On 09/16/2013 11:21 AM, Oleg Goldshmidt wrote:
guy keren <guy.choo.ke...@gmail.com> writes:
instead of going into theories - does your car have a fuel consumption
computer?
Yes, it does, that's how I know that it is more efficient at higher
speeds. I made a point to say that I never did systematic observations
or statistical analyses, just watched the numbers occasionally out of
curiousity. In effect it was exactly the kind of experiment you
suggested.
"watching the numbers occasionally" is not a proper experiment. you need
to reset the computer before you start the "drive under test", and check
the value after - and the length should be enough to even out the
fluctuations.
My car is different from yours, that's all. Your Prius, in particular,
may use relatively more battery at lower highway speeds giving you
momentarily better numbers (I don't know that, I am guessing). I assume
it is not a plug-in, so at some point it will consume some fuel to
recharge the battery and your numbers may be momentarily worse. I assume
it is smart enough to do it when the engine is not under load and when
you are in a lousy regime (in a traffic jam, etc.). This would be smart
on two levels: a) charge the battery when you have spare capacity; b)
this regime will improve the average numbers, exactly as I showed in the
previous email.
the experiments i performed were over lengthy periods of time. the
numbers i reported in another mail were taken by reseting the counter
every time after i refuel the car - and i usually refuel it in the same
gas station. i also did not take into account periods in which i
performed long out-of-town drives on road 2 or similar roads.
one thing to note - the car uses more then just fuel to recharge the
battery. every time i leave the accelerator (e.g. when coming to a
traffic light, or due to getting too close to a car in front of me) -
the battery is being recharged. without this mechanism, the car couldn't
have been able to go at 20km/l in "accordion" traffic-jams (i tested
this under a 15-minutes jam - that's the longest i encountered so far.
and the battery's charge level went up and down several times during
this period - implying the car could have supported the same level of
fuel consumption even if the traffic jam lasted much longer).
however, the car is able to sustain a 20km/l consumption rate also when
going at a speed of 110km/h on road 2. it's just that at 80 - it could
get even better consumption.
without you giving more exact numbers and how exactly you measured them
- i don't think we can make any comparisons. arguing about fuel
consumption *reality* using theoretical guesswork is, in my opinion,
pointless.
To emphasize again: all of the above regarding what your Prius may or
may not do is guesswork. Not so unreasonable guesswork, I hope. But even
if it is basically correct, it also may be just a component in the
overall picture. My car has a significantly larger engine, probably uses
a different AFR, definitely a completely different gearbox (and quite
probably lower RPMs at higher speeds), different aerodynamics. It is not
reasonable to expect a particular derived characteristic (optimal speed
for fuel consumption) to be similar for suc different models. Even the
markets for which the cars were designed by the manufacturers are
completely different: Prius's target market is definitely closer to
California than to Europe, while Passats are not very popular in the US
but common in the Old World. Guess what: Americans drive much slower on
average (highway speed limits between 55mph and 65mph). This could
easily affect design decisions. [Again: no, I did not watch over the
shoulders of Toyota or VW engineers.]
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