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Kinetic Energy Recovery Systems (KERS)

  1. Nov 3, 2008 #1


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    BMW is researching KERS - a way for cars to recover some of the kinetic energy by dynamic braking, as opposed to dissipating the energy as heat in the brakes.
    The system could be an small electric motor/generator and flywheel system, which BMW seems to favor or a pneumatic/hydraulic system.

    The same system may find its way into greener cars.
    BMW mulling a "green" supercar?
  2. jcsd
  3. Nov 3, 2008 #2
    I wonder why this is. Hydraulic KERS's are already employed in many vehicles such as UPS trucks and work very well. Perhaps there is a little weight to be saved by going with an electric system.
  4. Nov 11, 2008 #3
    A flywheel weighs as much as the casing of a pressure vessel for the same energy and materials (funny computation), but avoids much piping.

    Fast compression and expansion are adiabatic but storage tends to lose heat, and this limits the efficiency.

    Perhaps more important: electric machines can be controlled more accurately than hydraulic ones. And you get less worries with them.

    Anyway, the comparison is not obvious, as competing teams have made opposite choices.
  5. Nov 11, 2008 #4
    Flywheels will never be used unless someone can invent a cheap, lightweight, and durable CVT transmission. Flywheels are nice but there energy storage/recovery isn't very practical unless performed electromechanical. And at that point, its just better to use capacitors.
  6. Apr 26, 2009 #5
    why is connecting an ICE to an electric motor and a battery so difficult that a whole team of engineers have to work on this thing for 14 months? what's so exciting about that? hasn't this already been implemented in all modern electro-hybrid cars?
  7. Apr 26, 2009 #6
    I myself am a cyclist. I'm only 26, but I've learned the history of cycling innovation. This reminds me too much of what motivated some bicycle innovations. For example, an easily adjustable handlebar height was sacrificed for a few ounces of weight.
  8. Apr 28, 2009 #7
    it's already been developed for F1 - take a look at this:
    http://www.torotrak.com/Resources/Torotrak/IQPC_2008.pdf [Broken]
    Last edited by a moderator: May 4, 2017
  9. Apr 28, 2009 #8


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    It's an engine that runs at 20,000 rpm and generates 800hp, the system has to not reduce the performance or balance of a race car, it has to survive a 200mph impact into a concrete wall without risking the driver.

    Another mark against the hydraulic kers - the new rules allow them to start the race with energy stored from the timing lap.

    Not sure if this was introduced to try and make the races more interesting by allowing more opportunity to overtake (havign a turbo boost button for more power) or to try and improve F1's green image with advertisers.
    But I would expect the KERS to be in BMW/Merc/Porsche sports cars in the next few years.
    Last edited: Apr 28, 2009
  10. Apr 28, 2009 #9
    Have you ever tried designing such a system yourself? I have done something similar in terms of buck and boost modes in a hybrid. Coupling two very different power train systems together is a very difficult and complex task especially from a control standpoint.
  11. Aug 30, 2009 #10

    What other vehicles other than UPS trucks utilizes the hydraulic KERS?
    Last edited: Aug 30, 2009
  12. Aug 30, 2009 #11


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    So it has. The http://www.mclaren.com/f1season/2009/presspack09/tech-spec.php" KERS.

    And the bottom line in racing?

    Last edited by a moderator: May 4, 2017
  13. Aug 30, 2009 #12
    I think thats why Williams have spent so long getting their KERS ready. They have a flybrid system as opposed to a pure mechanical system.

    On saying that the flywheel system will be lighter than the equivilant battery/electric system.

    I cant remember exact figures but the McLaren system is 25kg and Williams will be 20kg or something like that.
  14. Aug 30, 2009 #13
    Damn, that's heavy. 20kg = 44lbs which is equivalent to 7 gallons of fuel. Do those things really recover as much or more than 7 gallons of fuel to justify the weight?
  15. Aug 30, 2009 #14


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    That doesn't make any sense whatsoever, Cyrus. It also displaces 44 pounds of diamonds, for example...and that doesn't have anything to do with how much energy they recover.
  16. Aug 30, 2009 #15


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    The minimum weight of an F1 car is set be the rules, most cars weight less and so need ballast. The KERS cars don't get a weight penalty other than they are constrained to where in the car the weight is.
    It's not so much the extra fuel (there are limits on the amount of fuel) it's having a few 100Hp extra at the push of a button for a few seconds.
    In practice it's been a failure (didn't make for more overtaking) and the teams are dropping it next year
  17. Aug 30, 2009 #16
    Sure it does. If that system does not recover more energy than 7 gallons of fuel, it's a net loss having in on the car. Why would to recover, say, 4 gallons worth of energy using this system, when you could just add 7 gallons of fuel. That added fuel would also be burned, meaning the car would get lighter over time. That KERS system will always be in the car weighting as much at the start of the race as it does at the end of the race.
  18. Aug 31, 2009 #17
    Can anyone help me answer this question? I tried googling it but found nothing much.
  19. Aug 31, 2009 #18
    Yeah it is heavy, this is why most teams just couldnt get one that worked and abandoned development, it just wrecks the balance of the car.

    The KERS can acutally store far more energy at the moment its restricted to 400Kj per lap, I heard some teams saying they can already do next years target of 800kJ per lap. Some said if it was unrestriced they could do far more.

    So it doesnt store as much as the equivilant fuel. Thats not the point of it though, the important thing is that they have the extra 80HP for 6 sec a lap on tap that carrying the extra fuel cant provide as the min weight of 605kg is without fuel. It'd be easier and cheaper if they wanted to introduce push to pass to simply raise the rev limit for 6 seconds.

    I think KERS is slightly useless, atm its ok but produces artifical racing, it just keeps slower cars infront of faster cars. If everyone had one the effect would be nullified as they would just all push it at the same time.
    Last edited: Aug 31, 2009
  20. Sep 2, 2009 #19
    The weight is also in the energy absorber that would house a flywheel system. In the event of failure, the little a-bomb needs to be contained.
  21. Jan 1, 2012 #20
    This post appeared on a ddwfttw forum:

    "For those who actually care, relative to any frame other than that of the ground, the ground does have energy. It is possible to get energy from the ground - in fact, this is exactly what happens, for example, in KERS. The non-ground frame analysis would go as follows:

    Say we have a 10 kg object initially moving at 10 m/s relative to the ground. We choose to start analyzing in the frame where this object is initially at rest - so the ground is initially moving at -10 m/s.

    We use KERS to brake the object at a rate of -1 m/s^2, or equivalently, a force of -10 N. By Newton's third law, that means that there is a force of 10 N on the Earth.

    As the object is at rest relative to this frame, there is no relevant kinetic power on the object itself. However, there is kinetic power on the Earth; using P = F*v, we get that the Earth is losing kinetic energy at a rate of -100 W, so by conservation of energy, the KERS can be storing energy at a rate of 100 W.

    Note that this is exactly the same as what we get in the frame of the ground, as there, F = -10 N, v = 10 m/s, so the object is losing kinetic energy at a rate of -100 W, so by conservation of energy, the KERS can be storing energy at a rate of 100 W."

    The above idea, seems to be quite commonly accepted amongst those claiming to have physics degrees, but it seems to me to be a the result of literal thinking, and a rather confused idea of what frames of reference means.

    The energy for the KERS, initially comes from the car's fuel, some of which ultimately ends up as kinetic energy of the car. It is that energy which is recovered by KERS, and does not come from the ground.

    I am interested in hearing options for or against either claim.
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