Comments on: Chevy Volt Will Have "Mountain Mode"

By: MrEnergyCzar

MrEnergyCzar — Fri, 07 May 2010 00:41:59 +0000

Thanks for the hill explaination…as far as the genset only charging the battery, the official answer is no it also runs the electric motor. to move the car..this bothered me for many months due to reading many poorly written media articles that got confused by GM saying the ICE never directly runs the wheels…the ICE does “indirectly” run the wheels buy forwarding electricity directly from the genset to the electric motor while also maintaining the battery SOC….

By: ex-EV1 driver

ex-EV1 driver — Fri, 07 May 2010 00:06:27 +0000

I guess the best test that I know of in the US is I-70 headed west out of Denver. If the Volt, in Mountain Mode, fully charged from Denver can maintain 75 mph all the way, it’s doing great. I remember that my brother’s old ’81 Olds Cutlass Ciera could barely maintain 50 mph up that grade.
The I-5 Grapevine grade north of LA is probably another good test case.

By: DonO

DonO — Thu, 06 May 2010 23:13:01 +0000

The Volts electric motor is rated at 110kw which the battery can handle in all cases. The issue in the mountains that could occur is, if there is a time you have brought the battery down to a level where in theonboard generator is called to duty because the battery charge has dropped below the 30% charge minimum and you are calling for full throtle to go up the hill you would need all 110kw, but the onboard generator is rated at 55kw so it could not provide enough power to keep the battery at its ideal minimum. You could in super rare instances find a long enough steep enough slope that you could reach a point of limited available power. Highly unlikly but possible. If you hit the mountain button before you get he hill the genset will on before the 30% ideal min. Is reavhed alowing you even more time to run full throttle up pikes peak before you would have limited power at hand. Once the ground levels off its a non issue qagain bevcuase it only takes 55kw to run the volt at its max speed rating of 100mph.
Also the genset never powers the motor directly it only and always just charges the battery.

By: ex-EV1 driver

ex-EV1 driver — Thu, 06 May 2010 03:52:17 +0000

@MrEnergyCzar
It isn't clear to me with the volt, whether the electricity from the ICE goes directly into the electric motor while the battery augments it or whether it only goes from the ICE into the battery while it goes from the battery into the electric motor.
You can be sure that the battery and electric motor have enough power to go up a very steep incline. The only problem is that the battery could run out before the top of long (maybe 20 to 30 mile) inclines if the ICE doesn't help out.

By: ex-EV1 driver

ex-EV1 driver — Thu, 06 May 2010 03:48:24 +0000

@Pablo,
I think your off a little. Remembering that there are 2 ways to get power: gas and electric.
Also, the EREV won't idle the gas engine. It will probably operate either in optimal mode or perhaps a surge mode P(m) which may not be particularly efficient (or perhaps they are the same).
However we also assume P(m) for gas isn't enough to climb the hill at the desired speed.
The issue is that using electricity alone, our battery would be flat before the top of the hill. Supposing the battery could take us 80% of the way up the hill, the computer that controls the EREV could have several options:

1) go on battery until it runs out, then crawl the remaining 20% of the way up the hill
or, in Mountain mode:
2) go on battery for a while (maybe until it gets to 80% state of charge), then turn the ICE on. The battery would be charged by the ICE while while the ICE charges the battery. This way, we'd get a longer climb using energy from both the battery and the ICE while still getting all the power that the battery can provide. If the ICE could provide half the power desired to climb, you'd essentially double your battery's ability to deliver the desired power, after which you'd probably be down to anemic ICE power.
I hope this clarifies it a bit.

By: MrEnergyCzar

MrEnergyCzar — Thu, 06 May 2010 00:05:47 +0000

Can’t the battery alone (assuming it has enough charge in it) push the car up long inclines with no speed problems? I always thought it could if it had adequate charge…..

By: MrEnergyCzar

MrEnergyCzar — Thu, 06 May 2010 00:02:57 +0000

OK, you guys are great, I now understand it….Just a note that always confused me. The ICE does power the wheels just indirectly……When the ICE comes on it produces electricity to mainly power the electric motor to move the wheels and to a lesser extent charge the battery up to its setpoint charge level…

By: Pablo

Pablo — Wed, 05 May 2010 21:49:44 +0000

Explanation of what ex-EV1 driver meant: ECE provides best efficiency at power P(best) somewhere near the middle between maximum power P(m) and idle power P(i).

P(best)= ~(P(m)-P(i))/2

So if you are going to need the ICE uphill at P(m) you would rather begin using it earlier at P(best)+battery and reduce the P(m) usage.

to ex-EV1 driver: Please confirm.

By: AP

AP — Wed, 05 May 2010 20:05:34 +0000

ex-EV1 driver is right. The normal mode of operation is to drain the battery down to the bottom of its working range before running the engine to charge the battery. This way, you have more "room" to charge up after your trip and can charge from the wall, which is much cheaper than charging from engine power. That's why it's called an EREV (extended range electric vehicle).

But in hill mode, you can prevent the "drain-down" and let the battery build up to the top of its working range, so once you're going up the mountain, you can use the electricity AND the engine to climb with, for quite a long time.

By: ex-EV1 driver

ex-EV1 driver — Wed, 05 May 2010 19:20:50 +0000

Dave K is right.
The ICE (Internal Combustion Engine) should not be powerful enough to quickly push a car up a steep mountain or it would be very inefficient most the time. Therefore, in mountainous terrain, one would like the ICE to come on even though the battery isn't low on charge, just to be more sure you'll have electricity in the battery to climb with.
In flat land, you want to run the battery almost out before starting the ICE, in order to maximize the distance travelled on battery.