Max regen - at what point do mechanical brakes engage?

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BestPal

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Location
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Sorry if this had been discussed and cleared before, the search didn't return anything. I want to understand optimal regen performance under normal braking. Is it safe to assume that brakes only engage after max regeneration has been reached (all circles on regen meter)? In other words, if i'm coasting to a stop in eco mode and seeing 2 circles on regen meter, if I slightly touch the brakes will the Leaf increase regen to 3 then then to 4 circles (max it out) before applying mechanical brakes or does the brake pedal automatically actuate hydraulics and more regen is just added on top of that?
 
whoa! not that cut and dried.

in my experience, the higher the speed, the more regen is available. I frequently am unable to light up regen circle 4 and 5 if my speed is low like 30-35 mph even when they are available.

as far as friction brake cut in, that is even tougher. the point at which the brakes engage is based on how fast you are going and how fast you hit the brake pedal and how hard you push after initial pressure.

I have hit the brakes a bit harder than I wanted before and got a medium regen response and tried to push harder to increase regen and was unable to. my only option is to release the brake pedal completely and reapply

best advice; pretend the brake pedal has an egg on it. push it gently
 
Generally you ask for some braking "force" with the brake pedal.
Whenever possible, the LEAF tries to satisfy that request with Regen
slowing, but as the crow goes slower, less and less force can be
created with regen. Also, if the battery is getting nearer full, the car
reduces the amount of Regen (battery charging) that it will allow.

When Regen is activated by the car itself, it is pure Regen, limited
to what the car requests, what it could produce, and what it is
allowed to produce.

With braking requests from team brake pedal, the car usually/often
first generates a very little braking force mechanically, by getting the
brake pads to just barely touch the discs, so that they will be
"instantly" ready to supply a lot more braking force, mechanically.
Owever, the car tries to provide as much of the braking force as it can
with Regen, only applying more mechanical braking force when needed.
 
Just to add.... B mode on the 2013 is more aggressive than D. I'm pretty sure i see 4-5 cirlcles of regen for a few seconds at 35mph. Things appear to even out at around 15-20mph.
 
garygid said:
Generally you ask for some braking "force" with the brake pedal.

...

When Regen is activated by the car itself, it is pure Regen, limited
to what the car requests, what it could produce, and what it is
allowed to produce.

With braking requests from team brake pedal, the car usually/often
first generates a very little braking force mechanically, by getting the
brake pads to just barely touch the discs, so that they will be
"instantly" ready to supply a lot more braking force, mechanically.
Owever, the car tries to provide as much of the braking force as it can
with Regen, only applying more mechanical braking force when needed.

Intuitively I thought that that SHOULD be the case but wasn't 100% sure. Now, form engineering standpoint, how is this accomplished, are the brakes "fly by wire" so to speak and the car engages them after max regen is reached and when you ask for more braking, or the brake system is basically the same as any other car with direct mechanics (pedal) to hydraulics action and regen is a stand-by function and even a slight touch of the pedal does lead to SOME mechanical braking + give a computer OK for more regen? Any Nissan engineers here that could confirm or disprove or correct my assumptions?

Thank you!
 
TickTock has made some measurements on how this works and summerized them in this recent thread, which links back to his original post containing the measurements:
TickTock said:
I posted some initial observations in this thread. Short of the long is friction brakes are applied immediately and regen displaces it shortly later except in heavy braking. Once you cross a certain threshold that friction is applied, regen is backed off even if it was already being applied.

I love my chirp mod on my SOC meter. I doesn't chirp much anymore now that I am trained but occasionally I start to slide and it's there to remind me.
 
BestPal said:
"fly by wire"

They are conventional mechanical-hydraulic brakes like you find in most power brake setups, except the boost is provided by an electrical servo in place of a vacuum booster. Regen is "fly-by-wire"
 
BestPal said:
Sorry if this had been discussed and cleared before, the search didn't return anything. I want to understand optimal regen performance under normal braking. Is it safe to assume that brakes only engage after max regeneration has been reached (all circles on regen meter)? In other words, if i'm coasting to a stop in eco mode and seeing 2 circles on regen meter, if I slightly touch the brakes will the Leaf increase regen to 3 then then to 4 circles (max it out) before applying mechanical brakes or does the brake pedal automatically actuate hydraulics and more regen is just added on top of that?

