Patent ID: 8341953

Claim:
An exhaust manifold comprising: a double collecting pipe that is formed of an inner pipe and an outer pipe, wherein the inner pipe includes a collecting pipe portion and branch pipe portions that are bifurcated from the collecting pipe portion, the outer pipe covers an outer peripheral portion of the collecting pipe portion and outer peripheral portions of the branch pipe portions, and the double collecting pipe is formed so that the thickness of the inner pipe is smaller than the thickness of the outer pipe; and an inner pipe retainer that has a thickness larger than the thickness of the inner pipe and smaller than the thickness of the outer pipe and that is formed of a pair of semi-circular portions and a connecting portion, wherein the pair of semi-circular portions are respectively connected to outer peripheral portions of branched portions of the branch pipe portions and an inner peripheral portion of the outer pipe, the connecting portion connects the pair of semi-circular portions, and the inner pipe retainer is interposed between the inner pipe and the outer pipe and is connected to the inner pipe and the outer pipe so as to define a certain gap between the inner pipe and the outer pipe, wherein exhaust gas exhausted from exhaust ports of a set of cylinders among a plurality of cylinders of an engine is introduced into the collecting pipe portion through the branch pipe portions, and the inner peripheral portion of the outer pipe and outer peripheral portions of the semi-circular portions are connected by spot-welding, the outer peripheral portions of the branch pipe portions and inner peripheral portions of the semi-circular portions are connected by spot-welding, the total area in which the outer peripheral portions of the branch pipe portions and the inner peripheral portions of the semi-circular portions are spot-welded is larger than the total area in which the inner peripheral portion of the outer pipe and the outer peripheral portions of the semi-circular portions are spot-welded.