Today GM announced that it will introduce changes to the Chevrolet Volt to guard against fires like the ones that occurred after crash tests last year.
New Volts will incorporate the changes, including steel reinforcements, starting this month. The approximately 12,000 cars that have already been built (about 8,000 have been sold so far) can also be retrofitted at dealerships starting in February. The retrofits will be part of a voluntary program, not an official product recall.
GM has also confirmed what caused a handful of Volt battery fires in testing last year. A side-impact test caused part of the Volt’s structure to break into the battery casing, and a small coolant leak was exacerbated when, as part of the test procedure, the battery was slowly turned over. When the battery pack was upside down, the coolant leaked onto a circuit board, which caused a short, and then the fully charged battery caught fire.
The fires could likely have been avoided if the batteries had simply been drained of charge after the test—much as a conventional vehicle would have its gas tank drained. The fires didn’t start right after the crash tests, so there would be plenty of time to do this. But the changes to the Volt are meant to prevent coolant leaks as the result of a side-impact collision.
Much has been made of the fact that the Volt battery pack isn’t encased in metal, while the pack for the Nissan Leaf electric car is. But the Volt pack is, in fact, well protected by a steel tunnel built into the floor of the car.
GM is adding extra steel braces to the steel tunnel to further protect the battery. The company says tests show this will prevent coolant leaks. GM is also adding coolant level sensors and a special tamper proof cover meant to prevent overfilling of the coolant.
Mary Barra, GM’s senior vice president of global product development, said today that the fires were not the result of a problem the battery cells inside the battery pack. She also said no changes will be made to the manufacture of the battery pack itself. And she expressed confidence in the safety of the lithium-ion chemistry GM is using, saying that the cells had been subjected to rigorous tests, including driving nails through them.
Despite all of those tests, apparently the cells—at least when fully charged—are still not robust enough to keep from catching fire after a short caused by a coolant leak.
It’s not clear whether a more stable battery chemistry, such as the lithium-iron phosphate materials used by companies such as A123 Systems, could have prevented the fires.
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