Popular Science, August, 1986, pp 76-79

Gasoline/electric sports car -- electric motors at each wheel deliver tailored torque for all-out performance

A small development company in Denver is working to eliminate the automobile's transmission, gears and drive shaft. With this totally new system, the engineers hope to achieve sports-car-like performance with 100-mpg fuel economy.

By DAN McCOSH
Detroit Editor

If Ray A. Geddes has his way, the street racer of the future will no longer rev his engine in noisy preparation for a stoplight blastoff. Instead, he'll sit quietly while his tiny constant-speed engine powers up an energy-storage flywheel in near silence. Then, as the light changes and he snaps his foot down on the accelerator, a flywheel/generator will release a massive surge of power to electric motors located at each wheel. Within seconds, the hybrid-drive racer will be a small dot on the horizon.

Since the beginning of the automobile age, power has been transferred from engine to wheels through drive shafts and transmissions. The goal with the new system is to break with that tradition entirely and convert the raw energy of an internal combustion engine -- still the lightest, most efficient source of on-board power for a car -- into electricity that powers a motor at each wheel. Such a system, if it can be made to work, would produce a host of benefits:

* Nearly infinity torque control, applying precise amounts of power at each wheel according to demand and road surfaces
* Outstanding economy -- in the range of 100 mpg -- both at highway speeds and in stop-and-go driving
* Regenerative braking, in which the energy now dissipated as heat would be used instead to rev up a flywheel and then be extracted again for the next acceleration cycle.

But if there are potential benefits, there are also big problems. Among them: Conventional electric motors are massive and heavy, and the electronics to control the relatively high currents with the necessary precision doesn't exist.

So is this another automotive fantasy, an idea to be shelved along with the car that runs on water and the James Bond specials? I recently visited a small development company called Unique Mobility, run by a couple of former Detroit heavyweights which just may have come close to solving the problems and converting the idea into reality. And more: Rather than pursuing a fantasy, Unique Mobility may be running only slightly ahead in a race to apply recent breakthroughs in high-strength magnets, electric motor design, and power semiconductors to a new generation of power transmission.

The moving force behind Unique Mobility is chairman Ray A. Geddes, who draws confidence from a 28-year automotive background that includes a stint at Ford supervising the team of Shelby Cobras that unseated a Ferari for the world championship in 1965. Geddes later worked with specialty-car programs, including the Ford GT 40 race cars that swept LeMans, and the original Shelby Mustang GT 350. His former mentor, Carroll Shelby, today is a major stockholder in Unique Mobility and sits on the board of directors.

The essential concept Geddes has been working on is an engine-driven generator powering electric motors at the wheels. Engineers call the concept "hybrid drive." It's not a new idea; a car called the Gas-A-Lec was on the market in 1905 that used an engine-driven generator coupled to an electric motor at the wheels. An automotive hybrid-drive system is basically a shrunken version of the diesel-electric drive used on locomotives and big earthmoving equipment. Hybrid drive promises numerous benefits, -- mainly near infinite control of speed, torque, and power at the wheels, while a small engine providing power runs steadily at a constant and efficient speed.

Today's on-board computer controls promise a whole series of benefits from hybrid systems. Even the simplest possible hybrid drive -- an engine-driven generator coupled to a drive motor -- becomes a promising route to a lightweight, infinitely controllable automatic transmission.

Geddes is staking his dream on an extremely lightweight, powerful new permanent-magnet electric motor developed by Unique Mobility that produces up to 40 hp in an eight-pound package. It's one of a new generation of small, powerful permanent-magnet motors. Coupled to power logic systems that allow the motors to be directly controlled by computers, the hybrid-drive system, Geddes says, can substitute for conventional mechanical and hydraulic transmission systems. Potential applications of hybrid drive in automobiles range from powering engine accessories to one of the most flexible, efficient, and responsive transmission systems ever conceived.

In an operating system, a computer senses the torque and speed demands of the car, feeding power to the driving motor on demand. It's a kind of electronic version of a standard automatic transmission, which uses a hydraulic torque converter and hydraulic logic to accomplish the same task.

"It's the ultimate constant-velocity transmission," says Geeddes. "The drive motors start at zero from a standing start, and are controllable over the full range of vehicle speed. No mechanical system even comes close."

Geddes sees even further possible benefits to hybrid drive in an automobile: eliminating conventional gearing altogether. "A separate motor driving each wheel would allow you to control torque individually under all driving conditions. Say in a high-speed corner when the car loads up the outside wheels, torque is applied to the wheels with the most traction," he says. More sophisticated traction control would cut power to a wheel spinning on ice, directing it to a wheel on dry pavement.

The full program Geddes envisions includes an energy-storing flywheel that accumulates energy from regenerative braking and low-demand periods, to release on demand for acceleration. Taking advantage of an electric motor's ability to act as either a generator or a motor, Geddes proposes a flywheel that consumes electricity to wind up to speed, and then generates current when the electricity is needed.

With the car at speed, tapping electricity at the wheels to spin up the flywheel makes the wheel motors act as brakes -- completely controllable with anti-lock sensors. The spinning flywheel then supplies short bursts of power to accelerate from a standing stop. Saving the energy normally dissipated as braking heat increases the overall efficiency of the car; theoretically, stop and go should consume no more fuel than steady highway speed. In addition, with the flywheel accommodating power surges, only a small engine is needed to supply the average power to the system -- a boon to overall fuel economy.

Now the problems

But what works on a locomotive has been impractical for passenger cars. Three key problems have held this system back: the electrical inefficiency of today's best motor-generator sets, the sheer bulk and weight of today's electic motors, and compact high-power electronics to handle the motor-control requirements.

