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Prius Parking Footbrake and N (neutral) Stick Position.

Discussion in 'Gen 2 Prius Technical Discussion' started by ronhowell, Nov 7, 2007.

  1. ronhowell

    ronhowell Active Member

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    Hi All,

    Two questions for the tech gurus out there, on my 2008 Prius.

    1. Parking Footbrake.

    Does the parking brake operate on the front discs or the rear drums? Is it a mechanical linkage?

    2. N (neutral) shift position.

    I have gotten into the habit on my last car (a Jeep Grand Cherokee) of shifting into neutral while waiting at long traffic lights, simply to remove my foot from the brake while on level ground. Is there a downside to continuing this habit on the Prius? I have read that charging does not occur when the shift is in "N", but the ICE is usually stopped then anyway. And when the car is in "D" with your foot on the brake, electrical power must be being drained from the HV battery, since the car is ready to move under MG2 power the second you release brake pressure. While when in "N", the car remains stationary as long as that position is selected. Thus to me "N" would be preferable to prevent power drain from the HV battery.

    Shifting immediately to "P" at stop lights, I have found, requires your foot on the main brake pedal before selecting "D" to resume forward motion.

    Ron.
     
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    1. It's a mechanical cable linked to the rear drum

    2. No issues but if the battery runs low, keep it in D so that the ICE can charge the battery if needed. There will be a drain in N or D.
     
  3. efusco

    efusco Moderator Emeritus
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    There actually is a slight battery drain in both N and D...but very small and the amount of drain is essentially the same in N as it is in D. Also, if the ICE does happen to still be running when you put the car in N it can't shut down and will burn more gas than it otherwise would. In D the ICE will shut off after about 5-6 seconds (if the ICE is warm) and you'll go into Stage 4.

    So, bottom line, no point in using N at a stop at all and several good reasons to stay in D.
     
  4. ronhowell

    ronhowell Active Member

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    <div class='quotetop'>QUOTE(efusco @ Nov 7 2007, 06:51 PM) [snapback]536503[/snapback]</div>
    Au contraire, Evan, the point of using "N" is to simply relax at the red light, rather than holding the car stationary by constant pressure on the foot brake against forward motion of the car with the shift in the "D" position.

    It occured to me that no drain on the HV battery would occur if pressure on the brake pedal activated an electrical switch which disconnects the HV battery from the traction motor MG2 while in "D". Release of the brake then re-connects the HV circuit for forward motion. Maybe this is what occurs, since the MFD shows zero current flow in this condition when stopped.

    What exactly is Stage 4?
     
  5. Tideland Prius

    Tideland Prius Moderator of the North
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    man.. you need the LS lol. It has an auto-hold feature that holds the brake for you.
     
  6. alanh

    alanh Active Member

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    Unlike a conventional automatic, the Prius is not "straining" against the brake while you're stopped. The electric motor is totally off. When you release the brake, the Prius feeds a small amount into the motor to simulate an automatic's "creep". It's not as simple as a switch on the brake pedal, but the effect is the same.

    If you just don't like holding the brake pedal while stopped... well, I can't help you there. I personally think stepping on the brake is less trouble than shifting.
     
  7. patsparks

    patsparks An Aussie perspective

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    You can see the affect of pressing the brake pedal on the energy screen. If you press the brake firmly there is no power but softly there is. You would be better to press the park button than neutral. You need your foot on the brake to get back in gear.
    The park brake works on the rear wheels. It has cables to actuate it.
    Only car I ever saw that had park brake on the front wheels is Subaru.
     
  8. Tenebre

    Tenebre Custom User Title

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    <div class='quotetop'>QUOTE(patsparks @ Nov 8 2007, 11:25 AM) [snapback]536656[/snapback]</div>
    Both SAAB and Citroën have older models that has the park break on the front wheels.
     
  9. Danny Hamilton

    Danny Hamilton Active Member

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    Ok, so I'll start by stating, "to each his own."

    We each choose the level of risk we are willing to accept for ourselves and those around us based on the rewards or potential rewards we get in exchange for the elevated risk. I might choose to accelerate into a yellow light, while you might choose to remove your foot from the brake while the car is in neutral and not moving on a level road. I won't tell you you shouldn't do it, but I figured it might be a good idea to point out the risks I'm aware of, just so you're making an educated decision.

    The first risk I can think of would be a situation where the car might need to sit still for an extended time. If you are in the habit of switching to neutral, and then something happens (an accident on the road ahead?) that prevents you from switching to drive in a short period of time, you could run the battery down with the A/C, your headlights, and the various other electrical devices that might be operating in the car. Since the car is in neutral, when the battery gets low it won't make any effort to recharge the battery. I suspect the car will shut off before the battery gets low enough to damage the battery or restart the car, but I'm not certain.

    Another risk I can think of would be that your brake lights won't be lit. These lights exist to communicate to drivers behind you that your car is slowing or stopped. Lacking this stimulus, you increase the risk of contact between the back of your car and the front of a car belonging to someone else.

    The last risk I can think of is the possibility that it might take a few fractions of a second longer to engage drive and get the car moving. I haven't tested this, and I might be mistaken, but it seems like a reasonable a possibility. If you happen to notice a situation where impact with your vehicle is likely, those few extra moments might have been what would have allowed you to avoid the impact, or at least might have reduced the severity of injury and damage. If you've already encountered the first risk I listed in the same stopping instance as an occurrence of the third risk, it would seem that it might significantly increase the time from awareness of impending impact to acceleration of your vehicle since you might need to restart it. The reduced battery power might also contribute to reduced acceleration.

