Transmission power rating

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I’d like to know more about gearbox power rating… How much power can a gearbox handle? What are the causes of failure?

If a gearbox can take 100 Hp, then does that mean that:
a) it can take half the torque at twice the RPM?
b) it can take twice the torque at half the RPM?

In other words, is RPM or torque the critical factor? And where does failure first occur? At the gears themselves or shafts, dogs, etc?

This is a motorcycle application with case harden heat treating


The are many variables that can impose operational limits on transmissions. With a conventional AT that has a rather low system efficiency at certain operating conditions and thus a high heat rejection rate, there would probably be an input power limit. For other cases, where fatigue life of gears, shafts, bearings, etc. is of concern, both the level of torque (load) and the rate of accumulation of load cycles is what matters. All other things being equal, fatigue cycles will accumulate faster at higher speeds. But the fatigue life of gears, etc. can vary greatly depending upon the combination of load/speeds it is subject to. For example, a gear may have an L10 life of 2000 hours at a mean load of X, but at a mean load of 2X that same gear may have an L10 life of only 100 hours (assuming the same speed).

To provide an answer to your question, you would need to provide a very detailed description of your analysis case and transmission design.

for starters
For the gears (carburized steel)
aerospace stuff AMS 6265 (AISI 9310 steel)
it obtains case hardness of 60 HRc min , core 33-43 Hrc
have a it heat treated to case harden to .020-.025 effective case depth after grinding.

for gears & shafts (nitrided)
again aerospace stuff AMS 6471 (nitralloy 135)
Nitrided steel case hardness of 60 HRc min core 35-40 HRc
case depth .015-.025 effective case depth after grinding

just recommendations you will need to do in depth analysis
down load the data sheet.