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Discussion Starter · #1 ·
I finally picked up my brand new blue 2013 from the dealer on Thursday. (Yippee! :D ) I don't have a fancy DashDAQ, but since the 2013 Volts have an instantaneous power display of kW's being drawn from or put back into the battery, this allowed me to observe some interesting things about how regen works when in Neutral and Drive...

As most people already know, when coasting in Drive ("D") there is a little bit of regen going on. It's sometimes hard to perceive, but at higher speeds (>50mph) it can be well over 5 kW. At lower speeds, say 30mph. And (of course) when you hit the brake pedal while in "D", regen increases to slow the car down.

What I was surprised to find was that when driving in "N" and applying the brake, there is zero regen. I'm guessing that there is a good mechanical/safety reason for this, but I was surprised nonetheless. (I searched the forum afterwards and found a few mentions of this in older posts, but I didn't remember ever seeing it myself.)

Furthermore, if you're in "N" and then shift back into "D" and press the brake pedal less than 3 seconds after making the shift, you STILL don't get any regen. But if you wait more than 3 seconds after shifting to press the brake pedal, regen will work just like normal. Also, if you shift from "N" quickly to "L", you'll get the normal amount of regen that you always get in "L" just from not having your foot on the accelerator, but when you press on the brake pedal you won't get any additional regen if it happens within that same 3 second window. This might be good to know for hypermilers who are getting creative with their use of Neutral.


Also, I was able to observe what saghost first noted in this post: http://gm-volt.com/forum/showthread...ew-For-My-Sanity-Driving-in-quot-L-quot/page2 ...that while coasting in Neutral, there's actually a small amount of power being used by the motor, and appears to be proportional to vehicle speed. I saw ~2 kW draw at ~50mph. This realization kinda ruins my idea for a Volt vs. Prius coast-down test (in neutral) to see which car is more aerodynamic. Oh well. But it does make me wonder what the Prius does in "N", since it has a similar drivetrain.
 

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Try L for regen and tell us what happens. I drive L in town for stronger deceleration and presumably more regen.
 

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I finally picked up my brand new blue 2013 from the dealer on Thursday. (Yippee! :D ) I don't have a fancy DashDAQ, but since the 2013 Volts have an instantaneous power display of kW's being drawn from or put back into the battery, this allowed me to observe some interesting things about how regen works when in Neutral and Drive...

SNIP


Also, I was able to observe what saghost first noted in this post: http://gm-volt.com/forum/showthread...ew-For-My-Sanity-Driving-in-quot-L-quot/page2 ...that while coasting in Neutral, there's actually a small amount of power being used by the motor, and appears to be proportional to vehicle speed. I saw ~2 kW draw at ~50mph. This realization kinda ruins my idea for a Volt vs. Prius coast-down test (in neutral) to see which car is more aerodynamic. Oh well. But it does make me wonder what the Prius does in "N", since it has a similar drivetrain.
Congrats and thanks for the report.

The power used by the motor in N is probably to offset the natural drag of the traction motor (which I don't think can be removed from the powertrain). The traction motor is permanent magnet so it would have drag if there was not some power applied. It might be interesting to see how much rolling force is needed for each of the Volt and Prius to decided if there is much difference -- it may just be balancing the loss.
 

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I made an interesting observation today . We are visiting Pagosa Springs , CO and I drove 4.9 miles into town with only 0.2 kWh using the low setting . It was mostly down hill so I figured I would use an extremely high amount on the return , but it only took 1.6 kwh to return . If I repeated this round trip with this average I would get 54.4 miles per 10 kWh , which is something I have never came close to before .
 

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I made an interesting observation today . We are visiting Pagosa Springs , CO and I drove 4.9 miles into town with only 0.2 kWh using the low setting . It was mostly down hill so I figured I would use an extremely high amount on the return , but it only took 1.6 kwh to return . If I repeated this round trip with this average I would get 54.4 miles per 10 kWh , which is something I have never came close to before .
Could be just a small sample and low speed artifact.

But also I think the air is cleaner and less dense here in CO, so you can slip though it easier ;-)
With my Volt have many days over 50 miles -- I just include it as one of the many pleasures of living in CO.
 

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Furthermore, if you're in "N" and then shift back into "D" and press the brake pedal less than 3 seconds after making the shift, you STILL don't get any regen. But if you wait more than 3 seconds after shifting to press the brake pedal, regen will work just like normal. Also, if you shift from "N" quickly to "L", you'll get the normal amount of regen that you always get in "L" just from not having your foot on the accelerator, but when you press on the brake pedal you won't get any additional regen if it happens within that same 3 second window. This might be good to know for hypermilers who are getting creative with their use of Neutral.
I have a feeling that the 3-second delay that you are seeing is a lag in the display system rather than any sort of lag in the actual regen system. My biggest criticism of the Volt at this point is the lag in the user interface and display, whether toggling between screens or keeping track of the energy recovery.
 

