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Thread: Regenerative braking

  1. #1
    After reading the 2013 Formula SAE rules I am still a little uncertain about the rules concerning kers. I am thinking of using an electric motor for regenerative braking together with an IC engine. I cannot find any rule that states it is prohibited but this rule (IC.1.1.1) makes me a little uncertain. It says:
    "
    The engine(s) used to power the car must be a piston engine(s) using a four-stroke primary heat cycle with a displacement not exceeding 610 cc per cycle. Hybrid powertrains, such as those using electric motors running off stored energy, are prohibited. Note: All waste/rejected heat from the primary heat cycle may be used. The method of conversion is not limited to the four-stroke cycle."
    This rule says electric motors running of stored energy are prohibited but what if all the energy used in the electric motor is generated while braking the car during a race? Or does this rule forbid any use of kers combined with IC engines?
    How do you think "stored energy" can be interpreted?

  2. #2
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    Where are you going to put the energy that is generated by the regenerative braking before you use it in the electric motor? As far as I know, you have to store the energy from the regenerative braking before you can use it again. And with that, stored energy is prohibited.

    There is a Formula Hybrid competition that allows for what you are describing, but FSAE/FS does not allow it.
    Any views or opinions expressed by me may in no way reflect those of Stewart-Haas Racing, Kettering University, or their employees, students, administrators or sponsors.

  3. #3
    I might be wrong here but my understanding is that you may not use batteries to drive an IC car. I believe KERS violates two rules. First being that you may not store energy in batteries to drive the car, and all the power must come from the engine.

  4. #4
    Thanks for you quick replies.
    But what if I instead of using an electric motor use a flywheel. Do you think this can be interpreted as stored energy?
    Personally I think this rule can be interpreted in several ways.

  5. #5
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    That is considered a Hybrid system, which is specifically prohibited.

    http://www.flybridsystems.com/
    Any views or opinions expressed by me may in no way reflect those of Stewart-Haas Racing, Kettering University, or their employees, students, administrators or sponsors.

  6. #6
    I'm not sure how practical a fly wheel is and how much your suspension guys are going to like the idea. As far as the rules go I believe that is ok. Honestly I don't want to read the rules again to check on this. I suggest that you read the rules, write down the explicit dos and don'ts and see if your idea fits.

    EDIT: you can't make a hybrid using stored energy, the rules won't allow it. The way it is worded any form of stored energy is prohibited.

  7. #7
    All of the above answers are correct. A flywheel is also a dedicated energy storage and thus the car would be considered a hybrid. The part starting at "such..." is only an example and does not mean that only using electric motors is prohibited.
    Regards,

    Tobias

    Formula Student Germany
    FSE Rules & Organisation
    http://twitter.com/TobiasMic
    http://TobiasMic.Blogspot.com

    Not many people know the difference between resolution and accuracy.

  8. #8
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    Tobias,
    Where is the line drawn? Sitting at the start of the accel run the typical fsae car will rev its engine up to a couple thousand rpm, storing kinetic energy in the crankshaft, engine flywheel etc...how is this different?

    I'd like to replace the differential with an erm.... "inertial device" which is connected to the rear wheels via independent clutches. Run your engine at full load all the time to generate the maximum amount of energy for your limited time on the track (aka you are always producing power, under cornering, braking...) and then drive the car with a right-foot clutch pedal.

    I've graduated and as I will not actually be pursuing this design I'm not looking for an official response (which I understand you are unable to give here regardless), but where do you draw the line?
    --
    University of Illinois at Urbana-Champaign
    http://illinimotorsports.net

  9. #9
    To be honest, I do not know where the line is drawn officially(this is always hard to predict as such questions will usually be discussed before an answer is given), but I know what I would add to the discussion:
    This rule prohibits any solution, where stored energy can be released in a controlled and delayed manner.

    Thus, if you intend to make your crankshaft heavy, fine. You don't have independent control over it. You can only use it to break the tires loose at the acceleration start, but you are unable to use it to boost on the last metres of acceleration.
    But if you plan to rev an additional weight up, keep it revving and then later reconnect it, then I would say, this is what the rule is prohibiting.
    Regards,

    Tobias

    Formula Student Germany
    FSE Rules & Organisation
    http://twitter.com/TobiasMic
    http://TobiasMic.Blogspot.com

    Not many people know the difference between resolution and accuracy.

  10. #10
    Thanks for all the replies everyone. Now I understand this rule much better, but still I wont give up the regenerative braking. Let's say I only use the electric motor for braking and not to power the car. And than I use this generated energy for something else. Would this been allowed or is regenerative braking only allowed for EV cars?
    I am sorry if this is a stupid question..

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