CVT trans
Junior User
Joined: Apr 2003
Posts: 55
Likes: 0
Some students invented a pretty cool CVT tranny that doesn use a belt. It was for one of the SAE contests. It uses a cone on a slide. It's hard to describe, but I bet it will be the next round of CVT since it will be lowe cost.
This is not anything like a CVT on a 4 wheeler or snowmobile. This is completely electronically controlled and until lately embedded systems didn't have the power for the price to make these things work. There is a hydraulic actuator on both variable width belt pulleys, and the tension on the belt and the gear ratio at any instance in time is determined by a number of factors, then a close loop position control is used on each and communication between the two is vital to maintaining the right hydraulic pressures, and respectively, belt tension.
There are other advantages to the CVT other than fuel economy and emissions. In theory, when you floor the car, the engine to quickly rev up to it's max HP RPM and stay there, while the CVT runs through the infinate resolution of gearing possiblem thereby accellerating the the car. You ussually also get a lower low gearing and a higher high gearing as a result.
This is not anything like a CVT on a 4 wheeler or snowmobile. This is completely electronically controlled and until lately embedded systems didn't have the power for the price to make these things work. There is a hydraulic actuator on both variable width belt pulleys, and the tension on the belt and the gear ratio at any instance in time is determined by a number of factors, then a close loop position control is used on each and communication between the two is vital to maintaining the right hydraulic pressures, and respectively, belt tension.
There are other advantages to the CVT other than fuel economy and emissions. In theory, when you floor the car, the engine to quickly rev up to it's max HP RPM and stay there, while the CVT runs through the infinate resolution of gearing possiblem thereby accellerating the the car. You ussually also get a lower low gearing and a higher high gearing as a result.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,730
Likes: 2,658
From: SE Florida
There were a few issues at launch, but they were quickly fixed and there were really no other issues with the trans, except it was expensive to produce.
I had one in a 2005 Five Hundred. It worked great until the car ended up wrapped around a tree.
Post Fiend
Joined: Feb 2002
Posts: 10,600
Likes: 3
From: Carhenge
We have the CVT in the wife's 2007 500, at 16,000 the transmission has been flawless, Once I got used to the "rubber band" feel of it I really have liked it. The Haldex coupler for the AWD was replaced at about 7000 miles, apparently wasn't properly filled with oil at the factory.
Elder User
Joined: Apr 2008
Posts: 727
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From: north shore, minnesota
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New User
Joined: Dec 2008
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I change the belt on snowmobiles at work at least once a year. Thats not to hard. Changing a steel belt, enclosed in oil bath must be alot harder. But maybe not worse then rebuilding a traditional transmission..
Do anyon know if the procedure is the same on a car CVT as on a sled?
Do anyon know if the procedure is the same on a car CVT as on a sled?
Super Moderator
Joined: Apr 2004
Posts: 34,503
Likes: 2,820
Dry rubber belt vs. wet enclosed metal? Apples and oranges.
One opinion I read is that CVTs lost favor due to the failure to deliver higher mpgs. Seems it takes power via pump that runs all the time to hold that belt where it belongs. Thus, the savings from the proper ratios are eaten by the pump.
Bring on a conventional 6 gear with electronic control, (or 8 speed if you want to be silly about it) and you get the right ratio w/o the pump.
So they said...
My '04 Audi A4 has one, ok so far at 45000 miles or so. The Audi guys say to drive it easy.... $4500 to buy a new one.
One opinion I read is that CVTs lost favor due to the failure to deliver higher mpgs. Seems it takes power via pump that runs all the time to hold that belt where it belongs. Thus, the savings from the proper ratios are eaten by the pump.
Bring on a conventional 6 gear with electronic control, (or 8 speed if you want to be silly about it) and you get the right ratio w/o the pump.
So they said...
My '04 Audi A4 has one, ok so far at 45000 miles or so. The Audi guys say to drive it easy.... $4500 to buy a new one.
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
Having a Honda Civic GX with a CVT in the family, im not convinced. It failed four times in the first 60,000 miles. The belt is not the failure point, its the automatic wet clutch that keeps the engine from stalling at a stop, as there is no clutch pedal and no torque converter or fluid coupling.
There is no pump that runs all the time like in a conventional automatic. That is why a CVT is used in hybrids that can move the car with the engine shut off. The GX used the same transmission as the hybrid more as an "experiment" as Honda went back to a conventional automatic on the CNG GX model.
Jim
There is no pump that runs all the time like in a conventional automatic. That is why a CVT is used in hybrids that can move the car with the engine shut off. The GX used the same transmission as the hybrid more as an "experiment" as Honda went back to a conventional automatic on the CNG GX model.
Jim
Postmaster
Joined: Aug 2004
Posts: 4,004
Likes: 1
From: North of Boston MA
I have two of the Escape hybrids with the eCVT and absolutely love the way they perform. I know it is a different animal from the CVT used in the other vehicles but as far as the performance of it, I'd rather have a cvt now than a regular automatic transmission. The difference between the feel of a CVT versus a normal automatic is like the difference between an automatic and a standard. Smooth, seamless acceleration is nice.
Four years of owning the hybrids and no problems at all.
And to compare them to the cvt in a toy is absolutely ridiculous. There is no comparison. There is a lot more to them than a belt. Once upon a time I heard there were people who wouldn't accept automatics.....
Four years of owning the hybrids and no problems at all.
And to compare them to the cvt in a toy is absolutely ridiculous. There is no comparison. There is a lot more to them than a belt. Once upon a time I heard there were people who wouldn't accept automatics.....
Post Fiend
Joined: Feb 2002
Posts: 10,600
Likes: 3
From: Carhenge
Having a Honda Civic GX with a CVT in the family, im not convinced. It failed four times in the first 60,000 miles. The belt is not the failure point, its the automatic wet clutch that keeps the engine from stalling at a stop, as there is no clutch pedal and no torque converter or fluid coupling.
There is no pump that runs all the time like in a conventional automatic. That is why a CVT is used in hybrids that can move the car with the engine shut off. The GX used the same transmission as the hybrid more as an "experiment" as Honda went back to a conventional automatic on the CNG GX model.
Jim
There is no pump that runs all the time like in a conventional automatic. That is why a CVT is used in hybrids that can move the car with the engine shut off. The GX used the same transmission as the hybrid more as an "experiment" as Honda went back to a conventional automatic on the CNG GX model.
Jim
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
When the chain goes bad in the Ford cvt - IT by itself is close to a grand for the part by itself. The build/rebuild requires specialised training and a kit from Ford made up mainly of specialised jigs.
It's an expensive little beasty, for all that it's smooth in operation. I saw a teardown on one at Certified Transmissions about a year ago (The dealership nearby had no one who could deal with it).
Personally, in terms of upkeep and dependability I prefer the plain old stubborn reliability of a classic "SQUISH - CLUNK - SQUEAL" manual gearbox and clutch...
It's an expensive little beasty, for all that it's smooth in operation. I saw a teardown on one at Certified Transmissions about a year ago (The dealership nearby had no one who could deal with it).
Personally, in terms of upkeep and dependability I prefer the plain old stubborn reliability of a classic "SQUISH - CLUNK - SQUEAL" manual gearbox and clutch...
