learn me some Leaf regen and braking

[DaveEV]

I do wish we had some indication of when the friction breaks are applied as it's awfully tempting to gently ride the breaks to come to a stop and I'm just not sure how much there is to gain from trying to stretch that out over a longer distance.

Yes - it would be awesome if there was a dial that indicated how much friction brake force was being applied to the car, even if only approximate.

 

[thankyouOB]

I always drive my 55-mile (mostly freeway and some streets) roundtrip in ECO, with AC on.
Today, I decided on an experiment--all D, and AC.
I got to work with just three bars down sted of the usual 4.

I will report on the return trip and then try it again tomorrow.
One variable this time-- I charged to 11 bars and got to work with 8 remaining. (that is instead of the usual 6).
Of course, the bar 8 could be on the cusp.

that is what it was....went to 7 bars almost at start up.

 

[DaveinOlyWA]

I do wish we had some indication of when the friction breaks are applied as it's awfully tempting to gently ride the breaks to come to a stop and I'm just not sure how much there is to gain from trying to stretch that out over a longer distance.

Yes - it would be awesome if there was a dial that indicated how much friction brake force was being applied to the car, even if only approximate.

would be nice but at the same time maybe too much to look at BESIDES the road?

 

[DaveEV]

I do wish we had some indication of when the friction breaks are applied as it's awfully tempting to gently ride the breaks to come to a stop and I'm just not sure how much there is to gain from trying to stretch that out over a longer distance.

Yes - it would be awesome if there was a dial that indicated how much friction brake force was being applied to the car, even if only approximate.

would be nice but at the same time maybe too much to look at BESIDES the road?

No - you could either indicate friction braking by changing the regen bubbles or adding a dial to the energy screen. It would only take a quick glance to figure out if you're using the brake too much or not.

 

[KeiJidosha]

I do wish we had some indication of when the friction breaks are applied as it's awfully tempting to gently ride the breaks to come to a stop and I'm just not sure how much there is to gain from trying to stretch that out over a longer distance.

Yes - it would be awesome if there was a dial that indicated how much friction brake force was being applied to the car, even if only approximate.

would be nice but at the same time maybe too much to look at BESIDES the road?

Argument made for Right Pedal regen – allows you to look at the road AND brake efficiently

 

[garygid]

Perhaps we will be able to find something like the "desired braking force" and the "percent disc braking" on one of the CAN busses.

If so, our "SOC-Meter" will probably gain a "Disc-Braking Force" (or some such) display mode.

 

[DaveinOlyWA]

maybe a type of HSI like the Prius but modified for braking/regen. so you can moderate your brake pedal pressure to insure no friction braking.

i am guessing after a few days of practice you could do it without looking

 

[tps]

it would be awesome if there was a dial that indicated how much friction brake force was being applied to the car, even if only approximate.

The "friction brakes" are actually more properly called Hydraulic Disc Brakes. It would certainly be possible to put an indicator which monitors the hydraulic pressure. This, of course, does not directly translate to braking force. I there might be some way to instrument the calipers, maybe some sort of strain gauge, but that sounds like a fairly complex project... Maybe the braking force could be computed, the mass of the car is known, and maybe even the mass of the payload could be determined during regenerative-only braking. We can measure the delta-V. IMHO, the main variable which isn't measured is the inclination of the road. What does the ABS computer already measure?

 

[DaveinOlyWA]

The Prius monitor braking force both hydraulic and regen. compares the info to the speedometer, accelerometer and "demand" (how fast you engage the brake pedal)

so it can be done, is being done, etc. now to monitor it would be nice

 

[kawh]

So, least (to most) wasted energy is to:

2. slow by coasting
3. slow using Regen
4. slow using the disc brakes


what is the difference between 'slow using regen' and 'slow using disc brakes" -- i thought the regen was tied into the brakes??

 

[DaveinOlyWA]

least to most wasted energy depends. regen would rank best because it recaptures some energy that can be re used.

 

[occ]

2. slow by coasting
3. slow using Regen
4. slow using the disc brakes


what is the difference between 'slow using regen' and 'slow using disc brakes" -- i thought the regen was tied into the brakes??

Your LEAF (and hybrids) braking "process" uses two very different ways to slow down the car:
Slow using regen gives you energy back into your battery - converts your forward momentum into electrical energy and subsequently stored into your battery.
Slow using disc brakes gives you nada - converts your forward momentum into heat on your pads and disc of your braking system (and wears them down).

 

[kawh]

2. slow by coasting
3. slow using Regen
4. slow using the disc brakes


what is the difference between 'slow using regen' and 'slow using disc brakes" -- i thought the regen was tied into the brakes??

Your LEAF (and hybrids) braking "process" uses two very different ways to slow down the car:
Slow using regen gives you energy back into your battery - converts your forward momentum into electrical energy and subsequently stored into your battery.
Slow using disc brakes gives you nada - converts your forward momentum into heat on your pads and disc of your braking system (and wears them down).

ok...thanks... but then how is "coasting" different from "regen." ??
sorry to be so slow (pardon the pun...)
kawh

 

[DaveEV]

ok...thanks... but then how is "coasting" different from "regen." ??
sorry to be so slow (pardon the pun...)

