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Discussion Starter · #1 ·
I've seen a number of discussions on the forum asking if the engine powers the drivetrain or charges the battery in ERDTT. My observations have always been that it does indeed charge the battery a little bit while active (which is one of the reasons I deliberately use it...get a little bit of battery charge with the added benefit of extra heat - the one thing an engine is really good at).

Today, I had just left my house and was on my way to work, and the ICE was in the initial warm-up phase (probably about 110 *F coolant). I hit a yellow light and wanted to make sure I made it through before red, so I floored it. The engine actually revved up significantly, as if I was in Hold mode. Given that I was only flooring it for a couple seconds, when I began to coast, the power bar went significantly down into the green area for a couple seconds before the engine went back to its typical "ERDTT idle". This was with a completely full battery and in Sport mode. A minute or so later, the engine warmed up fully and it resumed EV mode.

So, that settles it...the car does use the engine for power during ERDTT, but only under high power demand situations.
 

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I've seen a number of discussions on the forum asking if the engine powers the drivetrain or charges the battery in ERDTT. My observations have always been that it does indeed charge the battery a little bit while active (which is one of the reasons I deliberately use it...get a little bit of battery charge with the added benefit of extra heat - the one thing an engine is really good at).

Today, I had just left my house and was on my way to work, and the ICE was in the initial warm-up phase (probably about 110 *F coolant). I hit a yellow light and wanted to make sure I made it through before red, so I floored it. The engine actually revved up significantly, as if I was in Hold mode. Given that I was only flooring it for a couple seconds, when I began to coast, the power bar went significantly down into the green area for a couple seconds before the engine went back to its typical "ERDTT idle". This was with a completely full battery and in Sport mode. A minute or so later, the engine warmed up fully and it resumed EV mode.

So, that settles it...the car does use the engine for power during ERDTT, but only under high power demand situations.
I think there are three versions of this answer, though - 2011/12, 2013-2015, and then 2016+.

I know you're in the 2nd gen forum with this post, but I just want to remind readers that it isn't necessarily the same for all Volts.

(The 2011/12 runs exactly like Hold mode - which ironically they don't have. The 2013-15 runs differently, at around half throttle at low RPM and with the engine RPM not responding to throttle inputs, though of course it is taking power out with MG A to hold rpm and will use that power to move the car or charge the pack.)
 

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Discussion Starter · #3 ·
Yeah, this was just an observation on Gen 2...that's where I've seen most of the discussion on whether or not it provides power or not.
 

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I've noticed it does the same thing in EMM, under heavy throttle.

It's probably more efficient for the already-running engine to increase RPM to supply extra power to the battery pack at that point, rather than wasting your EV range.
 

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while I am using HOLD recently I am not really after engine heat but trying to burn off the tank of gas I got at delivery in March, so I have been doing 5 to 7 miles of my commute in on gas but I think I am going to ramp that up to 10-15 of my commute. don't really want to get trapped into burning off 8+ gallons all at once
 

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How is this different from the normal operation of the engine in Hold mode? In Hold mode, sometimes you remain on battery, sometimes the engine does the work itself, sometimes the engine works with the battery, and sometimes the engine does the work itself and charges the battery. These scenarios are all speed/load dependent. So I'm not sure your analysis sheds any new light. ERDTT does not alter the Voltec drive-train modes.
 

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I think the engineers want the engine to run at a relatively high RPM during ERDTT. But the high RPM would be obnoxious while you are sitting at a stop light or crawling through heavy traffic so during these times, they slow the engine down. Perhaps the OP just heard the switch between slow RPM and high RPM ERDTT settings?
 

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Discussion Starter · #8 ·
How is this different from the normal operation of the engine in Hold mode? In Hold mode, sometimes you remain on battery, sometimes the engine does the work itself, sometimes the engine works with the battery, and sometimes the engine does the work itself and charges the battery. These scenarios are all speed/load dependent. So I'm not sure your analysis sheds any new light. ERDTT does not alter the Voltec drive-train modes.
Normally during ERDTT the engine idles at somewhere around 1000-1200 RPM even if you're accelerating, whereas in Hold mode it'll rev up to probably 3500-ish while accelerating.

