Dave wrote:
>
> In article <41747C24.33791D3@junkmail.com>, Randolph <trash@junkmail.com> wrote:
> >
> >Dave wrote:
> >> the motor at this power! Basically, the engine has to run a
> >> generator to fully power the motor(!). This might seem strange,
> >> but it does make some sense from a system point of view.
> >
> >One reason is sounds strange is that it really isn't so. The (electric)
> >motor and the generator is one and the same unit.
>
> Yes ... and No. At least with the Prius and I'm 99% sure that the
> Escape is the same. Yes in that the traction motor is also a
> generator which captures regen braking. But there is a *second*
> generator (which doesn't double as a motor) that is also on the
> planetary that takes engine power, converts it to electric, which
> then either recharges the battery or feeds the traction motor.
> And the three speeds of the devices (engine, generator, traction
> motor) play a complex dance through the planetary gearbox to make
> it all work efficiently. Obviously, the traction motor/generator
> doesn't do both fcns at the same time.

Yes, the Prius has one electric motor (that doubles as a generator) and
one separate generator. The Honda Insight and the Honda Civic Hybrid
does not have this system. Honda has one single unit (that operates in
motor or generator mode) sandwiched between the engine and the
transmission.

I don't know if the Accord will use a system similar to the Civic and
Insight (mild hybrid) or if it will have a Prius-like system (full
hybrid). I know my preference would be the much simpler mild hybrid
system.

> The Escape uses a 94 hp (70 kW output) traction motor. If it has
> a 90% efficiency, that requires 78 kW of input electric. This
> cannot be met by a c. 30 kW battery! So, when the traction motor
> is running full out, well more than half of its power is coming
> from the IC engine!

I know that the Toyota site describes what you are saying, using the
generator and motor at the same time. To me it makes absolutely no
sense. For the Escape, let's say you want to run the motor full power,
70 kW. You need 78 kW of electric power. Let's say the battery is fully
charged and can deliver 30 kW, so you need an additional 48 kW. This
will come from the generator which I will assume to be 90% efficient.
Thus the engine needs to deliver 53 kW to the generator.

If we don't try to invent perpetual motion, and just run the electric
motor with as much power as the battery pack can supply, we will get 30
kW to the motor, 27 kW delivered from the motor. This is 43 kW short of
full power. So the engine can deliver 53 kW to the generator or 43 kW
directly for the same power at the wheels.

One could speculate that the engine efficiency can be better in one
operating mode than the other, but 20% more efficient?

Another thought is that it is unusual to rate batteries in kW or HP.
Certainly there is a limit to much power can be extracted from a
battery, but it is more common to rate the energy storage of the battery
in kWh. However, I believe the 30 kW power rating is correct. To
elaborate: The Prius battery has a similar power rating, 21 kW (not
kWh). Also, 250 D-cell NiMH batteries (let's be generous and say 10 Ah
capacity, though I have never seen more than 6.5 Ah) the storage
capacity is barely 3 kWh, again pointing the 30 kW being a power rating
as stated.