I understand how the electric motor engages to help capture the energy when I have the electrical braking engaged. I notice the gas engine rpm's increase quite a bit, ~4,500 rpm depending. How is the engine rpm tied to the motor braking?

 

It's a common misconception that the engine brake (shifting to the B gear) helps regenerate the battery, but this isn't true. It's real engine braking, where the car would downshift to a low gear. In the case of the CT, the transmission holds the engine at a high RPM to simulate a low gear to keep the car from increasing in speed as it moves down a steep grade.

While I'm not sure if the engine is actually burning gasoline when this is happening, or cutting fuel the way it does when you coast, engine braking isn't fuel economical.

If you want to use the regen brakes, you just use the brake pedal, but only within the "charge" meter in the gauge cluster. Anything more and you're using the friction brakes (normal brakes).

 

Thanks as that's what I was thinking too. I've noticed when you apply the 'B'rake, even when the car is in EV mode the car will exit EV mode. I often wondered if I should just let the car coast into EV mode (<=42mph) and apply the brakes as you mention. It makes sense now...

 

Here's a simple test to verify that your car will regen/brake more when in "B" mode:

While coasting in normal mode (not sport or ECO) and with no brake applied, note where the pointer is on the "charge / eco / power" gauge.
Pull on the gear shift lever (still coasting) to engage "B" mode - you will see the pointer indicate more regen charging
and notice the sensation of more braking...

 

This may happen at low speeds, but not at higher speeds. The rotation of the engine is actually part of the transmission. It's one of the reasons why the engine keeps moving even if you coast for a long time instead of it turning off completely. That's why using B gear (engine braking) will use the engine as part of the transmission to hold your speed without the need for braking.

The following is pulled directly from the 2017 CT 200h manual: