Is the Chevrolet Volt really an electric vehicle? David Booth looks at the arguments for and against.
When is an electric vehicle actually an electric vehicle?
You would think it's crunch time for Chevrolet and its new Volt. Though it's not likely to go on sale worldwide for some time now, it is the new halo vehicle under which the once-mighty General Motors will proclaim that its return to world-class status, if not quite in sales, then at least in advanced automotive technology.
The Volt's final unveiling is also at hand. The first pre-production versions are now in the hands of we, the world's assembled autoscribes, and GM's public relations officials are adamant that the first of the car-that-will-change-General Motors will be delivered to consumers by year's end. One would expect that GM, understanding how important the launch of the Volt is to its rejuvenated reputation, would have all its ducks in a row.
Unfortunately, there's a swirl of controversy surrounding this Volt launch. Read Edmunds.com - America's predominant automotive consumer website - and you're left wondering if the Volt is all that GM has promised and, indeed, whether it even is the electric vehicle The General claims or a merely better spec'ed hybrid as many critics decry. Edmunds.com has made its view known trumpeting a controversy-generating headline: GM Lied: Chevy Volt Is Not a True EV.
Like most stories, delving further reveals the truth far greyer than that absolute. Yes, it turns out, that in specific circumstances, the Volt can act like a Prius-like hybrid. Specifically, there are certain circumstances where the 1.4L petrol engine - previously claimed by General Motors to only be capable of generating electricity - can actually drive the wheels, just like a Prius or any other hybrid. On the other hand, in the vast majority of its operation, the Volt is the electric vehicle GM claims, even if its somewhat lackadaisical public relations has now muddied the waters. For those truly interested (and, to all those for whom hardcore technical explanation are a bore, I apologise), here's how the Volt's entire propulsion system works.
Like hybrids and plug-in hybrids, there's a vast array of electric motors, petrol engines, clutches, gear-sets, batteries and at least 10 computer sub-systems under the Volt's hood. How GM arranges that vast compendium of mechanised bits and, perhaps more importantly, how it makes those individual components interact is what separates current hybrid technology from future electric vehicle hardware.
For one thing, Volt has two electric motors. One - the traction motor with 111kW - propels the Volt via the front wheels; the second - the smaller 55kW version - is attached to the petrol engine and acts like a generator when the main 16kWh battery runs down. In its simplest form, then, the battery powers the traction motor, which, in turn, drives the wheels.
Now things start getting complicated. In some circumstances, mostly on the motorway at constant speeds, GM's engineers determined that spinning the big electric traction motor so fast (upwards of 6,500rpm and beyond) was unnecessarily wasteful. So, through the miracle of clutches and planetary gearsets, the second electric motor - normally, as I said, a generator - is brought on board to drive the wheels. Both motors, fed by the battery, now spin more efficiently at a lower rpm.
And things get even more complicated when the battery runs down. To maximise battery life, GM limits the big (198kg) lithium-ion battery from running below 20 per cent of its maximum charge (and from being charged beyond 85 per cent of maximum). When the battery is depleted, the 1.4L Ecotec petrol engine fires up. In most circumstances, its 84hp, or 63kW, are used to drive the generator, which, in turn, supplies power to the battery to drive the wheels.
But, like the script of a daytime soap opera, the plot thickens even further. At motorway speeds, the Volt's computer again tries to have both electric motors driving the wheels. But the petrol engine is already driving the secondary motor/generator. This means, if you've been following the plot at all, that the petrol engine - via that secondary generator motor - is actually connected to the front wheels, contrary, as Edmunds.com so vociferously pointed out, to General Motors' earlier claims that the electric motors, and the electric motors alone, drive the Volt's wheels. Under these limited conditions, the petrol engine does transfer 70 per cent of its torque - indirectly, via that secondary motor - to the wheels.
In reality, however, it's a minor technicality. The situation only occurs in light-load situations at highway cruising speeds.
Not revealing this until now, however, is proving a major public relations nightmare. GM officials claim it was a question of protecting crucial patent information from competitors. Nonetheless, the Volt is being unveiled under a cloud of suspicion. So hear it here first: The car is truly, incredibly wonderful, the company's public relations not so much.