Why regenerative braking belongs on the brake pedal

[JeffK]

When you said "by definition", I assumed you didn't mean some subset of cases. My mistake.

But let's see your math.

Simple example everyone can understand, let's use your original premise (what I mean when I said "by definition")

if no speed increase is involved in coasting,

Two vehicles go down a hill and maintain constant velocity of 75mph, one is using regen to maintain 75mph the other is coasting to maintain 75mph. Both get to the bottom of the hill and are on flat road still doing 75mph (same kinetic energy at this point).

Which one was more efficient? Which one has stored potential energy from the downhill travel?
Regen obviously.

No math needed as it's common sense *based on your premise* alone.

Now, in the real world it would be very difficult for the same type of car on the same hill with the same conditions to satisfy coasting and using regen to maintain 75mph. Realistically this would have to be two different hills. and if you used regen where you'd be coasting then you'd lose speed and if your coasted where you'd regen you'd increase speed.

 

[alseTrick]

So is mountain driving the only scenario where this even comes into play? In other words, is there more agreement that one option versus the other is better on flatter driving?

 

[JeffK]

So is mountain driving the only scenario where this even comes into play? In other words, is there more agreement that one option versus the other is better on flatter driving?

In flat driving I cannot think of a way you could maintain a speed with regen unless you had one heck of a tail wind. If you want to slow down in a hurry use regen. If you don't need to slow down in a hurry then coast or maintain speed.
Don't regen just to speed up again when you don't need to, that wastes energy.

 

[Topher]

Two vehicles go down a hill and maintain constant velocity of 75mph, one is using regen to maintain 75mph the other is coasting to maintain 75mph.

The trouble with that example is that it is physically impossible. If one is coasting at 75 mph (fixed) than one will get 0 regen going down the same hill at 75 mph. This is just simple physics. There is no energy to be had.

A proper example would be coasting at 75 mph versus regen at 60 mph.

Thank you kindly.

 

[JohnSnowNW]

My Leaf is never NOT driven in B mode. When I take my foot off the gas, I want strong regen...every single time.

 

[jgs]

This thread (https://teslamotorsclub.com/tmc/threads/hyper-miling-regen-and-neutral) touches on a lot of the same issues and has graphs!

So is mountain driving the only scenario where this even comes into play? In other words, is there more agreement that one option versus the other is better on flatter driving?

The one I can think of is approaching a stop (whether light or sign) -- you're better off energy-wise, coasting to a stop, than regen'ing to a stop. This means letting off the go pedal earlier, that's pretty much the sole difference. With the light, it's basically always better to coast to a stop if you can, since you're just minimizing the amount of time you spend sitting stopped at the light (in the best of all possible worlds, it turns green before you reach it). With the stop sign, it comes down to how fast an average trip speed you want to maintain, as the thread above points out -- the fastest average speed has you holding your full speed til you get to the sign, braking hard (friction brakes, duh), then peeling out again. The best average energy has you coasting to a dead stop, then gently pulling away. Real life for most of us is somewhere in between.

 

[Pando]

Two vehicles go down a hill and maintain constant velocity of 75mph, one is using regen to maintain 75mph the other is coasting to maintain 75mph.

Which one was more efficient? Which one has stored potential energy from the downhill travel?
Regen obviously.

No.

Your premise is true ONLY if the one "coasting" is actually using physical brakes to maintain 75mph going downhill.

However, if the one coasting manages to maintain 75mph without braking (when air and tire resistance balances out the acceleration due to gravity, which is possible with just the right grade), then there is no regen possible on the other to maintain the same 75mph. They would both be "coasting", and therefore they are both equal in efficiency.

 

[gregincal]

In flat driving I cannot think of a way you could maintain a speed with regen unless you had one heck of a tail wind. If you want to slow down in a hurry use regen. If you don't need to slow down in a hurry then coast or maintain speed.
Don't regen just to speed up again when you don't need to, that wastes energy.

I assume by "one option or another" he was referring to what is supposed to be the topic of the thread, what pedal regen should be on. This whole discussion of coasting is a huge detour. Coasting is generally better for efficiency, sure. That's why it's a good thing that the Model S is so great at coasting, I do it all the time.

 

[JeffK]

it is physically impossible.

See! that's what I said.

 

[alseTrick]

This thread (https://teslamotorsclub.com/tmc/threads/hyper-miling-regen-and-neutral) touches on a lot of the same issues and has graphs!



The one I can think of is approaching a stop (whether light or sign) -- you're better off energy-wise, coasting to a stop, than regen'ing to a stop. This means letting off the go pedal earlier, that's pretty much the sole difference. With the light, it's basically always better to coast to a stop if you can, since you're just minimizing the amount of time you spend sitting stopped at the light (in the best of all possible worlds, it turns green before you reach it). With the stop sign, it comes down to how fast an average trip speed you want to maintain, as the thread above points out -- the fastest average speed has you holding your full speed til you get to the sign, braking hard (friction brakes, duh), then peeling out again. The best average energy has you coasting to a dead stop, then gently pulling away. Real life for most of us is somewhere in between.

