Gear drive vs hydro

[Gizmo2]

I thought HST's with R4's were especially designed for sex appeal to sell to Yuppies...

Andy

NO! HST's with R4's are chick magnets and put me in the drivers seat it's all over.

 

[dynasim]

Larry,

un QED

The relief valve pressure/HST pump can be designed to stall the engine at, say 1/2(or 1/3 or 1/7, etc) the full pump capacity(go pedal actuation), with the appropriate downstream gear strengths, and therefore, the design torque to the wheels can be any value that the designer sets.

What I am saying is that the maximum torque does not have to exist at full go pedal actuation. This leads to the possibility that the maximum torque could exist at 1 mph(even if the gear ratio was 3 mph), or even lower. These are not inherent limitations, but design choices.

A gear/clutch given system would benefit from the impulse of the engine spinning as it is stalling out, but a designer would have to design that into the system as extra strength in the running gear, which could be utilized to full, not just impulse, effect by an HST(since that impulse does not exist in an HST).

What I am saying is that there are not inherent limitations to torque designable into an HST system, even if it only has 2 gears(as compared to a 8 or 12 gear system).

In an appropriately designed HST(with equivelant driveline strength design), the relief valve bypassing is telling the driver--if I were a gear tractor, my engine would have just stalled--.

re QED

I would note that tractors with creeper gears specifically and emphatically prohibit pulling significant loads while in creeper gears(presumably because one could pop something major).


Chris

 

[jake98]

the creeper gear warning may be for flippage. i agree with your explaination too. but i'm not all that edecated...

don't they compete these things in tractor pulls?

jake

 

[Gizmo2]

dynasim,
Got to tell ya, after the first read that is clear as mud.

 

[WilliamBos]

dynasim,
Got to tell ya, after the first read that is clear as mud.

I second that!! Totally clear.

 

[SPYDERLK]

Larry,

un QED

The relief valve pressure/HST pump can be designed to stall the engine at, say 1/2(or 1/3 or 1/7, etc) the full pump capacity(go pedal actuation), with the appropriate downstream gear strengths, and therefore, the design torque to the wheels can be any value that the designer sets.

[[[What I am saying is that the maximum torque does not have to exist at full go pedal actuation. This leads to the possibility that the maximum torque could exist at 1 mph(even if the gear ratio was 3 mph), or even lower. These are not inherent limitations, but design choices.]]]

[[[A gear/clutch given system would benefit from the impulse of the engine spinning as it is stalling out, but a designer would have to design that into the system as extra strength in the running gear, which could be utilized to full, not just impulse, effect by an HST(since that impulse does not exist in an HST).]]]

What I am saying is that there are not inherent limitations to torque designable into an HST system, even if it only has 2 gears(as compared to a 8 or 12 gear system).

In an appropriately designed HST(with equivelant driveline strength design), [[[the relief valve bypassing is telling the driver--if I were a gear tractor, my engine would have just stalled--.]]]

Chris

I thot about that when I was writing the post. However, when I followed thru on all the interacting variables it forced me to the conclusion that equipment is not set up that way normally. If you have a pump that will stall your engine while pumping only 1/2 its full volume at relief pressure you have got a pump rated for at least twice your engine power, or else a pump that is delivering higher pressure than designed for. The latter would only give short term benefit while destroying itself. So to be safe we need a 2x rated pump feeding a 2x rated motor. This case would give the HST range the ability to "gear" down hydraulically to equal the steady state torque capacity of a gear range twice as low. The pedal would be more sensitive tho, since it is capable of asking for twice the HP that the engine can deliver - it will stall quickly at full pedal. Also, costs of the bigger hydraulic parts factors against use of this method to an extent. Im guessing 2x is more cost effective than putting in another range, but that manufacturers would not go any further than this on tractors. Stepping up higher would be reserved for specific purpose built equipment where it is important to not have to shift, and that the $, weight, and size premium required by using much larger pumps and motors than actually needed to make use of full engine power would be worth it. Skid Steers probably fit this category.

[Since it takes slightly more pressure to flush more fluid thru the relief the max torque is only available at full pedal, at least momentarily. It is just not sustainable in your posited systems.]

[Dont see how you could possibly get it without eliminating relief. It would last til the 1st time you tried to pull a BIG load in hi range. No warning. Engine doesnt even bog with careful pedal. Pressure just keeps climbing til things move or break.]

[Not necessarily true, and most likely not. Rather - Sorry the wheels have stopped. If I were a gear tractor I might be losing rpm, but I wouldnt be wasting power pumping fluid into the sump thru a relief valve.]
larry

 

[patrick_g]

I had an opportunity to see a gear tractor in operation today. A friend brought his JD over to unload 50 gal barrels from my dump trailer. I put 14 each 50 gal barrels in the trailer so when the feed delivery guy filled me up most of it would already be in barrels and I wouldn't be scooping it out 2 gal at a time with a bucket to put into a barrel (like last year.)

His cute lil JD gear tractor (about 30 PTO HP or so) has an adjustment to set the speed (sensitivity) of the 3PH but none for the loader so with any reasonable RPM the loader is really herky jerky, way too spastic for delicate control but that is not because it is a gear tractor.

Being a gear tractor he has optimized his routing to fit it and it is different from my routing using a hydrostat. He drives and positions the tractor to reduce the number of shifts and clutch actions he is required to make. Boy oh boy what a difference between his gears and my hydrostat. He nearly crushed me against the side of the trailer (I will not work on foot so close around a gear tractor again.)

We were using my barrel lifting clamp (HF $29) which had always worked perfectly for me (smoothly engaging hydraulics) and NEVER lost a barrel. His herky jerky hydraulics (almost like having on off switches not proportioning valves) dropped two barrels but close to the ground and they didn't turn over.

The hydrostat is just head and shoulders over a gear tractor for working to load/unload a trailer with pallet forks or bucket or chain(s). It gives far superior control in tight quarters and when inserting a pallet fork or nudging forward or back just an inch or two with smooth control.

I might not have been able to do the job twice as fast but I could have reduced the time at least 30-40% for the job and had much smoother control of in-close work.

I'm not trying to persuade any happy gear heads to change tractors, I'm just reporting an actual observation of a real world task. If you don't need fine precision control or fast convenient direction changes don't worry be happy with a gear tractor.

It is like welding to a degree. If an AC only buzz box does all you need and you don't want or need better then be happy don't worry keep your buzz box and let others go MIG, TIG, flux core, or...

Pat

 

[MossRoad]

I had an opportunity to see a gear tractor in operation today. ...

Pat

Makes all the difference seeing it first hand. Everyone owes it to themselves to try them out.

 

[dynasim]

Larry,

I guess my point was that it wasn't necessarily true that HST's put less torque to the ground than gear tractors. I am not a tractor designer, so I don't know what they do. I do know what I would do.

Thanks for the insight.

Chris

 

[Soundguy]

His cute lil JD gear tractor (about 30 PTO HP or so) has an adjustment to set the speed (sensitivity) of the 3PH but none for the loader so with any reasonable RPM the loader is really herky jerky, way too spastic for delicate control but that is not because it is a gear tractor.
Pat

A 5$ flow restriction orificed fitting from the supply store would take car of all that...

soundguy