Why 540?

[mikester]

Why not 500 or 632 or whatever?

There must be some mechanical basis for standardizing on 540 rpm for PTO speed.

Let's light it up, tractor gurus!

I think its due mostly to engine RPM. Early motors were designed to run at 1800 rpm max. Put on a 3:1 gear box and that gives you 600 rpm at the PTO. Most engine torque curves peak before the max rpm then drop off. 540 PTO rpm is the closest to max engine torque curve peak for maximum power output without redlining the motor.

 

[CobyRupert]

I think its due mostly to engine RPM. Early motors were designed to run at 1800 rpm max. Put on a 3:1 gear box and that gives you 600 rpm at the PTO. Most engine torque curves peak before the max rpm then drop off. 540 PTO rpm is the closest to max engine torque curve peak for maximum power output without redlining the motor.

Seems like a good answer.

....but then why not a 2:1 gearbox (~810 rpm) or a 4:1 (~405 rpm)? Does torque vs. horsepower vs rpm and the universal joint technology of the day come into play? It seems that one would try to find a good balance in not having too bulky pto shafts and universals required for a higher torque/lower rpm ratio versus having them spin too fast, and wearing and being out of balance in a high rpm/low torque ratio.
Maybe 3:1 (540 rpm) was the sweet spot in balancing torque/rpm and the material construction of universals for the horsepowers they were dealing with in the 1920's or 30's, etc..?
...I'm just guessing...

 

[jeff9366]

International Harvester introduced the first practical pto on a farm tractor in 1918.

I have read in WWI histories that tractor PTOs were on at least some, perhaps many, French internal combustion farm tractors during the 1914 - 1918 war. American soldiers could see how PTO reduced labor with French men conscripted into the forces and women and children doing a great deal of the heavy farm work.

Was the flat belt (thresher) connection considered a PTO in this era?

Now, how practical these early PTOs were, rotational speed, location on the tractor (No Ferguson Three Point Hitch until 1930s) and how standardized, I have no idea.

 

[jeff9366]

It the shaft is too fast, then you might need a gearbox on the implement to slow it back down. Theres the odd 540 but then the nice even 1000. I once saw this awesome snowblower at a show, Videos showed it was truly amazing! What they didn't seem to think was worth mentioning, is that it ran at 1000 rpm!

Subcompact and compact tractor mid-PTOs, commonly used to power MMMs and front snowblowers, often rotate at 1,000 rpm.

Ag tractors with Category 4 and Category 5 Three Point Hitch installations revolve at 1,000 rpm, not 540. No need to gear PTO down for ample power on these powerful tractors.

 

[Atchuuu]

I have read in WWI histories that tractor PTOs were on at least some, perhaps many, French farm tractors during the 1914 - 1918 war. American soldiers could see how they reduced labor with French men conscripted into the forces and women and children doing a great deal of the heavy farm work.

Was the flat belt (thresher) connection considered a PTO in this era?

Now, how practical these early PTOs were, rotational speed, location on the tractor (No Ferguson Three Point Hitch until 1930s) and how standardized, I have no idea.

Yes, IH certainly did not invent the PTO but improved it to the point that it was "practical" - Having control over the implements that would make it useful, profitable and practical probably helped too.

From WIKI - "Edward A. Johnston, an IHC engineer, had been impressed by a homemade PTO that he saw in France about a decade before, improvised by a French farmer and mechanic surnamed Gougis.[2]"

 

[LouNY]

Subcompact and compact tractor mid-PTOs, commonly used to power MMMs and front snowblowers, often rotate at 1,000 rpm.

Ag tractors with Category 4 and Category 5 Three Point Hitch installations revolve at 1,000 rpm, not 540. No need to gear PTO down for ample power on these powerful tractors.

For Ag tractors;
The main reason for going to 1000 rpm was the ability to pass the available hp to the pto the torque for 100+ hp at 540 was to much for reasonably sized
u-joints to handle. The same physical sized and rated u-joints for 50 hp at 540 rpm can transmit a 100 hp at 1000 rpm.
The increasing hp is one reason that electrically powered implements are being developed and tested. PTO shafts are becoming unwieldy because of the physical size and weight to transmit the available and desired power.

 

[buickanddeere]

Subcompact and compact tractor mid-PTOs, commonly used to power MMMs and front snowblowers, often rotate at 1,000 rpm.

Ag tractors with Category 4 and Category 5 Three Point Hitch installations revolve at 1,000 rpm, not 540. No need to gear PTO down for ample power on these powerful tractors.

1000rpm is not fast enough for those HP levels but that is sort of where they are stuck with . In hind sight instead of 1000rpm they should have chosen 1800rpm.

 

[WranglerX]

Why do we have Metric and SAE....... Because there is having a standard better than everyone flying on their own... 540? does not really matter, it was just selected as a "standard"... Actually could have been anything but one engineering group decided 540 was good enough and it was adopted universally...

Dale

 

[CobyRupert]

Sidetrack: Why 78, 45, AND 33 RPM?

You're probably either old or a young hipster if you know what these rpm's refer to.

 

[LouNY]

Sidetrack: Why 78, 45, AND 33 RPM?

You're probably either old or a young hipster if you know what these rpm's refer to.

Well I certainly don't qualify as a young hipster, but I also don't consider myself old thats for them that are 75-80.:laughing: