CRANKSHAFT PIN BEHAVIORS IN THE CLEARANCE OF BIG-END BEARING UNDER THE TRANSIENT SPEED CONDITION INCLUDING MASS INERTIA EFFECTS

摘要

Recent engines are required to have better acceleration performance, low friction loss and longer endurance life. Better acceleration performance is easily obtained by optimally distributing the masses of moving components for low inertia loss. Low frictional performance is obtained by using the recently developed synthetic lubricant of low viscosity. However, most of the damages due to enhancing these required performances happen in the bearings systems, which are delicately influenced by small change of operating conditions such as mass redistributions among moving components and lubricant conditions. Many researches regarding big-end bearing dynamic behaviours have been performed by the Mobility method that uses database map of load carrying capacity from the hydrodynamic fluid film pressure over the bearing area to match the equilibrium with the external load. However, the modeling assumptions of the Mobility database restrict the applications of practical design changes such as for better acceleration as well as low frictional performances, because it is made on the assumptions of Newtonian lubricant, negligible mass inertia effects of journal system, zero oil supply pressure and steady speed condition, etc. Therefore, mass inertia effects in crankshaft system, non- linear characteristics of lubricant, submerged supply pressure effects of lubricant and transient speed effects are needed to be simulated with other appropriate computing algorithms rather than Mobility method itself. In this work, we have investigated the dynamic loading behaviors of crankshaft pin in the clearance of big-end bearing with four cylinder engine dynamics under both steady and transient speed conditions in order to find out the differences of load carrying capacity variations of lubricant film. The computed external loads from the four cylinder engine dynamics are found to have the modes of torsional vibrations even under steady nominal speed condition. The journal orbit including the mass inertia effect under the same engine speed condition shows absolute different patterns from the Mobility method that predicts only linear variations. The developed computing process also predicts the journal orbits under transient engine speed of acceleration and deceleration, while the Mobility method has no such function at all. Submerged oil supply pressure is also simulated in this research and some results of journal orbits according to supply pressures are found to be unique patterns. Acceleration and deceleration of engine speeds are the major inputs for our research for further optimization design of mass distribution among the moving components such as conrod, piston, crankshaft systems and non-Newtonian characteristics of lubricant. The calculated results will provide valuable design guidance for better mass distribution as well as lubrication circuits of crankshaft system.