The Kinetic Energy Recovery System (KERS)

     Hello again.  This time we’ll talk about KERS, or the Kinetic Energy Recovery Systems used this season in F1 racing.  Why is this important?  Well, this is also part of the whole “green movement” thing every car maker has been trying lately.  I’ll explain everything in a bit.  And even though this is a request, this also interests me as well.  So thanks for forcing me to research this.  =)

     First of all, what is KERS?  Let’s start with the acronym first.  The Kinetic Energy Recovery Systems.  To understand this, you must know some basic physics.  I won’t go into a detailed explanation, but kinetic energy is basically energy that in motion; ie. a car.  And since energy can be neither lost or destroyed, we must convert it to change its form.  Such is how brakes work.  If you’ve read my article(s) on brakes, you know that the basic function of brakes is to convert kinetic energy into heat energy (and maybe some sound energy).  How does it do that?  It uses friction to convert the moving energy of the car into heat.  If you rub your hands together, you’re using up energy and converting some it to heat and your hands heat up.  This is the same principle for brakes, but on a much larger scale.

     So now we know that KERS is used for braking.  And that we convert kinetic energy into heat in brakes.  And if the acronym is Kinetic Energy Recovery, then we must somehow “recover” some of the kinetic energy that is changed into heat from braking.  Well, that’s partially true, but we’ll get into that in a second.  First of all, when we brake, we convert all that kinetic energy of a moving car into  heat, but that sounds like a waste.  Can’t we somehow save up that energy that we’re NOT using to propel the car so we can use it later?  I mean, atleast when we’re accelerating, we use most of the energy from the engine.  But when we brake, we have no more use of that energy, and thus we get “rid” of that energy by changing it to heat.  What KERS is trying to do is to “save” some of that energy from braking, and let the driver use it later on when he actually needs it.  Thus, we’re Recoving some of the Kinetic Energy.

     Now.  How does it do it?  Contrary to popular belief, this system has pretty much nothing to do with the braking system.  The brakes still do their job even with KERS installed on the car.  KERS doesn’t interfere, nor does it somehow harness the heat energy generated from the brakes.  KERS is connected to either the crankshaft from the engine, or the transmission itself, and changes the kinetic energy of a decelerating car to either electrical, chemical, or mechanical energy.  What does that mean?  It basically means it stores the energy in either a battery, a superconducter, or a flywheel.  For the simplicity, lets stick with using a battery for this explanation.

     When a car is decelerating, even though the engine isn’t producing any power, the pistons are still reciprocating, and the crankshaft is still turning due to the circular momentum of the crankshaft.  Imagine driving along, and you suddenly stop pressing down on the acceration pedal.  The engine’s revoluations (rpms) don’t suddenly drop to 0, but it slows down gradually.  Why?  The energy released from one combustion cycle of a piston is more than enough to turn the crankshaft just one revolution.  Think of a pinwheel.  Blowing it just once won’t turn it only one time, but it’ll keep on turning until its out of energy.  This is the same in engines.  One combustion cycle can keep the crankshaft turning as long as the friction forces aren’t stronger than the kinetic forces turning the crankshaft.  Now, when a car starts to decelerate, the crankshaft is still turning, and thus giving out some energy (circular forces are called torque).  Instead of “wasting” it by turning it to heat energy and adding to global warming, we use some of that torque to power a small generator.  Remember, a generator converts mechanical energy into electrical energy.  So what’s the generator doing?  Turning all that “torque” into electrical energy and then storing it inside a battery.  Obviously not an everyday AA battery, but one that can hold alot more energy than that.  So that every time we brake, we convert some of the energy we don’t use anymore into electrical energy that is stored in a battery to be used later on.

     In the specific case of KERS (KERS is a type of regenerative braking), which is being used in F1 (Formula One) racing,  they programmed the system so that the driver can press a button, and have a motor (not the car’s motor, but KERS’ own motor) convert that electrical energy back into mechanical energy to accelerate the car.  And for this F1 season, they’ve limited each button press to about an extra 80 horsepowers for 6.67 seconds, enough to overtake an opponent.  So it’s sort of like a “boost” button which can give the car an extra “oomph” for the straights.

     When we convert types of energy, it’s never a perfect conversion.  For KERS, we’re talking a 70% conversion factor from the mechanical energy to the electrical energy being stored.  Evidence?  The KERS system is prone to overheating, and needs to be air cooled.  It also adds about an extra 66 pounds to the racecar, something that has prevented regenerative braking from being used in the past.  Its only until recently that we’ve been able to compact this system into such a “small” form so that it can be used efficiently.  Remember, even though this is a step towards a greener world, if its not efficient, no one will use it, and no one will buy it.


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April 2009
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© 2009 Rusi Li

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