Tuesday, November 29, 2016

Is LEAF Braking Breaking? Or Is It A "Regen Penalty?"

Waaaay back in the day when the 2011 LEAF was the only version around, there were some people that had grabby brakes. This seemed to happen the most in heavy, slow stop and go traffic.   A fix was issued and the results covered the entire range of possibilities. Some people reported it was fixed, others reported it was better, and a few reported it started out better but went back to bad within a few days to a few weeks. IOW; the fix did not address the cause of the issue.

Fast forward to 2013 and again the same braking issue.  A few differences here and there but basically the same symptoms. One would be gliding to a stop, feathering the pedal with the goal of getting the maximum regen with only enough friction braking to accomplish the stop and all of a sudden, the full braking force of the car kicked in causing a screeching stop.

Now during all this, I never experienced the issue.  I got the recall done because that is how I am. I pretty much never make a special trip to get any of these things done instead electing to do all of them on a random visit to the dealership. Now this all worked out well (except for AC issue on the 2013 when it decided to stop working on a record breaking day in April. Considering Global Warming, you can guess which end of the records spectrum we are talking about!)

Now, many claimed they could reproduce the issue at will.  I followed their process several times and it didn't happen. Not sure why. It just didn't. I chalked it up to the variances all products had despite the fact that this was not an isolated incident.  It actually became easier to ignore because the 2013 fix seemed to be much more effective and the sad fact that LEAF degeneration levels of the 2011-12's meant not that many surviving 2011's out there unless they were part of the small few who got replacement batteries.

But then Kelly Carmichael from BC Canada who still had his 2011 had the issue reappear.  He stated the change to colder weather seemed to aggravate the situation but the problem is that being in the Pacific Northwest, we rarely get that cold especially if hanging around at or near sea level.  So why was this happening? Why was the fix not working for him but working other people?

As always mynissanleaf.com was a great resource to find out what others were experiencing.  Many echoed the sentiment that the fix was at best temporary for quite a few.  Others mentioned some workarounds that seemed to work including one person who disabled traction control, depressed brake pedal to the floor, held it a few seconds, let go and re-enabled traction control and the issue disappeared immediately.   Kelly tried this and it worked for him.  But again, some reported the workaround had to be repeated on a regular basis.

All this got me to thinking. I never had the issue and never disabled traction control with the one exception. The following is a distraction completely unrelated to the topic at hand but was fun doing it!

With all this in mind, I took off for work and as always, got stuck in traffic and realized that I was subconsciously pressing the brake pedal way beyond the point I needed to complete the stop. It was sort of a stretching exercise that I realized I was doing because it also seemed to relieve a tiny bit of stress. This was actually in the Corolla (which had been sitting 5 weeks and needed to be driven) so my first thought was I had to get my LEAF and try this.

So I jump in my 2016 LEAF and a few things I need to remind you of first.  Eco B is nearly 100% effective for one foot driving.  I have only touched the brakes more than a tap one time and that was the Wednesday before Thanksgiving when exiting I-5 North at Sleater-Kinney/College St which was a good thing because I could see that the traffic was backing up a few hundred yards ahead. Well a truck (diesel no less...) didn't realize it and cut from the far left lane across 3 lanes and into the medium, across it and off on my exit causing me to have to brake pretty hard to miss him. If my car had not been shiny, I would have rammed him, but... anyway.

I drove around and at the first stop, I depressed the pedal and was immediately surprised the pedal became firm almost immediately making the distance from the onset of friction braking to the floor much farther than I had remembered.

So back to my 2011 and what I remembered.  The 2011 had the best user controlled regen. Now, maybe it was my imagination but I could ease on the pedal and max the regen and I could feel the boundary where friction braking would start.  But that level of control was short lived because the brake "fix" took away a lot of that feeling.  Now, anything beyond the very lightest touch resulted in a mix of regen and friction braking. I could no longer light up the last regen circle with the brake pedal without some friction braking.  I spent a lot of time experimenting before resigning myself to the fact that Nissan simply took that ability away from me.

