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Why isn't regen integrated with the brake pedal?

Discussion in 'Model S: Driving Dynamics' started by dennis, Jan 24, 2013.

  1. jomo25

    jomo25 Active Member

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    Yes, agree, in that scenario (wanting to maximize regen) it's better to know when the max is being used. But the tradeoff is that in order to "coast" or minimize regen, you need to keep depressing the accelerator to a point (which is indicated in the speedometer).

    Incidentally, the Volt does have a mode for max regen - the "L" gear. In this case, taking foot off the Volt accelerator gives max regen, akin to the S. And pressing the brake in that mode is simply applying the friction brake on top of max regen. It's why the Volt's implementation is nice. You have the option to choose.

    In the S, you can choose, BUT, in the "low" regen mode, you can't ever achieve the max regen. Because the brake pedal only does friction.

    So, to summarize: Volt in either mode can achieve min or max regen before friction. The S can ONLY achieve max regen in the Standard mode. It can't be achieved in the "low" mode. Thus, the difference, and some people's feeling (me included) that the Volt's implementation provides greater flexibility. In the Volt, I tend to use the "L" gear on surface streets. And "D" gear on the highways.

    Another question that I've seen asked and sort of answered: when the S is cold and "max regen" is limited, does the "feel" change? I.e. when max regen is available and you take your foot off the accelerator, you get the strong deceleration associated with the max regen. When the car is cold and regen is limited and you take your foot off the accelerator, does it still decelerate the same, even though you aren't getting the same amount of regen? Or do you have to compensate with the friction brake when the regen is limited?
     
  2. aviators99

    aviators99 Model S - R140

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    The latter (not just when it's cold, but also to avoid overcharging if you are close to max SOC). It is a bit unnerving.
     
  3. brianman

    brianman Burrito Founder

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    I'm curious to hear your thoughts on whether Low is any better for you than Standard (Regen setting), or if you really would prefer an "Off" option.
     
  4. Jason S

    Jason S Model S Sig Perf (P85)

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    What he said. I like that the brakes apply to braking and the accelerator applies to energy regen or usage. It doesn't approximate an ICE and I'm perfectly ok with that.
     
  5. dennis

    dennis P85D

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    #25 dennis, Jan 24, 2013
    Last edited: Jan 24, 2013
    That is not correct. I just conducted an experiment to verify.

    Coasting down my hill in the Model S, regen was ~40kw when I applied the brakes because I was 8mph over the speed limit and needed to slow down. Regen immediately dropped below 30 and then went to zero of course when stopped. Max regen is 60 kw - I wasn't there.

    Same scenario in the Karma. Coast regen was ~30kw, applied the brakes at the same speed as above, regen jumped up to 70kw and then dropped off to zero when stopped.

    In the Model S, the amount of regen is controlled by the car based on its speed and the steepness of the decline. There is no way to cause more regen, and any braking is just wasted heat loss. In the Karma I know the first .25g of deceleration will come from regen, whether it is letting off the throttle or applying the brakes. And there is no discernable difference in feel between regenerative braking and friction braking. The brake feel is similar to other cars I have owned with Brembo brakes, so there is no performance penalty for having regenerative braking.

    I realize it is hopeless to try to convince most of the people on this forum that another manufacturer might have a superior solution in some area, but I at least wanted you all to know the facts. :rolleyes:
     
  6. ElSupreme

    ElSupreme Model S 03182

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    Well by pressing the brakes you take energy and turn it to heat, so pressing the brakes always detracts from regen. And if you notice as speed decreases the amount of regen decreases also. I have noticed the behavior that you describe, but putting regen on the brake won't change what you are seeing. What you see is a result of lower speed, brakes engaging, taking away from regen. Not what pedal the regen is on.

    And you can't take your foot off the accelerator in a manual transmission car to coast either. I have never driven (long term) an automatic car. So it is natural for me to keep very light pressure on the accelerator.

    And I am not saying Tesla's solution is superior. But it makes more logical sense. You have a motor pedal, and you have a brake pedal. I always know what the car is doing, so I can accurately predict its behavior. Automatic cars have made people think the pedals are 'go' and 'stop' this is not what they are. They are brake pedals, and throttle/accelerator pedals. And you can have negative acceleration.
     
