BestPal
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Max regen - at what point do mechanical brakes engage?

Wed Apr 10, 2013 8:14 pm

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?
_ _ _ _
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20% of driving is on So-Cal freeways 65-75mph

DaveinOlyWA
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Re: Max regen - at what point do mechanical brakes engage?

Wed Apr 10, 2013 10:24 pm

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
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garygid
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Re: Max regen - at what point do mechanical brakes engage?

Wed Apr 10, 2013 10:28 pm

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.
See SOC/GID-Meter and CAN-Do Info
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MarvGordon
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Re: Max regen - at what point do mechanical brakes engage?

Thu Apr 11, 2013 10:14 am

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.

BestPal
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Re: Max regen - at what point do mechanical brakes engage?

Thu Apr 11, 2013 3:47 pm

garygid wrote: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!
_ _ _ _
2013 Leaf S with 6.6kW charger and DC
23,000+ miles driven
4.3 miles/kwh dash average
20% of driving is on So-Cal freeways 65-75mph

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RegGuheert
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Re: Max regen - at what point do mechanical brakes engage?

Tue Apr 16, 2013 3:15 am

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 wrote: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.
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Herm
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Re: Max regen - at what point do mechanical brakes engage?

Tue Apr 16, 2013 8:34 am

BestPal wrote: "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"

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ebill3
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Re: Max regen - at what point do mechanical brakes engage?

Tue Apr 16, 2013 8:59 am

Herm wrote:
BestPal wrote: "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"
I guess the definition of "fly by wire" could be argued, but this thread says brakes are fly by wire, with mechanical fail safe.

http://www.mynissanleaf.com/viewtopic.p ... 09&start=0
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JPWhite
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Re: Max regen - at what point do mechanical brakes engage?

Tue Jun 11, 2013 5:32 pm

BestPal wrote: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.
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TickTock
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Re: Max regen - at what point do mechanical brakes engage?

Sat Jun 15, 2013 6:26 am

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.



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

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