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Regenerative braking

1116 Views 20 Replies 11 Participants Last post by n6nl, 16 d ago

michiganDoug

Discussion Starter · 1 mo ago

Is there a difference in recharge effectiveness between the S-Pedal and max setting with the paddle shifter?

Also, my paddle shifter setting is not remembered from trip to trip. Is there somewhere that you can set what you want your default to be?

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jmwk

· #2 · 1 mo ago

Not sure what you mean by "recharge effectiveness". Regenerating from braking (or some downhill coasting) happens automatically and under almost all conditions so long as there's room in the battery. When the paddles are used or one foot drive is enabled, it will regen more aggressively - and slow you down more quickly - when you take your foot off the juice.

When you manually brake, it does the same thing, again so long as you don't exceed the limit of the battery's ability to take the charge.

Manually braking is more likely to exceed the battery's intake limit than using paddles/one foot driving.

michiganDoug

Discussion Starter · #3 · 1 mo ago

by effectiveness, i meant speed of charging. i assumed with the paddle increased, or with s-pedal, due to faster slowing you would get faster charging.

i would have thought manual braking would have been the slowest way to recharge the battery. why is it more likely to exceed the battery's intake limit?

jmwk

· #4 · 1 mo ago

michiganDoug said:
by effectiveness, i meant speed of charging. i assumed with the paddle increased, or with s-pedal, due to faster slowing you would get faster charging.

i would have thought manual braking would have been the slowest way to recharge the battery. why is it more likely to exceed the battery's intake limit?

Verbosity warning! Whatever system you use to slow down will produce regen charge up to the max the battery can suck in during normal driving. It really doesn't matter whether it's the paddles slowing you down or the brakes. Those are selections you make to interact with the car; the car manages the recharging either way.

If you're over 80% SOC or so, the regen system starts to limit the max charge that goes back to the battery. Too close to 100% and one pedal will stop working. Another reason not to charge past 80% other than when needed.

While the brakes recharge first, the brakes of course will work even when the battery can't take a charge, reverting to old fashioned friction and lost energy. Similarly, at some point of overly aggressive braking, the brake pads will get mixed in. I have no idea how Subaru/Toyota coded that "overly aggressive" curve though. Alternatively, slowing down by coasting - i.e., no paddle regen, just aero drag and internal friction - won't deliver charge. You do want to use the brakes or the paddles/one pedal to slow down.

EVs are optimized for "normal" driving, not the extremes on either end. And from what I've been able to find, under normal conditions regen is about 60-70% efficient, so cruising along is better than speeding up and slowing down for best range - just like our parents taught us!

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BinPNW

· #5 · 1 mo ago

60-70% regen is pretty decent-- is that Solterra specific or just EV regen braking in general? Will it get a little more efficient with future engineering? Regardless, sure beats friction brakes which are 0% efficient.

n6nl

· #6 · 1 mo ago

I see regeneration energy flowing into the traction battery through the OBD II data when I take my foot off of the accelerator and "coast". This is without any regen paddle setting or S Pedal mode being enabled. This is on level ground. When descending a hill, the energy is even greater.

Toyota attempts to recover whatever energy can be recovered, any time that the battery can accept charging current (depending upon State of Charge, battery cell temperatures, etc.)

Reactions: 3

jmwk

· #7 · 1 mo ago (Edited)

BinPNW said:
60-70% regen is pretty decent-- is that Solterra specific or just EV regen braking in general? Will it get a little more efficient with future engineering? Regardless, sure beats friction brakes which are 0% efficient.

EVs in general and very ballpark from multiple sources. And it seems to vary a lot depending on conditions.

n6nl said:
I see regeneration energy flowing into the traction battery through the OBD II data when I take my foot off of the accelerator and "coast". This is without any regen paddle setting or S Pedal mode being enabled. This is on level ground. When descending a hill, the energy is even greater.

Toyota attempts to recover whatever energy can be recovered, any time that the battery can accept charging current (depending upon State of Charge, battery cell temperatures, etc.)

