One pedal drive (vs) Brake regen

[Blue highway]

1PD may help the regen slightly but more important is that it will make your brake pads last a lot longer. Maybe we’ll never need a brake job.

1 pedal or two, I expect most users will never need to do pads due to wear because of regen braking.

However, you may want to use the actual brakes now and then as they can "freeze" in place if you don't exercise them once in a while, especially in a wet climate.

Fun fact, Tesla expects owners to lube the brakes once a year for this reason.

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[dtbaker61]

Was reading this thread and noticed this on the first page. This is not true. CONSUMING power is very efficient but regen is not. It is between 60-80% efficient. Typically not over 70% efficient. The other is lost as heat in the conversion process from AC to DC to charge the battery pack.

I'm not sure how efficient regen in our MME is... there are losses going thru the inverter for sure, but efficiency thru inverters typically varies with load, so I dunno what the AVERAGE efficiency would be in normal 1-p driving around town stop-and-go. It would depend on how fast you go, and stop.

Efficiency thru inverters is higher at higher loads, which would be decelerating from higher speeds, 0% throttle for max regen. Regen at lower speeds and feathering throttle are likely at lower efficiency. So the stop-and-go coaching would be to judge your distance approaching a redlight, and lift foot completely to max regen... unless you think you can feather your way up to a light, keep it rolling, and catch the green light without stopping.

 

[breeves002]

I'm not sure how efficient regen in our MME is... there are losses going thru the inverter for sure, but efficiency thru inverters typically varies with load, so I dunno what the AVERAGE efficiency would be in normal 1-p driving around town stop-and-go. It would depend on how fast you go, and stop.

Efficiency thru inverters is higher at higher loads, which would be decelerating from higher speeds, 0% throttle for max regen. Regen at lower speeds and feathering throttle are likely at lower efficiency. So the stop-and-go coaching would be to judge your distance approaching a redlight, and lift foot completely to max regen... unless you think you can feather your way up to a light, keep it rolling, and catch the green light without stopping.

Sure it varies on load but it's not "pretty darn efficient". That was my point.

Remember, coasting is more efficient than regen. In a vehicle you'll see more efficiency off of less regen and coming to slower stops versus maximum regen for a quicker stop.

 

[ctenidae]

Remember, coasting is more efficient than regen.

Can you explain this? It just doesn't make any logical sense to me, particularly if you factor in real world driving and more than just distance rolled.

 

[dtbaker61]

Sure it varies on load but it's not "pretty darn efficient". That was my point.

Remember, coasting is more efficient than regen. In a vehicle you'll see more efficiency off of less regen and coming to slower stops versus maximum regen for a quicker stop.

true hyperlinking techniques using coasting tends to make other drivers crazy if they are behind you and your speed is changing constantly.... if you don't have anyone behind you, go for it.

'pretty darn efficient' I guess is subjective when you compare it to 0% regen and 100% heat when you use mechanical brakes.... so let's not argue semantics on that one.

 

[breeves002]

'pretty darn efficient' I guess is subjective when you compare it to 0% regen and 100% heat when you use mechanical brakes.... so let's not argue semantics on that one.

I mean semantics aside I believe most people assume when you say "just losing a few percent" you mean a single digit number. Just trying to make sure the understanding is regen is not 90%+ efficient as you seem to have indicated. It is in reality about 60-70% efficient in most EV applications.

 

[breeves002]

Can you explain this? It just doesn't make any logical sense to me, particularly if you factor in real world driving and more than just distance rolled.

To elaborate it comes down to a situation where you can coast and possibly pick up speed over regenerating to maintain speed. If speed is constant it doesn't make a difference.

For example if you're going down a slight hill, allowing the car to coast to gain a few MPH is more efficient than regenerating power to maintain your speed. Of course how much does it really matter? Probably not much. Though if you're going down a big hill and can gain a large amount of speed and keep that momentum it can be significantly more efficient than regeneration then applying the power to maintain speed right away.

 

[ctenidae]

To elaborate it comes down to a situation where you can coast and possibly pick up speed over regenerating to maintain speed. If speed is constant it doesn't make a difference.

For example if you're going down a slight hill, allowing the car to coast to gain a few MPH is more efficient than regenerating power to maintain your speed. Of course how much does it really matter? Probably not much. Though if you're going down a big hill and can gain a large amount of speed and keep that momentum it can be significantly more efficient than regeneration then applying the power to maintain speed right away.

