CVT vs HST

[radman1]

Absolutely agree with you on that. I'm no expert on them but from what I understand they are very efficient. Speed is controlled by variably rotating the ring gear of a planetary set with a hydraulic motor. Power input is on the sun pinion and power out is from the carrier of the planet gears. Full power is available directly through the planetarys. They appear to be pretty simple to me. Not sure where the high pressures would be needed. Certainly not for the hydraulic motor as it is only for speed regulation, not power. Don't remember if there are hydraulic clutches involved, but if so they would not need more than a couple hundred PSI. Hopefully someone with more knowledge can shed more light on this subject.

Kim

You have the closest explanation yet for a tractor CVT. Lots of misinformation in the prior posts. Unfortunately, CVT has been used for various types of transmissions. The tractor CVT tranny is not quite like that of a car, combine or atv.

Exploring the rise in sales of tractors equipped with CVT | News | Farmers Guardian

Here is an article that is way over my head.http://asae.frymulti.com/data/pdf/6/cvtt2005/lectureseries29rev.pdf

 

[dieselfreak]

You have the closest explanation yet for a tractor CVT. Lots of misinformation in the prior posts. Unfortunately, CVT has been used for various types of transmissions. The tractor CVT tranny is not quite like that of a car, combine or atv.

Exploring the rise in sales of tractors equipped with CVT | News | Farmers Guardian

Here is an article that is way over my head.http://asae.frymulti.com/data/pdf/6/cvtt2005/lectureseries29rev.pdf

Combines DO NOT USE IVT/CVT. They are still HST - HUGE DIFFERENCE!!

df.

 

[Duffster]

Combines DO NOT USE IVT/CVT. They are still HST - HUGE DIFFERENCE!!

df.

I would have to look but I think the rotor may be driven by a belt version.

 

[Steve_Miller]

Interesting reading

Steve

 

[whistlepig]

Interesting reading

Steve

This was a very worthwhile post. When I think CVT I'm thinking the belt with the variable peed pulley as comes on some ATV's and a lot of other stuff.

 

[ModMech]

Absolutely agree with you on that. I'm no expert on them but from what I understand they are very efficient. Speed is controlled by variably rotating the ring gear of a planetary set with a hydraulic motor. Power input is on the sun pinion and power out is from the carrier of the planet gears. Full power is available directly through the planetarys. They appear to be pretty simple to me. Not sure where the high pressures would be needed. Certainly not for the hydraulic motor as it is only for speed regulation, not power. Don't remember if there are hydraulic clutches involved, but if so they would not need more than a couple hundred PSI. Hopefully someone with more knowledge can shed more light on this subject.

Kim

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.

 

[KWentling]

Interesting reading

Steve

Well I had the general idea anyway. I think I read that very thing a couple of years ago.

Kim

 

[radman1]

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 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) and conditons that demand high hp and even then difference is relatively small. The reason many claim the CVT is more efficient is because in many situations, max continious hp is not required. The CVT can better match tractor speed to the power requirements. Therefore, less fuel maybe required and greater productivity for tasks that may have changing power requirements.

 

[radman1]

Combines DO NOT USE IVT/CVT. They are still HST - HUGE DIFFERENCE!!

df.

Again read the earlier article I listed. It depends on the definition of CVT. The drive belt of some combines is a type of CVT. The drive belt is on a mechanical pulley system that is variable in how the belt rotates on the pulley. It is more similar to the CVT of an atv. It is not the type of CVT/IVT more typically associated with a tractor.

 

[whistlepig]

Again read the earlier article I listed. It depends on the definition of CVT. The drive belt of some combines is a type of CVT. The drive belt is on a mechanical pulley system that is variable in how the belt rotates on the pulley. It is more similar to the CVT of an atv. It is not the type of CVT/IVT more typically associated with a tractor.

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.