Pity the poor tire.
It has long been a joke among auto industry insiders that tires are the most important part of a vehicle because they’re the only parts that actually touch the road…which is humorous because auto companies traditionally have devoted so little time to improving tire design.
The joke, however, may have run its course. As the industry prepares for the arrival of all-electric and fully autonomous vehicles, high-tech design of the lowly tire is rapidly gaining traction.
“There is a realization in the industry that the tire will play a key role that will become more and more visible,” said Hans Dorfi, director of digital engineering at Bridgestone, based in Akron, Ohio.
New types of cars need new types of tires
Autonomous vehicles will not have steering wheels, so passengers will be just that—mere riders who don’t want or expect to fix a flat tire. This trend will be especially pronounced as people stop owning cars and move to renting them for set periods of time or hailing them on demand. As a result, tire makers are developing and introducing airless tires as well as tires with built-in sealants that can prevent flats for short periods, until a punctured tire can be repaired.
Preventing flats isn’t the only focus for tire makers, however. Electric vehicles are very heavy due to the weight of the batteries that power them. This weight will lead to more wear and tear on tires, as will plans to power the front and rear axles with separate motors; some designs even call for separate motors on each tire, leading to even faster wear and an even greater need for new, more durable materials.
The final factor in increased wear and tear is the fact that shared fleet vehicles could be in use 90% of each day, compared with 10% per day for single-owner vehicles.
Enter digital simulation
For help in predicting and responding to these challenges, tire makers are turning to virtual simulation software to ensure that their solutions are equal to the task.
“We can use digital tools both to design the product for a very specific use and to cut out many of the iterations that were required in the past to validate the product,” Dorfi said.
As the capabilities of digital simulation software have advanced, tire makers have gained the ability to simulate more of the conditions that their tires may face, allowing them to test the performance of new designs digitally, but in real-world conditions, long before deciding to manufacture them.
“The tire companies overall are at a stage where they can simulate just about all the performance events that a tire has to go through,” said Ron Kennedy, managing director of the Center for Tire Research (CenTiRe) in Blacksburg, Virginia. CenTiRe conducts research for a global consortium of tire makers through two universities—Virginia Polytechnic Institute and State University and the University of Akron—under the auspices of the National Science Foundation.
For example, the center can test handling and comfort as tires interact with rough, icy or slick surfaces, as well as how much noise they generate. Rolling resistance is another important variable, especially for tires on electric vehicles: the lower the resistance, the greater the mileage and the longer the batteries last between charges.
Given the wide variety of conditions, designs and materials that researchers must test, the speed at which simulations can be performed is increasingly important.
“How long does it take to run a model?” Kennedy said. “You want to be able to evaluate as many design variables as you can, as quickly as you can. If we can do only one a day, that’s not quick enough. You need to do three or four a day.”
Tires without air?
Simulation helped Michelin develop its puncture-proof UPTIS (Unique Puncture- proof Tire System) tire. UPTIS does not contain an inner tube; in fact, it contains no air at all, meaning that auto manufacturers who specify them will not need to include a jack or a spare tire with their vehicles, eliminating weight and cost. UPTIS is expected to be introduced on General Motors passenger vehicles as soon as 2024.
The vast majority of drivers will not notice any difference in feel or performance, Michelin said. Best of all, UPTIS improves safety because it eliminates the possibility of blowouts.
Steve Cron, UPTIS co-inventor and a senior principal product research engineer at Michelin in Greenville, South Carolina, said simulation was important to significant aspects of the novel new design particularly by helping engineers optimize the shape of the composite rubber spoke that contained the new fiberglass monofilament material that looks like strands of spaghetti.
“We provided a little bit of intelligence to the simulation software and let it search for the types of solutions we were after,” Cron said. “It saved us enormous amounts of time, and we got much better solutions without a human in the loop.” Today, monofilament glass-fiber is used in the outer band of the tires and to reinforce wheel spokes.
The other major advantage of virtual simulation came in figuring out how the UPTIS would be structured mechanically. Engineers sought to mimic the way that all parts of a pneumatic tire—the top, bottom, sides and spokes—help carry a car’s load, not just the part of the wheel that touches the road. “Without simulation, we never would have been able to figure this out,” Cron said. “The use of these tools has been absolutely essential.” ◆