HST - How Does It Work?

[DFB]

Here is the parts scan.

DFB

 

[MChalkley]

MossRoad - No, I don't think that would matter. The engine won't turn backwards, in any case. The internal porting takes care of the reversal, depending on the angle of the swashplate, not which part is rotating. (I think.) /w3tcompact/icons/smile.gif

 

[MChalkley]

DFB - No apologies necessary! And I wouldn't call it "confusion" you created, but "clarification" offered.

And, yes, the second example is the one I was thinking of. The question now is, which one do most CUTs use? Is it always the same one, or do they vary? More research is in order here... /w3tcompact/icons/hmm.gif

 

[jdrotert]

BOY, I'm glad Harv asked that question! I've been meaning to find out myself. I've been kinda thinkin' about looking for an HST Kubota to replace my gear masher, but looking at all that goes into the HST drive, FORGET IT!!! I do all my own work on my stuff. In another thread, someone mentions that when he presses down on the HST pedal, his tractor goes backward. Some said that the HST will need a rebuild and it would probably run around $2000!!! /w3tcompact/icons/shocked.gif Did I say I'll keep my gear masher?/w3tcompact/icons/smile.gif

 

[Bird]

Heck, John, I've known all along how the HST works; you push that little pedal in front of your toe and it goes forward and push that one behind your heel and it goes backwards./w3tcompact/icons/wink.gif

 

[Charlie_Iliff]

And if it backs up when you press the pedal for forward, it's broken.

 

[Harv]

<font color=blue>you push that little pedal in front of your toe and it goes forward and push that one behind your heel and it goes backwards.</font color=blue>

As much as I've learned on this thread, Bird, I like your explanation best. /w3tcompact/icons/laugh.gif

Having a "gear masher" myself, though, I understand where John is coming from. It starts to sound like yet another of the "trade-offs" that keep popping up in these discussions (and in life in general). Seems like if you do a lot of loader work, especially working a pile, then HST would certainly make life easier, but you do so at the expense of a little horsepower and the possibility of expensive repairs, in addition to the initial higher price tag.

Uh-oh! I think I may have just opened the door to a non-technical discussion about HST. For what it's worth, I'm happy as a clam with li'l manual shift 'Bota right now, but I'm betting my next one will have a little bigger muscles and HST.

 

[ronjhall]

Bird
I've been on my best behavior ever since I first saw Harv's post. /w3tcompact/icons/tongue.gif (Is there a smiley face for bite your tongue)? Thanks for answering the question correctly./w3tcompact/icons/grin.gif

 

[Bird]

<font color=blue>I'm happy as a clam with li'l manual shift 'Bota right now</font color=blue>

So was I for many years, Harv. Just don't drive any with HST and that way you won't know what you're missing./w3tcompact/icons/wink.gif

After all the technical discussions (and darned good ones, too), I just couldn't resist any longer./w3tcompact/icons/laugh.gif

 

[Bird]

/w3tcompact/icons/laugh.gifRight, Charlie, I overlooked that point, since mine's never broken so far./w3tcompact/icons/laugh.gif

 

[frank_f15]

BIRD : I LIKE YOUR DESCRIPTION BEST/w3tcompact/icons/smile.gif i don't really know how it works, just know that it works just fine. and if anything really goes wrong with it i will let the REAL MECHANICS(A.KA KUBMECH) deal with it.

 

[ewoss3]

actually, from experience $2000 is really not that high when it comes to fixing transmissions. We took our ford 601 workhorse in with a busted 2nd gear and the price was $1700. Two years before that we had the clutch unit replaced for $750. So from my viewpoint, it appears to be a moot point on wether either is more expensive.

 

[hwp]

I have read this thread through from one end to the other, including the various references, and I am still confused. Does anyone know of a site with a simple animation that shows how the system works?

 

[MossRoad]

There were some links in the third of fourth reply that had some animations. Did you see those?

 

[Harv]

Interesting that y'all are revisiting this thread exactly one year after it began, give or take a few hours.

Kinda spooky, now that I think of it.

 

[MossRoad]

Oh my gosh! That is weird!!!

 

[DFB]

What a strange coincidence! /w3tcompact/icons/shocked.gif

DFB

 

[DFB]

Howard,

I don't know of any other sites off hand. I'd like to see the inner workings of the TC hydro's myself.

Best I can do here is to try to better describe how the drive system works on my Deere. I've attached a scan of the internal components. In application there is a housing that covers over the piston motor and of course all the gear clusters behind the the valve block locate inside of either the center case and/or rear transxale cases which also contain all the hydraulic oil.(sump)

The engine input shaft turns both the charge pump and piston pump. Oil from the charge pump passes thru the valve block to the piston pump. The variable postion of the swash plate, linked externally to the foot control pedal(s) and controlled by the operator, determines the amount of oil the piston pump displaces by changing the length of the piston stroke. Pumped oil is then routed back thru the valve block to the piston motor. Piston motor turns by the same type of piston pumping action. The motor's output shaft then drives the toothed gear clusters.

On this tractor hydraulic flow is also used move the clutch and brake plates used to control the PTO.

Maybe this can help.

DFB

 

[hwp]

Thanks DFB:

I am starting to get the picture. One of the aspects I found confusing related to how the volume of the pump varied. What I had missed was that there are several pistons and that the angle of variable swashplate determines the length of stroke of the pistons as cylinder block of the pump rotates. This changes the volume of flow from the pump to the hydraulic motor. The swashplate in the motor is fixed so the speed of rotation of the motor varies with the volume of fluid coming from the pump. But how does changing the angle of the variable swashplate from one direction to the other change direction of the motor? Is the direction of the flow of oil reversed? Are there valves linked to the variable swashplate that open and close to make the oil flow one way or the other?

I found the attached diagram in the Service Manual for my tractor quite helpful.

 

[hwp]

This is another diagram from my service manual with my annotation about hte valving.