Abstract: In an air intake system (14) for internal combustion engines in which combustion air is led into a cylinder via an air inlet path, the air inlet path comprises a double structure of a main inlet path (7a) and a sub inlet path (8a) that the sub inlet path (8a) is placed in the main inlet path (7a) so as to be in close contact with a bottom wall of the main inlet path (7a), a downstream end of the sub inlet path (8a) being positioned near an inlet valve opening (10e) on its one side other than an exhaust valve opening (10d) side; and that an opening/closing valve (9) is disposed within the sub inlet path (8a), wherein the opening/closing valve (9) is closed in a low intake-air amount operating region of the engine so as to allow intake air to be biased from the main inlet path (7a) toward a center of the cylinder and to flow into the cylinder along a cylinder axis.

Abstract: A method of producing heat exchanger fins, comprising the steps of perforating an aperture of a small diameter in a predetermined portion of a sheet material, while simultaneously forming a projecting cylinder of a diameter smaller than that of the flanged aperture to be ultimately formed, and machining the projecting cylinder into a flange of a predetermined dimension by simultaneous burring an ironing operations using a punch of a predetermined size.

Abstract: A method of producing heat exchanger fins, comprising the steps of perforating an aperture of a small diameter in a predetermined portion of a sheet material, while simultaneously forming a projecting cylinder of a diameter smaller than that of the flanged aperture to be ultimately formed, and machining the projecting cylinder into a flange of a predetermined dimension by simultaneous burring an ironing operations using a punch of a predetermined size.

Abstract: A method of producing heat exchanger fins, comprising the steps of perforating an aperture of a small diameter in a predetermined portion of a sheet material, while simultaneously forming a perpendicularly projecting cylinder of a diameter smaller than that of the flanged aperture to be ultimately formed, and machining said perpendicularly projecting cylinder into a flange of a predetermined dimension by simultaneous burring and ironing operations using a punch of a predetermined size.