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Old 10-02-2007, 09:34 AM   #1
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Where does the energy go?

This caught me by surprise...



http://www.fueleconomy.gov/feg/atv.shtml
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Old 10-02-2007, 09:43 AM   #2
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Wait a minute...all the blue losses equal 100%, that's not including the 18.2% and the 12.6% in the drivetrain....how can that be? If you add up all the percentages it equals 130.8% that is one heck of an inefficient ICE!
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Old 10-02-2007, 09:44 AM   #3
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Those loss numbers seem high, but I think it includes idling, stop-and-go, etc. Driveline losses probably assume an auto tranny. Nevertheless, in a typical gasoline car, upwards of 75% of the fuel's btus gets converted into unused heat. The majority goes out the exhaust, some gets bled off the engine via the cooling system, some just radiates off the engine/driveline.

Yeah, not terribly efficient.
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Old 10-02-2007, 10:38 AM   #4
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Wait a minute...all the blue losses equal 100%, that's not including the 18.2% and the 12.6% in the drivetrain....how can that be? If you add up all the percentages it equals 130.8% that is one heck of an inefficient ICE!
The 4 big blue arrows are losses when reaching the tire, the 4 big blue arrows + the final 12.6% that reaches the tires adds up to 100%. That's where your energy goes.

The final break down box is just showing what the energy that does get to the wheels is used for. A little to overcome aerodynamic drag and a good amount to overcome rolling resistance. What's left is all the energy you get for acceleration (or changing your inertia). They throw braking in there to show how much energy you're wasting by braking (basically making the 5.6% used to accelerate useless since you're wasting it to slow down again).

So according to this your using 6.8% of your energy to maintain speed. That seems quite a bit out of proportion since that's actually 6.8/12.6 = 54% of your actual output energy used for maintaining speed. I thought it was substaintially less than this. That is, according to this, if I have a car that puts out 100bhp to the wheels I'm using 54bhp just to maintain speed. I thought it was something quite trivial like 10-15bhp to maintain speed and that difference (80+bhp) was being wasted when maintaining speed, which is why P&G is so powerful, since you're using a full 100% of the 100bhp to accelerate during the P and wasting nothing during the G.
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Old 10-02-2007, 10:59 AM   #5
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The diagram makes sense to me know, thanks itjstagame.

I know from personal experience on a dyno that my friend's turbo d16Z6 was only using 15HP to maintain the rollers at 40MPH, which seems about right. But take in account for drag and cross winds that number would have to increase to say, maybe 30HP, in strong winds. I'm just throwing a number up, because I don't want to take the time for calculate everything for my friend's car, lol.
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Old 10-02-2007, 07:04 PM   #6
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I personally would like to see a diagram for a diesel. I would guess that the engine losses and standby/idle would be the only things that would change, and that they would be fairly significant.
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Old 10-03-2007, 06:38 AM   #7
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I personally would like to see a diagram for a diesel. I would guess that the engine losses and standby/idle would be the only things that would change, and that they would be fairly significant.

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Old 10-03-2007, 06:51 AM   #8
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Makes me think that hybrids are really made wrong. They should have full electric drive and the ICE should only power a generator - like a locomotive (except with a plug in powerpack in between).

The motor/generator could then be much smaller in displacement and run ONLY at the RPM where it gets peak efficiency. Furthermore, it frees up different packaging options, especially with hub mounted drive motors that also do regen braking.
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Old 10-03-2007, 08:10 AM   #9
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Loco

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Makes me think that hybrids are really made wrong. They should have full electric drive and the ICE should only power a generator - like a locomotive (except with a plug in powerpack in between).

The motor/generator could then be much smaller in displacement and run ONLY at the RPM where it gets peak efficiency. Furthermore, it frees up different packaging options, especially with hub mounted drive motors that also do regen braking.
I like the idea of a loco-type hybrid as well, but I recall someone having a good argument against it at some point.

The only concern I have with hub-mounted motors is where they're located -- if too far outboard (in the wheel) you're adding unsprung weight...

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Old 10-03-2007, 08:47 AM   #10
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Now I'm curious what the argument against it is...

The unsprung weight issue is possibly offset by not needing halfshafts, brake discs & calipers. It would be far cheaper to build a vehicle that way (far fewer parts such as CV universals, and more freedom in suspension design). I guess it comes down to how much the drive motors need to weigh. With them at all corners, they only need about a quarter of the torque as having one big one.
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