Regenerative braking best practices

[bsommerhalder]

I get asked about regen braking a lot and best practices re: use of the paddles, so figured to create a post about it and also hear what others have to say.

After a few months with my 2020 (and 50,000km / 30,000 miles), here's how I now regularly use regen braking.

Really the idea is simply to use it like brakes, and like any car, try to reduce how much you use your brakes at all through driving habits.

• As a rule, I have regen set to 0. I use as much accelerator as I need, and then take foot off the pedal and coast as needed.
• When I need to slow down a bit to adjust my speed, I tap the left-hand paddle once to move up to regen 1. (Often I only need to let it stay on regen 1 for a few seconds, enough time to slow down a bit to correct my speed, then I right-paddle to bring back to regen 0 and simply accelerate / coast again.) If I need to slow down a little quicker, I'll paddle to regen 2 or 3 as needed.
  
• If I can see I am actually needing to come to an upcoming stop, I will paddle my regen up as I approach my stop, slowing down more and more as I approach the stop, ending at regen 3 and then holding the left-hand paddle down to use regen to come to a complete stop. Then, when stopped, I paddle back down to regen 0, ready to accelerate again.
• Most trips, I do not use the actual brake pedal *at all* -- or if I do it is to react to something that necessitates an immediate stop. (I often consider it a bit of a 'fail' if I have to use the brake pedal! --- I bet my brake pads will last the life of my car)

This technique has been the most energy efficient I have found, because 'coasting' is always going to be your most efficient mode of movement. Anything we do to get in the way of the car coasting is reducing its efficiency.

Let's say you are going down a steep hill. If the speed limit was not a concern and no one was in front of you, the most efficient thing you could do would be to turn off cruise control, set regen to 0, and let the car fall down the hill and pick up momentum, and then just let that momentum take you as far as it can go without having to apply more juice.

But of course, speed limits do matter and we can't just ram the backs of the cars in front of us, so WE get to use regen braking to reduce our speed -- when we need to -- rather than stinky ICE brakes. This same principle applies on a flat road too; no reason to "brake" more than you need to (even if it isn't hurting our brake pads).

 

[R P]

I use level 3 regen in ECO, 99% of my driving. Allows mostly 1 pedal driving until it slows near to a stop, and then have to apply some gentle braking. Works very well for me and my wife.

ECO mode allows for more throttle control, esp on acceleration. Too easy to spin front tires on Normal or Sport mode. Still have full power available, though, when you stomp it.

 

[Genevamech]

I also leave it at Level 3 in ECO, thought I've been thinking of trying setting it to Level 1 to see if I can get better efficiency taking more direct control and coasting freely. Now that the weather is getting better and more consistent I might give it a try...

The downside to such great regen braking, of course, is the brake rotors feel and sound like sandpaper for lack of use!

 

[R P]

The downside to such great regen braking, of course, is the brake rotors feel and sound like sandpaper for lack of use!

Not mine. I guess I still use them enough with stopping, they stay clean.

It may be my imagination, but after the brake recall (and I had several others done at same time) seems that the regen strength fades out more as you slow down, requiring more brake usage as you near the stop. Is anyone else seeing this?

 

[Seadog1272]

I have the 2021 Ultimate with Smart Regenerative Braking. This feature is like the adaptive cruise control in that it applies the regenerative braking as required by what is in front of you and what you are doing with your regular brakes. You can also still use the paddles and 4 levels of control if you wish.

 

[R P]

I have the 2021 Ultimate with Smart Regenerative Braking. This feature is like the adaptive cruise control in that it applies the regenerative braking as required by what is in front of you and what you are doing with your regular brakes. You can also still use the paddles and 4 levels of control if you wish.

Yes, that is a separate feature, too, and needs to be turned on in the settings. But the regen I was referring to is another setting from 1 -3 for each drive mode. Like I said, I have my ECO mode set to level 3 regen.

