Re: Automatic Transmission?

Roy LeMeur
Fri, 06 Sep 2002 21:30:33 -0700

Eric Patchem wrote:
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I had recently inquired about directly coupling the motor to the axles using
a fixed gear ratio. I had asked this because my car has an automatic
transmission. I had read that an automatic transmission is less efficient
than a manual. Which would be less efficient, the automatic tranny or the
fixed gearbox (or chain)? I have a 93 ford festiva which I want to convert.
A manual tranny probably wouldn't cost that much, but I am trying to do this
conversion with as little stress as possible. I have many ideas, but I would
like to bounce those ideas off anyone who will listen.
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As a start here are a couple of answers from the FAQs at evparts.com:

============
Can I build an EV with an automatic transmission?

An automatic transmission can be used in an EV conversion, but the
modifications required to it are likely beyond the scope of most
enthusiasts. The torque curve of an EV motor/controller combination is not
the same as the ICE it replaces, therefore the shifting points (what
speed/RPM the transmission shifts gears) will have to be changed. In older
transmissions this can be accomplished by modifying the valve body within
the transmission (the assembly that routes the fluid under pressure,
activating the bands), or in the case of more modern transmissions,
modifying the computer code that controls the electronic servos inside the
transmission. Since the benefits are rather minor, the work required
complex, and there is a decrease in overall efficiency compared to a
standard transmission, you don't see very many automatic transmission EV's.
Stick to donor chassis that came with a manual transmission from the factory
and it will save you a lot of time, trouble and money in the long run.

Mark Brueggemann 16JAN01
[EMAIL PROTECTED]


Good arguments for the convenience of automatics have also been posted on
the EV discussion list. An alternative to modifying valves and logic module
code is just to shift into "L2" or "L1" instead of "D". With an electric
motor, you may not even need to shift into "D" for the high gear. I would
tend to keep the torque converter, install an external fluid pump, and do
this. It would let me have more flexibility in choosing a donor vehicle.
Then again, manuals seem to be a whole lot easier to work with. As in many
other aspects of converting a vehicle, it comes down to what you want out of
the vehicle. For many, the convenience is worth the slight decrease in
efficiency. For others, premium efficiency and control is a requirement, and
this requires a manual.

David Brandt
5/21/01
[EMAIL PROTECTED]
====================




There are a couple (or more) other ways it can be done....


1 - Provide pressure with an "always on" dedicated pump motor, no torque
converter, always in gear, manual valve body.

2 - This is the setup in the Maniac Mazda: (GM powerglide), no motor to run
pump, no torque converter, manual valve body. Pump and input shaft coupled
directly to propulsion motors, (2 ADC 9" coupled end to end). Spin the drive
motors, pressure builds,(quickly), clutches engage, car is propelled
forward. (this feature contributes to the _maniac_ part, it makes for great
launches)

This setup may not be optimum for long clutch and band life :^D.
Though there are probably more aftermarket drag racing upgrades for the
powerglide than most any other automatic, it has been a workhorse in drag
racing for many years.

EV FAQ at evparts.com:
http://www.evparts.com/faq/index.php

More info on the Maniac Mazda:
http://www.evparts.com/about/index.php?show=mazda.ihtml

See GIF of Maniac Mazda make front suspension breakin' wheelie on this page:
http://www.dcpowersystems.com

Also, I believe that one or more of our controller gurus have also used the
auto trans setup as a test bed/science experiment.

Damon? Otmar?