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engineering question

J

john koritansky

New User
OK Guys, here's a puzzler that has my family and friends divided on an answer. We relpaced a hydraulic pump on our tractor (not IH, sorry) recently. The drive gear on the new pump was of the same circumference as the one on the old pump. BUT, on the new pump's gear there was one more tooth than on the old. So, question:will this new pump with the additional tooth rotate faster, slower, or at the same rpm as the old one in relation to the gear driving it? (I say slower. . . .) Thanks in advance.
 
Same circumference different number of teeth? Are you sure it wont bind when rolling being that your gear tooth seperation is now different.
 
My own thought is that this is probably a fairly small gear, and if the new gear truly is of the same diameter as the old one and has one extra tooth, there's a good chance you're either gonna wear out or break some teeth on either the new gear or the gear that drives it.

Have you tried to see if it will even mesh in with the drive gear yet and turn?
 
Howdy
Not an engineer (cant neven spell it)but that has never stopped me before. The only place I have seen a driven gear with a few choices of number of teeth used was on a auto speedo drive set up. The speedo drive gear used was a worm gear and would accept maybe 4 different driven gears. This is how the speedo was calibrated when it was off a bit when changing tire size etc. I say more teeth runs slower. (member I aint no engineer and my memmory is PRETTY BAD}
Bob S.
 
If you hsve one more tooth, and the same diameter, it's obvious the teeth have to be a little smaller on the new gear.
You're in deep do-do. Take it back if you can.

Gordo
 
The diametral pitch of the new gear cannot be the same as the old. As such the teeth will not be able to mesh or wear properly if they do get meshed. I believe that if it is installed and not making any noise, and working it has the same number of teeth, and got miscounted, Drive gears with little strain can accommodate some mismatch, but in my experience it will fail if it actually is a tooth different. Putting the old gear on it would be prudent if you still have it. Checking it is a great idea. I have designed gear systems for several hydraulic applications the teeth need to be very accurately machined as a set to function. replacement gears even from the same design are often noisy when used on an experienced mate.
 
If these two are spur gears, then with one more tooth (and the same circumference {or radius} of the replaced gear),the individual tooth thickness must be less in order to mesh. This means there is a lessened ability to transmit equivalent torque unless the new gear has greater material strength. Since the new gear is the one doing the driving (and not the driven one), the driven gear (the one NOT being replaced) will rotate faster by a factor of 1/N where N is the number of teeth on the drive gear. Because as you say the pump was replaced, these two gears in the new pump should have been "engineered" or developed together so there should be NO issue with meshing, strength/durability and the capacity of this new pump could be greater (because the driven gear runs faster).
 
> Since the new gear is the one doing the driving
> (and not the driven one)...

I"m assuming that by "the drive gear on the new pump" he means the gear that is on the pump shaft and so drives the pump. To be pedantically correct this is of course a driven gear.
 
Just to add, if the teeth of gears with a different diametral pitch do somehow happen to mesh (not sure that's possible) there will be significant impact loading and as JN posted failure will be quick.

If these are helical gears (which I suspect...spur gears get noisy) the "match" is even more critical.
 
I work at a transmission shop. Assuming that the gears properly mesh with each other, at a constant rpm of the driving shaft, more teeth on the DRIVE gear will speed up the DRIVEN gear output. More teeth on the driven gear would slow down the output.
 
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