dumb question about HST

[ArlyA]

My first 2 tractors were straight geared, next 2 HST. I could never go back to a geared machine for my use. I road my tractor between jobs a lot in High, do the majority of work in Medium, only use Low for stump grinding and pulling real heavy stuff.
I have a Hi-Lo in each range which is a big plus.

My thoughts exactly. What you need to do with your machine dictates the best drive.

 

[4570Man]

I just saw this on ticktok. Looks like a HST pulling trailers to me.

 

[LouNY]

Somebody believes in abusing equipment.

 

[oldnslo]

Is that a feed trough in the foreground of that video clip with skid pulling hay racks? Makes me wonder if just moving short distance on known flat ground. Either way could be interesting turning if pulling very hard.

 

[phantom309]

On the subject of HST vs gear...

In my search for a new tractor, I came across the Yanmar YT series. I have to say that I am impressed with the i-HMT trans they are running in those tractors. It appears to be the closest I've seen to "the best of both worlds" between HST and gear.

1. I like the small "power-reverser" lever to change between F/R, allowing for just one "go" pedal. That is obviously a matter of personal preference, but I think I would find this solution a little more convenient.

2. This TBN post (point #6) states that the IHMT transmission in the Yanmars has the ability to "lock up" on steady pulls. I've wondered if that is possible with HST and assumed not, but if the Yanmar trans somehow does this, that is great.

IMO, the above two items bring some of the best features of an expensive power-shuttle transmission to HST.

 

[ericm979]

My understanding is that the iHMT doesn't have a full lockup like modern torque converter automatic transmissions in cars do. HSTs are most efficient when pumping small amounts of oil, which is normally when barely moving. IHMT makes it so that most efficient range matches speed of normal use.

 

[ning]

My understanding is that the iHMT doesn't have a full lockup like modern torque converter automatic transmissions in cars do. HSTs are most efficient when pumping small amounts of oil, which is normally when barely moving. IHMT makes it so that most efficient range matches speed of normal use.

Yeah I can't imagine how a hydraulic drive could "lock up". With torque converter automatics, there's basically a magic hydraulic fluid clutch - a fluid coupling - between the two mechanical drives and the lockup just takes the fluid out of the equation by using an automatic clutch. The tractor hydraulic drive is very different because you have a hydraulic pump over here.................. and then way over there you have the other half, the hydraulic motor driven by the pump. You can't just stick a clutch between them without putting a driveshaft between the pump and motor, and if you did, it wouldn't be a hydraulic drive any more but a torque converter system.

 

[LouNY]

Yeah I can't imagine how a hydraulic drive could "lock up". With torque converter automatics, there's basically a magic hydraulic fluid clutch - a fluid coupling - between the two mechanical drives and the lockup just takes the fluid out of the equation by using an automatic clutch. The tractor hydraulic drive is very different because you have a hydraulic pump over here.................. and then way over there you have the other half, the hydraulic motor driven by the pump. You can't just stick a clutch between them without putting a driveshaft between the pump and motor, and if you did, it wouldn't be a hydraulic drive any more but a torque converter system.

If the drive is a hydraulic pump that feeds a hydraulic motor if doesn't matter if they are close coupled or separated. One combined unit or two separate units it is still a hydrostatic drive. Torque converter drives are completely different critters in them the torque converter replaces a clutch.

 

[phantom309]

Wow. Lots of i-HST lockup deniers on this board.

I guess y'all are just jelly that your tractor's manufacturer hasn't figured out how to do it yet.

 

[ptsg]

Check some videos about how the Fendt Vario transmission works. The i-HMT is a scaled down version of it.

Yes, the hydrostatic pump and motor will lockup by angling the swash plates in a way those are technically working against each other. This causes the the power to be transferred through a planetary gear and the tractor is then mechanically driven at higher speeds where the typical HST would fall on its face.