And the paddles is yet another way to apply regen braking. But I hardly ever use those, as with level 3 regen not needed, just control the amount of regen braking with your throttle pedal.

 

[KiwiME]

... because 'coasting' is always going to be your most efficient mode of movement. Anything we do to get in the way of the car coasting is reducing its efficiency....

That is certainly correct but I'd suggest that the use of regen levels when needed (or auto) is just personal preference, on an idealised level. The practical exception is that level 0 does avoid inadvertently imposing regen (and incurring the resulting losses) if you're not very steady on the accelerator pedal.

Using the brake pedal when regen is needed is not much different than using the paddles, and it's potentially better because it's variable. In fact I'd suggest that using the pedal may be infinitesimally more efficient because power cannot be recovered from the motor right down to zero speed. At some point input power is required to bring the motor to a controlled stop and hold it in a static position. The pedal reverts to the friction brakes rather than use that small amount of power.

 

[ttsherpa]

I do exactly what the OP described at 100%

 

[Orchardman]

That is certainly correct but I'd suggest that the use of regen levels when needed (or auto) is just personal preference, on an idealised level. The practical exception is that level 0 does avoid inadvertently imposing regen (and incurring the resulting losses) if you're not very steady on the accelerator pedal.

Using the brake pedal when regen is needed is not much different than using the paddles, and it's potentially better because it's variable. In fact I'd suggest that using the pedal may be infinitesimally more efficient because power cannot be recovered from the motor right down to zero speed. At some point input power is required to bring the motor to a controlled stop and hold it in a static position. The pedal reverts to the friction brakes rather than use that small amount of power.

I think KiwiME has got right. The foot pedal is 80-90% regen and only the last bit using the friction-brakes.
As for my driving style, I use two modes. By preference I use a L3 one-pedal approach and then the left paddle to pull up at lights. When my wife is in the car, this mode aggravates her motion-sickness, so I then use L1 and no-paddle, making it akin to an ICE car style.
One question for all: I found with a L3-all-the-time style that I was getting lazy with my right foot and getting to the brake pedal a bit late in some circumstances. With a mixed style, I'm keeping my brain tuned up to get to the brake pedal quickly. Anyone else felt this laziness with an L3 style?

 

[R P]

No, I like the one pedal driving. Still have to use the brake pedal to stop, so not like you never use it.

 

[KiwiME]

...Anyone else felt this laziness with an L3 style?

Primarily I'm concerned that when I drive my newly-acquired older ICE car that my subconscious reactions may be dulled if an emergency stop is required.
I certainly use the fixed regen levels on hilly long-distance driving but tend to avoid the left-paddle-hold for around-town stopping.

As an aside, I'll bet none of you have seen one of these roaming North America, a 2-door Suzuki Grand Vitara

 

[Ed C]

It really depends on the traffic conditions for me.

Regen 3 is left on during heavy bumper-to-bumper traffic, because it is great for 1-pedal driving. It slows down very dramatically when I let go of the accelerator. I pull and hold the left paddle when I need to brake instantly. But this level is very jerky. But stop-and-go bumper-to-bumper traffic is jerky even in an ICE car.

Regen 2 is left on for moderate to light traffic. I let go of the accelerator and it slows down like a normal ICE car, without the jerkiness of regen 3. I increase to regen 3 when I need to turn near corners, and the regen does well without using the friction brakes.

Regen 1 is absolutely great for steep downhills. I don't even use the accelerator. You don't get the dramatic increase in speed going downhill, as you normally would when you set the regen to 0, but your car maintain a static current speed with the regen sucking in as much energy back into the battery.

I hardly use regen 0, unless there are absolutely very little to no cars.

 

[bsommerhalder]

Using the brake pedal when regen is needed is not much different than using the paddles, and it's potentially better because it's variable. In fact I'd suggest that using the pedal may be infinitesimally more efficient because power cannot be recovered from the motor right down to zero speed. At some point input power is required to bring the motor to a controlled stop and hold it in a static position. The pedal reverts to the friction brakes rather than use that small amount of power.

