Why isn't regen integrated with the brake pedal?

[jerry33]

I still don't understand why people are so aggressively against the idea of making an option to move re-gen to the brake pedal (activated when the brake light switch comes on) for those who want to coast when you take your foot off the accelerator and rely on the brake pedal for stopping.

I'm not aggressively against it. I just understand how it would have to be implemented. It would take a boatload full of R&D dollars to get right and would add complexity and raise the car's price. Right now Tesla just buys off the shelf brakes and installs them--simple, cheap, foolproof. If they did regen-on-the-brake-pedal they would have to design their own brakes from the ground up plus all the controlling systems. There is just no way to make regen-on-the-brake-pedal simple--it's very difficult to get right. Toyota has been working on this for over sixteen years and some people would say they haven't got it right yet. (That's not my opinion BTW).

[dennis]

I'm not aggressively against it. I just understand how it would have to be implemented. It would take a boatload full of R&D dollars to get right and would add complexity and raise the car's price. Right now Tesla just buys off the shelf brakes and installs them--simple, cheap, foolproof. If they did regen-on-the-brake-pedal they would have to design their own brakes from the ground up plus all the controlling systems. There is just no way to make regen-on-the-brake-pedal simple--it's very difficult to get right. Toyota has been working on this for over sixteen years and some people would say they haven't got it right yet. (That's not my opinion BTW).

Well Fisker got it right on the first try, and so apparently did Chevy (Volt) and Nissan (Leaf). While there have been complaints about other aspects of the Karma on the FiskerBuzz forum, I can't remember a single one about the brakes or their integration with regen.

I disagree that Tesla would have to design their own braking system from the ground up. The friction brakes remain the same, it is just a question of when they get actuated. That is a function of the controller software that typically comes from Bosch who pioneered ABS systems. So my guess is that the manufacturers like Fisker who use regen for initial braking provide additional requirements/specifications to their provider of the braking system software, as opposed to having to do everything themselves.

[jhs_7645]

I'm glad to hear that.

About 6 or 7 years ago, I was driving a GMC Envoy. I had it in 2WD (driving the rear wheels) with cruise on. As I was coming down a steep hill on Hwy 9 outside of Orangeville, the vehicle downshifted (which it did sometimes to slow down and maintain the speed setpoint on downgrades) and due to black ice that I was unaware of, the vehicle spun out when the rear tires lost traction. I spun 360 degrees into the oncoming lanes (fortunately no cars coming) and when the vehicle hit dry pavement, I peeled two tires right off the rims and went backwards into the ditch. To this day, I am amazed it didn't roll (and am thankful there was no oncoming traffic). That car had traction control too. This is why I get concerned about aggressive re-gen on the rear wheels in slippery conditions. I know the Model S is no top-heavy SUV, but that experience has made me very sensitive to this issue.

I still don't understand why people are so aggressively against the idea of making an option to move re-gen to the brake pedal (activated when the brake light switch comes on) for those who want to coast when you take your foot off the accelerator and rely on the brake pedal for stopping. Those who like one pedal driving would leave it as is. I would likely leave it in standard mode all spring, summer and fall but would flip it over in the winter for these reasons.

I'm not sure people are as aggressively against it as you think. For the most part I think people who currently own and drive the car are trying to assuage your fears that something is wrong/dangerous with the car the way it is currently designed. You really shouldn't worry about the safety, behavior and performance of the way it is currently implemented. This reminds me of the pano sunshade. There was an uproar for months on the forums when people got wind of the fact that there might not be a sunshade. Then, when people actually got the cars, and drove them in Florida on sunny days, everybody agreed.. no sun shade necessary. I would encourage you to just leave the topic alone for a while and wait until you get your car, and trust the people who have their cars that this is a non-issue.

[Zextraterrestrial]

I'd be a little pissed if regen was on the brakes and love it as is. It is much nicer to be able to slow a bit without moving your foot over or flashing your brake lights at people.

The regen doesn't peak when you push the brake because of physics.
someone please correct me if I'm wrong

[dennis]

I'd be a little pissed if regen was on the brakes and love it as is. It is much nicer to be able to slow a bit without moving your foot over or flashing your brake lights at people.

