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Improving the Single-pedal Control Concept (Idea stolen from BMW i3)

The BMW i3 has an interesting feature which could be added to the Model S with a simple software update.

In slower (city) traffic, the accelerator pedal works in regenerative mode. When you let go of the pedal, the car "brakes", which means that you hardly ever have to touch the brake pedal. This single-pedal control is a very efficient way of driving with a single foot in start-stop type of traffic. (Although I know that some people don't like it. You can disable this feature in a MS).

However, at higher speeds (highway), the accelerator pedal works in coasting mode. When you let go of the pedal, the car simply coasts, as if you would have put it it in neutral. This allows for a more natural flow and more relaxed driving on highways. You can lift your foot of the pedal and relax you muscles, while loosing a minimal amount of energy built up by inertia (braking would be counter-productive in those circumstances).

The speed-sensitive accelerator pedal certainly would be something to get used to (now it brakes, now it doesn't). But what's your take on this feature? Should Tesla add it? Why or why not?

It is there... what to add?
Single pedal driving is one of model S charms... make it more complicated? Write a rule book ? Neeeh...

Are you sure BMW didn't steal the single pedal idea from Tesla? Their cars have had this feature for years.

@Winnie: BMW may very well have stolen in from Tesla. However, BMW has an interesting and new take on the concept (an improvement, if you wish). Read my full post above.

@chrisdl - what is the improvement? Coasting at higher speed ? How to I get my energy back going down hill? Add a paddle shifter ? To complicated - KISS ! If I want to coast I use the cruise control...
Probably someone at corporate BMW got an award to come up with this useless feature.

Definitely not an improvement - have you driven the MS? At highway speeds it does not slam on the brakes when you take your foot off the accelerator, but does regenerate. Works great for me.

If you want highway coasting use the cruise control. If I don't have cruise control on and I take my foot off the accelerator at highway speeds it's because I want to slow down.

I agree with Docrob (and others). When I'm on the highway and want to keep going, I keep my foot on the accelerator. When my foot comes off the accelerator, I want to slow down. The Model S works very well this way, and I would not want it to change. Keep it simple!

However, I would like an option for heavier regen braking. I hate when I have to hit the brakes and waste energy!

It is amazing how much the BMW engineers ( and others ) are entrenched in the ICE culture. What they haven't realized is that an EV doesn't require all these complicated procedures... like hold the car with the accelerator at a hill stop in SF - no double footing, press the gas pedal and then release the break... not needed, the engine has plenty of torque at zero rpm to hold the car at the steepest hill - true single pedal driving. GM, Ford, BMW,... engineers wake up before it is too late.

If you coast at highway speeds how do you slow down, then? Hit the brakes? What a waste of energy. No, the model S works great the way it is. If you want to give your foot a rest, simply engage the cruise control.

I'm not in favor of the car acting wildly differently at different speeds. Also you can coast, if you pay a bit more attention to the power use/regen bar in the cash; you simply don't take your foot ALL the way off. And of course, as moorelin says, it doesn't slam on the brakes anyway--it's a certain amount, so the faster you're moving, the smaller percentage of how fast you're moving that braking feel is. (Did that make sense?)

P.S. volkerize.com is your friend; I'm pretty sure I've read this suggestion here before. ;-)

A few people seem to indicate that applying the brakes in a Tesla is an immediate waste of energy. That's not the case. The MS has regenerative braking which works (optionally) when you let go of the accelerator pedal AND (always) when you put pressure on the brake pedal.

The disc brakes of the car will only be used if insufficient deceleration can be accomplished by the generator (i.e. the engine in reverse).

hmm, are you certain of that? I have never heard of regenerative braking being linked to the brake pedal in any way, mu understanding is regenerative braking is linked to accelerator release and the brake pedal controls the friction brake only.

@Kendall Thanks for the link to volkerize! I didn't know that yet.
Indeed it has been suggested before: http://www.teslamotors.com/en_BE/forum/forums/regenerative-braking?page=2

Happy to know that I'm not the only one who thinks this may be a useful addition.

If Tesla wanted to KISS they wouldn't have added the Creep option either, right. Personally, I think that the car should work optimally in whichever way you choose to drive it. Since not all drivers have the same driving style, optional settings to adjust to your personal style have nothing to do with making things complicated. In fact, the MS is the ultimate car in adapting to driver's wishes. It is a no-compromise EV, which is what makes it so attractive to so many people.

@chrisdl - it doesn't work that way. If you hit the brake pedal it creates heat only, but zero electricity goes back into the battery.

@chrisdl - I have no problem if Tesla adds features to suit your driving style, but don't sell it as an "improvement" when it is actualy a band aid to help you/me to transtion to EV. Creep is the prime example of such a band aid to help the transition.

@chrisdl - you are getting a lot of ??? here. I started out driving the MS like my previous car, but learned that many thing came be approached much simpler in the MS then any ICE. Now I just love the simple precise control you have driving this car - no ICE comes even close.

@Docrob You are right! I am surprised to learn this, but it is true. Unlike other EVs, Tesla's brake pedal only controls the friction brakes.

So now I also understand why Tesla can't copy this i3 feature.

