Hub Motors: Where EVs Smash Open Auto Design

Chrysler leapt back into relevance this week announcing no less than four EVs in development -- at least one of which it promises to sell in 2010. Most intriguing for this fan of EV technology is its claim to be experimenting with permanent magnet in-wheel motors for an plug-in hybrid version of the Jeep Wrangler. That step would be an exciting leap in auto design where the electric drivetrain frees the automobile from its heavy and design-constraining mechanical transmission and driveshafts.

For a sense of the hub motor's potential design impact, consider the experimental Reconnaissance Surveillance Targeting Vehicle that General Dynamics built for the U.S. Marine Corps. The "Shadow" is "a four-ton armored truck that has the payload of a Humvee and yet is svelte enough to deploy from a tactical aircraft." The Shadow used a series hybrid design in which the engine serves only to keep the lithium battery charged in extended range use--much like GM's vaunted Chevy Volt.

Unlike the Volt it transmits power to the wheels via power cables, rather than using its stored electricity to drive a central motor and mechanically distributing it to the wheels. The result is unprecedented traction thanks to the direct control of each wheel by its hub motor and the wheels' freedom to range up and down almost half a meter.

Then there's the Shadow's metamorphosis when it rolls out of a V-22 vertical take-off tactical plane. Sizing for the V-22's cargo hold constrained the Shadow's chassis to just 150 cm side to side -- way narrower than the 215-cm-wide Humvee. How to ensure stability in operation at that width? Upon exiting from the V-22 the Shadow extends its wheels sideways 20 cm beyond the chassis, achieving a total wheelbase of 190 cm. The key is a folding pneumatic suspension, something that's all but impossible with a mechanically-driven wheel.

The Shadow was General Dynamics' 2004 bid for what has since become the joint U.S. Army - Marine Corps Joint Light Tactical Vehicle program. Development contracts for the vehicles are expected to be announced next month.

The Shadow, Hub motors and all:

General%20Dynamics%20Shadow.jpg

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