freeeked out in traffic

Your car reacted exactly like mine does when I get caught in abysmal morning commute traffic. The Prius is very good at making sure the battery stays optimized. If you had been there too long, eventually the ICE would have kicked in to make sure the battery got charged.

There's a thread about about this here: http://priuschat.com/index.php?showtopic=37342

 

<div class='quotetop'>QUOTE(fwellers @ Nov 28 2007, 08:37 AM) [snapback]545149[/snapback]</div>

Hey, I only found it because it was listed under the "similar topics" when I was reading your post.

 

Your computer will handle everything. If you want to make your life easier then don't even look at this screen

 

What you describe is normal. The ICE will run as needed to keep the battery charged. Don't use B mode in this manner; it doesn't help. For most people B mode should never be used. Its only function is to burn off extra energy by spinning the ICE, much as you would do by down-shifting when descending a steep hill. B mode is intended for very long hills where the traction battery will charge to its highest allowed state, forcing the friction brakes to take over.

Tom

 

the horse is NOT dead--I saw it twitch!
MY understanding of the 'B' mode is that it acts alot like the decompressions in a trailer truck in that it actually bleeds OFF excess energy so that the system doesn't overload--is that not so? Simplistic terms, yes, but realistically, he should leave it in 'D' to get the most benefit from the charging systems, no?

 

<div class='quotetop'>QUOTE(skguh @ Nov 28 2007, 09:48 AM) [snapback]545176[/snapback]</div>

I'm not certain there is anything simplistic about it. I don't say this to be argumentative, but to express my lack of a complete understanding of the computer controls behind the "D" mode vs. the "B" mode. As I've understood it, there may be circumstances, when driving at very low speeds, where placing the car in "B" mode may get the engine to more quickly charge the traction battery. Of course, this is done at the expense of fuel. By staying in "D" the car's computer will control the charge of the battery at a more fuel efficient pace. I don't see any reason to use the "B" mode unless I'm driving down a long, steep incline and my battery readout is all greens.

At least this is my understanding of it. I'll defer to Hobbit for the definitive statements about "B" Mode. Hobbit's writing should be mandatory reading for every Prius owner.

 

<div class='quotetop'>QUOTE(a priori @ Nov 28 2007, 10:46 AM) [snapback]545208[/snapback]</div>

On a long, steep incline you want to switch to B mode in advance of a high SOC, otherwise B mode doesn't help. Here is why: When the SOC becomes too high, even in D mode, the control system will start to bleed off excess energy with the ICE, just as it does in B mode. The difference with B mode is that you are telling the controller to get on it now, and not wait until the SOC is too high. This is a form of feed-forward control where you use your knowledge of the road ahead instead of waiting until after the fact. This advanced notice will forestall the use of friction brakes.

Tom

 

<div class='quotetop'>QUOTE(a priori @ Nov 28 2007, 11:46 AM) [snapback]545208[/snapback]</div>

Even if that's true, why bother? "D" will recharge the battery as needed with no fuel economy hit. A faster recharge is purposeless.

 

It is worth remembering the charge display only shows 40% of the scale, even with no bars there is most likely 40% left in the battery and at full green the battery is at 80%. As said earlier, let th HSD look after it.

 

I'm kind of curious myself about the B mode but I need to have a clear definition of "long, steep hill." What that means in Western Pennsylvania might be very different than the interpretation of someone in South Carolina. If I'm on a road that's a fairly long downhill (the kind you see signs warning truckers to reduce gear) for 5 or 6 miles, is it smart to put it in B mode?
In my old car, I'd put it in neutral on such occasions just for fun. But are we instead talking about REALLY steep hills?

 

<div class='quotetop'>QUOTE(richard schumacher @ Nov 28 2007, 04:55 PM) [snapback]545416[/snapback]</div>

Exactly right! Please don't read my post as a suggestion that "B" mode should be used.

My statement in the post: "I don't see any reason to use the "B" mode unless I'm driving down a long, steep incline and my battery readout is all greens."

Let me clarify: I envision my only use of "B" is when I am going down an incline steep enough to provide numerous warnings about "Steep Grade", extra lanes going the other way (uphill), and "runaway" lanes. Even then, I think I would use it only if the MFD showed all eight bars bright green, my A/C was running full blast, I had miles to go, and the brakes were starting to fade. The HSD's computers know how to handle things, and I'll trust them to do the right thing.

Still -- for more information about the "B" mode, I think folks should read Hobbit's page. I learned enough to simply ignore that letter on the shift knob.


<div class='quotetop'>QUOTE(GreenIsGood @ Nov 28 2007, 07:52 PM) [snapback]545481[/snapback]</div>

 

<div class='quotetop'>QUOTE(GreenIsGood @ Nov 28 2007, 08:52 PM) [snapback]545481[/snapback]</div>

Use an operational definition: if you find yourself standing on the brake, shift to "B". Or do it if you get weary with hitting the brakes repeatedly, but be prepared to accept reduced fuel economy.

 

<div class='quotetop'>QUOTE(GreenIsGood @ Nov 28 2007, 07:52 PM) [snapback]545481[/snapback]</div>

The "long, steep" definition is variable. It depends on a variety of factors, including current SOC and battery temperature. B mode is good for any hill where braking is required AND you know that the regenerated energy will exceed the capacity of the battery. The only way to know when to use it is by experience. If you find yourself going down hills that max out the battery and cause friction braking to kick in, then next time you can use B mode. There is no hard and fast rule. I've never found a hill in Michigan that needs B mode.

Tom

 

Alternatively, you could just act like a normal person rather than a Prius owner who only does something if there's an MPG boost, and use B mode for the same reason any other car would use a low gear going downhill - to help keep control of the car...

 

In the UK we have "Select lower gear now" signs at the top of some long steep hills. I act as directed and put the car in B mode till I am at the bottom. I still end up breaking most of the way down the only local hill with this signage (Nether Broughton for those local to Melton Mowbray). I can't remember ever using B in another situation, apart from when I first got the car and wanted to find out what it did.