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What happens to E-Brake during power failure?

Discussion in 'Technical' started by derekt75, Oct 20, 2014.

  1. derekt75

    derekt75 Member

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    Does the E-brake require a constant voltage to keep it disengaged, so that a power failure would engage it?
    or does a power failure leave it in the same state it was before the failure?
    or is voltage required to keep it closed?

    On steep hills, I always used to put the car in gear (manual) (or P for an automatic) AND use the E-brake with a mechanical ratchet. What are the fail safes with the electronic brake?

    In related news, I'm surprised at how loud it is when it engages.

    In other related news, I'm surprised at how impotent the E-brake is while driving. yeah, it slows the car, but it's not nearly the "holy $#!+ the brake is on" that I'd expect from pulling stiffly on a handbrake.
     
  2. markb1

    markb1 Active Member

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    Power is definitely not required to keep the parking brake engaged. In fact, it's tricky to get the parking brake to disengage after a power failure. I presume it only requires power to change state.
     
  3. tom66

    tom66 Member

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    Similar to other cars, the E-brake is electronically actuated but this does not mean it requires power to hold the state.
    Such a system, requiring continuous power, would almost certainly not be legal or pass safety certification.
     
  4. green1

    green1 Active Member

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    From all reports power is required to change state, not to maintain either one.
    As a result, I recommend carrying wheel choks just in case you end up in a a situation where you loose power and can't set the parking brake. (beats keeping your foot on the brake pedal the entire time until a tow truck can get there if you happen to be on a slight incline)
     
  5. derekt75

    derekt75 Member

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    So, what maintains the state when power is removed?
    Is there a worm drive where friction prevents the spur gear from turning the worm?
    Is it hydraulic and after the oil is pumped a valve closes to prevent the oil from moving? If that's the case, is there any concern about oil slowly leaking over a timeframe of months?
     
  6. tom66

    tom66 Member

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    Is that a Tesla reduction gearbox? Where did you get that picture from?
     
  7. David99

    David99 Active Member

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    Think of a light switch, it stays put on either side but requires power to flip. A spring holds it in either position.
     
  8. rabar10

    rabar10 FFE until Model 3

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    Since we'r in the Technicsl forum, we need to be clear on which car or cars we're discussing.

    Most EVs, and most cars with automatic transmissions, use a parking pawl inside the gearbox like what is pictured above.

    The Tesla Model S does not use that method -- they have a second set of smaller electrically-actuated brake calipers on the rear wheels, which are activate when Park is selected. I'm not sure of their exact internal structure, but to pass safety regulations they have to maintain state (i.e. In park or not in park) without any external power being applied. So whether it's a worm gear or a cam lobe in conjunction with a spring, some mechanical force continues to press those small pads onto the brake disc once Park is selected.
     
  9. scaesare

    scaesare Active Member

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    Are you saying that's a Model S gearbox?

    You can see the separate emergency brake alipers on the rear wheels, and I know for a fact they engage, as these are the ones that tend to "stick" tot he brake rotors in colder damp weather.

    I've never heard it suggested that the S has a mechanical parking pawl in the gearbox as well...
     
  10. green1

    green1 Active Member

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    I've always assumed they would. After all, every other automatic transmission vehicle on the planet has both, why would Tesla only have one or the other? (Manual transmissions don't need it because you can leave them in gear to prevent movement by using the engine compression, but an EV wouldn't be able to) If Tesla does not have both, that's a major oversight, I enjoy redundancy in keeping my vehicle from rolling out in to traffic.
     
  11. HankLloydRight

    HankLloydRight Fluxing

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    I don't know one way or another for sure, but I would agree with this statement. From what I understand the Model S has a simple open differential with a single reduction gear. No parking pawl. The e-brake is just that -- the secondary calipers on the rear rotors.
     
  12. jerry33

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

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    There is no parking pawl. The second set of calipers on the rear disks perform this function.
     
  13. jdbob

    jdbob Member

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  14. green1

    green1 Active Member

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  15. HankLloydRight

    HankLloydRight Fluxing

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    It's a paradigm shift!!!
     

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