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Use brakes to simulate regen, when regen is not at normal levels.

Discussion in 'Model S: Driving Dynamics' started by SabrToothSqrl, Mar 9, 2016.

  1. SabrToothSqrl

    SabrToothSqrl Active Member

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    I propose that the Model S should utilize it's standard brakes and or simply 'waste' regen to ensure the car decelerates at the same rate, regardless of the current level of regen.

    The reason is, all vehicles, outside of the S, and other EVs, decelerate at the same rate, regardless of fuel level, or outside temperature. (All individual vehicles, obviously a suburban slows at a rate different from a Geo metro).

    When I get in my Tesla in the morning, sometimes going down a large hill, within 2-3 miles of my home, I don't always know how my car will decelerate. Yes I am fully aware the dash indicates what my regen IS, but not what it will be, before I want to start slowing down.

    Some mornings I have full regen available, and the car slows at what I'll call the "standard" rate. Other times it slows at a slower rate, and throws me a bit off guard as I'm just waking up and not a morning person...

    I fully realize it's my responsibility to not crash my car, and I'm not asking for anything else.

    I would just like, if possible, the car to always decelerate at the same rate, when using regen... it would simplify the driving process.
     
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  2. Larry93428

    Larry93428 Member

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    I second this suggestion. It is so rare that I do not have regen, it comes as a surprise when gone.
    So rare but as suggested the car should always act the same. Dump the power (somewhere) if the battery will not take it.
    ~Larry
     
  3. AB4EJ

    AB4EJ Member

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    Dumping power?

    To dump power electrically would require power resistors (like used in electric locomotives) - these require cooling, etc. Not practical- would need to use the (existing) friction brakes and dump the power mechanically.

    In my view, your best bet is to learn to recognize this condition and respond appropriately (i.e., use the brakes). I have noticed this happening (on very rare occasions) with the Nissan Leaf, but I instantly knew what was causing it, and could adjust brake pressure as needed. I don't think I want the car deciding automatically to use the brakes, but this could be a configurable option of the antilock braking system if you really want it...
     
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  4. mspohr

    mspohr Active Member

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    I too have a downhill from my house (then a short uphill and longer downhill). My ICE car (automatic transmission) does not have the same deceleration under all conditions. When the engine is cold, it barely decelerates at all and I have to downshift the transmission to get it to brake. At other times, deceleration is not constant based on outside temperature, altitude, hill slope, and probably a bunch of other things too. Over the years, I've just learned to drive it and it's not a problem. The Tesla has low regen when cold and I use the brake pedal to slow down. I'm not worried about wearing out the brakes.
     
  5. travwill

    travwill Member

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    No way IMHO. I don't have full regen or any at times in cold Chicago but know it, expect it, and still use it to be more efficient. You can use that roll to "coast" forward for a while when you look ahead and know you'll need to stop in time, etc. Tesla would never get rid of efficiency for us.

    Your best option is to turn it on low always and won't be as noticeable when have less of it perhaps.

    The efficiency of many, out way the efficiency of one ;-) hehehe
     
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  6. SabrToothSqrl

    SabrToothSqrl Active Member

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    Perhaps all can be satisfied with a check box: "Maintain consistent deceleration"

    And in my example, I should clarify, this is deceleration with your foot OFF either pedal.
     
  7. SabrToothSqrl

    SabrToothSqrl Active Member

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    Actually, this won't effect efficiency at all...

    youd still control deceleration by the go pedal. Full let up will be the max regen available and brakes if not 60kw.

    this only makes deceleration consistent regardless of regen. If you have only 1/2 available, you let up less, you still get the same regen regardless...
     
  8. jerry33

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

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    It would add complexity and reduce reliability. A no vote from me.
     
  9. brantse

    brantse Member

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    I really like this request. Another thing to consider is that this condition only occurs when the battery is cold, so why not try to leverage the "waste" energy through the existing battery and cabin heaters. At least this could provide 12 kW worth of braking.
     
  10. David99

    David99 Active Member

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    It would be difficult to use the energy. The motor could turn it into electricity but it would have to direct all this power somewhere. And that 'somewhere' would have to be able to take 60 kW of power instantly and possibly for an extended period of time if someone with a cold soaked car goes down a mountain. The battery cooling system isn't designed to take 60 kW of heating. A 60 kW resistive heating element would require some serious liquid flow to be able to take that power for a while. You also can't just blow 60 kW of heat into the cabin. It would require a significant redesign of the entire cooling system to be able to work.

    So I think using the brakes to mimic regen in cold conditions is the easiest way to do it.
     
  11. Todd Burch

    Todd Burch Electron Pilot

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    No thanks. It actually DOES waste energy, actually. (You're wasting it in the brakes!)

