HST Power Consumption

[CJONE]

HST is the work of the devil. The whine of the HST is actaully the banshee scream of beezlebub. Clutches make you tired and humble so you will stay out of mischief I tell you.

:thumbsup::laughing::laughing: I love it!!!

 

[xtn]

Where you said inherent. Design for design to a force spec the gear will stop after the HST. Also, I said nothing about 100% efficiency. At this level of discussion I regard std mechanical inefficiency as assumed. Only where special situations exist need they be drawn apart.
larry

Okay maybe I'm reading you wrong. When you say "to a force spec" I'm imagining two engine/drive systems designed to deliver some predetermined amount of force. Some project coordinator tells two engineers that he wants a geared system an an hst system that will both deliver X pounds-feet of torque to the driven axle before giving up. In that case, both systems will deliver that amount of force. Both will pull the same weight up the same hill.

Unless you're trying to suggest that all hst implementations fall short of their design goals. But I don't think you're trying to say that, right? What am I missing here?

xtn

 

[SPYDERLK]

There's a real difference between real world and theoretical differences. In the real world there are very few times where you notice a difference between the two power wise. Most times I've seen a tractor that had so much traction that it couldn't spin the tires yet enough power not to stall, guess what happens? The front end lifts off the ground, lots of YouTube videos. When it can't it spins the wheels or stalls the engine.

For the very few times where the gear tractor could keep moving without spinning the wheels. All one would need to do is slow down a little with an hst and hp will not be an issue. That's why people always say that gear tractors work best for things like pulling a bottom plow. However most people are willing to trade off that advantage for all the hst advantages.

Im talking force not power. Speed is not the issue. There must be enuf torque [~force] to make the wheels turn. The force capability is directly related to pressure and gearing. As long as pressure can be made to rise there will be more wheel torque available. As you let off the pedal you reduce displacement of the pump making it possible for the engine to keep turning it as pressure rises. With large resistance to moving, pressures, particularly with cool fluid, could easily go too high for the system to withstand and with so little engine load that you wouldnt notice. That is why the HST must have a relief valve. The setting of that valve gives you a sudden force limitation that occurs w/o warning, wastes all your power to sump while maintaining that force[pressure] set by the valve. Motion stops almost instantly. >> A gear designed to supply the same force would lug down when it encountered the same force limitation. Since there is a direct link from engine to ground, the wheels would continue to turn as it lugged down. If it was only a few % overload the gear tractor would move several feet while augmenting combustion power with energy stored by the spinning engine mass, before you had to clutch. ... Let the engine rebound and then go a few more feet. When you get beyond the area unload a few pounds and go tow the HST out. - Actually you could just pull/grunt it on up the hill with you in the 1st place if you could somehow preserve its ability to help by keeping it from burning its fluid. :confused3:
larry

 

[Redneck in training]

As I see it there no a manufacturer in the sane state of mind that would design a tractor that will not meet user expectation. Similar tractors, one HST and the other gear, will deliver similar performance but HST might use marginally more fuel to achieve it. Experience with my tractor shows that traction is the limiting factor to what the tractor can pull. I could probably hang way more weight on it to achieve more traction but something will break. With the number of hours most of us put on the tractor the higher fuel consumption is not too significant factor. In my opinion HST is the best tractor for first time users. They lack the "macho" factor though. They are too easy to operate.

 

[MHarryE]

If you go by a Kubota dealer who has Grand Ls in stock, different transmissions, look at the difference in size of the oil cooler between the HST and both the GST or manual transmission. What, you couldn't find the cooler on the manual or GST? Rule number one in hydro transmission design - provide an oil cooler equivalent to at least 30% of max engine horsepower because that is the heat rejection due to inefficiency. On these tractors the hydrostatic have oil coolers but the others get adequate oil cooling from surface heat rejection from the transmission case. That doesn't make a hydro bad. It is fantastic when you need to vary speeds a lot or shuttle back and forth. I have a hydro for work around my home, but on our 2 farms we have 18 other manual or power shift equipped tractors. I can load large round bales faster with my hydro than anyone on the farms can with the shuttle shift tractors, but I can barely pull our largest implements down the road with the wings raised let alone drop the wings and sink 30 foot of implement into the dirt, but that's not it's job.

 

[milkman636]

I specifically said PTO not DRAW BAR. So yes once you put the HP through a tractors powertrain either trans gears or HST they will be close but you WILL loose more through a HST at full HP. That is the key how hard you are running the HST. They are very efficient at low flow levels. The higher the flow/pressure the less efficient they are depending on their design. CJ

The published pto numbers provide a relevant reference for the turning force that can be applied to the pto shaft a 540 rpm, that's it.

The drawbar testing is valuable because it provides real measurments of ground speeds, fuel consumptions, and actual sustained forces being applied to the drawbar. If a specific model of tractor in both geared and HST were both subjected to the same test, the differences in the measurements could only be attributed to the transmissions that were applying the power to the ground. That would settle the discussion in less than 20 pages.

 

[beppington]

The published pto numbers provide a relevant reference for the turning force that can be applied to the pto shaft a 540 rpm, that's it.

The drawbar testing is valuable because it provides real measurments of ground speeds, fuel consumptions, and actual sustained forces being applied to the drawbar. If a specific model of tractor in both geared and HST were both subjected to the same test, the differences in the measurements could only be attributed to the transmissions that were applying the power to the ground. That would settle the discussion in less than 20 pages.

You can adjust TBN so this is "only" the 4th page ... but 156 posts?? :confused2:

 

[rsewill]

You can adjust TBN so this is "only" the 4th page ... but 156 posts?? :confused2:

Yes! I use my iPad and this topic is on its fourth page. There is a 'Settings' option along the bottom of my tablet that allows me to choose the number of posts to be shown.

 

[SPYDERLK]

Yes! I use my iPad and this topic is on its fourth page. There is a 'Settings' option along the bottom of my tablet that allows me to choose the number of posts to be shown.

Up to 40 as I recall. Thats where mine is set.
larry

 

[xtn]

Im talking force not power. Speed is not the issue. There must be enuf torque [~force] to make the wheels turn. The force capability is directly related to pressure and gearing. As long as pressure can be made to rise there will be more wheel torque available. As you let off the pedal you reduce displacement of the pump making it possible for the engine to keep turning it as pressure rises. With large resistance to moving, pressures, particularly with cool fluid, could easily go too high for the system to withstand and with so little engine load that you wouldnt notice. That is why the HST must have a relief valve. The setting of that valve gives you a sudden force limitation that occurs w/o warning, wastes all your power to sump while maintaining that force[pressure] set by the valve. Motion stops almost instantly. >> A gear designed to supply the same force would lug down when it encountered the same force limitation. Since there is a direct link from engine to ground, the wheels would continue to turn as it lugged down. If it was only a few % overload the gear tractor would move several feet while augmenting combustion power with energy stored by the spinning engine mass, before you had to clutch. ... Let the engine rebound and then go a few more feet. When you get beyond the area unload a few pounds and go tow the HST out. - Actually you could just pull/grunt it on up the hill with you in the 1st place if you could somehow preserve its ability to help by keeping it from burning its fluid. :confused3:
larry

Okay I agree with all of that. But you could just run more robust components and a higher relief pressure. It is NOT AN INHERENT QUALITY that an hst drive must give up before the engine does.

If you have a clutch (or gear set even) that isn't robust enough to transmit the engine's full torque, you will have the same result you describe; no drive when you need it most. You spec the parts right and either drive system will keep doing the job above and beyond the engine's output capability. If you don't, they won't. It's that simple.

xtn