Renze
Elite Member
Belts or padded chains can only transmit a limited amount of torque. Not suitable for heavy duty.
Why CVT's are awesome
- Thread starter daugen
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Belts or padded chains can only transmit a limited amount of torque. Not suitable for heavy duty.
OP
daugen
Epic Contributor
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.
OP
daugen
Epic Contributor
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.
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
Elite Member
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/
Here is how it works : http://fordfusionhybridforum.com/topic/6775-what-is-an-ecvt-how-does-it-work-here-is-the-answer/
Fallon
Super Member
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
Super Star Member
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- Bobcat Toolcat 5610G, Deere X744, Cub Cadet IH 982
They don't make CVT dozers though.
Fallon
Super Member
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
Elite Member
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
Elite Member
sikmusicfreak8
Silver Member
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.
