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NHTSA Complaint wrt Regen and TC

Discussion in 'Roadster' started by doug, Oct 20, 2009.

  1. doug

    doug Administrator / Head Moderator

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    There's been a NHTSA complaint about a safety concern with how the traction control turns off the regenerative breaking on the Roadster. Does anyone else have this issue? I want to emphasize that this is not a recall. As far as I can tell it's only one owner's complaint for a relatively specific set of conditions. It is, however, important to be aware of this behavior, if it is indeed common.

     
  2. DaveD

    DaveD EVs Kick Gas!

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    #2 DaveD, Oct 20, 2009
    Last edited: Oct 20, 2009
    Well, I've just passed the 10,000 mile mark on my odometer, and my Roadster is my daily driver. I go up and down plenty of twisty hills, under wet, as well as dry, surface conditions. I've not once had this described behavior happen to me. I'm not qualified to speculate on what might be wrong with his particular car, nor am I able to judge his driving ability.

    Is his reference to "traction control system" meant to be referring to the ABS?
     
  3. doug

    doug Administrator / Head Moderator

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    It does actually make sense for the traction control to reduce regen. Perhaps it shouldn't completely kill it like this owner describes. I can see how it might be a bit disconcerting (as it is when you lose regen because of a full battery). I don't, however, think it should be a problem if the driver is aware of it.
     
  4. TEG

    TEG TMC Moderator

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    #4 TEG, Oct 20, 2009
    Last edited: Oct 20, 2009
    Nitpick: It should say "brake" not "break".

    Also, for the roadster I would say "motor regenerative braking", not "engine regenerative breaking".

    The language also seems to suggested bursts of acceleration, but from my understanding the action of stopping the regen would not cause the car to "lurch" or have "sudden acceleration" rather it could be an effect of no longer slowing. Yes, if you are going down hill there could be some gravitational acceleration, but I envision that would be minor and not as dramatic as described.

    By the way, if you head down a hill with a nearly full charge in range mode, then switch to standard mode does the regen suddenly disengage since the computers consider the pack "already full" at that point?
     
  5. bolosky

    bolosky Member

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    The 20->40 mph behavior he describes isn't consistent with the regen just being turned off by traction control. The only thing accelerating the car would be gravity. To go from 20 mph to 40 mph is (of course) a 20 mph speedup, which is about 9 m/s. Gravity accelerates you at one g (of course), which is 9.8 m/s, so to go from 20mph to 40mph would require about a second of freefall or many times that long rolling down any sane slope.

    I guess his problem is that he's driving over a cliff. :rolleyes:

    He's also got a 5s reaction time.

    (OK, I really think that he's not measured this and he made up ridiculous numbers, and that there is a real issue where the car starts rolling downhill faster when TC cuts the regen. But, it's probably not a big issue, and I bet it's not going to generate lots of accidents like he says.)
     
  6. Tdave

    Tdave Member

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    I've seen the TC light illuminate going over a bump in the road while regen braking is occuring. I see this happen more than once a week. There are enough poorly maintained roads around here for me to see it that often. Perhaps my adjustable suspension set to very firm may also exacerbate the frequency of this condition.

    HOWEVER, I've never experienced any noticable reduction of regen causing any sort of change in expected speed. The condition is momentary, a fraction of a second. If regen is being disengaged for me, it's reengaging quickly enough for me not to notice.
     
  7. doug

    doug Administrator / Head Moderator

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    #7 doug, Oct 20, 2009
    Last edited: Oct 20, 2009
    The missing piece of information here is the throttle position. Is his foot completely off the pedal or is it partially depressed? To what percentage? (I wonder if the car's software records the conditions each time the TC engages.)

    His language does suggest an unfamiliarity with driving dynamics. Notice also that there is a separate but identical complaint about the "VEHICLE SPEED CONTROL". So perhaps he thinks the car is actively accelerating. Of course the relevant quantity here is "jerk" which is the change in acceleration. If you have a negative acceleration that is suddenly reduced in magnitude, that results in a positive jerk which would be perceived as a forward "lurch" in the non-inertial reference frame of someone in the car.

    At any rate, it is reasonable for the owner to make this complaint if he thinks there is a legitimate safety concern.


    .
     
  8. Mark06GT

    Mark06GT Member

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    I've had something similar to this happen to me twice, but in neither case was it as severe as this person describes. Both incidents were while traveling at low speed and hitting a bump. In both cases the car was not charged fully so regen had been working up until that point. In neither case did I feel like the car was out of control, but I did feel like the car lurched forward a bit after hitting the bump. I dismissed both incidents because I never felt like the car was uncontrollable, but maybe he’s on to something.
     
  9. J in MN

    J in MN S60 P12635

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    When the 2G Prius first became popular, there were similar complaints from some drivers about its sensitive traction control. They would try to irresponsibly enter a roadway in front of fast oncoming traffic, and then try to say that the car is "dangerous" because of traction control. (The TC would usually activate because of loose gravel or snow, or bumps causing the wheels to lift off.)

    I believe these are irresponsible drivers unable to adapt.
     
  10. mpt

    mpt Electrics are back

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    I experience re-gen being disabled almost every day on a steep downhill turn as the car struggles to grip over wet leaves and broken pavement.

    Three points:

    1. The momentary release of braking force does not unsettle the car, nor does it increase in speed in any way apparent to me.

    2. If the regen were NOT to release, an inbalance in the rear braking force caused by the lack of traction at one side would produce lateral forces de-stabalising the rear.

    3. Without re-gen, in my previous car, I'd slow down on friction braking alone; the ABS DOES trigger at the same point releaseing braking power and resulting in the same momentary response.

