B what is it good for?

<div class='quotetop'>QUOTE(psikot @ Sep 11 2007, 01:00 AM) [snapback]510478[/snapback]</div>

I used it descending large hills to keep the speed from running away without having to worry about stressing the brakes. Otherwise, I don't use it in ordinary driving.

Bob Wilson

 

It can add some engine braking to the mix which is useful on long descents, as otherwise all you've got is regeneration (which runs out when the battery's full) and the brake pads.

Without "B" mode, once the battery was full going down a long hill, the Prius would act like a normal car in neutral. Not a good idea, as your brake pads are likely to overheat. Putting it in "B" is the equivalent of putting a normal car into a low gear to take up some of the energy.

 

Do not use B except when decending long hills or it will increase your fuel consumption.

I only use B mode when I know my battery will be fully charged at the bottom of the hill. B mode uses the petrol engine to dump energy to slow the vehicle. If your battery isn't near fully charged it is better to lightly brake as that will increase regen braking charging the battery. When the battery is at full charge the computer will make the engine spin via the electric motor to dump some power preventing over charging. In a way B mode is optional on decents as the computer does the energy dumping for you if needed.
Don't use B to slow on flat ground, just leave the car in drive for normal driving to save petrol.

 

<div class='quotetop'>QUOTE(psikot @ Sep 11 2007, 01:00 AM) [snapback]510478[/snapback]</div>

Truly, there are very few people who are going to make any good use of "B" -- it is there to provide a way to dump energy and protect your brakes from long-term fade. Unless you are headed down a long, steep grade, there is no reason to engage B.

This topic gets covered periodically on PC. I think you are probably best served by taking a look at a very good description of the "B" mode in Hobbit's "B-mode made clearer" post.

a priori

 

<div class='quotetop'>QUOTE(KMO @ Sep 11 2007, 04:10 AM) [snapback]510497[/snapback]</div>

The Prius will use engine braking with or without shifting into B mode. When the state of charge (SOC) for the battery starts getting too high, the Prius control system shifts the engine valves to a high drag configuration and spins the engine with the electric motors to burn off excess electricity. What shifting to B mode does is explicitly tell the control system to start using engine braking right now, and not wait for the SOC to get high. This buys extra time before the friction brakes have to do their stuff.

If you live in a state like Michigan, you will never really need to use B mode. For our friends in Colorado, that's a different story.

Tom

 

<div class='quotetop'>QUOTE(psikot @ Sep 11 2007, 01:00 AM) [snapback]510478[/snapback]</div>

"B" is to prevent the brake fluid from boiling from overuse. Driving around San Jose you never need "B". Driving down from the top of Mt. Hamilton, *then* you need "B" (and of course the brakes also).

 

using B going down hill seems to make the ICE rev like a bag of nails :blink:

 

<div class='quotetop'>QUOTE(prius2go @ Sep 11 2007, 10:11 AM) [snapback]510563[/snapback]</div>

That's what it's supposed to do. It's burning up energy by spinning the ICE in a high-drag configuration.

Tom