No Subject

[Mr. Slate]

> >.... Hmmm, let's see...  How about electric motors
> >mounted in the hubs of each wheel that will not only be motors, but
> >regenerative brakes ... Let's put an onboard turbine engine to
> >generate power for these things so we have some acceleration,...

> Consider this, 4 off the shelf electric motors. Ridgidly mounted to chassis
> and connected to the wheel via cv joints.  A battery pack per current
> electric vehicle standards, and one off the shelf small gas engine DC
> generators. I think you know where I'm going. Generator is sized to propell
> the car at 55mph, stand alone. Generator and battery pack combined might
> give you 0-60 in 3 seconds.  Of course, all of this would require
> micro-processor control.  Ok experts, what are the real world physical limits?

This ideas already exists, it's called a series hybrid electric vehicle.
Essentailly, the electric motors run all the time, under any conditions.
When the battery goes below a certain depth-of-discharge (DOD) the
gasoline (Natural gas, propane, methanol, ethanol, .....) powered engine
is automatically turned on and the energy is fed into the batteries.  Part
of this is then removed to run the electric motors, the remaining portion
charges the batteries.  Sounds like a great idea, electric motors produce
no emissions, their quite, etc.  The gasoline engine can be optimized for
running under certain load conditions, minimizing exhaust emissions and
maximizing fuel economy.  Right?    

Now for reality.  As a student who has worked on the development of two
hybrid electric vehicles, and been to two hybrid electric vehicle
competitions, I have seen reality and theory collide head on.  On average
a vehicle needs about 10 to 15 kW of energy to maintain highway speed. 
This is a rough number, very dependent on type of vehicle, weight,
aerodynamics (marshmellow shaped vs. cinderblock shaped), etc.  In
reality, batteries only take about 50% of the energy you give them as
charging potential, the rest is dissipated as heat.  Your high power
electronics (invertors, etc)  are only about 80 to 90% efficient, and your
motor(s) and generator are only about 75 to 90% efficient.  So, as you can
see, the 10 to 15 kW has grown to between 28 and 43 kW.  That a pretty
big energy requirment.  It's no longer a small internal combustion engine,
like a kohler 20 hp, it's something like Suzuki 1.0L 3 cylinder.  Assuming
you want to keep the trunk, this is a lot of stuff to fit under the hood
of your average sized sedan.  In addition, the generator must be sized to
produce voltages around 170 to 200 volts.  This makes them large, heavy,
and expensive.    

At the 1995 HEV Challenge (held back in June of 1995) 40 schools competed
in three classes to see who could build the best hybrid.  In the Ford
Escort Conversion class 10 cars competed in the range event, a grueling
3.5hr event in 40C tempuratures.  Eight cars used a series hybrid system,
as explain above, the remaining 2 were parallel hybrids.  Each car had 11
liters of combustible fuel, and a charged battery.  The last two cars
running were the paralles, all the series cars ran out of battery energy
long before they ran out of combustable fuels.  They simiply couldn't
produce the energy to keep the car going, and charge the batteries.  So as
you can see, while the series hybrid looks really good on paper, in
reality it doesn't neccessarily stand up.  

By the way, if this will do zero to 60 in 3 seconds I'll buy one.  Our
car, a modified Ford Escort with 120hp of electric power and 45 hp of
gasoline power can only muster 1/8 mile in 11.8 seconds, at a speed of 60
mph.  Keep in mind though, our car is a parallel hybrid, using both the
ICE and electric motors to run the wheels. 

Hope this answers some of your questions,


Neall Booth
University of Alberta
Student Vehicle Projects 

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Neall Booth		 	nbooth at gpu.srv.ualberta.ca
   
Mechanical Engineering	 	LPGV Project (Fuel sys. leader)
University of Alberta		HEV Project (Mech. Sys. Leader)
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