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Re: [EVDL] Basic drivetrain questions, was Re: Looking for a Conversion Kit for a 19

Oooh...I never thought of that! A contactor controller might actually
work well with a belt drive CVT. I would think that the CVT would slip
a little between shifts of the contactors smoothing out the jerks.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Jack Murray
Sent: Thursday, August 09, 2007 12:34
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Basic drivetrain questions, was Re: Looking for a
Conversion Kit for a 1929 Ford.


Greg, thanks for pointing out my efforts.
The Comet CVT does change the gearing as the RPM changes, it seems to me
this does just what you want, although this is just unmeasured
observation, the motor tends to stay at about the same RPM and the
gearing changes as the torque and vehicle speed changes.
The "soft start" of the belt drive is useful, and in fact, I've been
thinking this may make a contactor controller work very well in
conjunction with this CVT. This would allow building a very inexpensive
lightweight EV.
Jack

>> 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.




Greg Owen wrote:
> 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:
>
> http://www.mail-archive.com/[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 considerations?
>
> 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.
>
> Thanks!
> Greg
>
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