GM causes controversy over whether the Volt is an electric vehicle or an advanced hybrid

General Motors has revealed that the Chevrolet Volt/Vauxhall Ampera extended-range electric vehicle (E-REV) can be powered by no less than three motors in certain circumstances – and as a result, has struck controversy with its claim that the Volt is always electrically driven and not a hybrid.

It has previously concealed the inner detail of the Volt’s propulsion arrangements because, it says, it has been seeking a patent for its Voltec drive system.

According to GM’s director of hybrid powertrain engineering Barry Nitz, the system is “patent-protected now, so we can talk about it”.

Read Autocar's first drive of the Chevrolet VoltEd Keohane blog: Chevrolet Volt - are we missing the point?

The additional motor in the system is the Volt’s generator, which can also become a motor and operate in tandem with the petrol engine under the heavy demands of high-speed cruising, assisting the main traction motor that always drives the car.

The reason for bringing in a second electric motor is energy consumption – at high cruising speeds, the efficiency of an electric motor drops off, placing heavier demands on the battery. To overcome this, a planetary gearset blends the outputs of both the combined generator/motor and the petrol engine, and the tractive motor. GM describes this as ‘indirect electro-mechanical drive'.

As proof that it is not the combined generator and petrol engine that are directly driving the wheels, it points out that if the tractive motor were removed from the system, the Volt would not drive. On this basis, it argues that the main tractive motor is always the driver of the wheels, and for this reason its claim that the Volt and Ampera are extended-range EVs holds good.

See pics pics of the Chevrolet Volt's controversial new tech

Whatever the semantics of the argument – which has lead to GM being accused of lying in some quarters – the result, says Nitz, is a “10-15 per cent improvement in fuel economy, and a mile or two of extra range” in pure EV mode when the petrol engine is dormant.

The planetary gearset blends the outputs of the two electric motors, allowing the main motor’s revs to drop from the 6500rpm needed to maintain the Volt’s maximum speed of 100mph to 3200rpm, where it operates more efficiently, while the generator/motor runs at 1500rpm.

It’s this ingenious arrangement that brings about the fuel savings, and it’s these drive kinematics, says GM, that it described in a patent application made in autumn 2007. The desire to hide this system from competitors is why it has not explained more about the system up to now.

Read Autocar's first drive of the Vauxhall Ampera

GM has also revealed that the efficiency of the battery, developed in partnership with LG Chem, now allows the pack to be depleted by 65 per cent rather than the 50 per cent originally planned, this allowing an improved electric-only range of “25 to 50 miles,” says Micky Bly, GM’s director of global electrical systems.

Up to now, GM has been claiming a maximum range of 40 miles for the Volt. GM’s eight-year, 100,000-mile battery warranty is unaffected by the increased battery depletion.

Richard Bremner

See all the latest Chevrolet Volt reviews, news and video

Our Verdict

Chevrolet Volt
The handsome Volt uses a petrol engine to charge the car's battery once it is flat

The Chevrolet Volt is an extended-range vehicle with an electric motor and a 1.4-litre petrol engine, and it makes the electric car viable for the masses

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Comments
27

12 October 2010

Interesting. So the Volt is essentially a plug in Prius, only with a slightly bigger battery. Not quite so ground breaking then. Shame.

12 October 2010

[quote MrTrilby]Interesting. So the Volt is essentially a plug in Prius, only with a slightly bigger battery. Not quite so ground breaking then. Shame.[/quote]

I think only the truly stupid would call it a plug in Prius.

The electric motor from the sounds of it, dirves the vehicle the whole time at legal speeds. If you go over 70MPH, then the petrol engine takes over the drive of the vehicle to increase efficiency... Thats nothing like a Prius.

Of all the Electric vehicles, the Ampera I feel will offer the best solution to the real world driver.

12 October 2010

[quote fhp11]The electric motor from the sounds of it, dirves the vehicle the whole time at legal speeds. If you go over 70MPH, then the petrol engine takes over the drive of the vehicle to increase efficiency...[/quote] This is not right, is it ? Does the article e not say that at no time is there a direct connection between the petrol engine and the driven wheels ? As I read it the petrol motor either charges the battery or supplies energy directly to the electric motor that provides drive to the wheels. The Prius is quite different, it is either driven by the petrol motor alone directly to the wheels, or by the electric motor directly to the wheels or, thirdly, by a combination of the two together. The petrol motor also sometimes runs at higher revs than needed to propel the car so that the battery is being charged at the same time. This is all totally different to a Volt. I think the Volt is the next logical step forward as battery only cars have such a limited range and drivers need more reassurance that they won't be unexpectedly stranded. Personally the idea of a plug-in Prius is most attractive and I think Toyota should bring it out as soon as possible.


