https://www.wired.com/story/evs-fire-pyroswitches-cut-risk-shock-crash/
EVs Fire Up Pyroswitches to Cut Risk of Shock After a Crash
10.06.2019 Alex Davies
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Photograph: Alamy
https://media.wired.com/photos/5d97daa428aa88000843488a/master/w_1280%2Cc_limit/Transpo_Bosch_Airbag_IC_Print-(300-dpi).jpg
EV chip Bosch developed the CG912 semiconductor chip for triggering
airbags, but it works just as well for sparking a tiny guillotine to cut an
electric vehicle’s high-voltage cables. Illustration: Bosch
]
Electric cars run on 400 volts or more. So automakers are designing systems
to protect EMTs and others from exposed wires following a collision.
After more than a century of powering their wares with engines that produce
hundreds of small, carefully controlled explosions each minute, the auto
industry is moving toward a battery-driven future. But that doesn’t mean one
without any helpful explosions. Last month, industry supplier Bosch revealed
details on what it calls the pyrofuse, a new safety tool for electric cars.
When the system detects a crash, its uses a bit of combustion to fire small
wedges into the high-voltage cables, severing the connections between the
battery and the power electronics. The idea is to reduce the risk of
electrocution for first responders.
Here’s why that’s necessary: Conventional cars run about 12 volts of power,
but many electrics use 400 volts. The new Porsche Taycan uses double that.
That power bump has pushed the auto industry to develop new ways to keep
everybody safe. Along with careful insulation of battery packs and
high-voltage components, automakers and suppliers have developed a variety
of pyrotechnic safety switches that activate in the event of a crash.
Autoliv’s Pyroswitch throws a switch to disconnect the power source from the
circuit board. Tesla has patented an “arc-suppressing gas blast in
pyrotechnic disconnect” [
https://insideevs.com/news/334322/tesla-patents-pyrotechnic-battery-safety-device/
] that appears to work similarly.
Bosch’s system goes further by actually cutting wires. “It’s a secure
disconnection,” says Thorsten Koepke, the company’s product manager for
semiconductors, “a physical opening of the wire.” His team produced the chip
that uses deceleration and other data from the car to identify a crash. They
originally developed the chip for use in airbags, but it serves the same
function here. The exact workings of the system, including the conditions
under which it will trigger, are up to the automaker, but the general idea
is that the chip triggers a small explosion, similar to the chemical
reaction that inflates an airbag. But here it will launch wedges into the
wires in question—as many as eight, if the car has a motor at each wheel,
Koepke says. And while Bosch declines to name its clients, Koepke says it’s
already in use in cars on the road.
“It’s like a little guillotine.”
-Huseyin Hiziroglu, Kettering University
Pyroswitches are relatively common, but this use case is novel, says Huseyin
Hiziroglu, an electrical engineer at Kettering University in Flint,
Michigan. “It’s like a little guillotine.” One that looks to save lives
instead of take them but that delivers the same sort of permanence. The
downside of this safety-minded system is that repairing a crashed electric
car will involve installing a lot of new wiring. Which means, most likely,
spending a lot of money. “I’m sure it will be quite expensive,” Hiziroglu
says.
Jason Siegel, a research scientist at the University of Michigan who studies
lithium-ion batteries, says pyrofuses “can provide a much-needed safety net
for first responders.” But it’s not clear that taking the extra step of
severing the wires will change how EMTs and others approach a crashed
vehicle, since they won’t know that the little guillotine has done its work.
“I don’t see first responders reaching for a [voltage-measuring] Fluke meter
to check if the wires are live before cutting when someone is trapped in the
vehicle,” he says.
There are more than a million electric cars roaming American roads, but, so
far, worries around high-voltage crashes haven’t come to fruition. Andrew
Klock, who works on EVs and other emerging issues for the National Fire
Protection Agency, says he doesn’t know of any first responders who have
been zapped. The nonprofit group has trained 225,000 EMTs, firefighters,
police, and others to deal with electric cars in the past decade. Relatively
simple advice has proven effective. “You just stay away from any broken
cables,” Klock says. First responders who need to cut someone out from a
mangled vehicle can check the agency’s Emergency Field Guide, which collects
and standardizes key information on all the electric car models on the
market, to make sure they’re well clear of any cables or components that
could deliver a deadly shock. Stay away from those, Klock says,
