GM's E-Motor Magic

By Bill Moore

General Motors gave a select group of journalists a tour of its new electric motor manufacturing facility in White Marsh, Maryland, including EV World. What they've accomplished in both engineering and production seems almost magic.

Two years ago, according to Maryland Governor Martin O'Malley, the site of General Motor's new electric motor production facility north of Baltimore was just an open, grassy field. On this day, as he stood at the podium, in front of him was one of the first of a new generation e-motor that will propel the Chevrolet Spark, an example of which stood to his right.

Now tens of millions, perhaps billions of electric motors of all shapes and size are manufactured every year, but this particular motor is special both in terms of its design and capabilities, something that only becomes obvious when you have the chance to sit across a cafeteria table for some one-on-one conversation with Larry Nitz, GM's Global Director of Vehicle Electrification and Peter Savagian, the Engineering Director of Electrification Architecture and the Electric Motor Research Center in Pontiac, Michigan.

General Motors invited EV World and some twenty other journalists to tour the new electric motor plant, which sits adjacent to its transmission plant where the dual-mode transmission is built for its SUV hybrids. The facility is one of GM's jewels in terms of environmental impact. It is a no-land fill facility, meaning it produces no waste that ends up in land-fills. Any waste that is produced is recycled, a process that became obvious as we toured the production floor and saw how the 100kW (130 hp) electric motor is built.

Additionally, the entire roof area of the e-motor section of the plant is covered in photovoltaic panels that can generate 1.2MW of electric power, or about 10% of the plant's electrical needs. The entire White Marsh facility has also been designated a wild life sanctuary, a fact immediately obvious from the flights of Canada geese, as well as their droppings on the surrounding grounds.

The tour began with introductions and presentations by both Nitz and Savagian, followed by small group tours on the plant floor where operations had been temporarily suspended for reasons of safety. While my particular group had a knowledgeable guide, we were fortunate to have Savagian join up with us, providing additional insights into both the electromechanical aspects of the motor, as well as the incredibly tight tolerances of the manufacturing process, where every bolt is torqued to very precise, computer-monitored standards. There is no 'slop' in this motor, I can assure you.

It was over lunch, however, that both Nitz and Savagian took the time to explain to several of us exactly what makes the Spark's electric motor so quiet, smooth and powerful.

Previously, and perhaps rightly so, much of the attention on electric car development has been on their batteries, viewed by some as the EV's proverbial 'Achilles heel.' Electric motors, because they are so commonplace, are little thought of and seldom talked about other than a passing reference to horsepower and kilowatt output and foot-pounds of torque. But designing an electric motor is a complex, highly technical process, especially if you want to get the most efficient utilization of the energy in the car's battery pack. A heavy, noisy, inefficient electric motor wastes that energy.

Savagian oversees a team of electrical engineers with PhD's who have applied all their knowhow to better understand the dynamics of e-motors and the magnetic fields they generate, so the motor can be optimized in terms of weight, power-output, durability and manufacturability. To the casual observer, the Spark Motor pretty much resembles any other industrial motor, but as Nitz explained to me over lunch, as he nibbled on a potato chip, a comparable, but less rigorously engineered e-motor destined to power a factory conveyor belt would be five times as massive as the 40 kg Spark motor. Five times.

GM engineers have packed a lot of punch into their motor, each of which requires, they estimate, one 8-hour sift to produce. The plant is currently running just one shift in anticipation of demand for the car once it goes on sale at Chevrolet dealerships in California and Oregon who also handle the Volt. Later in the year, the car will be offered in a number of international locations. There are no immediate plans to offer it in the other 48 states. However, the plant was designed to produce many more motors than it currently does.

Because this is the first electric motor plant that I've visited, I can't compare its level of technological sophistication to, say, a similar state-of-the-art facility in Europe or Asia. I have to assume it is right up there with the best given the level of robotics and materials utilized.

Permanent magnet electric motors pretty much consist of three primary materials: copper, steel, and the magnets, the latter made of rare earth elements. The Spark e-motor is no different. It's how they are arranged that would seem to set this motor apart, as well as the processes used to assemble each that are designed to minimize waste.

