bearing materials for planet gears

I have always used needle rollers with harden pins. I wish there was a way to make a pressured plain bearing work because of the loads and speed. I sometimes design high speed and high load PSRU's (power supply reduction unit) for aircraft.To make them last until the overhaul requirement I spray lubricant right on the spinning gear, even though the gears pick up some from the sump area..

Cheers

I don't know anything but the people that do.

High performance, aircraft planetary gearset planet spur gears, typically employ spherical roller bearings. The spherical roller bearings allow for pin misalignment due to torsional wind-up in the planet carrier. Otherwise, the gears will edge load.

If you're using a journal or plain bearing, as opposed to a rolling element bearing, and you have high radial loads, do everything you can to ensure the bearing operates in a hydrodynamic condition. The bearing substrate should be a material that has adequate fatigue strength, and it should have a thin overlay of a softer material to provide embedability of debris.

If, as you say, there is excessive deflections of the journal, then the bearing will edge load and fail. Regardless of what bearing material you use.

For automotive use, use whatever is currently used, there is no need to re-invent the wheel. This means needle roller bearings in the planetary. The GM powerglide is the standard drag racing transmission. Many companies are supplying upgraded powerglides. They have stayed with needle rollers which seem to work well. Using currently mass produced part numbers will mean much lower cost. Same argument goes for a differential. Use proven and mass produced parts if at all possible.

The gears should be a high quality low carbon steel that is surface hardened to HRC58-62. The bearing needles and pins are typcially SAE52100/100CR6 or equivalent through hardened steel brought up to HRC58-64.

All surfaces must be ground to size and super-finished beyond the quality that a normal machine shop could achieve.

Single digit microns make the difference between life and death in these parts. Some manufacturers will even sort components to optimize fit. Others size the loose rollers vs. the bore so that they will lock securely in the gear until the pin is inserted. Still other choose to use needles mounted in a cage - reducing life but improving speed and friction performance.

What I mean by this is to support Matt51 - in a modern automatic transmission don't go messing with this stuff unless you REALLY know what you are doing. Use OEM parts.

dicer
I reread your question and I remember a failure (not mine) of a PSRU. It was the planet carrier for a Ford C6. It seems the (3) planet carrier is a cheap aluminum casting, and after reading tbuelna's post I wonder if that is what caused the failure in deforming under load to edge load the needle bearing.
I have used OEM from an Allison trans before as it was close to the load and speed requirements that I needed at the time.

Also a side note is the gear vendors will offer different grade of gears. I use between 7 and 10 as budget allows.

Cheers

I don't know anything but the people that do.