Analysis of piston secondary motion considering the variation in the system inertia

Abstract

The secondary motion of a piston has a significant impact on the performance and reliability of an internal combustion engine. However, the variation in the system inertia, namely the variable inertia of the piston—connecting-rod—crankshaft mechanism due to the change in their positions relative to the crankshaft axis, has been neglected in most studies on piston secondary motion. A novel mathematical model is developed for piston—connecting-rod—crankshaft dynamics by taking the variation in the system inertia into consideration. Then a coupling model of the piston secondary dynamics and the fluid dynamic lubrication is built. The simulations show that the variation in the system inertia influences the piston secondary motion and piston side force, and that the piston side force plays an important role in determining the piston lateral motion. Results also show that the engine speed and the centre-of-mass (COM) positions of the connecting rod have considerable effect on the piston secondary motion. The analysis of the COM positions can be employed to optimize the design of the connecting rod.