Regenerative brake

[whitex]

Yes I did. I have a Bachelors and Masters in Engineering, which is why I understand concepts like the conservation of energy that seem to be eluding you. Maybe you can explain where that energy to maintain the same speed as coasting is going if it is not applying accelerative forces?
I’ll wait… (hint, if the forces are the same, then no energy CAN be getting used)

Once you dig deeper into this, you realize that the regen braking method is just better and more intuitive. The throttle pedal becomes a speed control pedal, instead of a mechanism for regulating fuel consumption. 30% pedal application will give you 30% speed regardless of whether you are going uphill or downhill, rather than 30% fuel consumption, which gives you rampant acceleration downhill and almost nothing going uphill.
eg I could be driving the Rivian down a steep hill with 30% pedal, getting a ton of regen despite being on the throttle. Or in the Taycan, I am on the brakes modulating the pedal all the way.

The reason coasting is more efficient is the human factor. If you are in fact able modulate your accelerator to maintain your speed to a high degree of accuracy (so your regen is never activated), then coasting vs. one-pedal driving are the same. However, most people don't have this level of precision on the accelerator foot, so they end up oscillating around the desired speed, accelerating up some, regenerating some, with the DC component of the sinusoid being their desired speed. Unfortunately regen is not 100% efficient, so slowing down from 70mph to 60mph using regen and then speeding up back to 70mph will not be a net zero energy used.

Another disadvantage of one-pedal driving is the maximum regeneration that can be applied. For example Taycan J1 (2020-2024) can regen up to 290kW of power. If you applied this strength of regen in one-pedal driving, it would be a horrible experience - when you lift off the accelerator pedal, you'd be decelerating at well above 1G, which would be jarring for the driver (and passengers). For reference, IIRC Tesla maxes out the one-pedal regen at 60kW, which is about a 5th of what Taycan can regen. For a long time Tesla also didn't have simulated regen (using physical brakes to simulate regen), which also meant that whenever my battery was cold or full, the Tesla would regen less (or not at all), creating a feeling of the car being broken, because it drove differently when battery was cold, hot, or near 100%. On a Taycan, the braking profile feels the same, even if you fill your battery to 100% so there is no regen - I'm sure it took a lot of tuning on Porsche's part.

I drove Teslas for a decade, I liked the one pedal driving. After switching to Taycan though, I actually prefer the blended system, though I do usually drive with the Taycan normal regen on, as that helps me maintain the exact speed I want (and what I'm willing to get clocked at ) - I don't recall ever having to ride the brakes as you describe. On my wife's Audi, I like their auto-regen mode, which varies regen based on traffic in front and road slope. Taycan's auto-regen is supposed to do similar, but somehow I don't like using it.

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[f1eng]

I actually prefer the blended system, though I do usually drive with the Taycan normal regen on, as that helps me maintain the exact speed I want (and what I'm willing to get clocked at )

Porsche "cheat" the coasting a little bit down hills. If you look at the power meter you can see a small amount of regen being applied, presumably to preven too much potential energy acceleration.

 

[or1]

The reason coasting is more efficient is the human factor. If you are in fact able modulate your accelerator to maintain your speed to a high degree of accuracy (so your regen is never activated), then coasting vs. one-pedal driving are the same. However, most people don't have this level of precision on the accelerator foot, so they end up oscillating around the desired speed, accelerating up some, regenerating some, with the DC component of the sinusoid being their desired speed. Unfortunately regen is not 100% efficient, so slowing down from 70mph to 60mph using regen and then speeding up back to 70mph will not be a net zero energy used.

