Max regen - at what point do mechanical brakes engage?

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For what it's worth, I might compare this discussion with my experience with my Renault Fluence. The Fluence has no [apparent] interaction between regen and brakes at speed - they appear to be two separate systems.

I am very happy with this, and would definitely advocate that this mode of operation is to be preferred for EVs. When you back off, you know all the decel is regen, and nothing is wasted in the brakes.

The max regen is 30kW. Decelerating down to approx 40mph (I'll test and check that figure in due course), the regen power then ramps off linearly (which serves to provide a constant deceleration rate). The Fluence has a slightly annoying creep function (I'd prefer it just came to a dead-stop, personally, to allow for full 'one-pedal' driving) and so the regen rolls of once down to ~7mph.

I think that, maybe, too much emphasis has been put on making EVs drive exactly like 'regular' cars, so that the Leaf coasts a bit like a large passenger vehicle with an auto slush-box. (And the Fluence has a 'creep' function - which, actually, doesn't work because if you keep your foot slightly on the brake it cuts the motor, so you roll back on a hill if you try that without using the hand-brake!)

Whereas, in actual fact, the sort of folks who will [currently] buy an EV want it to do what EVs should do, which includes one-pedal driving. Seems to me too much emphasis on making EVs drive in a way they VMs think the 'mass market' would expect, instead of focussing on the desires of their most immediate sales prospect. But maybe they have it right and need to do it this way, I don't really know, but I can say that it seems to be to be far more ideal for 'hypermile' type driving to have mech braking and regen work independently.
 
I try to make i regen brake as much as possible before the mechanical brakes kick in by barely feathering the brake pedal when just letting off the accelerator is not fast enough.. Sometimes I find it just gives up and stops it with the green dots.... but when you remove pressure from the brake pedal and reapply it gently, it goes back to regenerating.
 
Based on personal driving experiences, the regen/brake sys mixing is clearly software job, or we can say fly-by-tweakable-wire. The dynamics of brake pedal feedback can tell you sth. different than conventional gas cars. And that's why Nissan can come up with the B mode so easily.

But there is another point, when we go back to the fundamentals, there's more to look into than heavier regen is better.

In theory , from the energy efficiency point of view, the best scenario is no braking at all --which everyone knows; and all energy goes to regen when you have to brake. There are two problems in this part.

1. how much energy was allowed to goto regen sys. Nissan has addressed this with B-mode, or, in the far future, might allow you to tweak this limit to whatever you want, which i doubt due to safety concerns.

2. efficiency of Regen sys. Regen sys would save part of the energy lost to friction heat, but will never be 100%. regen sys has it's own efficiency limit even you input 100% braking energy into it. This would compromise more aggressive regen. tweaking.

When we come back to practical driving, the best efficiency strategy is not using regen as much as possible, but keep the car moving at constant speed as long as you can and use both pedals to achieve that. Like the most talked about long distance downhill situation, as long as the traffic permits, regen-off would be more efficient than regen invovled.
You use regen/brake, only when you have to - for your safety.

For the part we have to use brake, to satisfy everyone, we might need self-learning sys. to adapt to personal habit, then come up with the best tweak for that person--hey, we probably have had automatic driving machine for that purpose.
 
I posted this in the giant capacity loss thread:

I've noticed as I get closer to losing my first bar that regen is more limited at higher SOC. I was cruising this morning and I only had one regen circle at 191 gids! Battery temperature was 20 c. If I flog it on the freeway I typically won't get all my regen circles till nearly 50% SOC!

I use to have all regen circles available at an 80% charge now I'm missing one or more depending upon how fast I set my second onboard charger. I've also noticed from day one that the harder you drive the car the more it wants to limit regen at higher SOC.
 
has anyone else noticed some significant regen changes as the battery wears down. I know its cold , but here its only 39 and even after 4 bars down of driving. when coasting or breaking I only get 1 regen bubble. and no other double rings. I have not had the software update yet , and granted my son has been driving for the last month. before coasting I would get 2-3 bubbles and more with braking softly. I know when its fully charged there is less regen but after 1-2 bars down It seems work well and regen freq in the past . Now I hardly had any. anyone else see this. I have lost 3 capacity bars down to 46 Amphr .
 
drees said:
The drastic reduction in regen appears to be a result of the P3227 update and cooler weather. See this thread:

What happened to my Regen?
But, mksE55 reports that he has not had the software update. Temperature may have something to do with it, but I don't recall any noticeable effect last winter. And, now of course, since regen has been severely reduced by P3227, I can't tell if cold has anything to do with it.
 
mksE55 said:
has anyone else noticed some significant regen changes as the battery wears down. I know its cold , but here its only 39 and even after 4 bars down of driving. when coasting or breaking I only get 1 regen bubble. and no other double rings. I have not had the software update yet , and granted my son has been driving for the last month. before coasting I would get 2-3 bubbles and more with braking softly. I know when its fully charged there is less regen but after 1-2 bars down It seems work well and regen freq in the past . Now I hardly had any. anyone else see this. I have lost 3 capacity bars down to 46 Amphr .

