Genesis body has class-leading dynamic rigidity

  • 01-Aug-2008 04:11 EDT
genesis-7.JPG

Genesis body-in-white has impressive torsional and bending rigidity numbers, aided by high-strength steel (56.7%), shown in green, and ultra-high-strength steel (18.3%), shown in orange/red.

­The Hyundai brand is not one that would come to mind when the subject is a highly rigid body in a sports sedan for the entry-luxury market. However, the new rear-drive Genesis, Hyundai's first model to compete in that class, was benchmarked against the competition it would be facing and against cars with which it would like to be compared.

With a design that includes an aggressive use of high- and ultra-high-strength steels, the Korean manufacturer has produced a body-in-white with impressive dynamic rigidity numbers—40.9 Hz in torsion, 52.1 Hz in bending.  

These both are numbers higher than those for even such indirect competitors as the BMW 5 Series (35.9/47.7) and Mercedes-Benz E-Class (36.4/48.8) that Hyundai derived in its comparison tests, noteworthy because the new Genesis is a longer car with more interior room. Its overall length is 195.9 in (4976 mm) vs. about 190 in (4752-4754 mm) for the German models, and its U.S. EPA cabin volume is 109.4 ft³ (3.09 m³) vs. 99.1 ft³ (2.81 m³) for the 5 Series and 97.2 ft³ (2.75 m³) for the E-Class.­

The Genesis body is made up of 56.7% high-strength steel at 35-60 kg/mm² (50.8-87.0 ksi) and 18.3% ultra-high-strength steel at 60 kg/mm² and greater. Hyundai did not use the high-strength steels just to help make the body rigid but as part of an engineering effort to keep weight low. Despite its size, the Korean entry's curb weight is relatively low at about 3750 lb (1700 kg).

The B-pillars are part of a unified center structure that  includes a roof rail and the floor pan's front seat mount crossmember—all made of high- or ultra-high-strength steel and integrated with the ultra-high-strength steel body side rails. In addition, there is a tubular stiffener from each side rail at the B-pillars that runs parallel to and attaches to the floor pan crossmember. The stiffeners contribute to torsional rigidity, although their primary function is to enhance side-impact performance.

The C-pillar area has V-bracing across the opening between the cabin and the luggage compartment, so like most vehicles with high rigidity numbers, this leaves only a ski-type pass-through. However, Hyundai is developing a power 60-40 split rear seat and a high-rigidity C-pillar with a full opening for the next-generation model.

Generous use of structural adhesive bead adds to body rigidity and helps reduce NVH; there is a total of 85 m (280 ft) in the joints. The adhesive is the bake-to-strengthen type, so it achieves maximum effect after the body goes through the paint oven.

Hyundai characterizes the Genesis as a sports sedan, and its stiff body does contribute to good handling. However, the high body stiffness, combined with five-link independent suspension front and rear, also provides enhanced ride comfort.

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