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Fred,
I live on the San Francisco peninsula and when I go to "the city" I also get bad
mileage on
the hills there. Actually, going up hills is efficient because the engine is
running at high
rpm, and even if you have to stop when going uphill, the kinetic energy is
largely
converted to potential energy and much of the rest is stored in the battery
through
regeneration because you can use gentle braking. Going downhill is also fine if
can go in
stealth, but the killer in SF is that you often have to stop when going down a
steep hill so
you need to brake heavily and thus lose a lot of energy.
If you don't have to brake much, then going up and down hills can be more
efficient (only
in the Prius!) than driving on level ground. In fact, you can think of the Prius
HSD as
simulating hills to achieve its efficiency gains. Storing energy in the battery
is analogous to
going uphill and drawing on the battery energy is analogous to going downhill.
Gas
engines are inefficient when running at low rpm (low power demand): the Prius
avoids this
by either turning off the engine and using battery energy or increasing the
power output
and storing the extra energy in the battery. Instead of using battery energy, it
can also use
potential energy (going up or down hill) or kinetic energy (speeding up and
slowing down,
i.e. pulse driving). Driving so as to take most advantage of these three energy
stores will
increase your mileage (as well as driving slower on the highway to reduce wasted
energy
from air resistance as described in the previous message).
I am sorry if this is more analysis than you wanted!
stephen
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