In the race to be first to bring a plug-in hybrid to market, GM has released the latest details of its progress in developing the power system for the Chevrolet Volt.
It reported that engineers at its battery test facilities have developed a new computer algorithm to accelerate durability testing of the advanced lithium-ion batteries needed to power the car for up to 40 miles (64 km) of electric-only driving. GM says that the algorithm duplicates real-life vehicle speed and cargo-carrying conditions, and compresses 10 years of comprehensive battery testing into the Volt’s short development schedule.
The battery cycling equipment is used around the clock in GM test facilities in Warren, Michigan, 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 Chevrolet Volt and E-Flex systems global vehicle chief engineer Frank Weber.
Weber said the batteries would still need to be further validated in development vehicles, because the conditions in a vehicle are much more extreme than the controlled settings of the laboratory.
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By GlobalDataTo overcome the problem of engineering a vehicle around a battery that is around 1.8m long and weighs more than 170kg, the Volt will feature a T-shaped battery located down the centre tunnel and under the rear seats. This means the battery has to be treated as part of the vehicle structure.
Engineering innovations are also required to maximise the Volt’s 40-mile electric-only range and minimise the use of its range-extending internal combustion engine. To reduce mass, the car is being engineered with a relatively small fuel tank. This reduces weight, but still provides a driving range in excess of 400 miles (c. 600km) between fill-ups.
There have also been challenges in interior design. The battery location means that occupants are pushed apart to the side of the vehicles.
“Being an electric vehicle with a battery down the middle presented unique opportunities to our design team,” said Volt interior design manager Tim Greig. “The net result is a very creative and innovative design, appropriate for an electric vehicle.”
GM said that extensive work on the aerodynamics has resulted in a drag coefficient 30% lower than the original concept.