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Discussion Starter #1 (Edited by Moderator)
Since July of 2011 I have been driving my Volt alternating between D and L thinking that the much faster slow down in L was the result of more power being sent to the battery. Also, for some reason, I assumed the mechanical brakes were 100% separate and disconnected from the regenerate braking (electrical) system, i.e. if I pushed on the brake pedal, that action would activate the normal brakes, along with the computer trying to slow down the car by turning the electrical motor into a generator. Up until about 8 months ago, when the car had around 97,000 miles on it, EVERY time during that last 8 year period I let my foot off the accelerator, whether in D or L, the car slowed down - much more in L. But recently during the first few miles each day, the car does NOT slow down when I take my foot off the accelerator - in D or L. I thought something was wrong, and after several trips to the dealer, I was finally told it was functioning normally. Sometimes the computer decides to open the current, that is, NOT turn the electric motor into a generator. When this happens it may feel like the computer shifted the car into neutral where the regenerative braking would not engage. The "problem" I experience always "corrects" itself though. In addition to this, the dealer told me the my way of driving, shifting from D to L or simply driving in L, was not what was intended. Also, they said when you depress the braking pedal with whatever force, the computer decides whether to engage regenerative braking or the regular brakes or some kind of combination of both - depending on how hard I press the brake pedal presumably. And here is the kicker, they said there is a dump coil or two or three or four to which the power from the regen system could be diverted if the computer decided not to send the power back to the battery for some reason. When I asked why the car had NEVER behaved, in the first 8 years, by essentially shifting into neutral when I released the accelerator, they could not say. Sorry for the long post, but I wanted you all to have as much information as possible. Has anyone experienced this? Does anyone have technical expertise about exactly how all this works on the first generation Volts? Thanks!
 

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From what I have read your Gen 1 Volt (Gen 2 Volts too) are designed to limit the amount of regen when conditions dictate. These conditions can be that either the Volt's battery is already fully charged, at rated capacity, or perhaps the battery pack is too hot (unlikely) or too cold (certainly possible in winter when first setting out on a drive) to accept power from MGA (charge sustaining mode) or MGB (regenerative braking.) The Volt can reduce or eliminate the amount of regen that would normally be available until conditions are favorable for putting power back into the battery. As far as coils to accept excess power, I do not believe that the Gen 1 or Gen 2 Volt has coils (commonly seen on top of diesel electric locomotives with cooling fins.)
 

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I'm not a believer in low gear. Unless I'm slowly going downhill on a dirt road.

The brake pedal can spin the generator just as fast as L, seems to me.

I get more mileage from coasting then regen.

Haven't noticed it going into neutral like behavior.
 

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Let’s clarify a few things.

You don’t "slow down faster" in L on level terrain because more power is sent to the battery. You "slow down faster" because L consumes more of the car’s energy per crank when cranking the generator at the L output level setting (regenerative braking).

When you take your foot off the accelerator, the car’s momentum continues to turn the wheels. This momentum can then be used to "crank" motor/generator B (MGB) as a generator, recharging the battery. Adjusting the circuits to increase the amount of electricity created per crank makes it harder to "turn the crank," and so the car’s momentum is used up faster (it slows down faster) when the regen level is set at L than when set at D.

The quantity of power sent to the battery is a product of regen created per crank and number of times it was cranked, so using high regen levels while slowing down rapidly creates about the same amount of power as using low regen levels while slowing down over longer periods of time. Regenerative braking and friction braking both have the same primary function: braking the car. Your choice of D or L should reflect the braking habits you want to use (some find L helpful in stop and go traffic, for example, or for maintaining speed when using cruise control while driving downhill). The less regen you create, the more of the grid power in a full charge you can use to maintain speed, helping you go farther.

My understanding is that the pressure applied to the brake pedal determines the amount of "braking power" requested. If the request can be met by the regenerative braking system, it will be. Otherwise, friction braking will be blended in to meet the demand. This seems to be what your dealer told you.

One limitation to the regenerative braking system is that the generator output needs somewhere to go. There must be room in the battery to accept the recharging. A fully charged Volt battery has only a small buffer remaining between the "fully charged" battery state of charge and the "hard ceiling" state of charge (less than 100% of capacity, but above which you can’t charge, which helps maintain battery life). If you have a full charge, and you start driving downhill shortly after unplugging and driving off, that small buffer at the top can quickly be filled by regen, and then there’s no more room to put additional regen, and you lose the regenerative braking system until you use up some of the battery power. There has been some discussion as to what happens when there’s no more room for regen. I don’t think I’ve previously heard it explained by references to "dump coils," but this sounds wrong... if the generator output could be dumped into coils to be bled off as heat, the generator could continue to be cranked by the car’s momentum (i.e., the regen braking effect would continue to work).

