Unintended Immediate Cessation of Regen

[SSonnentag]

I've seen a few reports of unintended or spontaneous acceleration, and have generally chalked them up to driver error; bumping the cruise/AP stalk or some such thing. However, I had the following happen to me and I KNOW it wasn't driver error because I checked at the time and my hands and feet were all unmoved and not touching anything.

I was driving with cruise set at 70 mph, approaching my turn onto another road on a rural highway. As I was in a hurry, I did not feather the throttle to slow down gently, but simply removed my foot for maximum deceleration. I would estimate that the car slowed to roughly 50 mph and then it was like the car was on ice; the deceleration stopped and it felt almost like someone had hit the accelerator pedal. I quickly got on the brakes to slow enough to make the turn. Upon immediate mental review of the event, I know for a fact that my hands were both at the bottom center of the wheel and both feet were off the pedals and back against the seat in my normal cruising position. I also think that the car did not actually accelerate, but simply stopped all regen, which can feel similar to accelerating when it happens suddenly.

Of course I immediately attempted to send in a bug report, but did not have any cellular coverage.

Anyway, I'm curious if anyone else suspects they have had a similar event with their car.

 

[MattMatt]

For me this happens if I hit a bump or anything that makes the car think that it is losing traction for a second. The regen will immediately throttle off. My particular freeway off ramp has a bump on it that if I hit too fast will stop regen every time. Because of that I just slow down a bit more before the bump to hit it a little slower, then the car doesn't have any trouble and will keep regening. My Nissan Leaf also did this.

Matt

 

[jeffro01]

For me this happens if I hit a bump or anything that makes the car think that it is losing traction for a second. The regen will immediately throttle off. My particular freeway off ramp has a bump on it that if I hit too fast will stop regen every time. Because of that I just slow down a bit more before the bump to hit it a little slower, then the car doesn't have any trouble and will keep regening. My Nissan Leaf also did this.

Matt

Same here but it happens rarely... Certainly wakes you up when it does though...

Jeff

 

[SSonnentag]

Good to know about bumps causing loss of regen. This area is very smooth asphalt without even any cracks in it. I suppose it is possible that one tire slipped enough to trigger the traction control when driving over one of those round lane marker reflectors. It's a thought anyway.

 

[appleguru]

Indeed, this happens when one or more of the wheels loses traction. It *definitely* feels like the car is accelerating (which makes sense, because the rate of deceleration is significantly (and quickly) changed when regen gets disabled).

Is not a bug IMO, though Tesla could definitely warn drivers about this behavior to make them better prepared when it does happen...

 

[murphyS90D]

It will happen if you go over a sunken manhole cover. It happens because of the way a differential works. Regen braking is applied by the motor through the differential. Both wheels have to be in contact with the ground for the differential to work. I first encountered this false acceleration feeling in my 2013 Ford Fusion Energi with front wheel drive, Regen stopped immediately when one wheel was in mid air as it went over the sunken manhole cover.

 

[SSonnentag]

why doesn't regen start up again once the bump or hole is passed?

 

[randvegeta]

I had a similar sort of experience. Was driving down a highway with cruise-control engaged. The road is mostly flat but there some slight elevations in certain areas.

I rarely use the cruise control as I like to 'hypermile', which doesnt work well with the cruise control.

Any way, this one time it happened, it was when it was pretty wet and raining. It definitly felt like the car all of a sudden lost traction and started to accelerate.

Now that I think back on that event, I think it was likely that I drove over some body of water on a slight down hill where the regen may have been engaged, lost traction, and thus lost regen. This happened almost 2 years ago shortly after buying the car. Never happened since. I'm not worried.

 

[bhawkins4194]

Just also as a heads up your regen braking might not work when you top you battery all the way up to 100%. There is a warning on the dash about it, but def a first time experience when I took a long trip this weekend. The first 20 or so minutes of driving had to use the brake all the time to stop.

 

[TJtv]

It will happen if you go over a sunken manhole cover. It happens because of the way a differential works. Regen braking is applied by the motor through the differential. Both wheels have to be in contact with the ground for the differential to work. I first encountered this false acceleration feeling in my 2013 Ford Fusion Energi with front wheel drive, Regen stopped immediately when one wheel was in mid air as it went over the sunken manhole cover.

That doesn't explain why the regen doesn't come back on the instant that you regain traction. And imho that is the biggest problem. Once it cuts regen due to a loss in traction it won't come back on for multiple seconds.

 

[RGloverii]

My BMW i3 does the same thing. I agree with the others. It's caused by a temporary loss of traction in one (or more) wheel. The regen is immediately 'turned off' to avoid a larger loss of traction, which could escalate into loss of control.

In the BMW, the regen will SLOWLY start back up during the same 'braking event' if given enough time, but it's NOT immediate.

I have yet to experience the same thing in my M3, but I wouldn't be at all surprised if it behaved in a very similar manner.

 

[MattMatt]

why doesn't regen start up again once the bump or hole is passed?

The car only knows that there was a loss of traction so it reacts, based on my experiences once it has experienced a loss of traction it will rely solely on the brakes until you completely release the bakes, the programming seems to assume that if there was a loss of traction that takes away regen, it will not put regen back until it has met conditions to make it believe traction will be available. Basically it doesn't want to remove regen on loss of traction, reapply regen just to lose traction again. I suspect regen also may throw off the ABS system response?

This is just based on my experiences obviously we can't look at the code to check.

 

[insaini]

What was the temperature outside? I have experienced this before - the temperature was in the mid 30's (Celsius) and the batteries were hot so the regen was very limited ( but did not show any sign of this one the dash) ... i lifted my foot off the pedal and it started slowing down as normal and then regen stopped .... I looked at the dashboard and those little yellow lines showed up that show if the batteries or too cold or too hot for regen..

 

[SSonnentag]

What was the temperature outside? I have experienced this before - the temperature was in the mid 30's (Celsius) and the batteries were hot so the regen was very limited ( but did not show any sign of this one the dash) ... i lifted my foot off the pedal and it started slowing down as normal and then regen stopped .... I looked at the dashboard and those little yellow lines showed up that show if the batteries or too cold or too hot for regen..

It was probably around 108 F, but I've never seen reduced regen due to heat, at least not up through 122 F or so. I have seen reduced power after a couple of launches at these temps though.

I'm going with the momentary loss of traction theory. It sounds plausible to me. Just wish regen would kick back in. Oh well, no biggie.