Based on the unified Reynolds equation and Fast Fourier Transform (FFT) method, the mixed lubrication characteristics of piston pin bearing in diesel engine with high power density are numerically simulated. Firstly, the unified Reynolds equation and the elastic deformation equation are solved simultaneously, and then the effects of viscosity-pressure on the maximum film pressure, the minimum oil film thickness and the piston pin orbit are analyzed. It is shown that for the semi-floating piston pin bearing with high power density, when viscosity-pressure is taken into consideration, both the minimum oil film thickness and the maximum oil film pressure increase, while the elastic deformation of the area in which the maximum load applies decreases. The transient diagrams of the relative position between the piston pin and its bearing within a whole loading period are given. It is also indicated that the eccentricity ratio of piston pin bearing along the direction of piston stroke is greater because of the greater load exerting on the back of the semi-floating piston pin bearing and thus resulting in the obvious deformation in the back area. This result is in good agreement with the existing real failure mode of the piston pin bearing with high power density. In addition, the effects of bearing clearance and length on the minimum oil film thickness are investigated respectively. It is shown that the smaller bearing clearance and the greater width are beneficial for the increasing of the minimum oil film thickness of piston pin bearing.

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