If the brake pedal would use fancy logic to distribute the power between regen and friction, it would be a great option. But it doesn't, so it isn't.

@Kleist I don't see this as a band-aid to transition from anything. Why are you thinking that it would be?

To me, this feature would be an optimization of the energy usage. Pressing/lifting the accelerator or using the cruise control are certainly very practical alternatives, albeit less energy efficient when at higher speeds. Note, again, that this is for higher speeds only, where it costs a lot of energy to regain lost speed due to drag. However, since I now learned how the brakes of an MS work, the point is moot.

Anyway, I think the answer of Tesla-owners is clear: 1) keep it simple, 2) we don't see the point of that feature.

Thanks for the input, all who answered.

Please explain how Tesla's current solution of one footed driving where full regenerative braking only requires the complete removal of the foot off the accelerator is "less energy efficient at higher speeds". What you are suggesting makes the system no more energy efficient it just means to get the most out of regenerative braking you must use two pedals instead of the current one pedal solution. What you propose is no more energy efficient and certainly more complicated then the current system. The only "benefit" is making the model S marginally more "ICE like" by braking less when the accelerator is let off on.

In coasting mode power is regenerated to nor consumed from the battery. The vehicle rolls freely and gradually loses speed due to drag. Every meter you drive while coasting is a zero-operation. You could coast when nearing a freeway exit, for example.

Controlling the engine/generator with your right foot is typically less efficient (at high speeds!) since either you give a bit of power to the engine or you lift off a bit, causing a tiny sawtooth power/regen/power/regen/... cycle. At high speed, the power required to accelerate even a single km/h is much higher than a low speed due to drag. This makes the power/regen cycles less efficient than at low speeds. In practice, most drivers will "spill" more energy that way. If you have a steady right foot, this may not apply to you.

Obviously, the above only makes sense if you also regen energy while braking, which the MS doesn't. Therefore, moot point, as I said before.

It is much more complicated, that I certainly agree with! And yes, you'd have to use two pedals, but you'd have the option of using "no pedal" (at high speeds).

It'll be interesting to learn how it works in practice in the BMW i3. Not that the i3 is really suitable for highways, as far as I can tell. But that's another story.

I'm awayting production on my baby so don't kill me over my ignorance....

I was wondering about this issue too, can someone explain to me (in simple english since i'm Dutch) is it possible to put the S in neutral? (I am doing this on my ICE). Is it more efficient to regen than to let it coast of a freeway exit for example. Wouldn't it be even more efficient if the S would regen more aggressively if i press the brakes lightly and only use the friction brakes of i push harder?

I trust they have given it serious thought, but i wonder....

Bigbit

I think it is overly complicated. An accident waiting to happen. Hope tesla never does this!

@bigbit
Yes you can shift to neutral while driving. As far as efficiency, there is a loss in the regen process, you can't recapture all of the kinetic energy as potential energy in the battery. That said, it seems overly complicated (dangerous) to be making multiple adjustments while exiting a freeway just to maximize efficiency of the vehicle. I personally love the regen, rarely touch the brake and have learned how to use the accelerator to find the sweet spot and "coast" when I want to.

@chrisdl;
What you seem to be missing is that while braking your foot is also necessarily off the goose pedal entirely, and thus providing maximum regen. The braking is just adding some friction.

At moderate or more speed, no more regen can be added once your foot is off the goose pedal; the system is providing all that can be handled.

Further, the screen displays flow to/from the battery at all times, so the saw-tooth is easy to minimize.

I'm sorry that I'm not able to express myself any better.

I'm fully aware of what you are saying, Brian. I simply didn't mention that because it's obvious to me. It's always risky to assume that people know or understand things which appear obviously to yourself, so my mistake for not being clearer. Apologies.

@chris

People also, have already stated, that "no pedal" driving, at high speeds is already taken care of on the Model S by using cruise control.

How often do you really need to "coast" on the highway though? The only reason to slow down, would be if traffic in front of you is slowing down, and at that moment, you could just use regen to gain some energy back rather than coasting until you are too close and then have to use the friction brakes... That is just my opinion though.

+1 DFibRL8R - it is very easy to find the coasting spot. For folks who are not driving the MS every day it is very hard to imagine how well Tesla designed the drive train and the fine control it allows you. I am looking forward to test drive the I3 and B class next year... see how well the big guys did.

I'd actually prefer a higher level of regen. I'd entertain the idea of having a toe strap or click-in binding like cyclists that would allow you to pull back on the pedal for extra regen braking!

The way I understand it, whenever you take your foot off the accelerator pedal the car goes into regen mode. If you tap the brake, it is still regenerating (no foot on accelerator) in addition to having friction brakes applied. If this is true, then you already have the best of all possible worlds - a separate friction brake that you can use in addition to regen, or just regen alone (no brake), or no regen (depress accelerator). In this manner, you can best manage regen and friction braking in a manual, satisfying way rather than have the car and computer do it for you automatically like it's done in other vehicles.

If you need to coast, just keep your foot on the accelerator to the point where you are neither using nor regenerating energy and are at a net zero. That is coasting. Is your foot sore and just want to let go? No problem... just put the car in neutral using the shift lever.


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