Come to think on it, why don't devices with smaller engines have a PTO?
I could imagine a PTO on a lawnmower and a raft of attachements:
To expand on the just-a-minute-ago post, why not a PTO for an automobile?
I can imagine a hook-up that replaces a tire on an auto's drive wheel. This hook up could connect to a stationary item such as a generator or water pump.
A car at idle burns about a gallon of gas per hour, which is not too much different that the consumption of a medium-hefty generator.
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?
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)?
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.
Some trucks have a PTO. The ones I can think of run a hydraulic pump, like a dump truck and boom truck.
I think some cars and pickup trucks have an added engine driven hydraulic pump, which may be more flexible than a PTO.
Presumably if you ran a generator from a PTO the gas consumption would go up because you are supplying power that has to come from somewhere.
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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...
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.
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...
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Cost. Liability. Need more?
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Speaking of which, is that really any different than the throttle speed control on conventional gensets? They don't do anything more sophisticated than that, do they (at least the homeowner variety)?
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You and Roy both talked about a 540 RPM PTO. That sort of implies that it is a constant speed and I wondered if it was and how they did it - inquiring minds want to know. Your answer that it is not fixed answered the question, thanks.
Back when I was around farm tractors (when I was a kid) they had maybe 6 gears forward and one reverse. Now air conditioning and GPS control. Then again, the farm I used to spend time on was 160 acres, a significant part pasture. Wouldn't work so good now. Compared to now the machines were really simple, but I enjoyed nosing around the machinery shed and tractors.
My lawnmower has a very rudimentary governor using a blade in the cooling air flow. Would think small generators would have something much better, but I haven't looked at a generator control. There is a big change in mechanical load from low power use to max, for which there must be some kind of speed regulation to control frequency.
Or the DC generators feeding an inverter.
I was thnking the same thing. I would really like a snowblower / generator / power washer / pump. It would get used infrequently, but often enough to keep it in good order.
Wanna start a business? I can supply the ideas, you the capital. We'll make millions!
My ex's father had something along those lines. He called it a 'tractor'. I know his had snowblower, tiller, snow plow, garden plow, sickle-bar, attachments. It was in the 15HP range and had a pair of maybe 4x15" tractor tires. He could hook it to a 4x4 trailer and it would tow him and a jag of wood across a field and up a pretty steep incline.
I think it was a 1930-40 vintage Ariens--- might have been Gravely.
Jim
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