Chevrolet Voltec Drive

[Automobiles]

 

This animation depicts the function of the Chevrolet Volt's Electric Drive in detail for General Motors. VO courtesy of General Motors.

 

[Automobiles]

Higher voltage is much more efficient, requiring smaller cables and producing less heat. It is also easier on the batteries to deliver high voltage at low amps than the other way around. Using AC allows the use of brushless motors which are more reliable and powerful. It also allows easier control of timing on the electric motor.

[Automobiles]

 

DC-to-AC conversion is not that lossy. 99.5% efficiency is typical and that 0.5% loss is made-up by the greater propulsion efficiency of an AC motor
 

[Automobiles]

It doesn't need a CVT because the electric motor just changes speed continually.

[Automobiles]

 

[Automobiles]

 

[Automobiles]

 

[Automobiles]

What is it about the Chevy Volt that seems to elicit such heated discussion? After an article on Motor Trend a couple of days ago elucidated the Volt's complicated drivetrain in more detail than we've seen before, the internet green car ether has spent a huge amount of time debating whether or not the Volt can be considered an electric car because of the mechanical connection between the Volt's combustion engine and wheels.

Indeed the conversation has ranged the gamut from "who cares?" to "GM is a bunch of liars."

The fact of the matter is that the Volt drivetrain is complicated enough and different enough that even us so-called car professionals are having trouble understanding how it works. And, in the end, the average person likely won't care how the car does what it does, just that it does what they want it to do. Whether or not the Volt will do what the market demands is clearly something yet to be determined—as it is with the Nissan LEAF.

So, after getting pretty fed up with the he-said/she-said internet banter and infighting going on in the world of alternocar geeks (myself included), I decided to reach out to GM and ask if they wanted to fully explain how the drivetrain works and defend why they think it's an electric car. After all, even the venerable Motor Trend seems to have gotten it wrong, so who else can better explain it than the engineers themselves?

As a result, I had a very insightful and eye-opening conversation with Andrew Farah, Chief Engineer for the Volt, in which the entirety of the Volt's drivetrain is laid out for all the world to see. Rather than simply transcribing that interview here, I've posted the entire audio clip for you listen to below. Initially there is a hint of defensiveness in Mr. Farah's voice, but after he gets down to explaining the Volt's engineering I think you'll find the discussion enlightening.

Some highlights of the conversation:

• Farah says that in his mind the Volt is unequivocally an electric car. "The Volt is an electric vehicle...because for the first 40 miles you can get full performance running on nothing but an electric motor until the battery is depleted," he said.
• The Volt has three distinct motive forces in it: a large electric motor, a small electric motor/generator, and a 1.4 liter engine. Up to two of those three forces can be combined in select ways through the Volt's secret sauce drive unit—given the road demands and state of charge of the battery—to drive the vehicle.
• Only the large electric motor is capable of moving the car forward on its own. The small electric motor/generator and the gas engine can only ever be combined with one of the other motive forces to drive the wheels.
• Even when the gas engine is on and partially driving the wheels, it cannot operate without electricity flowing to one of the other motors.
• The gas engine, under most conditions, will be used to drive the generator and produce electricity, and will not be used to drive the wheels.
• There is no "direct" mechanical linkage between the Volt's gas engine and the wheels, rather there is an indirect linkage that is accomplished by meshing the power output of the engine with the power output of one of the other two electric motors.
• Motor Trend's reporting that the magic cutoff speed of 70 mph is what the car uses to determine whether or not to make the engine to partially drive the wheels is incorrect. The engine is used to partially drive the wheels when the car calculates that it will be a more efficient use of the engine's power. There is no hard cutoff point.

via Plugincars