Modified sprocket tooth profile of roller chain drives

Roller chain drive is widely used in timing mechanism of gasoline engine. However, its polygonal action and meshing impact effect resulted from the non-conjugated meshing feature may damage the synchronization and uniformity of transmission. In this paper, new sprocket tooth profile is developed to reduce polygonal action and meshing impact under high speed. A new conjugated profile is derived by modifying involute profile to guarantee that the moving distance of chain is equal to the arc length of pitch circle that a sprocket rotates at the same time and the center line of chain at tight side is always tangent to the pitch circle. An asymmetrical modification method for sprocket tooth profile is also proposed. A multi-body dynamic model of the timing mechanism of a gasoline engine with the intake and exhaust sprockets is developed. The fluctuation and meshing impact of the chain are analyzed under different rotational speeds. The results show that newly developed sprocket profile can efficiently reduce meshing impact and friction of chain. The stability of chain transmission under high speed can be improved.