Strain wave gearing

A strain wave gearing comprising:

• a wave generator that creates a state in which a flexible externally toothed gear is flexed into a non-circular shape and partially meshes with a rigid internally toothed gear, the wave generator including
• a wave plug having a non-circular outer peripheral surface, and
• a wave bearing attached to the non-circular outer peripheral surface of the wave plug, and including
• an outer ring having an inner peripheral surface and an outer-ring-side raceway surface formed on the inner peripheral surface,
• an inner ring having an outer peripheral surface and an inner-ring-side raceway surface formed on the outer peripheral surface, and
• a plurality of rolling elements rotatably inserted between the outer-ring-side raceway surface and the inner-ring-side raceway surface,
• wherein
• each of the outer ring and the inner ring is a component made of a super engineering plastic,
• wherein
• the plurality of rolling elements is cylindrical rollers arranged at equal angular intervals in a circumferential direction of the wave bearing,
• the number of cylindrical rollers is an odd number of 13 or greater, and
• a relationship,
• D≤PCD×0.2
• is satisfied, where D is a roller diameter of each of the cylindrical rollers and PCD is a raceway groove diameter of the wave bearing prior to being flexed into the non-circular shape,
• wherein
• the internally toothed gear and the externally toothed gear are gears having modulus m,
• a difference in the number of teeth between the internally toothed gear and the externally toothed gear is 2n, n being a positive integer,
• the externally toothed gear is flexed into an ellipsoidal shape by the wave generator, and a relationship,
• df≥2n ×m
• is satisfied, where df is an amount of flexure of the externally toothed gear as an ellipticity of the ellipsoidal shape,
• wherein
• a pressure angle of each of teeth of the internally toothed gear and the externally toothed gear is a low pressure angle equal to or less than 20 degrees, and
• wherein
• the inner-ring-side raceway surface and the outer-ring-side raceway surface are formed thereon with a transfer film made of fine powder of an ionic crystalline layered compound and are coated with grease.