This advanced computer program duplicates real-life vehicle speed and cargo-carrying conditions, and compresses 10 years of comprehensive battery testing into the Volt’s brisk development schedule.
The battery cycling equipment is used around the clock in GM test facilities in Warren, U.S.A. and Mainz-Kastel, Germany. It charges and discharges power from the prototype batteries based on the Volt’s approximately 40-mile electric-only drive cycle. Results from this test data will help predict the long-term durability of the battery.
“Production timing of the Volt is directly related to our ability to predict how this battery will perform over the life of the vehicle. The challenge is predicting 10 years of battery life with just over two years of testing time,” said Frank Weber, global vehicle chief engineer, Chevrolet Volt and E-Flex systems. “The battery team is able to utilize human and technical resources around the globe to reduce testing time.”
Testing the batteries in the laboratory provides a predictable environment to compare technologies under controllable situations. The batteries will soon be integrated into “mule,” or test, vehicles with other E-Flex system components for on-road tests.
Vehicle engineering
Engineering an electric vehicle with a battery roughly 6 feet (1.8 m) long and weighing more than 375 pounds (170 kg) requires innovation. The T-shaped battery will be located down the center tunnel of the vehicle and under the rear seats. This integration requires the battery to be treated as part of the vehicle structure. Simulation data also indicates that the center placement provides greater protection to the battery.
Engineering innovations are also required to maximize the Volt’s 40-mile electric-only range and minimize the use of its range-extending internal combustion engine. To reduce mass, the Volt is being engineered with a relatively small fuel tank. This reduces weight, but still provides a driving range in excess of 400 miles between fill-ups.
Designing the interior
The battery placement created interior design opportunities that led to several creative solutions that improve aerodynamics and overall comfort.
“We made a conscious decision to make the Volt a four-passenger vehicle to keep the roof low, an important aerodynamic enabler,” said Bob Boniface, design director, E-Flex. “As designers, we must be sensitive to the energy efficiency gains that can be achieved by optimizing aerodynamics. This not only contributes to improved fuel economy or extended range, but can produce beautiful exterior body shapes and innovative interiors.”
“By having the battery in the middle, we were able to move the occupants apart and give them more space,” said Tim Greig, interior design manager for the Chevrolet Volt. “We also shrink-wrapped the interior, particularly the doors, for comfort and spaciousness. There is no wasted space.
“Being an electric vehicle with a battery down the middle presented unique opportunities to our design team,” he said. “The net result is a very creative and innovative design, appropriate for an electric vehicle.”
Reducing drag
Aerodynamic drag, or wind resistance, accounts for about 20 percent of the energy consumed by an average vehicle, directly reducing fuel efficiency.
GM’s aerodynamics laboratory, located in Warren, is the center of expertise for optimizing airflow. In addition to fuel economy, range, emissions and acceleration are all affected by aerodynamic drag. The cooling of components like brakes is affected by airflow, as is cornering capability, crosswind response, directional stability and on-center handling. GM’s aero lab allows for the testing and development of each of these characteristics.
“After extensive aerodynamic testing of the Volt, the vehicle now has a coefficient of drag that is 30 percent lower than the original concept,” said Ed Welburn, GM vice president, Global Design. “It’s not easy, but it is a necessity.”
The ongoing development of the Volt is just one part of GM’s commitment to displace petroleum use in the auto industry through a range of propulsion alternatives, including:
GM is the leading producer of E85-capable biofuel vehicles, with more than 3 million on U.S. roads today. GM has committed to having 50 percent of annual sales volume E85-capable by 2012.
By the end of 2008, GM is expected to offer more hybrid models (eight) in the United States than any other automaker.
The Saturn Vue Green Line, Saturn Aura Green Line and Chevrolet Malibu Hybrid will feature GM’s mild hybrid technology.
GM’s two-mode hybrid technology is available in the Chevrolet Tahoe Hybrid and GMC Yukon Hybrid, and will be added later this year to the Cadillac Escalade, Chevrolet Silverado Hybrid and GMC Sierra Hybrid, delivering highly efficient performance and full functionality.
Going into production later this year is the front-wheel-drive Saturn Vue Green Line 2 Mode Hybrid, expected to deliver up to a 50-percent improvement in combined city and highway fuel economy compared with the current non-hybrid Vue XR, based on current federal test procedures.
Earlier this year, GM launched “Project Driveway,” the largest market test of fuel cell vehicles in the world, lending 100 Chevrolet Equinox Fuel Cell vehicles to everyday drivers. GM engineers will analyze customer feedback and use it to develop the next generation of fuel cell vehicles.-GM Europe
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