Losing all regen braking during a bumpy stop

[rogersleaf]

The brake response sensation is definitely unsettling on surfaces where traction is not consistent. It makes logical sense to disengage the regenerative braking with a front-wheel-drive car to maintain some steering control if front wheel traction is lost. Just try engine braking and steering in a front-drive on ice & snow. Not so sure this sensation is any worse (or unsafe) than other late model cars with ABS that I have driven. The ABS on my '08 Civic would engage on expressway exit ramps (on dry surfaces) and pot-hole cratered streets. Ironically, the sensation was noticeably reduced after replacing the factory Bridgestone EL-400 tires (tread similar to Ecopias) with a stickier tire.

 

[minispeed]

This isn't a nissan leaf thing, it's a regen braking thing. Both my Prii do it, the older one needs shocks and it does it a lot.

It's not even a regen braking thing, it's an ABS thing. My old Subaru did it a lot, too. Worse than my Prius.

I don't think it's an ABS thing. With my understanding of an open diff I belive that if one wheel (lets say the right) were to lose traction then the energy would want to go down the path of the least resistance. The energy had been travelling to the motor to be recaptured so there's resistance at the motor, the left tire still has traction, the right can spin. This will cause the energy coming from the left tire to pass right through the diff to the right tire and the motor to stop and give a feeling of being in neutral.

Think of a stuck car on ice with an open diff. The motor is spinning and one tire spins the same speed as the motor, the other tire with traction (resistance) just sits there and does nothing while the other one spins away at the same speed (multiplied through the ratios) as the motor. The only resistance that the tire with grip has is normal rolling resistance and a bit of snow that would easily be plowed through if both wheels had traction and that tiny amount is enough to make the diff transfer all 100+hp from that motor to the other wheel. Many times that amount of resistance is enough for you to push the car yourself, providing there isn't ice also behind or infront of the car.

They probably should have some kind of electronic wheel brake similar to the E-diff that simulate a locking diff. However this is a car that was designed at a time when it was going to be sold at a loss and was still a gamble if it would make money to expect that in the first gen is a lot. So it could have been sold to you at $X more, or it could mean that you replace your shocks twice over the life of the car instead of once, still costs you more money.

 

[DaveEV]

I don't think it's an ABS thing. With my understanding of an open diff...

It's not an open diff thing - you can see similar behavior if you brake over railroad tracks or similar bumps that affect both wheels at the same time.

Sure, a limited slip diff might help in some of these cases, but an open diff isn't the cause here - it's the ABS logic kicking in with insufficient force along with regen getting turned off - presumably to give the ABS system full control over wheel forces.

 

[lion]

What's your millage? It could be possible if you drive on bad roads a lot that your shocks are worn out and need to be replaced.

This isn't a nissan leaf thing, it's a regen braking thing. Both my Prii do it, the older one needs shocks and it does it a lot.

From my observations I would guess it happens on bumps where the car anticipates ABS might kick in and not when it actually does kick in. This is probably for safety, ie a loss of regen that causes you to give it more brake before you loose traction is better than actually losing regen when the wheels are already bouncing too much for the brakes to work. Because of this a shock that is not worn beyond it's limits yet but is close may cause this to happen more.

I'm at 20,000 miles, but it has been doing this since day 1, so I don't think it's shocks.

I have at least 200,000 miles on this specific route, in many different vehicles, including a Prius, and none have ever shown any brake performance issues (on any road). I hang out on many car forums, and I've yet to see this exact issue talked about on those forums.

 

[minispeed]

I don't think it's an ABS thing. With my understanding of an open diff...

It's not an open diff thing - you can see similar behavior if you brake over railroad tracks or similar bumps that affect both wheels at the same time.

Sure, a limited slip diff might help in some of these cases, but an open diff isn't the cause here - it's the ABS logic kicking in with insufficient force along with regen getting turned off - presumably to give the ABS system full control over wheel forces.

I'm not saying the open diff causes this I'm saying that because of an open diff regen probably has to be cut out before a bump would cause traction loss, that's why bumps to both wheels cause the car to cut regen, at that point the car doesn't know if one or both will break lose. The program cuts regen befor an open diff would cause the conditions I descried. This is safer because it gives the driver more time and distance from the intended stop to apply more Brakes.

This is a regen using front wheel thing not an ABS thing. If you're already at a point in any car where the front may be losing traction the regen cuts, you coast for a split second then you apply more Brakes. It's the sudden application by the driver as a reaction to the loss of regen that is probably causing abs to act as it should and would in any car. You can't drive a non regen car on the same road and compare and say that it's all the ABS programming fault because in that car over the same bump at the exact same starting speed and breaking point you never lost regen and never asked more from the caliper Brakes at that split second which is what is probably causing the ABS to kick in. If you were able to simulate this on the ice car with a sudden loss of brake pressure that caused the driver to push the pedal harder I bet you'd get a lot more abs kicking in too.

Try driving with the ABS fuse pulled if the car will let you and see what happens. I know in the early days of abs people use to do that all the time. Not sure if it can still be done on modern systems.

Anyone have any experience on a rwd regen car? Does it do anything similar?

 

[crawlspeed]

Is there any new updates anyone has on this issue. I have the same issue and its very annoying and dangerous feeling. I'm kind of surprised my wife has not mentioned noticing it yet and made me take the car to the dealer. I notice it very consistently at a few stop signs that have bumps right when your braking.

 

[Beardedjeff]

Just throwing in that my 2013 SV does this too... Catches you off-guard

 

[jjeff]

This also happens on both my Leaf's as well as Prius, I believe it may be common to all vehicles with regenerative breaking. I also really dislike the feeling but have kind of learned to live with it

 

[SebastienV]

I’ve been seeing something similar occur on my 2019 SV, but it seems to be a random event. Sometimes, regenerative breaking just stops working for no apparent reason. Very disconcerting and potentially dangerous!

