| 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 formed by a hard surface treatment method. In a cross section orthogonal to a crank shaft direction, an angle which erects from a horizontal face of an intake port wall (44) of an immediately-above portion of the first valve seat (41) at a cylinder center side is not larger than an angle being an acute angle which is formed of a linear line for connecting the most downstream point of the intake port wall (44) of the immediately-above portion of the first valve seat (41) at the cylinder center side and a point which is formed by the intersection of a bottom dead point of a cylinder wall (12) at an exhaust side and a piston crown face (15a), and the piston crown face (15a), or not smaller than an angle being an acute angle which is formed of a line passing through a tumble center while being reflected in a combustion chamber and the piston crown face (15a).SELECTED DRAWING: Figure 7 |
