donald
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Re: Max regen - at what point do mechanical brakes engage?

Sun Aug 25, 2013 4:32 pm

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.

johnrhansen
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Re: Max regen - at what point do mechanical brakes engage?

Sun Sep 15, 2013 9:13 pm

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.
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chrisie75
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Re: Max regen - at what point do mechanical brakes engage?

Thu Oct 10, 2013 12:10 pm

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.

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JeremyW
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Re: Max regen - at what point do mechanical brakes engage?

Thu Oct 10, 2013 12:38 pm

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.
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mksE55
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Re: Max regen - at what point do mechanical brakes engage?

Sun Dec 08, 2013 4:48 pm

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 .
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DaveEV
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Re: Max regen - at what point do mechanical brakes engage?

Sun Dec 08, 2013 7:07 pm

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?

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ebill3
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Re: Max regen - at what point do mechanical brakes engage?

Sun Dec 08, 2013 7:18 pm

drees wrote: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.
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JPWhite
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Re: Max regen - at what point do mechanical brakes engage?

Sun Dec 08, 2013 8:03 pm

mksE55 wrote: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.
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2011 Blue SL-e, 132,400 Miles.
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7/18/13 (29,206), 8/25/14 (51,728), 7/12/15 (71.108), 5/12/16 (88,362), 10/17/16 (96,532)
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Nubo
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Re: Max regen - at what point do mechanical brakes engage?

Mon Dec 09, 2013 1:58 pm

chrisie75 wrote: 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.
I noticed you're still working with polymers.

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TomT
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Re: Max regen - at what point do mechanical brakes engage?

Mon Dec 09, 2013 2:06 pm

+1
Nubo wrote: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.
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