Multiple disc clutch device and method of manufacture thereof

An improved method of manufacturing a multiple disc clutch device including a cylindrical clutch outer member having a cylindrical portion opened at its one end and closed at its other end by a closing end wall, said cylindrical portion being provided at an inner periphery thereof with a plurality of concave grooves formed along generated lines of said cylindrical portion at a constant circumferential pitch;

• a plurality of driving clutch discs each having a plurality of convex portions formed on an outer periphery thereof and slidably engaging with said concave grooves in said clutch outer member;
• a driven gear provided on an outer surface of said closing end wall of said clutch outer member, said driven gear being rotatable within a limited angle of rotation relative said clutch outer member;
• a plurality of first spring retainers formed on said driven gear;
• a plurality of second spring retainers formed on said closing end wall of said clutch outer member corresponding to and opposing said first spring retainers;
• and a plurality of buffer springs each disposed between said opposing first and second spring retainers;
• the improvement comprising:
• forming said clutch outer member of steel sheet;
• roll-forming said plurality of concave grooves in said inner periphery of said cylindrical portion of said clutch outer member;
• press-forming said second spring retainers on said closing end wall;
• welding a plurality of cylindrical bosses to said outer surface of said closing end wall of said clutch outer member;
• positioning said driven gear over said plurality of cylindrical bosses of said closing end wall of said clutch outer member, said plurality of cylindrical bosses being received in corresponding slots formed in said driven gear;
• and
• fixing a side plate lapping a disc portion of an outer surface of said driven gear to said plurality of cylindrical bosses by riveting.