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U.S. automakers’ team builds on Penn State University Drivetrain Center technology to eliminate ‘ghost’ noise from automotive transmission gears in pre-production research

SOUTHFIELD, Mich., Oct. 22, 2008 – Providing a solution to an identified problem is not always easy. So one can only imagine how difficult it can be when asked to fix a problem that virtually appears out of ‘nowhere,’ with no discernible source.

That was the challenge for a group of engineers from Chrysler LLC, Ford Motor Company and General Motors Corp., who recently discovered a technique to eliminate unknown source, or ‘ghost’ noise – which sounds like a high-pitched whistle – from the gears in pre-production automotive transmissions.

As part of the United States Council for Automotive Research LLC (USCAR) Transmission Working Group, a project team was assembled to work with the Pennsylvania State University Drivetrain Technology Center to develop the new technique.

The team uses a Gleason M&M analytical gear inspection machine to inspect the noisy gears. Then, by applying a newly updated computer program that predicts Kinematic Transmission Error, the researchers can analyze the gears and compare the results to measured noise data. The result is information that translates into specific manufacturing features related to given sound frequencies – and manufacturing ‘tweaks’ that can virtually eliminate annoying ‘ghost’ noise in automotive transmissions before they move into production.

“Solving gear noise issues early in the transmission development process with this computer tool is a significant accomplishment,” said Neil Anderson, lead researcher on the USCAR Transmission Working Group’s Gear Noise Prediction from Measured Surfaces Project Team and technical fellow at GM Powertrain. “This technique provides a powerful tool to analyze machined gear surfaces and find the cause of ghost tone noise.”

The collaboration between USCAR and Penn State began through GM’s knowledge of research conducted by Bill Mark, senior scientist and professor of acoustics at Penn State, and earlier software he developed under funding from the NIST (National Institute of Standards and Technology) Motor Vehicle Manufacturing Focused Advanced Technology Program.  

Mark perfected the methodology and developed a complete mathematical model to identify the source of gear ghost tones with incredible precision. This translated into research software, developed by Mark and his student, Cameron Reagor, which worked beautifully to identify the manufacturing error causing the noise.  A first-run test on a gear brought to Mark by GM yielded immediate success. Soon after, the USCAR project team began to work with Mark and Reagor to adapt and develop a user-friendly application of the precision software at Chrysler, Ford and General Motors.

“I am delighted to see this being used by our U.S. automotive industry,” said Mark. “For years, people didn’t understand at all what caused ghost tones. Now, we can determine what causes the unwanted tones to a degree of specificity as microscopic as the machined surface roughness pattern on a gear.”  

From a scientific point of view, this means that Mark’s software is predicting noise caused by long wavelength surface errors measured in fractional micrometers or micro-inches. Now, the gear noise project team is looking to further apply the research and software.

Founded in 1992, USCAR is the umbrella organization for collaborative research among Chrysler, Ford and General Motors. The goal of USCAR is to further strengthen the technology base of the domestic auto industry through cooperative research and development.


Oct. 22, 2008

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