Science & Technology
THESE MOTORS SHIFT GEARS ON THEIR OWN
In an era of megabit chips and gigabit fiber optics, the lowly electric motor is easy to overlook. Nothing "virtual" about a motor: It uses electricity to turn a shaft, which drives fans, pumps, compressors, and other holdovers from the Industrial Age. The basic science of motors isn't exactly racing forward either. Some of the best textbooks on it were written in the 1930s and '40s. In most motor purchases, the biggest factor is a rock-bottom price.
Suddenly, though, interest in new motor technology is on the rise. Credit for that goes largely to the U.S. government, which is pushing to raise the efficiency of motors. And for good reason. Motors use more than half the electricity generated in the U.S. The Energy Dept. estimates that systems powered by industrial motors consume about $30 billion worth of electricity a year--and indirectly account for 8% of U.S. carbon emissions.
NEW HUM. The drive for motors that use less electricity is coming mn several fronts. Under the Energy Policy Act of 1992, most general-purpose alternating-current (a.c.) motors from 1 horsepower to 200 hp sold in the U.S. after October, 1997, are supposed to meet an efficiency standard that is reached today by only premium units. And the National Appliance Conservation Act of 1987 requires steady increases in the minimum efficiency of equipment in the home, including refrigerators, heat pumps, and other devices driven by motors.
The government's initiatives please motor manufacturers, whose products are getting a closer look from blase customers. In the past, buyers focused on low initial price without much regard to lifetime energy costs. Even if they wanted to take these expenses into account, they had to cope with confusing and contradictory claims from manufacturers. The 1992 Energy Policy Act gave official recognition to an industry rating system. Says John M. Hooker, manager of advanced engineering for General Electric Co.'s GE Motors unit in Fort Wayne, Ind.: "There was nothing out there in the marketplace that was driving this. Now there is."
While government action has been instrumental, efficiency improvements couldn't have happened without new technology. The advances haven't come so much in the copper and iron of the motors themselves but in the electronics that control them. The biggest improvement is in variable-speed technology. Most alternating-current motors--the most common kind--run either full speed or not at all. That's an inefficient way to perform many kinds of work, such as moving volumes of liquid and air. If electronic controllers are added to vary the speed of a.c. motors, their energy consumption can be slashed by up to 50% in some cases. A new generation of low-maintenance direct-current (d.c.) motors is also fueling the transition to variable speeds. There's plenty of room for growth: E Source Inc., an energy-conservation researcher in Boulder, Colo., calculates that only about 10% of the machines that could benefit from 1 hp to 200 hp variable-speed motors have them today.
Exxon Corp. was ahead of its time with variable-speed technology for a.c. motors. Back in 1979, its engineers devised a box that would convert the standard 50 or 60 cycles per second of household current into whatever frequency a motor needed for a given speed. To market the "synthesizer," Exxon bought Reliance Electric Co. for $1.2 billion. But the box was too expensive to manufacture: Exxon gave up on it two years later and sold Reliance in 1986. With advances in power electronics, the Exxon concept has since become practical, and adjustable-speed drives for a.c. motors are sold by dozens of companies--Reliance among them.
Hooker's group at GE Motors is pushing another approach to variable speed: a direct-current motor it calls the Electronically Commutated Motor. Ordinary d.c. motors require frequent maintenance because their electrical contacts, known as brushes, wear out. The ECM is brushless. Its rotor is propelled by the complex interaction of electromagnets on its outer ring and nonelectrified permanent magnets on its rotor (diagram).
FEUDING CURRENTS. The concept behind ECM dates back to the 1920s, but credit for making it practical goes largely to David M. Erdman, a senior electronics engineer for GE in Fort Wayne. Erdman realized that brushless d.c. motors could be made much cheaper by doing away with expensive, delicate sensors that detected the position of the rotor magnets in relation to the outer ring of electromagnets. He devised a way to sense the rotor magnets' position by using a "back voltage" they created in the outer ring. That was in 1976. After a few false starts, Erdman built a controller that juiced the electromagnets just right so they drove the rotor. "The first time I hooked up that circuit, the motor ran right," he recalls. "There was no adjusting or tweaking."
Erdman says he ran into flak from GE's a.c.-motor loyalists, who argued that energizing electromagnets in quick bursts was inefficient compared with riding the smooth waves of alternating current. To prove them wrong, he wrote a new set of motor equations. Eventually, senior GE managers bestowed the ECM team with figurative "golden badges" that protected them from being undercut by the a.c. team.
PATENT SUIT. As hopeful as Exxon, GE bragged in 1983 when it introduced the ECM that within a decade, GE and others would sell 15 million of the type annually. But the price was too high. While growing, sales today remain a fraction of that, says market researcher Frost & Sullivan Inc. ECMs are most popular for blowers used in heating and central air-conditioning. Emerson Electric Co. has a brushless d.c. motor line called VarEpro, but GE leads in sales and has sued Emerson for patent infringement. (Emerson denies the allegations, and a trial is scheduled for January.)
Other efficient designs are coming out. One, the switched-reluctance d.c. motor, is compact, rugged, and handles a wide speed range, making it suitable for everything from coal-mining machinery to kitchen mixers. It combines a simple mechanical system with a sophisticated electronic controller that precisely times jolts to the coils to drag an iron rotor around in circles. Experimental switched-reluctance motors were noisy and jittery, but manufacturers say they have solved those problems. Dana Corp.'s Warner Electric Div. in Marengo, Ill., sells them to Ford Motor Co. for cruise controls and to Hewlett-Packard Co. for drawing machines called plotters.
Still newer are motors so unusual that they don't even use the principle of electromagnetism. They're made of piezoelectric materials, which bend when a voltage is applied to them. Disks of piezoelectric ceramics can be made to ripple in a stadium wave that nudges a rotor around in circles. Japanese companies hold most of the patents on the concept, with the top user being Canon Inc.'s EOS autofocus lens on cameras.
Motor technology was stagnant for so long that many manufacturers shy away from the likes of such odd ducks as switched-reluctance and piezoelectric motors. Timing, however, is critical. It could be risky to enter those markets too late--just as 15 years ago, it was risky for Exxon to push variable speed too early.Peter Coy in New York