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Regen whimsical ponder

Discussion in 'Electric Vehicles' started by kgb, Mar 29, 2011.

  1. kgb

    kgb Member

    Sep 22, 2009
    Houston, TX
    I was wondering if an EV could ever use regen as the exclusive method of braking. I guess friction brakes could remain as a back up safety feature.

    Currently on the roadster, regen is set at a constant... or at least, that's what the posts on this site lead me to believe. I was wondering if it would be possible to have "variable regen." One would set up the brake as a potentiometer that feeds the computer in a way that more pressure on the brake increases the amount of regen. For that matter, application of the brake would also inhibit creep (for when you are at a stop).

    Does that seem possible to anyone? I realize that I hardly use the friction brakes as it is, but every bit less I use would increase my efficiency.
  2. William13

    William13 Active Member

    Mar 19, 2011
    South Bend
    Four wheel drive would be needed. The regeneration on the Roeadster is variable. The Roadster owners report little wear on their brakes. Currently it would not be legal or feasible to use regeneration without brakes that work.
  3. TEG

    TEG TMC Moderator

    Aug 20, 2006

    #1: When the battery pack is full, or really hot or really cold you don't want to put charge energy into it so they disable regen.
    (Possibly solvable with some sort of giant heatsinked bleed off shunt/resistor.)
    #2: Regen is currently only on the rear wheels. As was said, AWD would be needed.
    #3: Legal/regulatory issues as mentioned.
    #4: I think regen doesn't work properly at really low speeds (e.g.: < 5mph), so it may not work for all situations requiring braking.
    #5: Max braking force / maximum slowdown might be more with disc brakes than it could be with regen alone.

    For many of these reasons, and probably more, I don't think we will see regen as an exclusive braking mechanism.
  4. Lloyd

    Lloyd Well-Known Member

    Jan 12, 2011
    San Luis Obispo, CA
    I would like to see a driver adjustable regen via a switch on the dash or steering wheel. This would be especially important for the upcomming sports version.
  5. Doug_G

    Doug_G Lead Moderator

    Apr 2, 2010
    Ottawa, Canada
    Sure, with proper servo control there's no reason you couldn't precisely hold the motor in a specific position. But it would have to be designed to do that.
  6. DrComputer

    DrComputer Active Member

    Jan 29, 2009
    Sherman Oaks, CA
    It can be done. My Segway only uses its motor for propulsion, braking and balancing. The only issue is that at some point the battery would be expending energy (not regenerating it) to stop the car if the speed of deceleration need to be faster than regen could create. This would defeat the purpose of regen, but could eliminate the need for friction brakes. I doubt it would every be tried in a car.
  7. vfx

    vfx Well-Known Member

    Aug 18, 2006
    CA CA
    The ACP E-Box has an adjustable slider on the dash and you can set it to no regen all the way down to a complete stop. Wish Tesla had implemented it on the Roadster.
  8. benji4

    benji4 Roadster 2.5 #0476

    Nov 7, 2010
    Tokyo, Japan
    Most of the time I'm able to get the car pretty much to a complete stop without using the friction brakes. I enjoy seeing how far I can go without applying the friction brakes at all, and it's amazing how well this works most of the time. Obviously you do have to step on the brake pedal to hold the car at the line though as it creeps just a bit.
  9. Ardie

    Ardie Member

    Oct 4, 2009
    While it is possible to stop a car using only a regen design, I doubt if it will come to pass.

    First of all, there's the legal (and practical) requirement for a parking brake.

    Secondly, there will have to be a long and complicated discussion on what exactly happens
    * When I take my foot off the accelerator:
    The car will (a) coast, or (b) brake using regen.

    * When I tap the brakes:
    The car will (a) slow down, or (b) coast, because the battery is full and there's no place to put the regenned electricity.

    * When I stamp on the brakes because my life depends on stopping NOW:
    The car will (a) regen for all its worth, hopefully using some kind of ABS technology, or (b) lock the tires, because there's no ABS, or (c) coast, because the battery is full.

    * I stamp on the brakes - on mud, water, ice, gravel, etc.
    The car will (a) cleverly regen -only- the tires that need braking, or (b) lock the tires, or (c) do nothing.

    I think you get the idea.
    It seems that most automakers that are dipping their toes into the electric car world are taking the safest path (for them) possible:
    Leave the mechanical / hydraulic braking system as it is, and add the regen capability to the accelerator pedal.
    When you stamp on the accelerator, you go.
    When you let up "just the right amount," you coast.
    When you let up all the way, the car slows down by regenning. (The driver's dial-a-regen preference will decide how aggressive that will be).
    When you step on the brakes, the car's braking system picks up where the regen left off.
    If anything goes wrong with the regen system, the braking system is still intact and will stop the car (Toyota's latest woes notwithstanding).

    It takes a bit of getting used to -- maybe about a day in city driving.
    Sort of like switching from a stick to an automatic. Different, but not beyond the learning curve of the average motorist.

    -- Ron
  10. Doug_G

    Doug_G Lead Moderator

    Apr 2, 2010
    Ottawa, Canada
    Also it would consume a small amount of power to hold the car stationary, whereas a friction brake doesn't need any power.
  11. frequencydip

    frequencydip Sig 100 - #52

    Dec 11, 2011
    Los Angeles
    What would be interesting about regen only is the huge savings in unsprung and rotational mass you would get by eliminating the disc and calipers. The car would accelerate faster and have significantly improved handeling and cornering.

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