HST Power Consumption

[xtn]

Oh good. Then let's continue with real questions...

You will never see such forces in proportion to its design goal in a system with an automated protective device. Turn your HST up 50%, and at load requiring that pressure you are operating beyond its safety limit with no indication. Turn it up 100% to make it able to deliver anywhere near the force induced in a gear stall and it might do it once ... Engine singing happily at lo pedal. But it made a new sound and now it doesnt seem the same...:confused3:
Fine.
larry

Why will I never see such forces in proportion to design goals in a system with an automated protective device? I submit that's only true inasmuch as manufacturers determine what "enough" is for their products and don't want to spend more. I think that while it may be a common limitation, it certainly doesn't qualify as an INHERENT limitation.

What if we put the entire hst drive line from my larger, more powerful tractor behind the engine of your BX and then max load it. I submit that the engine would lug and die or something else would fail before the hydraulic system gave up, and it would behave as such repeatedly without undue stress. I never said that just turning up the relief setting was adequate. I've been talking about raising the safe limit of all the system components.

I mean there are large dozers using hst. Do you really think there is some inherent limit condition that prevented the designers/engineers of your BX from installing a system that would break your case in half before it gave up transmitting torque? It could be done. And if something CAN be done, it isn't an INHERENT condition that prevents it being done. It's something else like cost, or space/packaging requirements, or some other design goal conflicts specific to any given design project.

xtn

 

[SPYDERLK]

You said earlier "could or can be designed". So that opens the situation to where both are designed to do the same thing with the same steady state limit...:confused3:
larry

Oh good. Then let's continue with real questions...



Why will I never see such forces in proportion to design goals in a system with an automated protective device? I submit that's only true inasmuch as manufacturers determine what "enough" is for their products and don't want to spend more. I think that while it may be a common limitation, it certainly doesn't qualify as an INHERENT limitation.

What if we put the entire hst drive line from my larger, more powerful tractor behind the engine of your BX and then max load it. I submit that the engine would lug and die or something else would fail before the hydraulic system gave up, and it would behave as such repeatedly without undue stress. I never said that just turning up the relief setting was adequate. I've been talking about raising the safe limit of all the system components.

I mean there are large dozers using hst. Do you really think there is some inherent limit condition that prevented the designers/engineers of your BX from installing a system that would break your case in half before it gave up transmitting torque? It could be done. And if something CAN be done, it isn't an INHERENT condition that prevents it being done. It's something else like cost, or space/packaging requirements, or some other design goal conflicts specific to any given design project.

xtn

It strikes me that you are designing on the fly to beat or match another system. Or else over designing the spec to allow peak matching another system, whatever system, whatever peak is needed, when necessary. ... Very wasteful, not to mention cheating - and the other system could just have another gear. Do you intend to make the system inherently unbreakable? The infinitely variable is always going to need a safety valve. It cannot be between the engine and transmission and still protect the system.
larry

 

[CJONE]

That is IMHO the big advantage with hydraulics, the relief can be set to bypass BEFORE something breaks. CJ

 

[xtn]

It strikes me that you are designing on the fly to beat or match another system. Or else over designing the spec to allow peak matching another system, whatever system, whatever peak is needed, when necessary. ... Very wasteful, not to mention cheating - and the other system could just have another gear. Do you intend to make the system inherently unbreakable? The infinitely variable is always going to need a safety valve. It cannot be between the engine and transmission and still protect the system.
larry

Yes. It would be wasteful to design all hst systems to overcome the low usage incidence of max load at max traction as you describe in your previous examples. That's probably why your BX and many other units fall slightly short under those rare requirements. I don't disagree.

But that doesn't mean you can describe that common shortcoming as being due to some inherent limitation that can never be overcome. It can be overcome. We agree it commonly isn't due to waste (mostly cost I imagine), but it can be if desired. The reason it commonly isn't is NOT that it's inherently impossible.

And no I do not intend to make anything inherently unbreakable. There is no such thing. The only requirement to get an hst drive system to perform up to par with a geared system in your examples is to bump up the relief pressure to whatever pressure is required to deliver as much torque as the clutch in the geared system, and of course upgrade all the other hydraulic components to be safe at whatever pressure that is. It would be a waste of money most of the time, for most people. But it could easily be done. So there is no physical limitation that is INHERENT to the hst type drive.

xtn

 

[crazyal]

Just so I am understanding correctly...

