Really Kubota! rated speed 395 RPM faster than PTO speed??

[bilrus61]

I know there is some fudging on the horsepower/pto but this takes the cake. I was looking at a cute M9540 Low profile tractor at my dealer today and came home and checked out the specs on the Kubota website. It says it has PTO power of 84 horses at rated speed of 2600 RPM. But wait! To get 540 RPM at the pto you have to lower the engine rpms to 2205?!?! Thats is almost 400 rpm lower to get at the speed where you need to actually work a implement on the pto. No mention of the horsepower at the PTO at 2205 rpm. I knew the rated speed on my 5040 is 2600 and the 540 pto speed is 2550. So 50 RPM.....not a big deal. But 400?? Even the standard M9540 runs at 2300 RPM to get 540 at the PTO. Goodness........the M9540 intstead of being a usable 84 PTO horsepower must be down to about 73 or less with that much drop in the engine speed to get it low even to get to 540 on the pto. I've always admired the bigger M series but now they kinda look like cheats. Anyone know where you could find the actual PTO power on a M9540 while its turning a mower at a actual 540 RPM?

 

[JoeL4330]

This is not my forte but it's torque that does the work and the torque curve rises with engine rpms but tops out (and actually turns down--i.e., reduces) at an engine speed that is just about where 540rpm is on the PTO [that is, PTO gearing is usually designed so that 540rpm at the PTO is just a little past the torque peak of the engine].

Horsepower, however, continues to climb with rpm and doesn't level off (on so-called "high-speed" diesel engines) until a substantially higher engine rpm, where the engine simply cannot (safely) go faster--the engine "red line"--because of friction in all the various moving parts, but principally because the combustion, depending on compression ignition, isn't "timed". That's why diesels are usually characterized as high-torque, low-speed engines.

So, was Kubota "cheating"? Well, it would be better if implement manufacturers quoted PTO torque requirements at 540rpm...and, tractor manufacturers provided that figure ...or, better yet, actually showed the torque and hp curves.

Some implement manufacturers just quote min. hp. without specifying engine or PTO measurement ...mostly works because tractors and implements are both forgiving over a modest range. But, if you are trying to operate at the bleeding edge, your calculation back to PTO hp. makes sense. The 83hp PTO operating point is providing less torque ...and less fuel efficiency, and more noise, and shorter engine life ...etc. etc.

 

[MHarryE]

Our JD 7730 is 153.29 HP at 2100 rpm rated engine speed, 168.19 HP at 1954 rpm engine speed to obtained standard PTO speed or 146 rpm lower than rated rpm, and maxes out at 172.51 HP at 1900 rpm. Peak torque is actually obtained at 1600 rpm, a 47.1% increase over torque at rated PTO speed. Do I feel cheated because rated engine speed is 146 rpm higher than it is to get 1,000 rpm or 540 rpm PTO speed (whichever we are using)? Not one bit. It has so much PTO power at rated PTO speed that it will probably rip the innards out of the baler which is the only PTO driven implement we use on this tractor. My thought of the large speed difference is the accidental possibility of overspeeding a PTO diven implement. The ISO standard is 540 ｱ 10 rpm. If you inadvertently run at high idle instead of rated PTO speed your PTO will be running 636 rpm which could cause damage. The tachometers don't work on most of my nephews tractors so when I help him out I have to set engine speed by seat of the pants and noise level. Fortunately I haven't blown up anything of his yet.

 

[bilrus61]

Our JD 7730 is 153.29 HP at 2100 rpm rated engine speed, 168.19 HP at 1954 rpm engine speed to obtained standard PTO speed or 146 rpm lower than rated rpm, and maxes out at 172.51 HP at 1900 rpm. Peak torque is actually obtained at 1600 rpm, a 47.1% increase over torque at rated PTO speed.

huh?? Your engine produces MORE horsepower the the slower it runs? I learn something everyday. I know torque will rise but are you sure your horsepower goes up 20 hp when you turn it down 200 RPMs?

 

[piller]

In my dealings with Kubota they have been straight up and I don't think they are fudging or cheating.