If you floor it in ERDTT, though, it revs up as if accelerating in Hold mode.
 

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As stated above, it behaves differently in different years as far as RPM and throttle response. But, the engine’s output is always used to provide some electrical power. The engineers weren’t stupid enough the just run it for heat without taking advantage of the mechanical power produced.

The bad thing about ERDTT is that a cold engine is very inefficient. So, cycling the engine to keep the coolant loop between 140 and 160 means the engine never hits full temperature or full efficiency. So, you’re wasting a lot of gas just for heat. It’s escocialky bad if your day’s travels could have been completed on battery alone, since then you’re really burning gas for no reason.
 

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Perhaps because it just got very cold here in MA, I was just wondering about this exact same thing earlier today. I noticed that with ERDTT running the acceleration seemed a bit sharper at low speeds -- even slightly jerky, at least compared to the usual smoothness. I think I did have it in sport mode, so maybe that affected things. In any case, it led me to wonder whether for those who occasionally want to trade efficiency for a bit more hot-rod, whether fooling the ERDTT into being on (the opposite of what most here have tried to do!) might give a faster 0-60 time. I'm not suggesting anyone actually do this (certainly not me), but it made me curious while driving around with ERDTT this morning.
 

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The engineers weren’t stupid enough the just run it for heat without taking advantage of the mechanical power produced.
Everything being observed and said here point to ERDTT simply being a short burst of HOLD mode. The Voltec system is complex enough as it is, it's ludicrous to think they would program yet another operating mode for use 10% of the time, in 10% of the markets where the car is sold. The explanations of the various Votec operating modes (low extended range, high ER, etc. not: Normal, Hold, MM) point to various uses of the engine based on speed and load. During ERDTT your car is going to be in one of those situations and operate just like that. Anything else would be overly complex and counterproductive for the car's overall efficiency.

https://www.greencarreports.com/new...ertrain-how-it-works-in-electric-hybrid-modes
 

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P... In any case, it led me to wonder whether for those who occasionally want to trade efficiency for a bit more hot-rod, whether fooling the ERDTT into being on (the opposite of what most here have tried to do!) might give a faster 0-60 time. .....
Wouldn't it be easier to use Hold mode to get that effect?
 

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As stated above, it behaves differently in different years as far as RPM and throttle response. But, the engine’s output is always used to provide some electrical power. The engineers weren’t stupid enough the just run it for heat without taking advantage of the mechanical power produced.

The bad thing about ERDTT is that a cold engine is very inefficient. So, cycling the engine to keep the coolant loop between 140 and 160 means the engine never hits full temperature or full efficiency. So, you’re wasting a lot of gas just for heat. It’s escocialky bad if your day’s travels could have been completed on battery alone, since then you’re really burning gas for no reason.
Engines are inefficient at very low temps, but not particularly bad at the intervals given. Much of the problem at lower temps is simply rejecting too much heat to the coolant. In this case, that's exactly the point...electrical generation + waste heat at something like 60-70% total efficiency. So as long as they keep the head/cylinder temps sufficiently warm to avoid too much fuel condensation on the walls (gas vaporizes at 140F at atmospheric pressure, so I'd say they're good), I'd imagine it's a fine use of fuel.
 

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Everything being observed and said here point to ERDTT simply being a short burst of HOLD mode. The Voltec system is complex enough as it is, it's ludicrous to think they would program yet another operating mode for use 10% of the time, in 10% of the markets where the car is sold. The explanations of the various Votec operating modes (low extended range, high ER, etc. not: Normal, Hold, MM) point to various uses of the engine based on speed and load. During ERDTT your car is going to be in one of those situations and operate just like that. Anything else would be overly complex and counterproductive for the car's overall efficiency.

https://www.greencarreports.com/new...ertrain-how-it-works-in-electric-hybrid-modes
It's absolutely obvious when driving in ERDTT that is isn't remotely similar to Hold mode...and why would it be? One is trying to maintain charge state and one is trying to produce the optimal combination of waste heat and electrical generation.
 

