| 摘要 |
PURPOSE:To aim at the simplification of a breather structure by installing a first passage in a crankshaft center, while installing a second passage in a bearing part of a crankcase supporting this crankshaft, and interconnecting these first and second passage within the specified turning angle range of the crankshaft. CONSTITUTION:A groove 23, being interconnected to the inside of a crankcase 1 while reached to the vicinity of a seal member 22, is installed in a part of the outer circumferential surface of a crankshaft 5 along the axial direction. In an upper bearing part 3 installed in an upper part of the crankcase 1, there are provided with a ring inner wall part 24 as a sliding bearing for supporting the crankshaft 5, and a ring outer wall part 25 surrounding the inner wall part 24. On an inner circumferential surface of the inner wall part, there is provided with a circular groove 26 along the circumferential direction so as to be interconnectible to the groove 23 installed on an outer circumferential surface of the crankshaft 5, extending over the range of a turning angle of the crankshaft 5 equivalent to an expansion stroke of an engine. |
