Regeneration in B

Man, we had a huge thread on the details of B mode just a few weeks back...but I know how lousy the search function can be at times.

As usual, the answer is "it depends".

B-mode has few legitimate uses. If you're unsure whether to use it or not you're usually better off not using it at all.

Here's a quote from a thread by Wayne Brown that should help answer your question:

`D' DECELERATION vs. `B' DECLERATION
Generally, if allowed by the HV Battery ECU via SOC level, `D'
deceleration will provide about 20 Amps worth of regenerative energy
& generally, `B' will provide close to 30 Amps. Most people seeing
these two values instantly rationalize that it is a no-brainer
that `B' is always the better choice. Ironically, `B' is almost
never the better choice. Now let's see why.

`B' INVOLVES UNECCESSARY ICE FRICTION & WASTES ENERGY
Most people know that `B' causes the ICE RPM to spin up and then
uses the rotational friction provided by the spinning ICE to assist
in decelerating the Prius. Many people feel that the extra 10 amps
generally provided by `B' offsets the frictional losses that the ICE
is wasting as heat. This simply is not correct. Many people figure
that using `B' will minimize brake wear. In the majority of
deceleration events, this too is not the case.

`D' or `D' + BRAKING IS ALMOST ALWAYS BEST
In almost all cases, Prius operators, especially those with HSD
equipped Prius, should shun the old idea that their brakes need to
be protected by choosing `B' over `D.' In almost all cases,
choosing to use `D' + brakes until the SOC is full, will not
increase brake wear whatsoever. In almost all cases, using `B' will
waste a significant amount of ICE spun energy that could have been
captured if the operator had chosen to use `D' + braking instead.
In almost all cases, using `B' causes unnecessary wear to the ICE.

USING `D' + BRAKING TO MATCH DECELERATION OF `B'
Using `D'+ Braking to match the deceleration that `B' alone provides
captures significantly more energy. Using D+ Braking in HSD
equipped Prius to match the deceleration of `B' alone will not cause
any wear to the brakes whatsoever.

`D' + BRAKING IS EVEN BEST IN THS EQUIPPED PRIUS
In THS equipped cars, hundreds of very intelligent users have tested
for thousands of miles & determined, very clearly, that the energy
captured using D+ Braking far offsets the minimal brake wear that
they get in their THS equipped cars.

WHEN, IF EVER, DO WE USE `B'
In almost all cases, choosing to use `B' after the SOC `tops off,'
is pretty much the only time that using `B' makes any sense at all.

Entire Thread

Short and sweet answer is that you can regenerate more with just the brakes than with B-mode, but occasionally B-mode will perform better...but those conditions are rare.

 

Below 20mph B does not spin the ICE...that is correct assuming the ICE wasn't spinning when you entered B-mode. If it was spinning, even below 20mph, at the moment you enter B-mode, B-mode will not allow the ICE to stop spinning...not until you're stopped--at least that's my understanding.

But the amount of regen is less than is possible (note I said possible) with manual braking. The problem is that at those speeds very little regen is possible in either case unless you're maintaining that speed down a very long slope.