Nearly 90 years after the early electric vehicles were swept away by the availability of gasoline and robust, low-cost combustion engines, the electric traction motor—more efficient and powerful than ever—is poised for a major return.
Demand for a new generation of vehicle electric drives is growing, as the industry prepares to launch numerous new electrified vehicles, both hybrids and EVs, in the next few years. Industry forecasters expect annual production of e-motors designed to power vehicles to grow well into the millions this decade. Every hybrid and EV has at least one electric machine, and some have multiple motors depending on their layout and intended use.
Motor technology development is increasing at OEMs and suppliers, buoyed by millions in R&D funding from the public sector. With the growth comes a new strategic focus: Some automakers have decided to design, develop, and produce their traction motors in house, rather than purchase off-the-shelf machines from specialist suppliers.
Last month GM announced it will be the first major U.S. automaker to design and manufacture its own e-motors for use in its second-generation Two Mode hybrid drive system beginning in 2013. Vehicle applications are expected to include a wide range of cars and trucks, including Cadillac luxury sedans and crossovers.
GM is setting up dedicated manufacturing for the permanent-magnet motors at its Baltimore, MD, transmission plant which builds the current Two Mode unit. The motor plant is being financed partially by a $105 million U.S. Department of Energy grant aimed at boosting domestic electric-propulsion knowledge and capacity.
GM has been developing the proprietary e-motors since 2003 in dedicated research and testing facilities, and it has hired engineers to boost its motor R&D capabilities. The company's total investment in the motor activity is $246 million.
“We’re doing this for the same reason we make our own combustion engines—it is core technology for us,” said Tom Stephens, Vice Chairman of Global Product Development.
Stephens told AEI he believes electric traction motors and their related development and manufacturing expertise will be a strategic advantage for GM, as vehicle electrification expands globally. Many of his competitors concur.
Honda, Nissan, and Toyota also are guarding their electric-drive system technologies and production base, noted industry analyst Toru Hatano of CSM Worldwide.
The Japanese OEMs want to keep tight control of e-motor manufacturing processes and quality. Their kieretsus are providing technical input and also managing the motor supply chain. Toyota, for example, uses its affiliate Toyota Tsusho to keep it supplied with neodymium, according to Hatano. Neodymium is a rare-earth metal used for making the magnets used to generate the electric field inside permanent-magnet motors.
The two primary types of electric machines—induction and permanent-magnet (PM)—currently used in hybrids and EVs are expected to continue to dominate the market. The two types differ mainly in the design and function of their rotors. In simple terms, those used in induction machines generate their magnetic fields from electric current flowing through the copper windings (actually copper bars in most cases) wrapped around the rotor’s iron core.
The rotors in PM machines use magnets to generate the magnetic field exclusively, without the need for current.
A combination of new design variations, new materials, and sophisticated electronic controls are making e-motors much more amenable for electrified-vehicle duty, said Dr. Heath Hofmann, Associate Professor of Electrical Engineering at the University of Michigan.
“The auto companies are focusing on machines capable of operating over a much wider speed range than typical fixed-speed industrial motors,” he said. “And the new motor designs provide a lot of torque and power density.”
For example, the motors GM is developing for 2013 will have more than double the rated output of comparable industrial motors, said Pete Savagian, GM's Engineering Director, Hybrid Powertrain Systems Engineering and Electric Motor Release Centers.
As with nearly everything in engineering, there’s no "ideal" with e-motors. Both inductive and PM machines have their pros and cons. PM machines generate less rotor heat than inductive types, which aids overall efficiency to a point. But as machine size grows, magnetic losses increase proportionately, reducing part-load efficiency.
Rare-earth magnets add capability to PM machines. Samarium-cobalt, dysprosium, and neodymium increase the rotor’s magnetic flux (its total amount of magnetic field), while providing superior thermal performance. Both are keys to greater power. Neodymium is the most commonly used and affordable rare-earth metal. For automotive use it is combined with percentages of iron and boron.
Increasingly PM machines in automotive are the interior-magnet variety—their magnets are embedded within the circumference of the rotor, rather than surface mounted. There are two reasons for this, noted Dr. Hofmann. First, embedding the magnets provides some containment safety—permanent magnets tend to be brittle and can be susceptible to damage under extreme use conditions. The main reason the interior-magnet design is favored (by Toyota, for the Prius motor and GM, for its 2013 motors) is it provides greater control of flux levels, enabling a wider range of operating speed.
