'B' Mode revs engine way up, normal?

Completely normal. in B mode, the car uses the natural resistance found in the engine to slow you down, essentially by having the wheels turn the ICE. That results in it revving up really high.

B mode should be used in long downhills, regardless of speed. In those types of downhills, you're worried about brakes heating up and being ruined, not to mention the fact that you're standing on the brake the entire time. B mode is there to help keep the brakes from heating up.

 

<div class='quotetop'>QUOTE(DaveLeePrius @ Dec 4 2006, 04:27 PM) [snapback]357621[/snapback]</div>

That's correct. I'm not sure what happens when the battery gets completely topped off and you're still applying brakes. I think it still uses the regen system and gets rid of the excess energy by spinning the ICE. Someone who knows for sure should confirm/correct this momentarily

 

<div class='quotetop'>QUOTE(DaveLeePrius @ Dec 4 2006, 03:03 PM) [snapback]357638[/snapback]</div>

You don't have any really long hills between Seattle and Portland, but if you were to head up I-90 to the summit, you could probably get it down to 3 bars. That depends how hard you push it though. Seattle has some good hills that should take the charge down on the way up the hills.

Dave M.

 

<div class='quotetop'>QUOTE(DaveLeePrius @ Dec 4 2006, 03:03 PM) [snapback]357638[/snapback]</div>

Flooring it (especially going uphill), will suck down a lot of charge.


<div class='quotetop'>QUOTE(San_Carlos_Jeff @ Dec 4 2006, 02:36 PM) [snapback]357624[/snapback]</div>

I can confirm that there is no regen once the battery is full. The ICE will spin faster to consume the excess energy.

There's a hill that I drive down at the beginning of my morning commute, and I fill the battery up. The SOC usually ramps up to 83% when I stop at the light at the bottom of the hill. As I'm stopped, I glance at CAN-view, and I see the ICE spinning at ~2.6k rpm, and the power consumption at 16A. After I turn, there is a quick stop, and I have to push the brake pedal down further to get any stopping action, and as I am stopping, the power consumption remains constant.

 

Another way I've seen the battery level drop is extended stop-and-go crawling traffic. (Travel I-405 thru Bellevue at rush hour to see what I mean)

It seams the ICE doesn't kick in when you creep along until you get down to two bars on the battery.

 

Regenerative braking uses MG2 as a generator to slow the car. This produces electrical energy from the car's kinetic energy. But by conservation of energy, this energy has to go somewhere. Normally it goes to the battery. But when the battery is full, there is no longer any place to send it, and regenerative braking cannot continue.

At this point, stepping on the brakes engages the friction brakes.

To avoid, or reduce wear on the friction brakes at this point, the "B" gear uses engine compression to dissipate energy. It is possible that you did not hear the whine before because your battery was not yet full, and even the "B" mode was using some regeneration.

But the engine whine is normal in "B" mode and should cause no concern. And you should always use "B" any time you have a long, steep downhill. It will not harm the engine, and it will reduce wear and heat on the friction brakes.

 

Speaking of 'B' mode vs. 'D' mode.

Is there any difference between the two when the gas is even lightly depressed?

I know the car behaves diferently if the gas pedal isn't pressed, one breaks quite a bit, the other quite a bit less... but what about while depressing the gas pedal? Is 'B' good for stop and go traffic where you don't feel like shifting your foot between brake and gas too often (sure try to maintain a constant low speed... not always possible though). Or is that bad practice?

 

The owners manual (i.e. Toyota and the people who designed the car) as well as all experienced Prius drivers all agree:

"B" mode is to reduce use of the friction brakes during long, steep downhill runs, and should not be used under any other conditions. "B" mode prevents the engine from shutting off, as it often wants to do in normal hybrid operation, and it dissipates deceleration energy as heat rather than recovering it back to the battery.

 

Recently i visited hill station, here one of the track is very steep and rough, on uphill it was ok but on downhill i engaged b mode but still speed was way fast due to steep, my question is how to control speed on such steep hills, i miss first gear of manual in these hills, please help

 

b mode and braking are your only options. if you are forced to travel that route frequently, keep an eye on your brake pads

 

Using your brake pedal will not engage the brake pads unless you are braking really hard. Using a combination of "B" and the brake pedal should be okay to control your speed for all but the steepest of declines. If it is so steep that your pads are engaged, then you really need to ask if the Prius is the right car for the job.

 

The brake pads engage much earlier than that. In a Prius, regenerative braking can supply only medium to light braking, depending on speed. Engine braking capacity is similar to regenerative braking. Beyond that, friction pads must supply all the rest.

Friction pad braking is also needed anytime rough or loose surfaces or potholes cause regenerative braking to cut out.

That is a serious exaggeration.

 

That's what I used to think, too.

 

If doing regenerative braking stronger than that, then where is the power going? The battery can accept only so much.