Spiderlk and I both graciously gave up our debate at your request, and you keep discussing it? The only difference is you're limiting yourself to real world conditions wherein your power exceeds your traction. Our discussion was assuming we've added enough weight to solve that problem, which is no less a real world situation than yours.

Have I understood correctly?

xtn

No I replied with clarification to someone who quoted me, guess I was raised to believe it's polite to do so.

I never said you needed to stop debating, I just said to me it wasn't worth my time reading.

 

[SPYDERLK]

And no I do not intend to make anything inherently unbreakable. There is no such thing. The only requirement to get an hst drive system to perform up to par with a geared system in your examples is to bump up the relief pressure to whatever pressure is required to deliver as much torque as the clutch in the geared system, and of course upgrade all the other hydraulic components to be safe at whatever pressure that is. It would be a waste of money most of the time, for most people. But it could easily be done. So there is no physical limitation that is INHERENT to the hst type drive.

xtn

No. You have skewed my example which was to establish a common task spec between different drives. You have not designed for the spec, but to beat the spec enuf to overcome the inherent peak force deficiency. A gear with exactly the same overdesign would tow that thing all over the place.
larry

 

[xtn]

No. You have skewed my example which was to establish a common task spec between different drives. You have not designed for the spec, but to beat the spec enuf to overcome the inherent peak force deficiency. A gear with exactly the same overdesign would tow that thing all over the place.
larry

I don't agree. Just as a gear and clutch system can be engineered to transmit torque without failure to some multiple of maximum engine output, so can an hst system be designed to transmit that same torque value without relieving. They need only be designed to the SAME output delivery spec.

The only inherent peak torque deficiency is one of efficiency. But you said we could disregard that for purposes of arguing potential drive system capability. Certainly with the same engine input maximum the hst will output less torque no matter how high a hydraulic pressure you design for, because they are less efficient. I didn't think that's what we were arguing. I though you suggested there was some inherent weak link in any hst system requiring it to give up before a geared system due to some imagined restriction on relief pressure... which just isn't so.

xtn

 

[xtn]

No I replied with clarification to someone who quoted me, guess I was raised to believe it's polite to do so.

I never said you needed to stop debating, I just said to me it wasn't worth my time reading.

Got it. In that light it's perfectly reasonable.

xtn

 

[k0ua]

In a theoretical way yes. In a practical sense all one would do is shift to a lower gear.

Here's a simple question for HST tractor owners. In low gear can you spin your tires? Yes or no. I can, actually pretty easily.

Question #2. Is there any difference between a gear tractor spinning it's tires and a hst tractor spinning it's tires?

I can easily spin my tires in Lo or Med. But not in HI.. It just goes into relief.
Oh, and that is with loaded tires, and 750 lbs on the back

James K0UA

 

[TBarD]

Certainly with the same engine input maximum the hst will output less torque no matter how high a hydraulic pressure you design for, because they are less efficient. I didn't think that's what we were arguing. I though you suggested there was some inherent weak link in any hst system requiring it to give up before a geared system due to some imagined restriction on relief pressure... which just isn't so.
xtn

I agree... The relief pressure limit isn't any fundamental issue for a properly designed HST system. In a lower gear range (which lowers the range of hydraulic pressures required) the maximum engine HP will be reached before the maximum relief pressure. A similar situation holds for a gear drive system with a clutch. The main drawback of HST is overall drive efficiency, with at best 18% (often more) loss of efficiency, according to various studies that have been done. A gear system will be better for ag applications or possibly some applications such as road grading. HST systems are less efficient but more flexible for many applications, and the engine HP can be increased to compensate for a given size machine - PTO HP and hydraulic GPM should also benefit as a result.

In my case I originally wanted a geared machine for maximum power delivery, and because that is what I had when I was growing up on the farm, but I am glad I ended up with HST as I think it will be better and safer in steep terrain, and for construction applications. If I was spending most of my time on field work I would get a JD with a conventional gear drive.

Someone asked about spinning tires - with my M59 it is easy to spin the tires, even with the backhoe on. One can also stall the engine, although with stall guard this is not likely to be an issue. In too high a gear range it will go into relief, as it should.