How GM's E-Flex Propulsion System Works

A look inside the Chevrolet Volt.
A look inside the Chevrolet Volt. The electric motor and range extender are up front and the battery runs down the center of the car. See more pictures of electric cars.
Photo Courtesy General Motors

In 1996, General Motors's EV-1 battery-powered electric car appeared in Saturn showrooms in California and Arizona. Over the next seven years, more than 1,000 models were leased to drivers who wanted to get around without the burden of putting gasoline in their cars. However, GM ultimately decided consumer demand and battery technology wasn't quite up to par, and most of those cars ended up at a crushing facility.

Since the 1990s, the price of fuel has skyrocketed and battery technology has advanced considerably, so GM has decided that it's time to take another crack at the electric car. This time, though, they're doing things a little differently.


The E-Flex Propulsion System is an all-new platform from GM that's expected to underpin the highly anticipated Chevrolet Volt sedan, due in showrooms by the end of 2010. The system puts what engineers call a revolutionary spin on the electric car -- one that's driven by electric power but can drive for hundreds of miles with the help of an internal combustion engine.

"[E-Flex vehicles require] no support from a gas engine to operate, unlike a hybrid, which cannot operate without the engine," said GM spokesman Dave Darovitz. "Our engine is not directly connected to the wheels and only comes on when the battery is depleted, acting as a stationary, on-board generator to create additional electricity to re-charge the battery and power the car." However, unlike hybrid cars like the Toyota Prius -- which uses a small electric motor for low speed driving and switched to an internal combustion engine for acceleration and faster driving -- GM considers cars built on the E-Flex platform to be electric cars rather than plug-in hybrids.

After a night of recharging (any household power outlet will do), the car's wheels are driven solely by electric power from its battery pack. The gasoline-powered engine is used only to recharge the battery once it runs out of power.

If all goes according to plan at GM, cars powered by E-Flex can run up to 40 miles (64 kilometers) on electric power alone, without using a drop of gasoline. After 40 miles (64 kilometers), the car's initial battery charge is depleted, and the internal combustion engine -- called a range extender -- seamlessly kicks in, operating a generator that charges the battery and keeps the car running on electric power.

In the next section we'll look at the heart of the E-Flex platform -- its battery -- and how much money you'd save with a car that runs on one.


The E-Flex Battery

Chevolet Volt and EV-1 battery packs side by side.
A 16-kilowatt battery pack for the Chevrolet Volt (right) is displayed next to the original EV-1 16-kilowatt battery pack at the GM Battery Lab in Warren, Mich.
John F. Martin/General Motors

The E-Flex battery is a 400-pound (181 kilograms) advanced lithium-ion battery that generates up to 16 kilowatt-hours of electricity.

The advancements in battery technology that have made these kinds of devices possible in recent years explain why a car on the E-Flex platform can do what it does. The EV-1, for example, used a lead-acid battery pack that had the same power output as an E-Flex-powered vehicle, but weighed about 2,200 pounds (998 kilograms) more.


The E-Flex battery is also flat, unlike the cylindrical lithium-ion batteries used by most cars of its type. Flat cells take up less space than cylindrical cells, so that more energy can be stored in the car's battery pack. These cells are also easier to cool and condition, since fluid can flow easily across a flat surface.

Unlike conventional batteries that are simply placed into a car's engine bay, the E-Flex battery is so large that's it actually built into the car itself. The T-shaped battery runs through the center of the vehicle between the front and rear wheels, with the top of the "T" under the rear passenger seat. This keeps the battery safe in the event of an accident.

Still, the platform's uniqueness creates challenges that GM must face.

"The heart and soul of [the E-Flex platform] is the battery, with a vehicle on top," said Tony Posawatz, the vehicle line director for the Chevrolet Volt. Engineers know how to design and build vehicles, he said. "But fitting the battery pack, heating and cooling, the types of materials used … that's all not known."

Unlike hydrogen fuel cells, the technology is one we won't have to wait for. "The infrastructure is already in place for electric vehicles," Posawatz said. "Electricity costs one or two cents a mile, versus 10 cents a mile for gas right now."


E-Flex Onboard Generator and Motor

The E-Flex battery is connected to an electric motor that drives the vehicle's front wheels. It's completely quiet in this mode, and all a driver will hear is the noise of the road.

