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The battle of the metals
Double-wishbone design
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The ULSAS double-wishbone design features a stamped HSS fore-aft arm and forged steel upright vs. a cast iron upright on the benchmark design.
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Normally a good overall compromise suspension used on sporty cars, the double-wishbone design from Lotus showed an estimated 17% mass saving, with no cost penalty. It features a stamped HSS fore-aft arm and forged steel upright, vs. a cast iron upright on the benchmark design. Lotus created the initial package layout and developed sectional properties in CAD. Engineers then refined the designs using structural analysis optimization techniques to establish the required material gauges and grades, as well as shapes, for the main structural components. According to Lotus, this approach ensured the designs met the stiffness and structural targets.
Initial analysis indicated that, in theory, the optimum solution for double-wishbone links is cigar-shaped tubular members. However, the structural advantages were found to be only marginal, being outweighed by the cost penalty of increased manufacturing complexity. The steel fore-aft arm and the forged knuckle designs were optimized by extensive use of CAE optimization techniques. The forged knuckle is made of 600-MPa (87-ksi) ultra HSS and the fore-aft arm stamped out of 3.0-mm (0.12-in), 500-MPa (73-ksi) HSS. The springs were made of a 1300-MPa (188-ksi) ultra HSS, with a diameter ranging from 9.1 to 10.9 mm (0.36 to 0.43), according to vehicle class.
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