  7. jomo25

    jomo25 Active Member

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    Again, the Volt has this mode also. My point is that it would be great to have the option.
     
  8. dennis

    dennis P85D

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    #28 dennis, Jan 25, 2013
    Last edited: Jan 25, 2013
    The accelerator pedal used to be directly linked to the throttle. But it has been "drive by wire" for some time now, so a computer is sensing the input from your foot to the pedal, interpreting how fast you want to accelerate based on that input, and telling the fuel injectors/turbos (ICE) or device that controls current output (EV) what to do. You think that is OK. But you do not think it is OK for the computer that is sensing your input to the other pedal (it has been there since ABS was invented) to be able to seamlessly decelerate the car with regen for the first .25g and add friction braking if your foot indicates a desire to decelerate faster than that.
    That is an interesting form of automotive purism. :confused:
     
  9. ChrisgG

    ChrisgG Member

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    You already can choose the regen level now to some degree. So what's missing is that braking should be regen. There is no reason why it's not other than it's more complicated to do. Every one Pedal driver still can do that and even gets additional regen if they finally step on the brake bedal. Win win situation everywhere I look....

    Whats a bit concerning thou is that I read that if the battery is cold the regen is limited, then the car will not 'regen brake' anymore. That sounds reall dangerous as we all will be used to that the car braking by itself when we leave the accelerator pedal. Especialy in cold conditions a shocked 'emergency' braking isn't the thing you want to do ^^
     
  10. Zextraterrestrial

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    I think the Model S regen is different at low speeds than the Karma because the motor is purely inductive maybe? What are the motors that the Karma uses?
     
  11. efusco

    efusco Moderator - Model S & X forums

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    And I disagree with your comment that it "makes more sense". To me it makes more sense to have a "go" pedal and a "stop" pedal. Let the software manage whether the stopping is done by the motor or friction brakes. What advantage is there to having pure friction brakes when a combination works fine?
    And for those who say you can't tell when the friction brakes start and regen cuts out, that's just a very simple software and display issue. We can still see the amount of regen displayed and a little light showing when friction braking starts would be very simple.
     
  12. Lloyd

    Lloyd Well-Known Member

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    I've said this in another post, but Toyota on the Rav 4 EV does this the best and the smoothest IMO. About 1/2 of the available regen is activated with your foot off the gas. The other 1/2 comes in with the first 1/2 inch travel of the brake pedel, but before the calipers engage. Very smooth operation. It also helps when the cruise control comes off and is not a jolt when decelerating. When in the "B" mode. the regen is more agressive with the foot off the gas. Perhaps 3/4 is activated with the foot off the gas. Anyone who has the chance should drive the Rav 4 EV to compare. I have both. Anyone wanting to stop and try my Rav is welcome.
     
  13. stevezzzz

    stevezzzz R;SigS;P85D;SigX;S90D;XP100D;3LR

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    Are you saying that just the fact you've pressed on the brake reduces the amount of regen, even before you've actually slowed down at all? I don't think that's the way it works, and it's counter to my own observations. I believe the regen braking and friction braking are completely independent of one another; that is, the regen algorithms are not sensing if the driver is pressing the brake pedal, or how much.

    Of course, I might be wrong. More experimentation is called for.
     
  14. ggr

    ggr Expert in Dunning-Kruger Effect!

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    I think that the regen and braking must be aware of each other to some extent. Remember that the regen only works on the rear wheels, but the brakes work on all four. The maximum regen was said to be governed by the most they could do without risking the rear wheels locking up or losing traction. You wouldn't want to add too much more real braking to those wheels while under maximum regeneration, but in a panic stop you want to add as much as possible to all four. So I think, at first, most braking goes to the front wheels. (Disclaimer: I'm just guessing based on how I would do it. The behavior Dennis claims is a different way to do it: apply front and back brakes always in proportion, then reduce the regeneration to avoid locking the rear wheels.)
     
