Creating the chassis of tomorrow - Engineer - GM's product innovation

Automotive Design & Production, Oct, 2002 by Gary S. Vasilash

While GM is working hard at developing fuel cells for vehicular use, don't overlook the implications of its new chassis architecture. It has the potential to affect everything from interior designs to the number of manufacturing plants needed to produce vehicles.

When most people think about chassis, they're probably thinking in terms of a conventional ladder frame, or something that consists of a stamped floor pan and structures that are attached and hung on it. They're not thinking in the way that Larry Burns, GM's vice president of Research & Development and Planning, and his colleagues think. These folks are thinking along the lines of something that resembles a flat platform with the wheels being attached at the corners. Earlier this year, at the North American International Auto Show in Detroit, General Motors introduced a concept model of what Burns has in mind: AUTOnomy (see Automotive Design & Production, March '02 or http://www.autofieldguide.com/articles/030203.html). At issue, of course, is the fundamental that this is a concept vehicle. Concept means an idea, an inspiration, a thought. Real car people deal with real things, right?

But Burns and his colleagues are committed to making the concept real. Their commitment was given a deadline. When AUTOnomy was revealed, Burns stated that there would be a drivable version by the end of 2002. This wasn't simply a matter of coming up with a skateboard-like chassis, putting a motor in it, and calling it good. First of all, the AUTOnomy is a vehicle that runs on hydrogen. A fuel-cell vehicle. That's one part of why there is a chassis that's like a skateboard: this does away with the internal combustion engine. In its stead is a configuration that includes the fuel cell, electric drive, hydrogen storage system, computer control module, heat exchanger, and motors at all four wheels.

Wired. And another major part of it is the fact that this deploys an X-by-wire system: which means that rather than the conventional mechanical linkages that are part and parcel of a conventional steering system, brakes and accelerator, wires send the signals to the devices that provide the relevant responses. This has manifold implications. For one thing, it allows the chassis to be comparatively flat. That is, all of those set linkages are eliminated. The X-by-wire system that GM is deploying, developed by SKF (Goteborg, Sweden), permits the so-called "X-drive," which controls the steering and the accel/decel, to be located practically anywhere.

While the fuel cell is often pooh-poohed by many automotive insiders as being nothing more than a lot of hot, expensively produced air, GM is seriously dedicated to making the fuel cell a reality. It has some 500 people working on fuel cells in the U.S. and Europe. Recently, for example, a 64,000-[ft.sup.2] operation was opened in Honeoye Falls, NY, the GM Fuel Cell Development Center. The objective of this center, which is a small parking lot away from the 77,500-[ft.sup.2] GM Fuel Cell Research Center, is to do the work that will determine the manufacturability of fuel cell components: the fuel cell stacks, fuel processors, electrolyzers, and associated systems. Burns says that one of the things that will be answered at the new center is the non-trivial question: "How do you make fuel cell technology into high-volume, high-durability, affordable products?" An additional 100 research and engineering jobs could be added to the center as it seeks the solution.

Working the Risk. But there is still that claim, the one about a drivable AUTOnomy by the end of this year. A giant step has been taken toward that with the launch of Hy-wire, which is a functional proof-of-concept: a fuel cell-powered vehicle that uses X-by-wire technology (the name is a collapsed version of hydrogen and by-wire; but someone less generous could also think of it in terms of being something found high above the ground in a circus). Burns admits that the 6-in. chassis that is part of the AUTOnomy has not been achieved in the Hy-wire. But they're not far off: at its thickest, the aluminum chassis structure for the Hy-wire is 11-in, thick. It tapers down to 7 in. at its edges. Given what is included in that width is rather impressive: the chassis contains a transversely mounted electric motor that drives the front wheels; the fuel-cell stack (which produces continuously available power of 94 kW, and a top speed of 97 mph) is located in the rear, and three hydrogen storage tanks (each rated at 5,0 00 psi) are located in the middle. (GM is working with quantum Fuel Systems [Irvine, CA] on 10,000-psi tanks that, Burns says, will bring them closer to the 300-mile-per-fill-up range.) Notes Chris Borroni-Bird, director of GM's Design & Technology Fusion Group (which is dedicated to determining how advanced technology can have an effect on such things as architectures--with the skateboard chassis being predicated on fuel cells and X-by-wire being an excellent example), "Most of the powertrain load has been evenly distributed between the front and rear of the chassis so there is a lower center of gravity for the whole vehicle, without sacrificing ground clearance. This contributes to the overall safety of the vehicle by enabling superior handling, while resisting rollover forces, with the tallest body attached."