MODELING PISTON-RING DYNAMICS, BLOWBY, AND RING-TWIST EFFECTS

A ring-dynamics and gas-flow model has been developed to study ring/gr oove contact, blowby, and the influence of ring static twist, keystone ring/groove configurations, and other piston and ring parameters. The model is developed for a ring pack with three rings. The dynamics of the top two rings and the gas pressures in the regions above the oil c ontrol ring are simulated. Distributions of oil film thickness and sur face roughness on the groove and ring surfaces are assumed in the mode l to calculate the forces generated by the ring/groove contact. Ring s tatic and dynamic twists are considered, as well as different keystone ring/groove configurations. Ring dynamics and gas flows are coupled i n the formulation and an implicit scheme is implemented, enabling the model to resolve detailed events such as ring putter. Studies on a spa rk ignition engine found that static twist or, more generally speaking , the relative angle between rings and their grooves, has great influe nce on ring/groove contact characteristics, ring stability, and blowby . Ring putter is found to occur for the second ring with a negative st atic twist under normal operating conditions and for the top ring with a negative static twist tinder high-speed/low-load operating conditio ns. Studies on a diesel engine show that different keystone ring/groov e configurations result in different twist behaviors of the ring that may affect the wear pattern of the keystone ring running surfaces.