hydrostat vs gear hp loss

[BillyP]

I assue you meant as a signature.. Yes it does!

Dang it! Yes, as

Thanks

 

[dieselsmoke1]

The reality is more drawbar HP allows the tractor to run a lot more efficiently with heavier loads.

Yes, I agree.

Just comes down to opinion if the hydro can gain back the lost efficiency with what some would consider an agility advantage. I expect it depends on the job and the operator.

Next time I get into a debate, I hope I'm on the fact side. The supposition side is a lot of work

Have a good night.

 

[_RaT_]

Yes, I agree.

Just comes down to opinion if the hydro can gain back the lost efficiency with what some would consider an agility advantage. I expect it depends on the job and the operator.

Next time I get into a debate, I hope I'm on the fact side. The supposition side is a lot of work

Have a good night.

Just think of what a Bobcat track or skidsteer or a ZTR would be like without a hydrostatic drive? Being a user of both, I know the answer...

 

[neverenough]

I am considering moving up to a hydrostat cab tractor. Does anyone know the amount of drawbar/rear wheel HP loss for a hydrostat compared to gear drive. I have a Kubota 3710 GST and dealer said expect to lose about 20% in pulling power with hydro. He recommended an increase from 37hp to 46hp (ie. 4630) to have the same pulling ability with hydro. This would suggest considerable power loss. Most bigger tractors talk about drawbar hp in specs but don't see this in the compacts. Is this because of so many hydro's in the compact class that companies don't want to show specs with lower drawbar hp for hydro tractors with the same engines?

The reason they don't do ratings for compacts, is becouse they are not considered farm equipment. Nebraska has a law that requires ALL FARM tractors to be tested by an independent testing facility for belt, PTO, and draw bar HP. The tests are almost alway's done by the University of Nebraska. Becouse the tests cost $$$, they don't do them for compact tractors as they are not required by any local, state, or federal government.

Hydro drive is more efficient than most people give it credit for ( depending on maker). Deere, for example, used to sell their hydro lawn tractors at a deep discount in order to get people to try them. People came back for more. Over the years, they have improved them to the point they are quite efficient. Fluid power, working properly, can produce a lot of torque (rotational "work"). This can then be easily transfered in to horse power (linear "work"). You can also "amplify" torque through the flow of fluid, just as you can with gears. Therefore, it comes down to the system in operation and how well it works. If you are losing 20% by going to a hydro tranny tractor, it's best you find a brand with a better system. I think they were just trying to feed into your "manlyness" and trying to get you into something bigger.

 

[john_bud]

So, if a hydrostat loses 20% in the drivetrain -- where does the heat go? 6+ Hp of heat is a LOT of heat.

Just wondering...

jb

 

[SPYDERLK]

So, if a hydrostat loses 20% in the drivetrain -- where does the heat go? 6+ Hp of heat is a LOT of heat.

Just wondering...

jb

Ive read this thread with great interest. Many times Ive wanted to reply, but the next 2 or 3 posts said what I was thinking. I have a perspective that I believe is borne out by the thread however, and a theory regarding that 20% quoted by the dealer. - - The ball park numbers from the 1980s were loss of 10% in a gear trans and 20% in a hydro. These #s hold close to references quoted here. I think the dealer has misused this comparison to get his 20%. In actuality tho depending on how you make your comparison you can say a lot of correct things that mislead. Like; the H is half as efficient as the G, the G is twice as efficient as the H, the G is 100% more efficient than the H. The opportunities to confuse boggles the mind. I try to keep it straight by comparing what the H transmits vs the G. Out of 100HP input this would be 80H vs 90G or 80/90 or 89%. You get 11% less power out of the Hydro. But it is true that the H is throwing away twice as much power as the G. Notice the large reservoir, finning, and auxiliary fans on Hydros to take care of this waste heat. Theres really no way around the extra losses because there is inefficiency in converting energy from one form to another. In the engine youre losing about 1/3 of your energy out the exhaust pipe, 1/3 thru the radiator, and getting the last third as mechanical HP. When you take that mechanical and convert it to fluid flow and then back to mechanical you have more losses. For this you get convenience and ease of finesse.
Larry

 

[normde2001]

Too many long-winded posts here to read them all; however, unless you have someway achieved perfect traction you are going to run out of traction long before you run out of horse power in either case, making it a non-issue.

