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Seat belt retractor mechanism

  • US 4,688,825 A
  • Filed: 05/05/1986
  • Issued: 08/25/1987
  • Est. Priority Date: 05/05/1986
  • Status: Expired due to Fees
First Claim
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1. In a seat belt retractor mechanism having a seat belt reel rotatably mounted in a support frame adapted to be assembled on a movable door of a vehicle, said mechanism including a reel having at least at one of its ends a generally circular ratchet plate, a locking element mounted on said support frame and movable between a first rest position allowing said reel to rotate and a second lock position engaging said ratchet plate to hold said reel against rotation in a seat belt protraction direction, an inertia sensor element carried by said support frame and having a normal rest position and forceable into an activated position in response to acceleration of said support frame whereat contact occurs within said locking member, an electromagnet having a coil and mounted on said support frame and having a deenergized first condition without current flowing through said coil and an energized second condition with current flowing through said coil, means for preventing movement of said inertia sensor element into said activated position only when said electromagnet is in said energized second condition and only until forces acting on said inertia element exceed a selected magnitude above the inertia forces resulting from normal movement of said vehicle door, and means for moving said locking element into said lock position when said inertia element is forced into said activated position, means for providing a source of current for energizing said electromagnet, and switch means responsive to said door being open for connecting said current source with said electromagnet coil, the improvement comprising:

  • said electromagnet having a fixed central core with an exposed, generally flat pole surface, said movement preventing means including a generally flat keeper surface associated with said inertia sensor element formed from a magnetically permeable material and engaging said pole surface in a co-planar relationship when said inertia sensor element is in said normal, rest position and magnetically attracted to said pole surface only while said electromagnet is in said energized second condition, and said means for providing a current source insuring a current having a field strength at least equal to a value which maintains said core in a saturated condition when said door switch means is activated whereby a constant magnetic force is exerted on said keeper surface.

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