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Discussion Starter · #1 ·
I have read the threads about MM games to increase overall mileage. As well as the thread where at a steady 55mph speed the engine will cycle on and off since it generates extra power to the battery (or through regen) to bring the SOC back up. And it is the second case where my question mostly applies. There was a graph recently that showed the SOC of the battery, and when in CS mode this oscillates between a min and max. When the battery hits the max, the engine turns off, and when it hits the min it turns back on again. At higher speeds I would suspect that the power requirement never allows the battery to hit this CS max level, so the engine runs all the time. My specific question is what "mode" is the car in when on the ICE off part of this cycle? And where is it counting the miles? To me it could go either way. It makes since to keep the car in CS mode and count those miles toward your non-ev mpg rating, since the engine ran to get you that power. However, the engine isn't actually running at that time, so the argument could be made for these miles to go on the EV side.

My suspicion is that these miles are getting added to the EV miles, and this could account for the sometimes poor CS mode mpg ratings we have seen, since the ICE is driving the car plus giving a little extra to the battery.
 

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The car counts them as CS/gas miles, unless you enter mountain mode with at least one mile left of EV; in that case, when you switch back to normal mode the charge gained will show up as EV miles. (While in mountain mode, any time with engine off is gas miles, just like in normal mode. It's only the built up charge that can be different.)
 

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When you are in CS mode, miles with the engine off are still counted as CS miles. This is because the energy for those miles were ultimately derived from the engine and not the battery.

The lower MPG numbers could be due to a few reasons. Some that come to mind include:

1) The MM gaming that will add EV miles and not CS miles.
2) The ICE runs less frequently, so a higher percentage of its runtime is with a cold start, especially when the engine runs due to cold temperatures. These situations will cause people to experience lower CS MPG. Of course, when long trips on CS mode dominate the usage pattern, the CS MPG seems much more reasonable. It's important to remember that CS MPG is, of course, only part of the equation. Many people are getting 100+ MPG when factoring in their electric miles.

I'm EC Volt on Voltstats.net, and you'll see my CS MPG is actually pretty high. I don't game MM and I am usually on a 350+ mile one way trip when I'm using the ICE.

HTH
 

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Discussion Starter · #4 ·
Do you think the CS MPG would go up if the min/max SOC were widened? This might only make sense for longer trips. I believe this would effectively have the same result as the MM games, except, if you are right, and the CS electric miles are counted as CS miles, then the MPG would not be penalized like it is with the MM games. Also the cycling would occur at higher speeds, or would be a longer cycle at lower speeds.
 

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The count as CS miles, unless you stop and start then you might convert 1-2 of them to EV miles.
Regen miles in CS mode also count as CS (again unless you stop/start).

If you use MM in CS mode to recharge it will all count as CS, unless you stop/start.

MPG_cs on voltstat is also impact by an unknown bias/error in the data reported by onstar that Mike uses to compute it. If you pull your data it may even be saying you've used more total gas than you have. For example my gallons used since last fillup are off by almost .5 gallons. The actual usage since last fillup being 4.96 gallons (Based of the Gallons of Gas Collumn) But the reported gas used (which determined MPG_cs) showing 5.68. If you don't use much gas, this type of error can be pretty significant. Since I've done about 151.75 CS miles, that is the difference between 30mpg_CS and 26.7MPGcs. (Those cold-starts for temp are really bad, often giving < 20mpg.. and when they hit me at the traffic lights on the way home, its even worse).


I've tried to find corrections to give mike, but so far no simple fixes seemed to work to correct it. My current hypothesis is that it is an accumulation error showing up in lifetime Fuel Economy, lifetime/trip EV Miles and lifetime/trip Miles. If you subtract them you'll find many days when you can see last trip EVmiles-LastTrip Miles miles are slightly different (like .01 to .02 miles). Of course that is meaningless for any trip, but if this accumulates it could be doing more significant . And if there are weird errors in those per-trip items, which just happen to be things one can check, then the ones that cannot easily be checked, like the lifetime fuel, may have their own problems.

If you really want to know your CS mileage the trip counters do better job per trip. And you can track it yourself per tank. (I use Fueley now, and track CS miles in a spreadsheet).
 

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Do you think the CS MPG would go up if the min/max SOC were widened? This might only make sense for longer trips. I believe this would effectively have the same result as the MM games, except, if you are right, and the CS electric miles are counted as CS miles, then the MPG would not be penalized like it is with the MM games. Also the cycling would occur at higher speeds, or would be a longer cycle at lower speeds.
I think it could potentially go up if these points were widened, paired with having the engine run at higher RPM's during the time that it's on. The engine would be more efficient at producing electricity at a higher constant RPM, but the trade off is a quality ride without a loud engine sound that doesn't track your vehicle's speed. I think GM made the right choice to have the car appeal to the masses, but a high constant RPM would be most efficient. Having a larger SOC window would also aid in this mode of operation.
 

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Do you think the CS MPG would go up if the min/max SOC were widened? This might only make sense for longer trips. I believe this would effectively have the same result as the MM games, except, if you are right, and the CS electric miles are counted as CS miles, then the MPG would not be penalized like it is with the MM games. Also the cycling would occur at higher speeds, or would be a longer cycle at lower speeds.
Changing the SoC limits alone won't help much (at all?) The key theory behind the mountain mode games is to make the car run the engine at the most efficient speed, by increasing the demand for the engine above the speed state cruising load.

I'm pretty sure that it can work, and also that it can backfire - depending on the speed you're going and the terrain, you can increase the demand enough that the engine goes over the top of the most efficient range to provide enough power.

The part I'm not sure about is the balance between the greater efficiency of the engine and the increased generator losses. One of the things I learned this week that surprised me is that the Volt spends a fair amount of it's CS time in "6th gear." That is, with Motor B more or less stopped and held by the inverter with ~200 Watts, while the engine provides 99% of the power required to drive the car mechanically, and Motor A operates as a generator extracting as much power as needed to keep the throttle wide open at current RPMs.

This means the engine is effectively driving the wheels alone at 3.1:1 - close to 6th gear on most cars, including the Cruze (the Cruze is a few percent lower I believe.) This mechanical transfer will be more efficient than running the power through the battery and back out. The question is whether the gain in engine efficiency can balance the loss in drivetrain efficiency.
 
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