My bad. You're right, of course. I was trying to simplify one of the really dense articles I'd read while waiting months for my Solterra to be delivered. I was thinking of a theoretical pure coast vs real world. (Trying to grasp the underlying science of tech helps me use it more intuitively; I'm geeky that way.)

I imagine part of being optimized for "normal" driving is not letting us truly coast without putting it in neutral.

Edit to add: I was playing around with the paddles this morning. One down arrow lets me coast with virtually no charging.

Reactions: 2

michiganDoug

Discussion Starter · #8 · 1 mo ago

thanks for all the info, it's starting to sink in. to restate, if i charge to 100% in the garage at night, i won't be able to recoup any energy from regen, since there is no place for it to go? so better not to top it off, so you can get the benefit of regen?

also, what recharges the 12V battery in the solterrra, or EV's in general?

finally, if my traction battery is 50% SOC, and i use the brakes, are the brake pads only used in extreme braking conditions? in other words, normal braking with the brake pedal, won't typically use the brakes pads at all, but it will slow the car and recharge the traction battery?

jmwk

· #9 · 1 mo ago

Yes, if you charge to 100% you do limit regen. I only charge to 100% now and then to rebalance batteries and before long trips.

As I understand it, the 12V battery charges when the “ready” light is on, meaning the traction battery is engaged. At least that seems to be the consensus here.

And, yes, for the most part the brake pads are only used in more aggressive braking. If you see the charge meter maxed while braking, you’re using brake pads. (And note that the max itself is limited when you’re somewhere around 80% or more. There’s a small tick mark showing that limit on the charging gauge.) Brake pads are also used when you’re almost stopped or fully stopped.

I’ve read where EV’s brake rotors rust for lack of use, and suggestions that we brake hard now and then to keep them clean.

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jg.

· #10 · 1 mo ago

jmwk said:
…I’ve read where EV’s brake rotors rust for lack of use, and suggestions that we brake hard now and then to keep them clean.

That’s for vehicles with true one-pedal-driving that use regenerative braking to fully stop the car, and maybe friction brakes just to hold the vehicle in place. There’s little chance for rust to build up on the Solterra like those articles report.

Rust builds up on rotors (or drums if you’re old school) all the time when any vehicle isn’t driven, so you really shouldn’t be concerned if you see any. It will naturally be removed as you drive and start building up again when you stop. I think the biggest difference in operating an EV is that since it is so quiet you can really hear the brakes grinding that rust down when you first stop the car in the morning.

Reactions: 1

Cassio

· #11 · 1 mo ago

michiganDoug said:
Is there a difference in recharge effectiveness between the S-Pedal and max setting with the paddle shifter?

Also, my paddle shifter setting is not remembered from trip to trip. Is there somewhere that you can set what you want your default to be?

I don’t think it makes a difference between the two ways but I know that when you use the S pedal it will act like you are breaking and your break lights will go on. I have not being able to ascertain if that also happens when you use the shifters on the steering wheel or it will just mimic “coasting”. Answering your other question unfortunately there’s no way to set a preferred level that will “stick” all the time. Every time you turn off the vehicle it will reset it - or even after you engage reverse in the same trip.

Reactions: 1

jg.

· #12 · 1 mo ago

I thought I recalled the paddle shifter setting came back to where it was previously set the first time I hit the left paddle (I only get to drive it occasionally on weekends, if my wife let's me -- she's very protective of it). I know it doesn't start up with the regen set, but honestly I would rather have it reset to off or the lowest setting each time I stop so I can slow down gradually like I am downshifting.

michiganDoug

Discussion Starter · #13 · 30 d ago

Cassio said:
I don’t think it makes a difference between the two ways but I know that when you use the S pedal it will act like you are breaking and your break lights will go on. I have not being able to ascertain if that also happens when you use the shifters on the steering wheel or it will just mimic “coasting”. Answering your other question unfortunately there’s no way to set a preferred level that will “stick” all the time. Every time you turn off the vehicle it will reset it - or even after you engage reverse in the same trip.

interesting comment on the brakes, i never thought of that.

i think i've settled on just coasting/braking like normal, since the regenerative braking works that way too, i now understand. for me, the s-pedal driving brakes too hard, so you need to wait longer than i am comfortable with to take your foot off the accelerator.

