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Discussion Starter · #1 ·
Based on GM's video and discussions here, I've always assumed the "Mode 4" operation - where the ICE is actually providing some propulsion power to the wheels - only happens at high (70+ MPH) speeds. In recent discussion on a FaceBook thread, though, someone is claiming this is false and that it actually will engage that mode at lower (sub 40 MPH) speeds too. They have no concrete evidence or documentation of this, however, and are solely going on feel:
If I drive in range extended mode, ICE running, 38 MPH at a steady speed (not accelerating), level road (not climbing a hill) and maintain this condition for over 30 seconds to a minute, the ICE will engage. I can feel it! It’s very subtle, similar to how an automatic transmission feels when the lockup clutch in the torque concert feels when it locks. At this point if I floor the accelerator pedal, there is a 1-2 second hesitation before the Volt starts accelerating. This delay is caused by the car transitioning between Mode 4 to Mode 3, disconnecting the ICE from the wheels and operating in pure generator mode. If I stab the throttle again within 10 seconds, the car will accelerate immediately. This indicates the car is in mode 3 still, with the ICE mechanically disconnected from wheels. However if I maintain steady speed at 38 MPH for over 30 seconds to a minute, it will again transition to mode 4, and the 1-2 second delay will be back if you stab the pedal. It will all happen below 40 MPH and above 35 MPH. It would be plain DUMB to limit this to over 70 MPH, because when operating in pure generator mode, there is quite a bit of conversion losses which lowers efficiency and MPG. They wanted to mechanically connect the ICE to wheels at a lower speed and have it operate in this mode for a much as the time as possible. Go try it for yourself!
I was thinking about testing this using my OBD2 wifi adapter to watch the RPM's of the ICE and 2 electric motors but the MyGreenVolt app I use (iPhone version) doesn't seem to have the RPM's of the electric motors. Any idea on a way to test this person's theory? (or has anyone posted evidence to support/challenge it already - my searching hasn't found anything)
 

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It will happen anytime you cruise at 60km/h or above.
I have measured it with OBD, but didn't log.
Either way, you don't need to measure it on OBD, you can feel it in the pedal.
Cruise at 60 for a minute or so and then floor the pedal, you should note the lag/weak acceleration characteristic of two-motor drive.

I've driven the volt enough that I can also feel when it shifts into this mode most times.
Part of my work commute is cruising right around 60 for a ways, experience it every day.

I will add that many likely don't see it at this low of a speed as you really need to be cruising consistently for it to switch. A lot of times there are traffic lights, other vehicles, etc such that the vehicle never really stays at a consistent power level long enough to switch.
I had a skim of my logs on hand and I don't have anything in the 60s showing MGA active with engine off. But I have one in the 70s/80s. And many in the 100+ range, though that is to be expected based on the 70mph that's been floating around for eons.
 

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I sometimes travel at 90 Kph with ICE, the speed limit on the TCH here, varying speed for the occasional light. I have never noticed any variation in the speed of the motor except the odd time when going up a steep incline it will go into the higher RPM to produce more electricity for the motors. I'm assuming it must happen at the 70 mph mark (112 kph) as I have never had the opportunity to go that high yet, once engaged I would expect it to stay engaged if it dips some below that for a period of time to prevent shifting in and out of that mode (the GM YouTube video suggests it engages at around 70 mph). If your motor is engaging below that on a regular basis I would suggest there is something wrong with the car and it should be taken into a dealer to get it looked at.
 

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I sometimes travel at 90 Kph with ICE, the speed limit on the TCH here, varying speed for the occasional light. I have never noticed any variation in the speed of the motor except the odd time when going up a steep incline it will go into the higher RPM range to produce more electricity for the motors or replace any used battery buffer. I'm assuming it must happen at the 70 mph mark (112 kph) as I have never had the opportunity to go that high yet, once engaged I would expect it to stay engaged if it dips some below that for a period of time to prevent shifting in and out of that mode (the GM YouTube video suggests it engages at around 70 mph). If your motor is engaging below that on a regular basis I would suggest there is something wrong with the car and it should be taken into a dealer to get it looked at.
 

