My first extended range trip today, wierd..

[dukecola]

Ok, so I had 14 miles left on the charge today when I left for a 72 mi round trip. As expected, battery miles ticked off, got to zero about 15 miles into trip and then the ICE kicked on as expected. What I didn't expect was the ICE miles remaining meter fluctuating so much and actually gaining miles, then the battery power kicking in for a bit, then back to ice, then back to battery, etc. I didn't use up anywhere near 72 miles off the Battery and ICE miles remaining tickers combined. What's up with that? How does the ICE software calculate? Does it "learn" as well? Why did it switch back and forth to battery power? This was not at stops or lights, this was while driving.

[tboult]

Ok, so I had 14 miles left on the charge today when I left for a 72 mi round trip. As expected, battery miles ticked off, got to zero about 15 miles into trip and then the ICE kicked on as expected. What I didn't expect was the ICE miles remaining meter fluctuating so much and actually gaining miles, then the battery power kicking in for a bit, then back to ice, then back to battery, etc. I didn't use up anywhere near 72 miles off the Battery and ICE miles remaining tickers combined. What's up with that? How does the ICE software calculate? Does it "learn" as well? Why did it switch back and forth to battery power? This was not at stops or lights, this was while driving.

Yes the ICE estimation learns. You can watch it change even when you are on battery.

The ICE cycles on/off because you were not pushing the car hard so hard, so it was using the excess ICE power, to recharge the battery a bit, then turn off the ICE to save fuel and run from battery. (A bit like how a Prius uses the ICE to recharge its hybrid battery). It would seem you were going < 65 or 70mph.. which is when it cycles on/off and at 55 it does cycles off a lot of the time.

[ShannonVolt]

I notice that when I have used ICE. Someone with more smarts will chime in shorty. I believe once ICE takes over to power the electric drive unit that a percentage goes back into battery especially during regen. At a certain threshold it resorts back to battery until depleted again. It's hart to tell where power is coming from unless you really keep an eye on the centerstack powerflow screen. It's amazing how little ICE is used.

Chevy Volt SS (Super Sipper)

[saghost]

Ok, so I had 14 miles left on the charge today when I left for a 72 mi round trip. As expected, battery miles ticked off, got to zero about 15 miles into trip and then the ICE kicked on as expected. What I didn't expect was the ICE miles remaining meter fluctuating so much and actually gaining miles, then the battery power kicking in for a bit, then back to ice, then back to battery, etc. I didn't use up anywhere near 72 miles off the Battery and ICE miles remaining tickers combined. What's up with that? How does the ICE software calculate? Does it "learn" as well? Why did it switch back and forth to battery power? This was not at stops or lights, this was while driving.

Assuming it still showed the gas on the main screen and you were judging the engine cycles by the power flow, this is normal for a steady state cruise at less than ~65 mph.

The Volt isn't like other cars - even when it's on gas. For efficiency, it never runs the engine at anything except wide open throttle (well, it idles at speed momentarily during transitions, and it has a ~50% throttle warmup cycle for cold starts.)

When you're driving slower than about 65, the engine produces too much power at wide open throttle at its lowest speed of 1400 RPM. Rather than throttle the engine, what GM decided to do was charge the battery a little (around 400 Wh,) and then shut the engine down and drive electrically for a mile or two. I haven't run all of the numbers, but GM undoubtedly chose this way because it's more efficient.

You aren't the only one to be confused by it - Car and Driver missed the behavior entirely, and thus posted a highly inaccurate and misleading MPG comparison between the Volt and the Cruze ECO - showing that the Volt gets worse mileage the slower you go from about 62 down. (Which is true instantaneously, since its charging the battery faster, but the longer engine off portions balance it out and result in improved overall economy.)

