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Aero braking and regen

Discussion in 'Cars and Transportation' started by TEG, Dec 10, 2010.

  1. TEG

    TEG TMC Moderator

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    #1 TEG, Dec 10, 2010
    Last edited: Dec 10, 2010
    Some topics recently have talked about how EVs can disable regen sometimes (such as when the pack is too full, or too cold), and how it is disappointing to compare the way the car drives without the regen.

    There has also been talk of keeping regen active, but "shunting" the power created if the pack isn't ready to accept it.

    It got me pondering some things.

    Some diesel-electric hybrid trains have a form of regen where they power cooling fans when slowing down. They don't have any storage batteries. They accelerate by diesel engines running generators directly powering electric motors. When they slow down the motors go into regen mode and take the power to run fans that cool the diesel engines.

    That also got me thinking about how jets "reverse the thrusters" after landing to slow down quickly without overheating the brakes. On many jets, a metal flap extends to redirect the jet gasses backwards so that the jet engines are effectively running in reverse to slow the plane down.

    I was watching a show on salt flat cars and noticed they all used parachutes to slow down. An owner said they tried to use friction brakes but they just kept overheating and breaking.

    So, couldn't we apply some of these ideas to cars?
    For instance, lets say you are going fast and pressed the brake pedal... perhaps the car should extend some flaps to make the aerodynamics "dirty" to help slow the car without using the friction brakes? Some cars (like high end Porsches) have wings that extend at high speeds for more downforce, so the idea of some mechanical wing/flap/fin doesn't seem out of the realm of practical technical possibility. I suppose the car could intelligently blend aero braking with motor regen depending on speed, battery state, etc.
    Another idea would be to use excess regen to run fans in reverse. For instance, many cars have radiators fans that suck air through the radiators to cool the engine/motor/battery/etc. Perhaps as part of regen some (or all when needed) of the regen power could be used to run the radiator fans in reverse to help slow the car?

    Just some ideas I am throwing out there.
     
  2. Jaff

    Jaff Active Member

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    #2 Jaff, Dec 10, 2010
    Last edited: Dec 10, 2010
    I personally like the parachute idea TEG...(cuts down on folks tailgating you) :wink::biggrin:

    It seems to me that almost any mode of cooling the battery is a good thing...if the regen power could be directed to run the fans (allowing them to engage at a lower pack temperature), might be a very good idea.
     
  3. dpeilow

    dpeilow Moderator

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    You mean like the McLaren Mercedes SLR?

    mbslrmclaren05realcar.jpg


    http://en.wikipedia.org/wiki/Mercedes-Benz_SLR_McLaren#Brakes

     
  4. TEG

    TEG TMC Moderator

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    Well, yeah, like that. Plus maybe some reverse blowing fans that take regen energy, so even when the pack is full or cold you can still get eMotor induced drag and use it to create blowing air to slow you down without the friction brakes. Perhaps the fans should be in the back blowing up to reduce tail lift and keep more downforce on the rear wheels like that SLR is doing with a flap, but even more so.
     
  5. PaulM

    PaulM Member

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    No fan in existence (that would fit on the car) could dissipate the amount of power created by regen. Trains have a large bank of resistor coils that dissipate the kinetic energy created by the electric motors (in regen mode). The fans simply cool these coils. This is not unlike a very large electric furnace. I think this system would be the most reasonable approach to resolve the lack of regen on the Roadster when the batteries are too cold.
     
  6. Kipernicus

    Kipernicus Model S Res#P1440

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    This is what you want

    attachment.php?attachmentid=1199&d=1292010983.jpg
     

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  7. doug

    doug Administrator / Head Moderator

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    #7 doug, Dec 10, 2010
    Last edited: Dec 10, 2010
    Interesting, but I don't think it's practical. You'd have to be going pretty darned fast and make a huge increase in drag to have an appreciable braking force. This is why parachutes work in this particular situation. But in say stop and go traffic, the speeds are too slow for drag to make much of a difference.