Another disadvantage of one-pedal driving is the maximum regeneration that can be applied. For example Taycan J1 (2020-2024) can regen up to 290kW of power. If you applied this strength of regen in one-pedal driving, it would be a horrible experience - when you lift off the accelerator pedal, you'd be decelerating at well above 1G, which would be jarring for the driver (and passengers). For reference, IIRC Tesla maxes out the one-pedal regen at 60k, which is about a 5th of what Taycan can regen. For a long time Tesla also didn't have simulated regen (using physical brakes to simulate regen), which also meant that whenever my battery was cold or full, the Tesla would regen less (or not at all), creating a feeling of the car being broken, because it drove differently when battery was cold, hot, or near 100%. On a Taycan, the braking profile feels the same, even if you fill your battery to 100% so there is no regen - I'm sure it took a lot of tuning on Porsche's part.

I drove Teslas for a decade, I liked the one pedal driving. After switching to Taycan though, I actually prefer the blended system, though I do usually drive with the Taycan normal regen on, as that helps me maintain the exact speed I want (and what I'm willing to get clocked at ) - I don't recall ever having to ride the brakes as you describe. On my wife's Audi, I like their auto-regen mode, which varies regen based on traffic in front and road slope. Taycan's auto-regen is supposed to do similar, but somehow I don't like using it.

This is exactly my view as well. Very few people are able to hold the right pedal at the no-battery-energy-applied-or-gained point, and they (we) are less energy efficient as a result. But great for those who can.

An auto-regen setting that more or less magically did what I want when I let the pedal up, would have been nice: coasting when the road is free, regen braking at MY preferred strength when needed. But I was happy and comfortable with the Taycan pedal at no regen on liftup not long after switching from Tesla, and prefer it now.

For those who think more of operating efficiency (convenience) than energy efficiency, I certainly see benefits of a wider range of speed control with the right pedal. But I agree with the above quoted description of downsides. Not least because Taycan regen on brake pedal use is so strong.

 

[Jhenson29]

I'm a Rivian development engineer.

Mental note. Don’t buy Rivians. Development engineers not very smart.

 

[Jonathan S.]

“On my wife's Audi, I like their auto-regen mode, which varies regen based on traffic in front and road slope. Taycan's auto-regen is supposed to do similar, but somehow I don't like using it.”

“An auto-regen setting that more or less magically did what I want when I let the pedal up, would have been nice: coasting when the road is free, regen braking at MY preferred strength when needed.”

Perhaps I'm in a small minority here, but I love the auto regen feature on my Taycan.
(Definitely one of the features I missed while driving my ICE A6ar for almost two months during the racoon repair.)
That features does behave a bit differently from our i4: the i4 auto regen is a bit more aggressive for slowing down in city driving, and the Taycan is a bit more aggressive in highway driving. But both of them are definitely reacting to traffic, and I think quite well, often sensibly slowing down in anticipation of inevitably slowing down better than my own judgement.
(The i4 is especially smart about slowing down to a crawl as I approach a tight traffic circle/roundabout near our daughter's school -- felt absurd the first time, but then I realized it was doing the right thing.)

 

[or1]

“On my wife's Audi, I like their auto-regen mode, which varies regen based on traffic in front and road slope. Taycan's auto-regen is supposed to do similar, but somehow I don't like using it.”

“An auto-regen setting that more or less magically did what I want when I let the pedal up, would have been nice: coasting when the road is free, regen braking at MY preferred strength when needed.”

Perhaps I'm in a small minority here, but I love the auto regen feature on my Taycan.
(Definitely one of the features I missed while driving my ICE A6ar for almost two months during the racoon repair.)
That features does behave a bit differently from our i4: the i4 auto regen is a bit more aggressive for slowing down in city driving, and the Taycan is a bit more aggressive in highway driving. But both of them are definitely reacting to traffic, and I think quite well, often sensibly slowing down in anticipation of inevitably slowing down better than my own judgement.
(The i4 is especially smart about slowing down to a crawl as I approach a tight traffic circle/roundabout near our daughter's school -- felt absurd the first time, but then I realized it was doing the right thing.)

I cannot fully explain why, but I am more comfortable with wife's i4 auto regen, than with my Taycan's auto regen.

 

[whitex]

I cannot fully explain why, but I am more comfortable with wife's i4 auto regen, than with my Taycan's auto regen.