    What a smart idea to have regen braking abs!

    Dismiss.
     
  11. mpt

    mpt Electrics are back

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    ...Oh, and, my 05' Honda Insight does the same but it doesn't automatically restore regen so I do pick up speed... eventually... after a hundred yards of no regen. Which is a bigger problem... I miss out on that lovely downhill recharge :-(
     
  12. Tdave

    Tdave Member

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    Sounds like what we have here is nothing more than a loss of traction and therefore inability to maintain the same braking force. ICE cars with ABS will behave the same way. It doesn't matter what causes the loss of traction. That's an argument between the tires and the road. The Roadster's choice is to either lock up the wheels and lose control, or do what it does and reduce braking to maintain control. Decades of ABS experience says the latter is the right choice.

    Scotty: "Ye cannot change the laws of physics, Captain"
     
  13. toutizes

    toutizes Member

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    Ahhh, this explains a similar puzzling behavior I've been seeing several times.

    I'm arriving a bit fast towards my driveway and brake medium hard to slow down. Then I hit a bump, always the same bump, and for a very short moment it feels like the brakes don't work at all. Then they bite again and everything's fine.

    The moment is very short, a heartbeat maybe, but it's always enough to send a jolt of adrenaline in my body. Think "Oh Sh*t!"

    I first thought that my was foot being jerked off the break pedal on the bump, but I made sure to keep the pedal pressed and it was still doing it.

    This explanation makes sense. To test it we could check that it does not happen in performance mode (the regen is less there, right?)

    Feels like a bug to me. Maybe traction control should not disengage regen if you're braking?
     
  14. malcolm

    malcolm Active Member

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    Sounds like a fault.

    In order to engage regen - just like engine braking on a conventional car - you have to have your foot off the accelerator/gas.

    A bump to one wheel is likely to cause reduced rotation of that wheel, which would indicate to the TC that the powered wheels are spinning too quickly in comparison.

    In both cases, why/how would more power be applied to the drive wheels?

    Momentary loss of brakes shouldn't increase speed as dramatically as described.
     
  15. raymond

    raymond Member

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    The question is how the car can distinguish between a bump and a patch of ice. Encountering a patch of ice while braking (explicitly or regen) you loose traction, and the only way to keep control of the car is to release the brakes (stop regen) until you regain traction.

    The effect of a bump is identical to a patch of ice, so whatever action the car chooses it should work in both situations.

    No matter what, regen only applies to the rear wheels. If the rear wheels lift off because of a bump, you will loose regen braking. The question is how long it takes for the car to see it has landed and re-engage regen.

    How long do the wheels loose traction because of a bump? How long does it take until regen is re-enabled? The latter should preferably be significantly less than the former.
     
  16. toutizes

    toutizes Member

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    #16 toutizes, Oct 23, 2009
    Last edited: Oct 23, 2009
    But, but, if you hit a bump with a front wheel, and this causes TC to shut-off regen to the rear wheels, won't you feel a noticeable decrease of your braking power?

    If this is right, I stil don't see how it would be different in a regular car. The regular car TC would start the ABS pumping the brakes and you'd temporarily loose braking power too.

    Could it be that the regen on/off/on/off cycle is much slower than the ABS brake on/off/on/off?
     
  17. mpt

    mpt Electrics are back

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    The TC light comes on whenever an issue occurs, it flickers when you go over speed bumps at an anlge or when one wheel hits a sunken manhole cover. Same on regen; it's really quick, 100mS-500mS tops. As soon as traction is restored the light is already out.

    For those who've not driven a roadster flat out, the TC has to be experienced. Unlike ICE vehicles where the lag between control and reponse is wide enough to fit a bus through, the TC on the roadster is invisible; on wet, greasy leaves you can floor the accelerator and the car rockets off with the TC light on solid but with the car accelerating wildly; there's no pulseing, juddering, surging, etc. so much power under such fine control; it's a marvel to behold really. Nice job by Drew Baglino and team - Tesla Motors - Engineering

    This is why I (and all owners I expect) find the idea of a complaint in this area to be quite incredible.
     
  18. Roger Reid

    Roger Reid Old but effective

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    As has been explaned to me the ABS and TC are separate. TC can be turned off. ABS cannot be turned off. In the case of this complaint, if the driver relied only on the regenerative braking going down a hill, in my opinion, inattentive driving.

    On the other hand it behooves all Tesla drivers to test and know the limitations of your brakes. Take the time to bed in the brakes. Push the peddle as hard as you can in order to get the ABS to start pulsing. The brakes are powerful but don't be afraid to push hard and don't let the regen braking lull you into a false sense of security. If you are letting the regen braking slow you down, have your foot at the ready in case you need the brakes. Drive safe and use common sense.
     
  19. Norbert

    Norbert TSLA will win

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    #19 Norbert, Oct 25, 2009
    Last edited by a moderator: Oct 27, 2009
    It sounds like the TC is already very good, but one could imagine that a car could have a sensor to detect when a wheel doesn't have weight on it, and handle that case differently (fully re-engage as soon as the weight is back on), than if it looses traction even with weight on the wheel. Not sure if that would make sense technically, though.
     
  20. BlackbirdHighway

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    I believe I have experienced this effect. I was slowing down using regen on a wet road and and suddenly felt a sharp surge forward exactly like the car was hit from behind. I quickly looked in the rear view mirror, and the car behind me was too far away to have caused it. I was on a level road, so I can imagine it would be much more pronounced while going downhill.

    I've seen the TC light coming on many times when hitting bumps in the road, but only one time felt the push forward during regen in over 6000 miles.
     

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