One pedal drive (vs) Brake regen

[mfbrown]

If you drive with a coasting mindset you will use a lot less energy. I coast for hundreds of yards without using nor losing energy to dragging brakes in whisper mode. I can coast out of my neighborhood which is flat with one burst of acceleration and it’s a 1/4 mile. Also it’s more fun to drive the car as you’re not trundling along at a boring constant speed getting an ankle workout. Here’s a video to show an example with data.

I just watched the video and like some commenters in his feed; I knew what the result would be based on how he described his driving. In one case he said he would coast as much as possible and try to time lights so he would not have to stop - the same thing I would do in a ICE long before regenerative braking was a buzz term. He then compared to 1P with quick acceleration and heavy braking. Gee, surprise, surprise; it was less efficient. Anyone who has taken basic physics knows that jack rabbit starts and heavy braking are going to be inefficient uses of energy. To the point made earlier; regen is nowhere near 100% and even if it was; it would not make up for wasted energy accelerating and decelerating. I would have been much more interested in the result if he tried to drive the same way in both modes - keeping speed even, trying to time lights so no stopping, etc. and then let's see how the two would have compared.

If everyone coasted into stops with virtually no braking and smoothly accelerated to constant speeds, then I wouldn't doubt we would not need 1P at all.

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[ca_jon]

Talk about a bad look it’s hilarious your telling me I don’t own a Mach e when it’s sitting in my garage.
read and weep I’ll take my 100 dollars. You need to get a handle on your emotions.
https://www.roadandtrack.com/car-cu...rily-the-most-efficient-way-of-driving-an-ev/

"on order" is not the same as "sitting in your garage." Either your bio is false, or your photo is false. Which is it?

 

[ca_jon]

I just watched the video and like some commenters in his feed; I knew what the result would be based on how he described his driving. In one case he said he would coast as much as possible and try to time lights so he would not have to stop - the same thing I would do in a ICE long before regenerative braking was a buzz term. He then compared to 1P with quick acceleration and heavy braking. Gee, surprise, surprise; it was less efficient. Anyone who has taken basic physics knows that jack rabbit starts and heavy braking are going to be inefficient uses of energy. To the point made earlier; regen is nowhere near 100% and even if it was; it would not make up for wasted energy accelerating and decelerating. I would have been much more interested in the result if he tried to drive the same way in both modes - keeping speed even, trying to time lights so no stopping, etc. and then let's see how the two would have compared.

If everyone coasted into stops with virtually no braking and smoothly accelerated to constant speeds, then I wouldn't doubt we would not need 1P at all.

Coasting is great, when you want to save gas or brake pads.

Is that true? I have used 2P and coasted (while in drive) and it certainly feels like there is very little regen slowing the car down. I have been amazed (coming out of 1P) how far it will coast. Never tried it in neutral, but I haven't done that with a car since I had a stick.

I'm not saying you are wrong, because I'm not doing any calculations to defend my statements, but from a conservation of energy perspective, I'm not sure they would be equal between 1P and 2P if you coasted to a stop. My reasoning is that If I am going 50 mph and take my foot off the accelerator in either mode, then measure how far the car rolled in each case: X feet in 2P mode or Y feet in 1P mode. I think we would agree that X > Y. Therefore, more of the energy stored in the car of mass M moving at 50 MPH at time 0 went into moving the car in the case of 2P and more of the energy in the case of 1P went into charging the battery.

You are correct, in 2PD, you can coast all day....regen only kicks in when you press the brake pedal. The same is not true in 1PD - regen kicks in as soon as you ease off the gas pedal far enough.

 

[ca_jon]

I do not know whether to laugh or cry at some of the comments that are being made. Your point about energy needing to be converted is right on and that does not matter if you coast or not. The thing that is driving me crazy; though, is that people do not realize that 2 PD is 100% regenerative braking if done smoothly. So my guess is both methods are close to the same efficiency.

Yes, absolutely true, with one caveat...in 1PD, regenerative braking is 100%. In 2PD, its much harder to get 100% regen as you cannot tell when depressing the brake pedal the point at which friction braking kicks in (reducing efficiency). I've tested this (I'm very good at both). I avg. above 99% brake score in 1PD but that number is reduced (as are the number of regen miles) to the low-mid 90's in 2PD. Bottom line, do what you like best.

 

[ca_jon]

That’s what the 1pd fanatics can’t understand is that yes you do regen with 2pd in a more efficient manner than constantly dragging the brakes and burning up that kinetic energy at a 60% recovery rate vs 100% retention minus the bearing drag by coasting in whisper in 2pd.

