[ausev] TRANSMISSION

[Brian Lasseter]

On Thu, Dec 18, 2008 at 9:21 AM, Jim Watson <osious at gmail.com> wrote:
>  I have had a question about gear boxes and transmissions for a long time. I
> have read on one site that in converting a gas to an electric you need to
> leave the 5 speed (or what ever it is) transmission in the car to be used
> with the electric motor.

As you stated... You do not NEED the transmission.    However there
are a number of reasons to leave it in there in a real world
situation... despite the minor friction loses.  Those include:
1 - Ease of conversion (how do you fit an aftermarket differential to a car?)
2 - Cost of conversion (stock transmissions come with donor cars)
3 - The need for more parts without the transmission (like a
fixed-ratio gearbox, or reversing contactors.)
4 - Safety (the clutch is convenient as a safety device)

--

1)  It makes the conversion much easier for a car (because the
transmission is often built into the differential), and it saves
electrical complexity by not having to have a reversing circuit for
the motor.  (Fitting an electric motor to a car is complicated
enough... imagine having to find, and fit an after-market differential
to a car as well.)  With a truck that has a separate differential, you
can add reversing contactors to allow the motor to run in forward and
reverse and then you do not need the transmission.

2)  Reversing contactors and the wiring to support them would add $400
at least... whereas the reverse gear of the stock transmission is
already in the car.   If I didn't have the transmission, and I needed
some gearing to get my motor into a fixed ratio with the wheels...
that would add more money to buy a gearbox, and more time to figure
out how to securely mount it in the car.

3)  I can say that with my own car... I pretty much leave my EV in 3rd
gear nearly all the time.  Sometimes I use 2nd when I want to impress
people with a burnout or accelerate fast uphill, and I use Reverse to
get out of my driveway.  However since I'm shifting maybe once or
twice for each road trip... I'm using my transmission a whole lot less
than a regular manual transmission would be used.  That helps with
maintenence, but if I didn't have the transmission... I'd need to
spend more $$$ on some sort of fixed ratio gearbox to emulate 3rd gear
all of the time.   (My ADC 9" motor is not strong enough to run 1:1
with the wheels all the way up to 80mph.  DC motors lose torque at the
high end of the RPM curve.)

4)  You should rummage through the AustinEV archives too... here's a
thread on whether to leave or pull the clutch from the transmission.
Obviously without a transmission, you would not have a clutch as a
safety device:
http://www.austinev.org/pipermail/ausev/2008-December/002922.html



-- 
TTFN,
Brian "Lasso" Lasseter

"No Sane man will dance."   -Cicero (106-43 B.C.)