Confused: CVT vs. Hydro??

[MiserableOldFart]

I have been trying to find out what the advantages of a CVT over a Hydro are, and just don't understand, probably because I'm old and thick in the head. Now, if it weren't for loader work, I would certainly have a manual shifting tractor of some kind, but the loader makes the hydro a nice convenience.. what makes the CVT preferable? Can anyone 'splain this?

Thanks!

 

[KennyG]

The CVT advantage is efficiency. It is usually fully mechanical (steel belt on conical pulleys) so there are almost no losses in the transmission. The hydro transmission has a pump that sends fluid to a hydraulic motor, both of which have significant energy losses.

The disadvantage is that you have to have a reversing gearbox to change directions, and shifting that is like a manual transmission, less convenient than a hydro.

Interesting point - my hybrid car, like most has a CVT transmission. It doesn't have a reverse gear. You can only back up with the electric motor.

 

[jdbnh]

well a cvt gives you a lot of options for one. where a hydro is jsut two peddles forwards and backward with your speed ranges. The CVT doesnt have the high pitched "whinny" sound liek a hydro does either. THE CVT is not jerky like a hydro, it is very smooth. you have many different settings on a CVT, down to how you want the foot pedal to react when you step on it. it gives your tractor and the operator a lot of choice depending on the job at hand. Higher horse power tractors have them and in applications like plowing, loader work, planting, baling, you can really set the speed, rpms, etc how you want them for the most efficient work. if you would let me know what your email is i can send you a more in detail explanation

 

[jdbnh]

The CVT advantage is efficiency. It is usually fully mechanical (steel belt on conical pulleys) so there are almost no losses in the transmission. The hydro transmission has a pump that sends fluid to a hydraulic motor, both of which have significant energy losses.

The disadvantage is that you have to have a reversing gearbox to change directions, and shifting that is like a manual transmission, less convenient than a hydro.

Interesting point - my hybrid car, like most has a CVT transmission. It doesn't have a reverse gear. You can only back up with the electric motor.

actually in NH CVT on the compact tractors, they have a shuttle shift to go along with the CVT and it just has forward adn reverse cltuches. no other gearboxes or anything. it is pretty simple. i can send you info to read if you like. just let me know your email

 

[farmall40]

The only downfall that I have found with the CVT is it takes about 2 seconds to change direction. Trust me it's no big deal. I owned 2 hydro units before the CVT, these things should't even be mentioned in the same sentence. The power and the smoothness of the CVT is incredible. Let's just say I won't be going back to a hrdro anytime soon.

 

[MiserableOldFart]

Thanks for the info, all. JDBNH, my email is "MiserableOldFart@aol.com." Does anyone have any thoughts as to which are more rugged and less trouble prone? I had leaned toward a manual shift until I read about loader work being easier with that hydro pedal, but I've always felt the manual tranny had less to go wrong long term than the hydro. Some dealers seemed to agree, others not. I certainly appreciate the hydro when I'm using the loader to move snow around.

 

[jdbnh]

what i am about to send you will probably answer that question on durabilty.

 

[MiserableOldFart]

Thanks for the info, jdbnh. Wow, tractors have certainly become high tech items! Wish they were simple like computers ;-)

 

[jdbnh]

Thanks for the info, jdbnh. Wow, tractors have certainly become high tech items! Wish they were simple like computers ;-)

i certainly agree with you on that. nothing is simple anymore. Anytime you have a questions jsut holler

 

[skspurling]

what i am about to send you will probably answer that question on durabilty.

Well, that's all fine and dandy for old fart, but the rest of us may want to know about the durability of the CVT.

I would imagine, because of the mechanical nature of the system, you would be more prone to stresses and wear than with an HST. Is that wrong? And how would that not be the case? If you properly maintain an HST, any abrasives in the working fluid should be filtered or flushed before they cause much wear, and the compressibility of the working fluid (which makes it less efficient than a mechanical system) should reduce the actual shock on the mechanical parts.
Some people may think of an HST like a big pump, some hoses, and a couple of hydraulic motors driving the wheels, but that is no where near what it is. It would be more like a torque converter with extra valving. It's not that inefficient. Not saying that a CVT isn't nice, but I don't think you get all benefit and no down side. Any one telling you that is a sales person. I would not be surprised if the overall lifetime of the components in a CVT were not shorter than a standard gear based transmission. They just don't know that yet because they have not been on the market long enough.

 

[jdbnh]

actually they (NH) has been testing and testing the CVT for the past 6 plus years before they even let it be known they were thinking about the CVT in compacts. The CVT is designed to last at least twice as long as a gear and hydrostat. They put 7000 plus hours on different tractors in different conditions. the chain that is used in the pulley system has a tensile strenght, or breaking point of 7500 lbs. it is designed to be maintence free and needs no adjusting.

The EasyDriveTM CVT emits less noise than a hydrostatic transmission.
Hydrostatic transmissions have an inherent noise due to the use of oil under
pressure to transmit power. This hydraulic noise is eliminated from the CVT,
resulting in a much quieter operating transmission at all speeds. Tests have
shown a 2 dBA reduction in noise compared to a hydrostatic transmission whenoperated under the same load conditions.
- The ability of the EasyDrive CVT to transmit power to the rear PTO whilethe
vehicle is moving is higher than for a hydrostatic transmission. The use of a
mechanical link (steel chain) is more efficient than utilizing fluid (oil in
hydrostatic transmission) for the transfer of power. In a dynamic mode, the
CVT requires less power to move the tractor, due to its mechanical efficiency,
and therefore has more power available to transmit through the PTO. Sincethe
majority of PTO tasks are performed while the tractor is moving (finish
mowing, rotary cutting, rotary tilling, snowblowing, etc) this is a significant
benefit. In a tractor equipped with a hydrostatic transmission, as the travel
speed increases, there is a corresponding reduction in power available at the
PTO, as more of the engine power is required to turn the wheels. In the working
speeds from 2 to 7 mph, a hydrostatic transmission can experience a reduction
in available PTO horsepower from 3% to 7% while the EasyDrive CVT will
maintain PTO horsepower and not experience a drop as the travel speed is
increased.

