is the b shift worth using?

only if you're coming down a long steep hill and you don't want to overheat your brakes.

 

B under the D in the Drive gears? | PriusChat

 

I use it when in EV mode (only) to pump a little extra regen into the system, particularly at higher speeds. Careful of tailgaters though because I'm pretty sure the brake lights don't come on when shifting into B and it drops your speed significantly. Also you can't set your cruise if you leave it in B.

 

This is a huge misconception. "B" mode is engine-braking mode, meaning that your momentum is being wasted on turning the engine over, using its compression for braking. All the energy going into turning the engine over could otherwise be spent regenerating electrical energy.

The only feasible scenario for using "B" is if you're coming down a mountain on a long, steep descent. Otherwise, use the brakes and use that momentum for regen.

It's sad, but none of the salesmen I've spoken with have a clue what choosing this shift option does. If they even read the manual, it's all right there.

 

I agree with Squirt. I haven't yet figured out how to get Torque to tell me what the brake system is doing, but to my knowledge you aren't using the friction brakes until the charge bar is at the max. I tried "B" mode down a long hill on my street and was disappointed to see the car leave EV mode immediately and spin the engine up. I was still showing about halfway on the charge bar when this was happening, but I believe lots of energy was being lost to the spinning engine.

I do in this car what I would never do in anything else, which is ride the brakes on down. I gain almost 10% SoC on that hill, and I'm enough of an energy miser to want every bit of it!

 

I agree with Bisco.

 

If you keep the HSI in the right 2/3 of the regen area you are not using your brakes and the B mode is only wasting energy that would be used for recharging the battery. For more braking the B mode is probably useful however you should use a Scan Gauge to determine if you are actually using friction brakes. My experience for an over 7000ft elevation change (includes some uphill and level) is no friction braking if you are careful to stay under 62 mph. That nicely fills the battery. The ICE will automatically go into compression braking at speeds over 62 mph or if the SOC reaches the maximum 85%.

 

agreed, only necessary if friction braking is needed to maintain speed limit or after battery is full.

 

interestingly, this question has been debated for over 10 years.

 

Two reasons: Toyota was too honest to label it L (no lower gears are involved) and nearly every automotive editor has misinterpreted B to mean battery, not braking.

If they had labeled it L no one would use it, just as no one uses L on any other transmission.

 

I was under the impression that B mode only engages engine compression braking if the battery is full. (CaliforniaBear, are you saying that if you are going faster than 62mph, that compression braking will kick in? Is that only in B mode? Can't the ICE turn without compression to keep the MG1 rpm under control above 62mph?) For the regular Prius, this happens very quickly due to the small battery (which may well be "full" already, depending on where it is in the HV charge/discharge cycle), but with the much bigger battery, the Plug-In can go a lot further downhill before having to resort to engine braking. Also B mode causes the regeneration to be more aggressive, so if you just let off the throttle, it will be "braking" more. If someone can quote a Toyota document specific to the Plug-In that contradicts this interpretation, I would appreciate seeing it.

It IS true that B mode has nothing to do with the friction brakes.

 

Oh yes, I use "B" all the time with irate drivers!

 

That's only true when you're NOT in EV mode. While in EV mode, it increases the amount of regeneration slightly. The engine never spins. The same effect can be achieved by slightly depressing the brake pedal. When in HV mode, the B behavior is the same as a regular Prius.

 

Above 62 mph the ICE revs up to 1400 rpm or so. Is it doing braking, I'm not sure, it could just be adjusting the relative speeds of the MGs.

If the B mode slows down the car which would otherwise be done by some other means, eg the friction brakes, what would you call that process?

Does anyone actually have this all figured out?

 

Tracksyde nailed it.

 

So in B in HV mode, the PiP will always kick in engine braking? That is, it won't trigger regeneration, like it would if you lightly pressed the brakes?

I wish Toyota would document this. But apparently they consider this sort of thing trade secrets that they would rather competitors not know.

 

Actually the owners manual is very specific about regeneration happening in both B and D regardless of whether in EV or HV. But it does use ICE compression in HV mode. I was going to provide a video showing the differences when I got a chance.

 

Tracksyde, so if you're in EV mode and going downhill and shift into B the engine does not spin. Under 62 mph of course. Correct?

 

Yes.

Although, from my experience, if you are even CLOSE to regenerating to "max" capacity, hitting B will start the ICE (for example, if you're at, say 80% SoC and you're' going down a hill and you hit B, the ICE may start because you're so close to the max of 85% SoC).

I actually use B every day, multiple times a day.. sometimes I forget and I drive in B, although you'll know right away when you lift off the throttle (my friend drives around in his Volt in their version of B.. and on the Tesla Model S, you can actually modify the amount of regen, on the big screen, when you're off the throttle)

I could use my brake pedal, but I dont like the idea that it looks like I'm riding my brakes (personal thing, I guess).