Chrysler’s traditional approach to vehicle development has taken a detour as engineers recently started using new computer tools and an advanced engineering process as a means of designing safer, lighter automobiles.
“The old version was you’d design the major subassemblies first and then integrate those subassemblies into a total vehicle structure. In many cases, we’re able to get the same end results, but we can now refine a design to a level that we previously weren’t able to do,” said Thomas Seel, Chrysler’s Manager of Component Integration, Knowledge Based Engineering.
Using what is referred to as “bio-mimetic topology optimization” combined with a refined engineering process, engineers can determine which body-in-white zones have the highest strain. The process highlights the prime location for the various critical-load paths on the vehicle.
“Taking a holistic approach to body-in-white is similar to concurrent engineering because unlike an iterative solution, the engineering process is looking at all the load cases—durability, stiffness, and safety—simultaneously,” said Seel.
Advanced high-strength steels (AHSS) are part of the optimized body structure design process. “Drivers for AHSS include safety, mass control, fuel economy, and affordability,” said David Jeanes, Senior Vice President of Market Development for the American Iron and Steel Institute (AISI), whose member companies represent more than 75% of North America’s steel capacity.
By using this proprietary process, Chrysler engineers select steels according to what is needed. “It allows you to peel away weight where you don’t need it,” said Bill Grabowski, Director of Body Core Engineering at Chrysler. Chrysler officials predict that as much as 120 lb (54 kg) could be shed from the body-in-white—essentially equating to a 1% fuel-economy improvement—by optimizing the vehicle’s skeleton.
“If you know the load requirements of the vehicle, such as torsional rigidity, side impacts, and roof strength, then these new computer tools can work with the available load paths to identify what’s strong and what’s weak so that engineers can design a better structure,” said Ron Krupitzer, Vice President of AISI’s Automotive Applications Committee.
Load optimization also occurs at the component level. For instance, an advanced design of a future production vehicle—by virtue of AHSS topology optimization—resulted in a weight savings of 1.12 lb (0.51 kg) on a front shock tower. “We predict an up to 13% weight reduction of the entire body structure, resulting in improved fuel economy because of the bio-mimetic topology tools and the engineering process,” said Grabowski, who was making a comparison to vehicles using conventional high-strength steels and design methods.
Current Chrysler vehicles use approximately 20 to 30% high-strength steel in the bodies, “but in the next three to five years, Chrysler vehicles will apply upward of 60% high-strength steels,” Grabowski said, noting that as early as 2010 Chrysler vehicle bodies could be made of 29% high-strength low-alloy steel, 30% AHSS, and 41% mild steel.
AISI, Chrysler, Mercedes Group Research, and MB Tech (Mercedes-Benz Technologies) all contributed to developing the new topology tools and the engineering process, which helps “accelerate the use of new AHSS to optimize body structures,” said Jeanes.
Although Chrysler currently is using the topology-modeling tools and engineering process for body structures, the body-in-white is only the first application. “The tools and process are not limited to just the body structure,” Seel said, declining to elaborate.