I have never used the b in my shifter

Discussion in 'Gen 2 Prius Main Forum' started by ski.dive, Jan 16, 2012.

  1. Codyroo

    Codyroo Senior Member

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    Out of curiousity, in the car you drove prior to this one, did you ever downshift while descending a hill? The B mode would be of similar use.

    I've only used the B mode a handful of times, and all have been when descending from the Santa Cruz mountains, where the grade is steep and there are often 90 degree turns. This way, I can put it in B mode, maintain my 40 - 45 mph speed and not have to brake too much when hitting a 25 mph turn.

    Even with all that, I still filled up my displayed battery bar to the top.

    Consider it a blessing if you don't live in an area with fairly steep hills that behoove you to use the B mode.

    Yes the brakes can last 100,000 miles. More importantly, the brakes will work effectively if you ensure they don't overheat, and the most likely time for this to happen is during a long, steep descent where you are on the brakes a lot.

    Save your brakes, save a life.
     
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  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    It may look like we are 'dogpiling' on you, but I bet we were all typing at the same time and did not see the other responses.
     
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  3. Feri

    Feri Active Member

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    I use it regularly for down hill control of the vehicle. It is also very useful on loose dirt roads to help prevent wheel lock and vehicle slippage. Even with ABS and traction control the B mode is useful.
     
  4. Bodgerx

    Bodgerx Junior Member

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    Ok. So B mode introduces engine braking, as in ICE braking through gearing?

    I originally thought that this mode would basically still allow regen braking even when the batt is full, effectively throwing away the energy while the batt is full. Is this not the case?

    On my Civ hybrid, on a long descent, if the batt got full, regen braking effectively disappeared. Which was a nice suprise when you were in the middle of braking to stop at some lights (!)
     
  5. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Toyota automatically adds engine braking as the regenerative braking goes away, so it should be less noticeable. (the engine is rotated by the electric motors via the planetary gearset, so in that sense it is still electrical, but it is not being saved, like filling the HV battery does)
     
  6. qbee42

    qbee42 My other car is a boat

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    Yes to both of these comments. B mode introduces ICE braking, which is how it throws away energy. Energy won't just go away, it has to be dissipated.

    Tom
     
  7. swi66

    swi66 Member

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    I took my Prius on a Rally last fall that included a few steep decents.
    For the first time I remembered to use it, just to try it.
    I think it worked good in slowing the car down the steep grade.
     
  8. fuzzy1

    fuzzy1 Senior Member

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    In Florida, B is a waste of console space, as the state does not have enough elevation difference to make it useful. Out West, there are many places where it is essential to prevent brake failure.

    Even non-hybrids can have the brake pads last 100k+ miles, under favorable traffic conditions and driver styles. After two cars in my household did it (including the spouse's daily driver), I was disappointed when the next went only 92k.

    On the other hand, I'd hate to see and smell the results of a single descent from the top of Pikes Peak without B mode. Even with the top 1100 feet of the road closed by snow, an F150 with Florida plates that descended behind me without downshifting, stank to high heaven at the safety checkpoint. It was ordered into the painted safety box for a mandatory 30 minutes cooling off period.
     
  9. bl117

    bl117 New Member

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    As most of you have stated, it works great in mountainous regions. Ever year I make a drive from Chicago to the southern tip of Florida which passes me through Tennessee. Having driven a Honda Civic Hybrid 03 and this year switching to an 07 Toyota Prius I thought I'd share the differences. At one point in TN you climb to the top drive a mile and go down a very steep grade. Here is what happens in either car:

    03 HCH: Battery lasts about half way to the top with cruise set at 55 going uphill. After the hybrid battery goes dead the car tries to charge it thus making it extremely difficult for the vehicle to maintain 55 mph. By the time I hit the top the battery was at 25% charge and I was down to about 48mph with the cruise still set. Now for the downhill. Regenerative breaking works great to fill the batteries back up however once the batteries are full the car begins a freefall. Shifting the vehicle into S (never did find out if this was sport or second. The dealerships have told it to me both ways) did help some but ultimately I would have to place the vehicle in L which made the engine roar and still required heavy breaking.

