An Analysis of the Simplified Two-Mass System of the Connecting Rod in Spark Ignition Engines

Replacing the connecting rod with a lumped two-mass system causes an error, which influences the inertia rolling moment, the thrust force between the piston and the cylinder liner, and the loading on the main bearings. Dimensionless relationships have been found that relate the inertia error due to the connecting rod simplification (the inertia error) to the errors of the forces and moments that are created by it. Additionally, the results of a statistical study of 19 SI connecting rods indicate that the mass moment of inertia of the two mass system is −2.65% to 22% higher than that the experimentally measured moment of inertia of the connecting rod, with an average error value of 9.65%.