Prevention is better than cure, and Audi has two genius ways of stopping a blaze before it gets going.
Fire safety is a lingering cause for concern with many buyers who may be considering making the switch to electric vehicles. The reality is that this issue is less significant than people may think; the chances of an EV self-combusting is less than 10% of the chance that an internal combustion engine (ICE) vehicle could set itself alight. That doesn't mean that car manufacturers rest on their laurels, though, because battery fire detecting- and extinguishing systems are constantly being improved.
CarBuzz discovered two recent patents at the USPTO related to this hot topic, and both of them were filed by Audi. These patents are very simple in concept, but they also move EV battery safety on by another increment and should hopefully find their way to future Audi e-tron models. In a way, these patents stem from the kind of thinking that brought us quattro and procon-ten. Look that up.
Lithium-ion battery cells heat up and cool down during the course of their normal operation. These trends should be almost uniform across all cells in a battery pack, indicating that all cells are sharing the work equally. But when a single cell operates outside of its neighbors' temperature and output ranges, it becomes a risk, as its volatile chemistry could result in a fire. But because the cells are connected in parallel to make up a battery, this issue is often difficult to detect in time.
The first patent solves this problem by identifying and isolating individual battery cells as needed, based on information gathered by cell-mounted sensors and processed by clever mathematics. This new battery control system can detect whether a cell is functioning within its safe temperature- and output range, compare the readings with its neighboring cells, and can switch off individual cells as needed.
If a problem is detected, it measures the now-disconnected cell's temperature and output voltage at various intervals. This information is then used to calculate whether the errant cell's behavior was a one-time anomaly, or whether there's an actual risk of thermal runaway in the battery.
With self-extinguishing battery cells still some way into the future, the only method of ending a battery fire is to starve it of oxygen - currently done with lots and lots of water, or with copious amounts of dry-powder extinguishers over the entire scene. But what if there was a way to bring the fire extinguisher right into the battery pack?
This is where Audi's next patent comes in, beautiful in its simplicity. If the battery control system detects a risk of thermal runaway (the precursor to a fire), it will flood the battery pack's interior volume with a flame extinguishing agent (typically a dry-powder type extinguisher) before it actually catches fire. And, if the onboard fire extinguisher runs out, a possible supplementary feed line from an external extinguisher reservoir may make it easier for firefighters to control a potential blaze.
EV fires are a big concern. While their frequency may be less than ICE fires, they're much more difficult to stop once they get going. But thanks to Audi's inventions, prevention may be better than cure.