Why CVT's are awesome

[Renze]

I found this explanation pretty confusing, but what jumped out at me is that Fendt is using a hydraulic motor(s) to actually power their tractor, not a chain or anything like other cvt's apparently.

Belts or padded chains can only transmit a limited amount of torque. Not suitable for heavy duty.

 

[daugen]

Belts or padded chains can only transmit a limited amount of torque. Not suitable for heavy duty.

that makes sense. I wonder where the horsepower/torque tipping point is, where the chains can no longer grip without damage, or the belts start to smoke...
Am curious what makes the Agco/Case/ IVT work. Sounds like it is going to have a hydraulic pump also because they are large engine tractors. John Deere also.

When I push the cruise control lever ahead on my Kubota in medium hydrostatic gear, I have "infinite" number of forward speed settings within the limits of that range.
Low range is for FEL work and High range for on the road, which I rarely use. But always a non detented variable speed selection.
Interesting how current hydrostatics seem to go up to about 70 horsepower, then there probably is a bit of gap and then the "heavy duty" hydraulic CVT's come in.

More gears has always been an option on geared tractors; do you want 12, 24 or 36, whatever. Though I chuckle when I think of all the years I spent driving a two or three speed car and a three speed floor shift
on an old Cub Cadet on the farm. Cars and trucks have now gone to ten speeds, so CVT/IVT
has that beat since technically one could say you have a thousand gears...or none.

 

[daugen]

How A CVT Works by TEAM Industries.mov - YouTube
a much better explanation regarding cvt operation
Glad to see so many US made products
Also seems like an awful lot of friction would be on the side of the belt,
not the flat part.

Makes me wonder if Kubota designed my rubber belt equipped CVT inhouse or
farmed it out. The engine is Subaru, curious who makes the trans.
The linkage and shifting process on the dash is pretty crude, though so far,
durable. I remain a bit baffled as to what is making the loud gear grinding sound when shifts
are rushed; usually due to not waiting for rpm to drop fully. The noise is clearly metallic.
I've never thought of what a metal belt would sound like because I've never had one...unless I do
now and don't realize it.

No wonder the instructions for my UTV include pretty limited towing capacity. As well as only
400 pounds in the bed. With a light load, the belts seem to work pretty well. But I can sure see why one would need the hydrostatic
trans that comes in the 500 and above models if one wanted to really work their UTV. Or a manual trans.

 

[Travelover]

I think the eCVTs (electronic) used in Fords and Toyotas are pretty cool. No belts, chains or pulleys - just constantly engaged gears and two electric motors. It seems like this design could be scaled up for much higher horsepower.

Here is how it works : http://fordfusionhybridforum.com/topic/6775-what-is-an-ecvt-how-does-it-work-here-is-the-answer/

 

[Fallon]

They make HST dozers in the several hundred HP range, so its not a matter of being able to handle the power. I assume it's mostly a cost vs use case & efficiency debate. I guess the ease of use gets overcome by efficiency in tractors around 50-60hp. Makes some sense as at around that range you shift from utility machines to more specific purpose ag type machines. It sounds like the CVTs might be a bit more expensive than HST, but more efficient than the 15% or HST HP tax.

 

[ruffdog]

They don't make CVT dozers though.

 

[Fallon]

They don't make CVT dozers though.

Ya, another one of those tradeoff things. The HST HP tax issue is offset by the fact it's trivial to set them up spinning one track forward & one track backwards for turning in place. Completely removes the need for clutches & brakes as well.

 

[Renze]

They don't make CVT dozers though.

As said, the power split hydrostatic CVT is an ordinary HST coupled to a planetary gear (aka differential) alongside a mechanical power branch with two (Fendt, and MF through Agco) three (new Holland) or four (ZF Steyr) ranges.

Hydrostatic transmissions work great at low speed high pressure. At road speed, they operate with high oil flow which results in high resistance, and low pressure.

The hydrostatic power split CVT works opposite: to lower the output speed, the hydraulic input speed must be increased (imagine your car with only the left wheel touching the ground and the right wheel lifted off the ground, attached to a hydraulic motor: when the car is in gear, the differential Cage would be spinning. With only the right wheel touching the ground, the left wheel would be spinning in thin air at double the differential cage speed. Now if we could slowly reduce the speed of this left wheel, the car would slowly drive away, faster if the hydrostat powering the left wheel was slowed. When the hydrostatic motor is powering the left wheel in reverse, it would speed the car even faster than the mechanical input (differential Cage speed)

Anyways, the functioning of the power split hydrostatic CVT, and the peak efficiency of HST explained, you can understand that the CVT isnt effici?t at low drive speeds because a high hydrostatic speed is required to transform a moderate mechanical input speed to a low output speed.

