Visteon Eyes Electric Supercharger

European auto makers are encouraging Visteon Corp. to develop an electrically powered supercharging system that will improve performance of small engines. The supercharger is needed because internal combustion engine/electric hybrids — and the 42-volt systems that will power them — for the most part remain just out of reach.

Visteon engineers are working with customers on engine projects for 2005-2006 that will use the Visteon Torque Enhancement System, or VTES, with a 12/14-volt electrical system.

It would be easy to adapt the VTES system to a 36/42-volt system, says Visteon engineer Jeff Brown, but the costs and complexity of such systems mean manufacturers are sticking with 12/14-volt systems longer than was thought a few years ago.

And they are looking for ways to improve fuel efficiency to meet the coming 2008 European goal of 140 grams of CO₂ per km, the equivalent of about 41 mpg (5.7L/100 km).

Visteon views VTES as a transitional system between today's engines and future gas or diesel/electric hybrid systems, but it predicts that hybrids will have less than 5% of the market in 2010.

The VTES system, as with a turbocharger, generates greater power by forcing more air into the combustion chamber. Traditionally, turbocharging has been the favored approach. But the problem is the annoying “turbo lag” that is inevitable, because the turbo compressor is powered by the exhaust gases.

In the VTES system, the compressor is powered by a brushless electric motor that turns an aluminum alloy compressor at 50,000 rpm — just 330 milliseconds after the driver demands acceleration.

Visteon has a dozen patents on aspects of its supercharger system, which has been in development for three years.

“We have patents on the motor, the application, electrical system management and the central interface, among others,” says a Visteon spokesman.

“The motor-compressor is about 30% of it, but integration is the difficult part. The competition might have a motor but not the integration.”

The motor requires 2kW of electric power in operation, so Visteon needs to manage the vehicle's entire electric network in order to stay within the limits of a 12/14-volt system.

Among other things, engineers packaged the battery next to the motor to reduce losses in the wiring and regulate output of the intelligent alternator. Boost pressure is 5.1 to 5.8 psi (0.35 to 0.4 bar), depending on the application.

To demonstrate the system, Visteon installed VTES in a naturally aspirated 1.2L Fiat Auto SpA engine and a 1.9L Renault SA turbodiesel. In the diesel, the airflow from the VTES is directed through the turbocharger, boosting the intake pressure faster than the turbo alone.

Ultimately, auto makers are interested in reducing the size of their engines if they can get the same performance, because fuel consumption will be lower. Reducing performance is not a marketable option.

Potential benefits are greatest in small- displacement engines. Brown says applications are impractical on engines larger than a 3L turbodiesel or a 2.3L naturally aspirated engine, because larger engines require more air than a 12-volt supercharger can deliver.

Thus, Visteon developed its program with Europe in mind, where engines are smaller than in the U.S. Most European car buyers express interest in enhancing performance, rather than downsizing, says Visteon, and there is more interest in enhancing turbodiesel engines than in boosting gasoline engines.

In a 1.9L diesel, torque is increased about 10% for engine speeds from 1,000 to 2,500 rpm, but there is some benefit even at top speed.

More dramatic results are possible with small gasoline engines. A 1.2L engine with the VTES system performs nearly as well as a 1.8L without VTES, yet fuel economy is 27% better.

Compared to a 1.2L engine without VTES, the more powerful VTES engine's fuel economy is unchanged at 39 mpg (6L/100 km).

“In everyday driving, you use only 30% of the torque available in your engine 90% of the time,” says Brown. “You pay a large penalty in fuel economy to have the extra power available that you rarely use.”

Compared to the 1.8L engine, drivers using a 1.2L VTES would save about $1,500 in fuel cost over 36,000 miles (58,000 km), with typical European fuel prices.