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If your motor is engaging below that on a regular basis I would suggest there is something wrong with the car and it should be taken into a dealer to get it looked at.
That's a bold presumption if I've ever seen one.
One marketing statement from 8 years ago should not be taken as law.
I can assure you, it's a feature, not a bug. It's the same threshold when the engine is on or off. They likely realized it made no sense to wait until such a high speed if they're already shifting at slower speeds when engine on, and aligned the programming to treat them the same.
 

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Based on GM's video and discussions here, I've always assumed the "Mode 4" operation - where the ICE is actually providing some propulsion power to the wheels - only happens at high (70+ MPH) speeds. In recent discussion on a FaceBook thread, though, someone is claiming this is false and that it actually will engage that mode at lower (sub 40 MPH) speeds too. They have no concrete evidence or documentation of this, however, and are solely going on feel:


I was thinking about testing this using my OBD2 wifi adapter to watch the RPM's of the ICE and 2 electric motors but the MyGreenVolt app I use (iPhone version) doesn't seem to have the RPM's of the electric motors. Any idea on a way to test this person's theory? (or has anyone posted evidence to support/challenge it already - my searching hasn't found anything)
The post you've quoted is correct. The threshold is 36 mph - at any speed above that if the engine is on for more than 30 seconds and not at full throttle, you're in mode 4. If it's already converted to mode 4 and you slow down, it holds on to the mode down to about 30 mph.

There has been a lot of confusion on this point over the years, largely because of the media presentation GM gave in 2010. In the videos of that presentation, you can hear them expressly saying that 30 and 70 mph aren't special speeds, just representative of what it does in different ranges. Despite that, virtually all the news articles said it happened at 70 mph the next day.

My guess is that GM showed 70 mph because they didn't want to talk about engine cycling. Below about 65 mph driving in steady state on flat ground, the car will run the engine with a power surplus, slowly charging the battery slightly, then shut it down for a mile or so and run on electricity and repeat, presumably because even with the conversion losses that's more efficient than running the engine at a less efficient point.

I'm not sure why you haven't found one of the dozens of discussions we had on the topic over the years. The keywords must not be coming up. A bunch of early owners with DashDAQ and similar OBDII instrumentation sorted it out years ago, and have then been trying to overcome the presumably inadvertent media misinformation ever since.
 

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Why does this matter at all? I come from the mindset of just driving and not worrying whether my car is in mode 3 or mode 4. The car will do what it want's to do. There's nothing to be gained by trying to game the system (either stay in mode 4 or force it to switch to mode 3). Stop looking at your DICs and pay attention to the road.
 

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I sometimes travel at 90 Kph with ICE, the speed limit on the TCH here, varying speed for the occasional light. I have never noticed any variation in the speed of the motor except the odd time when going up a steep incline it will go into the higher RPM range to produce more electricity for the motors or replace any used battery buffer. I'm assuming it must happen at the 70 mph mark (112 kph) as I have never had the opportunity to go that high yet, once engaged I would expect it to stay engaged if it dips some below that for a period of time to prevent shifting in and out of that mode (the GM YouTube video suggests it engages at around 70 mph). If your motor is engaging below that on a regular basis I would suggest there is something wrong with the car and it should be taken into a dealer to get it looked at.
Engine rpms actually drop after the transition, presumably because not having to do double conversion on most of the power reduces losses. In series and in power split, the car mostly runs the engine between 1500 and 2200 rpm in normal operation.
 

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Based on GM's video and discussions here, I've always assumed the "Mode 4" operation - where the ICE is actually providing some propulsion power to the wheels - only happens at high (70+ MPH) speeds. In recent discussion on a FaceBook thread, though, someone is claiming this is false and that it actually will engage that mode at lower (sub 40 MPH) speeds too. They have no concrete evidence or documentation of this, however, and are solely going on feel:


I was thinking about testing this using my OBD2 wifi adapter to watch the RPM's of the ICE and 2 electric motors but the MyGreenVolt app I use (iPhone version) doesn't seem to have the RPM's of the electric motors. Any idea on a way to test this person's theory? (or has anyone posted evidence to support/challenge it already - my searching hasn't found anything)
I had to read carefully the excerpted statement to make sure that it hadn't been mine from a while back. I enjoy taking road trips with my Volt and often sense (feel) the subtle transition from mode 3 to mode 4 at slightly above 35 mph with very light acceleration. In videos of Pam Fletcher explaining the design and how the car functions, she is heard to say "it's not about 70 mph" , but about a "steady-state road low horsepower demand". She stops and then chooses her words carefully to, in my opinion, not have the reporters end up reporting that the Volt uses the ICE to drive the car - something that GM was denying in earlier discussions ("It's an electric car!")