For example, the copper coils are fabricated using square wire that is cut, trimmed and bent by robots into the "hair pin" shapes required to create the windings. Savagian explained that using square wire is a more efficient use of space. While it takes an experienced technician 15-minutes to manually insert each of the 120+ copper 'hair pins' into their insulating wrappers in the motor, after that robots continue the assembly process, from seating the pins in the stator to welding the free ends into a continuous coil, to dripping the insulating vanish and epoxy onto the newly welded ends. This last step of dripping, instead of dipping, the exposed ends of the coil into their respective coating baths cuts production time and waste.

The magic of the Spark motor, however, starts to become obvious once you see how the rotor is assembled. This is where the tiny, Chiclet-sized rare earth magnets are mounted. There are two sizes of them and they are positioned at various angles to the radius of the rotor. But what's intriguing isn't so much the magnet themselves, but the how they are spaced and the tiny 'eyebrows' and pinholes that are part of the rotor assembly. These aren't there as an after-thought or by-product of a sloppy manufacturing process. They have a very precise purpose, as Peter Savagian illustrated using my luncheon paper napkin.

The Spark motor is a three-phase motor, meaning it has three overlapping sin waves in its power flow, the purpose being to smooth out the operation of the motor as it spins. But within in these sin waves are small peaks and troughs. The purpose of the air gaps in the form of the 'eyebrows' around the slots into which the magnets are epoxied, and the even smaller pin holes closer to the outside of the rotor are to reduce these peaks and valleys, directing the magnetic flux fields in such a way as to further quiet the motor and smooth out its operation.

The other key innovation is the reduction gear system that uses a planetary sun gear arrangement to eliminate the need for a transmission to reduce the rotational speed of the motor to deliver useful torque to two front wheels.

The drive motor and reduction gearing transaxle is encased in an aluminum housing. Above it, in the car, sits the control electronics. The entire package is smaller than a comparable ICE-age gasoline engine, though as one journalist pointed out, when you add the battery pack, the car ends up weighing considerably more than its gas engine counterpart. True, but that's changing too.

Nitz explained to me that lithium battery chemistry has a long way to go still in terms of its power and energy potential before GM moves on to something else: zinc air or what have you. When it's available this coming June,the Spark can be ordered with optional DC Fast Charge capability, which will recharge the battery to 80 % state of charge in 20 minutes or less.

Speaking of the battery, GM continues to use A123 Systems lithium batteries in the Spark despite the company's financial troubles in 2012 and eventual acquisition by Wanxiang, a large Chinese automotive parts maker. The battery packs continue to be built in Livonia, Michigan. They have a rated capacity of 20 kWh. Nitz said that he's not yet prepared to discuss the car's official EPA range yet, but he did say that it would be priced, with the $7,500 federal tax credit, below $25,000. He assumes that the warranty will be comparable to that on the Volt: 8 years, 150,000 miles (California law stipulates this, other states would likely see it warranted to 100,000 miles, which is what's stated on the company web site).

When asked about battery leasing, which is being offered in Europe by Renault and Bollore on their comparably-sized electric city cars, the ZOE and Bluecar, neither Nitz nor Savagian were keen on the idea, explaining they didn't really understand who benefits from the business model. They added that if you're concerned about the durability of the battery, then just lease the entire car instead, they suggested.

The Spark will be sold, battery, car and all, as well as offered for lease, though no details have yet been announced.

The tour ended with my taking a couple spins around the plant in one of a pair of Electric Blue Sparks - I'd call the color more 'powder blue'. It also will be available in Black Granite, Summit White, Silver Ice and Titanium.

The very existence of the White Marsh e-motor facility, along with other EV-specific infrastructure development, from the expansion of the battery lab at the Warren, Michigan Tech Campus, to the new electric motor R&D facility in Pontiac, strongly suggests that General Motors is committed to developing, refining and producing an ever-increasing range of electric drive vehicles beyond the Volt and the Spark.

Next up is the Cadillac ELR, production validation versions of which are just now being assembled, Nitz told me. Full production will commence in December at the Hamtramck plant in Detroit, the home of the Volt and its European-bound cousin, the Ampera.

When I mentioned the ELR, both Nitz and Savagian virtually swooned with excitement, but that's another story for another time.

Learn more about the Spark EV here. and here.

NOTE: The next edition of EV World Insider Illustrated will feature fuller photo coverage of the tour

Times Article Viewed: 13078
Originally published: 17 Apr 2013


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