The regen doesn't peak when you push the brake because of physics.
someone please correct me if I'm wrong

I think you are missing the point that cars like the Fisker Karma have regen on BOTH the accelerator and the brake pedal. If you lift your foot from the accelerator, you get some regen (you can select from 3 levels). Then when you step on the brake pedal the first .25G of deceleration is accomplished through regen, peaking at 90kW. If you need to decelerate faster than that, the Brembo friction brakes are actuated. It is all seamless, and maximizes regeneration without having to fret over whether or not to use the brake pedal.

[mknox]

I would encourage you to just leave the topic alone for a while and wait until you get your car, and trust the people who have their cars that this is a non-issue.

I think that's a fair comment as I don't have the car yet, and with receiving it in the spring, I'll have a whole summer driving season to get used to it. Having said that, I still think an OPTION to switch the re-gen mode wouldn't take anything away from those who like it the way it is, and appease those who would like it to work diffidently.

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It would take a boatload full of R&D dollars to get right and would add complexity and raise the car's price.

I don't think it has to be that complicated. Just an OPTIONAL mode that turns re-gen off on the accelerator (so that you coast when you lift your foot), and then switch in some reduced level of re-gen when the brake pedal is squeezed just enough to turn the brake lights on. Squeeze a little harder and the regular friction brakes kick in. Something that could prevent a sudden loss of traction is worth the time it would take to implement this in software, IMHO.

[Zextraterrestrial]

I think you are missing the point that cars like the Fisker Karma have regen on BOTH the accelerator and the brake pedal. If you lift your foot from the accelerator, you get some regen (you can select from 3 levels). Then when you step on the brake pedal the first .25G of deceleration is accomplished through regen, peaking at 90kW. If you need to decelerate faster than that, the Brembo friction brakes are actuated. It is all seamless, and maximizes regeneration without having to fret over whether or not to use the brake pedal.

my point...
Does The Fisker have an AC induction motor like the S? or are there some magnets in it?

2 motors on the Fisker? maybe that is the difference.
Until someone has an answer, I think it is the physics of the motor fields (someone educate us please? where are the ME/EE's)

[ElSupreme]

I think you are missing the point that cars like the Fisker Karma have regen on BOTH the accelerator and the brake pedal. If you lift your foot from the accelerator, you get some regen (you can select from 3 levels). Then when you step on the brake pedal the first .25G of deceleration is accomplished through regen, peaking at 90kW. If you need to decelerate faster than that, the Brembo friction brakes are actuated. It is all seamless, and maximizes regeneration without having to fret over whether or not to use the brake pedal.

There is NO reduction of regen when you press the brake pedal in the Tesla. I think you are thinking that Fisker/GM/Nissan have somehow figured out a way to increase regen. I can see some arguments for putting regen on a brake pedal, but most of those revolve around mimicking the behavior of current automatic transmission ICEs. I would argue it is much easier to maximize regen with one pedal because you won't accidentally use friction brakes while slowing down. Again I point out the simplicity of having one pedal work one system.

And we need to stop with 'Tesla should make this user selectable' on everything. What if I wanted the brake pedal to work the as the accelerator, and the accelerator to work as the brakes? In reality people HATE making all of these choices. I know we all want the car to work the way we want it but give it some time.

[jkirkebo]

Well Fisker got it right on the first try, and so apparently did Chevy (Volt) and Nissan (Leaf). While there have been complaints about other aspects of the Karma on the FiskerBuzz forum, I can't remember a single one about the brakes or their integration with regen.

I complain about the regen/braking on the Leaf. There is too little regen on the accelerator (and I always drive in eco) so the brake pedal must often be used. But there is no way at all to detect where regen ends and mechanical braking begins. Thus I often waste energy on the braking.

If there must be regen on the brake pedal there should be a defined point one could easily detect where mechanical braking begins. But my opinion is that the current Tesla system is much, much better as you always know which type of braking you do.

I often have no regen at all now in the Leaf, because of the cold battery. This has not caused any problems at all, I see this as a non-issue. I quickly detect the amount of regen available and adjust the driving automatically without thinking of it.

[Alpha]

If regen could be made exceptionally strong (like with multiple motors on the model X, or even one motor on each wheel) then it might make more sense to have regen integrated more into the brake pedal (and have the brake lights go on, etc. to warn people behind you of your sudden deceleration.)

In reality people HATE making all of these choices.

I agree that the average person is overwhelmed with too many choices, but a lot of geeks, engineers and scientists love to tweak things endlessly...
I think there are a lot of Model S owners who fit in that category