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FWD: Fast+Efficient? (long)
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From email@example.com Fri Aug 2 13:28:36 1996
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Date: Fri, 2 Aug 1996 11:29:23 -0600
From: David Detienne <firstname.lastname@example.org>
Subject: Fast+Efficient? (long)
I currently own a 1990 Audi 80. It is the best car I have
ever owned. I would immediately run out and buy another
exactly like it were it to be wrecked or stolen. My car has
the 2.0 liter VW Jetta motor. That fact is what got the
following chain of thoughts started...
Engine displacement has a weak correlation to gas mileage.
Indeed there are even some examples of cars that get better
fuel economy with a larger motor! However, a diesel motor
tends to get significantly better mileage, but you pay for
it with poor acceleration.
So what about doing a diesel/electric hybrid? I believe the
Audi 5000 Quattro might be a perfect candidate for such a
project. They are available for very good prices (in the
U.S., at least). (Stay with me on this one!) Put a Jetta
diesel motor in it. This would probably give it performance
and economy similar to a Mercedes 240D (around 30 mpg, and
very slow). Remove the driveshaft, and at the rear
differential and transmission tailshaft bolt on electric
motors, powered by some batteries. The usage would be that
the diesel motor would be for cruising and slow starts. The
electric motors would be used just for fast acceleration,
passing, and hills. While stopping, the electric motors
could recover some energy by recharging the batteries.
There would also be redundancy: If the diesel motor broke
you could limp along for a couple of miles on the batteries;
conversely, if the electronics went bad you could drive,
albeit slowly, on the diesel motor. The goal would be to
have the economy of a diesel with the speed of a gas car.
This leads to the questions Im hoping the Audiphiles can
answer or point me to good sources for anwers:
Will a diesel VW Jetta motor bolt right into an Audi 5000?
or perhaps into an 80 or 90? Has anyone out there tried
What are typical fuel economy numbers for the Quattro vs.
the two wheel drive? (My idea is also adaptable, with more
difficulty, to the 2 wheel drive car).
What is the coefficient of drag and the frontal area of the
5000 vs. the 80/90?
I know Audi used to sell diesels, how did their fuel economy
numbers compare to the gas versions?
As this is probably not of general interest, please send
your responses to email@example.com. For those
interested, please send me an email and Ill send you a
synopsis of what I find out.
Following is some technobabble for those that are really
interested and still reading at this point!
Why an Audi? In some ways it might be easier to start with
a diesel car (old Mercedes or VW Jetta, for example), and
add the electric motors. Also, it might be possible to bolt
a Jetta diesel into an old Porsche 924 (anyone know if this
is true?), but hooking up the electrics would be tricky in a
car that small. So why Audi?
1. Longitudinal engine arrangement gives more room under
the hood than a transverse placement. The big size of the
5000 would help even more.
2. Bolting an electric motor to a tailshaft or a
differential is probably easier than fabricating a system of
belts or gears to the flywheel, brake disks, etc.
3. The Audi is basically a front wheel drive design with
four wheel drive added. Doing a similar idea to a four
wheel drive truck could work, but heavy weight and poor
aerodynamics would defeat the original purpose of good fuel
economy. A Subaru might work well, but finding a diesel
motor for it could be difficult.
4. Used Audis in good condition can be had for a good
5. I have very long legs, and the leg room in Audis is
6. Four wheel disk brakes.
7. Good aerodynamics.
8. Commonly available with stick shift. The longitudinal
arrangement allows the shifter to go right to the
transmission, making for unusually good shifting feel for a
front wheel drive car.
The arrangement described is known as a parallel hybrid.
By way of contrast, a series hybrid typically powers a
generator by a gas or diesel motor, which then recharges
batteries that drive the electric motors that drive the
wheels. The parallel hybrid has some advantages over the
series hybrid and pure-electric cars:
1. As the power sources work together, better acceleration.
2. Redundancy allows the car to be driven even if either
system (diesel or electric) are down.
3. As both systems work together to drive the car, the
losses of going from gas to electricity to batteries to
electric motor in the series hybrid case are lessened
(although this point might be argued by some. Ill
forestall the argument by saying it depends on the type of
4. Keeping the batteries warm (batteries lose around = of
their energy capacity at cold temperatures) and keeping the
car warm are challenges for an electric car. The diesel
motor provides plenty of heat.
5. The cars existing systems for power steering, power
brakes, heating, etc, can be retained.
6. A ton (literally, in some cases) of batteries would not
7. Having two motors would allow for parallel / series
hookups for economy or speed modes. In addition, a
series mode would allow for better regenerative braking at
8. Probably cheaper to do than a pure electric or series
9. Can be done and debugged incrementally: First the
diesel conversion, then one electric motor with just a
couple of batteries, then add more batteries and a second
motor later. Eventually, possibly solar panels.
10. Safety: Diesel fuel is less flammable than gas, and
since a smaller number of batteries would be needed none
would be put in the passenger compartment (as is often done
with electric cars). Less electrical power would be needed.
11. Since the car would likely be plugged in nightly to
recharge the batteries, this could also be used to warm the
engine. This would reduce the startup emissions and make
those cold winter mornings a bit more bearable. Likewise,
if the car were plugged in during the day the electrical
power could run a small air conditioner or swamp cooler,
offloading the pollution creation for that to the usually
cleaner power plant. Solar cells might be adequate to run a
small air conditioner.
12. Solar panels cannot collect enough energy to drive a
typical car in real time. They are also expensive. With
the parallel hybrid, however, solar panels and regenerative
braking might be enough to keep the batteries charged, as
there are fewer batteries and they are only used a fraction
of the time.
13. A parallel hybrid has a much better range than a pure
14. While the parallel hybrid would pollute more than a
pure electric, it would hopefully pollute less than a
typical gas car, and certainly use less fossil fuel.
15. If it has the same performance, less fuel costs, and
better reliability (redundant power), a parallel hybrid
could gain rapid acceptance with the car buying public.
16. Diesels have been run on fuels ranging from plant oils
to kerosene, potentially making them good candidates for
1. I might wind up with a car that is slower and uses more
fuel than the original gas engine! Since the batteries are
heavy, this might be true for stop and go driving.
2. The differential gearing is not adjustable, unlike
bolting an electric motor to a transmission where you can
3. Battery weight would reduce payload and lengthen
4. Extra battery weight and limited battery capacity would
mean the electric powertrain may run out of energy up long
grades, or after several hard accelerations.
Please send comments to firstname.lastname@example.org. Thanks!
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