My feeling exactly. I cannot put my finger on it, but my wife's Q8 eTron auto regen just seems "intuitive" and very "transparent", i.e. operated in the background and I often forget it's there, while Taycan's seems more in the foreground. eTron's auto regen is also the default power-up mode, vs. Taycan you have to turn it on each time you drive.

 

[cometguy]

The reason coasting is more efficient is the human factor. If you are in fact able modulate your accelerator to maintain your speed to a high degree of accuracy (so your regen is never activated), then coasting vs. one-pedal driving are the same. However, most people don't have this level of precision on the accelerator foot, so they end up oscillating around the desired speed, accelerating up some, regenerating some, with the DC component of the sinusoid being their desired speed. Unfortunately regen is not 100% efficient, so slowing down from 70mph to 60mph using regen and then speeding up back to 70mph will not be a net zero energy used.

Another disadvantage of one-pedal driving is the maximum regeneration that can be applied. For example Taycan J1 (2020-2024) can regen up to 290kW of power. If you applied this strength of regen in one-pedal driving, it would be a horrible experience - when you lift off the accelerator pedal, you'd be decelerating at well above 1G, which would be jarring for the driver (and passengers).

It sounds to me as if your experience with one-pedal driving has been sub-par because of the design of the one-pedal cars that you have driven. I remember test-driving a Tesla Model S and feeling that the one-pedal driving was not designed well. My Volvo PHEV (XC60) has one-pedal driving that is superb; it is designed so that if you're driving at high speeds (expressways) and let off the accelerator, it will slow down gradually -- not suddenly -- until it gets down to about 40 mph, when it starts to get more aggressive, but not in a jolting way. I use one-pedal driving all the time in my XC60 (whether in all-electric mode in stop-and-go traffic or at highway speeds), and my passengers have never complained about jolting or uncomfortable slowing down. Plus, my wife will use the one-pedal driving occasionally it the same vehicle, and she's much less experienced with it, and yet she has no troubles using it smoothly and easily. There's no amount of hand-waving or arguing that lets Porsche off the hook on this topic: they should provide true one-pedal driving (especially at the Porsche price point), and let the driver decide whether to use it or not. One-pedal driving is far superior to two-pedal driving in ice, snow, and other slippery surfaces when you need to slow down or stop quickly without skidding, and it's much nicer to use in slow-driving conditions when you're driving down a steep hill or mountain. Any well-designed car should have a way to slow down, and remain slow (i.e., not just "coast"), when the driver wants to *without having to keep one's foot on the brake pedal*; ICEVs have paddle shifters or gear-shift sticks to slow down without applying the brakes, and this is a good reason for all BEVs to have one-pedal driving (at least as optional). I'd encourage all sub-par one-pedal car manufacturers to look at Volvo to see how one-pedal engineering can and hould be done well.

 

[Jonathan S.]

How is OPD preferable on slick roads?
I can think of plenty of situations when I don’t want to provide power to the wheels but I also don’t want to be braking.
And in such a situation, isn’t regen braking the same as friction braking from a traction viewpoint?

I’ll definitely believe though that OPD can be more sophisticated than when my wife and I test drove a Model Y, during the period Tesla did not allow any user setting for OPD.
The only reason our daughter didn’t howl in protest as my wife and I took turns essentially slamming on the brakes inadvertently is that she was so obsessed with Tesla that she wanted us to buy one, no matter how incompetent our use of OPD.

 

[Vercingetorix]

I bet one pedal driving with a rwd Model 3 on ice is an experience one doesn’t want twice. Lift off oversteer is built in even going in a straight line.

 

[whitex]

It sounds to me as if your experience with one-pedal driving has been sub-par because of the design of the one-pedal cars that you have driven. I remember test-driving a Tesla Model S and feeling that the one-pedal driving was not designed well. My Volvo PHEV (XC60) has one-pedal driving that is superb; it is designed so that if you're driving at high speeds (expressways) and let off the accelerator, it will slow down gradually -- not suddenly -- until it gets down to about 40 mph, when it starts to get more aggressive, but not in a jolting way.