If you knew how to use 1PD, you wouldn't make these ridiculous statements.

 

[ca_jon]

There's a misconception here that one-pedal mode automatically means that you are "dragging the brakes". You aren't. One pedal mode just changes the mapping of the accelerator pedal such that at certain pedal positions, more regen is available/requested than at other pedal positions. It is possible to feather the pedal such that you are "coasting" with very little power in or out. In my Prius, we called that "dead-banding" where the powerflow display would show no power in/out of the battery or from the engine to the wheels.

Part of the problem here is that most people associate "coasting" to mean that the foot is completely off of the accelerator pedal. Keep in mind that in a traditional ICE vehicle, you would have some drag from the engine/transmission that would gradually slow you down. I suspect that manufacturers, starting with hybrids, engineered in some regen "drag" to mimic traditional ICE vehicles. Toyota had to specifically add in a "creep" mode because of this into the Prius. People kept thinking the car was broken because when they'd move their foot from the brake pedal to the gas pedal, the car didn't start immediately moving forward, like in a normal automatic transmission.

I bet with an OBDII reader, a copy of CarScanner, it would be pretty easy to setup test cases that could satisfy the 1pd versus 2pd argument here.

Perhaps the concept of "coasting" in the EV world needs to be rethought...

Thank you, this might be the most accurate and useful comments in this entire dreadful thread.

 

[tmrqs]

It is possible to feather the pedal such that you are "coasting" with very little power in or out. In my Prius, we called that "dead-banding" where the powerflow display would show no power in/out of the battery or from the engine to the wheels.

Spot on!

The notion that there is only a 1 pixel range for the 1PD to be in that coasting mode is the basis for a lot of the inaccurate messages in this thread.

With very little practice, it is easy to get to it and effectively coast using 1PD.

Some may prefer 2PD and that’s fine.

But not knowing how to use 1PD and use their inexperience (such as using the pedal as an on/off switch only) does not mean 1PD is less efficient than 2PD.

Just that these drivers are less efficient using the 1PD mode.

 

[AKgrampy]

Yes, absolutely true, with one caveat...in 1PD, regenerative braking is 100%. In 2PD, its much harder to get 100% regen as you cannot tell when depressing the brake pedal the point at which friction braking kicks in (reducing efficiency). I've tested this (I'm very good at both). I avg. above 99% brake score in 1PD but that number is reduced (as are the number of regen miles) to the low-mid 90's in 2PD. Bottom line, do what you like best.

I am not 100% sure but I do not think my brakes engage (most of the time - grandpa driving) until just before I stop. Sometimes I can feel them but normally not. Almost always 100% on the fake regenometer.

 

[daemonic3]

Oh man, this thread has been highly entertaining!

What I'm noticing is there may be 2 definitions of coasting and so folks may be arguing against their own assumptions.

"Coasting" Definition 1) Shifting to Neutral to disengage the drive train, which will (in theory) reduce rolling resistance. I am not sure if that is the case in this vehicle, but would love to know! I think that is a completely separate discussion as MOST drivers are not going to do this.
"Coasting" Definition 2) The point at which there is zero throttle, and zero brake applied. This exists in ALL 6 drive modes (Whisper, Engage, Unbridled) x (1PD, 2PD). I am going to dub this 0T0B to disambiguate in the rest of my reply.

For your scenarios to be reasonable, 100% efficiency would need to be possible. Coasting is 100% energy loss - you recover none of the energy you put in to gain the speed you lose. If you feather the accelerator in 1pd just enough to decelerate at the same rate as you would in neutral, you're neither gaining nor losing energy. If you decelerate faster, say in the last 25% of your coasting distance, you will regain some of the energy used. Regaining some is more efficient than regaining none.

I feel like we've had this discussion before...

We have, and you were wrong then and wrong again now. Those 2 choices above will stop at 2 different points, and you keep thinking that rolling resistance is a CHOICE and not present in all modes at the same speed (ignoring shifting to Neutral). If you are not shifting to neutral, there are 3 ways to slow the car:

1) Pure intrinsic rolling resistance and drag. This is the 0T0B point in any drive mode, and many of us (including me) call this "coasting". Intrinsic rolling resistance and drag energy loss cannot be recaptured no matter how hard you try.
2) Intrinsic rolling resistance and drag PLUS regen braking. Note the word INTRINSIC as you cannot OPT OUT of this resistance, it is there always. All you can do is add more regen resistance on top. You STILL cannot recapture the intrinsic resistance loss no matter what mode you choose. You will ALWAYS slow down faster from point A to point B than mode 1). You cannot CHOOSE to apply some regen and slow down at the same rate as only mode 1).
3) Adding friction brakes on top of #2. We all agree this is least efficient, no arguments.

