Curious behavior

Discussion in 'Gen 2 Prius Main Forum' started by rdenneyutmb, Mar 16, 2006.

  1. rdenneyutmb

    rdenneyutmb New Member

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    I have had my first Prius for about 2 weeks, and am continuing to learn things, sometimes the hard way. I was driving my wife to a doctor's appointment today. Dear thing, she is so tolerant, I was showing off my "pulse and glide" skills that have been getting me upwards of 70 mpg under appropriate conditions. There is a brief section of the 25 mile drive that is on freeway (higher speed required), so I punched the cruise control button to hold speed at 55 mph. No response. Hmm. That's interesting. The first time that has happened. Repeated attempts to activate cruise control were to no avail.

    We exited the freeway onto a 45 mph, 4 lane road (perfect for pulse and glide). I checked the cumulative trip mpg and was shocked to see 50 mpg and under. This was despite rather serious pulse and glide segments that usually give me 70-75 mpg. Odd, I thought. I dropped my wife off in town and made my way the few blocks over to my work, where I was going to stay for a while, and further things seemed wrong. First, the ICE wouldn't turn off when I stopped. Second, it seemed like releasing the accelerator pedal resulted in more deceleration than usual. What the heck is going on, I thought.

    When I finished my work and headed out to the car, I thought about the persistent ICE and the exaggerated deceleration and I realized I must somehow have gotten the car in "B," but I couldn't figure out how. (It was definitely in "D" when I started out from home.) Could there be a software bug?

    Then I realized what must have happened. In our enthusiasm for protecting the beautiful, new carpeting, we had purchased some cheap plastic mats for the front of the car. My wife had spent some time on our way today cutting a piece to go over the middle between the driver and passenger seats, and in the process had leaned over toward me to get the plastic material in position. She must have inadvertently bumped the shift knob downward, shifting the car into from "D" to "B."

    I have looked in the manual to see what it said about the "B" mode, and I find very little except that it is designed as an engine break for prolonged, steep downhills. Here on the gulf coast we have no such hills (Alas!), so I had not tried out the "B" driving mode. Apparently cruise control cannot be activated in that mode. Keeping the ICE on (for braking) and greater deceleration make perfect sense for that situation, but it certainly can surprise you with low mileage if you don't notice your using it on the flat! (In desperation for a hill, we sometimes drive back and forth over the freeway overpasses just for excitement, but this gets old after a while!)

    Cheers!
     
  2. Excellerator

    Excellerator New Member

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    Yeah, "B"is for engine braking. From what I've learned, it's only for convenience. Therefore, you regenerate less energy and get worse gas mileage.

    For example, it would be more convenient to let the vehicle engine brake down a long, steep hill than to hold the brake pedal and risk overheating the brakes (unless, of course, it's the electric generator that's slowing the vehicle down).

    And, if I remember correctly, the engine should remain on in order to help slow the vehicle down, like you mentioned.
     
  3. tr_blankenship

    tr_blankenship Junior Member

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    I have an '01 and have used B on several road trip occasions. It is a braking mode for going down steep hills or switch backs. We went up to Montana and the Idaho/Montana border is at the top of a mountian. We switched it into B and got 100MPG for the 45 minute trip down the hill. It also generates more wattage in this mode and will charge your battery to it's fullest capacity. B)
     
  4. richard schumacher

    richard schumacher shortbus driver

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    You were doing this with the car "READY" (that is, ON) and in "D"? According to the manual one can shift into "B" only from "D"; from all other states it will go to "N" instead of "B".

    Sounds like operator error in any case :)
     
  5. rdenneyutmb

    rdenneyutmb New Member

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    Yes, I was definitely in D when it must have happened. (We were driving along on our way.)

    No mystery here, just interesting how easy it is to bump the shift lever without realizing it.
     
  6. sub3marathonman

    sub3marathonman Active Member

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    rdenneyutmb talked about bumping into B mode. I can tell you that he's not the only one. I was coasting up to a light and reached for something, and bumped the control into B. It was extremely easy to do.

    Also, you could tell right away that it wasn't acting as usual. I did stop at the light, but the engine kept running.
     
  7. keydiver

    keydiver New Member

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    Yes, thats one of the VERY few irritating things about my new Prius. I've bumped into "B" several times now while reaching for other things near it while driving. At first it scared me, but now when I do it I just shift back to "D" and keep right on going. I wish there was a way to disable it, as there are NO hills here in South Florida. ;)
     
  8. micheal

    micheal I feel pretty, oh so pretty.

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    The times I have switched into B (on mountain grades) I can tell a big difference in the sound of the engine. It makes the different sound every time you switch to B right? Or am I just anticipating a different sound?
     
  9. rdenneyutmb

    rdenneyutmb New Member

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    I suspected that others might have accidently bumped the car into "B," considering the design of the shift lever. Perhaps it would be a good idea to have the B mode position in a downward position but in an additional, vertical notch to the right of the rest position. Moving the lever to the right and down (and having it spring back to the middle position) would be less likely to achieve by accident, but no more difficult to negotiate than putting the car in "D" (to the left and down).

    Admittedly a minor issue. Just a thought.
     
  10. samkusnetz

    samkusnetz New Member

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    i am fairly certain that B does not employ the regenerative braking. therefore, the only way you generate wattage in B is by also using the brake pedal.
     
  11. efusco

    efusco Moderator Emeritus
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    You are mistaken.

    Moderate regen (in the range of 15-25 amps, does occur in B-mode. We used to believe that B-mode caused maximum regen, but this is clearly not correct and a well trained foot on the brake pedal can cause up to nearly 100amps of regen before the friction brakes kick in.
     
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