Not at all. I drove it on many Teslas for over a decade. They have had different approaches, and settable parameters too (such as strength, or aggressiveness, or full stop vs creep). I still like it. The slowing down was never jolting. I got very good (never perfect down to a Watt) at threading the needle with the accelerator too, watching actual power numbers on the display and through some debug equipment I added to see the actual regen numbers, since when cruising on the highway speeds regen in the order of 100's or Watts would be otherwise imperceptible. I got in a habit to use regen to its maximum when slowing down from faster speeds, by hovering my foot over the brake and adding as little mechanical braking as possible. As I said, I got pretty good at it. At the same time I watched my wife drive, or my mother in law, or my teenage kids, and they were not that precise (their cars also didn't have the more detailed regen measurement equipment).

At fist, I thought as you did, that Porsche should have gone with one pedal driving. But after driving the Taycan, I learned I like the solution better. For about a year I drove the Taycan and occasionally my wife's Tesla, and some rented Teslas when traveling, so I had some comparison time. The only time I miss one-pedal driving on a Taycan is crawling in stop-and-go traffic, but I just use ACC for that. I also use the normal regen on the Taycan for more precise speed control, but wouldn't want it any stronger (and definitely not the over one G regen Taycan is capable of) on the accelerator pedal.

There's no amount of hand-waving or arguing that lets Porsche off the hook on this topic: they should provide true one-pedal driving (especially at the Porsche price point), and let the driver decide whether to use it or not.

There is no need for hand waving. Look up the max regen factual numbers. Hookup an OBD scanner to your Volvo and see whether you really are able to cruise without ANY regen activation using one-pedal. If you want empirical data, drive at constant highways speeds on cruise control, vs. manual accelerator modulation, vs. regen off (if you can on that same car), all the while monitoring the electron consumption.

One-pedal driving is far superior to two-pedal driving in ice, snow, and other slippery surfaces when you need to slow down or stop quickly without skidding, and it's much nicer to use in slow-driving conditions when you're driving down a steep hill or mountain.

To the contrary. On low traction surfaces, such as snow and ice, regen can actually be dangerous. I experienced this first hand with my fist EV which was rear wheel drive, with one pedal driving. Even small decelerations of the rear wheels due to letting off the accelerators made the rear wheels more likely to break traction in a turn, which resulted in oversteer, and on some really slippery ice a complete spin-out. I always disabled regen when roads got really slippery. Being able to explicitly control when the acceleration or braking action is applied, vs. having to thread the needle keeping the accelerator "just right" so that the wheels are neither accelerating or braking, one pedal driving is much more error prone.

One-pedal driving is far superior to two-pedal driving in ice, snow, and other slippery surfaces when you need to slow down or stop quickly without skidding, and it's much nicer to use in slow-driving conditions when you're driving down a steep hill or mountain. Any well-designed car should have a way to slow down, and remain slow (i.e., not just "coast"), when the driver wants to *without having to keep one's foot on the brake pedal*; ICEVs have paddle shifters or gear-shift sticks to slow down without applying the brakes, and this is a good reason for all BEVs to have one-pedal driving (at least as optional). I'd encourage all sub-par one-pedal car manufacturers to look at Volvo to see how one-pedal engineering can and hould be done well.

Preference is always relative to a person. Efficiency on the other hand can be quantified and measured. There will still be a human factor, for example you might be controlling the throttle more precisely that others, but for that you can use a random sample of people and look at the distribution to draw objective conclusions.

Can less efficient way of driving be preferred by some people? Absolutely. I am fully aware the way I prefer to drive, accelerating quickly for example, is definitely not the most efficient in terms of energy or even tire wear. In this case you prefer a way that is less efficient for most drivers. That is your preference, no different that the location and layout of the buttons to control various functions of the car, or the color of the car, acceleration curve, or any other feature. I paid a premium price for my Turbo because I value acceleration, it doesn't mean I think Porsche should discontinue all trims under CT Turbo, because my acceleration is far superior to the CT4 or CT4S. If buying a Taycan CT today, I might be annoyed that the CT is not offered in Turbo GT version. But again, that is my personal preference that massive power provides superior driving experience, just like you think one-pedal driving provides a superior driving experience.

