Reverse Bending in Pnaetary Gear Set 1

[ukjay1]

Just looking for opinions on reverse bending of idler/planet geat in a planet gear set.
The AGMA de-rates and idler by 30%, from our experiance here from field observation and testing this
seems way to conservative for this,and this forces the planet gear to be wider or having to some addendum modification
to make up for this. Most of time we've seen the sun gear wear out long before planets with 3 or 4 flanks in engagement.

Just want to get some thoughts on what other are doing and any other recommendations.

Thanks
Jason

 

[tbuelna]

ukjay1,

The AGMA documentation I recall suggests using 70% of the unidirectional bending stress allowables for reverse bending like that seen in idlers/planets. With a simple epicyclic, there are many considerations with bending stress. One being the different contact ratios at the internal ring/planet mesh and at the sun/planet mesh. Another factor is the different number of load cycles each tooth on the sun and planet gear is subjected to. There is also the effect of face misalignments.

There are several commercially available gear design/analysis softwares that actually do a very good job of iterating the geometry of epicyclic gears to balance factors such as fatigue life, relative contact sliding, etc. Definitely worth looking into.

Good luck.
Terry

 

[mfgenggear]

reverse bending of idler/planet geat

http://www.gearcalc.com/index.html

HTH
mfgenggear