The Three
Fundamental Efficiencies of Hybrid Technology - Why Are Hybrid Cars
More Fuel Efficient than Regular Cars
March
12th 2006
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In
transportation based hybrid power production How the power is
produced takes a back seat to how the power is processed. The three
fundamental efficiencies of refined wheeled vehicle hybrid power
processes are "Prime Mover Power Averaging", "Regenerative Braking,"
and "Peaking Power."
Power Averaging:
"Power
Averaging", also referred to as "load averaging or load leveling",
allows maximum power output of the prime mover to be reduced to that
slightly greater than that needed to cruise on level terrain at
maximum sustained velocity. This reduces prime mover (engine) mass
and volume; offsetting the mass and volume of the required temporary
storage device.
Peak
process demand in an automobile or other wheeled vehicle occurs
during acceleration and grading (climbing hills). Existing hybrid
systems translate this demand real time to the prime mover. In the
next generation of hybrid automobiles the prime mover will operate
at a near constant output from start up to shut down. The prime
mover will feed near constant power into a temporary storage device
(battery, capacitor, flywheel, or hydraulic accumulator) and the
variable real time demand power will be pulled off that storage
device. This will allow for a very significant reduction in maximum
power requirements of the prime mover, optimize prime mover power
production, and allow the introduction of prime movers not well
suited to rapidly variable demand.
With
Power Averaging as a primary efficiency of hybrid technology, the
fueling algorithm of the next generation of hybrid automobiles will
be a bit more complex than a simple iterative program. The coming
generations of automotive control computers will "remember" power
use based on both "routes" and "habits", calculate average demand,
and de-couple operator control from prime mover demand with the
ability to handle unanticipated variability of daily commuting. How
that will be accomplished is beautiful in its simplicity.
The
reciprocating engine dominates automotive technology because of its
ability to respond rapidly through a broad power range. Power
Averaging will allow the adaptation of prime movers that, although
may not respond rapidly to power variation, operate at very high
efficiently when operated at a near constant output. Given modern
materials, the economics of scaled production, and the primary
fundamental hybrid efficiency of Power Averaging, the choice of
prime mover technology will be expanded to include Turbine and
Sterling technology as well as existing Clean Diesel
Combustion,conventional gasoline powered reciprocating engines, fuel
cells, or any other primary power technology.
Regenerative
Braking:
Regenerative Braking can be described as the recovery of
kinetic energy (energy of the vehicle mass moving) to stored energy
through numerous regenerative braking methods. Prior to regenerative
capable hybrids, highway driving was more fuel-efficient than city
driving even though aerodynamic losses of high speed highway driving
far exceeded that of low speed driving in stop and go traffic.
In stop
and go driving the energy conversion process can be described as the
conversion of chemical potential energy of the fuel source by the
prime mover, to kinetic energy of moving vehicle mass, to friction
braking heat loss. The energy loss is directly proportional to the
number of stop and go cycles. The multiple cycles of this conversion
loss in stop and go driving can greatly exceed that of aerodynamic
drag in constant state highway driving. Existing hybrid systems now
regenerate significant amounts of energy lost during braking and
this fundamental efficiency is expected to radically improve as the
power and energy density of the temporary storage devices continue
to improve.
Peaking Power:
"Peaking
Power," when described as a fundamental efficiency of hybrid
technology, refers to short term/ high power supply of energy to the
power train from a temporary storage device during the peak demand
periods of acceleration and grading (climbing hills.) This allows
the drive train to be supplied power at rates much higher than the
maximum power rating of the prime mover for short periods. The prime
mover must still be capable of producing a sustained power slightly
greater than the power required to cruise at maximum sustained
velocity on level grade, but the cruising (or average) demand is
much less than peak demand.
The
coming generations of hybrid vehicles will have the operator
controlled capability to rapidly accelerate to velocities
significantly greater than maximum sustained velocity. This will be
accomplished by summing the energy available in storage with prime
mover output. As the storage device discharges, the sustained
operating velocity will fall back to where prime mover power is
balanced against drag and grade. The drive train will be the
limiting factor in accelerative performance but the accelerative
performance of yesterdays "muscle cars" may pale in comparison to
the accelerative performance of a hybrid with a “muscled” drive
train.
I am sure
there will be more variations in storage and conversion methods but
"Prime Mover Power Averaging", "Regenerative Braking," and "Peaking
Power" will remain fundamental efficiencies in hybrid technologies
whether it be wheeled vehicles, small unit electrical power
production, or the myriad of other applications.
In
closing I want to say the potential for significant enhancement of
transportation efficiency still exists in both automotive and rail
applications. Energy saving returns can come a lot quicker and
cheaper than reinventing the technology. We have begun by sequencing
traffic lights to traffic patterns and may soon expand that concept
out to a 12,000-ton train that may never have to stop for a meet.
By
Mark J. Carter
I have been a
student of Transportation Hybrid Technolgy for over 25 years. I authored a
paper titled "Flywheel Storage and Regenerative Braking as Applied to
Wheeled Vehicle Transporation Processes" as a term paper at the University
of Northern Iowa in the Fall of 1978. I followed on with a "1984 Rolex
Award" entry in 1983, proposing an automotive application of hybrid
technology.
I am currently employed as a Safety Inspector with the Federal Railroad
Administration, United States Department of Transportation. Mark J. Carter
P.O. Box 765 Jefferson, TX 75657 MJCarter01@aol.com
Automotive Books
Keywords and misspellings: hibrid car electric pryus acord
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