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Firmware feature request - Option for Regen > 60 kW?

Discussion in 'Model S: Driving Dynamics' started by scaesare, Jul 25, 2013.

  1. scaesare

    scaesare Active Member

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    #1 scaesare, Jul 25, 2013
    Last edited: Jul 26, 2013
    Premise: I personally love the "one pedal" driving that regenerative braking offers. Having had my car for 2 months & ~5,300 miles, with about 2,000 of those miles being road trips, I'm of the opinion that an option for having a mode that allows for greater than 60KW of "deceleration force" would be useful. While the current regen mode serves well for many situations, there are three scenarios where I think I'd find more useful:

    1- High Speed Stop and Go Driving: While typical stop and go driving on city streets where the speed limits are in the 35-45MPH range are reasonably well served by the current regen mode, when things start getting congested on the highway (I-95, I'm looking at you!), it's not uncommon to be travelling at 60-80MPH for some time, only to have traffic grind to a halt, and then start back up again. Rinse & repeat.

    I found myself having to leave so much room between the car in front of me to allow the regen to be effective that I'd get lane jumpers cutting in front of me. A bit more regen available would keep me from having to ride the brakes as much. This is a "common, but not daily" issue for me.

    2- Loaded Driving: On two of our road trips, we had 4 of us in the car with bags of "road trip stuff" (laptops, tablets, books, snacks, drinks, etc...), luggage in the trunk, extra stuff in the frunk (coolers, etc...). It's easy to add another 20-25% of the weight of the car for a vacation trip. With the extra weight, I could definitely feel the effect on the regen... again causing me to have to leave too much room in front of me in highway traffic to be as useful as I'd like. Or I'd have to start slowing down awfully early on city streets approaching intersections. This is only an "occasional" issue for me.

    3- Some Intersection/Light Combinations:
    I find that for many intersections, the time to regen decelerate when the light turns yellow is often greater than the time to cover the distance to the intersection in 45MPH zones. Or if there's any slight downhill grade leading to an intersection it hard to bleed off speed quickly enough if you are generally matching the flow of traffic. There are several intersections in my daily commute that are like this, thus it's a "daily issue" for me.


    Considerations:

    1-
    I don't know if the hardware in the car is even capable of this. I've heard that other vehicles are capable of "1C regen", specifically one of the Fisker threads here mentioned it had greater regen capability. So it may be possible with the S, and if so might be changed via firmware

    2- Greater regen might be "too abrupt" for some folks. This might be true if some people aren't used to modulating the accelerator pedal. I've already gotten in habit of not simply "letting off" the pedal unless I immediately need max regen. Ditto for cancelling cruise control, I depress the pedal slightly to even out the transition.

    Adding a larger range (to 80KW or perhaps even more) simply means a greater range of regen I can modulate. I also suggest making it an option in the car settings ("Max Regen" vs "Standard Regen") for those who don't want it at all , or all the time.

    3-
    There might be other concerns, such as rear tires losing traction too easily, etc... but it seems to me that if the traction control in the car can manage 320KW of forward acceleration, than 80KW of deceleration force shouldn't be too difficult. Clearly the TC is already active on deceleration, as if you hit a slick spot it will cancel regen to avoid the car getting squirrely.

    4- Linearity... as acceleration force is non-linear with power applied, I assume deceleration is the same. As such, to really add materially to the braking force, only allowing 80KW might not do much. It may be that 100 or even 120KW is the correct number.

    Suggestion: Keep the current 60KW regen as "Standard Regen". Add a "Max Regen" option that allows 80KW (or 100, or 120...) of regenerative braking to be applied. Link this to the driver profile so it doesn't surprise my wife.

    Thoughts?
     
  2. mnx

    mnx 2013 P85

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    While I'd love more regen as well, we probably won't see any changes until a dual motor AWD Tesla is available. (Model X I'm looking at you).

    Going from current regen to none is unsettling if your not expecting it (cold weather or range charge, TC interruption). People already have complained about this a lot. The complaints would only get a lot worse if we had even more regen on the accelerator pedal...
     
  3. mulder1231

    mulder1231 Active Member

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    Some people actually would like less regen at highway speeds.

    In another thread someone mentioned he always switches the regen setting from standard to low when going from freeway to city streets driving. (I believe the comment was in the i3 thread, since the BMW i3 apparently has a feature that automatically adjusts to lower regen at higher speeds.)
     
