On 9/28/2011 4:36 PM, bud-- wrote:
On 9/28/2011 3:32 PM, dpb wrote:
On 9/28/2011 9:56 AM, dpb wrote:
On 9/28/2011 8:59 AM, bud-- wrote:
....

How do you get variable land speed and constant PTO RPM?

PTO RPM has nothing to do w/ ground speed--independent drive train
gearing from that to axle drive shaft.
...

Well, nothing related outside the obvious that both are (for a given
gear) directly proportional to engine RPM...for the pedants
....

If I am reading that right, the axle has a direct gear ratio to the
engine (which is changed by the gear shift) and the PTO has a direct
gear ratio to the engine (which may be affected by shifting, doesn't
matter). If that is right the PTO RPM depends on the engine RPM. If the
ground speed is faster the PTO RPM is faster?

Well, the ground speed may be slower/faster (down/upshift) at the same
engine RPM but the PTO is constant at that same engine speed
irrespective of drive axle RPM...

Are 540/1100 RPM fixed? The way to get a fixed RPM would be a hydraulic
drive or variable ratio transmission (as many cars have)?

They're fixed at the rated engine RPM. Tractors are by nature constant
RPM operations w/ the desired travel speed set by gear choice (which is
why modern tractors may have as many as 24 or more forward/12 or so
reverse gear selections). Smaller utility tractors may have hydrostatic
trannies but generally larger horsepower ones won't owing to the
efficiency losses.

In field operations that aren't at all demanding requiring all the
available torque, operators may throttle back and use a higher gear for
better fuel economy but when a tractor is loaded it generally runs at
full throttle and gear selection alone sets ground speed.


If 540 RPM is not fixed how do you run a genset? You don't have to run
the genset while moving, but it would be real nice if there was speed
regulation to control the frequency.

There is, it's throttle speed (and any tractor any more has a tach for
operator feedback that will show pto as well as engine rpm).

The input rpm is set by the engine throttle speed and it has some but
not perfect regulation w/ load. If one were looking for perfect
frequency control this wouldn't be the way (but very little on a backup
generator will really matter that much on exact frequency control,
anyway, so I'd not expect it to be an issue.

It looks like I was answering a different direction of the question than
the specific answer you were trying to get to which took longer to get
to (I think now) the final destination than perhaps necessary...

--