The "B" Poll (Revisited)

I use it a pretty fair amount.

 

"B" is needed for driving in winter weather. It is a big help going down hills on slick roads, much safer than pedal breaking. I rarely use it in good weather.

 

<div class='quotetop'>QUOTE(anj48 @ May 2 2006, 05:29 PM) [snapback]248731[/snapback]</div>

Really? I would think that, going down hill in the winter, you'd want the option of ABS, which should only be possible while you're foot braking. . .

 

On the drive home from the dealership when I bought it, I saw that I was in "B" rather than "D". I did freak out a little as I had no idea what "B" was. I must have bumped the shift lever because I know it was in drive when I started out. I didn't even know if I could put it back into drive while the car was moving so I pulled over, stopped and then put it back into drive.

That's my one and only time using "B".

Catherine.

 

Absolutely worth it. When descending a mountain it is necessary; for normal day to day on the flats, no I never use it.

 

virtually every day on the way to work as I go down a 10% grade for 3/4 of a mile with a traffic light at the bottom. If I use B I hardly ever have to touch the brakes and I stay right with the traffic flow. The amps of regen might be slightly lower than riding the brakes but I don't have to think about modulating the pedal pressure and just enjoy the view. The amp difference amounts to about 4-5 amps lower in B verses D and brake. Not enought to worry about and I'm at the bottom with the BSOC in the mid 70's.

 

I never used it in Fargo. Fargo is flat. I used it on 2 or 3 long downhill stretches coming down the mountains on my trip to Osoyoos. That's the only time I've used it. Guess I'll be using it again going through the mountains on my trip to Lacey for the Alternative Fuel Fair this weekend. And now that I have the CAN-View I'll be able to see how much regen there is with B mode, as well as how full the HV battery gets. Gonna be an interesting trip.

 

I thought that you were only supposed to use "B" when running on biodiesel!

 

There are a very few places to use B in its intended fashion. I am sure many many cities have them. That really, really steep grade where you will fill the battery if you use the brake to slow down. If you get all green bars half or 3/4 of the way down the hill, then use it, other wise if you can make it with all green at the bottom the hill you may need a EV mod to "bleed" off a bit of the riches you obtained going down. Otherwise don't bother.

 

Most people don't use the [1] or [2] gears on their automatics, either.

These are specialized gears that are only used in certain situations. Many people won't need to ever use them.

 

As far as extra installation, the B gear is basically one extra button the computer can monitor as well as the software to support it.
I don' t think there's actually any extra hardware associated with it, just programming that changes the computer controlled behavior of the existing components. (extremely low incremental cost)

 

<div class='quotetop'>QUOTE(hdrygas @ May 2 2006, 08:12 PM) [snapback]248898[/snapback]</div>

As much as I love my EV switch, I don't think it's necessary in this situation. On my trip to Osoyoos I noticed that after a long downhill had charged my battery up to all green, the car went into what most Prius drivers like to call "super-stealth" (poor name, in my opinion, since it implies a mode that is stealthier than stealth) even when I was accelerating up a hill. The car, left to its own devices, will use that extra charge as soon as it can.

Where the EV button could help is to drain the battery as much as possible before getting to that long downhill. But that only works if your speed is under 34 mph before you reach the hill, where the EV switch can function.

 

I voted for the never use category. But I am thinking I might use it if I lived in the rockies.
Nothing here big enough to bother with it. And it should never be used in winter. It works on only two wheels so all it can do is make you skid more and confuse the ABS system.

It really serves two purposes:

1 to reduce brake fade on long steep down hill runs.

2 to slow the car with if the brakes fail.

 

How soon they forget...
http://techno-fandom.org/~hobbit/cars/b-mode.html
which offers some numbers for regen in various modes, mentions
winter driving and/or autocrossing, and numerous other things.
.
Bottom line: wastes energy. But sometimes you need that.
.
_H*

 

Folks-
The 'B' position is included to satisfy an FMVSS requirement. An engine braking position is required per FMVSS. You'll need to look it up yourselves if you want the number of the standard, and what the specific deceleration rate, test protocol, is. From memory the standard number is something like 103 or 104 or 110. That's in section 571. The '1' or '2' positions on standard automatics are for the same requirement, and their inclusion in the auto shift pattern is independent of customer acceptance or the like.

 

<div class='quotetop'>QUOTE(efusco @ May 3 2006, 06:27 AM) [snapback]249013[/snapback]</div>

ABS does nothing to prevent what B is designed to avoid - overheating your brakes. Once the battery is full, the Prius uses the friction brakes to slow down - just like any other vehicle. On a long descent (e.g. coming down I-70 into Denver), there is a very real possibilty that you could overheat your brakes (e.g. boil brake fluid), rendering them completely ineffective.

Brake loss is a huge problem for trucks. The runaway truck ramps on I-70 are used on a regular basis by truckers who end up going too fast and don't have the ability to slow down (truck brakes are ineffective on a grade like I-70 at 75mph and downshifting is difficult).

To a lesser extent, it's also a problem for cars. B mode uses the engine to waste energy so that the battery doesn't fill up, avoiding the use of the brakes.

Use B when you would downshift in an automatic transmission vehicle - to go down hills. There is no real other reason to use B in the Prius.

 

<div class='quotetop'>QUOTE(Kiloran @ May 3 2006, 09:38 AM) [snapback]249040[/snapback]</div>

This is correct. The Prius already has the variable valve timing used to increase pumping drag during compressing breaking, so there is no extra equipment involved with adding B.

Diesel trucks use an exhaust compression brake, sometimes called a jake brake, which makes an unbelievable growling/roaring noise when it is engaged. Maybe we can get the Prius computer to synthesize that sound for us.

Another option would be a big electric heater on the roof of the Prius. That way we could dump the extra charge just like they do on diesel electric locomotives.

Tom