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

[David Lawyer]

On Thu, Feb 16, 2006 at 04:35:09PM -0800, Dustin Laurence wrote:
> On Thu, Feb 16, 2006 at 03:53:45PM -0800, David Lawyer wrote:
> 
> > On Thu, Feb 16, 2006 at 02:31:16PM -0800, Dustin Laurence wrote:
> > > Why do we claim a membership area at all, anyway?
> > 
> > We don't by perhaps we should :-).  One reason being energy
> > conservation.  Someone could use a shortest path algorithm :-)
> 
> Ah, yes, I imagine all the happy hackers writing C code to decide which
> LUG meeting to go to, or at worst using something like octave.  Cool
> world. :-)

There are a number of shortest-path codes available.  Actually the
problem is better called the "nearest neighbor" problem.  The LUG
meeting locations are your "neighbors" and you need to find the
nearest one.  At USC, people recently worked on the "nearest neighbor"
problem using a LA County road network and with real-time input of
current traffic congestion which changes the "length" of the links.  So
implementing this would not be too hard since it's just putting pieces
together, but then you need to supply the "nearest neighbor" utility
to the world and find sites to host it on.  These sites then need to
have digitalized road networks and make address tables of neighbors of
various types, such retail stores of various categories, etc.  Look at
the printed "yellow pages" to get an idea of the magnitude of the
task.  So one could then use this to find the nearest food market,
nearest bicycle shop, nearest gas station, nearest M$ :-) users group,
etc.

> 
> > ... So to encourage energy
> > conservation double the price b and the LUG membership regions will
> > change. 
> 
> It's much more effective to simply not open the door for anyone who
> isn't riding a moped. :-)
Aren't they a bit polluting :-).
> 
> > ...Doing this will likely get better miles/gallon than a hybrid.
> 
> No.  It cannot *ever* do so for engines tuned for their respective jobs
> and a hybrid that is meant to be the real thing (and not the "hybrid
> assist" stuff some are apparently designed for).

Never say never (via way of "ever").  First, the hybrid engine must be
able to achieve high speed on climbing mountains, in which case there
will not be nearly enough energy stored in the battery for this.  So
the engine size of a comparable non-hybrid only needs to be a little
larger.  The weight of the batteries and motor-generator tend to make
the hybrid heavier.  Hence more rolling resistance and a little more
aerodynamic drag since the body must be slightly larger.  This added
weight must include the increased weight of the frame, tires, etc. in
order to support the increased "payload" of motor-generator +
batteries.

But worst of all is the poor efficiency of regenerative braking.  It's
obtained by multiplication of generator efficiency, battery efficiency
and electric motor efficiency.  But there are some caveats.  Don't use
the rated efficiency since the actual efficiency in operation is
likely to be much lower.  An electric motor may have an efficiency of
only 1% if it's running at high speed and very low torque.  Also, bear
in mind that the mean of the products of efficiency is not equal to
the product of the means, it's often much lower.  

Thus the efficiency of recovery of kinetic energy of a vehicle via
regenerative braking is poor.  Perhaps only 50%.  So what could happen
with a non-hybrid if one drove optimally to conserve energy?  How
does on recover kinetic energy for a non-hybrid?  By simply coasting
with the engine off.  This way one recovers all the the kinetic
energy (=KE), not just 50%.  Even if one coasts (on level) only until half
the cruising speed is reached, KE recover is 75% since KE is
proportional to v^2.

> Non-hybrids must have a broad power curve, which greatly lowers peak
> efficiency.
Not at all, since the driver only powers the car at the points near max
efficiency and most of the time coasts with the engine off.

> A true hybrid, by comparison (one where the engine generates power
> only and is not directly connected to the wheels), can have an
> engine tuned with a very narrow--and thus very highly peaked--power
> curve and run at the most efficient point regardless of vehicle
> speed.
True, but what about the poor efficiency of KE recovery?
> 
> This is why, in fact, there has been interest in continuously
> variable transmissions--you can get a similar benefit without the
> electric drive train.  

You really don't need CVT if you shift at the proper points and coast
at the optimal points.  Car's aren't designed for this, especially
ones with automatic transmission.  They need to be redesigned.  When I
try to get max efficiency by pushing the gas pedal to the floor, the
AT shifts into a lower gear, decreasing efficiency.  Maximal
efficiency happens at near max torque and not too high rpm.

> However, you still don't get the ability to run a smaller engine
> that only needs to satisfy the average power demand (letting the
> batteries take up the slack).  Non-hybrids, even with a CVT, must
> size the engine to the *peak* demand, and this hurts average
> efficiency.
They can also just not supply what you call "peak demand".

At any rate I think that *if* one had a non-hybrid car that could be
fully controlled (so as to operate at full throttle in high gear) and
that traffic, signals, and laws were such as to promote coasting, and
*if( non-hybrids were designed to have bodies lighter than hybrids,
then such non-hybrids would be more energy efficiency *if* driven
optimally.  Some of the energy saving in hybrids is that they use more
lighter weight aluminum etc.  So in any comparison, one needs to
design a non-hybrid this way too.

I think auto manufacturers should be required to provide efficiency
curves for their engines so that drivers can select efficient
operating points.  Why not a display on the dash that would show
efficiency?  We already have the inputs: rpm and torque (which is a
funct. of throttle position and atmospheric pressure).

Efficiency curves can be iso-efficiency curves on a plot of x=rpm,
y=torque, since power = x*y (x in radians/sec), one can replace either
the x or y axis with power.

Over 30 years ago I drafted a long article about the energy-efficiency
of various types of transportation at various speeds which included
efficiency curves obtained from an ex-employee of an auto Co.  I had
57 references, many in Russian.  I was inspired from reading von
Karman's "What Price Speed ..." from 1950.  But I never got it
published even though I put a lot of work into it.  One objection was
that I didn't present anything new.  It was a survey article and
didn't seem to lead to any conclusions except that overall
efficiencies depend on a large number of factors including side-winds.
I failed to include Jevons law which says that increasing efficiency
tends to *increase* fuel consumption due to stimulating more demand due
to the lowering of cost due to improved efficiency.  Another major
problem with what I wrote is that I failed to account for the energy
lost by braking, which is exceptionally high in railroad
transportation.

			David Lawyer