Zexel Torsen Inc.

Charles T D'Agostino

Ward E Bowerman

A gear for use in automotive differentials and a method for its manufacture in which, initially, the gear teeth are roll-formed in a cylindrical rod workpiece between a pair of toothed dies so that a fissure is created in the top land of each rolled tooth, the roll-forming being continued until (a) the diameter of the top land of each tooth is slightly greater than the desired cylindrical outside diameter of said gear and (b) each fissure is narrowed to form a seam at the top land surface of each tooth. The gears are then further processed in a relatively short machining operation that removes the narrowed seam in the top land of each gear tooth to reduce the depth of the fissure so that the normal force vector of the highest point single tooth loading ('HPSTL') on the gear tooth is directed below the bottom of the fissure. Preferably, this same finishing operation re-opens the fissure and forms the cylindrical journal/top lands of the gear teeth to a finished outside diameter slightly smaller than the inside diameter of the cylindrical differential housing pocket into which the gear will be received and supported.

Roll-formed differential gear

Four different designs for the teeth of a rolling die are disclosed. A pair of the disclosed dies is used to form helical teeth in a cylindrical rod workpiece. All four of the disclosed die tooth embodiments are variations of a common design feature: Namely, at least one segment of the tooth profile for the first tooth of the start portion of the die is formed with a pressure angle substantially larger than the pressure angle of the final basic profile geometry desired for the teeth, and then the profiles of the successive die teeth for the start portion are formed so that the pressure angle of each successive die tooth progressively and gradually decreases in magnitude from the pressure angle of the first tooth until the pressure angle of the final die tooth of the start section is substantially the same as the pressure angle of the desired workpiece teeth.

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Rochester, NY, United States of America

Charles T D'Agostino