My 2013 was the same way. Regen simply was not as easy as before and it was also tougher to fill that last circle especially at lower speeds. This was disappointing especially when there were too many times a tiny bit of pressure on the pedal was needed in heavy traffic and the thought of using even a touch of friction braking really kinda pissed me off.  A LOT!

So imagine my surprise at how well Eco B worked. I loved it! The dozens of complaints from both the LEAF and Prius forum about "too sluggish" "like driving underwater"  I simply couldn't understand that attitude at even the very basic level. After all, I could punch the throttle and the  car took off just fine! Not $100,000 acceleration mind you, but I know me well enough to know I want to continue living so not having all that acceleration is a good thing.

So the days of slowly easing on the brakes was all but done.  Most of the time I could get down to under 10 mph before touching the brakes. So at the point, I didn't care what percentage of braking was regen verses friction because at roughly 8 mph, its all friction!

Then it hit me...

With a 2 mode braking system, an algorithm is needed to insure a safe stop in all situations.  This means both pedal position and pedal position acceleration have to be in concert with each other.  In a slow controlled stop situation, most of the top positioning is going to be primarily regen. In the 2011, I probably could coax close to 50% of pedal travel to regen only.

In an emergency stop, sensors detect greater pedal acceleration which charges the ABS system and friction braking kicks in much sooner as in almost immediately. After all, when 15 feet behind a bumper and closing fast, regen is not the priority any more!  IOW, almost all of the pedal positioning is now primarily friction braking.

I began to realize that the workaround of pushing the pedal to the floor was possibly a reset of the pedal positioning sensor. I seem to recall some people not liking the pedal going nearly to the floor in gradual stop situations but to be honest, can't remember if it the Prius forum or the LEAF forum or both

So we go back to Kelly's car and why his issue only happens in Winter but when only experiencing "Fall-like" weather?    Part of the 2013 brake fix was cycling the brake or ABS charge cylinder or something more frequently to keep it from freezing up.  Well as mentioned above, it aint freezing here and its not really even close. But its apparent that temperature is a factor at least for Kelly...

But Kelly has a 2011 with degradation and we do know that cold batteries do not regen as well which means even at lower SOC's sometimes regen simply either cuts out or is much lower than normal. IOW, can't light up that last circle!  Degradation multiplies that issue.

All this got me to thinking that the sudden braking was being caused by the shutdown of regen at 8 mph so when the friction brakes take over, they are overreacting to the pedal position not realizing it was the new boundary  of sorts for mostly regen verses mostly friction.

To clarify; normally the threshold between regen and friction braking moves depending on the driving circumstances, right?  We can "create" pedal play which allows us to vary the regen to get the most regen we can based on how much space we have and what speed we are traveling at. It would almost appear that the regen system is not talking with the friction braking system or at least is losing some of the information the two systems should be sharing.

Now does any of this make sense?

Lets look at the 2011 owners who had pretty much every possible solution to the brake fix. It ran from "fixed it!" to "a complete waste of my time"  So why the results so different in mostly identical cars?  What is the variance here?

Its the driver.  We all drive differently and we all pretty have our own ideas of how to maximize range.  Look at MNL discussions on regen verses neutral verses drive verses eco verses the day of the week! Everyone has their own ideas of how to get that last mile.

So I am looking for someone who has a 2011 and a 2013+ or one with B mode.  Is their a significant difference in brake pedal travel. Does your pedal slowly sink when you are braking primarily in regen mode?


Ok getting a lot of confusion so guess I need to clear up my muddy thinking a bit.  As mentioned the braking system is two parts regen and ABS or friction brakes.  Now the key thing is in an emergency stop detected by a fast change in pedal position, the ABS kicks in quicker.  Now we know regen cuts out at about 8 mph. So what happens if the regen pedal position is out of whack and it reports a position of 20 but when the ABS takes over under 8 mph, its sees 30? This ABS will read this as an emergency stop and you know the rest!

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