What does "At rated engine RPM" mean?

[TNhobbyfarmer]

I did some spraying this weekend with a PTO driven sprayer. It is helpful to know tractor speed when spraying. My users manual has a chart that tells speed in all gears "at rated engine RPM". What does that mean?

 

[kuboman]

I did some spraying this weekend with a PTO driven sprayer. It is helpful to know tractor speed when spraying. My users manual has a chart that tells speed in all gears "at rated engine RPM". What does that mean?

Usually means max underload rpm which is usually 2-300rpm below max high idle rpm.

 

[wrooster]

I did some spraying this weekend with a PTO driven sprayer. It is helpful to know tractor speed when spraying. My users manual has a chart that tells speed in all gears "at rated engine RPM". What does that mean?

i would take "at rated engine RPM" to mean the engine RPM associated with maximum torque.

For example, the gearing will be set up such that the PTO will be turning at 540RPM at (or slightly above) the engine RPM associated with maximum torque. This is by design.

Wrooster

 

[LD1]

I have always taken it at WOT. MAx RPM.

When you are looking at the speed chart, it will list the MAX speed for each gear "at rated RPM", and that is the MAX the tractor will go in that gear. (Unless you are going down hill and hit the clutch)

 

[dynasim]

It is the speed at which the pto(not engine) turns at 540 rpm. The power and speed references for all tractors I have been follow that rule.

Chris

 

[jonyyuma]

I have always taken it at WOT. MAx RPM.

When you are looking at the speed chart, it will list the MAX speed for each gear "at rated RPM", and that is the MAX the tractor will go in that gear. (Unless you are going down hill and hit the clutch)

Overspeed, which might be 750rpm above max rating, might get the connecting rods mixed up???

 

[LD1]

Overspeed, which might be 750rpm above max rating, might get the connecting rods mixed up???

That would only happen IF coasting down a big hill with the clutch in and you let the cutch out in too low of gear

 

[rbargeron]

I did some spraying this weekend with a PTO driven sprayer. It is helpful to know tractor speed when spraying. My users manual has a chart that tells speed in all gears "at rated engine RPM". What does that mean?

Pretty sure they are talking about the rpm that would give 540 pto rpm. Calibrating a sprayer for accurate delivery of material per acre takes some doing.

 

[murphy1244]

That would only happen IF coasting down a big hill with the clutch in and you let the cutch out in too low of gear

Would they switch cylinders then? I hate when that happens.

 

[jonyyuma]

Would they switch cylinders then? I hate when that happens.

I really don't know if you could get one to go into overspeed?? I remember seeing it on some big trucks dashes years ago?? As to breaking connecting rods only had that happen twice, and it was on single-cylinder engines. Once i promoted it by holding govenor on Mini-bike for a little more speed?? My tractor has a good govenor, but i still don't try to force revs...Only operated it WOT with the tiller fully engaged into the clay soil..But it is a mess when a diesel pops a piston and starts that old hard slap??Ask me how i know it sounds on a 1000+hp..Gen-set???

 

[LD1]

Would they switch cylinders then? I hate when that happens.

No. I dont think they would switch. But they may make a run for it and vacate their cylinder

 

[boggen]

you should have some sort of RPM meter in your dash, and then a mark on it, for 540 RPMs for the PTO. purely guessing, but i would assume when RPM's are right at the 540 RPM mark on the gauge. is the speed in given gear your tractor will move.

the 540 RPM for the PTO. will more likely be green, and max RPM's will be in red.

i figure many implements on tractor are setup to run at 540 RPMs. and the chart for ground speeds. are there to help figure out ground speeds when running an implement off the PTO shaft rotating at 540 RPMS.

to me it just sounds funky, to give max ground speed, speed ratings for each gear. for max RPMs of engine. it is not a truck or car. that drives down the road, but it is a tractor that will / could be used for many things, and need to figure out how long something might take.

then again folks are not always thinking and calculations or like could have went in one ear and out the other, while numbers were put together for the manual.

 

[284 International]

The rated engine speed is the maximum engine RPM for more or less continuous use. It is not always the same as PTO speed, but is frequently close. Here is a page from the Nebraska Tractor Test for a Kubota L245. The rated engine speed is 2800 RPM, yielding a PTO speed in low gear of 622 PTO RPM. To achieve 540 RPM, the engine is operated at 2430 RPM. The other two PTO gears require approximately the same engine RPM, just over 2400 RPM.

