Clutch system having means for converting transmitted torque into frictional force

A clutch system comprising:

• a clutch input member;
• a clutch output member;
• a primary friction clutch connected to said clutch input member, said primary friction clutch including:
• a first pressure plate slideably splined to said clutch input member;
• a receiving ring retained by said clutch input member and facing said first pressure plate;
• a pair of first driving friction disks positioned between said first pressure plate and said receiving ring and slideably engaged with said clutch input member;
• a first driven friction disk positioned between said pair of first driving friction disks;
• a dish-shaped clutch spring biassing said first pressure plate towards said receiving ring to engage said primary friction clutch;
• a plurality of radially extending guide grooves formed on an inner side of said pressure plate facing an outermost one of said pair of first driving friction disks, said guide grooves each having an inclined bottom portion at an outer radial portion of said pressure plate and inclined toward said outermost first driving friction disk, and a stopper end wall closing a radially outermost end of said inclined bottom portion;
• and a centrifugal ball-shaped weight positioned in each said guide groove and contacting said outermost first driving friction disk;
• a secondary friction clutch between said clutch input and output members and operatively associated with said clutch output member;
• means for selectively disengaging said primary friction clutch;
• and
• thrust generating means interconnecting said primary friction clutch and said secondary friction clutch for generating axial thrust to engage said secondary friction clutch under transmission of torque from said primary friction clutch.