All of us driving (again ignoring shifting to neutral) will use various combinations of the above 3 methods, across all 6 drive modes, and I argue that IF OUR FEET WERE PERFECT then every mode has equal efficiency. I prefer Whisper 1PD because it feels similar to my other vehicles, and I let the computer (adaptive cruise) worry about finding the 0T0B point and accel/decel optimally while on freeways. I will not shit on anyone else's choice of drive modes or pretend my choice is best for them.

There are others who have done sophisticated calculations but think of it this way - you put x amount of energy into you car to accelerate. As you slow down that is either lost to friction or reclaimed by regeneration. So maybe a higher regen has larger heat losses in the regen load but then a longer regen (coast) involves more friction. Bottom line, I believe, as long as you do not hit the friction brakes then the regen from 1PD is equal to 2PD. Unless someone can explain where the energy is lost between the two modes. We are speaking in general and not a special case such as “What about a long downhill drive?” (Which May still be the same but my brain already hurts!)

IF we are at speeds where drag is not much of a factor yet, then I believe both of those are equal as long as you never had to apply friction braking.

Only at high speeds would what @ctenidae is saying is correct, but it would be a choice between drag (not rolling) resistance vs regen resistance. If you are starting at freeway speed from point A to a stop at point B, is it more efficient to not apply regen brakes until the very end of the stop, or is it more efficient to start applying brakes quickly then crawl to point B? (both never using friction, only regen)

Answer is apply regen quickly then crawl to B, but people will hate you and you will hate yourself ? . Reason is while rolling resistance is a linear loss across all speeds, drag is exponential and dominant at high speeds. So you can choose to lose your kinetic energy to drag early or regen early. You can NOT choose regen vs rolling resistance though.

 

[AKgrampy]

I guess this really was all settled in the 60’s. Fred Flintstone could get his car up to speed quite quickly (I think it was 2PD) and he coasted for great distances. We are just re-inventing the wheel here.

 

[devmach-e]

I take back what I said about this thread, it’s turning into a religious war. Nobody wins those things.

Welcome to the internet. Providing entertainment and frustration at the same time since the 70s...

 

[ctenidae]

I take back what I said about this thread, it’s turning into a religious war. Nobody wins those things. 

If God's on our side, who is on their's?

 

[mkhuffman]

Well, I just want to know which is more efficient, WOT to 80 mph with 1PD, or with 2PD?

 

[devmach-e]

Well, I just want to know which is more efficient, WOT to 80 mph with 1PD, or with 2PD?

Yes.

 

[ctenidae]

​

Oh man, this thread has been highly entertaining!

What I'm noticing is there may be 2 definitions of coasting and so folks may be arguing against their own assumptions.
...
If you are starting at freeway speed from point A to a stop at point B, is it more efficient to not apply regen brakes until the very end of the stop, or is it more efficient to start applying brakes quickly then crawl to point B? (both never using friction, only regen)

Answer is apply regen quickly then crawl to B, but people will hate you and you will hate yourself ?. Reason is while rolling resistance is a linear loss across all speeds, drag is exponential and dominant at high speeds. So you can choose to lose your kinetic energy to drag early or regen early. You can NOT choose regen vs rolling resistance though.

Totally agree with the definitional exercise. "Coasting" is the wrong word to use. "Manual regen control" is closer to the proper term, I think.

The presumption that 1PD involves trundling along or ankle exhaustion or dragging brakes is also incorrect.

In your highway speeds to a stop scenario, you are correct - getting down below high drag speeds early is more efficient, but that's not really the comparison between 1PD and 2 PD. Instead, might I suggest this scenario:

1PD: From a stop, accelerate to highway speed. Maintain highway speed, then use regen braking to stop at point B as efficiently as possible.

2PD: From a stop, accelerate to highway speed. Release the accelerator to achieve 0T0B (assuming 2PD does not have any liftoff regen to simulate engine braking), then manually engage regen braking at a reduced speed to come to a stop at point B as efficiently as possible.

Both scenarios use the same amount of energy to reach speed. Both should have the same regen efficiency.

The net energy used in 1PD is the amount used to accelerate minus ((potential regen minus regen efficiency losses) minus (energy used to maintain speed)).

The net energy used in 2PD is the amount used to accelerate minus ((potential regen minus potential lost to drag) minus (regen efficiency losses)).

The question is, which is higher - the potential regen lost to drag, or energy used to maintain speed?

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