Pete C. wrote:
bud-- wrote:
Pete C. wrote:
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.
You missed that the gas engine use (traction and/or generator) can be
controlled to operate the engine in a more efficient point in the power
curve. Efficiency *is* tied to the hybrid setup. (In addition, for the
Prius, the gas engine is Atkinson cycle with variable intake valve timing.)

The engine is not "underpowered". As in any design the total package is
engineered to work together.

There is always battery energy available for acceleration. If you are
highway driving you are not usually driving on flat land.

You haven't spent much time driving in the Dallas area, have you. Flat
within a few degrees of slope on 70 MPH highways for 100 miles or
better.

It doesn't matter. The Prius is in the 40's for highway mileage.

It is also "recommended" by Consumer Reports. That is not based on
hybrid, but handling, reliability, safety, ....


On down slopes
you are regenerating. In any case you will often have 'excess' gas
engine power which will be used for generation (at the same time as
traction) when necessary. Your comments on not having battery power
available for acceleration are simply not true. Where does anyone who
has evaluated a Prius say that happens.

I'm sorry to say that I have not evaluated a Prius or other small car
since they would not meet more than 5% of my total vehicle needs, so
they wouldn't be economical for me even if they got 200 MPG. I have
friends who have hybrids in urban environments and they perform well
there. All the data I have seen indicated that a hybrid will provide no
advantage over a cheaper conventional car in the same high MPG small car
class when operated outside an urban environment.

Hybrids use smaller engines which can get higher base MPGs. You can't do
that with a conventional car because they do not have an electric motor
for power boost when needed. The Prius has a higher efficiency Atkinson
cycle engine with variable valve timing. You could maybe do that in a
conventional car. The bottom line is the highway MPG. A Prius is in the
40's. (EPA 45 highway, I think the 2010 model is 49 highway.) I believe
a well designed hybrid will always have higher MPG than an equivalent
well designed conventional car.

But different people can certainly need different vehicles. I am
certainly not arguing you should drive a hybrid.

CR had an article on savings when gas was $4.00/gal. I was surprised a
Chev Tahoe Hybrid paid for the higher vehicle cost in a year and was
about $4,000 cheaper than the equivalent over 5 years. (That is all I
know about a Tahoe.) (The payback and savings were only about 25% due to
gas mileage.)

--
bud--