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#Post#: 11761--------------------------------------------------
Torque convertors and RPM
By: Ade Colmar Date: October 24, 2024, 5:24 am
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Since joining the forum a few weeks ago I have been madly
researching all the ins and outs of cyclekart building. I’ve
been enjoying the research hugely and a big thank you to
everyone who posts and helps spread the word and the knowledge.
I’m beginning to believe (fear) that the area with the greatest
technical mysteries is the torque converter (and its interaction
with the engine) and I’m looking for more insights on this. My
understanding at present is that the driver (engine) pulley
sheaves respond purely to RPM, whereas the driven pulley sheaves
respond only to the rear axle torque resistance (load). As the
Vee formed by the sheaves is acute, then the clamping forces on
the drive pulley are quite significant, so extremes of clamping
forces are to be avoided to prevent unnecessary power losses (as
much as 15-20%).
This brings me to my question: High RPM and high axle load give
the greatest clamping forces, therefore the greatest losses.
Therefore, is what you really want from the engine high torque
at moderate RPM? This avoids the engine pulley being maxxed out
on diameter (high rpm) and still allowing some interaction
between the driver and driven pulleys. This is a little at odds
with governor removal on engines. I understand that 3600rpm is
unnecessarily low, but would resetting the limit on a suitably
tuned engine to around 4500rpm not be more effective? Setting
the max RPM at around 4,500 may loose say 1BHP, but is that
minimal additional horsepower actually useable, or is it just
lost in belt friction?
Ade
#Post#: 11763--------------------------------------------------
Re: Torque convertors and RPM
By: guest408 Date: October 24, 2024, 12:46 pm
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[quote author=Ade Colmar link=topic=1561.msg11761#msg11761
date=1729765495]
Setting the max RPM at around 4,500 may loose say 1BHP, but is
that minimal additional horsepower actually useable, or is it
just lost in belt friction?
Ade
[/quote]
Or is driver weight more important?
#Post#: 12088--------------------------------------------------
Re: Torque convertors and RPM
By: jim Date: December 10, 2024, 1:01 am
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This type of CVT is now available and doesn't wear out belts or
lose as much power through friction.
#Post#: 12089--------------------------------------------------
Re: Torque convertors and RPM
By: Jimr1999 Date: December 10, 2024, 1:57 am
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Read an article on what I think was that one a few days back
Jim. Writer said it was in late prototype stage pre-production
and was quite a noisy beast, even after reading it I still had
little clue how the inner workings make it infinitely variable.
Liking it though, doubt I will be able to afford one for the CK
until the Chinese get a hold of the design and improve it ;D
JimR
If I find the article I will post a link
Not quite the article I read but a bit more info...
HTML https://newatlas.com/automotive/geared-cvt-ratiozero/
#Post#: 12090--------------------------------------------------
Re: Torque convertors and RPM
By: guest408 Date: December 10, 2024, 2:56 am
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Wasn't about this 'new' type was it?
HTML https://www.youtube.com/watch?v=mWJHI7UHuys&t=1134s
#Post#: 12098--------------------------------------------------
Re: Torque convertors and RPM
By: StefanN Date: December 10, 2024, 5:11 pm
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[quote author=Ade Colmar link=topic=1561.msg11761#msg11761
date=1729765495]
My understanding at present is that the driver (engine) pulley
sheaves respond purely to RPM, whereas the driven pulley sheaves
respond only to the rear axle torque resistance (load). As the
Vee formed by the sheaves is acute, then the clamping forces on
the drive pulley are quite significant, so extremes of clamping
forces are to be avoided to prevent unnecessary power losses (as
much as 15-20%).
[/quote]
I believe it’s a balance between the forces. The drive end
weights are trying to close the sheaves and push the belt out
and hence away from the driven end of the TAV. The driven end
sheaves are being pushed together by the torque reaction from
the chain sprocket forcing the ramped buttons to move the
sheaves together (the spring also adds to this). So, each end
is trying to move the sheaves together but is resisted by the
force along the belt from the other end.
#Post#: 12114--------------------------------------------------
Re: Torque convertors and RPM
By: Ade Colmar Date: December 13, 2024, 10:08 am
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I guess what I was trying to understand is whether the torque
convertor can successfully balance the forces (driver sheave rpm
with driven sheave torque reaction) with a typical modified
stage 1 engine. I can see the balance of forces happening with
the governor still on the engine, but not on a modified engine.
The driver sheaves push the belt out to maximum diameter by
around 3,500rpm yet the engine can rev to 6000rpm. The belt is
a finite length, the driver sheaves are 2,500rpm past the max
diameter speed and so are locked out at max diameter. So if you
have a high load (say, trying to go as fast as possible) with
high torque reaction on the driven sheaves, there is no
possibility of the driven sheaves altering the belt running
diameter to balance the torque and change the ratio. The belt
simply gets squeezed harder by the driven sheaves causing more
friction and heat!
#Post#: 12121--------------------------------------------------
Re: Torque convertors and RPM
By: TomFDS Date: December 13, 2024, 1:46 pm
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Anyone tried the wet clutches from karts?
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