Downsizing and lowering engine speed is effective for fuel economy. However, such measures lead to severe lubrication condition and increase the risk of seizure because of higher load for the sliding surface. The bearing of the small end of a connecting rod is one of the sliding parts used under the severest lubrication conditions. Therefore, clarifying the mechanism of its seizure is an important subject. In the previous study, it is shown that higher the cylinder pressure thicker the oil film between the piston pin and bearing of the small end of the connecting rod. It derived a hypothesis that cylinder pressure causes a deformation of the pin and thicker oil film at around the center of the bearing and heavy contact at the bearing end. This study aimed clarifying the mechanism of the seizure occurring at around the piston pin. The calculated results showed that oil film could be generated by deformation of the piston pin. Further, oil film thickness was measured by laser induced fluorescence method for investigating the effect of pin stiffness. Measured result showed lower the stiffness of the piston pin thicker the oil film. It was found that the deformation of piston pin caused thick oil films. The fact that seizure occurred often the engine operation with the low stiffness piston pin also proved the hypothesis adequate.

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