If you’ve recently moved to a location that requires driving downhill shortly after departing with a full charge, the loss of the use of the regenerative brakes as you begin the daily commute (and the return of the use a little after reaching the bottom of the downhill drive) is understandable and normal. If your Volt (a 2011 Volt?) is starting to experience some loss of battery capacity from aging, that, too, would reduce the size of the upper buffer that can hold regen above the "fully charged" state of charge.
 

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Great explanation. I have a long downhill after leaving work every day. The regenerative braking would often drop out as the battery became "over full". The car would actually then engage the gas motor without starting it- to use it's compression braking.

Irritated me to no end because the car would put these in the gas miles on the display. Usually only 0.1-0.3 miles each day.
 

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bjenner - But recently during the first few miles each day, the car does NOT slow down when I take my foot off the accelerator - in D or L.
Just a guess here, but I would suspect that with a 2011 you have lost some battery capacity. Which means, when you start, you no longer have the overhead capacity that is required to dump regen power into. As you drive the car, your battery state of charge drops. After it drops, you now have a place to put regen power, and D or L will perform like you expect.

The only thing that makes sense to me is the following algorithm, use regen braking first (the amount of braking power limited by size of generator and the ability of the pack to take the power). Then, if regen can't handle the braking request, fall back to the brake pads, and mix in as needed.
 

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Just a guess here, but I would suspect that with a 2011 you have lost some battery capacity. Which means, when you start, you no longer have the overhead capacity that is required to dump regen power into. As you drive the car, your battery state of charge drops. After it drops, you now have a place to put regen power, and D or L will perform like you expect.
...
This sounds like a good theory.
If you want to set out with your battery less than full so you can regen, you could use the departure time charging option, and set your departure time later than you actually leave each day.
 

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Great explanation. I have a long downhill after leaving work every day. The regenerative braking would often drop out as the battery became "over full". The car would actually then engage the gas motor without starting it- to use it's compression braking.

Irritated me to no end because the car would put these in the gas miles on the display. Usually only 0.1-0.3 miles each day.
Volt does not use the ICE for breaking like that (though I've heard Prius does). It does show up on the display as gas miles when you regen too much with a full battery, but that is just a known 'energy accounting' bug... the engine is not spinning, gas is not being used.

OP, there are no dump coils for regen, your dealer is just wrong about that. If you still have issues in warmer weather (i.e. not during polar vortex), then I also suspect some mild battery degredation could affect your upper buffer, such that regen when full doesn't work as well. I don't think this has been documented though, but now that early Gen1s are getting older, perhaps we'll start hearing about things like this...
 

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Great explanation. I have a long downhill after leaving work every day. The regenerative braking would often drop out as the battery became "over full". The car would actually then engage the gas motor without starting it- to use it's compression braking.

Irritated me to no end because the car would put these in the gas miles on the display. Usually only 0.1-0.3 miles each day.
One way to think of it is that the Volt maintains numbers under two categories, Electric Mode (electric miles/km) and Extended Range Mode (gas miles/km). By definition, an electric mile/km is a mile/km driven using grid power from the battery or using regen that was put into the battery when driving in Electric Mode. If you are moving downhill, and regen has filled the buffer and can’t add any more, the distance you are covering is not being achieved by the use of either grid power or regen acquired under Electric Mode, so the only other option is to record it as Gas Miles/km.

Don't know what model Volt you drive, but keep in mind the Gen 1 gas engine’s primary function is to operate as a generator, and remains completely disconnected from the drivetrain in Electric Mode. Would it even be practical to clutch the Gen 1's engine to MGA and then clutch MGA to the ring gear as a means of providing negative torque from the engine to compensate for loss of regenerative braking via MGB when the upper buffer is full?
 

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I have also experienced the engine being used to assist in slowing and have done so a couple times to confirm it was in fact the engine turning (3K rpm according to mygreenvolt app) when descending a long grade with a full battery. It does not do this in D, but it does in L. I'm certain it's not using gas but it is using the engine as a braking source when the brake pedal is not being requested. My condition to cause this to occur involved the fairly long descent into the Castaic area just north of LA on I-5. There is a long steep descent for several miles. It only does so if I have left home with a full battery and in hold mode. Perhaps the next time I go to LA I will capture video and post on youtube. I'm certain it's not an intermittent event as I can do it successfully each time I've attempted. Basically it acts just as a standard transmission system downshifted to maintain a particular speed. When I shift back into D, the engine stops again but putting back into L results in the engine spinning back up again. In D it's definitely coasting with no obvious regeneration, even the display that shows engine/drive unit power reflects an elevated engine reading when this occurs.