    Better solution: let up on the go pedal earlier to both verify the current regen capability, and save energy that you instead propose to waste through the brakes.
     
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  12. SabrToothSqrl

    SabrToothSqrl Active Member

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    #12 SabrToothSqrl, Mar 11, 2016
    Last edited: Mar 11, 2016
    So does the defroster... at some point you have to balance driver comfort and drive-ability with actual energy 'waste.'

    The number of stops made before full regen is available is most likely not that many. Using what amounts to maybe a loss of 300 wH to ensure the car always decelerates at the same rate, when one is touching neither pedal... seems like a benefit to me. The AP cars can already control the brakes. This adds no complexity or likelihood of breaking... it's all software.

    We wastefully carry around a transfer case, driveshafts, and gears in other vehicles to ensure better drive-ability... (ICE 4x4s). I love me some low range on my wrangler... (god do I miss my last Jeep), but that drastically affected economy, for superior driveability... 4low and locked this thing was a beast! 35" tires :)

    And again, since it's all software, a simple check box could allow the drive the choice - similar to "standard" or "low" regen. So we can all chose to have the vehicle decelerate at the same rate regardless of regen, or what it currently does.

    Once again this morning 1/2 awake I was jarred when letting off the go pedal... as the cars deceleration was slower than 'normal'. I'm guessing temp, although it was 60 in my garage all night.... and outside this morning... and the charge was only 90%.

    Imagine if this occurred at more than just the start of your trips. or... my proposal... didn't have to occur at all.

    As Tesla adds more and more cars, and we move from early adopters to the masses, it may be easier to transition people and make them more comfortable with the regen idea, if the vehicles deceleration remains consistent regardless of regen capacity.

    that's all :)
     
  13. Todd Burch

    Todd Burch Electron Pilot

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    I guess I just don't see the need personally. If I let up on the go-ped and need to slow more quickly, I'll go to the brakes.

    It's a solution in search of a problem--just my opinion.
     
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  14. stevej119

    stevej119 Member

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    It also occurs when you are at or near a full charge.
     
  15. Cookie Monster

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    As an EV newbie, what is actually happening when I let up on the go-ped? Are the brakes engaging (I see the brake lights go on from the touch screen). How much is it the car not accelerating vs regen braking that's slowing the car down? Does regen braking really help recharge? How much range does it recover 5% / 15% / 30%?

    Coming from ICE-only, I've gotten used to the no creep pretty quickly, and I'm learning to slowly let up on the go-ped but the non-coasting is harder to adjust to after hating brakes for years and the feeling of losing control of when braking when I want to brake. Wondering what that tradeoff is.
     
  16. RDoc

    RDoc S85D

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    I agree with the OP, consistent behavior is a very good thing. What I'd actually like more would be a way to preheat the battery on shore power before starting out.
     
  17. freeewilly

    freeewilly Member

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    Compare with i3 and Smart EV, MS regen is not very consistent.
     
  18. Nikxice

    Nikxice Member

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    The OP has made an interesting proposal that is receiving mixed reviews. I tried to find a safety benefit to justify the idea, but it's not clear there is one. I agree with Todd. Better to observe the need to decelerate early and let up, rather than maintaining speed with an uncertain regen status. No matter the planning, the mechanical brakes will always be there. I would stick with the present system, for reasons of both simplicity and efficiency. There's a couple of unintended positive consequences too. Good reminder to start the day by checking the brakes. Also, my experience has been that limited regen keeps you aware and alert.
     
  19. Manuel

    Manuel Member

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    I wrote about that somewhere else last year.

    "Do you think it will be possible in new cars with digital control brakes to have a software update that make the actual brakes act as regenerative braking when reg is not possible?
    The driving esperience would always be the same. When releasing the right pedal the driver will always perceive a "reg braking", whether it's actually regenerative or digital controlled.
    At the beginning it would be 100% software controlled and 0% regenerative, then 80/20, 50/50,... until the battery is ready for 100% regenerative braking."
     
  20. Az_Rael

    Az_Rael Active Member

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    This isn't possible to do? The more I read these forums, the more features I find that my cheap Volt has that the Model S doesn't.

    I sure hope they add this feature as well as TOU time based charging to the Model 3.

    And to the OP: yes, inconsistent behavior from regen is very annoying and can be dangerous. I know of at least one person on the Volt forums who rear ended someone when he drove his wife's ICE after getting used to Regen driving. It seems to be a general EV problem though. The Volt won't take away regen when it's cold, but will when you lose traction. And since the brakes are blended brakes, that causes the brake pedal to suddenly drop under your foot. In a poor traction situation.
     

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