  15. dsm363

    dsm363 Roadster + Sig Model S

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    It may not be the perfect solution but after over 2 years if driving a Tesla I love the regen on the accelerator. I've never owned a manual transmission car either but the transition was very quick.
     
  16. DriverOne

    DriverOne Supporting Member

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    That makes sense. However the Karma is also RWD, so I don't know how they're applying more regen to the rear wheels when braking than the Model S can. Perhaps the Karma has more weight over the back wheels (I think that's what this datasheet shows - http://www.roadandtrack.com/cm/roadandtrack/data/f416d91038963118ebf7b8dafd5a2efa.pdf, 63% over the rear wheels? Kinda fuzzy there.)

    Karma 60-0: 116ft
    Model S 60-0: 108ft

    Despite less regen under braking, the Model S brakes a fair distance shorter.

    (Model S stats from 2012 Tesla Model S Track Test)

    And the Karma mpg on that data sheet's test? 20.5mpg. Ouch!

    BTW I don't think this thread is about one pedal driving or not. It's only about the amount of regen when the brake pedal has been applied.

    Complicating things, I wonder if the regen-under-braking knows about ABS and stability control?
     
  17. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Toyota turns off regen when any of the safety features engage, there is a fault found, the speed is below 10 km/h, or the battery is at maximum.

    Because the Model S regen is on the motor only, I don't think that the Model S needs to do this because the safety features are aware of the wheel rpm and adjust accordingly. Someone needs to verify this though.

    Having the brakes separate from the regen, simplifies design and reduces recalls. I suspect that's why Telsa did it that way.
     
  18. SuperCoug

    SuperCoug Model S Res #7734

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    I love to hear from guys that have both a Model S and a Karma. Which one do you like better? Would you mind posting some observations/opinions about each? Perhaps you've already done this on another thread but I'm always interested to see these two cars get compared. Obviously you like the regen better on the Karma but I'm going to be surprised if you think the Karma is the overall better car.
     
  19. dennis

    dennis P85D

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    I like both cars a lot, but each has its pluses and minuses.

    What I like about the Model S:

    • Performance
      User Interface
      Modern, high tech innovations like over the air upgrades
      Packaging/spaciousness
      Electric drivetrain
    What I like about the Karma:

    • Looks/exterior design
      Interior materials and design (it feels like a $100K car)
      Handling (it is better than the Model S, although the Model S is still very good)
      Electric drivetrain
    The Karma looks and feels like a luxury sport sedan, while the Model S looks and feels like a high end family sedan. The electric drive in each of them is superior to any ICE car on the road. The range extender on the Karma is more convenient for long distance travel than Supercharging with the Model S, but the downside is the weight penalty and the fact that for medium length trips you are using some ICE because of the limited battery range.

    While the Karma had a lot of initial problems, the service experience has been great and my car has been rock solid reliable and glitch-free since the latest software was installed about 3 months ago. I have 8600 miles on mine in 1 year and have averaged 48 mpg, only charging at home at night. I estimate about 5000 of those miles were driven battery only, with the ICE running to generate electricity for the remaining 3600 miles. Incidently, the median mileage for owners on the FiskerBuzz forum is 135 mpg.

    Like Tesla with the Roadster, Fisker had some initial execution issues. But they also had a lot of bad luck and there is more technology/engineering in the Karma than Elon gives them credit for. I'm optimistic they will attract a strategic partner and bring the Fisker Atlantic to the market. Tesla has executed extremely well so far with the Model S. I expect them to have continued success given that they add the missing luxury car features in a timely fashion so they can expand their available market beyond the EV early adopters.

    The Karma and the Model S are both breakthrough cars and I feel very lucky to own both of them and be on the leading edge of an automotive revolution!
     
  20. Alpha

    Alpha Member

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    I do agree the regen does have a lot of the same feel as downshifting in a stick shift... which was something I liked having during the many years I drove one.
    The thing that (I think) might get on my nerves is not being able to completely coast - (that is; having the choice to decelerate only on air resistance, giving my right foot a rest...)

    All of the above is said without a lot of experience with it (I've only ever driven one model S & I don't have my Model S yet...) Maybe I will grow to love it!

     

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