7% Better Fuel Economy

Baseball sometimes is referred to as a game of inches. Rising fuel prices are turning the automotive business into a similar battle over small increments.

Already, General Motors Corp. appears to be winning sales with the 1- or 2-mpg advantage its new Chevy Tahoe/GMC Yukon enjoy over their closest rivals in the fullsize SUV segment. The competition likely will get even more intense going forward, and that is opening the door for numerous suppliers offering, not replacements for the internal combustion engine, but simply better mousetraps.

One such device is a new “multi-function torque converter” for automatic transmissions developed by Germany-based LuK GmbH & Co. oHG. The new torque-converter design promises to improve fuel economy in the Environmental Protection Agency's city cycle by up to 6.9% simply by disengaging itself from the driveline during idle and going into “lockup” mode faster than a conventional torque converter during acceleration.

The new torque converter offers significant benefits when matched with turbodiesel engines as well, but in North America, officials say the technology delivers the most bang for the buck in big SUVs and V-8-powered cars, almost all of which are fitted with automatic transmissions. LuK's U.S. demonstration vehicle, recently shown off at its Troy, MI, research and development center, is a Ford Expedition SUV powered by a 4.6L V-8.

In general, the new design can be packaged in the space of the normal torque converter, says Jeff Hemphill, director-advanced product development, LuK USA LLC.

“We're ready to start a (production-vehicle) project,” he says, adding that LuK is in discussions with four OEMs in North America and two in Europe. Because of industry lead times, the earliest it could see production would be 2010.

The torque converter performs essentially the same function with an automatic transmission as a mechanical clutch does in a manual transmission.

It uses hydraulic fluid under pressure to transmit power from the engine, and allows the engine and driveshaft (or driveshafts, in front-wheel-drive vehicles) to rotate at different speeds.

But the lack of a firm mechanical connection between engine and drive wheels also means some energy is wasted, and slippage in the torque converter is a major reason why automatic transmission vehicles accelerate slower and are less fuel-efficient than those with manuals.

Lots of energy also is wasted when the vehicle is stopped, because the converter absorbs torque from the engine instead of letting it spin freely.

Modern torque converters do have a fuel-saving mechanical lockup mode between the impeller and the turbine that eliminates slippage once a certain speed is attained.

And some automatic transmissions in Europe also have torque converters with an idle-disconnect feature. But the current disconnect strategies, says LuK, involve too many torque converter and driveline parts spinning at different speeds. All that inertia is difficult to synchronize when the light turns green, and it's time to reconnect.

The key was creating a metal cocoon around the converter impeller and a simple pump clutch between the converter cover and impeller sheath that disconnects its fluid circuit.

This enables torque demand on the engine at idle to be reduced from between 22 and 30 lb.ft. (30 and 40 Nm) to nearly zero. This alone improves fuel economy about 2%, LuK says.

The ability to connect and reconnect at will, better coordinate power delivery with engine throttle position, and engage in full lockup mode much sooner, all add up to 6.9% better fuel economy overall compared with a conventional torque converter, in a vehicle such as the Ford Expedition, Hemphill says.

Big gas-guzzlers are the marketing focus in the U.S., but the multi-function converter also could have an impact on hybrid-electric vehicles and the turbodiesel market in Europe, Hemphill says.