CVT Belt Data

[driegels]

Hello all. I am researching a CVT gerbox to be custom built for sports racers. I would like the box to be capable of taking 100 ft-lbs up to 12000 rpm. Trouble is, I am having a terrible time getting any tension/speed ratings for any CVT belts (rubber-kevlar type, not a push belt). I have contacted Gates without any luck, so I am wondering if anyone here has any experience in this area. I am aware of the potential effeciency drop of a CVT system, as well as the high maitainence required, but I am interested if the power delivery outweighs its drawbacks. Thank you.
-Dan R.

 

[aabreu]

If your looking for a CVT to take high torque... look elsewhere.
The pressure required to hold the belt in the pully without slipping is very high.
Ford put allot of money in the CFT 30 and 23 trans.
A piston pump was needed to create the necessary pressures.
Ford is abandoning it and are closing that plant in Batavia Ohio soon. Many of overpaid UAW workers will be out looking for jobs.
The cost was terribly high.

The Japanese havn't abandoned it yet. Nissan Marano has it.
Japanese don't abandon things so quickly. Look at Mazda and the 13B engine.. rotary engine. Gotta give them something for not giving up.

Later
Andre

 

[driegels]

I have noticed that they are using push-belts (for longevity reasons?) which actively force themselves out of the pulleys, thus reducing their torque carrying capacity and/or requiring huge clamping pressures. But, where one can afford to wear out a belt, as in a limited use race car, I believe an exposed rubber/kevlar belt would be satisfactory. Currently, based on some rather large assumptions that the CVT belts from Gates perform equivalently their single moulded v-belts, one should be able to make the system work using a single belt up to 50ft-lbs input. Seeing how this is near what many sport bikes engines put out, it many be doable, but again, just brainstorming.
-Dan R.

 

[MikeHalloran]

What do they use in racing snowmobiles?



Mike Halloran
Pembroke Pines, FL, USA

 

[Fabrico]

"CVT" is a term used almost entirely for small to mid-sized late model production automobile transmissions that use a very special metal belt arrangement.

It sounds like you need to be looking into "variable speed belt drive". You should find plenty with that.

 

[tbuelna]

driegels,

100 ft-lbs @12K rpm is 228hp. That's a pretty tall order for a belt CVT variator. A rubber v-belt CVT variator (let alone a metal push belt variator) will likely not function well at 12k rpm. The belt relies on friction between it and the conical pulleys to transmit torque. The friction the belt experiences (and thus it's torque transmitting capability) is a function of the conical pulley's (or sheaves) axial clamping and the fiction coefficient (mu) between the metal pulley and rubber belt.

The torque capacity can also be increased by maximising the pitch radius that the belt travels around the pulley. But the inertia of the belt carcass tends to unload the belt/pulley interface at higher speeds and/or pitch diameters.

Belt CVT's must also be designed with very generous torque margins for safety, because once they begin to slip they will rapidly overheat and fail.

As for efficiency, you should expect that power losses through a CVT transmission will be about 3 times what a good manual transmission will experience. That's about an additional 10hp on your theoretical 228hp racer. It will also be heavier and have less favorable MOI characteristics, which will hurt your chassis performance.