Steel Industry Suspension Study Shows Mass Savings of up to 34 Percent

Multi-Link Design Matches Mass, Shows Cost Savings of 30 Percent, Compared to Aluminum Benchmark

DETROIT, MI, May 17, 2000 – Results of a two-year design study of automotive suspensions released today showed mass reductions of up to 34 percent at no increase in cost for four steel-intensive designs, compared to a range of benchmarked steel suspensions. The study also included a fifth steel design that showed a 30 percent cost reduction with a small mass reduction, compared to a current aluminum design.

All five designs meet or exceed a range of performance criteria including those for ride and handling and NVH (noise, vibration, harshness), manufacturability and packaging (the effect on underbody, occupant and luggage space).

Sponsored by a consortium of 34 of the world’s leading steel companies and conducted by Lotus Engineering Services, Inc., England, the UltraLight Steel Auto Suspension (ULSAS) study demonstrates how the use of iterative, holistic design, coupled with innovative use of high- and ultra high-strength steel sheet, tubular and bar products, and advanced manufacturing technologies can result in lighter weight, lower cost and better performing vehicle suspension systems.

The program is a companion to the UltraLight Steel Auto Body (ULSAB) study released in 1998, the UltraLight Steel Auto Closure (ULSAC) study, which is nearly complete, and ULSAB-AVC (Advanced Vehicle Concepts) study, which will be complete in 2001.

Peter Rawlinson of Corus Group – UK and Nick Sampson of Lotus Engineering Services, Inc., today on behalf of the ULSAS Consortium presented the results of the program at the Society of Automotive Engineers Automobile Dynamics and Stability Conference in Detroit.

"As was the case with ULSAB, ULSAS shows the potential of steel to reduce weight, lower costs and improve performance," said Darryl C. Martin, senior director, Automotive Applications, American Iron and Steel Institute (AISI). "For our vehicle-making customers, these criteria are foremost. We look forward to meeting with them to help them understand how they can incorporate in their suspension designs the advanced concepts that ULSAS demonstrates."

Extensive use of high- and ultra high-strength steels in all five designs made possible the substantial mass reductions. Also contributing to mass savings, as well as to cost savings and performance enhancements, are strategic use of large, thin-wall sections, hydroforming, tailored blanks and laser welding.

From a design standpoint, Lotus Engineering rigorously pursued opportunities for part consolidation and strategies to promote ease of manufacture and lower tooling costs. The design team also relied heavily on representatives of the steel companies, who early in the program provided expertise and advice concerning the steels, cost analysis and forming simulations.

Lotus benchmarked a representative, comprehensive range of automobiles from Europe, Asia and North America. Against these benchmarks, Lotus engineers designed five different rear suspensions, each advancing the state of the art of its respective type.

The Twistbeam design was the star of the show – with mass savings up to 32 percent at somewhat less cost. The design differs from conventional twistbeams because it features a transverse beam of thin-wall tube uniquely profiled to save weight. It sweeps in a U shape that provides continuity of structure from hub to hub. The design uses high-strength steel in the U-shaped tube, trailing arm, spring pan, springs and hub mounting plate. The two forward facing arms are hydroformed. The twistbeam design substantially exceeded benchmark performance targets.

This type of rear suspension is common in smaller cars, where passenger and luggage space is critical but ride quality is less so. However, because the design would perform significantly better than any of the benchmarks, it could be a leading suspension option for future small cars where good handling, as well as space and packaging, are key criteria.

The Strut & Links design achieved mass savings of 25 percent through extensive use of high- and ultra high-strength steels, coupled with an iterative design approach to optimize components. The design also achieved slightly lower cost and target-exceeding performance, and met all other target criteria.

Strut and links designs usually represent a low-cost approach with compromises in ride and handling and in vehicle refinement.

The Double Wishbone design achieved a mass saving of 17 percent with no cost penalty, while exceeding performance targets. All parts are high- and ultra high-strength steel and the design features a stamped high-strength steel fore and aft arm and forged steel upright, rather than a cast iron upright in the benchmark design.

Because they represent a reliable overall compromise, double wishbone suspensions often are used in sports cars.

The Multi-Link design is the only concept in the study whose benchmark is aluminum intensive. This suspension demonstrated a cost saving of 30 percent while showing a slight mass advantage compared with its aluminum-intensive benchmark. All major parts are of high- and ultra-high-strength steel. It matched the other target criteria.

Multi-link suspensions are more sophisticated and costly than the others in the study, but provide superior ride and handling and vehicle refinement.

Lotus also designed a Lotus Unique concept, which resulted in mass savings of 34 percent and a modest cost advantage compared to a conventional double wishbone system, to which it is similar. Created from a clean sheet and specifying the latest in steel materials and technologies, this design offers performance advantages of more complex suspension systems, while simplifying and minimizing the number of components. Featuring extensive use of high- and ultra-high-strength steel, the design exhibits good performance with a relatively efficient package. The study showed it would be easy to manufacture and assemble.

Lotus conducted the ULSAS project in two phases. First, Lotus engineers carried out a comprehensive benchmark study to test and evaluate suspensions in a variety of vehicles from North America, Europe and Asia. The process included road and track testing, detailed design reviews and weight, cost and manufacturing studies.

Based on those assessments, Lotus undertook a holistic review of suspension system requirements, identified opportunities for application of new steel technologies and established an extensive range of targets for the design phase of the ULSAS project.

ULSAS focused on rear suspensions because:

  • Although both front and rear suspensions have equal potential impact on vehicle handling and performance, rear suspensions have greater impact upon occupant and luggage space.

  • Most front suspensions on cars worldwide are of the McPherson strut design, whereas different size and class cars from different automakers use a wide variety of rear suspension types.

  • Lightweighting, cost-saving and performance-improving concepts developed in the study could apply equally to front suspensions.

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.

American Iron and Steel Institute/
Automotive Applications Committee:
AK Steel Corporation
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