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Question about B Mode - Page 2

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Posted by richard schumacher on January 30, 2008, 11:09 pm

No more counter productive than downshifting an old-style transmission
under similar circumstances.  Saving the friction brakes is a good
thing; you don't want to boil the brake fluid, which would otherwise be
easy to do when coming down from Mount Hamilton or certain places in the

Posted by Tomes on January 30, 2008, 11:11 pm
"G-Man" ...

Here is a pretty good explanation of B Mode:

Posted by G-Man on January 31, 2008, 12:48 am
 Perfect.  I understand what it was and was for, but I was looking for the
answer in that link.  It throws energy away.  I thought that maybe the drag
induced was somehow turning the generators and producing energy as does
braking.  According to that article, no.

Thanks to everyone who replied.


Posted by Diako on January 31, 2008, 11:19 pm
Consider what happens going on a long downhill: after some time the
battery will get to 'Full' thanks to regenerative braking. At this point
regenerative braking will stop and the mechanical brakes will do all the
job. This is the right time to use the B Mode if you don't want to waste
your discs and pads and if you don't want to boil the brake fluid, as
Richard says. The B Mode will give a Prius the same effect of engine
braking in standard cars. Right, this throws energy away but this is what
inevitably happens once the battery is full. In my experience the length of
time needed for a full battery is from 5 to 10 minutes, depending on how
steep downhill I'm driving. This energy could be saved only if our Prius
had batteries with bigger capacity: the feature the new Prius should have
in 2009 version.

Posted by David Kelly on February 2, 2008, 3:50 am
 Diako wrote:

...according to one who has obviously never driven a Prius under those
conditions.  I have.  When the battery is as full as the battery can be
the Prius ECU automatically starts "pumping air" to make up the minor
drag which was being produced by regeneration.

Having been in that situation and wondering why the heck my ICE had
started running going down a long steep grade, I tried B and found no
difference between B and D in that situation. Then I thought to look at
the other Info MFD screen and saw my battery was pegged at solid green.

By Diako's description if the battery filled then one would start going
faster when the ECU halted regeneration. As if one had pressed on the
throttle until all the arrows blanked on the energy flow animation.
Toyota is smarter than that. I was shocked when my ICE started "running"
but would have been really surprised had it started accelerating when
the battery was full.

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