I am sure this may have come up but in CUTs these CVTs are pretty new and I did get to sample one in a 3045 NH. I have a HST in my Kubota. Overall I like the new NH, not the price, but the tractor. However as I have sat and thought about the CVT I wonder if it really is that much of an advance over a shuttle tranny. That being because you have to shift with your hand from F to R, no clutch but you do have to flip the hand control. I do like the exacting cruise control and I see where spraying more accurately could occur over my manual semi speed control Kubota where I have to estimate my speed. Not such a problem now that I have used it for years but it took a bit of figuring the first times out. I do think like others the new L40 series has a better foot control, but other than that I just see much difference to my L3710. So have any of the rest of you tried the CVT? What are the main advantages and disadvantages you see?
CVT vs HST
- Thread starter ham
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Haven't tried one, but from what is said about them, the advantages/disadvantages are mostly the following:
Advantages:
1. Mechanical efficiency vs. hydro.
2. Precise speed management (however the new Kubota and JD hydros achieve the same result through electronic means)
3. Can be scaled to larger HP requirements
Disadvantages are mostly about cost, complexity and maintainability, which will probably recede over time.
On smaller platforms, such as the CUT's usually discussed here on TBN, the mechanical efficiency thing is a lesser issue, I think. If most of us spent an extra $10 a month on fuel because we have HST's, well that's not going to send us to the poorhouse. And these little tractors tend to have plenty of HP for their size.
But when you get into large scale ag equipment, improving the mechanical efficiency can make a difference of thousands in operational costs.
Advantages:
1. Mechanical efficiency vs. hydro.
2. Precise speed management (however the new Kubota and JD hydros achieve the same result through electronic means)
3. Can be scaled to larger HP requirements
Disadvantages are mostly about cost, complexity and maintainability, which will probably recede over time.
On smaller platforms, such as the CUT's usually discussed here on TBN, the mechanical efficiency thing is a lesser issue, I think. If most of us spent an extra $10 a month on fuel because we have HST's, well that's not going to send us to the poorhouse. And these little tractors tend to have plenty of HP for their size.
But when you get into large scale ag equipment, improving the mechanical efficiency can make a difference of thousands in operational costs.
jenkinsph
Super Star Member
Don't know about Kubota hydros but the Deere ehydro with upgraded cruise allows speed settings in .1 mph increments that are repeatable and are independent of pto and engine speeds.
I agree that for the smaller tractors fuel cost savings would be minimal.
Haven't had a chance to try out a cvt in a tractor, would like to see it though.
I agree that for the smaller tractors fuel cost savings would be minimal.
Haven't had a chance to try out a cvt in a tractor, would like to see it though.
ModMech
Platinum Member
A NH dealer I asked about the CVTs looked and just shook his head....
It's regarded as a gimmick and from what my automotive engineer aquaintenances tell me, it's the same in the automotove world. They take a LOT of HP off the FW (are inefficient) but maybe not as much as an HST. The bogger downside is repair cost.
In *theory* a CVT is the "ideal" transmission because it has lower power losses than a HST yet allows the engine to operate at a constant (peak power or efficiency) speed. In the field, it doesn't work that way because you just cannot get the theoretical efficiency from them so they wind up being only very slightly better than a HST but a much more complex.
It's regarded as a gimmick and from what my automotive engineer aquaintenances tell me, it's the same in the automotove world. They take a LOT of HP off the FW (are inefficient) but maybe not as much as an HST. The bogger downside is repair cost.
In *theory* a CVT is the "ideal" transmission because it has lower power losses than a HST yet allows the engine to operate at a constant (peak power or efficiency) speed. In the field, it doesn't work that way because you just cannot get the theoretical efficiency from them so they wind up being only very slightly better than a HST but a much more complex.
dieselfreak
Silver Member
Fendt (AGCO) Pioneered the CVT, released back in Europe back in 1996. I bet your engineer buddies do not have the stones to tell that to the folks who have 20,000+hours on their Fendts.
Auto engineers are NOT AG Engineers!!
df.
Can you explain how a CVT is inefficient?
IIRC the type of tranny in the little NH's isn't really the same as the tranny in the large Fendts and Deeres.
