| 摘要 |
PROBLEM TO BE SOLVED: To prevent or suppress the intrusion of a foreign matter such as wear powder to the guide face of a ball spline mechanism for moving a driving sprocket in the axial direction to improve the smoothness of the travel of the driving sprocket in the axial direction. SOLUTION: This shifting gear unit is provided with the ball spline mechanism 30 provided with an outer cylinder 32 rotatable with an inner cylinder 31 integrally through a ball 33 stored in guide channels 36, 37 and movable in the axial direction and a derailleur 70 for changing the winding of a chain C wound around the driving sprocket 39 moving integrally with the outer cylinder 32 among a plurality of gear shift sprockets 41 to 47. The inner cylinder 31 and the outer cylinder 32 have guide faces S1, S2 of the guide channels 36, 37 for guiding the outer cylinder 32 so as to move in the axial direction through the ball 33. A dust cover 150 for covering outer parts in the radial direction of the guide faces S1, S2 irrespective of a position of the driving sprocket 39 in the axial direction is provided in the outer cylinder 32. COPYRIGHT: (C)2006,JPO&NCIPI
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