Patent ID: 8905639

Claim:
A crankshaft main bearing assembly comprising: a journal portion of a crankshaft which is supported by a main bearing, wherein the main bearing is composed of a pair of semi-cylindrical bearings, and defines an axial direction and a circumferential direction, only one of the semi-cylindrical bearings comprises an oil groove formed on an inner circumferential surface thereof, the oil groove extends in the circumferential direction at least through a center portion of the one semi-cylindrical bearing in the circumferential direction, a depth of the oil groove from the inner circumferential surface decreases toward a circumferential end surface of the one semi-cylindrical bearing so as to define a circumferential end portion of the oil groove on the inner circumferential surface, so that the oil groove does not extend to the circumferential end surface, the circumferential end surface of the one semi-cylindrical bearing to which the oil groove does not extend, and a circumferential end surface of the other semi-cylindrical bearing which is joined to the one semi-cylindrical bearing respectively include inclined surfaces extending on an inner circumferential surface side over an entire length thereof in the axial direction, so that an axial groove is formed at a joint portion of the pair of semi-cylindrical bearings, and an extension portion of the inner circumferential surface extends between the axial groove and the oil groove, a plurality of circumferential grooves extending in the circumferential direction from the axial groove to the oil groove are formed on the extension portion of the inner circumferential surface over an entire width of the circumferential end portion of the oil groove in the axial direction, a depth of the plurality of circumferential grooves from the extension portion of the inner circumferential surface is smaller than the depth of the oil groove, so that an overlap region where the plurality of circumferential grooves and the oil groove overlap each other is formed in a region where the depth of the oil groove decreases, and the depth of each of the circumferential grooves is within a range of 0.002 to 0.015 mm and constant in the circumferential direction, a width of each of the circumferential grooves in the axial direction is within a range of 0.1 to 1 mm and constant in the circumferential direction, and a length of the overlap region in the circumferential direction is within a range of 0.03 to 0.15 mm.