Gross HP vs PTO HP - HST vs Gear

[art]

To sum it all up say you buy a rototiller that needs 17.7 hp. You say ok I'll be alright my tractor can handle that. Well now get that tractor going at max pto and max work for the tiller in the ground and all of sudden your tractor starts to bog down and heat up. You wonder what the heck is going on. Well because of the hst and anything else running it's going to drain your pto hp. So now you are only making say 15 hp and you are 2hp deficient. You won't have overstated specs. Your tractor will run the 17 pto hp if put on a dyno but when you run the hydro it will cost you hp.
Tell me where this is correct maybe I missed something.

 

[cowboydoc]

Tell me how it's not correct? I don't understand what you're saying. If you run a hydro you are going to lose more hp at the pto than if you run a gear tractor. Something has to drive that extra fluid and pump for the hydraulics to work for the hydro. The engine does and it does so at a loss of engine and thus pto hp. I don't understand why you are arguing about it? It may not be 2 hp I don't know for sure on that engine but it is going to be a loss. Maybe it's only 2% loss or 2 hp or 1 hp or .7hp. But it is going to be less pto hp to run an implement than a gear tractor. I don't know how else to say it.

The reason I used the tiller example is because most people here can't relate to a baler, chisel plow, planter, mower conditioner, combine, etc. You need to account for the decrease in pto hp when you are buying a tractor. That's why the smartest thing to do is decide what implement you are going to run before you buy a tractor. Alot of people don't even know the difference between pto and overall hp or how it's measured. To be able to have the hp to run the implement it's a pretty good idea to plan on at least 10% more hp than the biggest implement you are going to need. If you are getting a hydro I would plan on 12-15% more tractor.

 

[art]

The loss of pto horsepower is in the original pto dyno test. Most literature states for gear drive with one horsepower rating and then give one for hydro's. There is no more loss!!! From there it is the plus of a hydro to go 1/2gear or 1/2 mile per hour faster that a gear drive can't do!!

 

[JerryG]

Art,
I would like to thank you for participating on this site. I have always enjoyed your input. I also hope that you continue to do so.
If a hydraulic pump, motor or hydro drive is driven by an engine, then it will use part of the available hp. If that part is used by them, then there is less available hp for the drive wheels. Does everyone agree on the above?

 

[art]

Thanks Jerry, I tried to get the part of Doc's statement into italics but I missed the boat here. The tractor horsepower rating on the dyno doesn't go down more when operating the hydro transmission then what it is rated for on the literature. They have two numbers one for hydro and one for gear. Nothing major, but to say or infer that the hydro would overload and heat up do to the loss of the horsepower from the hydro is wrong to say on any pto operation. On a pull I would agree totally, Just like to try and keep a gear drive at the speed that a hydro might be able to rototill might stall or near stall a gear drive do to excessive lugging.

 

[cowboydoc]

"but to say or infer that the hydro would overload and heat up do to the loss of the horsepower from the hydro is wrong to say on any pto operation"

This isn't what I said Art. I didn't mean this at all. I even clarified later that it wasn't the hydro I was talking about but I was talking about having too little hp to run the implement. The too little hp is what would cause the tractor to heat up whether it was a gear or a hydro tractor. If a person maxes out their hp rating with an implement then they are going to heat up the tractor. I was trying to educate people that just because you may have a tractor rated at 17 hp doesn't mean you can run an implement that calls for 17 hp. Esp. if it's a hydro, and even with a gear tractor. Like I said before you are not going to have that full pto power that the tractor says it has to run the implement.

 

[Soundguy]

</font><font color="blue" class="small">( PTO work that is where a hydro will out perform a gear drive by about a 10% )</font>

Sorry.. but I've got to agree with the others... on a gear tractor.. when the clutch is engaged.. there is a direct coupling from the engine to the pto shaft.... not much loss except in the bearings.. etc.

On a hydro.. you are using a fluid coupling on that pto.. our technology level isn't at the point of a loss-less mediua transfer yet...laws of thermodynamics are against you.. and as cowboydoc pointed out.. wasted / lost energy in that conversion system is expressed as heat.. etc...

Soundguy

 

[ScottAR]

I think Cowboy's point was for the same engine hp, the gear tractor will lose less hp at the pto than the HST.

Example: JD 4610
Gross HP 44 ( I presume at the flywheel)
Gear trans PTO HP 37
HST PTO HP 35

Now, The HST has 2hp less than the gear trans for the same engine hp. Now this is moot if one looks in the correct blank in the brochure and sizes the tractor properly, but that wasn't the question.

 

[art]

All right it is a new day and with a couple of explainations things are clearer! Any tractor has the potential to overheat if over loaded. But Doc, PTO is the only tangible rating of a tractor! You could talk any horsepower you want, net engine or gross engine, other than the old drawbar horsepower rating and not be able to put it to a relationship. When you get a car dyno tested on a wheel dyno, that takes in all parasitic loss in and the results don't even come close to the auto literature rating much the same here. That is like a PTO test on a tractor or the older drawbar horsepower rating not used in 20 years. Now, for the minuses and the plus's of a hydro trans and the gear transmission to attempt answer the original question. If you did have a load that you couldn't move with a gear drive, mind you, not smoking the clutch or spinning to China this would be for pulling or lets say a pto horsepower over load you would have the best chance of moving or using it with a hydro do to the flexibility of the speed control baring the use of a 24 plus speed transmission maybe! The pto drives of tractors I'm familier with are not run thru the hydro unit so there is no loss with that aspect of it as suggested by sound guy, they are a direct shaft from flywheel connection to the clutch pack that engages it going around the hydro drive units. That means that is all the prasitic power loss of the stationary power is taken into account for the extra pump on pto horsepower. The hydro used for a direct or pulling transmission for a type of tillage tractor ie: plowing or discing would actually be off from a gear drive by about 10 to 15% on a hydro for you boys who like your gear drives. That loss would only show up on the old drawbar horsepower test at best and would only show on a long run as a hydro can start a heavy load easier then a gear drive without wheel spin or clutch slippage. On the otherside farmers and end users talk of improved efficency for loaders, and PTO work ie; mowing and tilling often gaining the 10 to 15% over the gear. There are places for both and thru the past 30 plus years I've found where they are both good and have there advantages. We all have our favorites for what ever reasons and just because we like our way of doing things does not mean something else might not come along and do it better. Just think, isn't bigger better? Only if the room is there to use it to begin with!

 

[JerryG]

<font color="blue"> The pto drives of tractors I'm familier with are not run thru the hydro unit so there is no loss with that aspect of it as suggested by sound guy, they are a direct shaft from flywheel connection to the clutch pack that engages it going around the hydro drive units. </font>
That was one of my questions. Thanks