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What I was surprised to find was that when driving in "N" and applying the brake, there is zero regen. I'm guessing that there is a good mechanical/safety reason for this, but I was surprised nonetheless. (I searched the forum afterwards and found a few mentions of this in older posts, but I didn't remember ever seeing it myself.)
Putting the car in "N" mode should open the relays giving an the electrical equivalent of neutral. Which would mean no regen is available.
 

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Why would anyone use N when moving?
 

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Discussion Starter · #10 ·
I have a feeling that the 3-second delay that you are seeing is a lag in the display system rather than any sort of lag in the actual regen system.
I highly doubt it. Rather, I think it's a safety consideration. When it's in neutral and there's no regen, the actuation/response of the brake pads has to be modified to compensate for the lack of regen. (Pure speculation after this point...) So maybe when you switch back to "D", either the engineers figured that a delay in re-mapping the brake response was prudent, or maybe there's some sort of calibration that takes some time to compute/implement. (Speculation complete.) Either way, I can think of no reason why they'd make the power displays deliberately (and unnecessarily) lie to the driver. Also, the green efficiency ball shows the exact same effect.

Try L for regen and tell us what happens. I drive L in town for stronger deceleration and presumably more regen.
There's a lot more regen in "L" than in "D" if you just remove your foot from the gas pedal, but you also slow down a lot faster. If you use the brake to decelerate at the same rate in "D", you should get about the same amount of regen.

Why would anyone use N when moving?
Hypermilers use neutral in regular cars when coasting to minimize drag and maximize effeciency. The realization that there's still a small amount of power going to the motor while coasting in "N" in the Volt might make this strategy a tad less effective, but still valid.

When coasting in "D", there is some regen (and drag) going on, which can be more wasteful than simply maintaining your momentum in some situtuations.
 

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\
SNIP

Hypermilers use neutral in regular cars when coasting to minimize drag and maximize effeciency. The realization that there's still a small amount of power going to the motor while coasting in "N" in the Volt might make this strategy a tad less effective, but still valid.

When coasting in "D", there is some regen (and drag) going on, which can be more wasteful than simply maintaining your momentum in some situtuations.
Hypermilers in regular cars would still have an ICE idling.. (expcept maybe in a prius that has enough HV charge).. so may be just a effective. And if ICE is off they may still need it to start on the uphill and that initial start is also a tad less efficient.
 

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...that while coasting in Neutral, there's actually a small amount of power being used by the motor, and appears to be proportional to vehicle speed. I saw ~2 kW draw at ~50mph. This realization kinda ruins my idea for a Volt vs. Prius coast-down test (in neutral) to see which car is more aerodynamic. Oh well. But it does make me wonder what the Prius does in "N", since it has a similar drivetrain.
How about a key-off coast-down?

Kills the power to and from the motor. Not sure about remaining drag / parasitic losses. Fun to try, anyway.
 

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Discussion Starter · #13 ·
How about a key-off coast-down?

Kills the power to and from the motor. Not sure about remaining drag / parasitic losses. Fun to try, anyway.
As much as this is discouraged for safety reasons, I used to do this quite a bit in my previous manual transmission car to try and maximize my MPG. I'd coast with the engine off and then pop it back into gear. Couldn't have been too good for the clutch or transmission, but I never had any issues. :p

Thankfully I never have to do this again driving my Volt. :D
 

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Could be just a small sample and low speed artifact.

But also I think the air is cleaner and less dense here in CO, so you can slip though it easier ;-)
With my Volt have many days over 50 miles -- I just include it as one of the many pleasures of living in CO.
I ran the same route last night and got the same results . I don't know if it is the elevation , speed , cool weather or the way the road is built . On the steep uphill return , it seems to have 4 or 5 semi-flat steps . It seems most posters claim better results on flat roads with no hills . I guess Colorado is the place if you want to join the 50 mile club with little effort . The amazing part is that it is a round trip scenario with no elevation drop to boost the numbers.
 

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I highly doubt it. Rather, I think it's a safety consideration. When it's in neutral and there's no regen, the actuation/response of the brake pads has to be modified to compensate for the lack of regen. (Pure speculation after this point...) So maybe when you switch back to "D", either the engineers figured that a delay in re-mapping the brake response was prudent, or maybe there's some sort of calibration that takes some time to compute/implement. (Speculation complete.) Either way, I can think of no reason why they'd make the power displays deliberately (and unnecessarily) lie to the driver.
I said lag, not lie. Remember that the display is nothing more than a graphical representation of what is going on with the car, but it would be very difficult to make it real time. Another example of lag in the display system is with the TPMS. The tire pressure does not update immediately, but rather, there is a delayed refresh rate. From my observations, about 10 to 20 seconds.


Hypermilers use neutral in regular cars when coasting to minimize drag and maximize effeciency. The realization that there's still a small amount of power going to the motor while coasting in "N" in the Volt might make this strategy a tad less effective, but still valid.

