What is "B" mode, exactly, again?

The Lexus driving performance guide for the RX400h says:

"Use the "D" gear position rather than the "B" position. During normal driving conditions, always drive in "D" for best fuel economy. Only use "B" gear position if needed to help maintain vehicle speed when going down steep grades."

http://www.lexus.com/assets/models/hybrid/...mance_guide.pdf

OK, this is my first post. We have his and hers Prius (would that be Prii?), a 2005 and a 2006.

Bob

 

<div class='quotetop'>QUOTE(Camerabug @ Apr 2 2006, 08:15 PM) [snapback]233897[/snapback]</div>

B is an "Engine Brake". If you have any 18-wheeler truck driving buddies, they might call this a "jake brake".
It uses resistance from the engine/motor to slow the car. If I remember correctly, this is not as efficient as stepping on the pedal from an energy regeneration standpoint but the effects can be profound.

Different people will give you different answers as to its use.

I've had to use it in in combination with the brake pedal a couple of situations where I needed to stop very quickly. Once a car decided to slam on its breaks in front of me on a country highway at about 60mph. The B mode plus foot brake got me stopped very quickly. I've done similar when looking up to notice that a red light has snuck up on me. - it makes for a very quick, yet surprisingly smooth stop.

I've also been known to thwap into B-mode taking turns fairly sharply while my foot is still on the accellerator pedal - makes for an interesting 'racetrack' feel to a turn - NOT a particularly efficient move, and I'm not suggesting it as a standard practice, but it's interesting.

To stick with the party line though, conventional foot breaking is more efficient. B helps maintain stable speed when going down steep grades. That's the story I'm sticking with.

 

<div class='quotetop'>QUOTE(Kaos1 @ Mar 4 2006, 07:05 PM) [snapback]220390[/snapback]</div>

Well I don't know where you live but I would bet that there are a few places it might be useful, but all of those are very steep hills. I have not been on really steep hills since I got my CAN View though there are a few within driving distance as I live out "west" I have only used B rarely and have never been able to find a time "around town" to use it yet. I have always got more bang for my buck with breaking.

 

Oh, bah. Another collection of mostly-misinformation. Doesn't
even mention the 42 mph threshold. Who the heck is writing
that crap?
.
[EDIT: to answer my own question... appears to be "kmf164", who's
on PC too but has fallen fairly inactive of late. I wonder if
there's a reliable way to poke him for corrections.]
.
_H*

 

Toyota should have called it GR instead of B. It would have saved a ton of confusion. Grade Retarder. Cause that is essentially what it is. For people who live on flat ground you would likely never use it, 11% grade for 3/4 mile I use it. The ICE is turning over with the camshaft positioned to give maximum compression and the computer shuts off the fuel flow. MG1 still regens, not as much as the MG2 with light brake application but "B" holds the car at 70Km per hour and that was all I wanted of it.

 

HA!
ask a locomotive engineer- we use it day in and day out!
for a simple explanation:

http://travel.howstuffworks.com/diesel-locomotive9.htm

instead of burning the energy off, Toyota has found a way to send it back to the batteries! hooray!

 

<div class='quotetop'>QUOTE(rposton @ Mar 4 2006, 07:15 PM) [snapback]220398[/snapback]</div>

Sorry to be several months late in this reply, but this is my first post.

From my own experience (I've driven down some long mountain passes that seemed to have fully charged the battery) and what I've read in this thread, it's such a time that you might want to use "B".

Normally, if the downgrade isn't too steep, I can keep the car in cruise control and it maintains the designated speed until the battery is fully (or at least neary) charged. After that I would have to use the brakes to keep the speed under control. It sounds like using the "B" setting would be useful for braking without overheating the brakes themselves. One of the other (aside from saving energy) advantages of regenerative braking is that it saves the brakes. I expect to get a much longer life out of my Prius brakes than those on any other car I've driven.

Incidently I accidently slipped into B (gear?) one time and found the car slowing down. I think I bumped the shift lever when reaching for the windshield wiper control. It took me a little while to discover what happened. After that I read up on that feature in the manual and it did say to normally avoid using it, since it did hurt fuel economy.

By the way, I'll eventually get around to providing an avatar.

Dave