This motor produces about 120 kilowatts of power, which is roughly equivalent to about 160 horsepower on an internal combustion engine. However, because electric motors provide instant torque -- you won't need to rev the engine to experience its full power -- the Chevrolet Volt will offer considerably better performance.


The Volt is expected to go from zero to 60 mph (97 kilometers per hour) in less than 9 seconds. However, it's the feeling of launching the car that will really impress performance-crazy drivers. The acceleration will feel more like that of a sporty car with a V-6 engine than a small economy car. The car also uses regenerative braking, which means that the car is collecting kinetic energy as it coasts or brakes, and uses this energy to recharge its battery. Having the battery in the bottom of the car means a low center of gravity as well.

The lithium-ion batteries utilized on E-Flex-powered cars are the same ones that operate cellular phones and laptops, only much larger. To charge the battery, simply plug the car into any 110-volt outlet -- any standard household socket will work. GM expects most customers will charge the car overnight in their garages, a process that takes about six hours to complete. On a 220-volt circuit, drivers will need three to four hours to charge the battery.

GM's engineers are trying to build a car that anyone can operate. While the many components of E-Flex vehicles sound complicated, Andrew Farah, the Volt's chief engineer, wants people to understand that keeping the car running is as simple as plugging in an appliance. The Volt has a plug on its side for insertion into wall sockets for charging.

Read on to learn about the role that an internal combustion engine plays in the Chevy Volt.


The E-Flex Range Extender

The Chevrolet Volt concept car is the first vehicle to be powered by E-Flex.
The Chevrolet Volt concept car is the first vehicle to be powered by E-Flex.
Photo Courtesy General Motors

Once the battery pack loses its initial charge, it's time for the range extender -- GM's name for the internal combustion engine in the front of the vehicle -- to go to work. On the Chevrolet Volt concept car, it's a 1.0 liter (1,000 cubic centimeters) 3-cylinder engine designed to operate a generator that keeps the battery charged. It runs on a 12-gallon (45-liter) fuel tank.

"On a typical electric vehicle, you've got a battery and an electric motor," said engineer Andrew Farah. "That's everything you need until you run out of your charge… then you have to push it home." With the gas motor on the E-Flex platform, that's no longer a problem, he said.


The purpose behind the gasoline-powered range extender is to have an electric car in which drivers aren't constantly staring at a gauge to see how much juice they have left before they have to turn the car around and head home to recharge.

Despite the effectiveness of the electric motor, drivers must remember keep their gas tanks full. While the car can run up to 40 miles (64 kilometers) on battery power, after that, it needs to have the gas motor running to power the generator.

GM says the average customer should save around 500 gallons (1,892 liters) of fuel each year and almost never need to go to the gas station or maintain typical engine service schedules. The company recommends that the car be plugged in as often and for as long as possible to keep the battery conditioned.

Currently, GM engineers are working to have the range extender be powered by gasoline as well as the E85 ethanol/gasoline mixture. In Europe, they're experimenting with diesel fuel as well. They're also working on a fuel cell variant of E-Flex [source: Farah]. On that vehicle, the range extender and generator would be removed and replaced with hydrogen fuel cells. On a vehicle like that, Farah said, "you'd be running the fuel cell most of the time, and the battery not as much."


E-Flex and the Environment

GM wants the E-Flex platform to be an environmentally friendly one in terms of emissions and fuel economy. They're on the right track so far: E-Flex-powered cars produce no emissions whatsoever for the first 40 miles (64 kilometers) driven. While the car's running on battery power, the electric motor puts out none of the chemicals and air pollutants for which gasoline-powered cars have been so maligned.

Once the internal combustion engine kicks in, GM engineers estimate that drivers will get about 50 miles per gallon (21 kilometers/liter) with the range extender. The Chevy Volt concept car touted an overall range of more than 600 miles (966 kilometers), but the production version has a range of about 360 miles (579 kilometers) due to a reduced gas tank size. GM engineers simply decided the extra tank space and additional weight weren't necessary.


GM officials insist that the change makes sense. "Since people almost never drive over 400 miles without stopping, why carry all that extra fuel around that you may never use?" Darovitz asked. In fact, most people may not ever use gasoline, since GM estimates that more than 75 percent of U.S. commuters drive less than 40 miles (64 kilometers) a day [source: Chevrolet].

