Needle roller bearings are often used for planetary gear bearings of a planetary gear drive in the consideration of capacity, shape and the like. Recently, full roller type needle roller bearings are often used to increase load capacity.
Patent document 1 proposes a lubrication structure for needle roller bearings used as the planetary gear bearing of a planetary gear drive. In this document, it is described that spiral lubricant retaining grooves are formed on outer peripheral surfaces of needle rollers.
Patent Document 1: JP 2007-71355 A
When needle roller bearings, especially, those of full roller type are used for a planetary gear bearing, lubricant retaining space is limited, so that there is a risk of poor lubrication if grease lubrication is employed.