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Hill Hold Function

Discussion in 'Model S: Driving Dynamics' started by grisnjam, Apr 11, 2012.

  1. grisnjam

    grisnjam P6316

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    Does anyone know how the Model S (or today's Roadsters) behave when stopped on a steep incline?

    I own a Audi A3 with the DSG gearbox (hydraulically operated dual clutch gearbox that is more like a manual then an automatic) and the car has a hill hold function that will apply the brake when you first let your foot off the brake on a steep hill to stop the car from rolling backwards until you hit the gas and the clutch engages.

    I assume that without something like this a single speed electric car would naturally want to roll backwards after lifting the brake on a steep hill. How Tesla is handling this today and with the Model S?

    Thanks,
     
  2. BYT_P1837

    BYT_P1837 Member

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    That is a very good question, how would an electric car with the regenerative breaking handle hill assist? I also have this on my Toyota Rav4 and trigger it on there by pressing hard on the breaks while on the hill to give me a few seconds to take my foot off and move it to the gas pedal to release.
     
  3. doug

    doug Administrator / Head Moderator

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    It's been discussed other places, but the Roadster does not have a hill-hold feature. Though, I'd say that's what the handbrake is for.

    Good question regarding the Model S, though, and I don't recall an answer. In principle the Model S could use a tilt sensor and engage the electric parking brake for this type of function.
     
  4. NigelM

    NigelM Recovering Member

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    That's why some of us like "creep" (see this Roadster thread). I find that on the Roadster there is enough to hold the car or at least keep it creeping uphill when I'm stopped. That said, the highest natural point in Florida is only 345ft above sea level so I have never been on what you might call a "steep incline".

    I have no idea what it might be on the Model S.
     
  5. ElSupreme

    ElSupreme Model S 03182

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    And it is practically in Alabama.

    30.988333, -86.281944
     
  6. Doug_G

    Doug_G Lead Moderator

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    In my experience it all depends on the slope; it can roll backwards. To me it seems like there is simply a forward bias, and that there's a balance point where it will more-or-less stay put.
     
  7. jerry33

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

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    The creep function uses a fair amount of energy. I don't know the number for Tesla, but in the Prius it's 500W. Best to put your foot on the brake rather than use the creep (other than the short time between when your foot leaves the brake and pushes on the accelerator.
     
  8. goyogi

    goyogi Member

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    I wondered about that in my Volt how much energy it takes at a stop. The hill holder on the Volt is nice. A nice solution could be at certain angles hill holder can be automatically applied.
     
  9. SByer

    SByer '08 #383

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    In the Roadster, you can always two-foot it (as long as the brake is on, no power goes to the motor, then lifting the brake gets immediate go-power), but I haven't found a need to. The creep is enough such that my roll-backwards amount is far less than I could do in my manual 911.
     
  10. goyogi

    goyogi Member

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    Good point. Can't stall an electric motor.
     
  11. woof

    woof Model S #P683 Blue 85 kWh

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    The BMW ActiveE has a hill holding feature. When the brake pedal is released, the friction brakes keep holding the car in place for two seconds, or until the accelerator is engaged. After two seconds, the friction brakes release and the car can and will roll backwards. In the ActiveE, regen is dialed back very smoothly at low speeds, so it won't hold the car still on a slope. One can use the accelerator to hold the car still up hill instead of the brakes. In that case, there is no hill holding--let up on the accelerator and the car rolls backwards. Only by using the brake pedal at 0 MPH triggers the hill holding feature.
     
  12. Discoducky

    Discoducky Active Member

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    Nice, I hope Model S doesn't roll backward. Our Civic Hybrid does this now and it is very scary when you don't expect it due to significant amount of torque lag. Do you know how ActiveE accomplishes this? Model S has a second brake caliper parking brake on the rear rotors, maybe they will be used for hill hold?
     
  13. vfx

    vfx Well-Known Member

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    No wonder uze guys want electrics. To stave off the melting icecaps!
     
  14. jerry33

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

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    I have a steep incline every time I exit from the office parking lot. The Prius never rolls backwards. I've even tried to make it do that since this thread started.
     
  15. grisnjam

    grisnjam P6316

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    The Prius has an automatic transmission right? As such I would not expect it to roll backwards.
     
  16. J in MN

    J in MN S60 P12635

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    No, the Prius has a two motor-generator power split (technically torque split) transmission that simulates a continuously variable transmission. It implements hill hold by commanding a forward torque from MG2 that is proportional to the rearward speed with a large proportionality factor. It will command the maximum 400 Nm MG2 torque for rearward speeds of 5 km/h, if my memory serves correctly. So, it will roll backwards, but only very slowly.
     
  17. woof

    woof Model S #P683 Blue 85 kWh

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    I do not. But it seems to be a standard BMW feature, not just on the ActiveE.

    I did discover it doesn't activate when facing down hill. Release the friction brakes with the ActiveE pointed down hill and it will roll forward.
     
  18. gmontem

    gmontem Model S P01707

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    So what's your technique for a driving an automatic car in a steep road with stop and go traffic? As soon as you let go of the brakes your car will reverse and hit the car behind you. If you try to quickly move your foot to the "gas" pedal, you will more than likely over throttle and hit the car in front of you.
     
  19. AnOutsider

    AnOutsider S532 # XS27

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    Automatic, or manual? Can't remember rolling back in any of my automatic vehicles.
     
  20. cinergi

    cinergi Active Member

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    Try driving the hills of San Fran -- they're steep enough to overpower any ICE's creep.
     

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