The "B" Gear

Sure - on any steep descent long enough that it's going to fully charge the battery anyway, B mode lets you enjoy a bit of braking effect to keep your speed down, while also treating the battery a little more gently (by being quicker to twirl some of the energy off in the engine, and charging the battery a little less aggressively), and the battery's still going to have a full charge by the end of the descent.

 

I use 'B' a lot on the downhill side of long steep passes. On the uphill side, outside of a few not particularly relevant corner cases, it is no different that 'D'.

 

I'm at the end of my experiment with how far you can wear the brake pads down without damaging the discs and the breaks are getting noisy and ready to replace so I've been using B-mode at times when I hear them make noise, but I only use the brake pedal when it's not in B-mode because there's no regen braking in B-mode and that would be the opposite of going easy on my brakes. So far discs are still smooth, brakes still work great despite the periodic noise.

Another cool thing about this experiment is I'm getting a much better sense of the percentage of regen braking versus percentage of mechanical brakes in different driving scenarios because I if I listen carefully I can hear it.

It almost sounds as though mechanical brakes are used a buffer to smooth out / strengthen the braking response when regen braking is primarily used.

As in folks like @ChapmanF and others have explained to us many times that it's far more complex than just saying you only use mechanical brakes below 6mph and in B-mode. I wonder if anyone has charted out the mechanical vs regenerative braking interaction? There's definitely lots of interaction going on that's for sure.

 

Is too. Only the balance changes: when you brake, the car can always send some of the power to the battery, some to twirl away in the engine, and some in the friction brakes.

In D, it prefers into the battery until the SoC is above 77% or so (I'm talking from a Gen 3, NiMH here), then tapering off the battery charging and sending more to twirling the engine; all engine twirling by 80%.

In B, it sends more of the power off to engine twirling earlier, so the battery just isn't charged as aggressively.

There are a couple ways you can get all-friction braking when you might not expect it. Any time the brake ECU thinks you are braking "urgently", it skips all the regen negotiations and goes straight to friction. One trigger condition for "urgently" is how fast you've mashed the brake pedal. Another one, at least in Gen 3, is it's considered "urgently" any time you use the brake pedal while cruise is on. It cancels cruise, of course, and also uses full friction, no regen. When that's not what I want, I just cancel cruise first by pulling the stalk, and then brake normally,

Since somebody's infinite wisdom decided not to allow cruise in B mode anymore (in Gen 1 you could), that particular case should never arise in B mode anyway.

 

I use it a lot when in town or driving in downtown Portland.

 

Your Prime has some added functionality in its EV-B mode, that is not present in the OP's or anyone's non-Prime.

In the non-Prime, the main thing it will do in such downtown driving is sacrifice a bit of MPG, for no meaningful benefit.

 

Use it for decelerating like a manual car. Sport mode mimics a manual decelerating as well.

 

We always use the 'B' selection. It recharges the battery faster and reduces need to use the brake pedal for us.

 

It does less charging.

 

Your Prime, in EV-B mode, can do things that a regular Prius, such as OP's, cannot do.

A regular Prius does not have EV-B mode (aside from a corner case at very low speed), instead using a different B mode (HV-B in a Prime) that diverts some energy away from the battery and into the engine to be dissipated in compression braking mode.

 

... or in engine-vacuum braking mode, where most of the effect comes from in our gasoline engines sucking air across a closed throttle. They also do compress the air on the upstroke, but (a) there's not much of it (because of that closed throttle), and (b) it's still there for the downstroke and pays most of that energy back.

Diesel truck engines do it differently, compressing more air (no throttle on the intake) and popping it off through the "Jacobs brake" mechanism at the top of the stroke, when all the compression work has happened but before it can get paid back.

 

... the technically correct description for what, in common vernacular, is labeled as 'compression braking' in gas engines.