The UltraLight Steel Auto Body (ULSAB) project was launched in 1994 by an international consortium of sheet steel producers. One of the drivers for that program from the point of view of North American steel producers was the work initiated by the Partnership for the Next Generation Vehicle (PNGV), a U.S. auto industry and federal government initiative that has as its goal the development of a full-size vehicle that will get 80 mpg. Materials researchers within PNGV announced that they were concentrating on several materials to cut the weight of vehicles, including aluminum, magnesium, and titanium. They even noted that they were working on something called "Polymer X," a plastic material that could be molded and machined. Although they didn't count steel out, it seemed fairly evident that non-traditional—if not out-right exotic—materials were the subject of PNGV focus.
So ULSAB contracted Porsche Engineering Services, Inc. (Troy, MI), a North American unit of Porsche AG, to engineer a lighter vehicle. Through the use of holistic design practices (i.e., looking at components as parts of a larger system, not just as single-function pieces) and existing but not widely used processing technologies (e.g., hot forming, hydroforming, and the extensive use of tailor welded blanks), they created the engineering for a steel auto body that has 25% less mass and, importantly, a cost reduction of 14% compared with benchmarked four-door sedans.
In other words, the ULSAB group showed that auto makers could make a fuel-stingy but highly affordable automobile with steel. (Who knows what Polymer X would cost.) That was the result of the first of three phases, with Phase III, which is scheduled for 1998, involving the production, with an auto maker, of a production prototype ultralight steel car.
Trucks Are Hot. Can They Be Light?
So what has happened in the North American auto market since 1994? One thing that has really garnered a whole lot of attention on car lots is the pickup truck. In 1996, the top selling vehicle was the Ford F-series pickup. It was followed by the Chevrolet C/K pickup. And if people weren't buying trucks, they were in the market for sport utility vehicles (SUVs). The third best-selling vehicle in '96 was the Ford Explorer.
Not surprisingly, the Automotive Applications Committee (AAC) of the American Iron and Steel Institute (AISI) figured that if steel is a good choice for a superior car, and if plenty of consumers are selecting trucks, it would be worthwhile to investigate the possibility of steel for light trucks and SUVs. As Douglas Tyger, manager, Applications Engineering, AK Steel Corp. (Troy, MI), remarked, "Steel has untested boundaries, too," so before some other group started looking at some alternative materials for the trucks of tomorrow, the Light Truck Structure (LTS) was initiated.
Porsche Engineering was commissioned to conduct the study. Unlike ULSAB, this was a paper-only study: design and analysis, not a prototype vehicle. The objective was to determine how to make a light-weight, cost-efficient truck structure. There were a couple of limitations that were to make this study one with a certain amount of practicality: no new steels and no new manufacturing technologies could be assumed. The AAC wanted to present to the auto makers a concept that can be realized in existing plants with existing materials. It is do-able, not just conceivable.
Starting with a Clean Screen
Light trucks are those vehicles that come in 1/4-ton, 1/2-ton, and 3/4-ton sizes. One thing that auto makers often do is take their light-truck platforms—which are typically body-on-frame structures—and transform them into sport utility vehicles. So according to Ronald L. Hughes, manager, Technical Affairs and Advanced Engineering and Technology, Rouge Steel Co. (Dearborn, MI), the LTS project directors determined that the study should encompass both the pickup and the SUV. Because they were starting with a clean sheet of paper—or a clean computer screen, to be more accurate—they had an opportunity to do something that is rare in OEM engineering offices, which is to create a total vehicle architecture for both vehicles.
One of the goals was to reduce part count whenever possible, and that thinking was conveyed through the program. The idea was to have as much commonality between the truck and the SUV as practical. The engineers recognized that there are functional differences between light trucks and SUVs. For example, light trucks are based on a model of a cab and a box. The box can be used for load carrying. Consequently, there needs to be some flexing between the cab and the box. SUVs aren't built as cargo carriers so, compared to a light truck, they should offer a more car-like ride. So, because SUVs and trucks have different requirements in the rear, Porsche engineers determined that it would be efficient if the front bolt-on subframe was used for both the SUV and the light truck. In order to create the truck, a full frame is produced by bolting a full rear frame to the front subframe. As mentioned, existing processes and materials were assumptions Porsche Engineering worked with. So, in the case of the truck frame, the side rails are traditional C-sections with reinforcements and stamped cross sections. The material gages are from 0.9 to 2.5 mm, with grades 180 to 380 Mpa yield. The pieces are put together with arc welding.
