Just wondering...

 

isn't this called Engine Braking? (vs. breaking?)

 

I kant spell, sorry!

 

There's that guy here who drives in B mode all the time but I guess he hasn't voted yet.

 

My understanding is in the Brake mode the generator turns many times faster on steep grades or when we use the brakes. Thats usually up to maybe 35 miles per hour. After that the engine takes over the for the braking.

The engine runs anytime your in the Brake mode. There is a point where the generator can provide braking then the engine takes over.
I never have tried the braking mode above 60 miles per hour. Actually I don't recommend it. Best to gently use the brakes at those speeds.

I find it best to gently press the brakes when going down a faster grade. Slow about 5 miles per hour then ease up to allow the generator to cool. If you press hard enough you may be using your physical brakes. Once the battery shows 100% then the engine would do most of the braking. That may include the physical brakes.

 

You can shift to "B" at any speed without risk. While the ICE will speed up (with fuel cut off) to brake the car, the engine speed is computer controlled so it won't over-rev.

 

Let's be clear on what happens in the different cases:

1. Coasting in 'D' under 65 km/h (~41 miles per hour) uses pure regenerative braking by MG2 — in principle all kinetic energy is recovered into the NiMH battery, as long as it isn't "full." In practice there are conversion losses, so this is less than 100%. Only mild regenerative braking is applied, simulating a "normal" car's behavior.
2. Coasting in 'D' above 65 km/h (~41 miles per hour) uses a combination of regenerative braking and engine braking — the electrical energy generated by MG2 is used to both charge the battery and to spin the ICE via MG1 (~1000 rpm) giving mild regenerative + engine braking (no gasoline is burned — this is fuel-cut spinning of the ICE). The engine-braking component is wasted energy. Again, not much braking is applied, simulating a "normal" car's behavior. [The ICE is spun to protect MG1 from over-revving, and this has been discussed in detail in other threads.]
3. Coasting in 'B' at any speed uses a combination of substantial regenerative and engine braking — more electrical energy is used to charge the battery as well as to spin the ICE faster (1000-4000 rpm depending on the car's speed). Again, no gasoline is burned (fuel-cut spinning of the ICE), but the engine-braking component is wasted energy. This is done to simulate the substantial engine braking one gets in 'L' in a "normal" car.
4. Applying the brakes gently in any of the above cases increases the regenerative component of the braking effort (provided the battery isn't "full"), and so increases the "lossless" part of the braking. Harder application of the brake pedal will bring the friction brakes into action, and they are, of course, always lossy, converting the car's kinetic energy into heat.

The conclusion I draw is that cases 2. and 3. deliberately waste energy, whereas case 1. doesn't. So, I would only use 'B' instead of 'D' when descending a steep slope if braking gently in 'D' isn't sufficient to keep the car at the desired speed. Braking gently in 'D' is purely regenerative, and in principle lossless, and is what one should normally use. If harder braking is necessary to control the car's downhill speed, then the friction brake pads ("lossy") would normally have to be used, and then using ("lossy") engine braking in 'B' instead of heavy braking in 'D' would be sensible (and would extend the life of your brakes). Then, and only then, would I use 'B.'

Stan

 

To supplement, the use of B would be a good choice in an emergency situation as well. Such as use on slick road to reduce the chance of wheel lockage (not a word). Although this has been debated.

 

The idea of "free" or "internal" braking was thoroughly debunked. Under laboratory conditions, using B mode to decelerate may not cause the vehicle to yaw.

 

One unfortunate(?) aspect of "B" (it isn't "L" since there isn't any "Low gear") is that it gives maximum effect with the accelerator not depressed and the engine braking is reduced, still without consuming fuel, by pressing the accelerator. Besides being weird that the engine slows when you press the accelerator, it means that to achieve maximum recovery of energy with the regenerative braking one would have to press the brake and accelerator simultaneously. I hope that's not too confusing! So, yes, your best strategy is to stay out of "B" unless you need more braking than the regenerative braking can provide.