| 摘要 |
PURPOSE:To improve the ignitability of an engine through enabling the stratifying condition of the fresh air and the exhaust air by providing a means for causing an exhaust valve to open earlier than an intake valve when the piston lowering speed is high so that the exhaust air in an exhaust port is caused to reflow into a combustion chamber, and then swirling the exhaust air at the time of its reflowing. CONSTITUTION:On each of the cylinders are provided exhaust ports 32a, 32b in positions opposite to intake ports 20a, 20b, and then, at least either one of the two exhaust ports 32a, 32b is of an eccentric port that is caused to be eccentric from the axis of the cylinder. In addition, there is provided an exhaust control valve 34 for permitting the part in an exhaust manifold 33, where branch pipes from each of the cylinders gather, to be either divided into a branch-pipe gathering part 33a for the No.1-No.3 cylinders and a branch-pipe gathering part 33b for the No.4-No.6 cylinders or combined into one. And further, on the circumference of an exhaust valve at a cylinder head 6 facing a combustion chamber 2 for each of the cylinders is provided a mask 5 which is shaped in such a manner that the exhaust air is swirled when it reflows from the exhaust ports 32a, 32b into the combustion chamber 2. And then, the exhaust control valve 34 is controlled so that it is caused to open when the engine is in the idling operating range or the light-load operating range.
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