At this time no easy way to determine exactly when mechanical brakes kick in.

In the not too distant future Turbo3 is due to release an update to his Battery App that will graph exactly when and how much regen/mechanical braking is used on every braking event and will be available in a graphical readout live at the time of driving. Should make an excellent braking coach. Keep your eyes and ears peeled and de-waxed.
 
Here is a very short video illustrating how friction braking is feathered in with regen. Bar graph on the top center display (to the right of the graph on the left CANary display) shows the total amount of braking force applied with the green portions indicating the amount of regen and the red indicating the amount of friction. Starting from 55mph, I modulate the break pedal slowly harder then softer and so forth. You can see how regen is diminished as friction is brought in. As I ease up, friction is reduced and regen is increased.

[youtube]http://www.youtube.com/watch?v=I-queMv9dks[/youtube]

(There is a 1080p version available under Settings if you view in YouTube)
 
TickTock said:
Here is a very short video illustrating how friction braking is feathered in with regen. Bar graph on the top center display (to the right of the graph on the left CANary display) shows the total amount of braking force applied with the green portions indicating the amount of regen and the red indicating the amount of friction. Starting from 55mph, I modulate the break pedal slowly harder then softer and so forth. You can see how regen is diminished as friction is brought in. As I ease up, friction is reduced and regen is increased.

[youtube]http://www.youtube.com/watch?v=I-queMv9dks[/youtube]

(There is a 1080p version available under Settings if you view in YouTube)

nice illustration and all the more reason why the B mode is such a valuable addition to the LEAF. A lot of people dont believe in one pedal driving but i consider it essential if you really want to get the full benefit of the LEAFs limited range. Its clear that touching the brakes will introduce some friction braking no matter what. Even on my 2011, i dont use brakes that much. With B mode, i should be able to reduce the usage just a little bit more.

i think Nissan was using this fact when boasting a big range and also the reason why it did not show up in Tony's Range tests
 
Interesting... sorry, I haven't had time to read all the regen discussion as I finally got my Leaf a week ago...

So, short of having a tool like TickTock's, what can we do to maximize regen? I don't really like driving in B mode (yet?).

To avoid using friction brakes as much as possible, should I just basically try to almost be at the max regen of the energy info screen? If I'm not on that screen, should I just try to be at the edge of engaging the leftmost regen bubble?
 
cwerdna said:
Interesting... sorry, I haven't had time to read all the regen discussion as I finally got my Leaf a week ago...

So, short of having a tool like TickTock's, what can we do to maximize regen? I don't really like driving in B mode (yet?).

To avoid using friction brakes as much as possible, should I just basically try to almost be at the max regen of the energy info screen? If I'm not on that screen, should I just try to be at the edge of engaging the leftmost regen bubble?

Using the energy screen helps with training your braking technique, but can be very distracting, so be careful where you use it.

Simply coasting in any drive mode will create regen without any danger of using physical brakes. So working on your hypermiling 'red light' techniques will help. If you don't like driving in B mode, why not use it decelerating to a red light, then switch back to D or eco once you come to a stop? Once you get over the thrill of the instant torque, you will find B mode more than adequate for everyday driving.
 
cwerdna said:
Interesting... sorry, I haven't had time to read all the regen discussion as I finally got my Leaf a week ago...

So, short of having a tool like TickTock's, what can we do to maximize regen? I don't really like driving in B mode (yet?).

To avoid using friction brakes as much as possible, should I just basically try to almost be at the max regen of the energy info screen? If I'm not on that screen, should I just try to be at the edge of engaging the leftmost regen bubble?

congrats on finally getting one! any details (or link) to share?
 
cwerdna said:
Interesting... sorry, I haven't had time to read all the regen discussion as I finally got my Leaf a week ago...

