How does a CVT engine work in reality? What does it do differently compared to a standard automatic transmission? Is it better? Better mpg?
Check Catmandews's links.most CVTs use some kind of variable-ratio pulleys with belts or chains. But the theory is that instead of being limited to 3, 4, 5 or so set gear ratios, the CVT has a virtually unlimited range of ratios for optimum performance at any speed, under any conditions. BUT - that also means that they continually are changing ratios in conditions such as a very minor incline - where a fixed-ratio transmission (manual or automatic) would not shift. That could account for somewhat lower mileage . and also somewhat more wear than a trans with a torque converter that doesn't shift all the time. We have a Ford Taurus with CVT and AWDwe really, really like it: it is super smooth, silent and always in the correct ratio (example: we have a very steep driveway - in any other vehicle we have to manually downshift to keep the engine from lugging . . . . but the CVT is instantly in the correct ratio). When we bought the car we were told to expect about 2 mpg less than with the conventional automatic and FWD.don't know how much is due to the CVT and how much the AWD which is also always in play. We get 28 mpg on the highway which we consider good-enough for a 4000+ lb car. We're keeping the car longer than usual because the CVT is no longer offerred.when we have to get a new one we'll start with a list of which cars do offer it. (BTW: one reason Ford developed CVT - and the one in ours was designed and built in USA - is that they owned Volvo at the time. Volvo in turn had purchased Dutch automaker DAF years ago - 1960s I think - because of their CVT patents. The DAF system was said to be extremely efficient and reliable - but of course, the DAF was a small, 2000 lb. car. I don't know if Double-Dafamatic Drive is still offered over there.)
Ok I know this very well. First off a normal transmission (automatic) works by taking a couple sets of planetary gear sets made up of 3 planetary members; a sun gear, a planetary carrier and a ring gear. Sets of servos and bands help change gears by holding drums while different members of the planetary gear set are held and driven to get different gears. For example holding the ring gear and driving the sun gear would be first gear. Now in a CVT (constant variable tramnsmission) There is a set of 2 pullys connected by a belt. When you start the car moving the driving pully is small and the rear pully is big. When a small member drives a large member this is called gear reduction meaning the torque coming from the engine is multiplied by this to get less speed but more torque to get the car moving. As the car starts to gain speed less torque is needed so the driving pully gets bigger and the driven pully gets smaller. This happens until the driving pully is at it's largest point and the driven pully is at it's smallest thus producing over drive. This is how it works. Now for getting better gas mileage. They do get better gas mileage as a whole as the transmission weighs less then a standard automatic (in most cars a 4T60E is common). They also have no shift points so they don't really ever stay in gear. Now are they better. Right now they are not and this is why. They are a new technology and there is problems with them at the moment. The number one problem is is that the belt that connects the drive and driven pully breaks around 100,000 miles. The big problem with this is Honda is the main car company using the CVT Transmission and when the belt breaks Honda does not let their techs disassemble the transmission an fix the problem a new transmission must be bought and replaced. So it costs a lot for a CVT transmission so it's usually better to just buy a new car. I hope this helps and I answered all your questions.
While a rather recent development in automobiles, CVTs have existed in agricultural equipment, lawn and garden equipment and recreational vehicles such as atv's and snowmobiles for many years. CVT is an acronym for constant variable transmission. In a standard automatic transmission there are clutch packs that hydraulically or electrically engage or disengage to shift up or down through a finite number of internal gear ratios. Most modern automatics have 4 gear ratios or speeds although some new models may have up to 8 individual ratios that the transmission can shift through. The engine rpms increase as you speed up and then decrease as the transmission shifts up to the next higher gear. In a CVT there are far less actual components and moving parts. In it's simplest form it usually consists of two pulleys with moveable sheaves connected by a V drive belt. The drive pulley is powered by the engine and the sheaves can be actuated mechanically with either a lever or a foot pedal. As the sheaves on the drive pulley move closer together they force the belt to climb outward which changes it's ratio to a higher speed. As this happens the secondary or driven pulley sheaves open up allowing the belt to drop down and turn the shaft it is connected to at a progressively higher speed. In a CVT the engine remains at a more constant rpm range as the clutches change ratios up and down. Because of the variable ratios a smaller engine that consumes less fuel can do the same work as a larger one. In an automotive CVT a metallic chain type belt is usually used and the moveable sheaves are either hydraulically or electronically controlled. It's all fully enclosed and runs in fluid/lubricant.
