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Drawing inspiration from the design of a classic Formula 1 Lotus, automotive engineer extraordinaire Chris Theodore (former vp of Engineering of Ford North America Product Development; vp of Chrysler Platform Engineering; CEO of American Specialty Cars; CEO of Saleen, Inc., etc.) has developed a third way for vehicle construction: Not unibody, not body-on-frame, but what he’s trademarked and patented as “Uni-Chassis.”
Essentially, there is a tubular backbone running down the center of the vehicle, an 8-in. diameter aluminum tube that connects the front structure that uses stressed engine to take suspension loads and a rear structure that uses the transaxle as a structural component. Based on FEA analysis, they’ve calculated that the backbone design provides in excess of 13,000 lb-ft/degree torsional stiffness and 47,000 lb/in. bending stiffness.
The setup makes use of four aluminum suspension corner castings and aluminum extrusions.
According to Theodore, the backbone is scalable, permitting the upward adjustment of the wheelbase by 20%. Should the vehicle manufacturer want something even stronger and lighter, the backbone could be fabricated with carbon fiber.
Theodore says that this design permits a return to “coach building,” as the chassis loads are decoupled from the body loads. (It would necessitate, however, engineering the body to handle side impact loads.)
Theodore, who now runs Theodore & Associates (theodore-associates.com), is working on a Uni-Chassis vehicle that will use Ford GT parts (he was the man behind the development of that vehicle) and a modified Shelby Cobra 427 body.
He says that plug-in hybrids and electric vehicles (think of using the tube as a battery housing) are ideal applications for the Uni-Chassis.—GSV