So, short of having a tool like TickTock's, what can we do to maximize regen? I don't really like driving in B mode (yet?).

To avoid using friction brakes as much as possible, should I just basically try to almost be at the max regen of the energy info screen? If I'm not on that screen, should I just try to be at the edge of engaging the leftmost regen bubble?
Seems strange to be making suggestions to someone who has been "here" so long but here goes:

Use regen only when slowing is needed. Coasting is usually more efficient so max regen is to be avoided unless significant slowing is required.

Example: the light up ahead turns red, coast until you either need to slow to a stop or the light changes and you can then speed up again. (I presume that it is obvious that this may not be practical in heavy traffic.)

Example: when descending steep hills where speed control is a safety or speed limit issue, use regen as needed to keep an appropriate speed. If it is safe, you can begin to coast near the bottom of the hill to keep momentum up. (If you can do this without the brake pedal, say in B mode, that is preferred because it eliminates any use of friction brakes.)


It is easier to drive this way in Eco, because the accelerator pedal is mapped to specific power levels: hold the pedal steady and it will keep the power level constant, whether it is 12 kW, zero (coasting), -7 kW (regen), or whatever level is needed to maintain the speed you desire (use the energy screen pie chart to verify this). With practice, you can control your speed with minimal use of the brake pedal or unnecessary regen. With use of B mode it ought to be possible to use single pedal driving much of the time, with use of the brake pedal only to hold the car still at a stop. But that would take some practice to get used to.

D mode is mapped differently from Eco. D seems to be constant acceleration, as opposed to constant power, and I find it harder to hold a constant speed in D, especially on undulating terrain. I also find that I tend to speed more in D, because the acceleration keeps going unless one backs off before reaching the desired speed, although one can learn to do that with practice. My impression is that most hypermilers, and many others, prefer Eco because constant power mapping makes it easier to modulate speed (and regen braking) precisely.
 
cwerdna said:
Interesting... sorry, I haven't had time to read all the regen discussion as I finally got my Leaf a week ago...

So, short of having a tool like TickTock's, what can we do to maximize regen? I don't really like driving in B mode (yet?).

To avoid using friction brakes as much as possible, should I just basically try to almost be at the max regen of the energy info screen? If I'm not on that screen, should I just try to be at the edge of engaging the leftmost regen bubble?

only way to do that is be in B mode. if you touch the brake pedal, you will start charging the braking system and seems to me someone has already shown that friction braking applies (however lightly) at first then backs off based on braking need.

but other than that, the real key is to try to adjust speed to avoid the changes in velocity. Having lived in your area, i do know that is a much tougher challenge than the sleepy hamlet where I live but I do daily "freeway coasting" here due to the traffic issues around JBLM (Joint Base Lewis-Mcchord)

But you had a Z before so guessing it would be easy for you to get used to going from N to D to B, etc... ;)
 
Interesting discussion...though as a newbie I have to read each thing 5 times to really understand it. Only had my LEAF less than a week and 110 miles, so it's all still very new. I have noticed the huge difference in how the car drives in ECO vs. non-ECO mode. I've also been trying to figure out the regen braking and how it all works. Like others have said, I notice that I'll get more regen circles at higher speeds...such as if I let off the gas at 50mph. But at lower speeds, coasting doesn't create much (if any) regen. Also noticed that with touching the brakes. At low speed, no regen circles light. I haven't dabbled too much in B mode yet.

So if I'm reading right, where possible the best way to get regen is to coast where possible? Learn to use the B mode to help slow the car?
 
Klayfish said:
Interesting discussion...though as a newbie I have to read each thing 5 times to really understand it. Only had my LEAF less than a week and 110 miles, so it's all still very new. I have noticed the huge difference in how the car drives in ECO vs. non-ECO mode. I've also been trying to figure out the regen braking and how it all works. Like others have said, I notice that I'll get more regen circles at higher speeds...such as if I let off the gas at 50mph. But at lower speeds, coasting doesn't create much (if any) regen. Also noticed that with touching the brakes. At low speed, no regen circles light. I haven't dabbled too much in B mode yet.