From what I have read a auto CVT and the CVT Fendt has been using for over a decade are like comparing a diesel electric train to a hybrid car. The CVT in autos is like snowmobile set up. The CVT used in tractors is a blend of hydo and mechanical. Deere and CNH have had CVT/IVT in Europe for many years now, they are just starting to sell them here. One thing about the Fendt, they claim 8000 hours is average life. I know of power shifts with well over 10000 hours that are still going strong. Since these smaller ones are just coming around, only time will tell how well they hold up. As far as compairing CVT vs HST I have no idea what is better. I do know in higher HP HST isn't used, yet the CVT is, I have ideas why, but can't say for sure.
Google Image Result for http://www.vibratesoftware.com/images/Jatco%20CVT2%20Inside%20View%20Small.jpg
Note: In this link the calim is 9000 hours average life.
http://www.farmdepot.biz/CVT-Fact-VS-Myth.pdf
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ModMech
Platinum Member
In *theory* a CVT is the BEST transmission you can have because it is an Continously (infinately) Variable Transmission - meaning that you can operate the engine at it's most efficient speed (in terms of fuel, power or a combination as needs dictate) yet have complete control over ground speed. This allows (in theory) lower fuel use for the same job, CVTs are essentially mechanical HSTs, exactly.
In practice, they need TREMENDOUS amounts of pressure to keep the mechanical elements from slipping and destroying the trans in short order. With pressure like that, the actual transmission efficiency is MUCH lower than theory would suggest and therefore most OEMs have stepped away from CVTs and back towards GSTs with more ratios.
Comparing a 4 or 5 spd GST to a model with HST makes a pretty dramatic arguement for the HST because it is very easy to match the load to the ground speed, unless you get into a stall condition and that's another discussion.
Moving from a 12F/12R to a HST model is, well, pointless. Yes, there are 12 distinct "speeds" with the GST but in practice there is slmost no real difference with that many gears AND you get a greater percentage of FWHP to the PTO and drawbar with GST than HST or CVT.
HSTs and CVTs make a LOT of heat that the tractor needs to get rid of. How? A radiator of some sort and to move enough air over that radiator in all conditions you need a bigger fan than with a GST. Bigger fans take more HP to turn and the HP is a function of engine RPM, double the RPM and it takes 4 times the HP to turn the fan.
Wikipedia.org on CVTs: http://en.wikipedia.org/wiki/Continuously_variable_transmission
In practice, they need TREMENDOUS amounts of pressure to keep the mechanical elements from slipping and destroying the trans in short order. With pressure like that, the actual transmission efficiency is MUCH lower than theory would suggest and therefore most OEMs have stepped away from CVTs and back towards GSTs with more ratios.
Comparing a 4 or 5 spd GST to a model with HST makes a pretty dramatic arguement for the HST because it is very easy to match the load to the ground speed, unless you get into a stall condition and that's another discussion.
Moving from a 12F/12R to a HST model is, well, pointless. Yes, there are 12 distinct "speeds" with the GST but in practice there is slmost no real difference with that many gears AND you get a greater percentage of FWHP to the PTO and drawbar with GST than HST or CVT.
HSTs and CVTs make a LOT of heat that the tractor needs to get rid of. How? A radiator of some sort and to move enough air over that radiator in all conditions you need a bigger fan than with a GST. Bigger fans take more HP to turn and the HP is a function of engine RPM, double the RPM and it takes 4 times the HP to turn the fan.
Wikipedia.org on CVTs: http://en.wikipedia.org/wiki/Continuously_variable_transmission
SPYDERLK
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That makes a lot of sense. HUGE contact pressures to avoid the unavoidable creep of the power transmission elements in CVT.