    As for technical reasons why it might be "bad for the car", no none that I can think of.
     
  10. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(Ron Howell @ Nov 7 2007, 11:13 PM) [snapback]536583[/snapback]</div>
    If you feel the need to 'relax' then park would be prefered, but it should be no more difficult to hold the brake in N than in D...and as stated above the MG turns off..there's a slight passive drain from the HV (around 1-3 amps depending on the accessories in use) in both N and D.
     
  11. ronhowell

    ronhowell Active Member

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    <div class='quotetop'>QUOTE(Tideland Prius @ Nov 7 2007, 11:09 PM) [snapback]536633[/snapback]</div>
    Translation please? :rolleyes:

    Thanks to all for the enlightenment!

    Ron. :rolleyes:
     
  12. ny biker

    ny biker Member

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    Adding to Danny's post, if you're stopped but your foot is not on the brake, and you get hit from behind, you'll get pushed into the vehicle in front of you, or if you're first at the light you'll get pushed into the intersection or the pedestrian in the crosswalk in front of you.
     
  13. ronhowell

    ronhowell Active Member

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    <div class='quotetop'>QUOTE(nybiker @ Nov 8 2007, 08:50 AM) [snapback]536743[/snapback]</div>
    Obviously, and that is a continuing hazard until you have a backup of several stationary cars behind you. Only then can you reasonably safely use neutral. Even then you have to watch it, because what initially may appear to be level ground often isn't!

    Cheers, Ron.
     
  14. Tideland Prius

    Tideland Prius Moderator of the North
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    <div class='quotetop'>QUOTE(Ron Howell @ Nov 8 2007, 08:25 AM) [snapback]536730[/snapback]</div>
    On the new LS460/LS600h L, there's a "HOLD" button on the steering wheel. Engage that and every time you come to a full stop, the car will hold the brakes and you can lift your foot off and rest. A slight touch to the accelerator releases the brakes and allow you to accelerate. You only need to engage it once and not every time you stop if you're wondering.
     
  15. ronhowell

    ronhowell Active Member

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    <div class='quotetop'>QUOTE(Tideland Prius @ Nov 8 2007, 10:22 AM) [snapback]536790[/snapback]</div>
    Interesting. Thanks.
     
  16. patsparks

    patsparks An Aussie perspective

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    <div class='quotetop'>QUOTE(Tenebre @ Nov 8 2007, 09:19 PM) [snapback]536674[/snapback]</div>
    Thanks, I do recall a Saab having front handbrake, a 900 model I think. It's been a while. Not many citroens went through our shop, thankfully.
     
  17. hobbit

    hobbit Senior Member

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    Straw-man hazards.
    .
    While stopped at a light you should be equally aware of what's behind
    you as you are that which is in front; if you see someone coming in
    too hot then it would seem that showing them a nice snappy transition
    by *lighting* the brake lights right then would do worlds more to
    wake them up than sitting there with the brake lights steady-on.
    .
    And in the "continued awareness" department, if you're keeping track
    of the other direction's yellow, you can already be in "D" well
    before you get your green. And of course that is not the time to
    blast freely across the intersection without a care in the world,
    because some yutz might be coming in too hot at 90 degrees from you
    while finishing up that earthshakingly important text message to his
    buddy about which bar to gather at instead of piloting his own two
    tons of scrap metal properly.
    .
    Let's try to be comprehensively realistic here, and both give people
    credit and give them absolutely no credit where either is due.
    .
    _H*
     
  18. Danny Hamilton

    Danny Hamilton Active Member

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    <div class='quotetop'>QUOTE(hobbit @ Nov 8 2007, 06:12 PM) [snapback]536932[/snapback]</div>
    Come on hobbit. All I did is point out the potential. I even went so far as to imply that the asker was welcome to weigh his belief of the likelihood of these risks against his belief of the rewards gained.

    You may be perfectly aware of every incoming object from every potential direction at every moment you are stopped, but the reasonable potential still exists for a driver to for some reason be unaware of some incoming object from some direction until such a time as that they need to react quickly to the developing situation.

    I didn't say it was a large risk, but still the risk does exist.

    Same for the possibility of becoming distracted when forced to be stopped for an extended period of time and forgetting that you left it in neutral. Perhaps not a high risk, but the original poster asked what the potential risks are.

    As for the transition to brake lights from no brake lights, I agree that if you press the brake pedal when you see someone approaching you are more likely to gain their attention than if the brake lights were already on. However, the original poster has not indicated that this is part of his habitual process, and as such I hope you'll agree that having the brake lights lit to start with is more likely to gain the attention of the driver of the approaching vehicle than having them off and leaving them off. With the foot on the brake, you certainly haven't removed the possibility of "flashing" the brake lights at a driver that hasn't seemed to notice you.

    Based on your response to these potential risks, I assume you would not discourage someone from using Cruise Control in snowy, icy, or wet conditions on a Prius with Vehicle Stability Control, Traction Control, and anti-lock brakes?
     
  19. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(efusco @ Nov 8 2007, 12:21 PM) [snapback]536728[/snapback]</div>
    My vote as best answer. There are many good suggestions posted above, but this is how I do it.

    Tom
     
  20. ronhowell

    ronhowell Active Member

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    <div class='quotetop'>QUOTE(qbee42 @ Nov 8 2007, 03:57 PM) [snapback]536953[/snapback]</div>
    Tom,
    The point is you don't have to hold the brake in "N", whereas you do in "D". And "P" requires stepping on the brake again to activate the "D" drive position. Shifting from "N" to "D" provides immediate traction.

    Ron.