GM will focus its electrification strategy on light electrification, extended range, and battery-electric vehicle technologies; major focus on the plug; preview of the Spark EV

Chevrolet Spark EV at GM’s Electrification Experience symposium at Fort Baker, California. Click to enlarge.

GM will focus its vehicle electrification efforts on three main technologies: light electrification, currently manifested in the eAssist systems; extended range electric vehicles (EREVs) such as the Chevrolet Volt; and battery electric vehicles (BEVs), such as the soon-to-be-introduced Spark EV.

In a vehicle electrification symposium for the media, GM Senior Vice President, Global Product Development Mary Barra noted that until recently, GM’s strategy had essentially been to “cover the waterfront” in terms of pursuing as many technologies as possible. “That’s not how GM is doing business today,” she said. “We need to refine our strategy and do focused work. We need to make educated bets on which technologes hold the most potential for creating value for our customers and our company.”

GM is tracking to sell more than 50,000 vehicles this year with some form of electrification, Barra said—the majority of which will be eAssist systems. From January through October, Barra said, GM had sold more than 26,000 vehicles equipped with eAssist. Also through October, GM has sold 19,309 units of the Volt in the US, and is the market leader of the plug-in vehicle segment in the US. “We are looking at new ways to provide EREV technology to provide more options for customers,” Barra noted.

Our commitment to eAssist is unwavering. In fact, our features portfolio calls for eAssist to be on hundreds of thousands of vehicles annually by 2017.

A major focus for GM’s electrification strategy will center on the plug. We think the plug offers a unique opportunity to change the way people commute. Plug-based solutions will play a significant role in our technology portfolio going forward. We have every intention of maintaining our leadership position in plug-in vehicles.

Traditional hybrid technology is important, of course. But we think plug-in technology will play an increasingly important role in years to come and that's where a significant part of our focus will be. In fact, our plan calls for producing over 500,000 vehicles annually with some form of electrification globally by 2017.

—Mary Barra

The new focus doesn’t mean that GM will entirely ignore the full hybrid segment, but those efforts will be relegated to point solutions for specific customer needs—the two-mode hybrid system for light trucks, for example. Barra noted that GM is well-positioned with respect to hydrogen fuel cell vehicles, and that the work continues, but for the success of that technology “a lot depends on the infrastructure.”

Leading off a later symposium panel on the global aspects of GM’s electrification strategy, Larry Nitz, Executive Director of GM’s Global Electrification Engineering Team, described the continuum of electrification solutions and noted that GM has “a footprint of leadership in light electrification and plugged-in vehicles.”

eAssist is probably the most modular electrification solution that I know of. It builds upon an efficient base transmission and engine. It enables quick engine starts. It is fully connected in a parallel configuration to the crankshaft. The electric boost allows us to do interesting things and get better fuel economy than you would normally think about for such light electrification.

—Larry Nitz

Spark EV. GM used the symposium to preview the Spark EV, the second vehicle in Chevrolet’s electric vehicle strategy. To be introduced in two weeks at the Los Angeles Auto Show, the Spark EV will arrive in California showrooms in summer 2013 offering what GM says will be among the best EV range in its class—as yet unspecified.

The Spark EV will offer a few firsts. It will be the first vehicle on the market to use the recently approved SAE combo charger for DC Fast Charging (J1772). (Earlier post.) Also, the approximately 20 kWh pack, developed with tailored A123 Systems Li-ion iron phosphate cells and GM controls, can handle multiple DC fast charges daily without impact on battery life. A fast charge can bring a pack depleted to the lower range of its state of charge window up to 80% capacity in approximately 20 minutes.

Charging can also be completed in less than seven hours using a dedicated 240V charge. A 120V charge cord set is standard. Charging can be managed and monitored remotely using the Spark EV’s smart phone application, provided by OnStar.

The Spark EV battery pack. Click to enlarge.		Cutaway of the Spark EV pack. Click to enlarge.

The battery system, supplied by A123 Systems from its Livonia, Michigan factory, has a volume of 133 liters; comprises 336 prismatic cells based on A123’s Nanophosphate lithium iron phosphate chemistry; is configured into four modules; and weighs a total of 560 lbs (255 kg). Like the battery system used in the Chevrolet Volt, the Spark EV’s battery uses an active liquid cooling and heating system, which ensures improved reliability over the life of the vehicle, while providing year-round performance in all climates.