  4. scaesare

    scaesare Active Member

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    Hence making it an option...
     
  5. dpodoll

    dpodoll Member

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    Would be nice if there was a UI where you could select (sliding bar) how much you want dialed in
     
  6. WarpedOne

    WarpedOne Supreme Premier

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    When reading the thread title I was set to play the professor and explain that stronger regen in RWD vehicle could/would be problematic from stability point of view.
    Wheels could easily loose traction etc. But reading through OP rationale it is clear that he understands the problems and that a stronger regen would be useful in some situations.

    The worst problem is stronger regen poses a security risk - person not used to it might panic when he "jumps" off the accelerator at 100mph only to find himself thrown at /pushed onto the steering wheel. 100+ kW is a lot of power.

    IMHO a good solution would be "variable mode" that by default has the same max power as standard setting but with a twist - it listens to some input.
    Just lift the accelerator and you get up to 80 kWh same as with standard mode. Turn the left scroller up and regen increases, turn it down it decrases.
    At next regen occurance, repeat the process or enjoy standard 80kWh max.
     
  7. Ben W

    Ben W P85 #61, Roadster #108

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    I would also like to see an option for 120kW regen. Especially at highway speeds (70+ MPH), 60kW regen can feel a bit anemic, considering that slamming on the brakes at that speed is equivalent to about 1000kW. (500kW front + 500kW rear.) I suppose the question is whether there is any safety testing required, or DOT regulations on this sort of thing.

    I do find myself trying to use only regen when possible on the freeway, so when the car in front of me starts to brake, I have a tendency to lay off the brakes as long as possible to see if I can slow down enough with pure regen. Having stronger regen would make this tendency a little less dangerous ;)
     
  8. J in MN

    J in MN S60 P12635

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    I've wanted stronger regen since my first test drive over a year ago. 90 kW or 0.20 g would be great instead of the current 60 kW or 0.15 g.
     
  9. trils0n

    trils0n 2013 P85

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    Seems like you only get the full 60kW regen above a certain speed. I'd like to be able to have full 60kW regen on demand at lower speeds. The way it is now is seamless and creates a consistent experience, but I'd like to be able to get more regen at lower speeds, especially at lower speeds coming to a stop on a downhill, or if I need to stop quicker than I anticipated.
     
  10. GSP

    GSP Member

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    I would like to control regen level with steering wheel paddles, like the ELR, or by shifter positions below "D."

    This allows good control of deceleration without using the friction brakes.

    GSP
     
  11. Charlie

    Charlie New Member

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    Simple question: why would anyone want a certain level of regen power?
    IMHO, if single pedal driving is to be used, automatic braking when letting go of the accelerator needs to provide a certain level of deceleration, not power, no matter what. Driving experience should not depend on the car being more or less loaded, rolling/air resistance, unavailable regen and other changing factors.
     
  12. CatB

    CatB Member

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    Fwiw, I love the regen exactly as it is. It is perfect for passing slow cars or bicycles - I get my whoosh and then the battery re-absorbs the extra momentum.

    Although obviously if Tesla makes that a configurable option for those who have another preference, that would be fine. As long as they come out with accident response screen and valet mode first.
     
  13. scaesare

    scaesare Active Member

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    As the speed of the car lowers, the speed of the rotor in the motor housing (which is what is acting as the generator during regen) is lowered as well. The kinetic energy available is dropping, and thus the "available regen" power is as well.

    - - - Updated - - -

    For an induction motor to function as a generator (which is what the car does to induce drag, or braking force, during regen), the motor controller has to excite the coils with a voltage that "leads" the motor RPM. How much/fast this is done by the controller (amongst other design factors) determines how much power can be generated, and how much deceleration force can be provided.

    Hence, the request for more regen power is really a request for greater braking effect during regen.

    As for providing "a certain level of deceleration no matter what", that's an interesting idea. I'll point out that's not the way brakes traditionally work, however. If you are more heavily loaded, headed down hill, etc... your deceleration for a given amount of brake pedal application varies. My original request was simply to allow for a greater range of deceleration.. similar to being able to push the brake pedal harder.

    But I wonder if "constant braking force" is something that car's computer would be capable of... it would have to use it's accelarometers and/or wheel revolution counters to measure measure deceleration and attempt to automatically modulate the regen function regardless of load. I'd have to think about if that was desirable... or if there would be other tradeoffs.
     