In the case of the SUV, the rear subframe is created by simply reversing the front subframe. Thus, there are manifold savings throughout processing (e.g., the same tooling and materials are shared by the SUV and the truck and the SUV; inventory requirements are reduced).
The SUV body consists of stampings and tailor welded blanks (the latter including the body side outer, front floor and the quarter inner). The gages: 0.8 to 2.3 mm. The grades: 180-380 Mpa yield. The body pieces are assembled with spot welding. The same pretty much holds for the truck cab. Here, the body side outer and front floor are tailored blanks. And the material gage goes up to just 2.1 mm.
Fewer Parts. A Bigger Vehicle. And Less Cost.
One thing the Porsche Engineering engineers did was assess the function of elements and calculate whether a given element could be combined with others, thereby reducing total part count. For example, generally speaking, a truck bumper is a bumper. But for the LTS, the bumper was developed so that it not only functions as a bumper, but also as a structural element.
In total, this holistic approach resulted in a reduced part count. There are 81 basic parts for the LTS SUV, as compared with 141 for a Jeep Grand Cherokee. Overall, the piece count reductions compared with the bench-marked vehicles are 32% for the SUV, and for the trucks, 53% for an extended cab version and 46% for the standard cab.
Note that these are sizable vehicles that have been designed, yet they are also lighter than the competitive products, thereby addressing the issue of fuel efficiency, which is an abiding concern among auto makers. For example, the benchmarked Nissan Pathfinder has a wheelbase of 106.3 in., an overall length (4-door version) of 178.3 in., and an overall width of 72.4 in. Its curb weight (including a V6 engine) is 4,020 lb. A Jeep Grand Cherokee has a 105.9-in. wheelbase, 176.3-in. overall length, 69.3-in. overall width, and a 3,940-lb. curb weight (with a V8).
The numbers for the LTS SUV are: 110-in. wheelbase, 185-in. overall length, and 73.7-in. overall width. A V8 engine is assumed. The curb weight is 3,600 lb.
Based on the safety tests that were simulated—35 mph New Car Assessment Program (NCAP) frontal, 35 mph rear moving barrier, European side impact, roof crush, 5 mph bumper front and rear—indicate that although the vehicle is light, it is safe.
Of course, the LTS trucks and SUVs exist only in cyberspace. State-of-the-technology analysis techniques (e.g., CSA/NASTRAN and LS/DYNA 3D FEA) were used to achieve the engineering results.
Possibility is one thing. Affordability is another. It would not serve the purposes of the Automotive Applications Committee if the LTS study came up with a vehicle that, due to cost considerations, would not be considered by the auto makers. So IBIS Associates (Wellesley, MA) was hired to perform a cost analysis of the LTS designs, which were compared with the baseline vehicles. The analysts concluded that the SUV can be produced with a 20% cost savings. The extended cab light truck can be produced with an 18% cost savings and the standard cab can come in at 12% less.
Will an LTS ever become real? That, of course, is entirely up to the Big Three. The information developed through the study is being made available. Although it may not be accepted lock, stock and barrel, there is a likelihood that certain elements are too good to pass up.
The Steel Participants
The member companies of the American Iron and Steel Institute that participate on the Automotive Applications Committee, which initiated the Light Truck Structure (LTS) study, are:
• AK Steel Corp.
• Acme Steel Co.
• Bethlehem Steel Corp.
• Dofasco Inc.
• Inland Steel Co.
• LTV Steel Co.
• National Steel Corp.
• Rouge Steel Co.
• Stelco Inc.
• US Steel Group, a unit of USX Corp.
• WCI Steel, Inc.
• Weirton Steel Corp.