If all goes according to plan with the E-Flex vehicles, those drivers will never use a drop of gasoline or produce any harmful emissions during their daily commutes -- although the reduced size of gas tank may ironically boost the vehicles' fuel economy. But just in case these drivers decide to test their new powertrains and hit the open road, the cars still get about 50 miles per gallon (21 kilometers/liter).

So, when can you buy the Chevy Volt and for how much? What else can drivers find on the E-Flex platform? Find out on the next page.


The Future of E-Flex

The Opel Flextreme.
The Opel Flextreme's range extender is a turbo-diesel engine instead of the internal combustion variety used in most American cars.
Cate Gillon/Getty Images

Unveiled at the 2007 North American International Auto Show (NAIAS), the Chevrolet Volt is the first vehicle on the E-Flex platform. Unlike the two-seat, two-door EV-1, the Volt is a four-door compact sedan with four seats. The interior should accommodate a 6-foot 2-inch man comfortably in the front and rear seats. The lack of a center seat in the back will allow room for the car's battery in the center of the car and keeps the roof low for better aerodynamics. In order to get the fuel economy GM wants, the Volt will be extremely aerodynamic.

It's going to take some work: Many have called the Volt's release timetable extremely ambitious. GM wants to have the cars on the road by the end of 2010, and that means extensive testing of the battery and development of the car itself.


The battery has to stay cool. It has to be safe. It has to handle bumpy roads and must be mass-produced as well. Engineers must also have the car itself -- everything the battery operates, in essence -- ready to go by the release date.

The company had targeted $30,000 as a reasonable price for the Volt, but in recent months, GM officials have waffled on that number and told reporters that the Volt's price would be linked to the price of gasoline at the car's launch [source: Blanco].

"Pricing of the Chevrolet Volt has not yet been determined," Darovitz said. "We will evaluate many factors including government tax credits, customer benefits and value, other subsidies, electricity cost versus gasoline savings and initial volumes before we finalize the price."

A few months after unveiling the Volt, GM introduced its cousin, the Opel Flextreme. An E-Flex vehicle aimed at the European market, it's a stylish five-door hatchback with the same heart as the Volt. The only exception is the Flextreme's range extender, which is a 1.3-liter (1,300 cubic centimeters) turbo-diesel unit rather than the Volt's internal combustion engine. This makes the Flextreme better suited to European countries like Germany, Opel's home market, where diesel fuel powers most vehicles.

In January 2008, the Cadillac Provoq SUV hit the auto show circuit. It uses an E-Flex system coupled with hydrogen fuel cells to deliver a vehicle that can drive 280 miles (451 kilometers) on hydrogen and 20 miles (32 kilometers) on electric battery energy -- all while giving off no emissions except water vapor.

While the Volt, Flextreme, and Provoq are all still in the concept stages, Farah said the E-Flex components are designed for use in a wide range of vehicles. "We should be able to broaden the availability of this kind of technology, to put it in all kinds of different cars people want," he said.


Lots More Information

Related HowStuffWorks Articles


  • Blanco, Sebastian. "What Will the Chevy Volt Cost? Depends on the Price of Gas at the End of 2010." Autoblog Green. March 27, 2009. (July 10, 2009)
  • Chevrolet. "Chevrolet: New Electric Car." (July 6, 2008)
  • Darovitz, Dave. GM spokesman for Chevrolet Volt and E-Flex Operations. Telephone and e-mail interview, conducted on July 6, 2008.
  • Energy Information Administration. "Weekly Retail Premium Gasoline Prices (Including Taxes)." (July 10, 2008)
  • General Motors. "GM Awards Advanced Development Battery Contracts for Chevrolet Volt E-Flex System." (July 10, 2008)
  • General Motors. "Chevrolet Volt Development Charges On." (July 10, 2008)
  • Farah, Andrew. Chevrolet Volt Chief Engineer. Telephone interview, conducted on July 8, 2008.
  • Posawatz, Tony. Chevrolet Volt Vehicle Line Director. Telephone interview, conducted on July 8, 2008.
  • Turner, Lance. GM Battery Test Engineer. Telephone interview, conducted on July 7, 2008.
  • Rauch, Jonathan. "Electro Shock Therapy." Atlantic Monthly. July/August 2008.