Lightweighting was one strategy pursued by SuperTruck teams during the first phase of the U.S. Department of Energy-sponsored initiative to improve heavy-truck freight efficiency by 50%. For example, the International Catalist features a “hybrid” front suspension that leverages lightweight alloys with composite materials, reducing weight and enabling an electronic ride height management system that provides dynamic ride height and pitch control for improved aerodynamics.
“Typically, air-ride front suspensions are very heavy, they’re very soft to drive—but we’ve integrated a composite leaf spring and an air spring into one suspension,” explained Dean Oppermann, chief engineer for advanced vehicles and the SuperTruck program at Navistar. “We’ve been able to do it in a way that reduces weight of the system, maintains our ride height control, but also offers more stability with the leaf spring-type suspension.”
Designed and developed by Hendrickson, the Catalist hybrid front suspension is approximately 40 lb (18 kg) lighter than a conventional steel leaf suspension with same load rating, he said. The hybrid suspension using a steel leaf, called AIRTEK, is ready for production now. “This production suspension is currently being updated with an electronic ride height control valve to productionize the pitch control that has been demonstrated on the Catalist property,” Oppermann shared.
The Catalist also makes extensive use of lighter-weight carbon-fiber panels, in the upper body, roof headers, back panel and dash panel. The Navistar-designed cab/sleeper composite surfaces were manufactured by a third-party low-volume composite component manufacturer.
“The continued reduction of raw material costs and manufacturing costs of complex composite components, coupled with the requirement for complex aerodynamic geometries to support GHG regulations, could make composites a viable alternative to conventional materials for low-volume applications,” he said.
Navistar’s emphasis on lightweighting continues unabated with its SuperTruck II program, which got under way late last year. Engineers are investigating WiFi technology for activating/deactivating features in the vehicle, according to Oppermann.
“One of the wasted weight attributes of a truck is we carry harnesses that we call ‘150% content.’ These harnesses support every feature that we sell for our products even though the feature may not be requested by our customers,” he explained. “Wireless and intelligent power distribution modules allow support of all content with a small common harness. This technology can result in a 25- to 50-lb reduction in wire length/complexity as well as simplified routing and clipping strategies.”
Other areas for lightweighting under investigation in Navistar’s SuperTruck II project include interior trim through design and material selection, as well as further use of composites in frame rails, cross members, cab/sleeper structure, driveshaft and trailer components.