 

[lebikerboy]

My 2019 Leaf started displaying a malfunction code showing the collision avoidance system not working as well as the lane departure warning.
Nissan Canada denied a warranty claim as the three year warranty had expired three weeks before. Luckily my dealer escalated the problem to the regional service manager and now the lane departure camera will be replaced by Nissan. Two thousand dollars I really didn't want to spend...

 

[alozzy]

Plenty of speculation on the root cause, but I have never once been able to recreate the problem with my 2013 SV if I turn off traction control. With traction control enabled, it's pretty easy to recreate. So, based on my limited testing, it seems to be traction control related.

 

[LeftieBiker]

The traction control is preventing the brake from locking the rotor and thus the wheel. This actually helps braking most times, but we perceive it as a loss of braking because we don't feel the wheel lock that we associate with hard braking.

 

[alozzy]

I respectfully disagree...

There is a man hole cover on a descent near my house which, if I brake while on the cover, will result in a momentary loss of braking. I'm not hard braking, just moderately applying the brakes. The system does fairly quickly return to normal, but it's when this happens unexpectedly that it's really disconcerting.

As a result, I have gotten in the habit of scanning for bumps at intersections and I try to remember to leave extra stopping room just in case. I never experienced this issue with any other vehicles, including those with traction control and ABS (such as my Hyundai Elantra Touring).

 

[LeftieBiker]

I'm open to the idea that there are cases in which the system gets tricked into poor braking. I'm just not sure how we'd test to determine which case a given situation is...

 

[knightmb]

The topic was started in 2013 and while the continued discussion is interesting, we should really put to rest how ABS systems work in cars and how they affect the Leaf or any car (EV or ICE) for that matter in a more logical way.

How does the Anti-Lock Braking System work?

ABS works by releasing and then reapplying or 'pumping' the brakes to a motorcycle wheel or car wheels in heavy braking situations. Sensors on each wheel are used to detect 'locking' or when a wheel stops moving and starts to skid. Although not all ABS systems are the same, with some only preventing wheels on the rear axle from locking up. When a lock-up is detected, ABS pumps the brakes, 100's of times a second. This stops the wheel or wheels from skidding and helps keep the driver in control of the vehicle. So essentially, ABS works in three stages:

1) Brake pedal is pushed
2) Wheel sensors detect skidding or 'locking'
3) ABS pumps the brakes

Now given this information, having a heavy Regen going would interfere with this process. The ABS is trying to help you keep the vehicle in control of your steering input. If the right wheel is "skidding" across a manhole and heavy regen was on the left side, it would cause the vehicle to steer to the left. ABS can't control which "wheel" is getting full regen. The Leaf has a single motor, not a motor for each wheel. The only way to insure that ABS functions properly on both wheels is to drop the regen from interfering.
I agree, it's annoying when it happens and I know of at least 2 areas in my city where I can reproduce it every time by braking hard because of a manhole cover in the travel lane of one and a bridge that has a large expansion join that "bumps" the left wheel into the air every time on hard braking for the other. I don't think we should look at it like some kind of glitch, it's working exactly as it should because there is no other way it could work.

 

[alozzy]

@knightmb

Try disabling traction control, then try to recreate the issue we are discussing. I'm curious if a newer Leaf responds the same way as my 2013 SV (i.e. with no loss of brake response as long as traction control is off).

 

[knightmb]

@knightmb

Try disabling traction control, then try to recreate the issue we are discussing. I'm curious if a newer Leaf responds the same way as my 2013 SV (i.e. with no loss of brake response as long as traction control is off).

Traction control shouldn't disable ABS, but it just so happen I read this message on the other side of town and double-bonus it was raining all day, so that manhole cover was going to be nice and slippery.
So I turned off traction control, my SOC was around 40%, so easily will have max regen when I brake. The time of day was good, very little traffic after lunch "ends" so to speak. I accelerated to around 45 mph and this spot is right before a spot light. I didn't have anyone behind me, so a sudden brake wasn't going to cause a rear-end collision. I actually made two brake-checks at this point (by circling around and trying again) and both times the ABS kicked in and killed the regen when I slide across that manhole cover on the right side with traction control disabled both times.

When I was driving my 2013 SV, I turned off traction control for snow all the time, but it never disabled any ABS because I could slam the brakes on the snow and regen would drop and ABS would always kick in. Seems to be the same way on my 2020, so thanks for giving me a fun experiment for day, I was curious if it changed on my 2020 also. :mrgreen:

I wonder if it was trim level dependent for the Gen 1 Leaf?

 

[knightmb]

I just thought, maybe turning off the traction control doesn't disable ABS, but makes it less sensitive. I was doing hard brake test, I should see if I can duplicate this on a place where light braking triggers the ABS and see if traction control affects it.

 

[LeftieBiker]

Look for 'washboard' type bumps.

 

[jjeff]

Look for 'washboard' type bumps.

Yes, that's where it rears its ugly head on both our '07 Prius and both '12 and '13 Leafs, all three have regen brakes. It happens basically every time I get off the freeway, using a route I don't normally go, which has downhill and a nonstop right turn merge lane. Right as you turn and are braking there are some washboards and it basically happens all the time. Actually, I've found a way to avoid it, braking hard right before the turn/washboards and then somewhat coasting through the turn but note I don't have to any of this on either of my other ICE vehicles both with ABS and traction control but no regen. This is why I really believe it's a regen thing rather than ABS.