What do the steering column of a 1999 Lexus, a 35 millimeter autofocus camera and a capacity crowd at the World Series have in common?
Yes, the movement of thousands of fans rising for a round-the-stadium cheer is similar to the way a new type of compact electric motor focuses automatic camera lenses and tilts and telescopes the steering wheel in the 1999 Lexus LS 400, LX 470 and Toyota Land Cruiser.
Unlike a baseball crowd, these ultrasonic motors are known for near-silent operation. That and the high torque they deliver from a compact and lightweight package could make them attractive to automakers bent on shaving pounds while loading up on electronic features. If prices ever come down, they someday could replace traditional electromagnetic motors in accessory-laden luxury cars.
The two ultrasonic motors installed in Toyota's steering columns are descendants of those developed for autofocus lenses, where real estate is limited inside a tightly packed camera body.
They were pioneered by the Shinsei Corp. of Japan more than two decades ago, and they generate high torque at speeds as low as 30 rpm and in a package that can be half the size and weight of a motor with similar power.
Although the technology is not new, its use in the auto industry is - so new, in fact, that Toyota declined to offer any details about its motors.
This may be because the ultrasonic motor has almost nothing in common with the ubiquitous electromagnetic motors in most cars. (Some of the new Mercedes-Benz S classes will have 124 of them.)
Conventional motors turn because of magnetic fields created when electric current is sent through the copper windings of the motor's armature, or central shaft. The fields alternately are repelled by and attracted to the permanent magnets positioned around the armature, causing the armature to rotate.
In an ultrasonic motor, there are no windings and no magnets. Instead, the housing contains two discs held together by a spring. One of these discs, the 'rotor,' is a simple friction plate of rubber or some other material that is fastened to the output shaft. The rotor drives whatever accessory the motor is for.
The other disc, the flexible 'stator,' turns the rotor using piezoelectric technology. (Piezos are crystal structures that change shape when electric current is applied.)
Bonded to the backside of the stator is a ring composed of 16 sections of ceramic piezos. Apply voltage to any one section and it deforms an imperceptible few microns to push the stator against the rotor. Turn the voltage off, and it pulls back.
This is where fans of America's favorite pastime come in.
Quickly zap each of the sections in succession with alternating current voltage and you create waves that travel around the ring. As the waves move, they distort the back-and-forth motion of the piezo sections so that in reality they scribe an oval path.
Each oval motion made by the piezos is like the crawling of a tiny caterpillar. The tramping of the piezo 'feet' move the rotor forward. The size of the piezo's oval path is determined by the voltage, while the alternating current frequency determines the wave's speed.
'The advantage of the piezos is that they can (expand and contract) really, really, really fast,' said University of Michigan engineering professor Diann Brei, a researcher into piezos and other 'smart' materials whose properties can be changed and then restored.
THERE'S A DOWNSIDE
Ultrasonic motors can start up or shut down in one-tenth to 1 millisecond. A conventional motor needs 10 to 100 milliseconds. The time lag is critical to some possible future applications, such as an active suspension system in which the motor constantly adjusts shock absorber valving.
Plus, the friction drive generates higher torque - no speed reduction gearing is needed for many applications (such as Toyota's steering column) - and is harder to turn once stopped.
The low speeds of an ultrasonic motor also means hushed operation and reduced vibration compared with ordinary accessory motors, which turn at 2,000 to 7,000 rpm through noisy gear drives.
But ultrasonics are not as efficient as electromagnetic motors. They convert about 50 percent of their power supply into power at the shaft, while typical 12-volt automotive accessory motors are about 70 percent efficient.
Another trade-off is cost. They can cost 10 times more than common mass-produced motors, said Stephen O'Neil, vice president of advanced research and planning for Micro Mo Electronics Corp. of Clearwater, Fla. The company makes advanced motors for aerospace and defense applications.
Said O'Neil: 'The control system is pretty complex and adds much of the cost.'