GM-VOLT : Chevy Volt Electric Car Site

A question that people like to ask about the Chevy Volt involves Pikes’ Peak.  For those not familiar with it, Pike’s Peak is 14,115 feet high and has a 19 mile road going up to the summit.

I had the chance to asked Volt chief engineer Andrew Farah that very question and here’s how he describes the result:

What happens if your 40th EV mile occurs at the foot of Pike’s Peak and you want to continue on to the top. Is it a problem?
It’s a problem if you want to do it at 90 mph. But it’s not a problem to get you to the top. As you know, the faster you go, the more energy it takes and hence the more power you need.

Will there then be a governor that doesn’t let you go too fast in that situation?
No its not really a speed limit. Envision an infinite hill that goes up forever. Now I’m at the bottom of it in my Volt and I just hit my 40th mile and I start to go up this hill and I want to do it at 80 mph. That will take a certain amount of power and total energy.

As I start up that hill, I’ll be going at 80 mph, no problem. I will be drawing roughly 50 kw of electrical energy from the generator and I’ll be drawing the additional energy required out of the battery. Lets say its another 10 or 15 kw out of the battery.

At some point the battery will become depleted, completely. Or to within a reasonable margin of safety. Then the car wont be able to continue to go 80 mph. Its only going to be able to go as much as the roughly 50 kw generator will be able to take it.

How far will it have gotten up the hill at that point? It depends how steep the hill is. How often will this affect the typical customer? Answer, not very often.

There are a few situations in North America where I could conceivable think about this such as Eisenhower pass out in Colorado on the way to Vail and Aspen, that’s a long 6% or so grade. Will you be able to do that in the Volt at top speed for the whole thing? Probably not. Will you be able to do it at a speed that’s reasonable. Yes.

There are limitations to the E-REV concept, but the people who will experience a problem with this are far and few between.

The way the Volt is designed, the first 40 miles of driving are powered by the electric energy stored in the battery. After that distance from full charge, somewhere around 30% state of charge, the on-board generator kicks in. The generator’s job is to keep the battery at that 30% level all the way until the driver can get to where he or she will begin charging again. That level is called the “customer depletion point”. Below is Volt chief engineer Andrew Farah explaining how the Volt will behave at and beyond that level.

How will the vehicle’s propulsion system work when you get to the customer depletion point?
When you get to the customer depletion point, the engine will come on seamlessly as it’s supposed to. But when the engine comes on to spin the generator, it does so with the idea that we’re generating electric energy to drive the wheels, not to charge the battery. People say the engine comes on to charge the battery, but that’s not what really goes on. The engine comes on to make enough electric energy to turn the wheels, because the wheels are always turning electrically.

Now comes the fun part. Remember the electric generator is about half the size of the motor. So you say, how come you don’t have performance problems if you’re trying to go up a hill with only basically half the power capability? That’s where the battery comes back into play. Because the customer depletion point is not full depletion, there’s still energy available. That’s by design. The idea is during certain other peak situations such as climbing a hill or merging into traffic, you will actually take some more energy out of the battery. So you may actually come down a little bit below customer depletion level.

And then when you take your foot off the gas, as an example when you’re done doing the merge, we had taken a little bit out and the battery has a little less in it. So what we’ll do then is we will opportunistically put that energy back into the battery either through regenerative braking or if we have to we will take some of the energy that’s not needed to turn the wheels and bring the battery up to the customer depletion level.

So we don’t recharge the battery. The customer wont actually see any of this, as their electric range indicator in the car will only say zero.

We are actually using that battery at that point as a peak buffer and we will keep trying to recapture energy as the opportunities allow.

Is the customer depletion point going to be exactly 30% state of charge (SOC)?
We are continuing to tweak and tune and develop exactly what that number is.

In an article in Autoobserver, Jon Lauckner, GM VP of technology tells the author:

“…although the addition of hundreds of pounds of batteries typically would be a detriment to any vehicle’s dynamics, because of their placement roughly in the center of the Volt’s chassis, the Volt’s weight distribution will much closer to the ideal -– and entertaining -– 50 percent front/50 percent rear ratio than any conventional front-wheel-drive vehicle displays.”

“…with near 50/50 weight distribution and the 0-60-mph target of around 8.5 seconds, “the Volt will not disappoint” in terms of driving dynamics.”

Balance is a good thing, and 50/50 weight distribution for a car suggests excellent handling and agility.

Source (AutoObserver)