General Motors will enhance the structure of its Chevrolet Volt extended-range electric vehicle to reduce the risk of a post-crash fire involving the car’s battery pack, but plans to stick with its current battery chemistry and cooling-system design.
The auto maker also will maintain its fire-prevention protocol of sending engineering teams out to de-power Volt battery packs involved in serious crashes, WardsAuto learns.
In addition, GM expects to unveil later this year a tool to perform the procedure.
The tool is bound for commercialization.
So far, no crashes have been serious enough to warrant dispatching engineers to de-power a battery pack, a key step in handling the high-energy units.
The National Highway Traffic Safety Admin. did not de-power the battery pack of a Volt it crashed last year during routine safety testing. The scrapped test car’s battery pack caught fire several weeks later.
The incident led to further investigation, and in November the agency was able to replicate ignition of a battery pack after crashing it separately. NHTSA then opened a formal safety-defect investigation of the car, which launched in limited numbers in late 2010. Through December, GM has sold 7,997 Volts, according to WardsAuto data.
NHTSA’s November test results prompted GM to launch a Volt customer-satisfaction program, providing loaner cars to Volt owners until fixes to their cars are made. If Volt owners prefer, the auto maker will buy back their cars.
GM earlier today announces it will enhance the vehicle structure of Volts now on the road, as well those on dealer lots and in transit, to better distribute the load of a crash and prevent intrusion into the battery pack.
Although GM’s original validation of the battery pack’s safety included severe tests, such as driving nails into the units, it never encountered fires because engineers de-powered them afterward. NHTSA did not follow this procedure and coolant leaked onto a circuit board, which created an electrical short and sparked the fires.
GM spokesman Rob Peterson does not elaborate when asked if the auto maker will market the de-powering tool itself. Before it can be released, a step-by-step procedure must be developed and published by the Society of Automotive Engineers, he says.
Instruction would then be made available for pack-handlers such as tow-truck operators and salvage-yard personnel, dealers and body-shop owners.
Only after these events took place would GM amend its policy of dispatching engineers to handle severely damaged Volt battery packs. “And that is the case for all electric vehicles,” Peterson says. “They all have to be de-powered.”
GM believes structural enhancement planned for the Volt’s body structure will better protect the battery pack in a crash.
“The enhancements directly address the concerns identified by the post severe-crash testing,” says Mary Barra, senior vice president-product development at GM.
To accommodate the design enhancement, changes have been made to the Volt’s production line at GM’s Detroit-Hamtramck assembly plant. When post-holiday output resumes in coming days, every new Volt, and its overseas-market Opel Ampera twin, will feature the modification.
“We ran a series of internal tests and all have successfully resulted in no battery-pack intrusion or coolant leakage, thereby eliminating the chance for a post-crash electrical fire for this test condition,” Barra says earlier today in a conference call with journalists.
Barra says the NHTSA test in May led to a puncture in the side of the battery pack, which resulted in a coolant leak inside the unit of about 0.25 cups (0.06 L). NHTSA then put the pack through a slow roll, where it was rotated at 90-degree increments and held in each position for about five minutes.
During the slow roll, an additional 4.25 cups (1.1 L) of coolant leaked. While the pack was upside down, the coolant came into contact with a printed circuit board of electronics. Three weeks later, the coolant reacted with a powered battery pack and sparked a fire.
Barra says GM will stick with the Volt’s current lithium-ion battery chemistry, which it buys from Korean supplier LG Chem. The auto maker also will retain the Volt’s liquid-based cooling system.
“The battery-cell chemistry is not the problem,” she says, calling it “one of the safest on the road.” She also considers liquid cooling the best approach for the Volt, despite some competitive EVs employing air cooling.
However, GM will add a sensor in the reservoir of the battery-cooling system to monitor cooling levels, and the addition of a tamper-resistant bracket to the top of the unit will help prevent potential coolant overfill.
GM conducted 1 million miles (1.6 million km) of Volt testing during its validation without encountering a problem. Volts on the road today have logged another 20 million owner-miles (32 million km) without incident.
GM North America President Mark Reuss says about 250 owners have taken GM up on its offer to provide a loaner until the fix is made, and “a handful” have asked for buybacks.
Reuss expects many will change their minds after learning of the structural enhancement, which GM will provide through Chevy dealers at no cost. It will take about one day to complete, and the extra 2-3 lbs. (0.9-1.4 kg) of structure will not impair performance, he says.
Volt owners will be contacted when the modification is ready sometime in February, he adds.
Reuss characterizes the fix as a voluntary customer-satisfaction effort and not a recall. He refuses to speculate whether it might close NHTSA’s formal investigation into the car’s safety, but says “we’re optimistic this will have a positive outcome” on the regulator’s inquiry.
GM executives said during a Jan. 4 conference call to discuss GM’s December U.S. sales that they believe the NHTSA investigation has caused some apprehension among prospective Volt buyers. But they expect the mood to blow over.
The Volt saw its best-ever sales month in December with 1,529 deliveries, although 537 units were destined for commercial fleets.
GM fell about 2,000 cars short of its 10,000-unit 2011 sales goal for the Volt. The auto maker plans to produce 45,000 this year for sale in the U.S.
Asked if demand for the car remains, Reuss says GM will adjust production to sales as it does on any of its models.
“The Volt’s no different,” he says. “The true demand is unknown because we haven’t enough supply…and then we had this to work through. We’ll see. But we will match supply with demand.”
