TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC

Slowing down to 0 upon accelerator release

Discussion in 'Model X' started by angel99, Aug 12, 2019.

  1. Saghost

    Saghost Well-Known Member

    Joined:
    Oct 9, 2013
    Messages:
    7,045
    Location:
    Delaware
    I drove with creep on the first several months, but eventually decided I like the control of creep off better.

    I always make sure vehicle hold engages every time I stop - it will stay engaged until I hit the accelerator or press the brake again (the car supposedly will shift to Park after ten minutes or so if just left that way or if the driver leaves the seat.)

    So it's like the car is heel and toe-ing for you.
     
  2. cucubits

    cucubits Member

    Joined:
    May 17, 2019
    Messages:
    399
    Location:
    TX
    I'd say it's more like the car is pulling the 'handbrake' for you every time.

    I tried this on a drive test and I'm not sure I'd like to hear those little electric motors putting the brakes on every time I come to a stop in stop and go traffic for example.
     
  3. ajdelange

    ajdelange Member

    Joined:
    Dec 10, 2018
    Messages:
    484
    Location:
    Virginia/Quebec
    No, not really.

    But you can make the field rotate relative to the rotor as fast as you want in either direction. Yes, you get into some hairy control issues when slip is greater than the breakdown torque point slip (IM) but in the PM motors you can position the field anywhere you want relative to the magnets and vary its strength in order to have torque in either direction relative to rotor position. There may be practical limitations and the control would certainly be more easily implemented by applying a bit of friction braking.
     
  4. Saghost

    Saghost Well-Known Member

    Joined:
    Oct 9, 2013
    Messages:
    7,045
    Location:
    Delaware
    But that's not regeneration any more - that's me powering the car in reverse now. To regenerate, I have to let the rotor pull the field forward, and you run out of headroom as the car slows down.
     
  5. Saghost

    Saghost Well-Known Member

    Joined:
    Oct 9, 2013
    Messages:
    7,045
    Location:
    Delaware
    ??? I don't hear anything when I do it, and I wouldn't expect to - the iBooster that is always active when you're braking provides the force for vehicle hold, just like it does when AP brakes and just like it does when you brake.
     
    • Like x 1
  6. cucubits

    cucubits Member

    Joined:
    May 17, 2019
    Messages:
    399
    Location:
    TX
    Then this is different from the brake hold which is set when you press the brake pedal a little harder? That's when I heard these.
     
  7. ajdelange

    ajdelange Member

    Joined:
    Dec 10, 2018
    Messages:
    484
    Location:
    Virginia/Quebec
    Nothing I said is to be interpreted as requiring any action on your part. I am simply pointing out that there are no fundamental limitations in these motors to prevent dynamic braking down to 0. They can produce torque (in either direction) at and near 0 rotational speed.
     
  8. V1VrV2

    V1VrV2 Member

    Joined:
    Mar 13, 2017
    Messages:
    12
    Location:
    Longmont, CO
    Ah, good to know - I experienced a slight roll backward leaving the Delivery Center parking lot and that was enough to spook me - all of those new Model 3 and S sitting around waiting for me to crash into them with my new MX, felt like I was back in my manual gearbox driving days. :)
     
  9. Saghost

    Saghost Well-Known Member

    Joined:
    Oct 9, 2013
    Messages:
    7,045
    Location:
    Delaware
    No, that is the feature we're talking about.

    Not sure what noise you're hearing, but there aren't any extra electric motors involved in the brake hold, just the same one that provides the power brake assist during every stop.
     
  10. lakemirror

    lakemirror Member

    Joined:
    Mar 17, 2019
    Messages:
    56
    Location:
    Polk County, Florida
    I think the holding brake has to be applied by a slight extra press on the brake pedal. I don't think it's automatic.
     
  11. Krazaak

    Krazaak Member

    Joined:
    Jul 30, 2017
    Messages:
    714
    Location:
    Charlotte, NC
    That sounds more like the brake being applied in park, hill hold shouldn't make any additional noise.

    The motors can bring and hold the car to 0mph, but at the expenditure of energy, not recovery. So it's more efficient to use the brake to stop the car below the speed at which the energy recovered by regenerative braking.

    It's automatic with creep disabled, once the vehicle comes to a complete stop. Only creep requires the extra pressure.
     
    • Like x 2
  12. Phil Seastrand

    Joined:
    Mar 4, 2014
    Messages:
    385
    Location:
    United States
    It's automatic on flat ground. If your on a hill, either up or down, you need to apply a little extra pressure to engage hill-hold.
     
  13. jboy210

    jboy210 Supporting Member

    Joined:
    Dec 2, 2016
    Messages:
    1,526
    Location:
    Northern California
    Hill Hold looks like this on your dash. It should come on after a sec or less at a full stop. But be aware if you press the throttle or brake it disengages fast.

    20190403_142708.jpg
     
    • Like x 1
  14. DCGOO

    DCGOO Active Member

    Joined:
    Nov 24, 2015
    Messages:
    1,094
    Location:
    Indianapolis, IN
    Try using TACC in stop and go traffic. Vastly less stressful.
     
    • Like x 1
  15. ajdelange

    ajdelange Member

    Joined:
    Dec 10, 2018
    Messages:
    484
    Location:
    Virginia/Quebec
    #35 ajdelange, Aug 15, 2019
    Last edited: Aug 15, 2019
    No question about that. People seem to be overlooking the fact that there just isn't, practically speaking, any energy to recover as the car slows down. At 1 mpH its kinetic energy (~250 J = 0.069 Wh) is 1/100th of what it is at 10 mpH (25,000 J = 6.9 wH) and that's 1/16th of what it is at 40 mpH (400,000J = 111 wH.)
     
  16. mbp11

    mbp11 Member

    Joined:
    Jan 30, 2019
    Messages:
    149
    Location:
    SF Bay Area
    Thanks for the information on Hill Hold. I now have a little more information.
     
  17. ebrown7b

    ebrown7b Member

    Joined:
    Sep 8, 2016
    Messages:
    12
    Location:
    Los Altos, CA
    The brakes used to have a separate caliper / pad on the rear wheels used for the parking brake. My 2013 Model S (P85) has a distinctive sound when it engages the parking brake. At some point, that was removed in favor of just keeping the main brakes engaged for the parking brake. I'm also not sure if the separate parking brake was a feature of all models or just performance models.
     
  18. Saghost

    Saghost Well-Known Member

    Joined:
    Oct 9, 2013
    Messages:
    7,045
    Location:
    Delaware
    Yeah, but that's the parking brake. Vehicle hold isn't a parking brake function - it uses the iBooster to hold the main brake circuits engaged and the brake pedal depressed while you have the car stopped.
     
  19. V1VrV2

    V1VrV2 Member

    Joined:
    Mar 13, 2017
    Messages:
    12
    Location:
    Longmont, CO
    Thanks for the explanation and pic, @jboy210!
     
  20. jboy210

    jboy210 Supporting Member

    Joined:
    Dec 2, 2016
    Messages:
    1,526
    Location:
    Northern California
    Agreed. Best part of the AP system.
    No Problem. Play with for a day and you too will be converted over to the dark side.
     

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC