B mode braking with sport shift

Never underestimate the owner's manual as another source of good information. It has never said that B mode would maximize regen. It does tell you it may decrease fuel economy if overused.

If you're at the top of a good long hill you know will max out your battery charge, you may as well start in B at the top. It doesn't eliminate regen, but caps it at a smaller limit, so the battery will still be fully charged by the bottom of the hill, just not as violently.

In contrast, even light use of the brake in D can pour quite substantial currents into the battery under the right conditions.

-Chap

 

I have never heard what happens when the battery SOC is full while regenerating.

 

Regenerating stops.

The friction brakes take up the slack, and in some circumstances engine braking is also brought in, even when not in B. My Gen 3 will routinely use it when on cruise control for a long descent, for example.

-Chap

 

Using Sequential as B on the Camry hybrids means better control, and it could provide more deceleration than trying to stay in regen while on the brakes in D.

 

I thought it would be useful to clarify that while in “B” the engine will spin at a higher rpm while coasting, the same as downshifting with a traditional transmission, the engine is effectively off. Almost since the advent of EFI and port injection in the late ‘80s, all cars go into decel fuel cutoff. The engine becomes extra drag to slow the car down, mostly due to compression, but the fuel injectors are off. It’s uskng zero fuel even though it’s spinning a moderately high rpm. The generic qualifications for DFI is foot off the throttle, usually a short time limit after the throttle is lifted, not more than a couple seconds and sometimes near instant, rpms above idle speed, and vehicle speed. The RPM and vehicle speed settings are to make sure should the driver suddenly upshift, or nail the brakes and reduce vehicle speed and rpm quickly, there’s enough time to fire the injectors and “catch” the idle without it dipping below normal idle speed or stalling. Obviously firing the injectors off happens in miliseconds but the computer has to have a lead on the engine to prevent any sort of perceived stumble and/or vibration which is also more noticeable as rpms decrease.

The mileage you get using “B” will be determined by your experience with your car. It took a lot of experimentation in the Prius on my 240 mile round trip to see how to get the best mileage when descending a steep 12 mile section. I use cruise control and it’s decel function held down on small hills and even on the hwy and in the city to maintain my speed and slightly lower it and this uses regen to do so. More regen than coasting but less than the max you get from the braking regen.

On my drive, the battery is quickly topped off before I’m 1/4 of the way down. I use B now because I know my battery will be topped off several times over so even if it takes longer it’s fine. There’s one spot where it levels out for 1/2 mile and with the topped off battery I’m able to use just electric to maintain speed.

Also, cruise control seems to use a fair amount of regen to keep the car from gaining speed downhill and once the battery is topped off it automatically does the same thing as “B” mode by “downshifting” to give the engine more leverage on the wheels while the engine is using zero fuel. This is a nice option because you don’t have to think and it tops the battery off first then goes to engine braking. Rarely on a particularly steep section I’ve rarely had the cruise use both methods to hold vehicle speed steady. Just another option. I can see how if you were in B and on and off the throttle where the injectors were turned back on while at a high rpm or the battery could have gotten topped off but didn’t because you used engine braking it could hurt. So many possibilities. Luckily I’m a nerd with a long drive 3-6 days a week and I’m always trying new things out of boredom. The downhill part of my commute is a nobrainer since it’s so damn long but around th city I experiment still between using cruise as a regen brake vs coast with minimal cruise and then full regen with the brakes.

I apologize if the fuel cut decel info is already known but I’ve seen posts from months ago before I registered that talked about the potential for using more fuel due to the engine revving up which is not the case.

 

Hybrid and EV Regenerative Braking Systems

Late in this video it is explained how reverse works, enjoy.

 

Just want to add that the emission controls are a potential limit of deceleration fuel cut off(DFCO). Fuel might get burned if the catalytic converter temp drops too much.