Model S regenerative braking with brake pedal

ualdriver said:

Per p57 of the manual, there are two settings for regenerative braking. Setting the control to "low" limits regenerative braking when one lifts off the accelerator and implies little regeneration is taking place.

When I press on the brake pedal for the Model S, is regeneration taking place, using the "resistance" provided by regeneration as a braking force, modulated by brake pedal application (like a Prius)? Or when I press on the brake pedal, am I always getting calipers engaging discs no matter what?

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Brake pedal uses friction brakes always. If you have your foot off the accelerator pedal and on the brake you'll be getting some regen (and probably not pressing on the friction brakes as hard as you would otherwise). But that's happening just because you don't have your foot on the accelerator, not from putting your foot on the brake pedal.

breser said:

unless you've disabled regen entirely.

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How?

ualdriver said:

OK, thanks. Surprised by that.

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yes i was too. it is a waste of energy to convert that car energy into heat and brake dust instead of capturing it through brake regen the way a prius does. I was hoping the new motor on the front wheels could be designed to capture brake regen, since most of the braking force should come from the front wheels, but that doesn't appear to be the case.

brianman said:

How?

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Oops, you're right. For some reason I was envisioning that there was a "Off" setting in addition to Standard and Low.

Edit: On second thought you actually can, just put the car in neutral but that's not what I was thinking about. Nor is it legal in many jurisdictions (search for neutral and coasting on google).

breser said:

Oops, you're right. For some reason I was envisioning that there was a "Off" setting in addition to Standard and Low.

Edit: On second thought you actually can, just put the car in neutral but that's not what I was thinking about. Nor is it legal in many jurisdictions (search for neutral and coasting on google).

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I couldn't remember if there was a fuse you can pull as well. Hence my question.

bhzmark said:

yes i was too. it is a waste of energy to convert that car energy into heat and brake dust instead of capturing it through brake regen the way a prius does. I was hoping the new motor on the front wheels could be designed to capture brake regen, since most of the braking force should come from the front wheels, but that doesn't appear to be the case.

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It's not a waste of energy if you don't use the friction brakes, which is precisely how most Model S owners drive their cars: rarely moving their foot from the accelerator to the brake pedal except for dead stops at traffic signals. One-pedal driving really is the more elegant solution, and it grows on you the more you use it.

bhzmark said:

yes i was too. it is a waste of energy to convert that car energy into heat and brake dust instead of capturing it through brake regen the way a prius does. I was hoping the new motor on the front wheels could be designed to capture brake regen, since most of the braking force should come from the front wheels, but that doesn't appear to be the case.

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I don't know why it's so hard to understand. Full regen is being applied when you lift your foot off the accelerator pedal. There's nothing more available. Other cars have zero regen applied when lifting your foot off the accelerator and apply full regen after a certain amount of travel on the brake pedal.

The physics are precisely the same and neither provides more energy capture than the other assuming regen limits are identical. One could argue about which is the better user experience but that's been done on multiple other threads.

It's a different way of driving with the Model S that takes a little getting used to. You regulate your speed and "brake" by varying the pressure on the accelerator. The only time you need to switch your foot to the actual brake pedal is to hard stop (stop sign, stop light, emergency, etc.) If you are taking full advantage of the Model S, you should rarely use the actual brake pedal.

JohnQ said:

I don't know why it's so hard to understand. Full regen is being applied when you lift your foot off the accelerator pedal.

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OP asked about regen set to low, is full regen available using the brake and the consensus is no; brake pedal is only friction.

Brass Guy said:

OP asked about regen set to low, is full regen available using the brake and the consensus is no; brake pedal is only friction.

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I'm troubled by the way you stated it. So I'll take a crack at it...

1. OP asked about regen set to low, is regen active while using the brake and the consensus is yes; brake pedal only controls friction braking but if you're on the brake pedal you're not on the accelerator* so regen is active because of that.
2. When the setting is on "Low" for Regen, which of "Low strength" and "Standard strength" regen is applied when you press the brake pedal? I believe "Low strength" is applied here but I could be wrong.

* Note that this is not strictly true. The two pedal case has added complexity so I'm not addressing it here.

