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

[David Lawyer]

On Mon, Feb 20, 2006 at 10:17:34AM -0800, Dustin Laurence wrote:
> A follow-up to my last message.  Tom and Ray
> http://www.cartalk.com/content/columns/Archive2/1992/September/04.html
> (well, not exactly a peer-reviewed source) think that pulsing the engine
> does save fuel.  Not that from the description these must be much
> shorter pulses than slowing down to half speed, which is the suggestion
> I was responding to.  Short pulses would avoid the problematic lost of
> efficiency to wind resistance.

Of course it saves fuel.  Just look at the efficiency curves and
you'll see that the efficiency may be 2 or 3 times higher at the high
torque used when applying the pulse as compared to the low torque used
while crusing.  That's for a large engine.  For a smaller engine, it
doesn't save as much.

As for wind resistance, you'll get better efficiency with long pulses,
since one goes from say 70 mi/hr down say 50 mi/hr while for short
pulses one would go day from 70 mi/hr to 65 mil/hr.  Which has the
highest v^2?  Of course the long pulses reduce your average speed from
say 67 mi/hr to say 58 mi/hr.  The coasting speed doesn't decrejQse
linearly with time due to the v^2 term, hence more time is spent at
lower speeds in the coasting phase.  Pulses?  Isn't this bang-bang
control theory?

> 
> Note the social cost of using up extra cars comment still stands, as
> do my other comments.
I haven't look at them yet, but I wouldn't be too sure about this :-).
> 
> Dustin
> 
			David Lawyer