Structural reinforcements to better protect the battery pack in side impacts and improvements to the pack’s liquid cooling system are the “fix” that General Motors engineers have developed to prevent a real-world occurrence of a post-crash fire in the Chevrolet Volt produced during testing by the U.S. NHTSA (National Highway Traffic Safety Administration).
NHTSA launched a formal investigation into the Volt on Nov. 25, 2011, about a half year after a Volt that had been crash tested by NHTSA three weeks earlier (on May 12) caught fire. It was determined that the side-impact pole test caused intrusion into and damage of the battery pack. In addition, the impact ruptured battery-coolant lines. During a portion of testing in which the vehicle is rotated upside-down, coolant leaked onto printed circuit board electronics on top of the battery. But it was only three weeks later that those conditions, plus a still-charged battery, resulted in a short circuit and fire.
After the fire, NHTSA undertook additional testing of the Volt’s lithium-ion battery and found cause to begin a formal investigation.
The investigation included a Dec. 22 side-impact pole test of a Volt that had been retrofitted with the fix that GM officials described in their Jan. 5 press conference. In a statement of its own on Jan. 5, the agency said: The results of that crash test showed no intrusion into the vehicle’s battery compartment, and no coolant leakage was apparent. As a precaution, NHTSA has monitored the crashed vehicle since the test and will continue to do so for one more week. However, the preliminary results of the crash test indicate the remedy proposed by General Motors today should address the issue of battery intrusion.”
Mary Barra, GM Senior Vice President, Global Product Development, said at the GM press conference that the structural enhancements “more evenly distribute the load to further protect the battery and the coolant lines in the event of a severe side crash.”
The structural enhancements and improvements to the battery-cooling system will begin at dealerships in February for existing owners. They will be incorporated into new Volts coming off the assembly line as soon as the holiday shutdown is over.
Barra said improvements to the battery-cooling system include installation of a sensor in the reservoir to monitor coolant levels and a tamper-resistant bracket at the top of the reservoir to help prevent potential coolant over-fill.
“I want to be clear that today’s actions have nothing to do with the battery pack itself,” Barra said. “None of these changes will touch the battery cell or pack. As a result we will not change any part of the manufacturing process at our Brownstown, MI, battery pack assembly plant. We have tested the Volt’s battery system for more than 285,000 hours, or 25 years, of operation.
"It’s important to note, the battery cell design used in the Volt was not the cause of the incidents that prompted the investigation. We’re confident in the robustness, quality, and safety of the cell chemistry used in the Volt battery, which is supplied by LG Chem."
And GM remains committed to liquid cooling for the Volt battery pack. Nissan uses air cooling for the Leaf EV battery pack.
Barra noted that there have been no instances of Volt fires outside of NHTSA testing.