Brass Guy said:

OP asked about regen set to low, is full regen available using the brake and the consensus is no; brake pedal is only friction.

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Wasn't out to irritate the OP, nor was my response directed to the OP, simply want to debunk the concept that it's less efficient to have the regen on the accelerator pedal than on the brake pedal.

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ualdriver said:

On my Volt, we have a little green sphere that moves up and down on a scale that lets us know when we're driving (braking/accelerating) efficiently. I was told that when we press on the brake and the little leaves (a graphic on the surface of the ball) start to gradually disappear, that's the point where the friction brakes are starting to meter in with the regeneration to help stop the car. If, when I lift my foot off the pedal of the S, that is max regen, it seems that I have much more regen available on the Volt, using perceived deceleration force as my guide- admittedly a tenuous means of measurement. That's why I was wondering about how much regen we get with braking on the S, and that's apparently no additional regen which answers the question. Thanks all for the info.

I think the beauty of "one pedal" driving is in the eye of the beholder. The same can be done on the Volt by driving around in "Low" vs. "Drive." I preferred to be in "Drive" which provided minimal deceleration when one lifted off the gas....er....accelerator. Then one could modulate regen with the brake if needed. Anyway, if this issue has already been beaten to death on other threads, no need to rehash. Either way, I couldn't be happier with my S.

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No worries, people have different preferences on the implementation of regen.

But don't you see, in a Tesla you don't need little leaf graphics to tell you how you're doing. If you're touching the brake pedal then you are using friction brakes, if you aren't then you are aren't. Tesla's model is so much cleaner than the hybrid model of trying to blend regen and friction brakes on the same pedal. You will quickly learn to "coast" but simply not lifting completely off the accelerator. Just put the car in Standard regen and drive it. You will adapt and I think you'll find it is a better system.

JohnQ said:

I don't know why it's so hard to understand. Full regen is being applied when you lift your foot off the accelerator pedal. There's nothing more available. .

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The accel pedal lift off doesn't apply full regen. Especially now that the front wheels, where most of the braking is done can brake harder and faster and well beyond the limited regen profile of the accel pedal lift-off.

If "Full regen is being applied when you lift your foot off the accelerator pedal" then the car (especially the D cars) would brake a lot harder than they do now.

I dont know why it so hard to understand that providing only limited braking through the accel pedal regen is not as good as providing full regen from applying the full regen capacity of the electric motor to fully brake the car. Since that braking would be very strong, the user input calling for the hard braking should come from the brake pedal. But it should still use the motor to capture the energy instead of making brake dust.

Any time you have to stop hard and quickly and use the friction brakes that is wasted energy (unless the battery is full, or the braking is so hard that it beyond the capacity of the motor(s) or the braking wheels). When the regen was only from the rear wheels that put a low cap on the braking power from regen. Now that an additional motor, and the front wheels are involved, the regen capacity has just greatly exceeded the accel pedal lift-off profile.

That additional and untapped regen potential should be accessed by the brake pedal. The brake pedal should engage additional regen (above the weak regen from the accel pedal lifted) to stop the car. Now that the front wheels have an electronic motor, the brakes should totally stop the car with all regeneration and no brake friction which is just wasted energy. The toyota/tesla rav4 uses accel pedal liftoff AND brake pedal capture regen. The S should also.

bhzmark said:

The accel pedal lift off doesn't apply full regen.

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Yes it does. The max regen available is when you are not pressing the accelerator. No additional regen could be added even if it was mapped to the brake pedal. It could be applied to the brake if Tesla changed the software. The software to apply regen being mapped to the brake or the accelerator doesn't change the limit of the regen.

I would assume the new Dual Motor cars will have slightly stronger regen, and it will all be available through lift-off of the accelerator, just like the current cars.

I would be very opposed to adding regen to the brake pedal. It is a much better user interface to apply it to the accelerator.

trils0n said:

Yes it does. The max regen available is when you are not pressing the accelerator. No additional regen could be added even if it was mapped to the brake pedal. It could be applied to the brake if Tesla changed the software. The software to apply regen being mapped to the brake or the accelerator doesn't change the limit of the regen.

