How do they work? My lawn tractor uses a system of variable pulleys and belts. I doubt we'd want to tow our trailers with something like that. Please enlighten me. Thanks
RRUGG
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There are using C.V.T. transmissions in the agricultural industy and have been for many years. I dont know if the auto industry has a heavy enough unit at the moment as the only ones I have heard of are in small cars.
I manage 23 dealership service departments and I can tell you I would not tow with a cvt transmission.
They have enough issues with heat breaking down the fluid and failing without towing. If you want sticker shock ask the service department how much to replace the fluid in one. You need a note from your banker saying it is ok to ask how much!
As one example and there are a few other way CVT are designed but all are very limited in using for high torque transfer. They can be systems in dry conditions or enclosed in fluids but heat and wear are the enemy.
Most CVT's like you are referring to use weights that fly open with centrifigual force in accordance to the rpm they are subjected to which determines where the drive belt will be positioned on the two tapered sides variable opening pulleys. The drive belt connects the engine rotation to the driveline thru the belt's width (sides) friction position in two pulleys with equal pressure always on the belt's sides. This force overcomes the spring loading that causes the pulleys to come together when not turning. The higher the rpm's, the more outward force the weights will have due to the centrifugal force which inturn normally opens or closes one side (the sliding on the shaft) of the tapered opening between the pulley side members. This causes the drive belt to be forced to the larger diameter area of the tapered pulley sides which in turn forces the belt to force the driveline pulley to open until the belt side pressures are equal. Think of it as similar to when a small dia gear on an engine shaft drives a large dia gear on the drive output shaft. Final rpm output will be much lower then the engine's rpm. Now think about a large dia engine output gear turning at the same rpm's as the previous example and it spins the output shaft small dia gear much higher rpms. The opening and closing of the two pulleys movces the drive belt closer to or farther from the shafts to pulleys are mounted on as the engine rpms control the weight's centrifigual force. Continously variable with changing rpms.
As said, I sure wouldn't try to use the CVT system with the present technology to do heavy work/pulling as the heat and wear would cause the belt to get very hot and will usually melt the rubber etc compound and render it useless very quickly.
Hope I haven't confused you.
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CREATO wrote: There are using C.V.T. transmissions in the agricultural industy and have been for many years. I dont know if the auto industry has a heavy enough unit at the moment as the only ones I have heard of are in small cars.
I'm suspecting that the 'CVT' used in agricultural stuff is actually a hydraulic transmission, with a continuously variable-displacement pump feeding hydraulic wheel motors. At least this was pretty much state of the art thru the 90's. Very good for transmitting lots of torque, but heavy and fuel hogs.
AFAIK, true CVT's are pretty limited in the amount of torque they can transmit in a package small enough to be practical in a car or pickup.
Jim, "His mind isn't so much twisted as badly sprained."
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CREATO wrote: There are using C.V.T. transmissions in the agricultural industy and have been for many years. I dont know if the auto industry has a heavy enough unit at the moment as the only ones I have heard of are in small cars.
I'm suspecting that the 'CVT' used in agricultural stuff is actually a hydraulic transmission, with a continuously variable-displacement pump feeding hydraulic wheel motors. At least this was pretty much state of the art thru the 90's. Very good for transmitting lots of torque, but heavy and fuel hogs.
AFAIK, true CVT's are pretty limited in the amount of torque they can transmit in a package small enough to be practical in a car or pickup.
Jim, "His mind isn't so much twisted as badly spr. ained."
I agree. Even more riding mowers are hydrostatic driven today.
Nissan leads the car industry in CVT (continuously variable transmission) trannys, Subaru, Audi ...and they seem to be doing alright. Not really new technology as it's been around since 1886 used in industry for lathes and drills. And came to be used in cars in Europe in the 1050's, and here in the States in the 1990's.
Now days, the CVT's are useful in that they only contain a total of 4 parts to make it work. And are so efficient that they generally increase fuel mileage by 10%.
A lot of folks complain about the "feel" of a CVT, and even tho regular automatics have been perfected to the point that you barely feel or hear them shift...a CVT will sometmes feel and sound strange to a new owner or someone test driving one for the first time.
Drivers feel no gear changes, but can hear a relatively constant engine note that may not seem in sync with actual acceleration. Sometimes people complain that the engine "drones".
If they were capable of towing, durable AND saving fuel..they would be standard on over the road trucks. But they aren't. Yet.
Instead, some car manufacturers now have 6, 8 and even 10 speed automatics for better mileage. Chryslers Ram 6 speed auto for example. ZF has some 9 speed automatics already in BMW, Audi, Bentley, and Rolls-Royce and also some Chryslers. Chrysler will build the transmissions in Kokomo, thanks to an $843 million plant investment and licensing from ZF. The German drivetrain maker said the nine-speed would raise gas mileage by 16% versus a current six-speed, which could mean three to four miles per gallon.
Actual results will depend on many factors, including how well the gearing is matched to the engine, the controller’s programming, and axle ratios.
My posts shouldn't be taken for factual data. They are purely fictional, for entertainment purposes and should not be constituted as actually related to scientific, technical, engineering, legal, spiritual or practical advice. Amen.
RRUGG wrote: How do they work? My lawn tractor uses a system of variable pulleys and belts. I doubt we'd want to tow our trailers with something like that. Please enlighten me. Thanks
You are right, a lawn tractor would not be good to tow our trailers.
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