Needle roller thrust bearing

A needle roller thrust bearing comprising:

• an annular cage having a plurality of cage pockets radially around the annular cage;
• and
• a plurality of rollers respectively housed in the plurality of cage pockets, the plurality of rollers being disposed between a first raceway surface and a second raceway surface of the thrust bearing that axially face each other, the cage and the plurality of rollers being provided in an annular space defined between the first raceway surface and the second raceway surface such that lubricating oil flows in the annular space from a radially inner side to a radially outer side, wherein:
• the cage includes:
• a plurality of inner grooves, each of the plurality of inner grooves connecting a circumferentially adjacent pair of the plurality of cage pockets by connecting radially inner areas of the pair of cage pockets,
• a plurality of drainage grooves, each of the plurality of drainage grooves extending in a radial direction of the cage to an outer circumferential surface of the cage and opening at the outer circumferential surface of the cage to drain lubricating oil radially outward in a circumferential area including radially outer areas of the plurality of cage pockets, and
• a plurality of middle grooves respectively located between and separating each of the plurality of inner grooves and each of the plurality of drainage grooves.