This is a good point -- although I think that using the regen paddle to come to a complete stop ALSO deploys friction brakes at the very end, right? In which case, if you drive like I describe in my original post (stay at regen 0 and use regen only when needed to slow down), then there might actually be no difference at all between using the regen paddle to come to a complete stop vs using the brake pedal.

 

[MSimpsonNJ]

OK this is a very interesting and informative thread. I clearly have to give more thought to my regen driving strategy (or lack thereof).

 

[KiwiME]

... using the regen paddle to come to a complete stop ALSO deploys friction brakes at the very end, right? ...

Not a chance, it's totally electromagnetic. You can feel it rock slightly after stopping in certain conditions like hills, something that would not happen if the calipers were clamped tightly on the disks. Engineers call that looseness 'deadband' and the purpose is to decrease winding heating when stopped. The motor's rotor is being being pushed in both directions by the windings at once to hold it still, so there is a small power draw. A deadband allows a larger tolerance around the target position.

The motor in our Konas has positional feedback and a four-quadrant controller. As a result the car has complete control of the motor down to a degree or two of rotation. This is the same as every industrial robot, programmable machining center, etc, and most other EVs and hybrids. This sort of precise control is why a Prius is able to start the engine without causing a perceptible bump in the driving.

The Auto Hold (pushbutton) setting is a different animal. It uses the sophisticated braking system to hold the brakes "on" after coming to a stop using the brake pedal. That's entirely separate from the motor.

 

[davidtm]

(Kia Niro EV EX Premium driver here)
I love Auto Regen, and have it on all the time. I use baseline level 1 regen otherwise. I was excited to see paddles on the early pix of Ioniq 5 and Ka EV6!

 

[FlexTail]

I am living in Norway, where they salt the roads quite a bit during winter. As much as I like to use as much regen as possible, it is necessary to friction brake once in a while to cleanup the braking discs. I am having a Czech produced Kona 2020 Ultimate and use the auto regen setting.

 

[bsommerhalder]

Not a chance, it's totally electromagnetic. You can feel it rock slightly after stopping in certain conditions like hills, something that would not happen if the calipers were clamped tightly on the disks. Engineers call that looseness 'deadband' and the purpose is to decrease winding heating when stopped. The motor's rotor is being being pushed in both directions by the windings at once to hold it still, so there is a small power draw. A deadband allows a larger tolerance around the target position.

The motor in our Konas has positional feedback and a four-quadrant controller. As a result the car has complete control of the motor down to a degree or two of rotation. This is the same as every industrial robot, programmable machining center, etc, and most other EVs and hybrids. This sort of precise control is why a Prius is able to start the engine without causing a perceptible bump in the driving.

Learned something here, thanks! I do notice and frankly enjoy the rocking of paddle-stopping -- like being in a boat lol -- and for that reason plus the joy of one-pedal driving means I'll probably keep paddle-stopping (apparently I am a deadband junkie?), but I buy your guess that "using the pedal [to come to a complete stop] may be infinitesimally more efficient" at those last few kmph's, for those hyper-rangers out there ...

 

[NRH]

I prefer not to overthink it, and I don't believe there's any reason to relearn how to drive with this car. Zero Regen and minimal use of both accelerator and brake pedal is most efficient in my understanding (just like any ICE car). The paddles are a clumsier way to apply the regenerative braking. The brake pedal does the same thing, allows modulation, and allows normal pre-EV efficient driving habits.

Nate

 

[Jeffrey Seuntjens]

Just a speculative note, that while the motor slowing is ever stronger for higher settings, the amount of energy that the batteries can re-absorb is finite. It seems unlikely that the batteries can restore a larger portion of higher regen settings. So for efficiency, range, and minimal carbon footprint, the setting would need to be as low as safe driving allows. The design engineers of these cars can further comment. Thanks.