What is going on in the B mode ?

It's using the ICE as a engine brake.......it will also charge the battery......down side is it won't go into EV when u stop moving so it will kill ur mpg.

 

Here is my last attempt to explain B mode: B under the D in the Drive gears? | PriusChat

 

B is the logical equivalent of selecting first gear in a normal vehicle. As you noticed, this results in a lower gear ratio which causes the engine RPM to speed up, causing more drivetrain drag to slow the vehicle down.

The battery is not charged faster when in B mode because some of the regen energy is being put into revving the engine faster than otherwise required for a given vehicle velocity.

Unless you are descending a very steep hill for an extended distance and need to control your speed by shifting into B, there is no need to select that gear position.

You would not use B for an extended period, for the same reason that you would not drive a conventional vehicle in first gear for an extended period. That practice results in excessive fuel consumption and unnecessary drivetrain wear.

 

True but you are losing some regeneration, which would have increased your MPG. B Mode wastes more energy creating heat, regeneration wastes less creating electricity.

 

The Prius will go into B mode automatically on a long hill as a protective measure, if the batteries are full green bars and starting to get hot from overcharge. I prefer to select it manually before this happens.

 

The 'automatic' engine compression braking on long hills is not at all equivalent to manually selected B mode. It is much weaker. If I depended on it on some hills on my route, I'd be smoking the brakes and staring down those runaway truck ramps at speeds well above the speed limit.

 

B mode is for going down long hills. The manual warns you not to leave it in B once you are down to the bottom. (In a Gen 2, you can't use Cruise Control in B mode)

Code:

Shift position Function
P Parking the vehicle/starting the hybrid system
R Reversing
N Neutral
D Normal driving*
B Applying moderate engine braking when driving
down hills or on steep slopes
 
*: For good fuel economy and noise reduction, the D position should usually
be used.

 

Suppose you are driving at the speed of 50 mph on level terrain, or driving uphill, while the gear selector is in B. Do you think that no fuel is consumed under those conditions?

If you are coasting down hill while in B, depending upon vehicle speed, it is possible that no fuel is being consumed, but some of the regen energy is being wasted by spinning the gasoline engine at a faster rate than necessary.

 

Try and avoid it unless necessary. It will run ice and lower MPG and the Regeneration is not that good.

The advantage of the B Mode is if you are on a long downward drive i.e. coming down one of those huge Rocky Mountains it will keep the brakes from overheating.

 

If the manual says that it's a poor translation. "B" will not damage anything. It *does* reduce fuel economy. The manual is trying to say, "use it only when needed", that is, when going down a long grade.