As for any battery degradation, with 130K on my '13 it's possible but I do know that even now I show a GOM of 43-45 with mild temps averaging 50-60 here which definitely puts my range well within and actually better than rated.
 

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I've also seen the rpm go up on my Torque Pro app. And yes, it only works in low. (In my Gen1)
 

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I have also experienced the engine being used to assist in slowing and have done so a couple times to confirm it was in fact the engine turning (3K rpm according to mygreenvolt app) when descending a long grade with a full battery. It does not do this in D, but it does in L. I'm certain it's not using gas but it is using the engine as a braking source when the brake pedal is not being requested. My condition to cause this to occur involved the fairly long descent into the Castaic area just north of LA on I-5. There is a long steep descent for several miles. It only does so if I have left home with a full battery and in hold mode. Perhaps the next time I go to LA I will capture video and post on youtube. I'm certain it's not an intermittent event as I can do it successfully each time I've attempted. Basically it acts just as a standard transmission system downshifted to maintain a particular speed. When I shift back into D, the engine stops again but putting back into L results in the engine spinning back up again. In D it's definitely coasting with no obvious regeneration, even the display that shows engine/drive unit power reflects an elevated engine reading when this occurs.

As for any battery degradation, with 130K on my '13 it's possible but I do know that even now I show a GOM of 43-45 with mild temps averaging 50-60 here which definitely puts my range well within and actually better than rated.
Interesting... our resident (though absent for some time now) expert, Wop-on-tour, was emphatic that the Volt does not do this. This is the second time I know of that he was emphatic about something not occurring, where users had some data that it was**. He generally blamed it on Torque/apps not having all the necessary capability to really determine what was happening (so they were showing misleading/incorrect information)

** The other was a related "myth", that under long descents where the battery couldn't accept more charge (due to SoC or temperature or whatever), that MGA and MGB would "fight" each other to dissipate the energy. Again, he said he was emphatic that this does not happen, while several users here had some Torque data that suggested it did.
 

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Well, regardless of what the app data indicates, my ears definitely heard the engine spin up as well. The first time it happened I was concerned that I may have broke something as I was using L to maintain speed and it didn't occur until about 1/2 way down when suddenly it sounded like the engine revved up and stayed revved. Fortunately I had my dongle already plugged in and pulled up torque pro and it showed the RPM at 3K. The descent I was using at the time is several miles giving sufficient time to experiment with both apps (TP and MGV) and the data was confirmed on both. Unfortunately I didn't check the fuel flow rate gauge in torque pro to verify gas use or lack thereof. Next time I make that particular drive I will see about getting video to document and post on youtube. Once I was driving on level ground it stayed in electric mode for a couple miles before the engine kicked back on to maintain my hold level.
 

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Perhaps someone could explain how "engine braking" could work in a Gen 1 Volt, where the engine’s only connection to the wheels is created by clutching it to the smaller motor and then clutching that motor to the ring gear. How would such a configuration enable the engine to provide negative propulsion torque as a means of consuming the car’s kinetic energy to compensate for the loss of the regenerative braking system?

Here’s an imaginative alternative explanation. Perhaps when the regenerative braking system is disabled because the upper battery buffer has been filled by regen as the car is moving downhill, if the car is in L (i.e., regen level set high enough to provide a downhill braking effect), the computer is programmed to clutch MGA to the engine to employ its function as the "starter" motor. Using battery power for the motor to "crank" the engine (without providing the fuel that would allow it to start) for a sufficient period of time would draw current and bring the state of charge below the "hard ceiling" point (and increasing the rpm would increase the current draw). You might hear or feel the engine spin in such circumstances, and engine rpm would register on the apps.

Once MGA draws enough current by cranking the engine to drop the SOC below the "hard ceiling," the regenerative braking system would be enabled again and engage L level braking. The process might make it appear as if the engine were providing the braking effect. Once newly created downhill regen refilled the upper buffer, the process would be repeated (regen disabled/MGA uses battery power/engine appears to be running/regen restored, provides L level braking briefly), providing the feeling that the engine is providing the braking effect without using gas.
 

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Why would MGA have to be clutched to the ring gear? When the throttle pedal is released in a conventional vehicle, at least with a manual transmission, the resistance of the pistons moving in a 4-cycle engine will slow the vehicle. More so in a lower gear.
 

