Chevrolet Volt Development Charges On
WARREN, Mich. – Engineers at GM’s battery test facilities have developed a new computer algorithm to accelerate durability testing of the advanced lithium-ion batteries needed to power the Chevrolet Volt for up to 40 miles (64 km) of electric-only driving.
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, Mich. 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.
“Extensive analysis in our battery labs is an important step in proving this technology. We expect to further validate these batteries when they are integrated into engineering development vehicles,” said Weber. “The conditions in a vehicle – where the battery is exposed to shaking, moisture and rapidly changing temperature conditions – are much more extreme than the controlled settings of the lab.”
Engineering an electric vehicle with a battery roughly 6 feet long (1.8 m) 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.
“The battery is more than just an energy carrier; it’s a structural component that affects many other aspects of the vehicle,” said Weber. “It’s an integral part of the vehicle that interacts with the vehicle’s thermal and safety systems and chassis components.”
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, whether it’s occupant packaging or overall styling. This not only contributes to improved fuel economy or extended range, but can produce beautiful exterior body shapes and innovative interiors.”
The battery pushed the occupants outboard, or to the sides of the vehicle, so the design team had to get creative with the sections of the roof structure to enable aerodynamics and provide adequate head room. The interior will accommodate a 6-foot 2-inch (99 th percentile) male comfortably in the front and rear seats.
“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.”
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.
Aerodynamics development begins with a 1/3-scale model where basic shape and major features are defined. The model includes a highly detailed underbody and engine compartment. Radiator and under-hood cooling flow are developed with computational fluid dynamic models. Simultaneously, computation development takes place to determine the aerodynamic drag of design alternatives. Development continues with full-scale models, where shape is refined and optimized for low wind noise. The development process concludes with a vehicle prototype validation of the math-based analysis and physical testing.
“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:
Additionally, GM provides more vehicles that achieve 30 mpg on the highway than any other manufacturer in the U.S. market. GM is also a member of the U.S. Climate Action Partnership (USCAP), a group of global companies and non-governmental organizations that support an economy-wide, market-driven approach to reducing carbon emissions.