bud-- wrote:

Pete C. wrote:

Rather similar to hybrid
cars getting lousy MPG in areas with high speed roads and little stop
and go traffic, the savings opportunities just don't exist.

The only hybrid I have read very detailed info on is the Prius. The EPA
mileage is 48 city, 45 highway (EPA gives an idea what mileage is like).
Consumer Reports *tests* had a higher highway mileage than city with
44mpg overall. (That is for the old Prius - there is a new 2010 model
out - haven't seen much info except mileage is higher.)

The Prius does not get "lousy" highway mileage.

The Prius gets high highway mileage because:
- I has a relatively small engine. You don't need high end power often
and when it is needed both the gas engine and electric motors are used.
The engine operates in a more efficient band.
- The gas engine is a more efficient Atkinson cycle - the intake valves
stay open part of the compression stroke making the compression stroke,
in effect, shorter than the power stroke. More of the energy is captured
on the power stroke. The engine can change the valve timing. I have not
seen it explained, but I believe the engine shifts toward a conventional
engine when high power is needed.

A Ford Fusion hybrid coming out has the features above - haven't seen
details.

--
bud--

A hybrid vehicle can only get MPG improvements in three possible ways:

1. Energy recapture from regenerative braking

2. Electric boost with energy from a battery pack during acceleration,
allowing the use of an under powered IC engine.

3. Electric boost using energy from an external source i.e. plug-in
hybrid.

Method 1 requires the normal driving pattern to include a fair amount of
braking in order to have any measurable effect on MPG. Where I live, I
drive about 300 yards on my street, then accelerate onto a 65 MPH road
and my trip is pretty much no stop at 65-70 until I reach my
destination, which provides virtually no regenerative braking energy
recovery.

Method 2 requires method 1 or 3 in order to have energy available to
provide the boost. If the engine is under powered and there is not
energy available in the battery to provide boost, you risk an 80,000#
enema when you find you don't have the acceleration to safely merge onto
the highway.

Method 3 isn't really an efficiency improvement at all, it's simply a
dual fuel option, you still need energy to do the job.

Improvements in the IC engine efficiency are not related to or tied to a
hybrid setup and can readily be applied to a conventional IC only
vehicle, without the extra expense of a hybrid setup.