Abstract: A four-cylinder four-stroke internal combustion engine is taken as the object, the 3D trajectory (including the plane motion of the journal in the cross-section of bearing and the movement of the journal at axial direction) of the journal center of crankshaft main bearing in the internal combustion engine is measured under a number of operating conditions. The position of the journal in bearing is obtained by the data measured using eddy current sensors and after-processed. The results show that, there is the movement of the journal of crankshaft bearing along the axial direction in internal combustion engine, the real trajectory of journal center of crankshaft bearing is a three-dimensional spatial curve, the trajectory of the journal center of crankshaft bearing in one working cycle is not a closed curve, there is the relatively large movement of the journal of crankshaft bearing along the axial direction, and its value is greater than the radial clearance of bearing. The more the speed and load of engine, the larger the axial movement of journal is. There is the periodic variation of the axial movement of the journal of bearing in one engine working cycle at low speed, and the variation periodicity is equal to the cylinder number of internal combustion engine. However, there is not the obvious variation regularity at high speed.

Key words: 3D trajectory of journal center, IC engine　Crankshaft bearing, Measurement