 

[SPYDERLK]

Too many long-winded posts here to read them all; however, unless you have someway achieved perfect traction you are going to run out of traction long before you run out of horse power in either case, making it a non-issue.

No. Not if you have a strong FEL and can push and lift at the same time.
Larry

 

[_RaT_]

No. Not if you have a strong FEL and can push and lift at the same time.
Larry

I suppose it depends on soil conditions but I can almost always run out of HP before traction. This applies to my hydrostatic drive and my gear drive. As you said, going forward into a pile of dirt, lifting and loading the front tires and my RPM's drop. The good news is that it is really easy to remedy. On the HST let off on the pedal pressure and on my gear, push in the clutch. Problem solved...

 

[SPYDERLK]

I suppose it depends on soil conditions but I can almost always run out of HP before traction. This applies to my hydrostatic drive and my gear drive. As you said, going forward into a pile of dirt, lifting and loading the front tires and my RPM's drop. The good news is that it is really easy to remedy. On the HST let off on the pedal pressure and on my gear, push in the clutch. Problem solved...

Yeah, I run out of traction before HP usually too. In 1st gear the 7520 4wd with FEL and loaded rears will spin its wheels with the throttle set at 1200rpm -- unless weight is augmented by lifting. Then I can use as much power as I have, and more. With a dirt pile its not too big a deal. The bucket is full, or you can always take a smaller bite. However, when pushing and lifting a large tree that I can not lift off the ground I sometimes need a little more than the engine can give. With the gear tractor pushes like this can be made a little at a time, letting the engine recover each time it boggs down. With a hydrostatic drive you cant do this because you hit its limit suddenly. The pressure relief operates and your horsepower diverts to that wasted flow. If you push the pedal down more you get more wasted flow and very little more push. On the gear drive that HP goes to the ground even as the engine slows.
Larry

 

[kensfarm]

If you push the pedal down more you get more wasted flow and very little more push.

You get less torque & more speed the farther you push the pedal down.

 

[_RaT_]

You get less torque & more speed the farther you push the pedal down.

You really don't suddenly hit a wall where a hydrostatic suddenly stops because of a relief valve popping, in fact, I don't know if those talking about hydrostatics in such a way have ever used one or at least a Kubota. On both my L48 and L3830, both HST, I could and did kill the engine without ever "popping" the pressure limit much like you do with a gear. I am not even sure how the HST in the Kubota works other then to say much of what I see folks posting here seems inaccurate as to how mine operates. In medium and low I can kill the engine or spin the wheels by depressing the pedal. I would like to drive a L3830 with gears to see just how much more effort I get transferred to the wheels, something I do not doubt will be inevitable. On the otherhand, as was mentioned, it is easy to quickly recover by backing off or removing your foot from the hydro pedal.

 

[SPYDERLK]

You get less torque & more speed the farther you push the pedal down.

This does not fit with my experience. Deducing from the ones I have driven, I believe the pedal controls a variable displacement pump. From the operating characteristics it seems that this pump supplies flow to a fixed displacement hydraulic motor. The flow pressure rises according to the load placed on the hyd motor until the pressure exceeds the setting of the relief valve. At that point the wheels will push no harder and you have a happily running engine that cant get to the ground because the pressure to the hydraulic motor has hit a limit. What makes me think that the variable displacement pump interpretation is correct is that if you floor the pedal you do get a little more push as the engine bogs. This would be explained by the higher pump flow and the increased pressure needed to cause this added flow thru the relief valve. If the pedal controlled a variable displacement motor you would lose torque if you floored it like you said, but I havnt seen that effect. Its time for somebody to talk who really knows how these work.
Larry

 

[_RaT_]

If the pedal controlled a variable displacement motor you would lose torque if you floored it like you said, but I havnt seen that effect. Its time for somebody to talk who really knows how these work.

