| 摘要 |
PROBLEM TO BE SOLVED: To improve stability in combustion by forming air-fuel mixture in the vicinity of an ignition plug stably and suppress reduction of tumble stream to the minimum extent. SOLUTION: A bottom face 22a of a substantially rectangular recessed part 22 on a crown face of a piston 4 forms a curved face being substantially parallel with a central axial line of a piston pin along tumble stream. A protruding bar part 25 being parallel with the central axial line of the piston pin is formed in a substantially central part of the bottom face 22a just below the ignition plug 7, and rising parts 25a, 25b on its intake valve side and exhaust valve side form circular arc faces. Radius of curvature of the rising part 25b on the exhaust valve side is larger than that on the intake valve side. An ascending current going upward occurs when a spray passes above the protruding bar part 25 at stratified lean combustion time, and a part of the spray is guided onto an upper ignition plug side, thereby achieving stable combustion. Since the rising part 25b on the exhaust valve side forms the circular arc face having large radius of curvature, flow of tumble stream at homogeneous combustion time is not obstructed. COPYRIGHT: (C)2007,JPO&INPIT
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