Regenerative Braking - D or B ?

B mode used engine braking in previous generations as well as far as I know.

 

i meant this thread, but we have a new president as well.

 

Hmm, had to look back two-plus years and four pages in this thread to see the bisco post this was a reply to.

Looks like bisco was replying to this:

and that was correct at the time (and hasn't changed in two years) when the car is a PHEV (Prius Prime or Plugin of gen 5).

The "Regeneration Boost" mode is described in the owners' manual for the PHEV models. It does not appear in the HEV manuals. The exact behavior of B is not identical between HEVs and PHEVs.

In either model, B will use engine braking when necessary (just as D will) to avoid overcharging the battery. It is not forced to use engine braking only, and will use some regeneration when the battery charge is low enough.

In the HEV, the B mode will immediately add a bias toward less regen and more engine braking, so it can be used on long downhills to reduce stress on the smallish HEV battery.

The larger PHEV battery does not have the same need to be babied, and the PHEV's B mode does not have to use engine braking as much (though it will, of course, still use it when conditions warrant).

 

My two points were:

1. The regenerative boost mode in the Gen 5 PHEV only changes the brake-pedal and accelerator-pedal modulation to enable one-pedal driving. With more boost, you need to press the brake pedal less or release the accelerator pedal less to achieve a given amount of deceleration. The boost level does not increase the maximum regenerative power or at what actual deceleration friction brakes are needed. Therefore, more boost does not result in more charge, which is the time integral of the current, going into the battery as the OP thought and you quoted. Chances are that, it results in slightly less charge going into the battery because the higher the regenerative power, the less efficient regeneration will be. Again, it only effects the pedal modulation: with more regenerative boost, you need to use the pedals less to achieve a given amount of regenerative braking.

2. In my Gen 4 PHEV, the B mode substantially worsens the fuel economy even when mostly cruising. This is what I have observed. Once, I had accidentally switched into the B mode without realizing and my fuel economy was so bad on the freeway that I thought my car had suddenly broken down. The owner manual for the PHEV also instructs not to use the B mode unless needed so that you get better fuel economy.

3. My third point is a question. Obviously, a larger battery can take in more current and hence more regenerative power. But does Toyota actually allow the PHEV models to use more regenerative power than the HEV models? Also, in terms of the battery C-rate, how many Cs full regenerative power uses for the Gen 4 PHEV, Gen 4 HEV, Gen 5 PHEV, and Gen 5 HEV? Does anyone know?