Downhill coasting I totally get - let gravity supply the energy. I could follow, but am pretty sure I couldn't do, the math on how wide the band around a "coasting" pedal position in 1PD would be where the little bit of extra speed gained with a little too much pedal balances against the little but if efficiency loss from too little pedal (and therefore too much regen). I suspect it's wide enough to be manually doable, so 1PD and 2PD would be, effectively, the same.

I wonder - if you regen just enough to maintain your speed down the hill, would you gain more energy than you lose to the increasing drag from letting gravity speed you up? Drag increases with the square of speed, right? At what point does that added drag outweigh the electricity you can generate using gravity?

/maths are hard...

Back of the envelope, falling straight down (no rolling resistance), terminal velocity for an MME looks to be about 143 mph, if that helps anything...

 

[AKgrampy]

To elaborate it comes down to a situation where you can coast and possibly pick up speed over regenerating to maintain speed. If speed is constant it doesn't make a difference.

For example if you're going down a slight hill, allowing the car to coast to gain a few MPH is more efficient than regenerating power to maintain your speed. Of course how much does it really matter? Probably not much. Though if you're going down a big hill and can gain a large amount of speed and keep that momentum it can be significantly more efficient than regeneration then applying the power to maintain speed right away.

The genesis of this discussion was/is whether 1PD is more or less efficient than 2PD. Of corse you can come up with some coasting situations but remember you only coast in N. There is no coasting in 2PD. Also maybe if you are alone you may coast down a hill but on a busy highway you place yourself and others in an unsafe situation if you elect to coast as you may need to instantly accelerate. You would also lose any benefit of the coast if you were to need to need to brake suddenly as you would lose all you gained to friction. Bottom line though is drive however you like. I chose go with 2PD Engaged as that has the same feel as my ICE rig but I am going to give 1PD a go this summer.

 

[Space Ghost GT]

The bulk of the article says 1PD and 2PD are effectively the same and it's up to you how you like to drive.

Porsche does lift-off regen (even though not true 1PD) that simulates engine braking. Meaning, it doesn't coast, either, because that's wasteful. Polestar says there's very little difference in reality between 1PD and 2PD (boat anchor comment notwithstanding). BMW actively manages the amount of liftoff regen for conditions, never, apparently, "coasting."

The article is interesting in its one conclusory statement, though: "If there's any conclusion to be drawn here, it's perhaps that you don't need to worry so much about one-pedal driving... if you don't like it, chances are you're not leaving a lot, if any, extra range on the table." If you don't use it, you're leaving some range on the table. That is their conclusion. Ergo, that article says 1PD is more efficient. Maybe not a lot, maybe none. It pointedly does not say that if you use 1PD you're leaving some range on the table, though.

Interestingly, the article opens with what I think is the #1 issue people have with 1PD - they don't know how to drive with it. From the article : "You lift off the accelerator pedal, and wham! You nearly come to a complete stop." That's known in the common parlance as "doing it wrong."

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.

 

[mfbrown]

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!)

Forget about what got you to speed, becasuse it is the same for 1P or 2P; what counts is the energy stored in the car moving at that speed. That amount of stored energy is going to be the same whether in 2P or 1P mode. Going from X MPH to 0 in each case will convert the same amount of energy into whatever. If the car travels farther in 2P mode, then more of that available energy is consumed in moving it the longer distance (against road friction, air resistance, etc.). In 1P mode, it traveled significantly less and thus consumed much less energy moving the car against those other forces. Where did the extra energy go? It went into the regenerative system. You have one bucket of energy in both cases; it is just a matter of how you allocate it.

 

[breeves002]

The genesis of this discussion was/is whether 1PD is more or less efficient than 2PD. Of corse you can come up with some coasting situations but remember you only coast in N. There is no coasting in 2PD. Also maybe if you are alone you may coast down a hill but on a busy highway you place yourself and others in an unsafe situation if you elect to coast as you may need to instantly accelerate. You would also lose any benefit of the coast if you were to need to need to brake suddenly as you would lose all you gained to friction. Bottom line though is drive however you like. I chose go with 2PD Engaged as that has the same feel as my ICE rig but I am going to give 1PD a go this summer.

Yes I agree, I was not responding to the original idea, I was just responding to the hypothetical. I'm not saying coasting makes sense 100% of the time just the it is more efficient on paper. Just the facts, not the reality of every situation. Every driving situation is different and your milage may vary...

 

[Motomax]

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.

You may be efficient but I guarantee the people behind you are not amused haha. The question isn’t really if it’s possible to be more efficient while coasting vs regen, it’s what’s more efficient when driven how the vast majority of people drive. That answer will always be regen (1PD or 2pd).

 

[devmach-e]

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.

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...

 

[Kamuelaflyer]

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

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