"One problem is that the average efficiency of a reasonable size motor is only about eighty percent," explains Dr. Victor Wouk, a New York-based consultant on hybrid drive. "That means with the losses in a motor and generator, you start losing about a third of the advantage -- unless you use very big engines and very big motors."

In addition to the problem of electrical inefficiency, the weight of a motor-generator set powerful enough to propel an automobile has limited its practicality. One of the best commercial 32-hp DC traction motors on the market today weighs some 240 pounds. Conventional AC motors cut the weight to 75 pounds or so, but still represent considerable bulk. Anyone with a standard ¼-hp motor driving a grinding wheel in the home workshop can appreciate how bulky an electric motor can be.

At Unique Mobility's Denver headquarters, Gene Fisher, vice president of research and development, tossed me the guts of a 1-hp motor he had designed; I caught it with one hand. I was holding what looked like an empty toilet-paper roll with fine wires embedded in the surface. Fisher calls it a "shell," or "cup," motor. It weighs less than a pound, can produce 1 hp, and can rev to 2,500 rpm in 0.5 milliseconds.

Fisher developed the motor to power a high-speed computer tape drive. Now he is expanding on the concept to build motors large enough to power cars. Unique Mobility's eight-pound 40-hp traction motor is considerably shorter and fatter than the tape-drive motor.

"You can spend forever trying to improve existing designs ten percent," says Unique Mobility president John S. Gould. "We took the basic principles of motor design and started from scratch. That improved everything -- even simplified the controller design."

"The breakthrough is the ability to use very high-strength permanent magnets," says Wouk. "They have a very high flux density, producing larger force, greater torque, and higher speed. But there are a few tricks to using very high-strength magnets," he adds. The permanent magnets used in the motor are neodymium -- one of a new generation of supermagnets that are 10 to 40 times as strong as ferrite magnets, the most common in use today.

Fisher says several engineering features contribute to the motor's power. Extremely thin armature windings are located far from the center shaft, increasing their effective torque. The close packing of each winding to the permanent magnets means the propulsive force is maximized. Also the thin windings help dissipate heat.

Smooth control of high horsepower is a problem with most motors, which would rather be "off" or "on." The new design actually has three sets of windings in layers -- one on top of another -- each powering the motor at certain speed range. The controller "shifts gears" by going from one winding set to another. "We should be able to develop the forty horsepower at about 2,500 rpm. It's not strictly a high-speed motor," says Geddes.

Like most permanent-magnet motors, the Unique Mobility system functions efficiently as either a generator or motor. "To make the flywheel, we weight the 'cup' of the motor, make it wider and flatter, and it becomes a flywheel storage system, about the size of a mini spare tire," says Gould. An early prototype weighted 250 pounds, but Gould notes most of that weight was heavy shielding installed to catch pieces if it broke.

"We were running it over 25,000 rpm and we thought it might explode," he explains. Later generations will be lighter and slower. "A small flywheel would store about one-sixth kilowatt-hour of energy, a real wheel-burner a full kilowatt-hour," Gould says.

What's a MOSFET?

The third major obstacle to automotive hybrid drive has been affordable and compact control electronics for the complicated switching duties. Fortunately, the new on-board computers promise a whole series of benefits, including smooth motor control. Electronic controls for the motor are based on a new generation of semiconductors called a Metal Oxide Semiconductor Field Effect Transistor (MOSFET).

"MOSFETs can switch high-power at high frequency, while being controlled by low voltages," Geddes says. "They were developed in the 1970s, but just recently there have been major increases in power handling capability." The Unique Mobility motor uses four MOSFETs in parallel to handle its 120-amp/200-volt demand. Each MOSFET is about the size of a one-inch cube.

Controlling the MOSFET is the job of the microprocessor. It's programmed to respond to throttle position and sensors signaling engine power loads, wheel spin, and torque requirements.

Today, the pieces that would make the "supercar" work exist, but only on the workbenches at Unique Mobility. The development program to get the sports car project on the road would mean taking the basic pieces -- the motor, flywheel and controller -- that are still in Unique Mobility's lab and developing them to where they could stand up in automotive use.

The full potential of the new motor has note yet been achieved, Gould says. Sustained tests have been run at about 20 hp, half its theoretical rating. But this is still an impressive output. A control system is also in the development stage.

Possibilities for Geddes include support by a major British sports-car manufacturer, underwriting a three-year project to develop a 130-mph sports car and put his dream on the road.

But first, hybrid drive is likely to show up in less ambitious roles than a full-drive system. One potential application is direct electric drive and control of engine accessories, including the water pump, camshaft and power steering.

The second place we can expect to see hybrid drive is in military vehicles. Recently the U.S. military became interested in the potential of hybrid drive for all its vehicles.

"They're merging control electronics with power transmission. We call it 'smart power,'" says Patric McCleer, assistant professor of electrical engineering at the University of Michigan, who recently completed a study on smart power transmissions for military vehicles ranging from tanks to light trucks.

The study indicated that even hybrid drives using currently available technology promise smaller size and lighter weight than today's mechanical and hydraulic transmissions. General Dynamics Corp (Troy, Mich.) recently completed a prototype medium-truck chassis using a motor-generator set as a transmission, based on the new permanent-magnet motors. Several similar projects are in the research stage. Development is expected to accelerate quickly, however, as other major manufacturers rush to develop the new generation of electric motors. General Motors launched a new plant manufacturing its Magnequench ["Mighty Magnet," PS , Feb. '85] magnetic material in production volumes only a few months ago, the first volume source in the U.S.

The era of smart power is here.