https://www.youtube.com/watch?v=an-VyIau-FM
https://www.youtube.com/watch?v=343-NQKOvLg
https://www.youtube.com/watch?v=IWSK8BR6LT8
 

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Discussion Starter · #10 ·
Why does this matter at all? I come from the mindset of just driving and not worrying whether my car is in mode 3 or mode 4. The car will do what it want's to do. There's nothing to be gained by trying to game the system (either stay in mode 4 or force it to switch to mode 3). Stop looking at your DICs and pay attention to the road.
It doesn't, really. Just interesting info that I didn't know before this discussion.
 

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Discussion Starter · #11 ·
The post you've quoted is correct. The threshold is 36 mph - at any speed above that of the engine is on for more than 30 seconds and not at full throttle, you're in mode 4. If it's already converted to mode 4 and you slow down, it holds on to the mode down to about 30 mph.

There has been a lot of confusion on this point over the years, largely because of the media presentation GM gave in 2010. In the videos of that presentation, you can here them expressly saying that 30 and 70 mph aren't special speeds, just representative of what it does in different ranges. Despite that, virtually all the news articles said it happened at 70 mph the next day.

My guess is that GM showed 70 mph because they didn't want to talk about engine cycling. Below about 65 mph driving in steady state on flat ground, the car will run the engine with a power surplus, slowly charging the battery slightly, then shut it down for a mile or so and run on electricity and repeat, presumably because even with the conversion losses that's more efficient than running the engine at a less efficient point.

I'm not sure why you haven't found one of the dozens of discussions we had on the topic over the years. The keywords must not be coming up. A bunch of early owners with DashDAQ and similar OBDII instrumentation sorted it out years ago, and have then been trying to overcome the presumably inadvertent media misinformation ever since.
Thanks.

I figured there were a bunch of threads on this but I just couldn't form the right search keywords to sift them out.
 

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If your engine is directly connected to the drive train the engine will speed up as you speed up. If it doesn't or shifts from low speed to high speed on it's own with out pressing the throttle it isn't.
 

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I have what some might think an unusual view of this Gen 1 issue. Seems to me there’s a point often glossed over in Chevrolet Chief Engineer Pamela Fletcher’s presentation on the 2011 Volt powertrain. She describes the large motor as capable of providing full performance in single-motor configuration in both Electric and Extended Range modes. The smaller motor’s operational role is to improve efficiency.

When cruising down the road at high speeds in Electric Mode, the motor becomes increasingly inefficient. The GM solution was to clutch the Gen 1's second motor to the ring gear, which allows both motors to propel the car at speed down the road while reducing the RPM of the primary motor, increasing driving efficiency by 10-15% and adding an additional mile or two of ev range at highway speeds. 70 mph was the "example speed" given for when this might happen.

In Extended Range Mode, the engine’s primary task is to operate as a portable generator. In effect, when the battery is depleted, or when Hold Mode is engaged, the motor switches its fuel source from grid power in the battery to the output from the generator. The question then is, if the smaller motor is used to generate electricity but is not needed for performance, how does clutching the smaller motor to the ring gear improve efficiency in Extended Range Mode?

As before, the primary motor becomes inefficient at high speeds (70 mph is the "example speed"), and using a two-motor configuration when cruising in such conditions increases efficiency.

Additionally, in Extended Range Mode, the "portable generator" under the hood is fueled by gas. My understanding is the fuel consumption rate of a portable gas generator is relative flat over a moderate output load. The Gen 1 Volt’s fuel consumption efficiency (gas used per unit of time), then, is improved by turning the engine on and off as needed to meet the power demands from the motor instead of allowing it to run constantly.

Switching the engine on and off as needed to modulate the generator’s fuel consumption is not an ideal method of controlling gas use. By clutching the generator motor to the ring gear when the Volt is traveling smoothly at relatively constant speeds (i.e., cruising at 35+ mph), the efficiency of the on/off cycles can be improved. Some of the engine’s torque is now channeled through the generator motor to the wheels, allowing a smoothing out of the on/off engine cycles, and providing the justification for saying the Gen 1 engine is directly connected to the wheels.

