Building Crash Safe Electric Cars

By Bill Moore

Posted: 25 Jan 2011

If the Top Gear television show's controversial crashing of an Indian-made Reva (G-Wiz) electric car at 40 mph in 2007 served a greater purpose besides forcing the manufacturer to strengthen its space frame and add a collapsible steering column, it made every other manufacturer keenly aware of the need to ensure their electric vehicles are safe, if only for purely pecuniary reasons. After Top Gear's revelations, sales of the G-Wiz in Britain plummeted two-thirds.

Several recent events promoted me to write briefly about EV safety, especially crash safety. The first was the Volvo C30 exhibit at the Detroit Auto Show earlier this month and my opportunity to interview two executives involved with their electric car program. Watch for those videos upcoming here on EV World.

The second catalyzing event was a conversation I had with a friend who attended the Paris Auto Show in 2010 and expressed what I think many of us quietly fear: that there will be some horrible collision between an EV and some other vehicle in which the "battery blows up." According to my Paris-based associate, he was shown a Peugeot iON electric car by a competing EV-maker, who pointed out how dangerous the rebadged Mitsubishi i-MiEV was with its lithium-ion battery pack installed just behind flimsy rear bumper of the vehicle. One good hard smack in a rear-end collision could not only have catastrophic effects on the vehicle and its passengers, but possibly sound the death knell of the EV industry… again.

The more I thought about it, the less plausible it all sounded. For starters, to my knowledge, lithium battery packs don't exactly "blow up." Certainly individual cells have been known to combust on test lab benches, but usually, if something goes horribly wrong, they short out and can go into what is known as a "runaway thermal event," causing a potentially destructive vehicle fire, but it would take seconds, even minutes to happen, not the milliseconds of a explosion.

Then there was the observation that the battery pack on iON/C-Zero/i-MiEV (they are all the same basic vehicle) is dangerously placed inside the crumple zone of the car. Everything I recalled about the power system layout on the vehicle told me this couldn't right. So, I did a little image search and came up with the following photo of the battery being installed in an i-MiEV, as was as accompanying illustrations showing the electric drive systems layout. The battery pack is located in the middle of the vehicle, below and outside the passenger cabin, in exactly the same location as in the Volvo C30 electric car prototype, as well as the Nissan LEAF and Renault Fluence ZE.

battery installation in Mitsubishi i-MiEV electric car

illustration showing placement of lithium ion battery pack in Mitsubishi i-MiEV electric car.

What is located at the back of the car is the electronic motor controller, inverter and battery charger, along with the heavy drive motor itself; none of which are overly vulnerable to exploding on impact, to my knowledge.

This impression was reinforced yesterday with the announcement that the i-MiEV has successfully passed the ADAC (Allgemeiner Deutscher Automobil-Club e.V.) crash tests in Germany. Quoting ADAC, Mitsubishi's press release states…

The test incorporating two impacts, one offset front crash (64 km/h, 40% offset), and a rear impact (by a 1,400kg movable barrier in 80km/h speed 70% offset), has proven that i-MiEV, although light weight, compact and equipped with a high voltage EV system, is equally as safe as any other gasoline-engine vehicle.

ADAC released the video below (in German) showing both the frontal zone and rear impact crashes, the latter causing minor damage to the battery, but causing on electrical or thermal events.
Certainly, no vehicle can be 100% safe, but fears of exploding batteries isn't something consumers are going to have to worry about when considering a well-engineered electric vehicle.

ADAC Crash Test Video of Mitsubishi i-MiEV (Auf Deutsch)

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