| 摘要 |
PURPOSE:To increase strength of a toothed pulley such as the one used as an engine timing pulley and to make transmission of a large torque possible by making the inner corner angle made by a tooth portion and an end portion an arc-shaped curved surface. CONSTITUTION:A toothed pulley 1 has trapezoidal teeth 4 punched out from a base body consisting of an end surface 3, a cylindrical surface and a boss 2 all formed with a pressed steel sheet. The tooth portion 4 is formed to an approximate trapezoidal form by fitting the base body having the end surface and the cylindrical surface to a die and hitting a punch against a die groove to recess both a bottom land 11 and a flank 12 leaving a top land 10 as it is. Corners made between the end surface of the die and adjacent portions are chamfered. As a result, inner surfaces corners 10a, 11a and 12a made respectively by the top land 10, bottom land 11 and flank 12 relative to the end surface 3 of the die are formed to curved surfaces having their centers inside respective surfaces. Of these radii, that of the corner 10a is the greatest. While the inner surface of the corner angle 11a is arc-shaped, its outer surface is a rectangular edge.
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