[B] - "Engine Brake" -- when to use

Is there actually real benefit from using B-mode compared to brake pedal in normal situations, like going downhill on a mountain side or long underwater tunnel etc. ?

When the battery is full, will the disc brakes be used instead of generating more energy (and somehow throwing it away) ?

 

This question has been asked and answered many, many times. A quick search will save everyone time. That said, the answer to your question (again ):

B mode is only useful on long downhills that will exceed the capacity of the HV battery.

Once the HV battery hits the high limit, the only sink for regenerated energy is engine braking. The Prius spins the engine as a big air pump, throwing away energy. If more braking is required, the Prius uses the friction brakes. This happens in normal operation as well as in B mode.

B mode differs in that engine braking starts immediately, without waiting for the HV battery to fill. This means that there are two sinks for the regenerated energy: the HV battery and engine braking, i.e., spinning the engine as an air pump. This allows for higher regenerative braking for a longer period of time, forestalling the need to use friction brakes.

Tom