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Engines are inefficient at very low temps, but not particularly bad at the intervals given. Much of the problem at lower temps is simply rejecting too much heat to the coolant. In this case, that's exactly the point...electrical generation + waste heat at something like 60-70% total efficiency. So as long as they keep the head/cylinder temps sufficiently warm to avoid too much fuel condensation on the walls (gas vaporizes at 140F at atmospheric pressure, so I'd say they're good), I'd imagine it's a fine use of fuel.


I can tell you my gas mileage suffers noticeably once I start getting hit by ERDTT. Maybe it's just the unnecessary additional cold starts that ERDTT forces. I have a 2012, which can't be set lower than 26F for ERDTT activation.

I had a 3rd party ERDTT temperature bypass installed for a couple years and it helped my gas mileage a lot. But, it went bad and I haven't yet gotten a new one yet.
 

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I can tell you my gas mileage suffers noticeably once I start getting hit by ERDTT. Maybe it's just the unnecessary additional cold starts that ERDTT forces. I have a 2012, which can't be set lower than 26F for ERDTT activation.

I had a 3rd party ERDTT temperature bypass installed for a couple years and it helped my gas mileage a lot. But, it went bad and I haven't yet gotten a new one yet.
You can't really use a MPG number to gauge the thermal efficiency of a heat + power application. I would expect your MPG number to drop...that doesn't mean the gas use was in vain.
 

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You can't really use a MPG number to gauge the thermal efficiency of a heat + power application. I would expect your MPG number to drop...that doesn't mean the gas use was in vain.


I'm not using the MPG number since the one shown by the car is meaningless (EV miles mixed in to inflate it). In any case, ERDTT forces gas to burn on days when my total driving could have been covered by the car's electric range. So, it's bad in my book.
 

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I'm not using the MPG number since the one shown by the car is meaningless (EV miles mixed in to inflate it). In any case, ERDTT forces gas to burn on days when my total driving could have been covered by the car's electric range. So, it's bad in my book.
I don't have a Gen 1, so I don't know how it does MPG (Gen 2 allows one to look at gas-only, mixed, and MPGe). However, I do agree that if you could go all-electric, it would be nice to do so. With Gen 2 allowing deferment down to 15, I am fine with it, because a little engine heat is helpful when it's that cold. Can Gen 1 electric heat keep up with battery conditioning and cabin heating when it's super cold?
 

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I don't have a Gen 1, so I don't know how it does MPG (Gen 2 allows one to look at gas-only, mixed, and MPGe). However, I do agree that if you could go all-electric, it would be nice to do so. With Gen 2 allowing deferment down to 15, I am fine with it, because a little engine heat is helpful when it's that cold. Can Gen 1 electric heat keep up with battery conditioning and cabin heating when it's super cold?
Nice that they have MPG display options in Gen2. The electric heat in the Gen1 has never been insufficient for me.
 

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Discussion Starter · #20 ·
Perhaps because it just got very cold here in MA, I was just wondering about this exact same thing earlier today. I noticed that with ERDTT running the acceleration seemed a bit sharper at low speeds -- even slightly jerky, at least compared to the usual smoothness. I think I did have it in sport mode, so maybe that affected things. In any case, it led me to wonder whether for those who occasionally want to trade efficiency for a bit more hot-rod, whether fooling the ERDTT into being on (the opposite of what most here have tried to do!) might give a faster 0-60 time. I'm not suggesting anyone actually do this (certainly not me), but it made me curious while driving around with ERDTT this morning.
I think it's a placebo. The jerky feeling is because having the engine running at very low vehicle speeds means there are parts of the transmission moving that don't usually move, and it adds extra vibration and jumping.

Nice that they have MPG display options in Gen2. The electric heat in the Gen1 has never been insufficient for me.
Gen 2 electric heat is wonderful and will roast you out of the car if you let it, but for someone like me who can't make their full round trip commute on electric (only time I can do that is if it's 75 degrees, dry, and I don't go out to lunch), ERDTT extends my "electric-like driving" significantly by using the engine for the thing it's good for. Personally I prefer EV + ERDTT to having to use extended range mode more. The acceleration just feels better in EV mode, even if the engine's running for ERDTT.
 
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