This week, General Motors unveiled the production Chevy Volt: an extended-range electric car that rolls into dealerships late next year. Electric cars are nothing new: early models date back to the mid-1800s. Nor are they new to GM, which produced an all-electric model called the EV1 in the mid-1990s.
What makes the Volt unique is its incorporation of lithium ion battery technology, and its range of up to 400 miles. The Volt can run up to 40 miles on pure electric power. Top speed is 100 miles-per-hour.
When the battery charge runs out, the Volt automatically shifts to a gasoline-powered electric generator that powers the Volt's electric motor and maintains the battery. The on-board generator gives the Volt its extended range.
In the Wind Tunnel
Engineers spent hundreds of hours inside General Motors' wind tunnel at the Warren, Michigan tech center, in order to minimize the car's coefficient of drag. Designers began with a one-third scale model that included a detailed underbody and engine compartment. Then they moved on to a full-scale model, to refine the exterior and test the car for wind noise.
Since aerodynamic drag accounts for twenty percent of the energy consumed by the average vehicle, wind tunnel improvements would have a major impact on the Volt's range.
"There was a time when (car design) was a lot of cake decorating, but now it's a lot of problem solving," said Bryan Nesbitt, vice president of design for GM North America. Nesbitt, who coordinated the Volt design team, spoke recently with a group of Phoenix-based journalists about the project.
Using the wind tunnel, designers were able to improve the production model's coefficient of drag thirty percent over the original concept. Despite that, many design cues from the concept car remain in the production model: its closed front grille, forward stance, rear graphics and outside mirrors.
A rounded front fascia and tapered corners allow air to move around the front of the car, while sharp edges and a rear spoiler deflect air off the rear of the car quickly.
Refining the Volt's aero exterior was one of several challenges the design team faced.
The interior presented some unique problems as well, due to the size and shape of the battery pack. The T-shaped battery extends from the back of the car into the second row, so rear passengers need to sit outboard of where they would in a conventional car.
The battery pack is roughly six feet long, and weighs over 375 pounds. Its size and weight dictated that the battery be treated as part of the vehicle structure. By locating the batteries in the middle of the car, they are protected against collision damage and temperature extremes.
Designers had to keep the roof low for aerodynamic reasons, yet provide adequate headroom for the rear passengers. The production model accommodates a six-foot, two-inch male in all four seating positions.
Lengthening the car would have improved its aerodynamic efficiency, but it would also add weight. The front-wheel drive chassis is more compact and lighter than rear-wheel drive.
While a two-passenger car might have offered even better fuel efficiency, developers felt more seating capacity was important to give the Volt widespread appeal.
Nesbitt explained that designers used the "Sam's Club, Costco model." In addition to commuting, Volt owners will use their cars to go grocery shopping, pick up supplies for home improvement projects, and go out on the weekends with friends. Buyers want what Nesbitt calls the "emotional security" of a four-seat configuration.
While most new cars have wide squat wheels to enhance performance, the Volt's must be spindly thin to minimize rolling resistance. At the same time, wheels and tires must provide adequate traction for four-season driving.
Maximizing Comfort While Minimizing Weight
Despite weight considerations, the Volt had to have all of the necessary passive safety features to meet 2013 federal rollover standards, and include the comfort and convenience features Americans expect in a passenger car.
The production model will have touch-screen climate and infotainment controls, and a separate seven-inch touch screen vehicle information display. An optional on-board navigation system also stores music on its hard drive. All models will be Bluetooth compatible
By thinking outside the box, designers were able to maximize interior comfort and minimize weight. For example, heated seats keep passengers warm while solar panels maintain a comfortable temperature when the ignition is off.
Cutting-edge Battery Technology
General Motors worked with A123 Systems of Massachusetts to develop battery cells to meet the needs of its new electric vehicle architecture. While the Volt uses lithium ion technology, its batteries are not the same as those used in personal computers. They are less affected by cold temperatures, and they last longer.
How much longer? According to engineers' estimates, the battery pack in the Volt should last ten years. Since engineers only had two years to test their durability, they used a computer program that continuously cycled the batteries, based on the car's forty-mile electric-only drive cycle. The battery tests took place simultaneously at GM test facilities in Warren, Michigan and Mainz-Kastel, Germany.
Engineers had to gather real-world data as well. They integrated the battery packs into test mules: development vehicles driven in extreme hot and cold temperatures, rain and snow.
Vibration is a major contributor to battery degradation: the Volt's battery packs must be able to withstand shaking when the car travels over rough roads.
Home Recharging Stations
Buyers will be able to recharge their cars at home, using conventional 120-volt outlets. It will take about eight hours to recharge the car using conventional outlets; about three hours if the home is equipped with 240-volt plug-ins.
General Motors is partnering with the non-profit Electric Power Research Institute to accelerate development of an electric car infrastructure that allows owners to recharge their cars at stations outside the home. In addition to the Volt, General Motors will be introducing a plug-in version of its Saturn Vue hybrid.
Reaping the Benefits
The Chevy Volt produces zero emissions when the car is running on pure electric power. In addition to doing something good for the environment, buyers will see financial benefits, since the cost of electricity per mile is about a fifth the cost of gas.
General Motors will build the new Chevy Volt at its Detroit-Hamtramck manufacturing facility.