It Still Performs Same Function, but Does It Much Better
Back down the dusty road of automotive history, a chassis was considered little more than a steel rack on which to mount a car’s running gear. Hang wheels and leaf springs at each corner, sling the motor and drive train down the center, nail a body to the top, and off you went.
Even well into the 20th century, chassis design wasn’t exactly cutting-edge technology. Early makers borrowed their structural principles from designs used in building girder bridges. Two steel beams were set side by side, then joined at right angles with hefty cross-members and bound by rivets or nuts and bolts.
Engineers overcame the inherent lack of stiffness in these basic structures, plus a tendency to sag in the middle, by using heavier materials or adding joists at various angles. This “ladder” chassis was extremely strong, and is still used in vehicles such as buses, motor homes and sport-utility vehicles.
Yet the sway and twist of those elementary chassis were never enough to produce the smoother ride and easier handling characteristics demanded by the automobile, particularly today’s high-speed, highly maneuverable cars.
The modern chassis, more correctly referred to as a “unitbody” or “unibody,” is a complex structure utilizing the roof, inner fenders and other major body panels to add strength and rigidity to the entire vehicle. Overall integrity of the car has also been improved through advances in metallurgy and laser welding.
While new materials are starting to appear, most are exotic offerings--such as carbon fiber, Kevlar, magnesium and laminates incorporating aluminum honeycomb--that remain exclusive to multimillion-dollar race cars.
That said, and with the majority of the auto industry staying with elderly and conventional chassis construction (the unibody, for example, was patented in 1931), one European auto maker is taking a radical approach to chassis dynamics.
“I’d like to think we are somewhat of a leader because we are the first manufacturer ever to produce an aluminum space frame vehicle,” says Marc Trahan, product planning manager for Audi of America in Auburn Hills, Mich. Although referred to as a space frame, the substructure of Audi’s flagship--the high-tech, luxurious and V-8-powered A8 sedan--is more akin to a unibody design.
By definition, a true space frame would utilize an assemblage of tubes forming a series of boxes that in turn would enclose and support the passengers and drive train. But they complicate the design of passenger vehicles, especially the shape and functioning of doors. Which is why the famed Mercedes 300SL of the ‘50s used gull-wing doors that lifted up to avoid a standard configuration that would weaken the side structure of the chassis.
There is no denying that Audi has made tremendous strides with the A8. Advanced aluminum alloys make the car’s framework 40% lighter and 40% more rigid than conventional steel. This technology has a price, however, as much of the cost of the $65,000 A8 comes from developing and structuring its aluminum frame. Audi, therefore, is working hard to perfect the old standby, the steel unibody chassis.
“The key is that [a car] has to be viable in terms of production costs,” Trahan explained. “We believe we can optimize steel unibodies by further metallurgical research while developing new alloys that are not only lighter but also stronger than what we have today.”
Steve Saleen, president of Saleen Performance, an Irvine-based builder of high-performance Ford Mustangs for track and street use, agrees with Trahan’s view of the steel chassis.
“It is not obsolete by any means,” Saleen said.
As an example, he noted, although the 1999 Mustang retains the venerable unibody chassis, it has been vastly improved through fine-tuning of the original design and enhanced assembly line techniques.
“In the last couple of years, we’re really spending a lot of time going back to some of the fundamentals,” said Paul Ashburn, chief engineer in chassis engineering at Ford Motor Co.’s advanced vehicle technology division in Dearborn, Mich.
Although hesitant to reveal Ford’s plans for their next-generation chassis, Ashburn did acknowledge that the company isn’t preparing a major change in chassis architecture. But it will be taking full advantage of emerging materials and computer-aided engineering.
Saleen chuckles when reflecting on the qualities of the early Mustang chassis.
“Part of our market is the enthusiast, so we are around a lot of the 1964 and 1965 cars,” he says. “From a styling point of view, you can’t beat the original Mustangs. But if you actually got in and drove some of the older cars, you’d be amazed at the handling because of inferior chassis.
“It’s a shock to one’s system to realize how far the auto industry has really come in the quality and construction of the car’s frame.”
So in the near future at least, the automobile industry doesn’t seem poised on a drastic revolution. Continual improvement of the proven chassis looks to be the trend.
As with old bridges, there appears no reason to wipe the drawing board clean and reinvent principles that have worked so well for so long.
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Highway 1 contributor Mitchell Sam Rossi can be reached via e-mail at speedwrtr@aol.com.