The EasyDriveTM CVT found in the Boomer 3000 Series is based on a simple
design
that uses variable diameter pulleys connected by a steel chain to alter the transmission
ratio and adjust for speed and power requirements.

How does it work ?
Input power from the engine flows to a set of hydraulic clutch packs which control theforward and reverse direction. From there, the power is transmitted to a Chain Drive
Variator which is used to adjust the transmission ratio, thereby determinig
the speed
of the tractor and its ability to transmit power under different loads. The Chain Drive
Variator is made up of 2 variable diameter pulleys that are connected by a
steel chain.
From the Chain Drive Variator, the power feeds directly into an epicyclical
gearboxthat transmits the power to the rear axle.

 

[Red Horse]

sounds like we are getting some inside info-which is good. In my mind, I have a tough time accepting the fact that a chain and variable pulley system is less prone to failure than a system that basically relies on the non compressibility of as liquid to transmit power.

On another point, any reason why Ford dropped it like a hot potato? Also are any big machines going to CVT?

 

[Hematite]

"This hydraulic noise is eliminated from the CVT,
resulting in a much quieter operating transmission at all speeds. Tests have
shown a 2 dBA reduction in noise compared to a hydrostatic transmission whenoperated under the same load conditions."

2 dba in noise reduction is MUCH quieter? I beg to differ. 2 dba is almost a nominal difference and when comparing different units the opposite may even be true. My Hydro is actually pretty quiet. If it were 20 dba quieter, THAT would be much quieter!

As far as Ford dropping the CVT, that trans was a product of Volvo. I don't even know if Ford still owns Volvo. If they sold Volvo, Ford would no longer handle the unit.

 

[jdbnh]

sounds like we are getting some inside info-which is good. In my mind, I have a tough time accepting the fact that a chain and variable pulley system is less prone to failure than a system that basically relies on the non compressibility of as liquid to transmit power.

On another point, any reason why Ford dropped it like a hot potato? Also are any big machines going to CVT?

well i havent heard they are changing the CVT in the compacts. but yes CVT has been in the 125hp up to 250hp for a couple of years now. Awesome driving. really easy and gives the tractor and engine a lot of choices and power compared to a powershift or other

 

[farmall40]

Having owned 2 hydro units(tc35d, tc40d) I can tell you for a fact that my Case Farmall 40 with the CVT is a huge improvement over a hydro tractor. It is WAY more quieter than a hydro, and puts WAY more power to the ground.

 

[WM75Guy]

I much prefer my CVT over my HST. It is quieter and more responsive, seems to have more power to the ground. The Boomer 8N CVT is my tractor, the TC40DA HST is my wife's.

 

[stlawrence]

I love the CVT. It does not have the hydro whine, which means I just listen to the diesel rumble that I love in a tractor. In addition, all the power is transferred, so the 50 hp 8N is a legitimate 50 hp of useable power.

I think the 8N is currently the best buy on the market. CVT trans, 50 hp, and kicking good looks. How could you go wrong?

 

[skspurling]

I can see how a CVT would be more reliable than an automatic transmission (no rubbing clutch packs). I can even see how it would be more reliable than a geared system with a clutch. I can see how it would deliver more power to the ground than a pure HST. What I don't see is how they can say there would be less wear than an HST, or how they can make claims that it puts as much power to the ground as a purely geared unit.

If I am understanding the application correctly you would still need to clutch this or use a torque converter to decouple the engine from the drive system. You also have to have some sort of reversing gear. The torque converter would have losses similar to a very efficient HST. Just think automatic transmission. The reversing gears would still wear. I am just not seeing how this would have less wear than a really good shuttle shift type system that replaces the clutch with a torque converter. I would be concerned with wear in the meshing of the vari-pulley/sprockets and the drive chain. You have to have some sort of mechanical contact to transfer power. That means wear.

You'll have to excuse me if I remain skeptical. A lot of the info in here sounds more like marketing material than an engineering analysis. I am sure they are nice and work well. I just don't buy all the hype. I doubt most people can really tell if there is 48 vs 50 hp making it to the ground. Usually it's the feel and responsiveness of the controls that make the difference.

 

[farmall40]

It's not hard to tell how much more power is going to the ground. I started a job with the hydro unit, dealer delivered my CVT to the job, took the box blade off the hydro and put it on the CVT. It took about 1 hour to get the hang of the Farmall 40 and after that I was sold on the CVT. I used both units in the same day, doing the same thing under the same conditions. Trust me, the CVT puts more power down.

 

[JasG]

well i havent heard they are changing the CVT in the compacts. but yes CVT has been in the 125hp up to 250hp for a couple of years now. Awesome driving. really easy and gives the tractor and engine a lot of choices and power compared to a powershift or other

The CVT in the 125 Hp and above that has been used for years is nothing like the system used in compacts. The larger ones use a planetary gear set and a partial hydo to vary speed.

The one NH is using is more like a snowmobile set up.

http://www.farmdepot.biz/CVT-Fact-VS-Myth.pdf

YouTube - ‪New Holland T7000 Easy Drive CVT Transmission‬‏