“Noise you can measure, and vibrations you can measure,” a veteran GM powertrain engineer says. “But how do you measure harshness?”
Ed Groff among GM engineers now using “N&V” term.
SOUTH HAVEN, MI – The vernacular among automotive powertrain engineers appears to be evolving, at least at, where one component of “noise, vibration and harshness” has gone the way of leaded fuel and the carburetor.
For the past year or so, GM engineers have been referring to “N&V,” for noise and vibration.
“The harshness got dropped off in GM lingo because it’s too subjective, and noise and vibration are directly measurable,” Ed Groff, GM Powertrain assistant chief engineer, tells WardsAuto at a media drive event here.
Today’s advanced electronics enable diagnostic tools that can identify and analyze every pleasant and unpleasant sound an engine makes, as well as any unwanted vibrations.
“Noise you can measure, and sound pressure levels and vibrations you can measure,” says Groff, a 35-year engineering veteran. “But how do you measure harshness?”
The initial term, NVH, dates to the earliest days of automotive development, when engines were loud and coarse. NVH became a catch-all phrase that guided auto makers as they refined vehicles from generation to generation.
The harshness component has been an elusive element that requires subjective impressions as a study of “psychoacoustics.” That inability to mathematically quantify the specific qualities of harshness left GM engineers frustrated, Groff says.
With regard to engine development, he describes harshness as sound quality.
“You step on the gas and there’s a sound that you don’t like,” he says. “It’s not necessarily loud or a vibration, but it’s got a bad pitch or tone to it.”
GM engineers now consider tones under the heading of noise, which means harshness is not being overlooked but reclassified.
“Tones you can measure with frequency analysis,” Groff says. “We do a lot of work to eliminate tones.”
That process begins when an engineer returns from a test drive and says simply, “I hear a whine.” The driver gives a detailed account of the conditions at the time, including vehicle speed, grade and ambient temperature, and engineers then set out to replicate the event.
“We can go out with instrumentation and record it and analyze it,” Groff says. “And then we can say, “Aha, it’s coming out of our oil pan or out of our front (engine) cover.’ Then we can go in and stiffen it or do something else to fix it.”
At least one competitor disagrees with GM’s willingness to ditch the word harshness.North America still uses the term NVH, and Carla Bailo, Nissan North America’s senior vice president-research and development, sees no reason to change.
“Harshness is what the customer feels,” Bailo tells WardsAuto. “Some things you just can’t measure. We have a lot of targets that are purely subjective. We make sure we have the right people with the right skillset who can do that properly.”
Bailo came up through the engineering ranks and is intimately familiar with NVH, having worked as a vehicle performance development manager.
“People always said I had a calibrated rear end because I could feel everything, any slight vibration, any issue,” Bailo says. “And I also have really good ears, so I could hear any noise or switch or anything.”
Customers can be amazingly perceptive in detecting unwanted sounds and vibrations, which means auto makers must sweat the details.
“Some things won’t be on your radar screen from a hertz standpoint or a decibel level,” Bailo says. “But it will happen at a time when maybe the radio is off, the car’s really quiet, it’s early morning, and suddenly the customer hears something from the HVAC. Each vehicle has its own personality.”