SAE 2008-01-1529 : 2008

The work presented in this paper outlines the development of a simulation model to aid in the design and development of a compliant sprocket for balancer drives. A design with dual-mass flywheel and a crank-mounted compliant chain sprocket greatly reduces interior noise levels due to chain meshing. However, experimental observations showed the compliant sprocket can enter into resonance and generate excessive vibration energy during startup. Special features are incorporated into the compliant sprocket design to absorb and dissipate this energy. Additional damper spring rate, high hysteresis and large motion angle that overlap the driving range may solve the problem during engine start-up period. This work develops a simulation model to help interpret the measured data and rank the effectiveness of the design alternatives. A Multibody dynamics system (MBS) model of the balancer chain drive has been developed, validated, and used to investigate the chain noise. This model includes a cranktrain system coupled to a full balancer drive system that includes the chain drive, balance shafts, and water pump. The nonlinear stiffness and damping effects of the baseline compliant crank chain sprocket and its design iterations are added to the model to understand the basic characteristics and find an optimal setup for the engine start-up period. New MBS solver methodologies were implemented and the subsequent productivity increases are quantified. For subjective noise assessment, simulations of a solid sprocket versus compliant sprocket balancer drive were carried out and compared for certain operating engine speed.

Cross Reference: