| 摘要 |
A bicycle sprocket assembly includes a small sprocket wheel, and a large sprocket wheel coaxial with the small sprocket wheel and provided with several guide units each of which includes a notch formed in the large sprocket wheel, and a chain guiding piece that is secured to the inner side surface of the large sprocket wheel and that is adjacent to the notch. The notches are respectively formed in some spaced-apart sprocket teeth of the large sprocket wheel. Each of the notches is formed by an outer guiding surface which extends from a tooth tip to the corresponding tooth valley and which makes a junction with the inner guiding surface of the corresponding piece, so as to slide the chain between the inner and outer guiding surfaces. The pieces are inclined with respect to axial and radial directions of the sprocket assembly. Each of the outer guiding surfaces has a bottom end which is spaced apart from the middle point of the corresponding tooth valley at a predetermined distance so as to contact a tooth tip with the lagging edge of an inner link plate of the chain when shifted the chain from the small sprocket wheel to the large sprocket wheel.
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