set parameters for suppliers up front.”
The infotainment systems that help make connectivity a factor can also be used to reduce noise. Noise cancellation is beginning to see some acceptance. Low-frequency sounds can be canceled in the cabin regardless of driver and passenger positions.
“We do project that noise cancellation will grow over time,” Stickler said. “Integrating acoustic noise cancellation is complex. You need the right audio system, and there are significant costs. You need to decide it’s part of the solution early on, you can’t tag it on at the end.”
Electronics can also be used to alter engine sounds. Sound enhancement is expected to grow as it becomes possible to make small three- or four-cylinder engines sound much larger.
“With sound enhancement, you can put in parameters to sound like a V8 or a Harley motorcycle,” Swanson said. “I can see a large market for that capability.”