Patent ID: 7768184

Claim:
A spark plug for an internal combustion engine, said spark plug comprising: a hollow cylindrical metal housing which has an open top end portion to be exposed to a combustion chamber of an internal combustion engine; a ground electrode of L-shape joined to said metal housing; a center electrode disposed in said metal housing to define a spark gap between itself and a radially extending leg of said L-shaped ground electrode; a porcelain insulator disposed in said metal housing to electrically insulate between said metal housing and said center electrode; and a stream shaper geometrically formed on an outer periphery of a top end portion of said metal housing to shape tumble vortexes of air-fuel mixture into vortex streams oriented toward a central portion of the combustion chamber, wherein said porcelain insulator has a nose protruding from a top surface of the top end portion of said metal housing; wherein said stream shaper is defined by a portion of the outer periphery of said metal housing, the portion continuing to a top surface of the top end portion of the housing and being slanted towards a longitudinal center line of said metal housing to have an outer diameter of the top end portion of said metal housing which diameter decreases towards the top surface of the top end portion; wherein an angle θ defined by (a) a line tangent to the slanted portion of the outer periphery of said metal housing at an intersection with the top surface of the top end portion of said metal housing and (b) a plane extending over the top surface of the top end portion lies in a range of 10° to 60° ; and wherein the slanted portion of the outer periphery of said metal housing is so shaped that the line tangent to the slanted portion passes through the spark gap.