The plot below shows what we were told by GM as to how the software would charge the main battery in CS mode.

http://images2.snapfish.com/232323232%7Ffp53836%3Enu%3D3387%3E%3A55%3E7%3C5%3E WSNRCG%3D32%3A5346%3B75347nu0mrj

Is this still correct??
If it is then you should notice the engine cycle on and off at 55MPH. Have any owners verified this cycling?? It would probably only happen when power split is NOT engaged.

I noticed it during city driving. It sure would be fun to see daily charts like this for our own volts.

If the need for power occurs during acceleration, hills, or fast driving, the engine tends to speed up. During lower power requirements, the engine will slow or stop. GM has done a good job to make it sound normal 90% of the time.

If it is then you should notice the engine cycle on and off at 55MPH. Have any owners verified this cycling??

Yes. I noticed it doing that at 70MPH.

Yes. I noticed it doing that at 70MPH.

Thx for the responses. Stresstool that is an exremely interesting situation. What was the duration of the off time?? Was it flat and level?? At 70 the road load is around 20 kw. If the battery buffer zone is 10% of 16 kwh=1.6 kwh then the car should run for approx 4.8 minutes off the battery. So the gearbox is flipping back and forth between modes. ICE on with power split engaged to charge the battery AND supply power to the wheels (ring gear clutch open, C2, C3 closed..... then, when the top of the buffer zone is reached, the ice is desengaged and shut down and the generator remains connected to the ring gear and acts as a speed controller to bring the traction motor speed down (ring gear clutch open). It's cycling C3 open and closed and turning the ICE on and off.

So you think at 70mph it should cycle the engine every 5 minutes?, recharge the battery up to the upper buffer level and shut off?.. it would be nice if an owner could report on this.. set the cruise control on at 70mph on level ground and time how often the engine cycles.

So you think at 70mph it should cycle the engine every 5 minutes?, recharge the battery up to the upper buffer level and shut off?.. it would be nice if an owner could report on this.. set the cruise control on at 70mph on level ground and time how often the engine cycles.

I've made two round trip 4 hour trips since owning my volt. I've averaged speeds of 70-80mph with cruise on. When driving at that speed, I was hard pressed to hear the engine turing on and off, so it could be that it "found it's groove" and stayed at fairly low rpm to keep me going.

When I'm commuting in traffic and shifting between acceleration and coasting, there most certainly is an ebb and flow to the generator. I'd actually prefer a more constant low purr to the occasional higher rev the engine makes once it realizes i've stepped on the gas. That is where I most notice the engine is when I'm starting up from a complete stop.