If a hydro fails what part of it fails ???

[jinman]

</font><font color="blue" class="small">( Well Jim, on my Kubota I push down on the go pedal and it goes. That is, unless I want it to back up in which case I push on the back pedal.
)</font>

I asked for a "brief" description and Fishman comes through like a champ. /forums/images/graemlins/laugh.gif

...I guess I asked for that. /forums/images/graemlins/grin.gif

 

[chickenfarmer]

/forums/images/graemlins/cool.gif

 

[djradz]

Jim, regarding your question on the Kuboto servo pump versus NH's mechanical linkage. I don't know all the details, especially since I'm the proud owner of a TC-40D, but when I test drove a Kuboto a few years ago, I was amazed at the much lighter pedal pressure necessary over the NH. Best part was, where in our NHs, the pedal pressure increases with load on the tranny, with the Kubota, pedal pressure was constant. That was defineately one idea I thought NH should pick up and use in the next vintage of the TC series.

By the way, nice explanations. I've copied all the pictures and copied all the text into a Word Document I've appropriately titled, "Hydrostatic Transmissions - According To Jim".

 

[slowzuki]

The last poster is right, kubota just uses the servo circuit with no feedback to the pedal. This can be back too as many new kubota owners try to use it like a gas pedal, not receiving and load feedback telling them what they are really doing.

To an educated user is sure is nice though!

So older hydros had spring and damper linkages so the tranny could gear down automatically when under load. This was an early version of load match in the JD's I suppose!

 

[keeney]

I think there is a difference between "failure" and the slower deterioration we would call "wearing out".

"Failure" in an HST would be some type of catstrophic siezing where a bearing surface, or one of the piston surfaces has started rubbing so much that the metal starts galling/welding/siezing. Just like a mechanical tranny, any bearing surface that runs dry, or becomes fouled with contaminants such that it is rubbing metal on metal would be susceptable to this.

Other types of failures would be actual cracking or shearing of parts due to over-stressing them. Enough torque shock can rip the teeth off of a gear or spline, bend a shaft, or crack a bearing housing be it connected to HST internals or a gear.

What most people really worry about with HST's is the wearing-out thing. As the close-fit between the pistons and the bores open up with wear, the amount of oil being pumped vs. the amount that squeezes past the piston decreases. This ratio is known as the volumetric efficiency of the pump (or motor).

This wear is caused by friction, contaminants, voids caused by micro-boiling, corrosion/ oxidation, etc. All of these things tend to accelerate at higher temperatures. The best thing to do to prevent wear is to keep the oil cool, clean, and moisture-free.

Note that the higher the pressure the system operates at, the more critical the tight tolerance of these moving parts becomes, and the more susceptable the system becomes of wear caused by contaminants.

One way to measure the efficiency is to measure pressure the pump can develop at near-zero flow at low speed. With 100% efficiency, the pump can always provide enough pressure to hit the pressure relief of the system, no matter how slow it is turned. As efficiency drops off, and some of the high pressure oil is able to escape past the pistons, the maximum prssure at low RPM's will no longer be able to achieve the pressure-relief.

In real usage of an HST driveline, what this means is that as efficiency falls from 100%, there is a maximum gear ratio the system can effectively operate at. It can no longer provide an infinite gearing-down. Instead, it starts acting partially like a torque converter. The torque goes up in proportion to speed, and the "slippage" is the oil that is squeezing past the pistons and not being pumped (or not driving the motor).

All this oil squeezing past the pistons generates heat. When the amount of heat generated by the inefficiency of the system starts to be more than the cooling system can handle you start to get to the end of the life of the system. The higher temperatures start to accelerate the wear in a death spiral of heat-induced failure.

The good news is that rebuilding the pump and/or the motor is generally possible. The pistons, cylinders, and other bearings can be replaced with new parts, and they are not all that complex or expensive of parts. Its just a lot of labor to disassemble everything to replace those parts.

- Rick

 

[slowrev]

Good point there Rick. I probably fall into the fear of wearing out bunch. I like tractors to last longer than I will. Heck, getting a bit older.... a Murray might outlast me though /forums/images/graemlins/smile.gif

Ben

 

[jinman]

</font><font color="blue" class="small">( Note that the higher the pressure the system operates at, the more critical the tight tolerance of these moving parts becomes, and the more susceptable the system becomes of wear caused by contaminants.
)</font>

I guess that's why some/most hydro transmissions have a separate filter for the oil just before it goes through the pump. I think your analysis and description are excellent. Good points! /forums/images/graemlins/cool.gif

 

[OrangeGuy]

Here is an excellent link to an Eaton Corp document regarding servo controlled hydrostatics.

http://hydraulics.eaton.com/products/pdfs/03-205.pdf

OrangeGuy

 

[rockyridgefarm]

This is a great discussion.

I thought I would try and give an overview of Deere&Co.'s setup. I am NOT attempting to do a My Dad is bigger than yours, Each of these sytems has inherent advantages and all have excellant track records.

The older hydros Deere offered were like NH's design (less the bunny switch...) They were stiff, since they were direct, not having Kubota's servo circuit. Both the servo design and two speed setup really offered advantages.

Deeres answer is eHydro. This doesn't change the basic design, it is really still as simple mechanicly, (probably simpler...) The electronics are external, and are between the operator and the transmission. Pushing either go pedal is actually turning a potentiometer, which gives instruction to the computer which then adjusts the servos on the transmission.

This route gave the engineeres some ability to do other things simply.

<ul type="square">
[*]Reduce effort required to operate pedals by 70%.
[*]Monitor engine speed and compensate to eliminate lugging. (LoadMatch)
[*]Allow adjustment in the rate of direction change. (MotionMatch)
[*]Allow adjustment in the sensitivity of the pedals. (SpeedMatch)
[*]Provide a creeper function through electronic control.
[*]Allow more featured cruise control.
[*]Simplify connections to allow most ergonomic location of controls.
[*]Enhance diagnostc capabilities.
[*]Put cool "e" symbols and switches all over...
[/list]

So, in some ways, they leap frogged what the other guys were offering. Not that any of them are bad systems. All seem to have excellant service records, sisnce the inherent designs are so well done. The electronics have done very well on the Deere's.

LoadMatch is really cool to use. With it on, the operator can move the tractor at high speed, but the controller will automatically turn down the ratios to compensate for heavy load. Its like the bunny switch on the NH loader, but lightnig fast and self adjusting. It works for any situation like loader work; get a full bucket every time, mowing; set speed for light grass; it compesates when you hit that thick patch. Even hill climbing.

I am NOT saying that the other systems arenyt good, thay are Just showing what that little "e" does...

Of course, all this is on the Outside, I need to do more diggin for the Inside...

 

[jinman]

E-hydro seems like a very good system and a leap forward in innovation. Deere didn't just settle for one advanced feature. They seem to have done their research very well and designed several new features that fit their CUTs. Innovation like this will drive the competition to improve their products too. We all win because of competition.