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Why would MGA have to be clutched to the ring gear? When the throttle pedal is released in a conventional vehicle, at least with a manual transmission, the resistance of the pistons moving in a 4-cycle engine will slow the vehicle. More so in a lower gear.
The Gen 1 Volt uses only a single planetary gear. MGB is connected to the drivetrain via the sun gear to provide propulsion torque. The car is capable of full performance using only MGB, the large motor. The primary function of the smaller motor, MGA, is to generate electricity to extend the car’s range. MGA has no fixed connection to the drivetrain, but can be clutched to the planetary gear’s ring gear. Under certain conditions, this two-motor configuration improves overall efficiency.

The Gen 1 Volt’s engine has no connection at all to the drivetrain, but can be clutched to MGA. In CS mode, this clutch is engaged, the engine starts, and cranks MGA as a generator. The Gen 1 Volt then continues to operate as a 100% electric car, MGB uses the gas-generated electricity, and, in one-motor configuration, the car’s range is extended with no connection at all between the engine and the wheels (series hybrid).

Under certain conditions in CS mode, clutching MGA to the ring gear (split-power configuration) improves overall efficiency (better "gas mileage"). Clutching MGA to the ring gear while it is also clutched to the engine is the single configuration under which a connection exists between the engine torque and the wheels.

That’s why MGA would need to be connected to the ring gear for any movement of the engine’s pistons to have any influence on the car’s speed.
 

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The Gen 1 Volt uses only a single planetary gear. MGB is connected to the drivetrain via the sun gear to provide propulsion torque. The car is capable of full performance using only MGB, the large motor. The primary function of the smaller motor, MGA, is to generate electricity to extend the car’s range. MGA has no fixed connection to the drivetrain, but can be clutched to the planetary gear’s ring gear. Under certain conditions, this two-motor configuration improves overall efficiency.

The Gen 1 Volt’s engine has no connection at all to the drivetrain, but can be clutched to MGA. In CS mode, this clutch is engaged, the engine starts, and cranks MGA as a generator. The Gen 1 Volt then continues to operate as a 100% electric car, MGB uses the gas-generated electricity, and, in one-motor configuration, the car’s range is extended with no connection at all between the engine and the wheels (series hybrid).

Under certain conditions in CS mode, clutching MGA to the ring gear (split-power configuration) improves overall efficiency (better "gas mileage"). Clutching MGA to the ring gear while it is also clutched to the engine is the single configuration under which a connection exists between the engine torque and the wheels.

That’s why MGA would need to be connected to the ring gear for any movement of the engine’s pistons to have any influence on the car’s speed.
Thank you for your explanation. What about with a Gen 2, would the ICE be used to slow the Volt if regen was not an option due to a full battery?
 

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Thank you for your explanation. What about with a Gen 2, would the ICE be used to slow the Volt if regen was not an option due to a full battery?
Ah, that’s the question that has yet to have a definitive answer. I wouldn’t want to speculate.

One could say the Gen 2 Volt configuration makes it possible. The Gen 2 Volt has two planetary gears, and the illustrations I’ve seen in the reviews when the Gen 2 first came out show MGA connected to the sun gear of the first one and MGB connected to the sun gear of the other. The two motors are more equal in size than in the Gen 1 Volt, and more often operate together for efficiency. The Gen 2's engine is connected to the first PG’s ring gear, and I suppose the engine could thus be used to apply some engine braking if the programming enabled the correct configuration under the appropriate conditions. One review mentioned that the Gen 2's new Extended Range operating modes increase efficiency, in part by allowing the motors to be dynamically "mixed" with the gas engine output in an eCVT mode.

My alternative explanation earlier in this thread was intended to point out that one remedy to the loss of the regenerative braking system because the battery is "full" is to turn on something that uses power - blasting the heat or the a/c, for example, might work - to bring the state of charge below the upper ceiling limit, freeing up space for more regen to be created and the "brakes" to be applied.

I don’t really know if using MGA as a starter motor draws sufficient power to accomplish this task.
 

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Let’s clarify a few things.

You don’t "slow down faster" in L on level terrain because more power is sent to the battery. You "slow down faster" because L consumes more of the car’s energy per crank when cranking the generator at the L output level setting (regenerative braking).

When you take your foot off the accelerator, the car’s momentum continues to turn the wheels. This momentum can then be used to "crank" motor/generator B (MGB) as a generator, recharging the battery. Adjusting the circuits to increase the amount of electricity created per crank makes it harder to "turn the crank," and so the car’s momentum is used up faster (it slows down faster) when the regen level is set at L than when set at D.