    Considering the fans... think how powerful the fans would have to be accelerate the car from rest. (It's not a symmetric problem, but it works to first order.) They would have to be moving some serious air to slow the car. It's also not particularly efficient (a fraction of the energy used to turn the fan is converted to thrust, compared to turning a tire on pavement) and would add a lot of mass. Actually most of the breaking force would come from the regen and the energy would be lost as heat in the fan motor coils and the air that got pushed around. You might as well dissipate the energy directly at the wheels through friction.

    A "better" solution would be to store the energy in a flywheel or a capacitor, or maybe even batteries.
     
  8. mpt

    mpt Electrics are back

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    Problem with the parachute; it's a dead giveaway when you round a bend going 90' and there's a copper parked at the side of the road. "What, me, speeding?" as the 'chute crumples to the ground.
     
  9. mpt

    mpt Electrics are back

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    Which is sad; trains in the late 1800's used to push the power back into the rails to help the other train on the next track coming up the hill.
     
  10. TEG

    TEG TMC Moderator

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    Amusing that we are contemplating having extra energy and not knowing what to do with it. Usually the inverse is the problem. I started this whole topic not so much because we need more effective braking, but rather as way to keep the regen effect consistent so people always know what to expect when they let off of the accelerator pedal.

    (Thanks for the KITT reference by the way!)
     
  11. doug

    doug Administrator / Head Moderator

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    Short of putting power on the rails, maybe they could use a flywheel or a capacitor, or maybe even batteries.
     
  12. dpeilow

    dpeilow Moderator

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    All these things are being done...
     
  13. doug

    doug Administrator / Head Moderator

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    That was my point, I suppose. Though a train with a drag chute might be kinda cool (to see anyhow).
     
  14. TEG

    TEG TMC Moderator

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    #14 TEG, Dec 10, 2010
    Last edited by a moderator: Mar 13, 2016

     
  15. cinergi

    cinergi Active Member

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    How about a supplementary energy storage system that CAN withstand up to 40 KW of brief input at cold temperatures, but may not have all the benefits of lithium ion? A buffer of sorts that doesn't get used all the time, need to store as much, need to withstand as many charge/discharge cycles, etc... Don't use it to supply energy unless it's full; drain it when plugging in the car (by using it to charge and/or heat the batteries). I wonder what the typical daily regen is -- but something on the order of needing to store just a few KWh should be enough ... ?
    Getting that to actually work well is probably pretty complicated, however.
     
  16. TEG

    TEG TMC Moderator

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    Yeah, as Doug mentioned a flywheel or (Ultra) capacitor could do the job.

    Maybe a 25kW mega-CHIMSEL to let those behind know you are really slowing down! :^)
     
  17. Doug_G

    Doug_G Lead Moderator

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    Most of these ideas seem like a heck of a lot of trouble for what really is a minor nuisance that lasts maybe 15 minutes.

    That said, I do find it detracts from the driving experience and it would be nice to eliminate it. But obviously only a simple, reliable, and inexpensive solution will ever get implemented.

    Probably some kind of firmware feature to turn the heater on at a predetermined time would be helpful. Either that or someone has to come up with better battery chemistry...
     
  18. TEG

    TEG TMC Moderator

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    http://web.cecs.pdx.edu/~strom/ev1/articles/supercap_regenerative_braking_nomura.pdf
     
  19. edo

    edo Member

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    Actually an ultracap could increase the efficiency of regen even in normal driving conditions, so it wouldn't be a waste

    I'll give away one of my possible patent Ideas here:
    dual brakes - the friction break disk rotors can double as energy absorbers for electric coils placed around the rotor that would induce a current in the rotor
    the electromagnet technology is used on many electric and maglev trains
    the disks are definately big enough (they would be absorbing the same amount of energy either way)

    Eddy Current Brake|Wikipedia (dual friction-eddy would have been the patent)
     
  20. mpt

    mpt Electrics are back

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    You can see the value of regen on the the VDS: Handbrake on, Information, page 2, Energy History.

    For me, this morning I used 9.8Kwh and recovered 1.1Kwh so 11%. For the month, I've used 142Kwh and regenerated 33Kwh or 23%.

    Go Super-capacitors!
     

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