CVT vs HST

[keyser soze]

Let's set the record straight....

A number of people have CLAIMED that CVTs offer better efficiency, I said they did not and explained why. Because people won't look for themselves and LEARN the various CVT designs and how they operate in the vehicle (car, bus, tractor) does not mean assumptions about pressure are valid.

I did some research, Deere does offer a few IVT/CVT models in the US but there are many more offerings overseas for all mfgrs. I also said, and said again that CVTs are GREAT for the control of ground speed but are NOT more efficient because what looks good on paper does not prove out in the field. There are engineering limitations and to get traction of the friction elements you need PRESSURE or you will get SLIP and that makes heat, LOTS of it. The drive pressure of a CVT/IVT can be hydraulic of mechanical, but it is still there. Doubt it all you want, that's fine. Let me know how your clutch works w/o a pressure plate.

According to the Nebraska Tractor Test....

Deere 7430 w/IVT (http://tractortestlab.unl.edu/Deere/JohnDeere_7430 IVT.pdf)
Max PTO HP = 161.22
Max Drawbar HP = 126.57 (78.51% of PTO)

Deere 7420 w/GST (http://tractortestlab.unl.edu/Deere/JD_7420.pdf)
Max PTO HP = 127.38
Max Drawbar = 102.86 (80.75% of PTO)

So, do tell, which transmission got more HP to the ground as a percentage of the PTO power? Yea, the gear.

BTW, I quoted the original sources above, feel free to notice those numbers are not my opinion but tested facts.

I think the main advantage of the CVT is that it's more efficient in the fuel department. You can match your ground speed to your PTO and engine speed to match your application.

Also.. the CVT that New Holland is putting in Compact Tractors isn't the same animal as what they are putting in actual farm tractors. One of their engineers told me that it was closer to Hydro than a CVT in a Fendt. That was at a farm show over a year ago and I think it was just a prototype. So it may be different now.

Also, for the record... the IVT is junk compared to the CVT in a Fendt or other AGCO product. The IVT doesn't appear to be nearly as reliable or efficient as the CVT which they tried to copy. This is according to people who have ran / operated both for a lot of hours, and my own operation of both transmissions.

 

[jagyzf]

Let's set the record straight....

A number of people have CLAIMED that CVTs offer better efficiency, I said they did not and explained why. Because people won't look for themselves and LEARN the various CVT designs and how they operate in the vehicle (car, bus, tractor) does not mean assumptions about pressure are valid.

I did some research, Deere does offer a few IVT/CVT models in the US but there are many more offerings overseas for all mfgrs. I also said, and said again that CVTs are GREAT for the control of ground speed but are NOT more efficient because what looks good on paper does not prove out in the field. There are engineering limitations and to get traction of the friction elements you need PRESSURE or you will get SLIP and that makes heat, LOTS of it. The drive pressure of a CVT/IVT can be hydraulic of mechanical, but it is still there. Doubt it all you want, that's fine. Let me know how your clutch works w/o a pressure plate.

According to the Nebraska Tractor Test....

Deere 7430 w/IVT (http://tractortestlab.unl.edu/Deere/JohnDeere_7430 IVT.pdf)
Max PTO HP = 161.22
Max Drawbar HP = 126.57 (78.51% of PTO)

Deere 7420 w/GST (http://tractortestlab.unl.edu/Deere/JD_7420.pdf)
Max PTO HP = 127.38
Max Drawbar = 102.86 (80.75% of PTO)

So, do tell, which transmission got more HP to the ground as a percentage of the PTO power? Yea, the gear.

BTW, I quoted the original sources above, feel free to notice those numbers are not my opinion but tested facts.

The Deere design they are running through a 2nd transmission, on some models a 4 speed power shift (one made by ZF for Deere). Probably to get around the Fendt/Agco patents. I don't know if that is a fair apples to apples look.

 

[MessickFarmEqu]

I have read articles that a CVT is less efficient than a pure gear driven tractors and there are studies that show that is true. However, these studies are at heavy tillage (or in the NE studies at max performance)

Spot on. The efficiency of a CVT depends on how much work the hydrostatic part of the system is doing. When the hydro is not running its nearly as efficient as a gear system, as it works the efficency tails off.

Any comparsion is cars, buses, ATV's, etc is pretty flawed. There are so many variations of CVT/IVT technology any generalities break down pretty quick.

 

[dieselfreak]

I think this is a correct statement. CVT can be the variable speed pulley/belt set up. I have seen this on a Gleaner combine.

Gleaners are HYDROSTATIC NOT CVT!!

 

[radman1]

Gleaners are HYDROSTATIC NOT CVT!!

Older gleaners used a CVT type belt system that connected to a more conventional gear type transmission. The tranny had a clutch and gears. The CVT belt drive was electrically controlled. By varying the pulley diameter, the belt speed changed. Thereby the tranny speed changed within that gear. Kind of similar to an ATV CVT belt drive connected to a tranny with hi and low ranges. We owned one. Worked fairly good and reliable. Could increase decrease ground speed as combining. Again depends on the definition of a CVT. Nothing like the tractor IVT/CVT.