Split-power mode improves the generator fuel consumption efficiency (i.e., it improves the Gen 1 Volt’s MPGcs "gas mileage"), but connecting the engine to the wheels via the generator motor is not done to maintain performance. Indeed, if you are cruising in split-power configuration and step on the accelerator to merge onto the freeway or to pass a vehicle on the road, there will be a brief pause as the car returns to one-motor configuration before the power demand is supplied and the large motor responds.

As Canehdian suggests above, if you’re not cruising smoothly while in Extended Range Mode, you are driving an electric car fueled by gas-generated electricity. If GM had chosen to keep the Gen 1 in one-motor configuration while in Extended Range Mode, you would have had a fully electric car with a 350+ mile electric range.
 

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I have what some might think an unusual view of this Gen 1 issue. Seems to me there’s a point often glossed over in Chevrolet Chief Engineer Pamela Fletcher’s presentation on the 2011 Volt powertrain. She describes the large motor as capable of providing full performance in single-motor configuration in both Electric and Extended Range modes. The smaller motor’s operational role is to improve efficiency.

When cruising down the road at high speeds in Electric Mode, the motor becomes increasingly inefficient. The GM solution was to clutch the Gen 1's second motor to the ring gear, which allows both motors to propel the car at speed down the road while reducing the RPM of the primary motor, increasing driving efficiency by 10-15% and adding an additional mile or two of ev range at highway speeds. 70 mph was the "example speed" given for when this might happen.

In Extended Range Mode, the engine’s primary task is to operate as a portable generator. In effect, when the battery is depleted, or when Hold Mode is engaged, the motor switches its fuel source from grid power in the battery to the output from the generator. The question then is, if the smaller motor is used to generate electricity but is not needed for performance, how does clutching the smaller motor to the ring gear improve efficiency in Extended Range Mode?

As before, the primary motor becomes inefficient at high speeds (70 mph is the "example speed"), and using a two-motor configuration when cruising in such conditions increases efficiency.

Additionally, in Extended Range Mode, the "portable generator" under the hood is fueled by gas. My understanding is the fuel consumption rate of a portable gas generator is relative flat over a moderate output load. The Gen 1 Volt’s fuel consumption efficiency (gas used per unit of time), then, is improved by turning the engine on and off as needed to meet the power demands from the motor instead of allowing it to run constantly.

Switching the engine on and off as needed to modulate the generator’s fuel consumption is not an ideal method of controlling gas use. By clutching the generator motor to the ring gear when the Volt is traveling smoothly at relatively constant speeds (i.e., cruising at 35+ mph), the efficiency of the on/off cycles can be improved. Some of the engine’s torque is now channeled through the generator motor to the wheels, allowing a smoothing out of the on/off engine cycles, and providing the justification for saying the Gen 1 engine is directly connected to the wheels.

Split-power mode improves the generator fuel consumption efficiency (i.e., it improves the Gen 1 Volt’s MPGcs "gas mileage"), but connecting the engine to the wheels via the generator motor is not done to maintain performance. Indeed, if you are cruising in split-power configuration and step on the accelerator to merge onto the freeway or to pass a vehicle on the road, there will be a brief pause as the car returns to one-motor configuration before the power demand is supplied and the large motor responds.

As Canehdian suggests above, if you’re not cruising smoothly while in Extended Range Mode, you are driving an electric car fueled by gas-generated electricity. If GM had chosen to keep the Gen 1 in one-motor configuration while in Extended Range Mode, you would have had a fully electric car with a 350+ mile electric range.
Well, we were promised an unusual view, and it is. :)

According to the SAE papers GM provided, the 10-15% efficiency gain is only for tying the engine on during power split mode. Two motor EV mode is done for efficiency, but the gain is only 2-4%, which is probably why that happens only after longer waits and at higher speeds (over 55 vs 36 mph.)

I'm not sure where you got the idea that generator efficiency is largely independent of load. All the generators I've seen have very large changes in efficiency as they go away from peak load, especially the ones that have to run at constant speed.

Saying that the Volt would have been a 350 mile range EV if GM hadn't connected the engine to the wheels is creative semantics - choosing to focus on one aspect of the operation rather than the whole or what people generally mean by the words. By that logic, every train in the U.S. is electric, since none of them drive the wheels directly with their diesel engines.
 

