Why CVT's are awesome

[daugen]

Why CVTs Are Awesome Transmissions

this is an educational video explaining the math and physics behind CVT transmissions and why/how they keep
the engine in the power band so effectively. if you like equations, you will like this, but interesting comments on hp and torque.

The funny thing is trans makers often have to build in phony shift points for many models because the public complained of the weird sensations and sounds, probably like listening to a city bus take off.

Hard to explain cvt when folks tend to think it's a giant centrifugal gocart clutch.
I have one on my Kubota UTV with a high and low speed position.
Many smaller foreign cars now have them, great for mpg apparently.

I believe in tractors they are called either CVT or IVT depending upon brands. But with infinite number of speeds, like pushing the cruise control lever ahead in my Kubota, no detents, and the potential for more economical operation, CVT may be a growing trend.
My understanding is that CVT has less parasitic loss than hydrostatic so efficiency is improved.

 

[ArlyA]

Thanks for posting this. Hydrostatic power loss is pretty high and not getting into exact applications, its around 20%. Of course some transmissions are better or worst. Engineering Essentials: Hydrostatic Transmissions | Hydraulics content from Hydraulics & Pneumatics
Where as CVT's loss is in the 2-5% area. Pretty darn good

This is why Hydrostatic transmissions have not been successful is some applications. We won't consider one in a UTV.

 

[LD1]

Bought a nissan with a CVT in 08. I am actually disappointed in how slowly the tech is coming around. CVT's IMO are the best there is. Provided they are designed and programmed correctly. You are ALWAYS in the optimal gear selection for whatever you want to do. Max power. best economy, etc.

Funny how people hate step-pulley mills and drill presses, and prefer variable speeds, but not the same way when it comes to autos. Variable speed (variable pulleys and belts) has been around for decades and decades. In hindsight its hard to believe it has taken this long to adapt into other things, and that the planetary gear automatic transmissions have been so prevalent.

 

[WilliamBos]

Your Kubota UTV uses a hydrostatic transmission, it's NOT a CVT.

The Fendt Vario is the Pioneer example of a CVT, and it's the only clutch less version. All others like JD & CNH use clutch packs.

 

[daugen]

Your Kubota UTV uses a hydrostatic transmission, it's NOT a CVT.

sorry friend, I own the 400 model with the single cylinder Subaru gas engine and a CVT.
The 500 and above models all have hydrostatic.
This thing will grind gears with the best of them if you hurry the shift.

 

[Garandman]

The first car with CVT in the US was the unlamented Subaru Justy. Since then, almost every manufacturer has had a class action lawsuit against them over their initial implementation of CVT.

A local guy just had his 2013 Outback CVT fail (Subaru is one of the few that doesn't have a class action lawsuit - yet, at least). He was quoted $7,000 for a replacement.

 

[Midniteoyl]

Bought a nissan with a CVT in 08. I am actually disappointed in how slowly the tech is coming around. CVT's IMO are the best there is. Provided they are designed and programmed correctly. You are ALWAYS in the optimal gear selection for whatever you want to do. Max power. best economy, etc.

Funny how people hate step-pulley mills and drill presses, and prefer variable speeds, but not the same way when it comes to autos. Variable speed (variable pulleys and belts) has been around for decades and decades. In hindsight its hard to believe it has taken this long to adapt into other things, and that the planetary gear automatic transmissions have been so prevalent.

Because up until recently, CVTs broke.. They did not scale up well with increased weight and HP. I feel they are just now becoming reliable enough to start hitting the mainstream.

 

[KYErik]

I have a 09 Nissan Sentra with CVT. It now has 171K miles on it. My wife and I drove out to Yellowstone and the Grand Canyon over the summer and came back through Colorado- it handled the mountains wonderfully.

I did buy and install a supplemental trans cooler just for extra insurance.

 

[WilliamBos]

Your Kubota UTV uses a hydrostatic transmission, it's NOT a CVT.

sorry friend, I own the 400 model with the single cylinder Subaru gas engine and a CVT.
The 500 and above models all have hydrostatic.
This thing will grind gears with the best of them if you hurry the shift.

Thats a belt drive, not in the same league as the Vario CVT. Yours is no different that what you see on snowmobiles And atv's.

 

[ovrszd]

Thats a belt drive, not in the same league as the Vario CVT. Yours is no different that what you see on snowmobiles And atv's.

That was going to be my question?? In this discussion, when referring to a CVT, you are NOT referring to a dry belt system??

Educated me, I know nothing about a "wet" CVT??

 

[Midniteoyl]

That was going to be my question?? In this discussion, when referring to a CVT, you are NOT referring to a dry belt system??

Educated me, I know nothing about a "wet" CVT??

This is the Vario: Fendt Vario Transmission - YouTube

 

[WilliamBos]

I love my Polaris Sportsman belt drive, as simple as can be.

Here's the Fendt CVT explained. You can lower RPM to save fuel but maintain the same groundspeed.

