DIY Electric Car Forums banner

[EVDL] Basic drivetrain questions, was Re: Looking for a Conversion Kit for a 1929 F

746 Views 0 Replies 1 Participant Last post by  EVDL List
Jeff Shanab wrote:
> Actually if I had the ability to play there is one more idea I would
> like to try.
> Use a locking torque converter. It would start at 3:! or 4:1 then
> transition smoothly up to near 1:1 then you lock it in to 1:1.

Jack Murray is trying it and posted about it a week or so ago:[email protected]/msg08016.html

See #8, "CVT results update"

Please pardon me for a moment as I talk through and ask some basic
questions. I've been trying to absorb a lot of information and want to
check some of my assumptions.

It sounds like some people directly connect their motor output to their
wheel output, in the sense that some number of axles or gears maintain a
X:Y rotation ratio at all motor speeds. This has the advantage of
simplicity, but the disadvantage that the high starting torque of motors
places strain on the components and causes shearing and breakage (as
seen by all the pretty pictures this morning). Another disadvantage is
that the motor cannot operate in its most efficient mode across all speeds.

Jack Murray, at least, has tried a Torque Converter. This seems to
soften the impact of high initial torque on the rest of the connection,
yet allow a locked X:Y rotation ratio once a certain speed is reached.
The advantage is that it takes the stress off the components, the
disadvantage is that the motor is still unable to adjust into the most
efficient mode across all speeds.

Although Jack called it a CVT, I don't think a torque converter is truly
a CVT - it's variable only up until it locks, and the variable stages
essentially trade off efficiency for smoothness.

As I understand it, a real CVT would allow the gear ratio to be adjusted
at any speed to allow the motor to run at its most efficient RPM, and to
lessen the impact load during high-torque starts. Doing this would
require somewhat smart coordination between the motor and the CVT.

So, that's my set of assumptions and beliefs based on what I've been
reading. Are these correct, or am I missing aspects?

My followup questions are essentially these:

1) Is some sort of impact softening mechanism like a torque converter
generally necessary, except in racing vehicles where off-the-line torque
trumps the goal of "not breaking stuff"? Or is this something dependent
on calculations such as motor characteristics, drivetrain design, and
weight of vehicle?

2) Are there other advantages to the Torque Converter I'm missing? Or
is the 1:1 ratio at speed a better end case than I imagine?

3) Does the stress of high torque overcoming inertia impact the motor as
well as the drivetrain?

4) Is anyone running a CVT? What kind? Native or aftermarket? Special

Any insight people can share on these questions is greatly appreciated.
I'm a newbie and a techie so trying to understand all the car details
is both difficult and fun.


For subscription options, see