| 摘要 |
PROBLEM TO BE SOLVED: To prevent excessive front-gear stress from concentrating into a key groove of a sun roller. SOLUTION: In a planetary roller type friction gearing provided with a follow-type sun roller 23 key-connected to the outer circumference of an input shaft 21, a plurality of planetary rollers 24 externally contacting with the sun roller 23, a ring roller 25 with the planetary rollers internally contacting therewith, and a carrier 26 arranged in an axial one side of the rollers and rotatably supporting the respective planetary rollers 24, the length of a key groove 51 formed in the inner circumference of the sun roller 23 from the axial one end to the other is so set that its tip stops on the way to the sun roller 23 in the axial direction to secure a non-formation part 55 of the key groove in the range of a contact width H.
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