I think the idea behind listing the speeds at rated engine speed is to assist in matching implements or doing calculations for, say, mowing or seeding per acre. The machine allows for some minor adjustment of ground speed by the throttle, but should generally have the throttle set in the operating range, from say a bit below PTO rated speed to rated speed. Outside of that variability, a different gear should be selected to keep the engine at the appropriate point in its power band. There are obviously exceptions, but I think that is the general idea.

 

[jonyyuma]

AS Stated, the Maximum RPM, is in RED..but not a red line....I thought---that the governor would slow the engine,Before it reached the speed to wreck itself...Sort of like a REV-Limiter...I really don't think it will now, the governor only picks up the speed when it needs it pulling a load?

 

[LD1]

The rated engine speed is the maximum engine RPM for more or less continuous use. It is not always the same as PTO speed, but is frequently close. Here is a page from the Nebraska Tractor Test for a Kubota L245. The rated engine speed is 2800 RPM, yielding a PTO speed in low gear of 622 PTO RPM. To achieve 540 RPM, the engine is operated at 2430 RPM. The other two PTO gears require approximately the same engine RPM, just over 2400 RPM.

I think the idea behind listing the speeds at rated engine speed is to assist in matching implements or doing calculations for, say, mowing or seeding per acre. The machine allows for some minor adjustment of ground speed by the throttle, but should generally have the throttle set in the operating range, from say a bit below PTO rated speed to rated speed. Outside of that variability, a different gear should be selected to keep the engine at the appropriate point in its power band. There are obviously exceptions, but I think that is the general idea.

Good post with sources to back it up:thumbsup:

I wasnt for sure, But like I said, I had always thought that "rated" speed was max speed that the governor allowed. Because for the speed charts, if it gave speed listings for PTO speed, I believe it would say "speed @ PTO rpm."

 

[MHarryE]

If you move your engine speed control to its max position with no load except for parasitics like the fan and alternator, you are at high idle. For my particular Kubota, an L5740, this is 2920 rpm. When I start to drive the engine speed quickly drops until it reaches rated speed which is 2700 rpm. This is where the engine produces its maximum power. A governor on a mechanicaly controlled engine such as all current Kubota CUTs works with an overspeed range, typically about 5% to 7% over rated engine speed. Its physics - the governor needs to sense a speed change for it to do its thing - deliver more fuel - so they will have this band from hi idle to rated speed. All of the CUT Kubota power curves I have seen then drop off in power once they are lugged down below rated engine speed. Then there is PTO speed. My L5740 is 540 rpm at 2590 rpm or 110 rpm below max power. The performance curve for the engine in my L5740, a V2403-M-T-E3B shows about a 2 HP drop from 2700 rpm to 2590 rpm so it isn't significant. Some of our tractors have a much larger difference between rated engine speed and their either 540 rpm or 1000 rpm PTO speed.

My L5740 drops from its 2920 high idle quckly when I start doing anything, but the power comes on quickly and it takes some pretty good pulling to get it to 2700 and then it keeps on dropping. Our largest John Deeres on the other hand, with their electronic engine controls, have faster power response. Nice, but they cost a whole lot more and the L5740 works a whole lot better for the utility jobs it is designed for.

 

[284 International]

Thank you for the compliment.

... I had always thought that "rated" speed was max speed that the governor allowed. Because for the speed charts, if it gave speed listings for PTO speed, I believe it would say "speed @ PTO rpm."

I think you are right in saying this; it's kind of a choice of definitions. The governor is designed to limit the engine RPM to whatever the manufacturer says. That is the "high idle" RPM, as MHarryE said. The machine should be working at "rated RPM," which is the engine speed where it can operate indefinitely until service intervals are reached.

The ground speed would be listed according to PTO RPM, rated RPM, or whatever else the manufacturer thinks. To find the difference, you could divide PTO RPM by rated RPM, then multiply by the travel speed to get the tractor's velocity at PTO RPM. I think they probably use rated RPM since everything else in their data set likely has that, and most people are lazy.