Exclusive: Is the Volt an Electric Car or Not? Volt's Chief Engineer Weighs
By PluginCars at PluginCars
Wed Oct 13, 2010 1:45pm EDT
by Nick Chambers
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
lying sack of $&!+."
The fact of the matter is that the Volt drivetrain is complicated enough and
different enough that even the 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. 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.