 

[cometguy]

How is OPD preferable on slick roads?
I can think of plenty of situations when I don’t want to provide power to the wheels but I also don’t want to be braking.
And in such a situation, isn’t regen braking the same as friction braking from a traction viewpoint?

I’ll definitely believe though that OPD can be more sophisticated than when my wife and I test drove a Model Y, during the period Tesla did not allow any user setting for OPD.
The only reason our daughter didn’t howl in protest as my wife and I took turns essentially slamming on the brakes inadvertently is that she was so obsessed with Tesla that she wanted us to buy one, no matter how incompetent our use of OPD.

In my experience, the wheels don't slip during one-pedal braking like they do when you engage the physical brakes/pads to "freeze" the wheels.

 

[Jhenson29]

In my experience, the wheels don't slip during one-pedal braking like they do when you engage the physical brakes/pads to "freeze" the wheels.

My guess would be the OPD regen torque is relatively low, and exceptionally low compared to available friction brake torque, so less likely to generate a torque to create slip.

There’s nothing special about electric motor torque that would prevent slipping. I have to deal with managing slip from both electric motors and friction brakes all of the time in industrial controls.
If the surface force from the applied torque exceeds the friction force, it slips. Doesn’t matter what the source of the torque is.

 

[cometguy]

If you want empirical data, drive at constant highways speeds on cruise control, vs. manual accelerator modulation, vs. regen off (if you can on that same car), all the while monitoring the electron consumption.


To the contrary. On low traction surfaces, such as snow and ice, regen can actually be dangerous. I experienced this first hand with my fist EV which was rear wheel drive, with one pedal driving. Even small decelerations of the rear wheels due to letting off the accelerators made the rear wheels more likely to break traction in a turn, which resulted in oversteer, and on some really slippery ice a complete spin-out. I always disabled regen when roads got really slippery. Being able to explicitly control when the acceleration or braking action is applied, vs. having to thread the needle keeping the accelerator "just right" so that the wheels are neither accelerating or braking, one pedal driving is much more error prone.

I notice that the power meter in my Taycan's instrument panel shows much more regen charge (green bar at upper left) when in Regen mode than when not with the foot off the brake (i.e., it can be significant when "coasting" in Regen mode vs. almost zero when "coasting" in Coast mode). I would have a hard time believing that when my foot is on the brake pedal, there's more regen in "Coast mode" than in "Regen" mode.

As for slippery conditions with one-pedal driving: from my personal experience, there is much less slippage than when using two-pedal driving and having to touch the brake pedal. Granted, I am going much slower anyway when it's slippery out, so maybe you and I differ in that regard.

 

[cometguy]

I notice that the power meter in my Taycan's instrument panel shows much more regen charge (green bar at upper left) when in Regen mode than when not with the foot off the brake (i.e., it can be significant when "coasting" in Regen mode vs. almost zero when "coasting" in Coast mode). I would have a hard time believing that when my foot is on the brake pedal, there's more regen in "Coast mode" than in "Regen" mode.

Also, in my Volvo PHEV, I do definitely see more range (i.e., more regen power going back into the battery) when going down long hills/mountains with one-pedal driving on than I get with one-pedal driving off (whether using the brake pedal or not in such situations with 2-pedal driving)... Curiously, on those same long hills, my Taycan doesn't seem to regen as much (i.e., add as much charge back to the battery pack) as my Volvo does.

As for slippery conditions with one-pedal driving: from my personal experience, there is much less slippage than when using two-pedal driving and having to touch the brake pedal. Granted, I am going much slower anyway when it's slippery out, so maybe you and I differ in that regard.

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