On the Stability of Chain Drive Systems Under Periodic Sprocket Oscillations

Experimental observations have shown that periodic torsional oscillations of engine camshafts induced by powertrain loads can cause significant tension variation in the timing chain and magnify the chain transverse vibrations and noise level. This result indicates that the sprocket dynamic characteristics and the chain vibration behavior are closely coupled. The chain drive models to-date are not able to address these phenomena. This paper presents a nonlinear model of an integrated chain drive system which couples the sprocket motion with the transverse and longitudinal vibration of the axially moving chain spans. With this model, the effects of the sprocket shaft periodic loads upon the total system are investigated. It is concluded that the sprocket oscillations will cause chain longitudinal vibrations. This could destabilize the system and induce the chains to undergo large transverse vibration. Both the subharmonic and summation types of parametric resonance are found and the instability regions are derived. The effects of various system parameters, such as the sprocket inertia, the chain speed, and the speed dependent excitation frequencies upon the instability regions have been studied. The significance of the gyroscopic terms of the stability boundary has been shown.