[SGVLUG] OT: Hybrid efficiency (was:New Linux Lug)

[Emerson, Tom]

> -----Original Message-----
> Behalf Of David Lawyer
> On Tue, Feb 21, 2006 at 12:03:20PM -0800, Emerson, Tom wrote:

> > Note I said that I "kicked it into neutral" [...]

What I didn't say (but perhaps should have said) was "and left it that way as I coasted back up the next hill"  In other words, there was NO further input from either the gas engine or electric motor.  The only things slowing down the car would have been air friction and rolling resistance (oh, and perhaps gravity)  Basically, this "proves" that the car has a very low CD, and with 90psi tires, very little rolling resistance as well.  It was really more of a measure of how well potential energy was converted into momentum and back
 
> Well, if the conversion is only 36% efficient, you would only reach
> 36% of the way to the top.

About the only way to test & prove that would be to start with a totally "flat" battery and no gas in the car, and let it "charge" the batteries as it rolls DOWN the hill, [regeneratively] braking to be at a "full stop" at the bottom, then see how far back UP the hill the car goes based on the few seconds of charging from going downhill.  As much as I like the hybrid system, I doubt you'll get much out of a test such as this.

[...]
> > usage: battery usage when the engine isn't running, battery charging
> > due to "coasting"
> 
> You mean braking, not coasting.  I have frequently seen coasting used
> when what is meant is braking.

yeah, that's a fine line.  Most people would consider "fully removing your foot from the gas pedal" to be "coasting", when in reality the Prius would actually be "braking" due to the fact that you are now turning the motor into a generator.  Because it "takes energy" to turn the motor, and that energy has to come from somewhere, this action will effectively slow the vehicle more than friction and drag alone, so you're right in that this is technically "braking".  Putting the car "in neutral", thus disconnecting the motor & engine from the tires, would indeed be true "coasting".

On the "prius_technical_stuff" forum, I heard of a technique where you put the car "in gear" and press on both the gas and brake pedals.  The gas engine wants to push the car, but the brake holds it back, and everything then dumps into the battery [providing a "quick charge" to the battery]