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Posted by Bob & Holly Wilson on October 9, 2008, 11:19 am
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>
> > Technology moves along...
> >
> > As mentioned in another thread, the Prius engine must
> > operate over a wide range of RPM and load because it
> > provides a combination of propulsion and
> > battery-charging. The electric motor means that the
> > Prius engine will not have to meet the challenge of
> > acceleration from zero speed, thus limiting its range of
> > RPM and load and permitting improved efficiency.
>
> Mostly correct. Both the Toyota and Honda hybrid systems, although
> different, are using the electric power system to make up for the
> defficiencies of an ordinary heat engine.
>
> > Engines can be made extremely efficient when designed
> > for a constant load and rpm. The Volt, for example, will
> > charge from the grid and then drive for (supposedly) 40
> > miles, and then the engine kicks in to begin charging
> > the system. That engine will always see the same load,
> > etc. so can be designed to run very fuel-efficiently.
>
> Yes and no. The thermodynamic efficiency of the engine should be high.
> But it wiill have these energy conversions:
> (1) engine->generator ~95%
> (2) generator->motor ~95%
> (3) generator->battery ~95%
> (4) battery->motor ~95%
>
> In the engine->generator->motor conversions:
> .95*.95 = 90% (assuming the 95% is maintained)
>
> In the engine->generator->battery->motor conversions:
> .95*.95*.95*.95 = 81% (assuming 95% is maintained)
Opps:
.95*.95*.95 = 86% (assuing 95% is maintained, not a trivial problem)
>
> The typical Prius efficiency is a little more complex:
> (1) 72% of power is: ICE->transaxle ~95%
> (2) 28% of power is: ICE->generator->MG1 (.95*.95 = 90%)
>
> .72*.95 = .68
> .28*.90 = .25
> -----------------
> .93%
>
> >
> > From an engineering viewpoint, the Prius is a great
> > achievement.
>
> We agree and the Prius has been on the roads since 1997.
>
> > . . . The Volt and the many cars to follow that
> > model are far simpler - and in engineering, simplicity
> > is always better than complexity. In fact, there's a
> > good argument that the Volt is not a "hybrid" - it's an
> > electric car that carries an onboard charger...
>
> No argument here. The 'plug-in' is just tapping a different power
> source.
>
> > Like most, I hope GM does a good job of executing the
> > Volt,
>
> Agreed and some of the stuff that has leaked out sounds very promising.
> The environmental chamber for the batteries is a very good solution to a
> difficult problem.
>
> > ... that Toyota soon introduces its plug-in car, and
> > that many other car companies follow suit.
>
> My current thinking is if the plug-in energy can keep the ICE in a
> 'thermal warm-up idle' until the block reaches the right temperature, it
> will be a very good thing. Beyond that, the rest is keeping the ICE in
> the high efficiency range.
>
> > . . . And I
> > especially hope that emerging ultracapacitor
> > technologies overtake electrochemical batteries for car
> > applications.
>
> My studies suggest that if the ultracapacitor unit handles surge charge
> and drain with the traction batteries for sustained loads (aka., hill
> climb and warm-up,) we'd have an optimum mix.
>
> Bob Wilson
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