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Rolling backwards on an incline

Discussion in 'Model S: Driving Dynamics' started by kuttakamina, Jul 11, 2015.

  1. kuttakamina

    kuttakamina Member

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    Ok so, a manual rolls back easily when you are on an incline, nose headed upwards.
    An automatic, if you roll backwards with the transmission in "D", you could damage the transmission.
    What is the recommendation for Tesla? It seems to rollback a lot easier than a typical automatic.
    Will rolling back hurt the transmission? Should I keep the brake pedal depressed when on an incline to prevent any rollbacks?

    TIA~
     
  2. meloccom

    meloccom Moderator Aus/NZ

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    #2 meloccom, Jul 12, 2015
    Last edited: Jul 12, 2015
    The car does have hill-hold function but in my experience it only works on steep grades.
    You Must come to a complete stop with your foot on the brake and if it's steep enough the hill hold will kick in.
    It would be good if you could manually apply hill hold, say by double tapping into D, as it would be useful in tight parking spots and other awkward spots.
    I doubt it would cause the car much stress if you rolled back whilst in D as the difference between the two states D and R is just the polarity of the motor.
     
  3. Ugliest1

    Ugliest1 S85: "Sparky"

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    I believe: no problem whatsoever. I'll leave it to the tech folks to describe why. I'll use the wrong words.
     
  4. EV_Steve

    EV_Steve Member

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    Parking in my garage is on an incline requiring tight cornering. I have to engage creep to prevent rollback. Without it I've tried parking as if it were a manual but then I get the 2 pedal warning. If hill hold worked properly as it does in my Jeep I could leave creep off. But as it is now I have to park once I get out of the garage to disengage creep and hopefully remember to engage it befor starting my parking maneuvers. I prefer to drive without creep to get the most out of regen braking. So in my opinion Teslas hill hold needs lots of work. I've already had one close encounter with a post in my garage because of it...
     
  5. deonb

    deonb Active Member

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    You can roll back all you want, and you can also hill hold the car with the accelerator pedal*, if you don't want to press the break.

    The stator doesn't really care or know in which direction the car is going - it's all just applying magnetic force to the rotor.

    In fact, when the car goes into regen it's magnetically the same thing as if the motor were to spin backward (i.e. sliding backward down a hill).


    The Seattle Tesla service center confirm to me in person, that they hill-hold & roll back using just the motor themselves. It does no harm.


    * It's of course not a good idea to do this if you're at a stop sign or school zone, and a slip means you can accidentally jump the car into traffic or pedestrians. Rather use the break for cases like that.
     
  6. HankLloydRight

    HankLloydRight Fluxing

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    This is not true. Automatic transmissions can, and do, roll backwards on a steep incline, and it won't cause any damage to the trans. Maybe what you're thinking about is if you are rolling backwards in NEUTRAL and then put it into DRIVE, yes, that could cause some damage (or if you're rolling forward in NEUTRAL and slam it into REVERSE).

    But under normal circumstances when a car is already in Reverse or Drive, it can roll in the opposite direction without any damage occurring.

    For the Tesla, I often "hill hold" myself using the accelerator pedal while waiting for a light at an incline. It's a fun little game.

    Hmm, they're really two different things. I don't think having Creep affects regen braking at all. The only thing it does is use up slightly more energy to simulate an automatic transmission when at a full stop. It's not like regen braking is diminished with creep being on. At the point creep kicks in, the car is essentially stopped and creeping forward. Regen isn't going to be a factor at that point.
     
  7. EV_Steve

    EV_Steve Member

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    Hank - for clarification, what I meant was that I get a more complete stop without creep engaged. You're right regen is the same with or without creep up until below 5 mph.
     
  8. Saghost

    Saghost Active Member

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    This is undoubtedly fine for short periods (seconds). For longer periods, I was warned on another EV that holding it with power was unwise - the logic being that you were pushing current through the same couple of poles on the rotor/stator and could locally overheat them. I don't know how much a real risk it was on that car, or how applicable it is to the Model S, but I suspect it potentially applies.
    Walter
     
  9. ecarfan

    ecarfan Well-Known Member

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    Rolling back on a hill while in Drive will not hurt anything as far as I know, unless you roll back into a fixed object. [emoji6]
    Just turn on the Hill Assist function so that when on an incline and you stop by pressing the brake, upon taking your foot off the brake pedal the car will not move for about one second, plenty of time to put your foot on the accelerator and move forward.
    In my experience Hill Assist works on gentle slopes as well. I cannot give you an exact grade percentage value. Experiment for yourself and you will get a feel for it.
    I have on occasion held position on an incline solely by modulating the accelerator pedal, just for fun. It can be done. I doubt it damages anything unless done continuously for many minutes.
     
  10. scottm

    scottm Active Member

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    rolling backward in an ICE auto doesn't hurt the transmission, there is fluid coupling between engine and tranny

    There is no transmission in model S, it is permanently in gear, the motor is always connected firmly to the wheels, the motor spins either way freely.

    tesla's position on the matter is to use brake pedal when driving to prevent rolling.
    Hill holder Brake assist is there to keep an invisible pedal pressed when you let off the real pedal.