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Well, we were promised an unusual view, and it is. :)

According to the SAE papers GM provided, the 10-15% efficiency gain is only for tying the engine on during power split mode. Two motor EV mode is done for efficiency, but the gain is only 2-4%, which is probably why that happens only after longer waits and at higher speeds (over 55 vs 36 mph.)

I'm not sure where you got the idea that generator efficiency is largely independent of load. All the generators I've seen have very large changes in efficiency as they go away from peak load, especially the ones that have to run at constant speed.

Saying that the Volt would have been a 350 mile range EV if GM hadn't connected the engine to the wheels is creative semantics - choosing to focus on one aspect of the operation rather than the whole or what people generally mean by the words. By that logic, every train in the U.S. is electric, since none of them drive the wheels directly with their diesel engines.
Thanks for the feedback. Your observations have led me to a need to correct my recollections. I’ve just reviewed the Pamela Fletcher video again, and when she speaks of efficiency gains in Electric Mode via two-motor configuration, she mentions only the one or two extra electric miles provided at highway speeds. The 10-15% efficiency gains are part of her discussion of using the split power configuration when using the range extender.

When I bought my new Volt in 2012, little information was out there describing just what "seamless transition to gas" meant when you depleted your battery. Some, I suppose, thought it meant the electric motor was turned off and a gas engine propelled the car.

If it meant, as it seems it does, that the car transitions from grid electricity to gas-generated electricity, then Extended Range Mode could be thought of as using a portable generator to create electricity for the motor. My Volt’s "gas mileage" was really a measurement of how far I could drive during the time it took the generator to burn one gallon of gas. That led to wondering how one would measure the "gas mileage" of a portable electric generator. Was gas consumption proportional to speed (i.e., to the power needed to drive at that speed)?

Most portable generator specification sheets speak about fuel use in general terms based on the size of the generator’s fuel tank: "12 hours at 1/4 load," "8 hours at 50% capacity," "large 7 gallon steel fuel tank for up to 9.5 hours of runtime at 50% load." A few available graphs indicated relatively flat consumption curves over the mid range of output, ramping up as output approached full load.

To translate that into my speculation about the Volt generator, it seemed there might be a range of travel speeds obtainable as the motor’s power use varied within a "medium load range" of the car’s generator. For a continuously running generator, it would take a given amount of gas to generate enough power to drive the car at 20 mph for one hour, and it seemed likely it would take less than double that amount of gas to generate enough power to drive the car at 45 mph for one hour. In the car generator’s "medium load range," the "gas mileage" would increase as you drove faster.

Clearly, Volt gas consumption is controlled by turning the engine off and on as needed instead of letting it run continuously. By including a battery buffer in the operating parameters, fuel use is reduced as speeds decrease and power is generated as needed to meet the car’s power demands. Additionally, by clutching the generator motor to the ring gear under relatively steady state driving conditions (e.g., cruising at 35+ mph), the engine torque can contribute to the propulsion torque and help smooth out the off/on cycles, leading to better overall efficiency and better gas mileage.

The point remains that the Gen 1 "Mode 4" configuration improves efficiency, not performance.

As for my reference to the Gen 1 as an electric car when driving in one motor configuration using gas-generated electricity as fuel, most people do think of electric cars as vehicles fueled by grid power stored in a battery, but is there any performance difference in the Gen 1 Volt that depends on the source of electricity being used to fuel the motor?
 

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As for my reference to the Gen 1 as an electric car when driving in one motor configuration using gas-generated electricity as fuel, most people do think of electric cars as vehicles fueled by grid power stored in a battery, but is there any performance difference in the Gen 1 Volt that depends on the source of electricity being used to fuel the motor?
Nope, not for the Volt Gen 1. (At least if you factor out the transmission mode switching and battery limitation vis-a-vis big hills, etc.) It'll always go for the 149 HP (111kw) MGB when there's DEMAND, so the output performance will always be "as it is with MGB going all out". There are differences for the ELR with the performance pack. I'm a little fuzzy about non-perf ELR and Gen 2, but I think it's "yes, but trivial" for both but that's almost an ass-pull guess. All of them are on the improvement side.
 
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