Reactions: 1

monty

· #14 · 20 d ago

Cassio said:
I don’t think it makes a difference between the two ways but I know that when you use the S pedal it will act like you are breaking and your break lights will go on. I have not being able to ascertain if that also happens when you use the shifters on the steering wheel or it will just mimic “coasting”. Answering your other question unfortunately there’s no way to set a preferred level that will “stick” all the time. Every time you turn off the vehicle it will reset it - or even after you engage reverse in the same trip.

The other night I did a little experiment in my neighborhood when I was coming home and noticed in my wing mirror the brake lights going on. So I went up and down the road with different settings. On the shifters 1-3 the brake lights didn't come on coming off the pedal. Going to level 4 or S pedal, as soon as coming off the gas, the brake lights came on.
I don't know that if the brakes are actually being applied, or the thinking is that the deceleration is so aggressive that they put the brake lights on to advise others.

Reactions: 1

n6nl

· #15 · 20 d ago

The service and training manuals seem to indicate that it is based upon the amount of deceleration. I am glad that they light up the brake lights so we don't all get rear-ended.

jmwk

· #16 · 20 d ago

monty said:
The other night I did a little experiment in my neighborhood when I was coming home and noticed in my wing mirror the brake lights going on. So I went up and down the road with different settings. On the shifters 1-3 the brake lights didn't come on coming off the pedal. Going to level 4 or S pedal, as soon as coming off the gas, the brake lights came on.
I don't know that if the brakes are actually being applied, or the thinking is that the deceleration is so aggressive that they put the brake lights on to advise others.

"Brakes" on an EV are something of a misnomer. For brake lights, it's really about how aggressively the car is slowing and warning any driver behind you.

So long as the recharging system can accept the regenerative energy, slowing - whether by paddle/one-foot or pressing the brake pedal - pushes energy into the battery with no brake pads involved. (Except at very slow speeds, of course.)

bobleon39540

· #17 · 20 d ago

It would be helpful if the dash had a light that told you when the brake lights were on.

davidsmartin

· #18 · 19 d ago

bobleon39540 said:
It would be helpful if the dash had a light that told you when the brake lights were on.

My 2017 Outback had a dash light that would go on when the adaptive cruise control had to brake to slow the car. I agree that such a light would be a good thing, if only to reassure me that the car is doing its job by turning on the brake light at appropriate times.

Reactions: 1

Greg M

· #19 · 17 d ago

bobleon39540 said:
It would be helpful if the dash had a light that told you when the brake lights were on.

I agree!!

Whoabear

· #20 · 17 d ago

michiganDoug said:
i think i've settled on just coasting/braking like normal, since the regenerative braking works that way too, i now understand. for me, the s-pedal driving brakes too hard, so you need to wait longer than i am comfortable with to take your foot off the accelerator.

In my ICE care when I needed to slow down I would do the following (under ideal gradual stop regular driving)

Immediately take foot off of gas entirely and allow car to coast to begin slowing.
Begin gently applying break as approach place need to stop
Continue to apply more and more break
Finish applying break all the way to final stop and hold car.

In the Solterra with S-Pedal I have had to retrain my brain to achieve the same phases in slightly different ways as it works more like:

Back off accelerator slightly from position it was in to being slowing in more of a "coast" capacity
Begin backing off accelerator more at the point I would have previously started applying breaks in my ICE car. Still have foot on accelerator here. This may blend a bit with portion three above.
Remove foot from accelerator to achieve full regen breaking force which should approach final position of car.
Use break to stop and hold car in final position

If I am in S-pedal I am trying to remind myself to not pull the foot off all the way to get to that coast function of my ICE.

Still learning.

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