The Chevrolet Volt - (II) - How it Works

Anyone who read the earlier article about the Chevy Volt, or who is following all the talk of future propulsion around the Detroit auto show this week, might reasonably be a little confused as to what is or isn't an electric car by now.

'Pure' electric cars, such as the original GM Saturn EV1, or the forthcoming Tesla Roadster are driven by an electric motor that is fed by batteries charged up from mains electricity (they are plugged in). A 'hybrid' electric car, such as Toyota's Prius, is a car which uses two forms of propulsion - in the case of the Toyota, a small petrol engine coupled to an electric motor.

The Volt is a hybrid too, but of a different kind. Like the Prius it has a petrol internal combustion engine, an electric motor and a set of batteries. Here the similarities end. In the diagram, I've tried to clearly identify the major aspects of the Volt's drivetrain. It works thus:

1 – Car is ‘plugged-in’ (orange) to mains electricity, this charges up the battery pack (blue).

2 - Battery pack (blue) provides energy to drive electric motor (red), which turns the wheels.

3 - For 45 miles (approx) of driving after each charge, car works solely thus, until the batteries (blue) reach a certain level of ‘discharge’.

4 - At this point, a small, petrol internal combustion engine (yellow) starts. Unlike a normal internal combustion engine car, or indeed the Prius hybrid, this petrol engine cannot drive the wheels. Instead, it drives an onboard generator (green) to continue to power the electric motor (red), which continues to provide drive to the wheels.

5 - When mains electricity is available again, car is plugged in once again (orange), to charge the batteries (blue), and the process starts over again.

This sounds quite complicated, and in a way it is. Critics, particularly fans of pure electric cars will point out that this is a very complex system, using more than one engine, which fundamentally still uses petroleum. Although this is true, the Volt could provide a realistic way forward, at least in the medium term, for two reasons:

• The primary concern (according to the auto makers) of most people about electric cars is the limits of their range. Lithium-Ion batteries as used in the Volt have good range properties, to the point that the Tesla roadster (which uses the same kind of batteries, albeit a lot more of them than the Volt) claims to get 250 miles off one 3-hour recharge. The problem is that, good though this is, it still precludes people from embarking on that great American road trip. The Volt's small internal combustion engine and generator basically provide it with unlimited range. Like current cars, one simply keeps filling up with petrol until mains electricity becomes available again to recharge. This ‘compromise’ smoothes the path for people to adopt vehicles that they become used to plugging in, whilst allowing them to continue to use their car as they do currently.

• Secondly, the car functions purely on its battery and electric motor combination for the first 45 or so miles after each recharge. According to GM, that means that in this mode alone, the car should meet the needs of 78 percent of people - the average American drives only 29 miles each day. Therefore, assuming that one is able to plug the thing in each night, many people might find themselves never having to put petrol in their Volt.

As a roadmap to the future, the Volt therefore makes a lot of sense, not just for America, but potentially, more densely populated and urban Europe.

Posted by Joseph Simpson on 09th January 2007

Comments

[Joseph Simpson]

Author's follow up note:

Since I wrote the pieces on the Volt, numerous comments and other pieces of analysis have appeared. Of particular note was this report on the bbc news site:

http://business.guardian.co.uk/story/0,,1984803,00.html

It suggests that the timescale to building this kind of car is in fact two to three years, which I'm quite surprised about. Obviously new technology needs thorough testing by a big auto maker, but everything I read, everyone I speak to who is knowledgable about the subject of battery technology and drive systems, suggest it can be done today.

So I'm even more suprised to find established auto analysts questioning the viability of the technology:

"Walter McManus, director of automotive analysis at the University of Michigan, said at this stage it was tantamount to a "magic" car: "They didn't tell you when this E-Flex was going to be ready. The battery technology they're dependent on is not ready yet. It's a physics issue and just pouring money into it isn't going to solve it.""

As I understand it, the Volt will use very similar batteries to those being employed in the Tesla roadster. So I don't see how this battery technology is "not ready yet". The cost is a problem, I admit - although with a big company like GM on board this will improve, but the technology exists now, and is improving by the day.

I'd love to know your thoughts on the matter, or any insight you have on battery technology and electric drive.

[Thomas Bjelkeman-Pettersson]

This type of hybrid powertrain has in fact been in use in Stockholm city busses for a number of years already. These busses run on E85 and have a small car engine (2.3 litre SAAB engine) powering the buss. Details about the design can be seen in this following PDF document p.17 (unfortunately only in Swedish, the Swedes are not got at this PR thing).
http://www.kfb.se/pdfer/R-00-54.pdf

[Joseph Simpson]

Further comment and analysis was made on NPR's science programme last week. There's a 17 minutes audio discussion here:
http://www.npr.org/templates/story/story.php?storyId=6835607

The comments suggest that the timescale for the Volt really is going to be more like 3 to 5 years, rather than 1 or 2.

Interestingly, the show host asks some of the guests whether the europeans are closer to launching this technology than the Americans, to which he gets the reply that the American's are ahead.

I think the general perception is that this is true, but I'm not so sure of the reality. The European auto industry has generally hung its hat on the hydrogen fuel cell as being the answer, but in fact, if it does take GM 5 years to get the Volt to market, then there's a probability that the Renault-Nissan alliance will beat them to an electric car launch:
http://www.forbes.com/business/feeds/afx/2006/12/11/afx3243786.html (skip past the intro page).

[Daniel Sjöholm]

Dude!
Now check my website as well. www.formadera.com
not much on there for now but hopefully will change in the future.
See you around, man!
Keep up...all that writing!!