August 3, 2001
Engineers 'tread' toward quieter tires
WEST LAFAYETTE, Ind. Engineers have developed a new technique for analyzing tire vibrations by creating a "fingerprint " that identifies which features produce the most noise, a step toward designing quieter tires and reducing the dominant source of highway noise.
"Most of the environmental noise nuisance from interstate highways is tire noise," said Stuart Bolton, a professor of mechanical engineering at Purdue University. "If you are anywhere near an interstate, much of the noise that you hear is generated by the tire-road interaction, with the exception of some noise from heavy trucks. "
A tire's tread contains block shapes that smack against the road surface like tiny hammers. Those tread blocks and underlying reinforcing belts vibrate and radiate energy outward, producing sound much like the vibrating cones in stereo speakers. Different portions of the tire vibrate faster than other portions, producing more noise.
Bolton and graduate student Yong-Joe Kim are using a mathematical model to identify which parts of a tire produce the most noise. The vibrations are characterized on a graph, a visual representation that's like a fingerprint of each tire's vibration pattern.
"We've introduced a way of experimentally looking at tire vibration in a way that identifies components that can generate the most sound," said Bolton, who wrote a research paper with Kim that describes the work. The paper will be presented Aug. 27, during the 30th International Congress and Exhibition on Noise Control Engineering in The Hague, Netherlands. The conference, also known as Internoise 2001, is organized by the Acoustical Society of the Netherlands, and the International Institute of Noise Control Engineering.
The work by Bolton and Kim represents an attempt to relate specifically how a tire's design, and its associated vibrations, produce noise.
"We created this numerical model that we can pretend is a tire, giving it the properties of a tire and running a 'test' in the computer as if we were doing a real experiment," Bolton said. "This illustrates the fact that you can predict the vibration and noise differences related to various design features.
"It's a new approach to looking at tire vibration."
Tire noise and vibration are both a nuisance and a consumer issue because they account for much of the unwanted noise heard inside a car, as well as outside, Bolton said.
The engineers measure various vibrational waves that travel along a tire's treadband, which is the outer segment of a tire that includes reinforcing belts and the tread pattern that meets the road's surface. Specific vibrations are assigned "wave numbers," and those numbers are then used to create graphs that illustrate which vibrations are coming from which portions of the tire and which vibrations are likely to produce the most noise.
"I won't claim to have totally succeeded in that," Bolton said. "This is the first attempt to form some simple theoretical models."
The analytical model represents the treadband as a flat belt connected at both ends to form a circle. However, to be more accurate, the entire tire not only the treadband should be modeled in a three-dimensional cross section, Bolton said.
"We are working to make the model much more tire-like," he said, noting that engineers will use findings from such models to help design quieter tires.
The work is being conducted at Purdue's Institute for Safe, Quiet and Durable Highways as part of a contract supported by the U.S. Department of Transportation, Ford Motor Co., and tire manufacturers Michelin Tire Corp., Continental General Tire Inc., Goodyear Tire & Rubber Co., and Hankook Tire Co. Ltd.
Bolton said the modeling work is based partly on ideas from graduate students who completed a project in 1995 as part of a class he teaches.
Source: Stuart Bolton, (765) 494-2139, firstname.lastname@example.org
Writer: Emil Venere, (765) 494-4709, email@example.com
Other source: Bob Bernhard, (765) 494-2141, firstname.lastname@example.org
Purdue News Service: (765) 494-2096; email@example.com
With the help of a mathematical model, engineers created these graphs, which are visual representations, much like a "fingerprint," of a tire's distinctive vibration pattern. The engineers measure various vibrational waves that travel along a tire's treadband, which is the outer segment of a tire that includes reinforcing belts and the tread pattern that meets the road's surface. Specific vibrations are assigned "wave numbers," and those numbers are then used to create graphs that illustrate which vibrations are coming from which portions of the tire and which vibrations are likely to produce the most noise. The graph on the left shows specifically which parts of the tire are producing the most intense vibrations. Those data are then used to create the "fingerprint" on the right. Because highway noise is largely caused by tires, tire manufacturers are trying to design quieter tires. Findings from such research will likely enable industry to reduce highway noise in the future. (Image from Stuart Bolton, Purdue University School of Mechanical Engineering.) A publication-quality photograph is available at the News Service Web site and at the ftp site. Photo ID: Bolton.tires
Modeling Tire Treadband Vibration
Yong-Joe Kim and Stuart Bolton, Ray W. Herrick Laboratories, School of Mechanical Engineering, Purdue University
It has been shown previously that a wave number decomposition of the radial vibration of a tire reveals the propagation characteristics of the waves that contribute to the tire's dynamic response. To help understand these experimental results in detail, here the tire treadband was modeled as a ring-like, circular cylindrical shell with air pressure acting on its interior surface; the effect of the sidewalls was modeled using a distribution of springs and dampers. The shell model was able to reproduce the waveguide modes that dominate the experimental results. In particular, relatively slow, predominantly flexural wave modes were identified, as were fast, in-plane waves that are potentially significant radiators of sound at high frequencies. The latter waves were found to be driven by finite curvature effects.