  14. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    First of all, regen is measured in kW, not kWh. Sorry for the nit, but the engineer in me won't let it pass.

    Charlie makes an interesting point. We've all noticed that 60 kW of regen, as displayed on the instrument console, feels less effective at 75 mph than it does at 40mph (I just picked the latter out of the air: I don't actually know at what speed threshold the software allows for max regen). You may also have noticed that the greatest deceleration due to regen happens at an even lower speed, when the power meter shows that regen is already tapering off. Why not instead implement a regen profile that provides constant deceleration, feathered with the accelerator and with some upper limit on kW? The car has built-in accelerometers, so it's 'only' a matter of software...

    Tesla has somewhat arbitrarily made 60 kW the regen upper limit, and defined the way it tapers off with diminishing speed. The software also imposes more severe limits at high SOC and/or low temperatures. The former design decisions are presumably driven by desired driving dynamics and the latter by battery longevity concerns. It's a balancing act: on the one hand, regen allows for better range in real-world city driving, where regular deceleration is a fact of life. On the other hand, the population at large has decades of experience with ICE cars that don't have anywhere near the amount of engine braking available when you lift off the accelerator of Model S. The Standard regen profile is a compromise: it provides meaningful energy recovery during braking but not so much braking that driver retraining cannot be safely left to the individual. And because the regen profile can vary so much with conditions that the driver may not be aware of, it's undoubtedly safer to limit max regen when taking into account the driver population as a whole. Even with almost 30,000 Tesla miles under my belt it's still a bit of a shock when I lift off the go pedal and regen is not available. I've come to depend on it and if more were available I'd probably opt in, but I don't imagine Tesla wants the extra liability that comes with straying too far from what the average driver is used to.

    It would be really useful at next year's TESLIVE to have a panel discussion with members of the Tesla engineering team responsible for things like regen profiles and other aspects of driving dynamics.

    [edit: looks like scaesare and I were composing our replies at the same time; sorry for any redundancy]
     
  15. scaesare

    scaesare Active Member

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    I agree some input/dialog from the engineering folks at Tesla would be most welcome.

    As an addition to this thread, given that accelerating twice as fast to a given velocity requires something along the lines of 4X the power to accomplish, than similarly twice the deceleration force should require 4X the energy.

    My experience bears this out... 60KW of regen feels roughly twice that as 15KW. I'll try and test this a little more specifically.

    Thus going from 60KW to 80 or even 120 of regen shouldn't be too huge of a jump...

    (and thanks for catching the KWh error... i'm too used to typing that on the forum. Unfortunately I can't change the thread title.)
     
  16. GlennAlanBerry

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    I would also like to be able to adjust the regen behavior and limits as Scaesare suggests.
     
  17. kjl

    kjl Member

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    Seems like the best option would be to have 0-60 kW regen as currently implemented, controlled by letting off the accelerator, and then 60-100 or 60-120kW regen controlled by depressing the brake pedal, after which actual brakes are applied (like a Prius).

    I wonder if there are other limitations (like how fast the battery can be safely charged from the motor), since you'd expect something like this to be implemented already. 60 kW regen is quite high - that's, well, 60 kWh of regen in just an hour, which is starting to approach supercharger speeds.


    A question: I've never used Low Regen mode - if you drive in low regen mode, and you press the brakes, does it just engage the physical brake, or does it first increase the amount of regen and then engage the physical brake if you push the brake harder?
     
  18. Stoneymonster

    Stoneymonster Active Member

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    Integrating and feathering regen with the physical brakes is very complicated, adds a ton of parts and is just not necessary. It is not something that can be added with firmware or a retrofit. The Prius system includes all kinds of things like back-pressure simulators etc. to make it feel natural.
     
  19. brianman

    brianman Burrito Founder

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    I'm pretty confident this isn't arbitrary. Maybe not publicly explained, but not arbitrary.

    - - - Updated - - -

    I don't want to pay for the R&D nor the "bad stuff that happens" with Tesla going this route. So, no, I don't consider this the "best option".
     
  20. GlennAlanBerry

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    Unlike a Prius, the Model S does not involve the actual disc brakes in the regeneration process (which is a good thing). The Model S has some very good Brembo brakes that are quite effective and have a natural feel. They should not change that, IMO. Just software/firmware changes to the current system, within the limits of safety and what makes sense technically are all that is required.
     

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