2012 NAIAS: GM's new global RWD body architecture is light and stiff

  • 09-Jan-2012 08:22 EST
Cadillac ATS front compartment.JPG

View of a bare ATS white body's engine compartment reveals fully braced cast-aluminum strut towers and fabricated aluminum engine cradle with beautifully cast magnesium multi-point engine mounts. The cross-car beam is a tubular aluminum fabrication. (Lindsay Brooke)

Claimed by General Motors leadership to be the most mass-efficient car in its segment, the 2013 Cadillac ATS will enter production later this year with a curb weight of approximately 3200 lb (1451 kg), thanks to the automaker’s new global compact rear-drive body architecture.

Known internally as Alpha, the new platform makes its first appearance on the new ATS, which is designed to directly challenge BMW’s iconic 3-Series (see related story at www.sae.org/mags/aei/10545). The compact Cadillac’s body structure is second only to the Chevrolet Corvette’s among GM vehicles in its use of a broad matrix of materials and component manufacturing processes aimed at minimizing mass and optimizing structural rigidity.

ATS Chief Engineer Dave Masch noted that "all the grams" were counted in each component during development. Extensive benchmarking of individual components from competitive vehicles led to prototype ATS components being weighed, including fasteners, throughout development, GM engineers said during the car’s global media debut as part of the North American International Auto Show Jan. 8 in Detroit.

This approach extended to inside the car’s cabin, said Phil Kucera, ATS Interior Design Manager. “It’s amazing how we attacked mass on this program,” he told AEI. “On the interior, we had to keep track of the weight of not only door trim, but carpet fibers.”

To match GM’s claims, the rear-drive ATS will have to weigh in under BMW’s redesigned 3-Series (F30 program) which is new for 2012. Curb weight of the base 328i with four-cylinder engine is listed as 3153 lb (1430 kg).

An ATS body-in-white on display at the media launch showed a host of interesting materials applications. A pair of multi-point engine mounts, beautifully cast in magnesium, are among the engine compartment highlights. The mounts are part of an aluminum-intensive front engine cradle that’s rigidly mounted to the body. The front strut towers are thin-wall aluminum castings. Also in aluminum is the tubular fabricated cross-car beam and IP support.

Martensitic steel and other high-strength and ultra-high-strength steel alloys are used extensively in the BIW. Bake-hardenable types form the A- and B-pillar outer stampings. The entire BIW resembles a fighter aircraft fuselage in its liberal “hole count”—engineers used FEA tools

to determine the precise location of the hundreds of holes in the stampings; the holes are designed to take weight out of the structure, and they also allow electro-coat access.

The ATS will feature an aluminum hood inner and outer, and engineers said one of the car’s transmissions will feature a magnesium case. However, not all materials used are classic lightweight alloys: the rear differential housing is cast iron, rather than aluminum, because the team found the ferrous metal to better improve fuel efficiency. The fully isolated cradle for the rear multilink suspension is a lightweight steel-tubing fabrication.

The ATS body features a full pass-through between the passenger compartment and trunk area. To achieve this, the open rear bulkhead is extensively gusseted around its perimeter, particularly in the corners.

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