Hi Larry, I think that is how it works. The farther you push the pedal the greater the flow and the more load on the engine yet the less torque which I assumed was because the engine was losing RPM. I know the HST in the Kubota (and others I think) use a swasher plate to vary the flow. I think your right though, someone with a whole lot more understanding of how this stuff works is needed because I don't.

 

[Doc_Bob]

I have a TN70A with R1. I run out of power before my tires loose traction. Might be different if I had R4s. 70 HP with R4s might spin a little easier than R1s. The only time I spin is in very loose or wet soil.
Bob

 

[dieselsmoke1]

I don't have a lot of understanding, but I do have a lot of experience.

Lot's of folk's have raised the point that a hydro gives up drawbar HP to an essentially similar geared, and they are right.

A CUT, whether geared or hydro, should develop enough dbhp to spin it's wheels on demand. Personally, if I ever got one that would not turn the tires I'd get rid of it post haste.

One of the most significant features of an HST is that you don't "have" to spin the tires to get the maximum amout of force delivered to the ground that the unit, traction and conditions will allow. I have pushed mine to the ragged edge of breaking traction and held it there many times while other activities took place, such as a buddy sawing down a tree that was heavily leaning towards the house or working the bucket against a stump. No worries of spinning or of smoking a clutch, when the load and traction allows I will move forward.

 

[_RaT_]

I have a TN70A with R1. I run out of power before my tires loose traction. Might be different if I had R4s. 70 HP with R4s might spin a little easier than R1s. The only time I spin is in very loose or wet soil.
Bob

Boy thats for sure, R1's do indeed take more to spin and when they do, they make a hole fast.

 

[john_bud]

In a Kubota, the peddle controls a hydraulic servo piston connected to the variable swashplate. There are 3 main elements to the hydro, variable displacement piston pump, fixed displacement piston motor and a charge pump.

The charge pump runs all the time off the input shaft. The swashplate angle dictates the amount and direction of fluid pumped from the variable displacement pump (on the input shaft). The motor takes the fluid from the variable displacement pump and turns it into motion on the output shaft.


See the Kubota WSM page 3-NM10-12

 

[Soundguy]

Hmm... wasn't there a fellow with a kubota at the bottom of a hole that the kubota wouldn't crawl out of.. relief would pop.. tires wouldn't move, and engine didn't stall??? Was a couple years ago when this discussion came up. Anyone got that saved thread??

Soundguy

You really don't suddenly hit a wall where a hydrostatic suddenly stops because of a relief valve popping, in fact, I don't know if those talking about hydrostatics in such a way have ever used one or at least a Kubota. On both my L48 and L3830, both HST, I could and did kill the engine without ever "popping" the pressure limit much like you do with a gear. I am not even sure how the HST in the Kubota works other then to say much of what I see folks posting here seems inaccurate as to how mine operates. In medium and low I can kill the engine or spin the wheels by depressing the pedal. I would like to drive a L3830 with gears to see just how much more effort I get transferred to the wheels, something I do not doubt will be inevitable. On the otherhand, as was mentioned, it is easy to quickly recover by backing off or removing your foot from the hydro pedal.

 

[_RaT_]

Hmm... wasn't there a fellow with a kubota at the bottom of a hole that the kubota wouldn't crawl out of.. relief would pop.. tires wouldn't move, and engine didn't stall??? Was a couple years ago when this discussion came up. Anyone got that saved thread??

Soundguy

He apparently did NOT hit a pop off or relief. The only thing that was deduced was that the tractor was on a steep enough hill that the pickup tube pulled air (now that would be a very steep hill). The final conclusion was never 100% other then the tractor would not move but then, the engine would not load up either. Bad linkage as John Miller III sugests, maybe, we may never know. I know I have been in similar circumstances with my front end buried down hill to where it took all my bucket force and spinning tires to get me out. No popoff popping. Heres the thread for folks to browse.

http://www.tractorbynet.com/forums/showthread.php?t=20041&highlight=L4610