Saturday, November 24, 2018

E-Pedal Verses B Mode

Why is this even a question!!  E-Pedal is by far the best innovation on the 2018 LEAF!  I like AEB but E-Pedal is a dream!

But some feel that E-Pedal uses friction braking too much which lowers efficiency. Now, how they got this idea is anyone's guess.  E-Pedal does use friction braking if the SOC is high, E Pedal will engage more friction braking in order to minic E Pedal at lower or "normal" SOC levels but for the most part, friction braking is used primarily at VERY low speeds.

Well, it became quickly apparent that just saying E-Pedal is better wasn't going to work. People simply got it in their heads that certain things were happening and and that was that so this is my attempt to "data dump" naysayers into submission!

So armed with a good charge (75% is highest SOC my LEAF has seen in months) Fully charged LEAF Spy phone (and LEAF Spy of course)  off I went.

Now the first thing we need to know is that LEAF Spy on your phone changes rather slowly.  You can see this by watching power output.  Take your foot off the E Pedal and the motor power should show regen. The delay from the pedal movement to the LEAF Spy screen is significant. a few seconds.  Depending on timing of that delay, it can be hard to get values especially when we are only looking for max values and with regen levels we are expecting, max values will only last a few seconds unless going down very steep hills.  So several runs will be needed to determine a good close approximation.  Then the best course is downloading and reviewing the log files which can be opened in any spreadsheet program.  This allows sorting of any value which makes gathering peak values quite easy. 

To lessen the possibility of errors, I decided to do this over several days hoping for different temperature ranges to see if they had an effect. I also QC'd before each run to heat pack at least into the low 80's.  Was aiming for the upper 80's but one day, pack started at 51º and temps basically stopped rising about 75% SOC so had to settle for low 80's.  Close enough, I think.

I also separated the E-Pedal runs and Eco B mode runs into separate days as well.  So if LEAF Spy's granularity is so poor, why use it?  Well, the ability to download the data and sort in a spreadsheet is obvious but if that isn't enough consider...

We have a power meter on the dash that shows power or regen and like most Nissan instrumentation, it should be ignored. Ok, maybe that last statement was a bit over the top.  There is a small meter that is visible on most screens that has 8 regen segments and 16 power segments or we can use the dedicated screen that doubles the segments for both.   Should be enough, right?  WRONG!

Well... maybe not "completely" wrong as long as one understands the meter uses different scaling for each drive mode. In retrospect I do understand why people might think  E-Pedal uses a lot of friction braking because everyone knows the slowdown in E-Pedal is much more severe than B mode but what if they found out that E-Pedal's regen has a 50% higher ceiling?

The Test

We all know E-Pedal slows the car dramatically faster than B mode does although B mode does a pretty good job as well, just not quite as fast. If there is a slight upwards slope to the road, B mode will slow the LEAF to nearly a complete stop. But creep will allow the car to continue to... well, creep.   Sadly, even E-Pedal has creep enabled.  Creep power is small, roughly 150-200ish watts or so but even at a standstill, E-Pedal is still using this 150 watts just like D mode, B mode, and likely reverse (You will have to check on that)

Now both E-Pedal and B mode do quite well with moderated regen.  And this is how most (including me) drive 90% of the time.  Its gradual slowdowns mixed with shorter more aggressive deceleration.  So all this is dealing with the remaining 10% where speeds are much less predictable due to traffic, controls, crazy drivers, etc.   So the target of the test is finding out why E-Pedal slows faster.

B Mode

I did several runs using B mode only (no braking) at high speeds on steep downhill slopes in order to hit max regen as long as possible. After collecting several data points, the best B mode could do was 36.8 KW.   Below is an edited version of LEAF Spy logs. No values were changed. I simply removed extra fields that do not pertain to the topic for clarity.

B Mode Regen

What I did is sorted the values based on amperage to show highest readings of the day.  I highlighted the regen entries. The other entries are charging at a DCFC which is easy to discern since we were not moving at the time. I used the formula Volts*Amps for regen power.  I have SEVERAL data points but I am showing this because it shows two different battery temperature ranges. This resolves the small difference.  With batteries colder, regen was lower at 35.6 KW; not significant as we shall soon see. 

B Mode Regen High SOC

Here we see even lower regen  of 34 KW but this is at a higher SOC which is to be expected.  I suspect in a brand new pack, max regen in B mode is likely close to 40 KW. Unfortunately LEAF Spy does not designate what drive mode (at least I don't think it does. the log files are HUGE) so I was unable to go back to earlier logs to see if the regen profile had changed.  So this is only a guess based on the actions of previous LEAFs with degradation. 

E-Pedal

I wrote in my blog back in March 2018 that I was able to hit 60 KW in regen. At the time I wondered why I could not charge at that rate (Note; The charge restriction is obviously a programmed restriction by Nissan illustrated by "Rapidgate" issue that plagues all 40 and 62 kwh North American LEAFs) but I guess the short duration of that very high regen level could be endured by a system designed to do only 50 KW...  So I already knew going in that the reason E-Pedal slows the car much faster is because it regen's on a completely different level. 

E-Pedal Regen

It was my plan to do 3 days of E-Pedal just like I had done 3 days of B mode but after reviewing the first day, I felt the point is well proven. This chart we will break down in segments. 

Line 1; Cold pack, low SOC; 57.6 KW

Line 2; warm pack, higher SOC; 57.5 KW

Line 3; "low" speed  52 KW

Well, the difference couldn't be any more dramatic. Even at street level speeds, the regen in E-Pedal is nearly 50% higher. I am relatively sure this negates any friction braking losses which I still contend, only happen at speeds likely under 3-4 mph or... the same time you would have to brake in B mode if a complete stop is needed. 

