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
- Start date
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
Super Star Member
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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