    Tesla's position on preventing rolling for parking is to use Park selector, push the button.
    there is no parking gear as would an auto tranny have, and might strip if you push the car while parked.
    tesla only has a second set of brake calipers on rear discs dedicated for that purpose.
    putting the S into Drive or Rev releases the parking brake.

    if it didn't release (by fault) and you tried pushing the car around you'd be fighting an engaged brake caliper on the disc only.

    there is a Tow Mode that also frees the parking brake that allows the car to be pulled around.

    don't push the car from the rear, ever. If you must roll a dead car push it by A or B pillar with window down.

    Yes the S does seem to roll back easier than an auto tranny ICE because there's no viscous coupling friction at all pulling or holding the car from rest.
    Tesla invented Creep Mode to help emulate viscous coupling at low speeds while driving forward.
    tesla also has Hill Hold to emulate viscous coupling (but only for a couple seconds) when resuming moving from a rest while on an incline.

    However, yes you should keep your foot planted on brake pedal on inclines to prevent rolling. Hill hold is a minor convenience feature that does not replace the need for using brake pedal. On some cars' implementations of hill hold, they will continue to hold the invisible brake pedal until driver presses the go pedal, but not in model S. (It could do that some day, its a software change).
     
  11. sorka

    sorka Active Member

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    The torque converter on an ICE automatic is never locked below 30 or 40 MPH so since there's no physical connection between the engine and the transmission except via fluid, nothing will happen.


    The MS should always prevent rollback when you're in drive. If you're not in reverse, it should always apply enough juice to at least prevent backwards travel at any grade PERIOD. I can't fathom why it doesn't do this as they've already demonstrated they can do it for a finite amount of time. Why not always??????
     
  12. Ugliest1

    Ugliest1 S85: "Sparky"

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    There's two schools of thought on this, as usual both well outlined in some other thread, can't remember the title. I for one am very happy not having any prevention of backwards travel, except for the hill assist (i.e., I like hill assist too for the normal situations it engages). Helps with small manoeuvres on an incline, not having to explicitly shift to reverse.
     
  13. jcaspar

    jcaspar Member

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    I would strongly disagree with this. I think this feature would be fine for those who are not used to driving a manual (I guess that's most Americans) and I would be fine with it as long as you can turn it off. It is, to me, counter intuitive to not have the car roll back on a hill and may make some situations, such as slowly backing down a hill, more difficult. I cannot fathom how people have trouble on a hill with the Model S, even without the hill hold feature. There are two pedals and we have two feet. It's not like driving a manual on a steep hill in San Francisco without hill hold, on a rainy day. That is challenging!
     
  14. HankLloydRight

    HankLloydRight Fluxing

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    There are lots of reasons, but mostly the car shouldn't think it's smarter than me and prevent me from doing something I might want to do, like roll backwards to give another car more space, or parking on a hill, etc, etc, etc.
     
  15. ecarfan

    ecarfan Well-Known Member

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    I disagree. And the fact that Hill Assist can be turned on or off gives users the option, which makes sense.
     
  16. sorka

    sorka Active Member

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    We can agree to disagree. I have about million miles of driving in the last 30 years and about half of that is on manual transmissions. In fact, whenever I buy a new car I always pick a manual with a clutch if it's an option.

    - - - Updated - - -

    That's what reverse and brakes are for. I've never used a clutch in a forward gear to help me back into a spot pointing upwards on a hill. And I've spent years driving around SF.
     
  17. ecarfan

    ecarfan Well-Known Member

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    I've been driving for 36 years and a majority of my miles have been with manual transmissions. I think the Model S is easy to drive on hills with or without Hill Assist on, and I drive in San Francisco on hills almost every week because I often work there. Though these days I usually drive my Roadster [emoji3]
     
  18. HankLloydRight

    HankLloydRight Fluxing

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    Huh? I've never used a clutch in a forward gear to back into a spot either. I've had the transmission in a forward gear and used the clutch (disengaged of course) and the brake to either move forward, or roll back as needed when parking on a hill. No shifting required. How else are you going to do it? Under your scenario, if the Tesla ALWAYS did hill hold, I'd have to shift into reverse to go backwards or back into a spot that I could just roll into. Do you not have parallel parking in SF?

    BTW, you're not the only one who has driven a lot of miles in a manual trans, as-if that makes you smarter then everyone else. I know plenty of people who have driven millions of miles, and they're still pretty bad drivers.
     
  19. scottm

    scottm Active Member

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    I didn't know you could turn off hill hold assist. Thought it was an always on special and just algorithmically decided when (slope) it would happen.

    The feature we need for hill hold is a switch for telling it to stay engaged until go pedal is touched.
     
  20. kuttakamina

    kuttakamina Member

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    Sorry, but really dumb question - how do you turn hill assist on or off?
    Its not the same as creep mode, is it?

    Release notes say this --

    Hill Start Assist makes it easier to start driving on an incline. When Model S is on a hill, Hill Start Assist will automatically hold the car for one second when the brake pedal is released, preventing the car from rolling while the driver switches from the brake pedal to the accelerator. This function will engage when the car is in Drive and facing uphill, or in Reverse and facing downhill.

    .. I have noticed that too, it gives you 1 second, which is good. But I don't see a mechanism to turn it on or off.
    Also, summarizing all replies here, it sounds like,
    - Holding the brake pedal on a downwards incline is a good idea.
    - Rolling backwards is not going to hurt the car since there is no transmission.

    And I do like the idea that hill hold assist should keep itself on until the accelerator is pressed.
     

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