I think that the M9540 will make advertised PTO HP (84) at the 2205 engine rpm (540 pto rpm) speed. I base this on looking at the Nebraska Tractor test reports available for other Kubota tractors which use variants of the Kubota V3800DI-T engine used in the M9540. Reports are available for the M100X and M108S which show that the Kubotas make advertised PTO power at 2600 rpm, 2500 rpm, and 2205 rpm. See:
TTL test reports/Hurliman, Valmont, Zetor

By the way, I have the M8540 and I think it's a great tractor

In the Kubota sales brochure that I have (Cat. No. 5304-01-US) it shows a graphic with net internal engine power, torque, and fuel use vs engine speed for the M9540. The graphic shows engine net internal data not PTO data. The net internal engine HP does indeed rise all the way from 1000 rpm to it's maximum at 2600 rpm as expected. However, the Nebraska test reports show PTO power output is fairly flat at the 2600, 2500, and 2205 rpm data points.

Hope this helps.

 

[bilrus61]

Thanks for the info. Interesting reading. I appreciate the time ya'll spent with your replies.

 

[5030]

This is not my forte but it's torque that does the work and the torque curve rises with engine rpms but tops out (and actually turns down--i.e., reduces) at an engine speed that is just about where 540rpm is on the PTO [that is, PTO gearing is usually designed so that 540rpm at the PTO is just a little past the torque peak of the engine].
Horsepower, however, continues to climb with rpm and doesn't level off (on so-called "high-speed" diesel engines) until a substantially higher engine rpm, where the engine simply cannot (safely) go faster--the engine "red line"--because of friction in all the various moving parts, but principally because the combustion, depending on compression ignition, isn't "timed". That's why diesels are usually characterized as high-torque, low-speed engines.

So, was Kubota "cheating"? Well, it would be better if implement manufacturers quoted PTO torque requirements at 540rpm...and, tractor manufacturers provided that figure ...or, better yet, actually showed the torque and hp curves.

Some implement manufacturers just quote min. hp. without specifying engine or PTO measurement ...mostly works because tractors and implements are both forgiving over a modest range. But, if you are trying to operate at the bleeding edge, your calculation back to PTO hp. makes sense. The 83hp PTO operating point is providing less torque ...and less fuel efficiency, and more noise, and shorter engine life ...etc. etc.

It may not be your forte' but you are right on. My M9 and my 105S are both rated a peak horsepower above the recommended 540 PTO rpm engine speed of 2250.

The PTO speed is geared to the maximum torque output of the engine, taking into account factors like torque rise and boost pressure.

Pto power has little to do with available horsepower and everything to do with torque output or that ability to peform meaningful work at an rpm that's the most efficient rpm the engine is designed to run at and that's not maximum horsepower but rather maximum developed torque.

Anytime I buy a tractor, I look at available torque and at what rpm, not horsepower. Horsepower is for cars, not tractors.

 

[5030]

huh?? Your engine produces MORE horsepower the the slower it runs? I learn something everyday. I know torque will rise but are you sure your horsepower goes up 20 hp when you turn it down 200 RPMs?

I don't think so. An electric motor does but not an internal combustion engine. An electric motor produces maximum torque at stall because of magnetics but an internal combustion engine produces lower tirque at lower rpm because torque is the direct result of induced centrifugal force, piston speed, fuel delivery. compression and other factors.

It don't work that way, even if it's green.....

Come to think about it, the only thing green does is empty your wallet faster.....

 

[hizoot]

John Deere Green Carpet

look at the video entitled "powerful advice"

 

[crazyal]

Horse power is torque times RPM and it's a unit of measurement of an amount of applied force over a measured distance vs how long it takes. Torque is just force, neither time or distance are a part of it's measurement.

Since the torque curve for the engine rises to a peak then drops off as RPM increases the max torque will not be at the same RPM as the max HP. Since torque is what turns things (force) it's where you want the PTO geared to match up with your engine.

Kubota could have given the rated HP at the PTO speed but they couldn't call it the max HP. I'm sure every brand of tractor out there uses the max HP as the number they like to publish, bigger is better, right? It's also why when buying a tractor using HP is not the best way to compare tractors.