OT: Hybrid cars

[guy keren]

On 09/16/2013 11:21 AM, Oleg Goldshmidt wrote:
> guy keren <guy.choo.keren at 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.]
>