So if I'm reading right, where possible the best way to get regen is to coast where possible? Learn to use the B mode to help slow the car?

well the amount of regen surely has to do with the RPMs of the device (motor) creating the regen which would be higher at higher speeds so more regen at higher speeds is implied.
 
Klayfish said:
Interesting discussion...though as a newbie I have to read each thing 5 times to really understand it. Only had my LEAF less than a week and 110 miles, so it's all still very new. I have noticed the huge difference in how the car drives in ECO vs. non-ECO mode. I've also been trying to figure out the regen braking and how it all works. Like others have said, I notice that I'll get more regen circles at higher speeds...such as if I let off the gas at 50mph. But at lower speeds, coasting doesn't create much (if any) regen. Also noticed that with touching the brakes. At low speed, no regen circles light. I haven't dabbled too much in B mode yet.
Yes, if you back all the way off the accelerator you will get more regen at 50 mph than, say, 20 mph. The reason is that your kinetic energy is greater so there is more regen available; another way to think of it is that the motor is spinning faster so the magnetic fields generate more energy to put back into the battery.

However, when the battery is nearly full you may see that you get a bit more regen at slower speeds than higher ones. I presume that this is done to protect the battery or that it is a quirk in the regen algorithm. (Abasile first mentioned it I think, but I see it all the time also. Maybe it is the sort of thing one notices in the mountains.)
So if I'm reading right, where possible the best way to get regen is to coast where possible? Learn to use the B mode to help slow the car?
Not quite. Coasting, in most cases except at high speeds (high drag), is more efficient than regen braking followed by accelerating. Why? Regen is fairly inefficient because there are losses in generating the electricity, putting it back in the battery, pulling it out of the battery, then using it again to power the car. How inefficient has been the subject of much debate here and I don't want to revisit it. That said, it is obvious that regen is a lot more efficient than plain old friction braking: at least some of the kinetic energy of motion is recaptured rather than being lost to heat in the brakes.

In general, it is better to keep the momentum of the car unchanged than to slow and then accelerate it again, even if you recover a bit of the kinetic energy from regen during slowing. I learned it during the gas shortages of the '70s as "pretend you have an egg under the gas pedal and are trying not to break it", i.e. try to accelerate and decelerate gently for the most efficient driving (highest gas mileage). The most gentle deceleration is to just let the car coast and slow through aerodynamic drag and drivetrain friction.

B mode helps with "single pedal" driving: controlling the speed by just modulating the position of the accelerator. Many EV fans consider single pedal driving one of the advantages of driving electric. Others can't be bothered. B mode also helps with hill descents. The regen without B mode is too little to keep the LEAF at a safe speed on steep hills. To me that's a big deal and a frustration with my 2012 model LEAF, which lacks B mode. For flatlanders it is irrelevant.

Finally, you need to display and learn to use the energy screen on the center console (push the "zero emissions" button, then the energy button). The pie chart on the left will show energy going out of or into the battery at any given accelerator position. It is much more detailed information than the dots on the dash. And, before someone else says it yet again, you should keep your eyes on the road in heavy traffic but, when conditions permit, using the energy screen will teach you a lot about driving efficiently. Including how to hold the accelerator at zero power, which is coasting without shifting to neutral.
 
dgpcolorado said:
To me that's a big deal and a frustration with my 2012 model LEAF, which lacks B mode. For flatlanders it is irrelevant.

I test drove a 2013 LEAF recently and was spectacularly unimpressed with the B mode in the LEAF. It is still quite insipid. Having experienced the B mode in the Misubishi I-Miev I do have a frame of reference. Shame Nissan couldn't come closer to how Mitsubishi implemented their 'B mode'. With the Mitsubishi single pedal driving is very easy, with the LEAF, you still need the brakes more than I'd like.
 
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