Geared trannys-more low end torque than hydro ?

[slowrev]

Strangely enough, no. Many tractors have a peak Torque/HP output that is not quite at PTO RPM. Not really sure why, Bad engineering or some more sound reason ??? This has been discussed on this board a few times.

It is never at Peak RPM of the engine, because the governor needs some headroom to maintain PTO speed durig heavy loads.

 

[cowboydoc]

<font color="red">It is never at Peak RPM of the engine, because the governor needs some headroom to maintain PTO speed durig heavy loads.
</font>

You would be surprised at how many tractors this isn't true. It's mostly in your lower priced tractors where they manipulate #'s to get at a max. pto hp that isn't even close to that. Most people will never even know it though because the biggest hp equipment they run is a mower. Your bigger name tractors usually give you a true pto hp but the farther down the chain you go the farther you are from that true pto hp. There is no headroom built into and usually it's taken away from to the negative even without a load.

 

[MicroPilot]

Wouldn't the tractor be designed to run the engine RPM is at maximum HP, and choose appropriate gearing to drive the PTO at 540 at max engine HP RPM?

Peak HP and Torque RPM's are not the same. Usually peak torque RPM is lower than peak HP RPM.

 

[slowrev]

Richard,
I would think that maintaining PTO speed for up to the rated PTO HP load on a tractor is a requirement. Also with no overheating. Seems a bit misleading otherwise. My 12HP Gravely rider will do that!
Hmmm, guess I have to re-think what a tractor really is .

And people are trying to run PTO generators on these tractors ?

Another good reason to have an independent testing organization like Nebraska testing the CUT's so the consumers can make an educated decision.

Ben

 

[cowboydoc]

It certainly is a requirement for the tractors that are subjected to the Nebraska Tractor Tests. Other than the tractors tested here there is NO independent testing. A mfg. can say whatever he wants about what his hp on the tractor is and there is nothing to make them prove it. There is no govt. regulations or anything else besides maybe a false advertising claim. This was the whole reason that Nebraska originally passed the law to make tractor testing mandatory. Unfortunately nobody else followed suit. And if they are called on it they manipulate the #'s in some abstact way. This is where I have tryed to tell people about the lower end tractors not being up to par with the more expensive tractors and I'm always told I'm full of it. I have seen time and again these tractors put on a dyno and they aren't anywhere close to what they are supposed to be rated for.

 

[BillyP]

<font color="blue"> Some in here have spoken of driving into a dirtpile and stalling the drive out with hydro tranny CUT's </font>

I have no reason not to believe what they say or any reason to make anything up. I'm just telling you my experience with my tractor. You're welcome to come try to stall it anytime. It ain't gonna happen.

 

[rambler]

</font><font color="blue" class="small">(
I have no reason not to believe what they say or any reason to make anything up. I'm just telling you my experience with my tractor. You're welcome to come try to stall it anytime. It ain't gonna happen.

)</font>

I'll have no problem stalling the tractor. Yes, you can lose traction long before you stall it. But trust me, I will be able to create conditions that _will_ stall it. /forums/images/graemlins/wink.gif

Now, which part is overbuilt on your tractor model? Some the hyd pump is the big heavy part, & the engine will stall out before the hydro bypass goes. Some, the engine is the strongest link, & the hydro pump will bypass before the engine dies. This latter is more typical, and actually probably a better setup. We assume some of the engine power is going to the power steering, pto, etc. etc. So the engine is probably a bit stronger on most tractors than the hydro pump bypass setting. You don't really know, because you haven't stalled your tractor - you have lost traction before it stalled.

Not that it is important. As I said many messages up, what every you like or I like is what is a good & right tractor for you or me. Nothing wrong with either type of tranny. Buy what works for you.

--->Paul

 

[rambler]

</font><font color="blue" class="small">( here's a question - how does the manufacturer determine what sets a tractors PTO rpm - is it the peak HP rpm for the given engine ? )</font>

Peak hp is actually often produced at near stall speed - when the engine is about to die. Max torque is produced at roughly 2/3 of max engine rpm - the torque bulge which diesel engines are famous for.

The manufaturer determines engine rpm by deciding at what point the engine will fly apart, & then backing off some revolutions to give it more dependability. The engine max rpm rating is just a random number the manufaturer determines to be 'right' for that assembly of parts to give good performance & power & durability.

A big huge slow turning engine will run forever, but a small faster reving engine will be more responsive, have higher torque & much higher hp ratings, and not last as long and cost more to design but cost less to manufature. They get to decide the tradeoffs of all of the above as they design the things...... We buy them & hope we get about what we wanted....

--->Paul

 

[BillyP]

<font color="blue"> I'll have no problem stalling the tractor. Yes, you can lose traction long before you stall it. But trust me, I will be able to create conditions that _will_ stall it.
</font>

There's no doubt you could "create" conditions that will stall it. Even I could do something as simple as that. /forums/images/graemlins/wink.gif It ain't gonna happen by driving into a dirt pile with the right amount of ballast.

 

[Bird]

We've discussed this in the past, and yes, I'm one who stalled the engine on my little Kubota a couple of times. I think we've also discussed the fact that pushing the hydro pedal down farther does not give you more power, but is roughly equivalent to going to a higher gear. If I went into a pile of dirt slowly in low range until the pile stopped forward movement, I'd just spin the wheels. If I went into it slowly in high range until forward movement stopped, I'd just load the engine. And if I went into it too fast, too far down on the hydro pedal, when movement stopped suddenly it would kill the engine. Of course, it didn't take long to learn (I'd never used a hydro until I bought the '95 B7100) to avoid both killing the engine and spinning the wheels because if you spin a wheel, you make a hole in the dirt and a rough spot to run over on the next load.