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coming to a stop smoothly

Discussion in 'Model S: Driving Dynamics' started by David99, Aug 16, 2014.

  1. David99

    David99 Active Member

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    I love my Model S and especially being able to drive it mostly with just the accelerator pedal contributes a lot to the very positive driving experience. It makes driving so much simpler than constantly going between accelerator and brake.
    Having said that I really wish regenerative braking would make the car come to a stop rather than fading out at around 5 mph. BMW's i3 does this. It allows you to stop the car perfectly smooth. In the Model S I have to switch to the brake which, by nature, has the effect of making the car come to a stop with a slight jolt when the brake pads go from friction to holding the rotor still. That transition is never smooth causing a slight jerk and metallic noise. I know its common to every vehicle with friction brakes. But the example of the i3 shows that by using the electric motor, stopping the car can be made 100% smooth matching the otherwise perfectly smooth ride of an EV. This could be done entirely via software, similar to 'creep' that was introduced with an earlier firmware.

    Of course the next question is, what happens after you stopped the car using just the electric motor. Does it go into 'neutral' which could cause the car to roll because we don't have the foot on the brake? Or will it continue to hold the car still? I think it should. And if I understand correctly, that is what the i3 does. When you come to a stop, even at a hill, it will hold the car preventing any roll back or forward. Yes at speeds below 5 mph there is no regen. The speed is too low to generate power. What the drive inverter and electronics do is creating a perfectly smooth transition from actual regen (down to 5 pmh or whatever it is) to feeding a slight amount of 'reverse power' to make the car come to a complete stop. The power needed to do this is so small that it's not in any way a concern. For lower periods of standing still it could simply switch to friction brakes just like the Model S already does with it's so called 'hill assist' feature. It engages and holds the brake when you let go of the brake pedal and then let's go as soon as you press the accelerator.

    I sent this as a suggestion to Tesla. Hopefully it will become at least an option (like creep) in the future.
     
  2. v12 to 12v

    v12 to 12v Active Member

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    If you do not have your foot on the brake it will roll easily even if it is in drive. It is not safe to stop in traffic with your foot off the brake. You could be found at fault if you are hit from behind and roll forward to hit someone else. (I was in front of that kind of sandwich before.)

    Hill Assist lasts only a few seconds. I pull up into my driveway and hit the button for the garage door. I let my car roll backwards after hill assist lets go to re-align my approach to the garage after it is open and then touch the accelerator to pull forward into the garage.

    The noise will go away on your brakes after they are broken in. It takes a while.
     
  3. Cosmacelf

    Cosmacelf Active Member

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    David99, I agree 100%. I've had my Model S for over a year now, but just recently drove an i3 for an hour.

    The i3 regen single pedal driving experience is substantially better than the Model S.

    It isn't just the fact that it brings you to a complete stop, they have also implemented a smoother deacceleration profile. When you partial or completely lift your foot off the go pedal in the Model S, the car often jerks. You don't get that in the i3. They must have some smoothing function such that the car smoothly transitions to the indicated regen, rather than jump to it.

    I am hoping Tesla realizes there is still some software improvements they can make in the regen function. Please learn from BMW!
     
  4. Cosmacelf

    Cosmacelf Active Member

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    Which is why the i3 engages the brake when it comes to a stop and keeps it engaged. I have no clue why Tesla limited their hill hold to one second, but it is kind of annoying actually. There is more than one way to implement regen braking and hill hold, and IMHO, BMW i3 does it far better.
     
  5. v12 to 12v

    v12 to 12v Active Member

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    Personally I prefer a more aggressive deceleration profile. It is more like driving a manual transmission. If that feature was taken away I would be crushed.

    Better yet would be a selectable deceleration profile. No cushy coasty cars for me.
     
  6. Cosmacelf

    Cosmacelf Active Member

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    Oh yes, selectable regen profile would make sense. But the auto brake feature of the i3 is also very nice.
     
  7. jhs_7645

    jhs_7645 VIN: #3305

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    I’m not disagreeing that the regen profile and deceleration could be better, but I think you have something wrong here. The tesla regen uses electric motor braking for regen when you lift your pedal, the caliper braking system is completely independant and works in parallel to the regen system. There is no ‘switching’ from regen (friction) to caliper braking. I’m not sure what ‘metallic noise’ your hearing, but when you apply brakes at any speed in the Tesla if it feels any different than applying brakes in any other car, you may have a problem with your brakes.
     
  8. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    ^^^^ This. All disk brakes have a slight jar when going from movement to stop unless you are very, very careful (I can do it about one in ten times if I try really hard each time). Only drum brakes allowed you to stop without a slight jar because, well, they didn't brake all the effectively to start with.
     
  9. David99

    David99 Active Member

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    What I mean is the slight jolt all friction brakes cause when you come to a stop. The friction increases (even when you keep the pressure on the brake paddle the same) as the relative speed between pads and rotor decreases. Just before the stop the friction gets so strong that it gets stuck and brings the car to a stop with a slight jolt. That's the transition I'm talking about. It's so common with any car that most people never pay attention. It annoys me and it looks like BMW feels the same and made stopping perfectly smooth by using the electric motor.
     
  10. pete8314

    pete8314 Vendor

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    I agree, I don't think it's that bad on the S though. On my A5 it used to really bug me, especially if I had napping passengers (mostly my wife!). It would be cool if Tesla could implement an option to regen all the way to zero, realizing this is for comfort, as opposed to energy reclaim, as I don't think you get much, if any, at less than 5mph.
     
