Uni-Chassis concept the backbone for unique vehicle architecture

  • 11-Mar-2011 11:42 EST
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The proof-of-concept chassis from Theodore & Associates is made of four cast-aluminum suspension nodes and aluminum extrusions. Powertrain is the Ford GT supercharged 5.4-L engine and six-speed transaxle, and the 8-in (203-mm) tubular backbone doubles as the torque tube. Suspension is also from GT.

With the exalted promise of enabling a new way to manufacture vehicles, Uni-Chassis from Theodore & Associates LLC purportedly offers the highly sought-after benefits of being lighter, less expensive, and more flexible than current vehicle architectures.

“We are confident that this innovation is state-of-the-art and have built a proof-of-concept chassis, which will be displayed for the first time at the SAE World Congress,” said the company’s President and inventor of the technology, Chris P. Theodore.

Automobiles traditionally have been assembled using either unitized or body-on-frame construction. Uni-Chassis provides an alternative by connecting stressed front and rear powertrain/suspension structures to a rigid backbone, eliminating the frame. The U.S patent application for Uni-Chassis was submitted four years ago and is currently being studied by the patent examiner.

Theodore believes Uni-Chassis has significant potential for three types of OE customers: specialty vehicle makers, PHEV (plug-in hybrid-electric vehicle) and BEV (battery-electric vehicle) manufacturers, and coachbuilders and the aftermarket.

Advantages include the ability to adapt different bodies to the same chassis, create a “rolling chassis” before installation of the body, and decouple chassis loads from body loads. A modular front structure also allows different powertrains within the same architecture.

“For the front-engine, rear-transaxle configuration shown, the backbone structure is essentially a larger torque tube (similar to Corvette) but eliminates the need for side frame rails,” Theodore explained to AEI. “I believe it is reasonable to expect a 10% reduction in weight. The proof-of-concept frame weighs considerably less than the Ford GT frame upon which it was based, but that is not an apples-to-apples comparison as the GT frame provides a roof structure and is, of course, a mid-engine configuration.

“For PHEVs and BEVs, Uni-Chassis offers the potential for weight and cost savings by utilizing the backbone as the battery box, much like the tubular backbone doubles for the torque tube. Why should you have to design a battery pack to support itself, and then design the body structure to support the battery box? Uni-Chassis could eliminate this redundancy, although we haven’t done any detailed studies yet.”

In terms of variable cost, Theodore admits that a unibody structure is still the most cost-effective way for mass production—but adds that the aluminum proof-of-concept Uni-Chassis is less costly than typical supercar aluminum spaceframes. The Uni-Chassis is essentially made up of four cast-aluminum suspension nodes, two cast “bell-housings,” and aluminum extrusions, so there is less welding and machining.

“We did one comparison that showed variable cost could be as much as 50% less than a typical supercar spaceframe,” he said.

Because of the heavy use of extrusions and the six castings, tooling costs also are lower than a typical spaceframe, according to Theodore: “Conservatively, we estimate 10% less, although one study indicates more. The real investment savings comes when you apply Uni-Chassis to a family of vehicles. Wheelbase can be increased basically by increasing the length of the backbone extrusion and quill shaft (of course, front and rear structures need to be designed to handle the platform bandwidth), spreading investment costs among multiple vehicles.”

Front, rear, and offset impact loads are handled in much the same manner as conventional structures, with crush beams attached to the front and rear of the Uni-Chassis. And because most of the vehicle mass is carried by the Uni-Chassis in front and rear impacts, body impact loads are minimized—much like body-on-frame construction.

“One potential advantage is that Uni-Chassis decouples chassis and body crashworthiness requirements, such that the decel pulse can be ‘tuned’ by both the Uni-Chassis and the interaction of the body to the Uni-Chassis,” Theodore explained. “On the other hand, the body structure must still be designed for side impact, rollover, and restraint system loads, much like a pickup cab.”

Finite-element modeling indicates that torsional stiffness is equal to or greater than competitive supercar chassis. Bending stiffness is claimed to be much higher.

“We’re also studying a filament wound carbon-fiber backbone, which could triple stiffness and cut weight in half,” Theodore shared. “While carbon fiber is typically quite expensive, tubular structures are more cost-effective since they can be automated—think of golf club shafts. We are currently quoting carbon-fiber backbone parts.”

A remaining engineering challenge—other than proving the claims noted above—is NVH.

“Because the engine and transaxle are stressed, body mounts have to handle isolation of both road/chassis inputs and powertrain vibrations,” he said. “This remains to be proven, although the stiffness of the Uni-Chassis should aid in tuning the isolation between Uni-Chassis and the body.”

Theodore plans to have a proof-of concept Cobra running yet this year, and he believes low-volume production could be accomplished within three years, if an interested client is found.

He recognized supporters of the proof-of-concept project, including Derrick Kuzak of Ford Motor Co., Caroll Shelby of Shelby Automobiles, Inc., Manfred Rumpel of Advanced Vehicle Technologies, and Robert Nowakowski of Technosports.

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