    07 Prius: Battery doesn't seem to matter while climbing however it does slowly drop during the accent. The Prius doesn't seem to be working super hard though I did notice the MPG drop to 10-20mpg. Upon reaching the top the battery indicator was purple with 2 bars left however during the trip uphill not once did it attempt to charge the battery (my Fiance watched for me so I could keep my eyes on the road. She reluctantly makes notes about the vehicle for me while we drive but hates that I am always asking her to look back through it.) The mile journy across the top is the same as the HCH with it throwing a little charge into the batteries. Now for the downhill. At first regenerative breaking was enough to roughly maintain speed but soon it was time to throw it in B. This brought the battery charge up much faster and added the noise of the engine breaking though much less than the HCH. By the time we reached the bottom the batteries were fully charged and unlike the HCH I was at about 65MPH (i'd be at nearly 80mph in the HCH).

    Over all, the Prius seemed to handle it much better than the Honda but this was just my experience. It's the only time I've ever had to use either vehicle in anything other than D for forward travel.
     
  10. Bodgerx

    Bodgerx Junior Member

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    That's pretty much what I used to see on my Civ Hybrid.

    One thing I used to do to control the regen on a long descent was to put it in neutral for the first third and then put it back in gear and then regen all the way to the bottom. If you have a hill that you come across regularly you get a feel for how it can be done.

    Basically trying to avoid the switch off of regen braking at all costs, because the feel is totally different.

    Granted, the Prius seems to handle this better.
     
  11. gdbelden

    gdbelden Gator Hator

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    More of a B -
     
  12. hill

    hill High Fiber Member

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    I never used the b in my shifter either.
    Fletch told me it works the Fetzer Valve:

    [​IMG]

    Before I go messing with that, I'd need to get a set of 30 weight ball bearings.

    .
     
  13. uart

    uart Senior Member

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    ^^^ It looks like a problem with the muffler bearing to me. :)
     
  14. ski.dive

    ski.dive Active Member

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    After 9 years of driving the 2008 Prius, I've never used the B
     
  15. bisco

    bisco cookie crumbler

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    me neither. 13 years. course, there's no mountains round here.
     
  16. srellim234

    srellim234 Senior Member

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    I use it almost every weekend coming down the Cajon Pass from the high desert. I-15 with it's 70 mph speed limit and a downhill grade of 6% over the first 5 miles. A lot of people ride their brakes coming down that pass.

    It also got used on our multi-state trip last summer. Northern Arizona, Colorado and Utah all provided ample opportunities for the "B". I suspect it will get even more use this July as we head all the way to the East Coast and back.
     
  17. andrewclaus

    andrewclaus Active Member

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    Before I bought the Prius, I was trained as a water truck driver for my foothills area volunteer fire department. Those trucks have two retarder systems in addition to service brakes and emergency brakes. One of the retarder systems is an electric generator on the drive shaft which dumps energy into a resistor bank. controlled by a turn signal-type switch on the steering column. After that training and driving experience, the Prius "B" mode makes perfect sense and I use it all the time, even coasting to a stop in the city.
     
  18. dolj

    dolj Senior Member

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    Using it this way does not make the best use of the regen, as B replaces some regen with engine braking. Engine braking wastes energy as heat. If you use D instead, that energy, which is wasted in B, will be captured into the battery.

    Remember, also, that the first part of brake pedal travel increases the current into the battery as the added current increases the generator resistance (and hence increased braking force) so it is better to use the brake pedal to increase energy into the battery. In this regard, I am talking about driving on the relative flat road, not descending mountains.
     
    #38 dolj, May 9, 2017
    Last edited: May 9, 2017
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  19. andrewclaus

    andrewclaus Active Member

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    I get it, thanks for the clarification and lesson.

    I think I do it more out of habit from driving the heavy trucks, saving the wear on the friction brakes.
     
  20. dolj

    dolj Senior Member

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    No problem.

    You have the right idea, just a different process to achieve it.
     
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