'B' When slowing at stop lights.

there's no need to put it into b mode. i'll bet you can't find it in the owners manual.

 

some say there is a benefit, but i have a hard time believing it's worth the hassle. i think pulse and glide gives you the most bang for your buck.

 

For stops from moderate speeds like 45 mph in flatish terrain, definitely don't bother. NOT using "B" charges the battery most. "B" is to purposely waste energy on long mountain descents that fill up the battery, or possibly on a downhill stop from high speed, especially if the battery is already hot. Best to stretch out your stops as long and gentle as possible, traffic and time permitting.

 

You weren't wasting time if you'll use descending hills taller than a 10 story building. Your traction battery will last an extra 10-20 years on top of the expected 20-30 years.

"B" on hill descents measurably helps the battery stay cooler.

Bob Wilson

 

…one other useful (?) feature of using B is that since the brake-lights will not be activated, B will annoy the hell out of anyone following so close up your chuff that it might just make them back-off (use at your own risk!)

 

It is not clear where you read this, but it was not in any Toyota documentation. MANY automotive reviews do contain this misinformation however. (They assume B stands for Battery, I assume B stands for engine Braking) Under very select speeds under 24 MPH and above 7 MPH, B may charge better than D, but there is not much energy to save that slow. better to focus on safety in my opinion.

B under the D in the Drive gears? | PriusChat

 

See, you've brought out the B mode trolls. Myself included.

Reserve B mode for mountain descents. Other'n that: put it in D and fugedabout it.

 

I pulled out the handy Quick Reference Guide:

The *engine brake* is equivalent of downshifting. Shift to "B" when engine braking is desired (i.e. downhill driving, coasting to a stop, etc.)

And in the Owner's Manual:

Shift Position Purpose for B -- Applying engine braking or strong braking when the accelerator pedal has been released on steep downward slopes, etc.

When shift position B is selected, releasing the accelerator pedal will apply engine braking. The vehicle can be accelerated even when shift position B is selected.

When the vehicle is driven at high-speeds, compared to ordinary gasoline-fueled engines, engine braking deceleration is felt less than that of other vehicles.

* For good fuel economy and noise reduction, the D position should usually be used.

 

^ The phrasing in the Owner's Manual seems to compound the confusion. Doesn't do it justice.

 

My comments above, disappeared. I was saying that I need to go to the same steep hill and practice my B mode. It didn't seem to work right the first two previous times. I never slowed down. Had to hit the brakes hard.

 

"engine braking deceleration is felt less than that of other vehicles."

 

I started off from a stop sign at the top of the hill. Just started rolling in B mode, with my foot off the gas, and foot off the brake... and I zoomed down that hill. Had to jump hard on the brakes. I did hear the engine rev but never slowed down. Yeah. A bit confusing. This "B" mode thing is my last pet peev to conquer. I understand the EV mode now, thanks to pakitt.Back to the drawing board tomorrow.

 

The b mode isn't going to regenerate as much electricity as the brakes, just check the gauges, the brakes are always better, butt.. when descending a gentle 5 mile incline the b brake is good, it won't work well on long "steep" inclines, but the brakes work well at all speeds on all inclines, and they regenerate electricity until the vehicle is below 21mph.

 

I only use B coming down a local ski mountain, and it get's freaky: engine revs pretty high. I push it back into D during near-level stretches. When in B when you apply brakes I find revs go up even more. My sense is the engine braking increases with speed, but not sure. One way to get a feel for what's happening: shift back to D, it should start to roll more freely.

Even with all this the battery is full-to-the-gills by the bottom, so full that I've seen it stay in EV with the HSI indicator a bit beyond medium.

 

B is for "engine Braking" and nothing else, which means, when not accelerating, the ICE is used as an air pump (like in all regular cars). Using B to brake normally is a waste of energy, energy that could go into the battery in form of current instead of hot air and metal in the engine. This lowers the MPG because you cannot use that energy anymore to drive the electric motor afterwards (the battery is a buffer of otherwise wasted energy). As long as one brakes by filling the CHG area in the HSI indicator, and doesn't press the brake pedal once the little area is filled beyond that, the mechanical brakes are not used. And you are generating current for later use. If you are in B it all goes wasted.
BTW: if you are in B and use the brakes, you do regenerate some energy, but less than normal because the engine acts like as if you had already reached a full CHG area and you are braking more, when in fact you are not braking that much to justify, in D, the usage of mechanical brakes already.

In all regular driving use D.

B is to be used only when one doesn't want to stress the mechanical brakes (that could lead to failures and overheating), when going down very long or very steep slopes.

BTW, if the battery is full, the Prius starts going into a sort of "B" mode by itself, as it has to stop generating electricity to avoid over-charging (?) and convert the kinetic energy in something else - that is, compressing air in the engine, like all cars do...The only difference I have noticed, is that when the Prius does that in D, it is not as aggressive (at the beginning) as B would be. Otherwise said, in D engine braking is used to avoid over-charging the full battery. In B, it is actually to brake, regardless of battery charge (hence, the braking is more aggressive).

I also use B when I am extremely lazy and I don't want to move the foot from the accelerator, and I want to brake for a very short period (couple of seconds maybe), e.g. when about to reach a speed camera and need to adjust the speed faster than what the "simulated engine braking" would do, when simply not accelerating in D.
BTW, why do they keep that still today, is beyond me. If I don't press the accelerator, the car should just slide like in N. And brake itself to a stop, when speed due to friction goes down to 0mph. Like the i3 does.

Last but not least, if you are in B, don't worry about the engine making a lot of noise and worry about "breaking something". The engine is not burning fuel and compressed air generates far less heat than exploding fuel. The cooling system is active, so there is plenty of cooling going on to keep temperatures at their nominal levels, and no charging is done and currents are really low, so the whole power conversion and electric motor driving is essentially off.
Braking down a steep slope in B, when regular braking is not enough anymore or not desired, may sound horrible, but it is the best thing to do.

 

Does anyone have a video showing the progress to 8 bars, then "full," then "really truly full," with RPM readout and display of how much regen is happening the whole time?

 

Hi All, I commute over a small, 1,200' mountain pass every day.

B-mode definitely slows the car down a great deal more than Drive does, and it charges the battery until it's full (I'm not saying it charges it more than in Drive, but it does charge in B with gas off). When the battery's full, the engine braking come on with a vengeance. If i put it in D at that point, the engine-braking stops, and the car speeds up.

Does it hurt the Prius at all to keep it in B for the full descent, even after the battery's full? My battery's always full about half-way down the west side of the pass.

Thanks, Dave.

 

The car knows how to handle excessive charge. It will spin the engine (without fuel) to create drag. Your battery will be fine.