So, the HST is effici?t at low speeds and big torque, which makes it great for dozers. It is ineffici?t for high speeds which makes it ineffective for semi-transport vehicles and useless for on-road tractors.

The CVT however, works opposite so it has a high hydraulic loss at low speeds. It therefor is a bad choice for dozers.

For loaders that both need high torque to penetrate the pile, and effici?t at higher speeds at load and carry applications, a German independent manufacturer has made a transmission that drives purely hydrostatic at low speeds pushing into the pile, speeds up the hydrostat and at a given speed, it engages the mechanical branch with a clutch, after which point the hydrostatic part is slowed down again to increase the transmissions output speed.

 

[Renze]

Hytrac GmbH - Power split CVT gear

 

[sikmusicfreak8]

I do like the CVTs in the new side by sides. Seems to be the quickest way to put power to the ground, off the line they are unbeatable. I have a Maverick Turbo, and as long as you keep the belt cool, they seem to be pretty reliable for what they do. As far as in automotive applications, I have only heard of the Subaru's but don't know anybody who has driven one. Be interesting to see how the technology evolves.

 

[Diamondpilot]

We just bought a 2016 Honda Civic 1.5 Turbo EX-L with a CVT. I really like everything about this car.

I am a Ford guy but in this class Honda rules hands down. I looked at Ford, Subaru, Kia, Chrysler, Toyota, Hyundai, GM, and probably a few others. To even come close to the Civic you had to spend 10K more and still give up something plus it was built just 25 miles from my house!

Chris

 

[My Hoe]

The CVT in our Toyota Highlander Hybrid works seamlessly.

 

[Travelover]

The CVT in our Toyota Highlander Hybrid works seamlessly.

I think the Highlander uses a an eCVT like I linked above - no belts or pulleys, just gears and two electric motor generators..

 

[ultrarunner]

In the early 90's my boss bought a brand new Subaru Justy 4wd for his daughter in Montana... they had no end of CVT troubles and it was attributed to snow driving... they had to go a distance to get to a plowed road and why 4wd.

Since then I have avoided anything with a CVT... even bought an older Corolla just to avoid it.

 

[joefromga]

Do you base all your purchases on 80s technology?

 

[ProjectKing]

I think the Highlander uses a an eCVT like I linked above - no belts or pulleys, just gears and two electric motor generators..

That is correct. It's actually planetary gear train. Motors rotate it at different rates creating variable gear ratios. Really slick design.

 

[ultrarunner]

Do you base all your purchases on 80s technology?

Pretty much older for the most part... been there done that when it comes to being an early adopter.

1930 Model A Ford is the first car I owned and bought it at age 12 and paid for it in full with money I had earned... still have it.... many more A's and T's...

For 20+ years my daily driver and college and career is the 1972 Plymouth Valiant I bought for $800... towed 1 yard concrete gondola's with it... too many to count.

My "New" car and only new car I ever bought is a 2002 BMW 325iT that I was able to get a special deal when I was working in Europe at the time... brought it home as a souvenir.

Currently my collection is about 50 vehicles from 1905 newer.

I grew up around the car business and am happy to leave the latest and greatest bells and whistles to those with money to burn...

Also am certified as a California Lemon Law Arbitrator and have seen first hand who gets stuck when technology doesn't live up to the promise.

Anyone remember the GM 8-6-4 cylinder engines or the Diesel Oldsmobile?

The there are the supercharged cars or the Ford Fiesta debacle with the dual cone automatic... can't give those cars away...

http://wheels.blogs.nytimes.com/201...-ford-but-too-late-for-consumer-reports/?_r=0

 

[Diamondpilot]

In the early 80's my boss bought a brand new Subaru Justy 4wd for his daughter in Montana... they had no end of CVT troubles and it was attributed to snow driving... they had to go a distance to get to a plowed road and why 4wd.

Since then I have avoided anything with a CVT... even bought an older Corolla just to avoid it.

That was 35 years ago!

Chris

 

[ultrarunner]

It was a 93 Justy... my bad.

Failed twice before it hit 10k miles and he donated the car...

The reason he bought it was because it was 4wd and Subaru said the reason the transmission went out is because of driving through the fresh snow/snow drifts.

Subaru Justy - Wikipedia, the free encyclopedia

"Because of the long distances, the CVT was considered unreliable, but this has not been the case in other countries"

I'm open to data to support real world experience and Corolla has now had a CVT several years and I would like to see if these CVT Corollas are just as reliable is the non CVT

CVT isn't new technology...

 

[Travelover]

That is correct. It's actually planetary gear train. Motors rotate it at different rates creating variable gear ratios. Really slick design.

I know, I posted the video above on how they work.