When coasting in "D", there is some regen (and drag) going on, which can be more wasteful than simply maintaining your momentum in some situtuations.
While you are right that neutral is better than in gear in terms of driveline drag, I believe that you have misattributed that drag as being the reason for coasting. Reduction of drag is not the purpose for coasting, it just so happens that engine-off, neutral is the most efficient coasting method for ICE vehicles. The actual reason hypermilers coast is to conserve energy/momentum. Once you get two tons of metal moving, the most efficient thing to do is to keep it moving.

And I'm finding that (for that reason) neutral coasting is every bit as valid in the Volt as it is in a traditional ICE vehicle, and maybe more so (given the added weight). The regenerative braking feature appears to be about 70% efficient, which is very good, but that doesn't account for all of the energy to start the car moving again. In my opinion, even if there is still some energy being fed to the motor while in neutral, the best course of action is to neutral coast toward a stop light (attempting to maintain as much momentum as possible) and only regenerative brake if it is obvious that you will have to slow down or come to a complete stop.

I starting to think that someone should make a hypermiling hierarchy... maybe I'll work on that in my spare time.
 

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And I'm finding that (for that reason) neutral coasting is every bit as valid in the Volt as it is in a traditional ICE vehicle, and maybe more so (given the added weight). The regenerative braking feature appears to be about 70% efficient, which is very good, but that doesn't account for all of the energy to start the car moving again. In my opinion, even if there is still some energy being fed to the motor while in neutral, the best course of action is to neutral coast toward a stop light (attempting to maintain as much momentum as possible) and only regenerative brake if it is obvious that you will have to slow down or come to a complete stop.
So what makes coasting in neutral superior to coasting in D or L (with the appropriate feathered pedal position to achieve the coast)? AFAICT, the car will have exactly the same consumption in both cases, with the added safety of being "in gear" - able to move off of the feathered coast instantly if necessary.
 

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And I'm finding that (for that reason) neutral coasting is every bit as valid in the Volt as it is in a traditional ICE vehicle, and maybe more so (given the added weight). The regenerative braking feature appears to be about 70% efficient, which is very good, but that doesn't account for all of the energy to start the car moving again. In my opinion, even if there is still some energy being fed to the motor while in neutral, the best course of action is to neutral coast toward a stop light (attempting to maintain as much momentum as possible) and only regenerative brake if it is obvious that you will have to slow down or come to a complete stop.

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Just leave it in D and coast. Trying to coast to a stop light (in N)as you suggest would get you "shot" in most parts of the world if there is anyone behind you. If it is 2 am and you are the only one around, go for it. But in traffic, seems not to be the wise choice. And while in N, the minute you need power, you are out of luck. And if you need to hit the brakes while in N, just friction braking with no regen.

Feels like a lose lose.
 

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The point is that the deceleration that occurs during neutral coasting is significantly slower than "D" coasting, which is again significantly slower than "L" coasting. I'm actually very surprised that owners of an economy car would have so much difficulty visualizing what I am describing. What I am talking about is timing, pure and simple, and the goal should be to neutral coast in a way that maximizes your speed as the light turns green. Here is a scenario:

You are driving at 40 mph approaching a red light that is an 1/8 of a mile away. The classic American driving technique is to maintain 40 mph until you are less than 100 feet away and then hit the brakes so that you come to a complete stop (usually moments before the light turns green again). The way it seems that most of the Volt drivers here are approaching this scenario is similar to the classic American approach. The only difference is, at about 100 feet out, the Volt driver switches to "L" or regen brakes in "D" for some of that braking period.

The best approach is to time the light and coast. In this scenario, a neutral coast would probably only lose about 10 mph out of the 40 mph over the course of 1/8. That's not enough to get you shot, even in the mean streets of Los Angeles. At this point, if you've timed the light properly, you'll hit the intersection doing 30 mph, and you'll only need to recoup 10 mph of speed (not the 40 mph of speed that you lost by coming to a complete stop, regen or not).

Anyway, the whole point is to time lights so you don't need to stop. I wish I had a dollar for every time someone told me that it sucks to follow someone who is coasting. It's just good driving practices, and anytime anyone has ever passed me as I decelerated for a light, I ended up passing them in short order because they burned out their brakes coming to a complete stop.
 

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The point you seem to be missing is that I can achieve exactly the same result - the same car speed sequence and power flows - by coasting with the accelerator not quite released in D, or moderately depressed in L. The only thing I can see that N does for me is make it easier to find that coasting spot - and throw out regen while preventing acceleration if I get forced out of that spot. It seems like intelligent feathering of the accelerator can achieve everything you're trying to, with less hassle and risk. :)
 

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The past few days I have taken trips to a small town . I use 0.6 kWh to get to the top of a hill . Later I make the descend using L , and it not only keeps my speed down without using brakes , it generates 0.4 kWh so the entire trip only consumes 0.2 kh .

If I try the coating in N method , I would use more energy and braking .
 
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