Basically - if you regen when it's not necessary - and then have to use power to keep on moving later, you've lost efficiency since regen is not 100% efficient.

In some cases, regen can be more efficient than coasting - this is most likely to occur on longer hills at higher speeds.

 

[abasile]

how is "coasting" different from "regen." ??

Coasting: No power to or from the motor, aka. "freewheeling"
Regen: Motor acts as a generator, producing power and slowing the car

When the "Energy Info" screen shows zero power, you are coasting. This actually requires some pressure on the accelerator, since the LEAF otherwise applies some regen to simulate the feeling of engine drag on a gasoline car.

 

[planet4ever]

ok...thanks... but then how is "coasting" different from "regen." ??
sorry to be so slow (pardon the pun...)

I think the best way to get a feel for this is, as abasile just suggested, to watch the pie chart on the left side of the 'Energy Information' screen. [Push the 'Zero Emission', bottom right side of center console; then touch the 'Energy Info' option, top right corner of the menu.]

• When you see a pie slice going up into the positive numbers, energy from the battery is being used to drive the wheels. That only happens when you are pushing the accelerator (or letting Cruise Control push it for you).
• When you see a pie slice going down into the negative numbers, energy from slowing the car is being put back into the battery. That is regen. It can happen when you take your foot off the accelerator or when you touch the brake pedal lightly.
• If you are moving but don't see any pie slice at all, then you are coasting. That happens only if you put the car in neutral [move the shift lever straight left and hold it there for a couple of seconds] or if you are feathering the accelerator pedal very carefully.

Now, Gary makes it sound like a simple 1-2-3 choice among coast, regen, and disk brakes, but it's really much more complicated than that. The only way to make a car speed up is to add some energy to it, and the only way to slow down is to take some energy away from it (or away from what scientists like to call the car's momentum).

• With coasting the energy is being converted to heat rather slowly using friction - friction of the air against the car body, of the tires against the road, of the bearings in the wheels and gears and motor. But those things are always happening while the car is moving, so they are added to whatever else is being used to slow the car.
• With regen, part of the energy is being converted to electricity by making the motor work like a generator. But only part - the conversion process isn't perfect, and does generate heat. Besides, there is still the 'coasting' friction from above.
• With disk brakes, part of the energy is being converted into heat as the brake pads rub against the disks. But, again, only part of it. There is still the 'coasting' friction, and there is still the regen! (Well, unless you are in neutral.)

Ray

 

[aqn]

I always drive my 55-mile (mostly freeway and some streets) roundtrip in ECO, with AC on.
Today, I decided on an experiment--all D, and AC.
I got to work with just three bars down sted of the usual 4.

Sounds like a worthwhile comparison test, but one data point of something as squishy as the SoC bars is... suspect. I suggest repeating each scenario multiple times, and take the average.

 

[thankyouOB]

I always drive my 55-mile (mostly freeway and some streets) roundtrip in ECO, with AC on.
Today, I decided on an experiment--all D, and AC.
I got to work with just three bars down sted of the usual 4.

Sounds like a worthwhile comparison test, but one data point of something as squishy as the SoC bars is... suspect. I suggest repeating each scenario multiple times, and take the average.

yes, turns out I was on the cusp of the fourth bar going down, and when I left work that afternoon, it disappeared either at start up or within the first block -- when I checked it out.

 

[davewill]

That reinforces my feeling that D is not bad for range unles you're a leadfoot and jackrabbit around. I now think of ECO as a "low gear" for hills only. It is also handy as training wheels for someone who hasn't got the knack of driving smoothly.

 

[aqn]

I always drive my 55-mile (mostly freeway and some streets) roundtrip in ECO, with AC on.
Today, I decided on an experiment--all D, and AC.
I got to work with just three bars down sted of the usual 4.

Sounds like a worthwhile comparison test, but one data point of something as squishy as the SoC bars is... suspect. I suggest repeating each scenario multiple times, and take the average.

yes, turns out I was on the cusp of the fourth bar going down, and when I left work that afternoon, it disappeared either at start up or within the first block -- when I checked it out.

If you do the commute in 'D' 20 times, do it in 'ECO' 20 times, and observe that, say, 15 out of 20 times in 'D' you use one extra bar, whereas only 2 times out of 20 in 'ECO' you use one extra bar, then I'd say we have a reasonable case that 'D' is less efficient.

My commute is too short (4.x miles) for this test to be meaningful. Your commute of 55 miles is a much better "test environment" for this: same long distance, same terrain, same time of day (therefore same traffic and traffic light patterns), etc. It'd certainly provide some solid and interesting figures for discussion.

I think I will start driving in 'D' over the next 20 "tankfuls" and see if there is discernable departure from my past energy use record, all in 'ECO'.