BUILDING A WORLD-CLASS SUV WITH THE GUTS OF A TRUCK: STEEL INDUSTRY OFFERS WEIGHT AND COST SOLUTIONS TO LIGHT TRUCK MANUFACTURERS

Industry’s light truck structure study shows big savings with optimized steel design

DETROIT,MI, March 17, 1997 – The North American steel industry has presented its customers with the results of its Light Truck Structure (LTS) study that offers steel-based potential for major savings of weight, parts and cost in the design and manufacture of the body and frame for sport utility vehicles (SUV) and light-duty trucks.

The study proposes a way to produce an SUV that combines the robust characteristics of a pickup truck with the refined performance that drivers of these vehicles have come to expect. It also incorporates methodology for design and manufacture of a family of SUV, compact pickup and extended cab variants that can be made on the same production line.

The North American steel industry through American Iron and Steel Institute (AISI) commissioned the study and contracted Porsche Engineering Services, Inc., (PES) Troy, Mich., to conduct the work.

The LTS design for SUV is estimated to reduce the number of parts in the body and frame structure by 32 percent, reduce weight by 19 percent and save 20 percent in cost, compared to representative generic baseline vehicles.

The savings in the LTS compact pickup truck for part count, weight and cost are 46 percent, 13 percent and 12 percent, respectively. For the extended cab pickup, the savings for part count, weight and cost are 53 percent, nine percent and 18 percent, respectively.

IBIS Associates, Inc., a technology strategy consulting firm in Wellesley, Mass., used its proprietary Technical Cost Modeling methodology to estimate the savings. The LTS concept employs commercially available steels and current manufacturing processes. Crash simulations show that the design has the potential to meet today’s car crash standards.

The LTS design concept applies an integrated suspension and employs a structural subframe in both front and rear for an SUV and at the front for a truck. For the SUV, the front and rear subframes attach to a body structure. In the pickup truck variants, the same front subframe attaches to a conventional full frame which carries a conventional cab body.

The LTS platform approach allows for the construction of both SUV and light truck on the same manufacturing line, resulting in lower manufacturing costs. Optimized design saves mass over the entire family of vehicles, leading to less fuel consumption and lower environmental impact.

The LTS is the next logical step to follow the UltraLight Steel Auto Body (ULSAB) project, commissioned in 1995 by an international consortium of sheet steel producers to address auto manufacturers’ need for cost-effective weight reduction. Promising preliminary results of that project – and the growing popularity of truck-based vehicles in North America – led AISI to undertake the Light Truck Structure study.

As with ULSAB, the LTS approach set targets based on benchmarking best-in-class vehicles. The aggressive targets included those for stiffness and strength, occupant package, mechanical package, and crash energy management.

PES researched technical specifications of ten vehicles to determine best in class. The project goal was to exceed those targets. PES benchmarked the following 1995-1996 model year vehicles: Toyota 4 Runner; Chevy Blazer; Ford Explorer; Jeep Grand Cherokee; Nissan Pathfinder; Chevy Tahoe; Ford Bronco; Isuzu Trooper; Range Rover; and the Mitsubishi Montero.

In optimizing the attributes of steel in LTS, PES provided a "hybrid" solution, which uses a structural subframe that serves as the front subframe for all members of this family and as the basis for the rear subframe on the SUV. This approach allows for the pre-assembly of chassis and powertrain components for easy, efficient and simple mating with the body and frame structures.

The occupant package for the LTS is equivalent to that of a mid-sized luxury car, and the mechanical package includes a large V8 engine, four-wheel independent suspension, 21-gallon fuel tank and four-wheel drive capability.

SUV

The SUV design incorporates a body structure to provide the rigidity this vehicle requires. The common front subframe is bolted onto the unibody. It holds the engine and suspension assembly and provides crash energy management functionality. For the rear of the vehicle, the design approach rotates the front subframe to become the rear subframe.

Both front and rear subframes use conventional stamping and spot welding assembly as well as cast or hydroformed coupling at the major joints with the unibody.

The unibody (body-in-white) uses traditional stamped body construction, is assembled by spot welding and employs tailor-welded blanks. This design enables the engine and the front suspension to be pre-assembled with the front subframe and for the rear suspension to be pre-assembled with the rear subframe prior to bringing them to the body on the assembly line. The front section of the SUV body is used for the standard and extended cab trucks. A rear end panel closes off the rear of the structure at appropriate locations, either a "B" or "C" pillar.

Truck

LTS uses a full frame for trucks, as they have different rigidity and bending requirements than SUVs. Joining the full rear frame to the front subframe of the SUV creates the full truck frame. Rubber mounts isolate the cab and bed from the frames. Different frame sizes allow for standard and extended cabs, as well as multiple bed sizes. The frame is common for ¼ ton, ½ ton and ¾ ton trucks. It features stamped cross members and is assembled by welding.

Both the standard and extended cabs are made by traditional stamped parts and assembled by spot welding. Like the SUV, the truck body employs tailor-welded blanks.

Both the SUV and truck designs met or exceeded most targets for torsion, bending, towing capacity and structure mass. Crash targets that the LTS design met or exceeded included: 35 MPH NCAP frontal; 35 MPH rear moving barrier; European side impact; roof crush; and 5 MPH bumper (front and rear).

"Our focus on optimizing designs and manufacturing, such as with the LTS program, coupled with our continuing work on improving our products, provides our customers with solutions to key concerns – weight, safety, cost and recyclability," said Darryl Martin, director, Automotive Applications, AISI.

The LTS reinforces the commitment of the steel industry to early vendor involvement, optimization of designs, providing engineering tools and concepts, and providing customer solutions. Other initiatives of the steel industry include participation in the Auto/Steel Partnership (A/SP), the Auto Steel Design Manual (ASDM), Computerized Application and Reference System (CARS), and ULSAB.

The American Iron and Steel Institute (AISI) is a non-profit association of North American companies engaged in the iron and steel industry. The Institute comprises 50 member companies, including integrated and electric furnace steelmakers, and 170 associate/affiliate members who are suppliers to or customers of the steel industry. For more news about steel and its applications, view American Iron and Steel Institute’s website at http://www.steel.org.

The Automotive Applications Committee (AAC) is a subcommittee of the Market Development Committee of AISI and focuses on advancing the use of steel in the highly competitive automotive market. With offices and staff located in Detroit, cooperation between the automobile and steel industries has been significant to its success. This industry cooperation resulted in the formation of the Auto/Steel Partnership, a consortium of DaimlerChrysler, Ford and General Motors and the member companies of the AAC.

This release and other steel-related information are available for viewing and downloading at American Iron and Steel Institute/Automotive Applications Committee’s website at http://www.autosteel.org.

American Iron and Steel Institute/
Automotive Applications Committee:
AK Steel Corporation
Acme Steel Company
Bethlehem Steel Corporation
Dofasco Inc.
Ispat Inland Inc.
National Steel Corporation
Rouge Steel Company
Stelco Inc.
United States Steel Corporation
WCI Steel, Inc.
Weirton Steel Corporation