Sustainable Energy

A New 42-Volt Standard

An MIT-based consortium is helping ensure that future cars have all the electrical power they need for features galore.

Nine years ago, engineers at Daimler-Benz in Germany issued a cry for help. They realized that luxury trimmings on the automobiles they were designing would eventually gobble up more power than existing 14-volt electrical systems could handle. So they gathered together researchers from MIT to discuss the problem and advise them on selecting a more powerful system and-more importantly-to help convince other automakers to adopt it.

The talks paid off. In 1995, the industry agreed-with help from MIT’s Laboratory for Electromagnetic and Electronic Systems-on a new standard of 42 volts. Industry leaders also realized it made sense to create a formal consortium, headquartered at MIT, to help implement the standard. Today some 52 companies-automakers and major suppliers-each contribute $50,000 annually to the lab in support of the MIT/Industry Consortium on Advanced Automotive Electrical/Electronic Components and Systems, based in the electromagnetic and electronic systems lab.

“We are the major place where the international automotive community can meet in a neutral forum to address issues of common concern and resolve them,” says lab director John Kassakian ‘65, SM ‘67, EE ‘67, ScD ‘73.

Of course, the international interest isn’t all about building luxury trimmings. Higher voltage will also lead to higher fuel efficiency.

Less than 30 percent of the energy in gasoline actually makes cars move; the rest is waste heat burned off during idling and squandered by inefficient components. A more powerful electrical system could allow efficient electronic components to replace the comparatively inefficient systems found today, which are driven by belts connected to the engine. And if cars had starter motors powerful enough to provide “instant start” at the tap of the gas pedal, then they could shut down at most traffic lights, eliminating wasteful idling. Individually, some of these electronic components can be supported by existing 14-volt systems. Taken together, however, they will require 42 volts.

These more powerful systems will take a decade to reach showrooms in any number. But the big car companies are making early moves. Toyota Motor has already begun selling (in Japan only) a 42-volt luxury sedan. And General Motors plans to unveil its first-generation 42-volt system in a hybrid gas-electric pickup truck in 2004.

Automakers share some common concerns about these 42-volt systems-and that’s where MIT comes in. The automakers need to prevent destructive short circuits, find ways to meld old and new systems and perhaps even create entirely new power sources beyond the familiar alternator-and-battery combination. To those ends, automotive competitors from Tokyo to Stuttgart to Dearborn are turning to the researchers in a cluttered warren of basement labs in Building 10.

From Mundane to Visionary

Just down a dim hallway from the time clocks punched by MIT’s custodial crews, the labs’ researchers do things like autopsy the electrical system of a skeletal Mercury Sable. “We run a range of programs, from the mundane and practical to the visionary,” says Thomas Keim, SM ‘70, ScD ‘73, the consortium’s director. Keim is also principal research engineer at the electromagnetic and electronic systems lab, which includes nine faculty from electrical engineering and computer science, six researchers and about 50 undergraduate and graduate students.

First, Keim says, automotive electrical systems need to be safe and reliable. Take arcing-electricity’s tendency to make lightning-like leaps through the air. A single arc-from, say, a frayed wire-could ruin a previously good part, or even cause a fire.

And arcing in a 42-volt system is a much more serious matter than in a 14-volt one. Just how much more serious was confirmed last year when former research assistant Alan Wu verified that arc energy is 50 to 100 times higher in 42-volt systems. This finding helped auto parts companies worldwide begin designing new parts to suppress such arcs. Now the lab is researching better ways to detect them.

Then there are practical concerns. The group is working on mapping out how one car can house both a 42-volt system and a 14-volt system. That’s because automakers will not replace the entire electrical system at once; the old system will still power the windshield wipers, radio and headlights, while the new, higher-voltage system will fire up the electrified brakes or engine valves. In the interest of compatibility, David Perreault, SM ‘91, PhD ‘97, dismantled an off-the-shelf alternator and figured out how to use it to supply a 42-volt system by rigging it with new switching controls.

But that’s just a stopgap measure. Eventually, cars will need to look beyond the alternator for a power boost, because if a car’s engine shuts down at a traffic light, the alternator is useless. And that leaves components-especially gluttonous air conditioners-without a power source.

One solution is to create a little power plant onboard. A group in the lab is designing a device that would borrow tricks from photovoltaic cells, which produce electrical power from sunlight, to generate electricity under the hood. Inside the proposed device, light from a brightly glowing ceramic emitter heated by a gasoline flame would act as the “sunlight,” while a semiconductor such as gallium antimonide would transform the photons’ energy into electricity.

Such a device would only be about 15 percent efficient-which may seem low but is in fact a considerable improvement over the nine percent efficiency of a conventional alternator. What’s more, waste heat could help fuel a so-called absorption air conditioner, which uses a heat exchanger instead of a compressor. Ultimately, “this would be the one electricity source on the vehicle,” says Keim, who concedes that the project is “out there toward the visionary end.” Nonetheless, the lab is in talks with an unnamed industrial partner to develop a prototype.

“This has required a lot of up-front analysis because it is so revolutionary,” Kassakian says. “Most people think fuel cells will provide this auxiliary power, but this onboard generator is much more near term than fuel cells.” The device could be developed in five years, he says, whereas fuel cells that use gasoline are farther off.

Work on both the mundane and the visionary makes the consortium valuable to industry, says John Miller, an electrical engineer and coleader on hybrid-technology governance at Ford Motor’s research labs in Dearborn, MI. “There’s a high value in the consortium, because now we are getting into the nuts and bolts of implementation,” he says. “They help deal with issues that are still of concern for the broad automotive community, like fusing, relays and switches for 42 volts.”

Indeed, Miller says, Ford is planning to roll out a hybrid sport-utility vehicle, the 2004 Escape, with an instant-start motor. Though this change will be made within the 14-volt system, Miller says the nascent effort is benefiting from the tinkering in the basement of Building 10.

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