Conclusions

This blog is NOT intended to say one mode over another is the best. Again, each mode with its regen profile allows X time to react to changing driving conditions.  This makes it obvious that the mode that can react the quickest, is the best in most circumstances. We have all heard Gerber Collision and Glass radio commercial about the guy bee bopping down the road without a care in the World because all situations developed slow enough that he had time to react. Unrealistic? Yep and that is how Gerber Collision and Glass makes money. Because things can happen in a split second, but "most" things happen with a 3-5 second window. 

Just because E-Pedal can regen at 58 KW doesn't mean you need all that. It can regen as little as you want and yeah, in emergency situations, braking will still be needed but that teeny tiny bit of extra slowing caused by an "additional"  29 KW of regen could be the difference between a racing heartbeat and a ticket and a $1500 front end repair for tapping the car in front of you. 

Safety

After all that is said and done, lets be personal.  I can't for the life of me understand anyone who does not use E-Pedal ALL the time.  I stand by my statement that this is THE best thing Nissan has put on the LEAF since heated seats!

**WARNING SARCASM ALERT ***

Finally; I do not have much to say about this simply because EVERYONE has very strong opinions about this but E-Pedal has simply gone overboard with the brake lights.  Have you ever driven around on an empty dark street and watched your brake light action? Its INSANE. They come on all the time for even the slightest slow down and whats worse. They stay on until you speed up!!

I mean this fact alone means that B Mode is much more efficient since it NEVER ACTIVATES THE BRAKE LIGHTS EVER!!  Think of the power saved by not having to light up! 

So if you are into driving in bumper to bumper traffic in B mode with your brake lights hardly ever coming on, then there is no need to read this blog. 

EDIT; Had to add the sarcasm alert since a few people simply missed the humor I was trying to input.


EDIT;

After several people contended that friction braking is enabled in E Pedal even at higher speeds, I have begun a test of efficiency that will last several weeks. Since I am not going to just "drive around" in a circle or any other type of attempted close course, I can only average my results over an extended period of time. I did start the testing before the weather got warmer and drier but did miss the colder part of the year so will be adding that later this year but will be posting at least initial findings when I have enough "hot weather" data collected so stay tuned.

It does look like the best for efficiency is B mode for most driving using E Pedal for rapid slowdowns and full stops.  This does not change the fact that E Pedal is still a dream come true in stop and go traffic!

15 comments:

  1. Dave, I am puzzled by your conclusion. First you say that E-Pedal is the best innovation on the new LEAF and we should use it all the time. Then you say B-mode is much more efficient because it doesn’t activate the brake lights.now which is it?

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    1. My comment was intended to emphasize the increased risk of a rear ender. Brake lights hardly use any power at all. One Pedal driving is much more convenient.

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  2. Merry Christmas,
    You are so interesting! I don't believe I've truly read through anything like that before. So wonderful to discover another person with a few unique thoughts on this issue. Seriously.. many thanks for starting this up. This website is something that is required on the internet, someone with a bit of originality! If you want to read Christmas Quotes you have to see the link
    Thank you,

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  3. Hi,
    The very next time I read a blog, I hope that it does not disappoint me as much as this particular one.New Year Wishes I mean, I know it was my choice to read, but I truly thought you would probably have something useful to say. All I hear is a bunch of crying about something that you could possibly fix if you were not too busy searching for attention.
    Thanks

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  4. I drive in B mode for the most part since I have more control on the throttle(or should I say acc) and all the fun from the instant torque EVs have.
    Tried eco+B+e-pedal permutations and I think pure B suits me best.

    All the eco and epedal retards the acc, which I don't like. It's much harder to resits to step on the acc when in D or B.

    Interesting point on the break light, although SoCal traffic is bumper to bumper so nobody is really paying attention to the break lights I guess.

    In your opinion, which is more efficient B or epedal?
    I'm trying to coast more hence the reason I use B.

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    Replies
    1. First off; Neither E Pedal or B mode retards acceleration. They have the same acceleration as drive mode. Eco smooths the motor response to pedal movement. IOW; push pedal real fast in any mode, acceleration will be the same. But push it slightly like when you are trying to maintain speed, Eco will dampen the acceleration to keep a more even power output.

      As far as which mode is better for efficiency; It depends on the situation. E Pedal regens a lot stronger so if hard short distance stops are needed, E Pedal will regain more of the power back thru regen. But that can also mean slowing down faster than you might need to if not careful to monitor your speed. TBH; Its hard to argue against E Pedal because it can do everything any other mode can do while using only one pedal.

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  5. Dave, agree on the retard part. Guess I didn't word it correctly. I just need to press harder on the acc to get it going. And yes it just smooths it out in case you have heavy foot but if you feather it it's more fun just to be in D or B mode for that matter.
    I'm new to EVs and the leaf (3 months in) but used to drive HCH(hinda civic hybrid 2003) for 5 years.
    Enjoying your blog and it is good food for though.
    Keep it up...
    Might invest in LELink bt adapter and leaf spy but wonder if this is TMI.

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    Replies
    1. I have been experimenting with all the drive modes lately and its easy to understand the draw of B mode w/o Eco. Its like driving a race car after E Pedaling!

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  6. Very interesting article. I can't comment yet as I am still waiting for my new LEAF 40kwh to be delivered to the main dealer. But I am looking forward to trying e-pedel out.

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    Replies
    1. I would definitely try all the modes as an argument that there is a "right tool for the job" has a lot of ammunition but to me; E Pedal is the lazy way out. One pedal driving is very liberating!

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