I would assume the new Dual Motor cars will have slightly stronger regen, and it will all be available through lift-off of the accelerator, just like the current cars.

I would be very opposed to adding regen to the brake pedal. It is a much better user interface to apply it to the accelerator.

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If by "max regen available" you mean the full amount of regen that is currently designed into the accel lift off deceleration curve, then yes you are correct.

But what I meant by "full regen" was the max regn available from the full potential of the electric convertor motors to convert even more energy into electricity which could be obtained by allowing a stronger braking effect and more powerful regen.

Why don't they do that now? Two reasons: 1) the braking effect would be too strong -- it would be like applying a moderate (not just minor) force on the brake and the car would decel too quickly; 2) creating braking resistance with only the rear wheels is not desirable (this is demonstrated in a video clip in an earlier thread posted on this same topic that shows a decelling S fishtailing on a slick service because of the strong braking effect applied only to the rear wheels).

Problem 2 can be fixed with the current addition of the front motor to use the front wheels to apply the braking power. Problem 1 can be fixed by using the brake pedal to capture that currently unavailable (but potentially available) additional regen from a stronger braking effect.

If you still don't understand and you think that the maximum braking effect that Tesla designers thought was an acceptable driver experience from the accel lift off just happened to coincide exactly with the maximum possible regen that was possible from the rear motor and rear wheel in full regen mode, then consider: now that we have the front wheels and the front motor to create even more than twice the regen, shouldn't the accel lift off now be much stronger and slow the car much quicker on mere accel lift off?

Can't you see how the potential regen from all four wheels and two motors might be too much to have with just accel lift off and so some of that regen would be left untapped unless it could be responsive to the appropriate driver input of, say, the application of the brake pedal?

If Toyota can do it, I"ll bet Tesla can do it even better. --eventually. As they did with adaptive cruise.

bhzmark said:

The accel pedal lift off doesn't apply full regen. Especially now that the front wheels, where most of the braking is done can brake harder and faster and well beyond the limited regen profile of the accel pedal lift-off.

If "Full regen is being applied when you lift your foot off the accelerator pedal" then the car (especially the D cars) would brake a lot harder than they do now.

I dont know why it so hard to understand that providing only limited braking through the accel pedal regen is not as good as providing full regen from applying the full regen capacity of the electric motor to fully brake the car. Since that braking would be very strong, the user input calling for the hard braking should come from the brake pedal. But it should still use the motor to capture the energy instead of making brake dust.

Any time you have to stop hard and quickly and use the friction brakes that is wasted energy (unless the battery is full, or the braking is so hard that it beyond the capacity of the motor(s) or the braking wheels). When the regen was only from the rear wheels that put a low cap on the braking power from regen. Now that an additional motor, and the front wheels are involved, the regen capacity has just greatly exceeded the accel pedal lift-off profile.

That additional and untapped regen potential should be accessed by the brake pedal. The brake pedal should engage additional regen (above the weak regen from the accel pedal lifted) to stop the car. Now that the front wheels have an electronic motor, the brakes should totally stop the car with all regeneration and no brake friction which is just wasted energy. The toyota/tesla rav4 uses accel pedal liftoff AND brake pedal capture regen. The S should also.

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So, you're saying that putting the regen on the brake would allow Tesla to increase the regen power from the current 60kW max to something more. Presumably because it would be unsafe to have more than 60kW on the accelerator pedal liftoff. Is that right?

Does anyone know if the 60kW max is a legitimate power train limit or if it's designed to prevent things like lift-off understeer?

Edit: Let's ignore the new dual motor announcement for the moment and consider only a rear wheel motor.

JohnQ said:

So, you're saying that putting the regen on the brake would allow Tesla to increase the regen power from the current 60kW max to something more. Presumably because it would be unsafe to have more than 60kW on the accelerator pedal liftoff. Is that right?

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In cars with regen on the brakes there is limit as well, if you go over that limit you're using the friction brakes for any stronger braking. If any of the safety systems come on, you're using only the friction brakes. This often leads to a poor brake feel. In addition, cars that have regen on the brakes always use some friction braking (to minimize the transition feel) so they're less efficient by design, and far more complex.