[Jordan]

Wow, this is totally not our experience in the four days we've had our Volt. First day and a half were all electric - three 40 mile commutes from / to / from work. Then a 240 mile round trip to the train station (we live in the country). ICE kicked on at highway speed and never kicked off, net of 190 miles ICE, 39.8MPG on ICE at freeway speeds (60-70MPH). Tonight, a 60 round trip to another train station (plus some miles around town), the ICE kicked on at 50.1 miles and averaged in the mid 40's MPG (I forget the exact number) for the last 10 miles back home at country road speeds (40-50MPH).

In neither scenario did the ICE shut down and return to battery power.

We'll keep our eyes out for a return to battery power before charging, as I expect we'll be driving on ICE more than your average Volt owner, given where we live.

Jordan

[saghost]

Wow, this is totally not our experience in the four days we've had our Volt. First day and a half were all electric - three 40 mile commutes from / to / from work. Then a 240 mile round trip to the train station (we live in the country). ICE kicked on at highway speed and never kicked off, net of 190 miles ICE, 39.8MPG on ICE at freeway speeds (60-70MPH). Tonight, a 60 round trip to another train station (plus some miles around town), the ICE kicked on at 50.1 miles and averaged in the mid 40's MPG (I forget the exact number) for the last 10 miles back home at country road speeds (40-50MPH).

In neither scenario did the ICE shut down and return to battery power.

We'll keep our eyes out for a return to battery power before charging, as I expect we'll be driving on ICE more than your average Volt owner, given where we live.

Jordan

If your speed is over the threshold (and terrain, wind and HVAC play into the exact threshold speed, so it varies on different drives,) the engine won't turn off. The other thing is you might not realize when the engine shuts off. If you aren't watching the powerflow screen or external instrumentation, it can be pretty hard to tell when the engine cycles sometimes. The car will still have the gas gauge up, and the miles will still show as gas miles. Unless it's all up hill, it's almost certain that in 10 miles at 40-50 mph the car cycled the engine at least once.

[Jordan]

That would explain the high gas MPG as reported by the trip odometer. And it provides the only reason I've heard yet to use the powerflow screen. Thanks for the info.

... If you aren't watching the powerflow screen or external instrumentation, it can be pretty hard to tell when the engine cycles sometimes. The car will still have the gas gauge up, and the miles will still show as gas miles. Unless it's all up hill, it's almost certain that in 10 miles at 40-50 mph the car cycled the engine at least once.

[volt11]

The Volt isn't like other cars - even when it's on gas. For efficiency, it never runs the engine at anything except wide open throttle (well, it idles at speed momentarily during transitions, and it has a ~50% throttle warmup cycle for cold starts.)

I may be misunderstanding you, but as I'm reading it this is not at all true. In CS mode, the engine runs at fairly low RPMs most of the time to sustain charge. Like when cruising along at 70MPH on level ground. It's certainly far from WOT. I think it peaks at 4,000 RPMs under heavy load, when it becomes extremely obvious and not very pleasant, but most of the time it hums along unobtrusively at decidedly part throttle. Agreed it also shuts down in various conditions, and whether or not it's operating is visible on the Energy Flow display.

[tboult]

I may be misunderstanding you, but as I'm reading it this is not at all true. In CS mode, the engine runs at fairly low RPMs most of the time to sustain charge. Like when cruising along at 70MPH on level ground. It's certainly far from WOT. I think it peaks at 4,000 RPMs under heavy load, when it becomes extremely obvious and not very pleasant, but most of the time it hums along unobtrusively at decidedly part throttle. Agreed it also shuts down in various conditions, and whether or not it's operating is visible on the Energy Flow display.

You are misunderstanind him. Wide-open throttle is not the same as maximum RPM (what many think of as throttle). WOT means max airflow given the fuel provided and is the most efficient way to run the engine at any given RPM. The amount of fule provided then determines RPM. The Volt does vary the RPMs, but at lower RPMs it may stil have more power than needed.

[2BeLivingGreen]

Watching the powerflow screen will help to see how the VOLT uses regen and any excess energy. Many of the senior members comments here are correct in the VOLT use of the ICE and battery.