Parallel Shaft Gearbox With Two Motor Input
Parallel Shaft Gearbox With Two Motor Input
(OP)
I'm looking into a Falk V Class parallel shaft gearbox. This will be driven by two inverter duty motors at 10 hp each. Would it be correct to size this gearbox for 20 hp times necessary service factor? Would the motors have to be speed matched to get the 20 hp? Seems like a simple question, but it's got me puzzled. If one motor was slightly slower than the other would it then actually provide power? See attached sketch for clarification.





RE: Parallel Shaft Gearbox With Two Motor Input
Yes, it needs to size for the 20 hp. Not for drive itself, but because at some time or another, one of the motors will fail (or will be "behind" the first motor) and so the entire load will come up to the first motor for a short time. At that overload, the first motor (you hope!) will fail/drop out due to over-currrent, and then both loads will fail.
Under the real world, one or the other loads will vary up and down as things come up and vary: clumps, torques, seizures, feed rates change, humidity, pressure, temperature, etc. You've got a difficult problem. Can you use clutches on the two loads to drop off one or the other rather than kill both?
RE: Parallel Shaft Gearbox With Two Motor Input
Thanks for the response.
RE: Parallel Shaft Gearbox With Two Motor Input
RE: Parallel Shaft Gearbox With Two Motor Input
As for clutches, if both motors were either equipped with mechanical one-way clutches, perhaps centrifugal, or electrically actuated so that you could wire them to be mutually exclusive (only one could be engaged at a time), then I think this would work fine using a gearbox rated at 10-hp and non-speed matched motors.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
RE: Parallel Shaft Gearbox With Two Motor Input
RE: Parallel Shaft Gearbox With Two Motor Input
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
RE: Parallel Shaft Gearbox With Two Motor Input
In any case I would recommend designing for the full 20 hp and until you are told otherwise no additional controls, clutches, torque matching, etc. These are simple units and if they are not in the design they may have a reason to not be included that they haven't been told.
RE: Parallel Shaft Gearbox With Two Motor Input
Thanks again.
RE: Parallel Shaft Gearbox With Two Motor Input
But another idea not mentioned would be to just make it 20hp as Doug says for CYA, and run both IDENTICAL motors off the line or THE SAME 20HP VFD [put both motors on its output in parallel - with proper TOL], if variable speed required. Because of the asynchronous motor's slip, BOTH motors WILL share the load close enough to be no problem. They won't fight each other, the total energy used will be what the load required (assuming your description is right, 5hp each) and all pieces should last a very long time.
www.KilroyWasHere<dot>com
RE: Parallel Shaft Gearbox With Two Motor Input
David