One point FYI: Doubling fan speed to double flow causes an eightfold increase in power use. Three doublings occur; #] twice as much air is flowing, #] it is flowing twice as fast, #] the fan only has 1/2 the time to act on each unit of air as it crosses. ... So - twice as much going twice as fast and being accelerated to speed twice as quickly.
larry
jagyzf
Gold Member
I think as someone pointed out, you are thinking of car trans, the auto industry is going away from there style. What OEM in AG is moving away from them? Deere, CNH, AGCO are all moving forward with CVT's, and coming out with more machines that use them. From what I have been told a CVT like Deere is using in the larger tractors makes less heat and is more efficent at putting power to the ground than HST. Deere has powershift with 15 speeds, and CNH 18, so if IVT/CVT were not an advantage, why would they be moving towards this? I can't imagine it would be just to offer it because Fendt did, Fendts are expensive and have no dealership support around here.
Here Deere is just adding CVT to the track tractor line. The article is from a few weeks ago.
http://www.fwi.co.uk/Articles/2010/05/05/121096/VIDEO-Tracks-v-tyres-John-Deere-8R-tractors.htm
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ModMech
Platinum Member
The auto industry DID the same thing stating about 10 years ago. Everyone (in the press) was talking it up, sound familiar?
Less than HST but still 3-4 times more than a GST, that adds up to wasted energy that you need to deal with.
You can't get get it in the similar US models, which would indicate competition is the driving factor, not building a more useable or reliable product.
whistlepig
Elite Member
Goodness. I didn't know they made tractors with CVT. I have a Polaris Sportsman with CVT. This works very well on the Polaris. It's a very good ATV transmission. But it is a "mushy feeling" type of drive system. I think about the CVT on the Polaris when driving my HST tractor. I wouldn't trade the hydro for the CVT. The hydro is much more precise and responsive. The CVT seems to sit and stall until the RPM's build. And then it surges forward.
May I ask where you get this figure? I have to wonder if it is a apples to apples comparison.
Can't get what?
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Not the same thing.
jagyzf
Gold Member
As stated, the Auto trans IS NOT THE SAME tran. They are totally different.
Where are you getting information on a powershift/GST vs IVT/CVT?
What trans can't you get in a similar US model? Deere actually has 15 speed, and 18 speed powershift, and up to 24 gear manual shift. These are just a few, all along with the IVT/CVT can be purchased here and overseas.
Here is a story on Valtra, they just came out with a new tractor that can get either powershift or CVT. The CVT came out ahead in testing of when measuring fuel usage for work being done.
VIDEO: Valtra - powershift versus CVT - 17/03/2010 - Farmers Weekly
ModMech
Platinum Member
Typical PUBLISHED efficiency for HSTs range from as little as 40% to as much as 91% (under ideal, steady-state operation).
Normal GSTs operate in the 89% to 94% efficiency range, we can use 91% as a respective average (it's not the same in every gear after all).
Low end HSt systems used in consumer goods (this would include tractors of most descriptions) rarely achieve 85% overall efficiency and most are closer to the 75% number with a few bad examples nearer to 60% efficiency. The pump and motor seperately are not too bad, but efficiencies of each are multiplied to make a bad overall efficiency.
A GST with assumed 91% efficiency "consumes" 9% of the FW power as it moves thru the transmission.
A HST with assumed (but typical) 85% efficiencies in both the motor and pump will result in a HST SYSTEM efficiency of about 72%. This means that 28% of the power produced by the engine is "consumed" by the HST drive. That is, 3 times more wasted energy than with a GST and it's in the form of heat.
GST example: 24 FWHP x 1.00 (clutch) x 0.91 (trans) x 0.89 (diff) = 19.4376 HP to the wheels
HST example: 24 FWHP x 0.85 (pump) x 0.85 (motor) x 0.89 (diff) = 15.4326 HP to the wheels
To jag, Auto or Ag, the DESIGN is the same. There are only so many patented CVT designs, you've GOT to pick one regardless if in a car or a tracked tractor.
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MessickFarmEqu
Super Member
there is alot of information in this thread thats not correct...I don't have time to set things straight right now.
whistlepig
Elite Member
I do know that they use CVT on some combines. My neighbor bought a used Gleaner combine last fall and he let me crawl around inside it. I was surprised to see a giant pulley and CVT belt on a piece of equipment this large. He gave me a ride in this combine while he was harvesting last fall. It's a nice combine and he is very pleased with it. This is the first post about tractor CVT's I have seen on TBN. I would very much like to read more.
