How gear train losses vary with speed
How gear train losses vary with speed
(OP)
Hi-
I am want to know how gear train losses (friction) vary with RPM. I suspect that losses increase in a non-linear manner.
Suppose that I had two spur gears with a 5:1 reduction ratio, and I increase the speed from 1000 RPM to 5000 RPM, how would the plot of friction losses versus RPM look?
I found a little bit on gear train friction at this link:
http:// gltrs.grc. nasa.gov/r eports/200 6/TM-2006- 214344.pdf
Can anyone recommend other references?
I am want to know how gear train losses (friction) vary with RPM. I suspect that losses increase in a non-linear manner.
Suppose that I had two spur gears with a 5:1 reduction ratio, and I increase the speed from 1000 RPM to 5000 RPM, how would the plot of friction losses versus RPM look?
I found a little bit on gear train friction at this link:
http://
Can anyone recommend other references?





RE: How gear train losses vary with speed
A turbine design engineer would have a governing design point of 'cold start,' when figuring starting torque. The existence of ice can greatly boost this starting torque.
RE: How gear train losses vary with speed
Thanks, but I am confused.
When I look at the experimental results in the attached plot from the NASA link above, it shows the efficiency being lower (and hence friction higher) as the speed goes from 15,000 RPM to 12,500 RPM.
This seems to contradict the argument about " more heating in the lube and a lower friction will result."
Any thoughts?
RE: How gear train losses vary with speed
Ted
RE: How gear train losses vary with speed
Am I missing something?
V
RE: How gear train losses vary with speed
Ted
RE: How gear train losses vary with speed
The NASA plot shows efficiency versus load, NOT friction versus load.
The NASA data shows that low speed (black line) has better efficiency than the high speed (red line)
This contradicts what plasgears said above.
RE: How gear train losses vary with speed
RE: How gear train losses vary with speed
You are correct that efficiency is plotted versus power. So torque is varying - good catch.
I am used to how friction torque varies in IC engines: goes up slightly faster than linearly with speed over the normal engine speed range.
Surely there is a plot in a book somewhere that shows how friction in a gear train changes with RPM, assuming constant torque.
RE: How gear train losses vary with speed
RE: How gear train losses vary with speed
With gears it's not really RPM that's important, it's pitch line velocity. At low pitch line velocities (<5000 fpm), sliding losses at the tooth contact will likely predominate. At higher pitch line velocities, gear tooth windage losses and bearing churning losses can get out of hand quite rapidly. At pitch line velocities above 10,000 fpm, windage and churning losses can be several times the gear tooth sliding losses, unless the oil scavenge system is carefully designed. Just picture the gear teeth as little propellor blades spinning through a dense atmospheric mixture of air and oil droplets.
And ultimately, all of these windage and churning losses are converted to heat in the lube system.