[brian_]

Are there CVTs that support high torque applications, such as 3,000 to 5,000 ft lbs of torque?

That's a lot of torque, assuming that's the input. At that level, a continuously variable transmission is likely - as in a locomotive - an electric drive of generator and motor, rather than a mechanical transmission. Or it could be hydrostatic. The automotive CVTs which are available handle about one-tenth of that input torque.

With more robust components, would a go kart style CVT be feasible with the high torque application? One challenge is the chain or belt being strong enough, as well as having enough grip with the pulleys that there is limited slip.

In belt CVTs, rubber belts are for power toys (snowmobiles, ATVs...) and steel "belts" are used in automotive applications. It isn't just strength - a rubber-belt CVT for high torque would be very bulky, and the heat generated due to hysteresis and slippage would be a problem.


If you don't mind my asking, why do you want a CVT, anyway? Assuming this is for a vehicle converted to electric drive, a fixed ratio is usually enough and a few ratios are plenty... continuously variable is pointless.

 

[Civil]

The CVT seemed to be simper to build than a geared transaxle.
With the 3,000 to 5,000 ft lbs of torque produced, the car has enough torque to drive without gears. One challenge for a vehicle that is meant for street and track is that without gears, the motor rpm must be low at city driving, or else the tires would spin and lose traction.

There are hydraulic torque converters with lockup that support the high torque. The challenge is how to engage lockup and oil circulation with the torque converter without a transmission and transmission pump.

Thus, a torque converter might fit. As the CVT is similar to a torque converter and did not have the lockup oil circulation challenge, the CVT was considered.

If you know of a way to achieve lockup with a hydraulic torque converter or achieving lockup with a transfer case, without implementing a transmission, please let me know.

 

[brian_]

The CVT seemed to be simper to build than a geared transaxle.

But it's not. A rubber belt CVT using just centrifugal weights might be simpler, but would be inadequate.

With the 3,000 to 5,000 ft lbs of torque produced, the car has enough torque to drive without gears. One challenge for a vehicle that is meant for street and track is that without gears, the motor rpm must be low at city driving, or else the tires would spin and lose traction.

Okay, so you understand that multiple or variable gear (or belt)reduction ratios are used to match the motor to the load, providing more reduction for adequate torque at low road speed, but less reduction to avoid excessive motor speed at high road speed.

Changing the reduction ratio is not required to avoid spinning the tires. Just don't apply more torque (controlled by motor current) than the tires can handle, and the tires don't spin.

I still don't understand how you are getting 3,000 to 5,000 ft-lbs of torque from any reasonable motor. What motor are you planning?

There are hydraulic torque converters with lockup that support the high torque. The challenge is how to engage lockup and oil circulation with the torque converter without a transmission and transmission pump.

The lack of a supply of hydraulic fluid when stopped (because the motor isn't turning) is one reason that when conventional automatic transmissions are converted for use in an EV, the torque converter is usually eliminated. With an engine, the torque converter slips to allow the engine to keep turning at an adequate speed to not stall when the vehicle is stopped or moving very slowly; with an electric motor there's no reason to do this and so the torque converter is a pointless waste of space, weight, and power.

Thus, a torque converter might fit. As the CVT is similar to a torque converter and did not have the lockup oil circulation challenge, the CVT was considered.

Torque converter allows moderate torque multiplication, equivalent to a really inefficient reduction gear, but mostly it allows slip, as I just described. If a CVT is slipping, it is rapidly wearing out, wasting drive power by turning it into heat. High-torque automotive CVT transmissions almost entirely avoid slip, and need a separate clutch or torque converter to keep the engine from stalling. A torque converter and a CVT are very different.

If you know of a way to achieve lockup with a hydraulic torque converter or achieving lockup with a transfer case, without implementing a transmission, please let me know.

I just don't see any point in the torque converter, so locking it up without the rest of the transmission is pointless - just don't use a torque converter. In fact, rather than torque converter without the rest of the transmission, the possibly useful configuration is the rest of the transmission without a torque converter (which is done with Powerglide conversions, and with clutchless manual transmission installations).

 

[Civil]

The motor is combustion, not electric. The question was posed on the forum since there is much CVT experience in the forum.

The motor produces approximately 2,000 ft lbs of torque. The torque converter increases the torque drastically. As there are few transaxles that support 2,000 to 5,000 ft lbs of torque and since the high torque can spin the tires without gears, a torque converter would be feasible.

In terms of the CVT, the simple centrifugal belt style you mentioned could work, if the CVT can be built to support the high torque.

Are you aware of a way to engage the torque converter lockup without a transmission?

 

[brian_]

The motor is combustion, not electric. The question was posed on the forum since there is much CVT experience in the forum.

It would have been very helpful to have said that from the beginning!

As I explained, torque converters are not useful with electric motors, so this really isn't the place to be looking for ideas on this.

The motor produces approximately 2,000 ft lbs of torque. The torque converter increases the torque drastically.

So that's output, not input torque.

As there are few transaxles that support 2,000 to 5,000 ft lbs of torque and since the high torque can spin the tires without gears, a torque converter would be feasible.

Just as with an electric motor, not spinning the tires is simply a matter of not applying excessive power... but with an engine, whatever you use must be able to slip enough to keep the engine from stalling.

In terms of the CVT, the simple centrifugal belt style you mentioned could work, if the CVT can be built to support the high torque.

The power and torque level are probably far too high for any reasonable rubber belt CVT.

Are you aware of a way to engage the torque converter lockup without a transmission?

As for the details of lockup clutch construction and operation... I can't help there.

Decades ago, I considered using just a torque converter for the transmission in a competition car... but it's not a good idea, and is ineffective over a wide speed range. If the overall gearing is suitable for highway or high track speeds, it is not low enough for low speeds. The Koenigsegg Regera is described as having "no transmission" and just a torque converter, but in fact it is a hybrid system.

 

[Civil]

The torque converter works if the stall rpm is low. As you mentioned, to have street and highway performance would be a challenge. If the differentials are geared to highway, the wheels would easily spin when on the street. Thus, the torque converter could be a buffer on the street, so the wheels do not instantly spin and lose traction.