| 摘要 |
To realize a reduction in the size of a cylinder block by simplifying the structure of an exhaust control valve, and to realize smooth flow of exhaust gases. There is provided an exhaust path for connecting to an exhaust port 39, comprising a first path 44 extending in a direction orthogonal to the central axis of the exhaust port 39, and a second path 43 connecting the first path 44 and the exhaust port 39, and a control valve 40 is provided in the first path 44. The rotational axis of the exhaust control valve 40 is parallel to a direction in which the first path 44 extends. The surface area of an opening 45 connecting the first path 44 and the second path 43 is variable as the exhaust control valve 40 rotates, so as to carry out control by activated heat atmosphere combustion and control of exhaust timing, etc. This makes it no longer necessary to provide a hollow section for housing an exhaust control valve at a position close to the exhaust port of the cylinder, or a bearing for supporting the exhaust control valve, and it is possible to reduce the size of a cylinder block and to realize smooth flow of exhaust gases by making the inner peripheral surface of an exhaust path smooth.
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