AGCO's Continuously Variable Transmission (CVT) Explained - YouTube

 

[ovrszd]

Good stuff guys. Thanks for the videos and opinions. Sometimes the simplest things are the hardest to understand.

 

[KennyG]

CVTs in lower horsepower applications are pretty well proven. Hybrid cars (Prius, Camry, Escape, Fusion, etc) have always had CVTs and the failure rate is almost zero.

 

[Garandman]

The Subaru CVT has a low ratio of 6:3 to 1 (versus no lower than 4:1 for the manual) minimizing the need for low range. Apparently it was not very effective for engine braking downhill.

In 2014/15 they added "X-Mode" to most models to remedy this. Pretty interesting.

 

[AGRIMAN]

The Fendt Vario is the Pioneer example of a CVT, and it's the only clutch less version. All others like JD & CNH use clutch packs.

CNH has a full CVT in some models of their compact tractors.

 

[daugen]

Thats a belt drive, not in the same league as the Vario CVT. Yours is no different that what you see on snowmobiles And atv's.

Utility Vehicles | RTV4Ci/RTV5 | Kubota Tractor Corporation

So something that says CVT Plus is not a CVT? I understand there is a belt in there, but you are saying the entire drive is by belt?
What grinds?
Is "inertial clutch" a fancy name for centrifugal clutch?
CVT Plus: Continuously Variable Transmission
This RTV has a newly-designed Continuously Variable Transmission with inertial clutch (CVT Plus) for excellent response and reliability, while providing dynamic braking to help maintain control during descents with engine-assisted deceleration. CVT Plus also features a full protection cover to minimize mud or dust intrusion to ensure longer belt life.

 

[KYErik]

The Subaru CVT has a low ratio of 6:3 to 1 (versus no lower than 4:1 for the manual) minimizing the need for low range. Apparently it was not very effective for engine braking downhill.

I'm not sure how the Subaru system works, but my Nissan Sentra CVT did pretty good engine braking in the Rockies on downhill grades up to 2%. The trans also has an "L" mode that was good to about 4% grades (but I couldn't go over 45 mph without over-revving the engine). I still had to tap the brakes occasionally on the 5-6% grades.

 

[daugen]

well, yes, I'd have to say I have a belt drive transmission. Talk about abusing the term CVT when the industry knows it as something
quite different. Now I wonder how long those belts will last...I can't imagine (oh yes I can) what Kubota charges for those trans belts.
Bottom line, it works fine, though if you don't wait 1001 1002 between changing gears, it grinds. Loudly...so some kind of teeth aren't meshing.
Very odd engine and trans combination, you look down at the powertrain and it's hard to figure out what is what. For a number of years I believe this was the only
fuel injected single cylinder engine on the market until Honda just started putting them on a high end GX series single cylinder. So an odd engine hooked up to a hybrid
somewhat odd transmission. Or maybe the Kubota engineers just drank way too much of their own Koolaid in naming this transmission.


"Our CVT transmission is not the same as our competition," he says.(no it sure isn't. Theirs is heavy duty metal and sophisticated, yours is
made of rubber bands) "This is a Kubota designed CVT. We are calling it a CVT+."

All transmissions of this type feature a variable belt and a centrifugal clutch. Allen says that with most CVTs when an operator lets off the accelerator and the transmission is running faster than the engine, the belt "flops." He says on Kubota’s new transmission the belt stays taught all the time which results in a longer lasting belt and also adds dynamic breaking.

 

[daugen]

Hydrostatic is cheap and proven. CVT is likely still more expensive and do all trans shops work on them? I wonder what the failure parts are.
So yes, for a bottom of the line Kubota UTV one should not expect a sophisticated car like trans.
And to cut cost Kubota would not use a trans more expensive than a hydrostatic, so my belt drive makes sense.
But an infinitely variable transmission that keeps the engine in an efficient power band without roaring away like a metro bus
sure seems like an attractive idea.
Regardless of how Kubota's belt drive variable trans works, it is smooth and has no problem with putting the power down. Never had it bog or die on me.
Never had a burning belt or any odor at all, or squeal. Only grinding on shifting and a throttle and brake layout that has cables making some strange bends.
I'd give the trans a B. Not very sophisticated, even less now that I know how it works, but it does work. As i would expect a Kubota to frankly.

A car CVT trans can't be too expensive or they would not have brought it out first on economy cars. I guess they could only handle so much power to begin with.
I think they are now up to the high 200's in max hp to a CVT. Nissan has been using them for a long time and now their Maxima uses one I believe, so that's close to 300hp. The Germans all use dual clutch automatic boxes, most high performance cars do today I think. For faster shifting.
10 speed transmissions now. I wonder why not just go CVT unless they are catering to traditionalists or the CVT's can't handle four to seven hundred horsepower engines now out there.
Interestingly I first drove the $21K full boat a/c cabbed RTV, and thought the hydrostatic trans in it was super jerky and unpleasant to drive. The smaller gas powered model was actually fun to drive and scoots right along. Remarkable what 16hp can do.