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"B" (engine break?) mode

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by JShorr, Jan 4, 2005.

  1. JShorr

    JShorr Junior Member

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    When it comes to cars, I'm a pretty big idiot.

    I guess I don't really understand the application for the "B" mode... Just to make you slower on a hill? Doesn't the break do the same thing?

    Can someone (in idiots terms) explain?

    Jeremy
     
  2. bruceha_2000

    bruceha_2000 Senior Member

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    Geez I wish people would learn the difference between break as in to destroy something and brake as in things used to stop a car! ;-)

    B mode uses engine compression to slow the car down. It causes 'drag' on the transmission so it doesn't turn as fast. It is the same general feeling of downshifting a standard or automatic transmission so you don't have to ride the brakes down the hill, thus heating them up, causing them to fail, causing your car to smash into something and break. Plus, you get more regen with 'B' mode down the hill than just using the brakes.

    There are many hills steep enough that B isn't enough to maintain speed and you will use the brake pedal as well. By the way, Cruise Control will not engage if the transmission is in B mode.
     
  3. JShorr

    JShorr Junior Member

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    Thanks, and sorry for my spelling faux pas.

    Jeremy
     
  4. Tempus

    Tempus Senior Member

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    Remember that if you're traveling below 20 MPH when you engage "B" Mode, it does not spin the engine. Instead it employs Maximum Regenerative Braking to slow you down.

    Some Hypermilers use this in city traffic to maximize battery recovery, but it risks getting you hit in the rear because your brake lights don't come on and the person behind you doesn't have any indication that you're slowing.
     
  5. bruceha_2000

    bruceha_2000 Senior Member

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    As you might infer from the first line of my post, you are in a suitably large crowd with the 'break' vs 'brake' thing . :)

    There are any number of people who think 'B' mode means 'Battery charge', as in the reason it exists is to charge the battery. Nope, just a nice side benefit.
     
  6. bruceha_2000

    bruceha_2000 Senior Member

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    <div class='quotetop'>QUOTE(Tempus\";p=\"61404)</div>
    Especially because it slows the car a LOT faster than just taking your foot off the accelerator. Watch your rear view mirror just in case.
     
  7. jamarimutt

    jamarimutt New Member

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    English has a very poor correspondence between grammar and pronunciation. This, in addition to break-brake, you also have bear-bare, beat-bit, boar-bore, cheek-chick, deer-dear, dock-duck, do-due, fare-fair, feel-fill, hole-whole, incite-insight, it's-its, launch-lunch, lead-lid, leave-live, lose-loose, lock-luck, marsh-March, muscle-mussel, principal-principle, son-sun, steak-stake, suck-sock, tail-tale, their-there, this-these, verses-versus, waited-weighted, way-weigh, weather-whether, were-where...
     
  8. richard schumacher

    richard schumacher shortbus driver

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    If you are going down a hill and find that you want to use the brakes most or all of the time, that's when you should use "B". Continuous use of the brakes can cause the brake fluid to boil, and then the brakes will stop working (obviously very dangerous). Don't forget to go back to "D" at the bottom of the hill.
     
  9. DanMan32

    DanMan32 Senior Member

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    <div class='quotetop'>QUOTE(jamarimutt\";p=\"61426)</div>
    Half of those words do not sound the same.
    Lead-lid: no, however, lead-led: Yes!
     
  10. bruceha_2000

    bruceha_2000 Senior Member

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    Worse:
    live: Where do you live? - soft I
    live: Live bait. - hard I

    There are 4 major definitions for WELL, all pronounced the same, in my little 840 page desk dictionary, including 21 specific descriptions. I'd hate to look in the BIG dictionary.

    English, as a language, stinks. Unfortunately, it is the only one I know.
     
  11. Charles Suitt

    Charles Suitt Senior Member

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    :) Hi bruceha_2000

    If you think English is strange.... take a look at French and Spanish.
     
  12. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(richard schumacher\";p=\"61456)</div>
    This isn't accurate, even for a car with standard brakes.

    Unless you are braking heavily with the Prius you will be using only or at least mostly regenerative braking which is 'by-wire' and thus will not involve the brake fluid at all.

    B-mode, as far as I can tell, is a convenience mode where you don't have to use your foot on the brake pedal much or at all in many cases. The down-side is it's not a 'cruise control'...if the hill you're on is quite steep you'll still gain speed in B-mode and need to use the brake pedal anyway. If the hill you're on isn't very steep then it may slow you more than you want and you'll have to disengage and use the brake pedal.

    I've found one or two select places that I tend to use B-mode, but I don't know that it's particularly advantageous, but I can predict what it will do and it gives me an excuse to use it.

    I don't really know why Toyota decided to provide the B-mode at all. It's certainly not necessary, it creates lots of confusion...even amongst hard core Prius folks. It would simplify the car a bit to leave it off completely.

    Oh, on a regular car it's the brakes themselves that tend to overhead on long brakings, not the fluid.
     
  13. richard schumacher

    richard schumacher shortbus driver

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    I'd say that your hills are either not very steep or not very long :_>
     
  14. lscritch

    lscritch New Member

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    I'll say. Coming down a Sierra Nevada pass, I'm very much used to downshifting, either with a manual transmission or an automatic. Not to do so will burn out brakes - though I think it's by actually wearing them out/overheating them by friction rather than boiling the brake fluid.

    Though I am still looking forward to my first chance to try B mode in the Sierras.
     
  15. skruse

    skruse Senior Member

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    There is no such place as the "SierraS" - the term "Sierra" is already plural and adding an "s" is akin to "mountainses."

    B-gear works very well in all aspects of the Sierra Nevada, Coast Ranges, Cascades and Rocky Mountains. In B-gear you don't want cruise control and it is a pleasure to watch the battery turn green in those long down hill grades - without any braking.
     
  16. IsrAmeriPrius

    IsrAmeriPrius Progressive Member

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    Can you also get the City of Los Angeles to change the name of Los Feliz Blvd. to a grammatically correct one?

    :mrgreen:
     
  17. SyZyGy

    SyZyGy New Member

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    Very True. This is how it is like when you use the friction brakes. When the brake pedal is pressed down, one of the computers meashures how much is pressed down (variable) and sends it to the pump by wire. Then the pump receives the signal and takes that variable and pressurizes accordingly. That pressure in the brake lines pull the pads together making them "squeeze" on the rotors.
     
  18. SyZyGy

    SyZyGy New Member

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    Wait, or does it have frictional brakes like a standard car?
    Does it just have a simple piston that pressurizes the lines and squeezes the rotors?
    I'm confused. :|
     
  19. Ron Dupuy

    Ron Dupuy New Member

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    Every workday I climb from sea level to 3000' and use B mode on the way down. Without it I am constantly on the brakes, with it I use them infrequently. I go in and out of B just as I would conventionally downshift depending on the specific grade and find it a great brake saver.

    I've had my seaside pearl for a month down and love it. The daily climb has hurt my milege, 45 usually, but I laugh when I realize that a month ago I was getting 18 in my Grand Cherokee.
     
  20. richard schumacher

    richard schumacher shortbus driver

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    Yep. A quick glance at the map confirms that there are indeed more and more severe grades in California and Nevada than in Missouri.

    Brake fading is caused by boiling brake fluid: the vapor, unlike the liquid, is very compressible and so does not transmit force from the cylinder to the brake shoes. Severe downgrades have pull-outs for vehicles to stop so that overheated brakes can cool down. Brake pads don't grind down to nothing in a half hour, and if they did they don't grow back.

    So, what are the errors in that last paragraph?