Interesting that you haven't had the s/w update and are experiencing this. This is my third winter with the LEAF and I don't recall the regen fading off as badly as it has this year. I lost my first capacity bar this summer.

I know as a battery ages it will accept quick charges more slowly, regen could be considered another form of quick charging. I wonder if this is another 'undocumented feature' of this battery pack?

This is a cold winter for sure. so maybe we are experiencing more fade due to that, however I suspect we maybe seeing the birth of another issue with the pack.
 
chrisie75 said:
For the part we have to use brake, to satisfy everyone, we might need self-learning sys. to adapt to personal habit, then come up with the best tweak for that person--hey, we probably have had automatic driving machine for that purpose.

Oh, Dear God, no.

I've had enough of cars trying to "learn" me. My habits vary according to the conditions I encounter, my mood, or other factors that the genius car will never be able to anticipate. I don't need the car to be a genius; I just want the ability to change the regen as suits my need, or my whim. Within safe limits, of course.
 
+1

Nubo said:
I've had enough of cars trying to "learn" me. My habits vary according to the conditions I encounter, my mood, or other factors that the genius car will never be able to anticipate. I don't need the car to be a genius; I just want the ability to change the regen as suits my need, or my whim. Within safe limits, of course.
 
drees said:
The drastic reduction in regen appears to be a result of the P3227 update and cooler weather. See this thread:

What happened to my Regen?

historical analysis of my regen from day one contributes little to this conclusion. there seems to be less access to the full 30 KW but overall, the numbers are not much different than before.

granted averages covering different days has the normal amount of error which can be considerable especially when there is no effort to duplicate any driving event which is why i took time periods covering several different overlapping periods to see if there was any change and other than the change when i changed driving patterns, there was no significant difference including a periods where my regen levels actually went up after the SW update.

** FYI; all the data used for my study came from Carwings. unlike most of you, i did not get an updated version of carwings so am using the old inaccurate version. but the inaccuracy i have to think is no worse than it was before so for a simple comparison analysis, i felt it ok to use...the other reason is that its the only resource i have with regen data.

now, I also have anecdotal observations which is what is used elsewhere and I too feel that the regen profile is different. as mentioned above there is little doubt that access to the full 30 KW is not as easy as it was before but the cold weather has hampered that as well (keeping in mind the poster above has not had the update)

but wondering if this "hidden" adjustment is related to pack longevity and the ramp up in regen is mirroring the ramp down seen during a fast charge?
 
Correct I have not had the Update. I am do to take the car in for the 2nd year service battery check, and likely will get the update. but this is a major change in regen. I was under the impression that it had to be really cold to affect regen. battery pack that day was 57 by the leaf spy program. after some driving and 4 bars showing on battery temp. I have not checked carwings but I will look into this. since my son is driving it more now , I am not sure how accurate that can be since he drives it differently than I ,and does really care about regen/battery driving distance.
 
mksE55 said:
Correct I have not had the Update. I am do to take the car in for the 2nd year service battery check, and likely will get the update. but this is a major change in regen. I was under the impression that it had to be really cold to affect regen. battery pack that day was 57 by the leaf spy program. after some driving and 4 bars showing on battery temp. I have not checked carwings but I will look into this. since my son is driving it more now , I am not sure how accurate that can be since he drives it differently than I ,and does really care about regen/battery driving distance.
And I would add that I observe a similar regen reduction in my log files from last December (pre-update). I was at 78% SOH then.
 
mksE55 said:
Correct I have not had the Update. I am do to take the car in for the 2nd year service battery check, and likely will get the update. but this is a major change in regen. I was under the impression that it had to be really cold to affect regen. battery pack that day was 57 by the leaf spy program. after some driving and 4 bars showing on battery temp. I have not checked carwings but I will look into this. since my son is driving it more now , I am not sure how accurate that can be since he drives it differently than I ,and does really care about regen/battery driving distance.

I've seen significant reduction of regen (one bubble) with a 50F battery, though it was 25F outside. It makes we wonder if the LEAF is taking ambient temps into consideration as well or exclusively in deciding on the regen available.
 
On the Chevy volt forum a super user plotted the max regen vrs speed.

Has anyone done this for the leaf?
 
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