Enjoying a Fabia VRs - affordable performance

12 October 2010

[quote ordinary bloke]This is not right, is it ? Does the article e not say that at no time is there a direct connection between the petrol engine and the driven wheels ?[/quote]

Oh it's right alright. GM just kept denying that little fact untill yesterday. I really don't think that it affects the appeal of the car ( although some US magazines are reporting less than impressive mpg figures ), but it just sounds really bad. It's going to be a PR nightmare.

 

Please insert paragraps where needed.

12 October 2010

Still 40 miles all electric range, the clutch engages over 70 mph only when the Volt’s battery is depleted, here is an article describing the system...

Unbolting the Chevy Volt to See How it Ticks

You don’t need a weatherman
To know which way the wind blows
—Robert Allen Zimmerman

12 October 2010

Interesting article, thanks Jack. So the plug in Prius and Volt are the same in the sense that they both have epicyclic gears with an electric motor, motor/generator, and petrol engine connected. But different in the sense that they're connected to different points of the gearbox.

Interesting first drive report from the article you linked too. Volt looks a well thought out car. For those interested, Robert Llewelyn has posted an interesting (if rather enthusiastic) first drive video of the plug in Prius: search for "Fully Charged" on YouTube or iTunes. It'll be interesting to see some side by side comparisons of them both in real world driving conditions.

12 October 2010

[quote tuga]Oh it's right alright. GM just kept denying that little fact untill yesterday[/quote] I was talking about the facts of how the Volt is driven compared to the Prius rather than whether the fact they kept something commercially confidential was right or not. [quote tuga]but it just sounds really bad. It's going to be a PR nightmare.[/quote] I can't see what all the fuss is about, most commercial organisations keep some things confidential for good business reasons (such as not letting their competitors copy the technology they have spend millions developing) and now that they have a confirmed patent for the technology they are going public with it. Perfectly normal, nothing to do with controversially lying to the public etc - that's just a red herring.


Enjoying a Fabia VRs - affordable performance

12 October 2010

[quote jackjflash]here is an article describing the system...[/quote] Thanks for posting the link - it's all as clear as mud now, I never was very good at understanding gearing etc.


Enjoying a Fabia VRs - affordable performance

Myk

12 October 2010

[quote ordinary bloke][quote tuga]Oh it's right alright. GM just kept denying that little fact untill yesterday[/quote] I was talking about the facts of how the Volt is driven compared to the Prius rather than whether the fact they kept something commercially confidential was right or not. [quote tuga]but it just sounds really bad. It's going to be a PR nightmare.[/quote] I can't see what all the fuss is about, most commercial organisations keep some things confidential for good business reasons (such as not letting their competitors copy the technology they have spend millions developing) and now that they have a confirmed patent for the technology they are going public with it. Perfectly normal, nothing to do with controversially lying to the public etc - that's just a red herring.[/quote]

That's where you're wrong. The point is that up until now GM have been stressing that the engine is not directly linked to the drivetrain in any way and thus could not power the car. That's not simply keeping things confidential, that's actively lying.

I too don't think this actually makes the car any less attractive, but it's a PR headache that GM could have easily avoided.

12 October 2010

At the end of the day this is all semantics - the Volt/Ampera is a hybrid, not an EV. The very fact that it has more than one power source makes it so.

The Ampera/Volt is a series hybrid - only the electric motor can drive the wheels, the petrol engine is there just to re-cahrge the batteries

Whereas the Prius is a parallel hybrid - both the electric motor and the petrol engine can drive the wheels either individually or together.

Only the Nissan Leaf & Renault Fluence/Twizy/Zoe are EVs - their only motive power source is an electric motor.

For me, the Ampera/Volt hybrid system is the best solution - a 'real' pollution free driving range (not just 3 miles like the Prius), backed up with the on-board charging unit to allay range anxiety.

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