| 摘要 |
PROBLEM TO BE SOLVED: To provide an engine which enhances a tumble flow by adding a contrivance to a shape of a downstream end part of a valve seat-less intake port, and can suppress the generation of knocking without increasing a fuel amount in, particularly, a middle rotational speed high-load area.SOLUTION: A first valve seat (41) is applied with hard surface treatment. In a cross section orthogonal to a crank shaft direction, an intake port wall (46) of an immediately-above portion of the first valve seat (41) at a side opposite to a cylinder center is formed so that intake air which progresses along a low-side wall (40b) of an intake port, and flows into a combustion chamber (30) with the intake port wall (46) of the immediately-above portion of the first valve seat (41) at the side opposite to the cylinder center as a guide passes an upper part rather than a valve center of an intake valve (50) at a full-lift time, and progresses toward a combustion chamber (30a) at an exhaust side from the cylinder center.SELECTED DRAWING: Figure 16 |