Rare-earth metals tend to be costly. And their long-term supply has come into question, since China holds a near-monopoly on known sources. With year-on-year demand projected to grow steadily, efforts are underway to open new mines in the U.S., South Africa, and Brazil.
Induction machines also have losses proportionate to size. But the difference is that flux levels are easily controlled by reducing currents, whereas in permanent-magnet machines current must be added to cancel the magnet flux.
“In induction machines, reducing torque results in reducing conduction and magnetic losses,” Dr. Hofmann explained.
The induction machines’ design makes them capable of generating high specific power by operating at high rpm—the induction motor in Tesla Motors' Roadster spins up to 14,000 rpm. (GM also used an induction motor in its EV-1, but today the type is comparatively rare in the hybrid and EV world.) They’re generally less expensive to produce than PM types, but they’re also more difficult to control over a broad speed range, engineers claim.
Specialist motor developers, including Unique Mobility, Remy Electric Motor Technologies, Siemens, and Azure Dynamics, have been improving automotive e-motors since long before hybrid cars became popular. Remy, for example, launched a new family of e-motors called HVH, which stands for High Voltage Hairpin. In this technology, the stator-windings use special rectangular-section wire rather than round-section wire. The windings are arranged in multiple layers, interlocked by tiny hairpin-like connections. The company claims the HVH design improves cooling, thus boosting torque and power.
For hybrid and EV planners, the choice of motor type will likely be application-specific, Dr. Hofmann reckons.
Induction machines appear to be the choice for battery EVs where high performance is a key requirement, although Nissan is using a PM motor in its upcoming Leaf EV. For hybrids and plug-in hybrids a PM motor may be more appropriate.
Tesla, which has the distinction of being the first modern-era EV maker to design and produce its own AC induction-type traction motors, also considers them to be a strategic asset.
According to Tesla Chief Technology Officer JB Straubel, there was really no argument during the formation of the California-based start-up automaker that it would develop a proprietary motor rather than purchase and modify an off-the-shelf unit.
Straubel explained that for an EV maker, the traction motor is key to the “synergy of the electric powertrain”—his description for the overall functionality of the battery, e-motor, power control electronics, and charging system. He said off-the-shelf motors, no matter how extensively they are adapted for a specific application, can compromise the efficiencies of the propulsion system.
OEMs that purchase their motor expertise rather than develop and sustain it in-house also risk never being a technology leader in EVs—“you end up as just an assembler of cars,” he said. Developing core engineering strengths in e-motors will also help automakers build their brands as the industry becomes increasingly "green," Straubel noted.
The prospect of OEMs bringing inside what traditionally has been an outsourced engineering and manufacturing function is making some motor suppliers uneasy.
According to Kevin Quinn, General Manager of Remy Electric Motor Technologies, GM’s Baltimore plant announcement was not quite a surprise. But there was sufficient concern for the company to issue an explanation to its customers and suppliers that it intends to remain firmly in the e-motor game.
Remy’s permanent-magnet e-motors are used in the GM, BMW, and Mercedes Two Mode hybrids, as well as a growing list of commercial vehicles. The Indiana-based company, once part of GM, traces its roots back to the Remy brothers’ first automotive magnetos in 1896. It was recently selected for a $60.2 million federal grant to accelerate hybrid and EV motor development.
Quinn considers the news of GM and others getting into the e-motor market as “a short-term trend.” He noted that the emerging EV makers and smaller OEMs lack the major resources needed for motor R&D. And he said the larger companies will eventually confront Remy’s “head start in electromagnetic technology, manufacturing, and patents.”
He is confident GM and other major automakers will end up shifting only part of their e-motor development and production to their own plants. As it electrifies its products, the industry will continue to purchase off-the-shelf motors. Overall market growth has prompted Remy to undertake a major expansion of its production capacity in 2011, Quinn added.
At BMW, engineers behind the company’s Project I are responsible for investigating advanced-propulsion opportunities for future vehicles. According to Project I Director, Dr. Ulrich Kranz, BMW management has not yet decided on its e-motor strategy. He said the challenge for the near-term is how to transfer the driving character of a traditional BMW combustion-engine powertrain into the electric-drive systems being developing for a new range of city EVs, expected by 2015.
Speaking with AEI at the Detroit auto show, Dr. Kranz acknowledged that virtually all EVs currently in production tend to be too quiet, too smooth, and too…un-BMW.
“We are being watched closely to see how we make electric vehicles that meet expectations of what BMW vehicles are famous for,” he said.