Thanks for the info and attempting to get the link.

But it's not working for me:

Tesla Motors Club - Error
The requested page could not be found.

 

[Pando]

To put it simply:

Flat road vs. mountain driving:

Flat road = say baseline = 100% energy.

Mountain driving = spend twice as much energy (200%) going uphill, regenerate half of the 'extra' energy (-50%) you spent coming back down. Net result is still less efficient than on flat road (150% of energy on mountain driving vs. 100% on flat road).

Coasting vs. regen:

Coasting = using air/tire resistance to slow you down, no energy recapture. But, you're not using energy as long to maintain constant speed.

Regen = using MORE energy to maintain constant speed longer, but later putting 'some' of that spent energy back to the battery when slowing down.

Given equal amount of initial acceleration from stop to the same cruise speed, coasting would use less net energy because (1) the constant cruise speed isn't maintained as long - less air resistance over the entire course on the average, and (2) the inefficiency of energy consumption/regen on the Regen mode.

 

[jgs]

Thanks for the info and attempting to get the link.

But it's not working for me:

Tesla Motors Club - Error
The requested page could not be found.

Sorry, truncated the URL too much and then broke a cardinal rule by not checking it. Corrected URL is Hyper-miling, regen, and Neutral (I'll also go fix it in the original post, or rather, I would if I could. I still don't understand what rules the new forums apply for when you can, and can't, edit an old post.).

 

[bhzmark]

Two vehicles go down a hill and maintain constant velocity of 75mph, one is using regen to maintain 75mph the other is coasting to maintain 75mph. Both get to the bottom of the hill and are on flat road still doing 75mph (same kinetic energy at this point).

Which one was more efficient? Which one has stored potential energy from the downhill travel?
Regen obviously.

No math needed as it's common sense *based on your premise* alone.

You still don't get it.

Further discussion is waste of time.

When you realize why your example above not only doesn't prove your point, but demonstrates a fundamental misunderstanding, and you own a tesla, then come back, to post like I did, that you were mistaken.

 

[Johan]

Well argued by the original author but the "appeal to nature" argument has no validity - there is nothing that's more or less natural about having regen on lift off of accelerator or on the brake pedal. It's all convention (which mustn't be confused with "naturality". There's nothing "natural" about cars anyway).

The appeal to safety argument is clearly wrong since millions of Tesla miles driven disproves the way Tesla implementing regen being dangerous.

The appeal to efficiency/coasting argument has some merit but is probably for the vast majority outweighed by the convenience of one foot driving.

The rest is, as they say, purely subjective that is no right or wrong answer.

 

[Johan]

One more safety aspect in favor of heavy regen on accelerator lift off, that the OP author conveniently bypasses, is the fact that the time to lift the foot from the accelerator to the brake pedal and depress the brake will ALWAYS be longer then the time to just lift off the accelerator. This can buy precious 1/100's of seconds in an emergency. (I'm assuming very few people practice two-foot driving).

 

[Topher]

The appeal to safety argument is clearly wrong since millions of Tesla miles driven disproves the way Tesla implementing regen being dangerous.

Nope. There are plenty of things that make Tesla safer. Unless you have a control group, you don't know what any particular variable does in terms of safety. Tesla has three versions of black cars, therefore having 3 black versions is safer. See, fallacious.

If you have a control group and a correlation study, then we can talk about it.

Thank you kindly.

 

[Johan]

Nope. There are plenty of things that make Tesla safer. Unless you have a control group, you don't know what any particular variable does in terms of safety. Tesla has three versions of black cars, therefore having 3 black versions is safer. See, fallacious.

If you have a control group and a correlation study, then we can talk about it.

Thank you kindly.

Fair enough. The "evidence" I refer to its anecdotal and observational in nature without a proper control group. But non perfect data isn't always worthless. It's also appropriate to ask with who the burden of proof should lie: he who claims Tesla's implementation of regen is unsafe or he who claims it seems not unsafe?

 

[Craig9080]

I am blown away buy the amount of arrogant and willfully ignorant hate over a guy pointing out the practical effects of regen on the throttle. If your "rebuttal" doesn't include an empirical rebuke of the science at hand, the it holds no relevance but feel free to exercise your freedom of speech...if you live in the USA...because Canada doesn't have that.

 

[gregd]

One more safety aspect in favor of heavy regen on accelerator lift off, that the OP author conveniently bypasses, is the fact that the time to lift the foot from the accelerator to the brake pedal and depress the brake will ALWAYS be longer then the time to just lift off the accelerator. This can buy precious 1/100's of seconds in an emergency. (I'm assuming very few people practice two-foot driving).

I do drive with two feet (feels the most natural when I don't have a clutch to mess with). It's still faster with accelerator regen, because the left (brake) foot is usually resting on the floor, not sitting on top of the brake pedal, unless I'm already expecting to stop. Always bit quicker than driving with one foot (shorter distance, single direction of motion), but perhaps not as instantaneous it might seem.

 

[csphili]

Why won't this thread die?