Brainy, not Brawny

BMW will use technology to boost performance, mpg of next-gen engines.

Detroit – The era of making engines bigger is over at BMW

"The time to increase horsepower by increasing displacement is over," said Klaus Borgmann, senior vice president of powertrain development for BMW, during an interview at the SAE World Congress here last week. "I am very convinced that the time to increase displacement will never come back because increasing displacement automatically increases fuel consumption."

The move is part of a growing industry trend to improve performance without increasing engine size or hurting fuel economy, said Bill Rinna, an analyst with CSM Worldwide, a consulting company in suburban Detroit. "You are seeing a lot more engines with variable valve timing, direct injection and either supercharging or turbocharging," he said.

Rinna said BMW buyers expect safety and technical advances that improve handling and performance, and boost fuel economy through technology.

General Motors and Ford Motor Co. also plan to build smaller but more powerful and fuel-efficient engines. Ford's new 3.5-liter V-6, for example, makes 40 more horsepower than its current 4.0-liter.

Borgmann outlined several ways BMW will boost fuel economy starting this fall

• BMW is spreading its Valvetronic system, which varies the duration and lift of the intake valves to maximize fuel economy, emissions and performance, to the 2007 Mini Cooper. The sporty S version of the British-made hatchback will use a turbocharger, instead of the supercharger in the current model, and have direct fuel injection, Borgmann said, for about a 10 percent fuel economy gain over the 2006 car. Instead of bigger engines, he said, turbochargers will be used on other BMWs to improve performance.

• In 2007, European BMWs will be equipped with a stop-start feature that turns off the gasoline or diesel engine when the car comes to a stop. The engine restarts immediately when the driver lifts his or her foot off the brake pedal. Borgmann said the feature is being evaluated for North America. Stop-start may not be suitable for hot climates, he said, because the air conditioning compressor stops working when the engine is off. The stop-start system will use a specially modified starter, instead of a belt alternator system, and a heavier-duty battery. The Mini Cooper also will have the stop-start system.

• A new alternator management system BMW calls Brake Energy Recuperation makes more efficient use of the car's charging system. The goal is to capture some of the energy normally lost when a car is braking. Borgmann said the system keeps the battery charged at 80 percent to reduce the load, or drag, that the alternator places on the engine while the vehicle is cruising. When the driver applies the brakes, a sensor commands the alternator to produce a short blast of electricity to bring the battery up to a 90 percent charge. When the driver accelerates, the alternator is allowed to spin freely so no drag is placed on the engine. BMW will begin installing the Brake Energy Recuperation systems in 2007 on European market vehicles, along with stop-start.

• Hybrids: In 2009, BMW will use a version of GM's Two-Mode heavy-duty rear-wheel-drive transmission that enables large cars and rwd SUVs to get an estimated 25 percent fuel economy improvement in city and highway driving. GM, which developed the transmission, is selling it to BMW and DaimlerChrysler.

BMW has not said which of its vehicles will get the Two Mode transmission. About 60 BMW engineers are working alongside GM and DaimlerChrysler engineers in Troy, Mich., to adapt the GM transmission to the BMW engine.

The fuel economy gains from the stop-start and Brake Energy Recuperation systems are borne out of some of the first technical ideas to come from BMW's Department of Energy Management, a special team of 100 engineers that BMW formed in 2003.

"BER, together with the stop-start system, it's about an 8 percent fuel economy improvement, depending on the driving cycle," Borgmann said. "That's about half the value of a hybrid system with very simple systems. We will introduce this in Europe in a broad range of cars because it is not so expensive," he said.

BMW is also looking at ways to capture energy wasted in the exhaust system to create steam to reduce the load on the engine.

"The outcome of the thinking of Energy Management is how can we deal with all the energy flows in the car and what can we do so that the customer has the most benefit," Borgmann said.

Several BMW cars in the United States are considered gas guzzlers and are subject to a special tax by the government.

"The BMW brand is not known to be very fuel efficient," Borgmann said. "It is important for BMW to be good there as well."