Using "B"

You'll get more regen if u just brake normally. Using B mode uses engine compression to slow you, thus regen is potentially not being used to the max. I use B mode for those REALLY long downhills, where a green battery happens halfway down: I-70 outside of Denver. Engine revs pretty high, but no fuel is being burned.

 

What he said... My understanding is that the 'B" mode uses the ICE as a friction brake and this slow down is not used to regen the battery. So I think you are better of lightly using the brakes as more energy will de directed towards the battery. That said on long slopes where the battery will reach green anyway I would use "B" as it is more convinient

 

I would not worry about engine braking being illegal. Diesel engines often use a "Jake Brake" to dump the compressions on their engines and use the engine to actively break the truck. This is typically illegal inside towns due to the loud noise it makes. As for your real question I'm not qualified to answer....my prius will be here in one more week

 

finman and SomervillePrius are conveying the knowledge and belief that many people have on this board about the "B" mode. HOWEVER, just yesterday there was some discussion about whether this actually was correct. Just to briefly summarize, there is a "Prius expert" (i.e. works for Toyota) that contends that the "B" mode leads to more efficient braking.

I'm not sure that I believe that, but just figured I'd make you aware of an alternate possibility.

 

What they are describing also matches my experience. Over the past couple of days shuttling my son to camp I encountered some long declines that topped off the battery followed by engine braking. I thought... hmmm. I'll bet that is what B is for. It is the first and only practical use for it that I've encountered to date.

 

There are evidently a lot of misguided "experts" who think B mode
gains something, when in fact it is ENGINEERED to LOSE something.
Your "toyota expert" needs to dip into some of what's been
documented by the instrumentation fiends, and learn from it.
.
_H*

 

It's not that energy is stopped from going to the battery but that a lot of energy is being used to turnt he ICE around. So in 'b' a lot of energy goes to turning the engine. In normal mode the enegy that same energy would be used by 1) sending even more energy to the battery for regen and 2) being consumped as friciton heat by the bake pads.

I'm not sure what the difference really is but if the 'b' button would work magic then I'm sure the same technology would be used when applying the brakes! I'm sure Toyota wouldn't leave this magic function to the initiated few.

I think 'b' is a more aggressive slowdown for when going down hills. It's more concerned about slowing the car down then regaining energy and normal mode is more concerned with regen then slowing down. So to me normal mode wins as I'm playing the FE game

 

the net difference in regen to the battery using B and brakes is about 7 amps as near as I can tell vs D and brakes. I'll flush the CAN-view formatted data and test it but just a look I'd say it's about 7 amps. The highest regen I've seen is 97 amps on the screen but when I look at the Formatted screen I see 120. There are some pretty good hills here so I'll probably take a drive in the wifes car this weekend and get some definitive results. The OP does what I do. I don't bother to try and modulate the brake pedal when I can just put it in B and let the computers do it. I don't drive on the flat in B. As a experiment try this the next time your dirving along with your foot on the gas at 50 miles an hour. Reach over and put the car in B.........ya nothing happened. CVT's are cool!

 

the difference between D and brakes looks to be about 7 amps more than B and brakes. I have not seen the regen go to 120 amps because it probably only happens under extreme brake applicaton and then I'm concentrating on the goof that just cut me off and I'm trying to avoid a collision. But that gets stored in CAN-views memory.

the only time difference is the time the computer takes to switch from B to D with your foot on the brake.

when I'm in B I'm already getting regen if I'm in D and hit the brakes I get regen If I'm in B and hit the brakes I get regen above the regen I was already getting.

 

I really don't know the relevant differences, but here is a factoid to consider:

A Toyota master technician stated during a new users's seminar that he doubted he'd ever have to replace Prius brake pads since they aren't used until the car has slowed down to something like 16 mph.

I have some misgivings about that. It seems to be a generalization. I wonder about emergency braking and suspect the pads do engage under dire circumstances at higher speeds. However, I suspect that normal braking and the "B" setting are the same under a lot of circumstances, too.

I am really curious about the real answer to this question!

 

8 mph and under there is no regen braking. You should be able to feel it switch over to the pads from 12mph down to 8mph. It's fun to use B around here because you slow down to 12mph and then it starts letting up as you get to 8mph where it then just lets you glide right off at 8mph.

Someone wondered why the arrows still show regen from the wheels under 8mph. I believe it's just the slight delay in the MFD. You can also see the delay when you feel the engine kick in and it takes a second before it kicks in on the MFD.

If you're braking harder than the regen braking can handle at higher speeds, I'm sure the pads will kick in.

 

once your past the limit of the stroke sensor your into friction braking and it's not a lot of pedal travel to get past the limit. Once into friction braking that is energy that's wasted. If you look way in front of your car and anticipate what is happening in traffic and use B to slow you capture the energy anyhow less that required to spin the ICE. There is no fuel used by the ICE so no loss there.

 

http://techno-fandom.org/~hobbit/cars/b-mode.html
.
please go read this NOW if you haven't yet, before hammering
in yet more guesswork
.
_H*

 

I commute daily downhill at a significant grade and use B frequently to help control my speed. The only thing I wonder about is whether it is harmful to the engine to shift into B while going at hgh speeds (like 60+mph). As someone mentioned previously, B can be quite loud when engaged while going quickly on a significant downhill.

 

Capital article. Very informative. Going east of the continental divide with a maxed out battery you can really "hear the engine ring", to quote the Eagles. Switching between D and B in that scenario is great. You hardly have to touch the brake pedal is traffic is flowig well.

Thanks 'obbit!

 

Summarizing: the only the thing that "B" will harm in normal driving is your fuel economy and air quality. "B" reduces kinetic energy recovery, and the extra gas you burn may cost more than you save in brake pads.

 

if your decending hills and in B and you monitor your CAN-view you will see that the fuel flow drops to "0" non in non out so no harm to the air quality and if it avoids using the brakes, less brake dust in the air you breath.