Hi Ben,
I'm a little surprised at the light response you've gotten to your
question.
I would have thought there'd be more folks here who at least have put
some
thought into homebrewing a hybrid this way, if not done it themselves.
So, even though I'm about the worst person to do so since I'm a EE
dropout
and have never built a hybrid, I'll post a few random ideas about them
that
have popped into my head over the years.
First, some thoughts on why or why not.
ICEVs' efficiency has improved immensely from microprocessor engine
control,
but it's still pretty abysmal on short trips. For some folks, short
trips
can amount to a lot of driving - take the kids to school, come home,
run to
the store, come home, pick the kids up, come home ... repeat to 40 or
50
significant digits. That kind of use is also hard on an ICE, because it
never gets properly warmed up.
OTOH, EVs excel at short trips. They don't need to warm up, they don't
idle, and many have regen to claw back some kinetic energy normally
wasted
as heat in the brakes..
For folks who need to make both short and long trips, intuitively the
true
hybrid seems like an ideal compromise. However, the devil is in that
little
word, "compromise." It's because you have two vehicles in one.
To stick with conversions here, you're in effect doing a full EV
conversion,
but still leaving the engine and all its supporting hardware in place.
You
have to find a place to mount the EV drive components and the battery;
but
unlike a BEV conversion, you don't have nice big chunks of space where
the
ICE and gas tank used to be. So you have a packaging challenge.
Your vehicle also gains a fair bit of weight. And there are other
little
places where you miss out on efficiency. For example, with the exhaust
still there, you probably can't add a belly pan to smooth out the
underbody
aerodynamics, as you could with a BEV.
The result is that your hybrid isn't going to be optimized as either an
ICEV
or an EV. It's likely that its EV range will be less than a similar
BEV's,
and its fuel efficiency less than a similar ICEV's.
So after thinking all this over, I've decided that I'm more in favor of
having multiple vehicles. Each can be optimized for different needs -
an EV
for local trips, and an ICEV for long trips, for example. This is a
great
solution where you have two drivers and two cars. With just one driver,
I
guess it depends partly on what it costs to license and insure two
vehicles
in your area.
I also really like the station car concept, where you commute using
mass
transit, and lease an EV for daily use between your house and the train
station. In the best of these proposals, you can also swap your EV for
an
ICEV car or van or truck, when you need that instead (you want to go on
vacation with the kids, or to fetch a load of lumber). Alas, I don't
see
many of these on the horizon.
Not that I'm trying to talk you out of this project, just presenting
some
things to consider.
Now, again, I'm not really the right person to advise you. But maybe if
I
cast out some ideas here, someone else will pop up and disagree with me
;-)
First a little of my somewhat quirky nomenclature. I'm an old guy, so
"hybrid" still means to me what it meant in 1969. To me, a hybrid is a
vehicle that can use multiple energy sources.
The cars most folks call hybrids today get all their energy from
gasoline.
Others here disagree with me on this point, which is fine, but I don't
consider a car like a non-plug-in Prius a true hybrid. In my book, most
of
the factory "hybrids" are really ICEVs with electric superchargers
and/or
sophisticated transmissions. The Prius power splitting device is a
really
clever gadget that amounts to an electomechanical torque converter, for
example.
So let me use the term "true hybrid" here for the real stuff.
You may already know this, but true hybrids come in two flavors, series
and
parallel. A series hybrid has its motor (only) permanently linked to
the
driveline. The ICE drives a generator or alternator that supplements or
replaces the battery's energy. Diesel-electric locomotives are series
hybrids.
The downside of the series hybrid is that you lose some efficiency in
the
conversion of mechanical energy to electrical energy. Back in the 1960s
and
1970s, before the days of microprocessor ICE control, you gained ICE
efficiency by running the ICE at a constant speed and load. This helped
to
make up for the conversion losses. With today's computer engine
control,
that's not true any more. ICEs are now much more efficient over a wider
range of speeds and loads. So there are fewer situations where a series
hybrid is apt to give you improved efficiency.
This is where the parallel hybrid comes in. A parallel hybrid can
mechanically link either the motor or the ICE to the driveline -
sometimes
both. This is the system you're proposing.
In theory, you should get the best of both systems this way, with
(theoretically) fewer conversion losses. As I said above, though, I
don't
see any way for a hybrid of any flavor to ever be as efficient an EV as
a
pure EV, nor as efficient an ICEV as a pure ICEV.
From what I can see, it's (not surprisingly) any hybrid is tougher and
more
expensive than a straight BEV conversion. I think this is especially
true
of a parallel hybrid, because you have somewhat less flexibility in
positioning components. (One possibly more flexible parallel hybrid
variant
is the "through the road" hybrid, where you drive the front wheels with
one
fuel and the rear wheels with another.)
To get a final result that's as efficient and as seamless as one where
a
team of automotive engineers designed it (Volt or Plug-in Prius), you
probably need to have some automotive engineer chops yourself.
But I do think you can build something that will work, to one degree or
another. After all, hobbyists homebrewed hybrids back in the 1960s and
1970s; they can still do it today. That reminds me to mention that
maybe in
some ways you might indeed be better off converting a 1960s car than a
later
one; certainly you don't have to worry about fooling the body computer
into
thinking the engine's running.
Just remember that you have to provide all the patches that you'd have
to do
in a BEV - power brake vacuum, power steering pressure, and aircon
drive.
You need a DC:DC converter (or, somewhat cruder and less efficient, a
motor-
driven alternator) to provide 12v house power. You need an electric
heat
source for cold weather driving. (It occurs to me that in a homebrew
hybrid
you might be able to dispense with some or all of those items burdening
the
ICE. Just remember that the energy to run them has to come from
somewhere.)
You have to fit all this stuff in - and a motor, controller, and
battery -
without emptying out the engine bay or removing the gas tank or exhaust
system, as is done in BEV conversions. So, again, packaging is more of
a
challenge than with a straight BEV.
Now, if you decide that you just want to make your car a "mild hybrid"
-
where the motor boosts acceleration and recaptures energy when you slow
down, but the ICE still runs all the time - then that's likely to be
easier
and cheaper.
You can even make it a "charge depleting" hybrid. In this case, the
motor
assists the ICE all the time to at least somewhat improve its MPG. When
the
battery runs flat, the ICE takes over full motive duties.
I've seen mention of a few "hybrid kits" for light trucks. I think
we've
talked about a them here, so a look in the archives might be worth it.
I
just did a web search for pickup truck hybrid kit" and turned up a
couple of
them, but I don't know what their production status is.
In the kits I've seen mentioned, a motor unit goes between the trans
and the
driveshaft. As above, it's like an electric supercharger, and it
usually
also captures some kinetic energy when the vehicle slows down.
Whether you could adapt one of these kits for a car, I don't know.
However,
it looks like you'd have a better shot at it with an older front engine
/
rear drive car such as yours, than with a modern FWD car where the
whole
business is in the nose.
Kits aside, if you're a good hacker (in the positive sense) with lots
of
spare time, a machine shop and the expertise to use it at your
disposal, and
nice deep pockets, what you describe would be a fascinating project.
I hope a few more EVDLers who've done something similar will hop on
board
here, and give you an idea of what they went through.
David Roden - Akron, Ohio, USA
EVDL Administrator
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