Seat belt retractor

A seat belt retractor of a type having an emergency locking mode and an auto-locking mode, said retractor comprising:

• a take-up shaft by which a webbing is to be retracted;
• a ratchet wheel connected to said take-up shaft to rotate therewith;
• an annular cam member connected to said take-up shaft through a speed reduction mechanism, said cam member having a first group of projections formed thereon;
• a pivotal switching arm having a second group of projections formed thereon, said second group of projections being engageable with said first group of projections;
• a toggle spring for biasing said switching arm in a given direction;
• a pivotal tooth member actuated by said switching arm and engageable with said ratchet wheel;
• and
• biasing means for biasing said pivotal tooth member in a direction away from said ratchet wheel;
• wherein said first and second groups of projections are arranged in such a manner that when, after full feeding of the webbing from said take-up shaft, the webbing is retracted by the take-up shaft by a given small length, the retractor is subjected to switching from the emergency locking mode to the auto-locking mode, and
• wherein said speed reduction mechanism comprises an externally toothed gear member which is connected to said take-up shaft through an eccentric shaft;
• and an internally toothed gear defined by said annular cam member and meshed with said externally toothed gear member, the number of the teeth of said internally toothed gear being greater than that of said externally toothed gear member by one.