Rotation transmitting apparatus, vehicle steering system, and intermediate shaft

A rotation transmitting apparatus including a first rotary shaft on which multiple external teeth projected radially outward and extending in an axial direction are formed so as to be arranged in a circumferential direction, and a second rotary shaft in which multiple internal teeth projected radially inward and extending in the axial direction are formed so as to be arranged in the circumferential direction, the second rotary shaft being fitted to the first rotary shaft so as to be slidable relative to the first rotary shaft in the axial direction and so as to be engageable with the first rotary shaft in a rotational direction through the use of the external teeth and the internal teeth, wherein

• the external teeth and the internal teeth have tooth flanks that are engaged with each other in the rotational direction;
• a protrusion is formed on the tooth flank of the external tooth, the protrusion being projected toward the corresponding tooth flank of the internal tooth and extending in the axial direction;
• and
• the protrusion is made of a resin that is more elastically deformable than the tooth flank, wherein an area of contact between the protrusion and the tooth flank of the internal tooth is made smaller than an area of contact between the tooth flank of the external tooth and the tooth flank of the internal tooth to allow the protrusion to be deformed elastically.