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 200ish watts or so but even at a standstill, E-Pedal is still using this 200 watts just like D mode, B mode, and likely reverse (You will have to check on that) but at least "friction braking" still brings the car to a full stop. 

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) 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.  We also need to realize that regen is AC power,  Fast charge is DC so two completely different systems at work.  FYI; DC is a direct dump into the battery while AC must be converted thru the charger before hitting the battery.  

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 than the max B mode regen at any speed.  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!

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.

EDIT

It does look like the easiest method 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! 

There was still very little efficiency differences but I found B mode to simply be easier to not slow down too rapidly.  Many times a situation would develop in front of me and my knee jerk reaction was to completely lift my foot from the accelerator rapidly slowing in E Pedal. Nearly every time, it was too much slowing.  B Eco seemed to be a good compromise. D Eco proved to be too unresponsive to deceleration much more situations I tended to see. 

Eventually the driving style that seemed to work the best and the one I have since adopted is B Eco for all driving scenarios that are not full stops and go.  I will still engage E Pedal when an expected stop is suspected and at that point, I will return to B Eco within a few seconds or continue to a stop in E Pedal.  Over the long term, this appeared to give me a .1 - .2 miles/kwh advantage. I hesitate to say that because the results were inconsistent but against the  average of the same time period taken in both 2018 and 2019, the numbers did nudge upwards.  

Since D and B do provide a different driving feel, it really becomes up to the driver's preference. I think if I lived in an area with less traffic congestion, I might prefer D as well but I live in the land where camping in the left lane one mph over the speed limit is all too common. 

Finally

What mode is best? Answer; ALL OF THEM! 

That's what they are there for. Changing driving conditions means each mode has a role to play.  Now, we can be lazy, simply pick one and stick to it. I choose to constantly shift from D, B, E Pedal and even N depending on the road (and cars) in front of me.  

Am I doing it better? Well, I think I am above the efficiency curve but it is enough to justify my actions?  The answer is dependent upon your opinion.  Its your car so your choice. I do say that is does make me more aware of the traffic conditions and probably makes me a safer driver.