Monday, August 2, 2010

Why the Chevy Volt Should Drive Its Wheels with Gas

Chevy Volt on the Highway

This opinion piece was contributed by Chris Ellis, CEO, HyKinesys.

The UK�"s Telegraph caused a stir in June when it speculated that G.M. soon might turn the Chevy Volt into a hybrid by directly linking the engine to the wheels. also reported that the 2011 model already has hardware, like a planetary gear set, which makes it possible for the Volt to work more like a hybrid than an electric car. Here�"s the question that hasn�"t been discussed: Why would G.M. ever want to use the engine to directly drive its wheels?

In a nutshell, the main reason is to make the car more efficient and economical when cruising at high speeds. It�"s the same reason lock-up clutches were added to automatic transmissions decades ago�to improve efficiency at more than 50 mph in top gear.

How It Works Now

Let�"s be clear. I�"m not talking about when the Volt's battery pack initially has more than 8 kilowatt-hours remaining of its total of 16 kilowatt-hours. As long as there�"s enough juice in the battery, it operates just like a battery-only vehicle. The engine stays off until the battery drops below the trigger level. Only at that point does the engine start up and the Volt begins to operates as a charge-sustaining series hybrid. The control system doesn't attempt to re-charge the pack much above the trigger level. Full re-charging must wait until the Volt is next plugged in.

When the engine is running, the principal flow of energy is from the gas tank via the engine and its generator to the electric motor connected to the differential and the front wheels. The battery is still involved, but only as an energy buffer during regenerative braking and strong acceleration.

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