Sure. A lot of Cushman three-wheeled vehicles had (have) this. You know the little vehicles that meter-maids and zoo employees drive. They are small, simple and off the shelf. Two variable pulleys and a belt. Quite a few other manufacturers have this same design, especially golf cart manufacturers.
Oh, you wanted one for a car. That's a little different.......
no this is to use for a weight lifting system, so it can be any CVT... I just found a mini moto CVT which is quite cheap. Not too sure on the ratio between the diameter of the two pulleys though (what the max/min diameter of each pulley is).
Also, what mechanism controls the distance between the two plates to vary the diameter of the pulleys? And how is this mechanism controlled?
Snowmobiles have CVT.
Now that you mention it, several years ago I bought my son a Dingo (something like a go-kart) which had a variable belt type transmission.
It was a bit problematic, but then when you give a young boy a hard use toy, you expect some problems.
controlled?
Engine RPM controls it. There is a cam system on the driven pulley that tries to hold the sheave together. The drive pulley is controlled by various methods, most use weights, either flyweights or roller weights, as the engine RPM rises these weights move the sheaves on the drive pulley tighter while springs try to keep them apart. By adjusting the weights, ramps and springs you can fine tune the clutch unit to whatever characteristics you need.
"John S." wrote
Correct. To avoid slipping, the belt or chain must be firmly pressed on/between the pulleys. Imagine a bicycle chain pressed onto the toothed wheels (although in this case unneccessary). That must produce a noticeable amount of friction.
In small motorcycles strong springs enforce a constant pressure, designed for maximum torque -> constantly maximum friction.
In modern cars the electronic monitors torque and power needed, electric/hydraulic actuators apply the variable pressure.
Cheers
Thomas
But is a planetary transmission continuously variable? I thought it was a two speed (for each planetary gear set).
Almost every major manufactur sells or has sold a vehicle with a CVT Here are some examples - Ford - 500/Freestyle, GM - Saturn Vue (and Ion?), Nissan - Murano, Honda - Civic Hybrid, Volvo (old DAF designs).
Ed
I know but I need a much smaller CVT than a car CVT.
"Don Stauffer" wrote
In the special configuration of the Prius it is a true CVT.
wrote
Look at small motorcycles! Those CVTs are also sold seperately or in parts (tuning, ...).
Thomas
This is the gokart type drive, called a torque convertor.
what is going on in that animation?!
wrote
- Select English/US (or the simulation will try to show japanese signs)
- Check the Driving mode-Checkbox on the right
- Select D-Range (like standard automatic) in the right Combobox (B[rake]-Range is special for Prius with more recuperation downhill)
- Use the Accel and/or Brake-throttle with your mouse
Thomas
A chain that is so tight that it exerts pressure on the sprocket wheels could cause considerable friction --- in the hubs of those sprocket wheels. But also, because of the way the chain engages with the teeth, excessive tension could cause some friction at the points of engagement and disengagement where the chain is tangential to the sprocket. And of course, the bicycle chain is composed of links which bend and straighten and are lubricated. More chain tension means more friction in these links.
A belt, such as a rubber fan belt, generates heat from being deformed as it bends around the pulleys and straightens. A CV transmission's V-belt minimizes the friction deformation of the belt by its composition of many thin steel bands that hold together trapezoidal pieces with enough gaps between them to allow for bending without compressing any material.
You'd think that if the V-belt does not slip with respect to the pulleys, there wouldn't be frictional losses. But the details of the reality are different. :)
Check out the Ph. D. paper of one Sam Akehurst, from the University of Bath:
On simpler machines like scooters it is a mechanical control. Below is an interesting and detailed discussion of how one works and how it may be modified.
do you think it would be possible to modify this mechanical control so that someone could vary the diameter of the pulley by hand (as I'm thinking of using one on a weight lifting system).
Could I literally buy something like this and set it up easily;
"John S." wrote
The scooter vario itself has a ratio of about 0.75 to 2.4. A second fixed gear (near rear wheel) reduces the rpm by another ca. 1:10.
Thomas
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