Newbie question abput regenerative braking...

[tas7107]

We've had our '13 Leaf S about two weeks now. Really enjoying it. I'm curious about the regenerative braking though. When I am slowing down I have noticed that the amount of regen indicated on the dash really goes up if i rest my foot on the brake. What I would like to know is if I am barely applying any brake pedal am I slowing on regen alone and therefore taking the most advantage of it? Or does even a small amount of pedal pressure always engage the brake pads. Thanks, Terry

 

[UBUYGAS]

Yes.

 

[planet4ever]

Talk about an ambiguous answer, Lasareath! My understanding is that friction braking is blended with regen, so that a very light touch of the brake has a negligible loss from the friction brake, even though initially there is a momentary pulse of friction braking. TickTock has done some research on this, which I'm not sure I ever understood fully, and don't remember much of now. Here's a more recent thread on the topic: Max regen - at what point do mechanical brakes engage?

Note that regen itself has a very significant loss to heat (which, of course, is where the friction brake energy also goes). Energy conversion is never 100% efficient, and regen involves kinetic energy to AC electricity; AC to DC; DC to chemical state in the battery; chemical state to DC; DC to AC; and finally AC to kinetic. Some optimists here have hoped for 70-80% regen efficiency. Others here claim it can't possibly be over 50%.

Ray

 

[DNAinaGoodWay]

Well, yes, and yes, but not fully engaged, they just touch, ready if you should increase pedal pressure.

 

[epirali]

Talk about an ambiguous answer, Lasareath! My understanding is that friction braking is blended with regen, so that a very light touch of the brake has a negligible loss from the friction brake, even though initially there is a momentary pulse of friction braking. TickTock has done some research on this, which I'm not sure I ever understood fully, and don't remember much of now. Here's a more recent thread on the topic: Max regen - at what point do mechanical brakes engage?

Note that regen itself has a very significant loss to heat (which, of course, is where the friction brake energy also goes). Energy conversion is never 100% efficient, and regen involves kinetic energy to AC electricity; AC to DC; DC to chemical state in the battery; chemical state to DC; DC to AC; and finally AC to kinetic. Some optimists here have hoped for 70-80% regen efficiency. Others here claim it can't possibly be over 50%.

Ray

Interesting question is whether a longer light regen is better at capturing energy or a shorter stronger one.

 

[dweller92]

I found if I just release the power pedal and coast to the light or slow traffic I am regen small amount of power, I try not to use my breaks to much for wear, try coasting to a stop sign or light and you will see regen

 

[tas7107]

The for the response Ray. Although I did find Lasarath's funny :lol:

 

[lonelyp]

I would like some info on the difference in A and B mode braking?

Since they list B mode as standard equipment on the SV model What's the diff?

 

[surfingslovak]

The B mode is new in 2013. Although I don't have the technical spec or further details on this, I imagine that it behaves like regen in 2011/12 LEAFs or the 2013 S trim. The only difference would be the amount of braking resistance the motor offers, and consequently the regen power level.

Below is an older post from TickTock on the question raised by the OP. I think designing a smartphone app, similar to what Jim has done with LeafSpy, to help the driver to learn brake efficiently through audio or visual signals would be a worthwhile undertaking. It's not uncommon to see this type of training aids in other EVs and PHEVs.

Every-time you touch the brake pedal, regardless of how gently you drive, the friction brakes are engaged (at least momentarily). However, you *can* minimize it.

I hacked Gary's SOC meter so it chirps at me whenever friction brakes are applied (geiger-counter style proportional to the amount of energy being wasted with the friction brakes). It has definitely altered my braking style. I have learned that overshooting the target braking force a smidgen, and then backing off stops the application of friction the best. If you just slowly increase the brake force, the friction tends to stay on. Also, I've noted in the CAN bus logs that not only does application of friction waste heat, you get double-impacted because regeneration is reduced when friction is applied (exception during long downhill applications - regen can be made to stay at full along with friction if the brakes are applied long enough).

The highest I've ranked on CarWings is 4. However, I cannot figure out how the kWh number is related. I've had days with 5.6kWh but only ranked 3, and others with 2.2kWh and ranked 4.

Finally, don't be fooled into thinking you can feel the friction application. Before hacking my box, I though I could because there is a noticeable non-linearity in the brake response as you increase the braking force. I always thought that was friction being employed. Turns out the opposite. Friction started the moment I pressed the pedal and that non-linearity I was feeling appears to be related to entering max regen (although friction may or may not be engaged when you feel it).

Click to open

 

[planet4ever]

I would like some info on the difference in A and B mode braking?

I'm wondering if you might be confused, as several others have been, by the letter at the bottom dead center of the dash. It's just to the right of the shift position letter and the (sometimes present) ECO indication. That has nothing to do with braking; it's just an indication of which of the two trip odometers (A or B) is currently displayed. The big letter in the box, B or D, is what tells you whether you are in B mode or not. In a 2013 SV or SL you switch in or out of B mode by moving the shift selector to Drive when D or B is already selected.

This is confusing, because in the 2011/2012 models, and also in the 2013 S model, that same action is used to switch in or out of ECO. The manual even describes it that way in section 5. Their description is (approximately) right for the S model, but not for the SV or SL. Switching ECO on or off with the SV or SL is done using the ECO button on the steering wheel, not with the shift selector.

Ray

 

[stjohnh]

As Ray said, there is no B mode on the S. We have both the 2013 S and SV. The B mode on my wife's car is nice, but not manditory. It is nice to have extra instruments to learn efficient driving techniques, but not manditory.

For efficient driving, but not hypermiling, and w/o extra extra gauges you can:

1. Keep your speed constant, with very gradual speedup from stop and anticipating slow downs well in advance, using the Power Dots on the dash, try always to keep no more than 2 green dots and 2 white dots. It is impossible to do this all the time, but in city driving, you can do it most of the time.
2. Never use your brake pedal unless you are at less than 10 mph and need to stop (or it is an emergency or you have planned your stop poorly).
3. If you drive in hills, max speed up is 45, max speed down 55 (use regen if going over 55 on dips).
4. On S, use ECO. On SV/SL, use ECO or B or B-ECO