  11. J-Philipp

    J-Philipp Member

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    I thought that having to use the brake pedal to bring the car to a complete stop had to do with the necessity of keeping the discs surface smooth and clean in case you need emergency braking. Sort of maintenance task performed each time you stop the car.
     
  12. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    That too, but it takes a bit more than the default from-four-mph-to-zero to keep the rotors really clean--especially in the salt belt.
     
  13. woof

    woof Model S #P683 Blue 85 kWh

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    BMW claims the i3 has an automatic "cleaning" feature for just this reason. I say "claims" because I recall reading that long ago, but cannot find anything online that corroborates it. It may be incorporated into the documented "brake drying" feature. I've also never noticed if my i3 does this or not.
     
  14. Zythryn

    Zythryn MS 70D, MX 90D

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    I felt the same way after I first drove an i3.
    However, I started paying more attention to when I actually want to come to a complete stop.
    I now believe I would find the regen bringing me to a complete stop in rush hour traffic would be more annoying than the Model S not bringing me to a complete stop.
    As for the transitional 'jolt' when using the friction brakes, I have never felt that unless I'm stopping quickly.
     
  15. PoweredByRain

    PoweredByRain Member

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    Correct. This is why you compensate for that by decreasing the pressure on the brake pedal just as you reach that point. If you think the final "dive" at the end is bad in cars, try it in a small plane. Especially a "conventional gear" airplane (one without a nosewheel). :)

    I would far rather have a simple, reliable, predictable braking system than one which attempts to do everything for the driver. I used to drive a Leaf, and I thought the idea of blending regen and friction braking on one pedal was a good idea, but now that I've experienced the Model S I actually prefer the separate systems. One pedal for telling the motor what to do, and one to operate the brakes. It's simple to understand, and it has the advantage that I know that I am avoiding wasting energy on friction brakes if I am not pressing the brake pedal.

    For those who are suggesting using the motor to do that last bit of stopping - ummm, you can't. Not as a generator (i.e. with regenerative braking). It can't provide enough resistance. I suppose you could apply some power to the motor to cause a torque which would slow you down faster, but that seems silly compared to just using the brakes.
     
  16. TES-E

    TES-E Member

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    +1. I prefer to keep the way it is.
     
  17. David99

    David99 Active Member

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    Yes it would use a tiny bit of power to make the car stop. It's so little that it's insignificant in terms of energy usage. It's just continuing the concept of driving the car with one pedal, from start to stop, 100% smooth. BMW did it for a reason and is getting great feedback on it. The Model S fades out regen because below a certain speed the motor simply doesn't generate any power. That's just a technical limitation and not a conscious decision based on any good reason. BMW thought about it and realized, when the pedal is used for accelerating and braking, it logically shouldn't stop doing that at a certain speed just because of a technical limitation.

    It's the same with creep. It's a technical limitation of gas engines that can't go below a certain RPM without stalling. So all automatic transmissions allow some slippage and causing the car to creep forward without even touching the accelerator. It makes no sense whatsoever that the car wants to move forward without the driver giving it the signal. So we have to remember to step on and hold the brake. Electric cars don't have that technical limitation, yet some people got so used to creep that they requested this for the Model S, which makes absolutely no sense for an EV, and Tesla added it. VW fixed the annoying creep in their ICE cars by adding an 'auto hold' feature. When you hit the brakes and the car comes to a stop, it holds the brakes for you and only releases them once you touch the accelerator again. So much better!

    Fading out regen is, again, just a technical limitation of electric motors. There is no practial advantage to it, there is no good reason. It is trivial to make the electric motor slow down and stop the car perfectly smooth. Tesla just didn't think of it. BMW did and since it's easy to implement via software, I suggested it to Tesla to make it an option.
     
  18. martinwinlow

    martinwinlow Member

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    I would be interested to know if anyone who has the same issues as the OP (and the OP) have creep enabled or disabled on their MS. If you all have it enabled, perhaps you should try disabling it to see if it improves the smoothness of your complete stops. MW
     
  19. flashflood

    flashflood Member

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    Good suggestion. I have tried it both ways, and it's still a little rough both with and without creep.

    One thing we all have to keep in mind is that unlike changes to the infotainment system, changes to core driving dynamics like braking behavior require a ton of testing. And when all of the behaviors are optional, the test matrix explodes. It's not even clear what some of the option combinations should do. If both "smooth stop" and "creep" are enabled, what should the car do? It would be strange if taking your foot off the gas* caused the car to slow to a perfectly smooth stop, but then applying and releasing the brakes caused it to start moving forward. In any case, it wouldn't be surprising if Tesla has thought of all this but simply can't offer it because BMW has patents on it.

    * I know, I know, sorry. I will always call it the gas. Just like we still 'dial' phone numbers, even though phones haven't had rotary dials for decades.
     
  20. eledille

    eledille TMS 85 owner :)

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    I love smooth stops and I hate creep. Creep also makes the brake jolt impossible to avoid.

    I can get a completely smooth stop with my Model S, but only when the terrain is so flat that it will not roll by itself. I do that by gradually releasing the brake pedal as it slows and releasing it completely just before it stops. Then it will coast to a stop by itself, without the tiny creak/jolt from the brakes when they transition from moving friction to sticking. But this is impossible in a hill, and it's much more difficult than the BMW system.

    I'm with David99.

    But I too would like to be able to coast more easily. I'm not sure what would be the best way to achieve this, but one idea would be letting the zero point of the accelerator be a narrow zero zone instead of a point. Then it would be easier to find. Maybe one could add selectable accelerator curves or driving modes. But as flashflood says, the testing required might make this impossible.
     

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