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

[jinman]

Ben, think of the cylinder section of the pump like the cylinder section of a revolver pistol with multiple chambers. The entire cylinder would have to be replaced if it went out of tolerance, but the pistons could be individually replaced like bullets in a revolver. ...only not so easy. /forums/images/graemlins/smile.gif

The tolerances are very close, but really no closer than the control valves used for our FELs. Many of those are metal-to-metal close tolerance fits also. /forums/images/graemlins/cool.gif

Later this weekend I'll post an illustration from my parts catalog that shows every component of the NH hydro tranny in an exploded view. Then we'll be able to talk about individual parts by reference number callouts on the diagram.

 

[RobS]

<font color="blue"> The tolerances are very close, but really no closer than the control valves used for our FELs. Many of those are metal-to-metal close tolerance fits also </font>

Interesting point Jim. When I think of piston/bore my mind immediately jumps to an IC engine but this is entirely different. The temperature range alone is almost minimal compared to what an engine cylinder sees. In addition, the parts are all at the same temperature, expanding and contracting evenly and they're completely surrounded in hydraulic oil for heat dissipation and lubrication. Come to think of it, a pretty easy life for a hydrostat piston /forums/images/graemlins/laugh.gif

And again unlike an engine, there would be no need for piston rings and all that associated friction/wear. Any idea the materials? Cast iron is pretty abrasive. Probably cast aluminum? Maybe hardcoated pistons to prevent galling?

Always a few more questions: Does the pump turn at engine RPM? How is the high pressure fluid plumbed to the motor side? How big are some of these components (bore/stroke etc.)?

All this may warrant a trip to a salvage yard to pick up a junked hydro for dissection /forums/images/graemlins/smile.gif

One more thing... Why do some hydros (maybe all?) have clutches?

 

[eee]

RobS,Jinman...

You guys are taking this thread to a whole new level....( I like it !!! ) /forums/images/graemlins/cool.gif

 

[jinman]

</font><font color="blue" class="small">( Does the pump turn at engine RPM? How is the high pressure fluid plumbed to the motor side? How big are some of these components (bore/stroke etc.)?

One more thing... Why do some hydros (maybe all?) have clutches? )</font>

Rob, I posted the illustration of the NH TC35/40/45 (class III) tractor's hydro before, but I'm doing it again here with some additional labeling. As you can see in this new diagram, the low pressure charge pump sits at the front of the transmission snout. The fluid is drawn from the reservoir and immediately leaves the transmission and heads up to a hydrostatic cooler and filter (this will be shown in the next diagram)

When the oil returns to the transmission, it goes to the rear of the valve plate where it enters the pump. The top section of this transmission is the pump and the bottom section is the motor.

Notice how the shaft at the front of the transmission (label 1) is directly inline with the shaft that leaves the transmission at label 2, PTO input shaft. This shaft just goes straight through the transmission and to the PTO drive and reduction gears. Both of these shafts turn at engine rpm. On the class III NHs, there is no input clutch or clutch pedal. The PTO is completely independent of the transmission because it has it's own hydraulically driven clutch and brake. All smaller NHs do have an input clutch and I believe that clutch must be depressed prior to engaging the PTO.

Detailed plumbing will be shown in my next post. /forums/images/graemlins/cool.gif

 

[johnday]

Jim; It sounds like what is being called a motor is similar to a tilting plate proportioning pump in reverse. Is this true? /forums/images/graemlins/confused.gif

 

[jinman]

In this diagram, I'm showing NH's plumbing, because it shows that the hydraulic fluid to the transmission gets drawn through the same line/fliter (item 3) that supplies the main hydraulic pump. The amber line at the top is the supply and the amber line from the top of the transmission back to the sump is the return line.

The purple line is the charge pump pressure going up to the cooler that sits in front of the radiator. From there the blue line brings cool oil to the hydrostatic filter. The filtered blue fluid continues on to the back of the transmission valve plate an also down to the two-speed solenoid assembly that uses hydraulic pressure to change the angle of the motor's swashplate.

What is not shown in this diagram is the outer transmission casing and bell-housing that surrounds the transmission. This is the casing that I've indicated is just a shell with no sump inside. In this illustration, you can clearly see that all oil leaving the transmission will be routed to the rear transmission/differential case (amber line noted above).

Now, get ready for some real details... /forums/images/graemlins/wink.gif

 

[jinman]

Here are the details. This is an exploded view of the transmission from the parts catalog. It will probably raise more questions than it answers, but it really lets you see that the bottom motor section is just like the pump, but works in reverse. It's also physically a little larger than the pump.

Rather than describe the function of every detail, I'll just mention a few things and then answer any questions I can about other transmission parts.

Item 3 is the part that attaches to the pedal mechanism. It changes the angle of the pumps swashplate.

Item 4 at the bottom is the swashplate for the motor.

Items 42-45 are the 5000 psi relief valves for the pump.

Item 67 is the shuttle valve controlled by the solenoid that changes the motor's swashplate angle for two speeds.

Item's 7 & 8 are the pistons for the pump and motor (only one is shown for each assy).

Item 2 is the valve plate that provides all the plumbing and valves to make the transmission work.

One last comment:
I haven't made a post saying what part of a hydro is likely to fail because I don't have a clue. What I do think is that the hydro transmission (even a complex one such as NH's two-speed type) may have fewer parts than an 8-speed or 12-speed transmission. I don't know this for a fact, but I'm constantly amazed at how simple this transmission is. I sure hope some other folks with other types of tractors will post some details so we can compare brands. I think that would be fun. /forums/images/graemlins/smile.gif

 

[jinman]

</font><font color="blue" class="small">( Jim; It sounds like what is being called a motor is similar to a tilting plate proportioning pump in reverse. Is this true? /forums/images/graemlins/confused.gif )</font>

John, as you can see from the detailed diagram, you are exactly right. The motor is just a "tilting plate proportioning pump in reverse."

BTW: The size of this assembly might be a little hard to tell, but I think it's about 14" - 16" tall and 10" - 12" at the widest point of the casing (not including splined input/output shafts).

 

[RobS]

This is great Jim, very informative. I'll have to study further later, got some real tractor work to do right now /forums/images/graemlins/laugh.gif

I agree, if others could post similar details from other brands we could raise the collective intelligence level of TBN by several points. Look out OEMs, the TBN brand tractor is soon to be developed /forums/images/graemlins/smile.gif

 

[fishman]

</font><font color="blue" class="small">( I'd love to hear how JD or Kubota trannies work if anyone wants to give a brief description. )</font>

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. /forums/images/graemlins/smile.gif

It's so simple a trained monkey could show anyone how to use it. Not nearly as complicated as your New Holland, obviously. /forums/images/graemlins/tongue.gif /forums/images/graemlins/laugh.gif