The quantity of power sent to the battery is a product of regen created per crank and number of times it was cranked, so using high regen levels while slowing down rapidly creates about the same amount of power as using low regen levels while slowing down over longer periods of time. Regenerative braking and friction braking both have the same primary function: braking the car. Your choice of D or L should reflect the braking habits you want to use (some find L helpful in stop and go traffic, for example, or for maintaining speed when using cruise control while driving downhill). The less regen you create, the more of the grid power in a full charge you can use to maintain speed, helping you go farther.

My understanding is that the pressure applied to the brake pedal determines the amount of "braking power" requested. If the request can be met by the regenerative braking system, it will be. Otherwise, friction braking will be blended in to meet the demand. This seems to be what your dealer told you.

One limitation to the regenerative braking system is that the generator output needs somewhere to go. There must be room in the battery to accept the recharging. A fully charged Volt battery has only a small buffer remaining between the "fully charged" battery state of charge and the "hard ceiling" state of charge (less than 100% of capacity, but above which you can’t charge, which helps maintain battery life). If you have a full charge, and you start driving downhill shortly after unplugging and driving off, that small buffer at the top can quickly be filled by regen, and then there’s no more room to put additional regen, and you lose the regenerative braking system until you use up some of the battery power. There has been some discussion as to what happens when there’s no more room for regen. I don’t think I’ve previously heard it explained by references to "dump coils," but this sounds wrong... if the generator output could be dumped into coils to be bled off as heat, the generator could continue to be cranked by the car’s momentum (i.e., the regen braking effect would continue to work).

If you’ve recently moved to a location that requires driving downhill shortly after departing with a full charge, the loss of the use of the regenerative brakes as you begin the daily commute (and the return of the use a little after reaching the bottom of the downhill drive) is understandable and normal. If your Volt (a 2011 Volt?) is starting to experience some loss of battery capacity from aging, that, too, would reduce the size of the upper buffer that can hold regen above the "fully charged" state of charge.
In regen, the electricity IS sent to the battery for storage through the action you have further described. Nubies might get confused by your declarative sentence , although I understand why you made it.

Do we really know how the software handles the reduced capacity of the aging battery? Is the same 13%-65%-20% (for Gen1) applied as the overall capacity of the battery is reduced through aging? Anecdotally, Sparkie saw no reduction in battery capacity in over 450,000 miles in his 2012 Vol, IIRC, which would make one think that the buffers were reduced. I may be altogether wrong and someone, please, step in to correct me. If the first 15% is, indeed, being reduced because of overall diminished capacity of the battery, then that could be why the OP has had this experience.

I agree with your feeling: no dump coils...battery storage in the buffer is the answer.
 

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In regen, the electricity IS sent to the battery for storage through the action you have further described. Nubies might get confused by your declarative sentence , although I understand why you made it.

Do we really know how the software handles the reduced capacity of the aging battery? Is the same 13%-65%-20% (for Gen1) applied as the overall capacity of the battery is reduced through aging? Anecdotally, Sparkie saw no reduction in battery capacity in over 450,000 miles in his 2012 Vol, IIRC, which would make one think that the buffers were reduced. I may be altogether wrong and someone, please, step in to correct me. If the first 15% is, indeed, being reduced because of overall diminished capacity of the battery, then that could be why the OP has had this experience.

I agree with your feeling: no dump coils...battery storage in the buffer is the answer.
I could have said more clearly that it’s not the amount of power sent to the battery that slows down the car. Using L to brake likely sends no more total power to the battery than using D.

I’m not sure how effective expanding the usable SOC window would be to compensate for the reduced capacity of an aging battery if the raw SOC points for the "switch to gas" and "hard floor" levels remained where they are (~20% and ~15% for both Volt Gens?). As the quantity of power maintained in that 5% Extended Range Mode operating buffer shrinks via degradation (it’s less than 1 kWh when the battery is new!), the sooner you encounter driving conditions that require more "borrowable" power than available in the buffer, leading to Propulsion Power Reduced episodes (remember that Mountain Mode’s function is to increase the "switch to gas" SOC so that more borrowable power is available when driving in high power demand conditions to avoid PPR episodes).

It seems possible to me, for example, that the MGA starter motor power draw might be one source of PPR episodes in older Gen 1 Volts whose batteries have started to degrade (i.e., have even less than 1 kWh in that 5% extended range operating buffer). When driving in CS mode with a fully depleted battery, if the car is turned off while the engine is still running (indicating the battery is not yet charged back up to the "switch to gas" state of charge), when the car is then restarted, the amount of power used by MGA to start the engine perhaps lowers the state of charge too close to the "hard floor," and the car protects itself by going into Propulsion Power Reduced mode.
 
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