Ia a presentation at the symposium, Jeff Kessen, Director of Automotive Marketing for A123 Systems, presented data showing tremendous voltage stability for the pack (ranging from between approximately 360–375 volts) on the aggressive US06 driving cycle with the external temperature set at 35 °C (85 °F)—i.e., simulating aggressive, hot-weather driving.

A123 has had our chemistry in the field on transportation applications since 2008; the first production application was a hybrid bus. What we have done, based on those 300 million miles of field experience, is taken a chemistry that is well-vetted in the field and adapted and tailored it in terms of the cell design to the particular application in the Spark. We changed the thickness of the coating, we changed many other parameters on the internal design of the cell in order to maximize energy density and get the most range out of the product.

—Jeff Kessen

The squared-shaped battery pack is located below the rear seats and directly over the rear axle, in a single, sealed enclosure. The enclosure is constructed from an advanced composite material that improves performance with reduced weight—the first production automotive application that uses this high strength material. The battery pack is positioned in the same space used for the fuel tank in internal combustion engine-powered Sparks resulting in minimal body modifications.

Spark EV drive unit cutaway. Click to enlarge.

Electric motor and drive unit. With a 100 kW (130 hp), 400 lb-ft (542 N·m) electric motor mated with a coaxial drive unit, the Spark EV can accelerate from 0-60 mph in under eight seconds.

The heart of the Spark EV’s propulsion system is the GM-designed, oil-cooled, permanent magnet motor. Putting more than half a million road miles on development versions of the Spark EV enabled engineers to optimize the performance of the motor by using a specifically designed bar-wound copper stator and unique rotor configuration. Bar-wound differs from wire-wound designs in that the copper used is in the form of solid bars bars, rather than wire bundles. (Earlier post.)

GM uses square wire technology. This is what enables us to get the improved performance and improved power density over a conventional electric motor. This is one of our key enablers. Copper is a critical aspect of pulling current through the motor, so in a traction motor application we want as much copper as possible in the motor. In this case, square wire is much better than round wire.

—Matt Laba, Engineering Group Manager for Electric Motor Development and Validation

Drive unit with power electronics. Click to enlarge.

The motor and drive unit will be manufactured beginning in early 2013 at GM’s transmission plant—which also assembles the two-mode hybrid transmissions—in White Marsh, Md., near Baltimore. It will be the first time a US auto manufacturer has built both a complete electric motor and drive unit for a modern electric vehicle in the United States.

This notion of GM...we are fully independent and capable in motor research, design, manufacturing and motor controls. Any time you start talking about automotive technology, that flexibility of being to develop our own controls, our manufacturing, makes us pretty nimble in that arena. Frankly we think that’s a huge advantage for us.

Whether we are talking about induction motors, permanent magnet motors, or other things we explore, we have the team from research, controls, manufacturing to work through that solution. It’s really important, everyone of those steps is associated with efficiency.

—Pam Fletcher, GM Global Director of Engineering for Electric Vehicles

The cast aluminum case provides structure and weight benefits, while the coaxial design enabled a compact package for the drive unit, which is mounted directly to the cradle for improved noise and vibration performance.

The team was able to reduce development time and cost by using many of the same components and systems from the Chevrolet Volt and GM’s two-mode hybrid truck programs. More than 75% of the propulsion system components used are from other GM vehicle programs.

GM permanent magnet electric motor. Click to enlarge.

For example, the bar wound stator technology used in the motor has been proven in the Volt, two-mode hybrid and eAssist electrification systems. The motor control and oil-based cooling system used in the Spark EV motor is largely shared with the Volt, as are the power electronics.

The single stage planetary gear design was selected as the best choice for optimum efficiency. The differential assembly chosen for the drive unit is used in GM’s 6-speed transmissions found in the Chevrolet Sonic, Cruze and Malibu.

Driving impressions. Driving exposure to the pre-announcement Spark EVs was brief (loops around the parade ground at Fort Baker). However, with its power-dense motor and smooth controls, the Spark EV felt spirited, almost feisty, in that limited drive.

Handling and regen is very smooth, although if the driver shifts down to “L” from “D”, regen is much more aggressive. There car seems quiet both from the outside and the inside—i.e., no noticeable motor whine. (The Spark EV is equipped with a audible pedestrian alert. Although the engineering team reportedly had fun with a variety of sounds (such as a “moo” to match the dappled exterior of the engineering vehicles) the production versions will use something more conventional.)

Source: Green Car Congress