Inertially locked hinge for motor vehicle seat

a lower hinge element fixed to said seat part;

• an upper hinge element fixed to said back part;
• means for pivotably connecting said upper hinge element to said lower hinge element;
• a positioning element pivotal on said lower hinge element and formed with an outwardly open recess having one end forming a stop formation and another end forming an abutment engaging said upper hinge element in a rest position thereof;
• an inertial pawl in the form of a two-arm lever pivotal on said upper hinge between a blocking position and a freeing position, one arm of said lever being directed toward said stop formation on said positioning element and having a stop face engageable with said formation when said pawl is in said blocking position, the other arm of said lever being directed substantially horizontally and weighted so as normally to pivot by gravity in one rotational sense into said freeing position;
• said another end on said positioning element having a support surface adapted for engaging said other arm against the force of gravity to urge said pawl into said blocking position and for releasing said other arm into said freeing position only [[upon a slow forward pivoting of said back part]] .Badd.when the resultant of gravity and any inertial force, together with pivot reaction provide an effective unblocking couple on the inertial pawl during initial forward seat back movement.Baddend.;
• and
• means for locking and positioning means in any of a plurality of angularly offset positions for adjusting said rest position. 2. The hinge defined in claim 1 wherein said upper hinge element is displaceable in said rest position between a rear rest position and a front rest position, said step formation and stop face being spaced apart in said rear rest position and abutting in said front rest position, said support surface engaging said other surface and supporting said other arm of said pawl in said rear rest position and being out of effective engagement with said other surface in said front rest position. 3. The hinge defined in claim 2 further comprising means including interengaging formations on said release pawl and said upper hinge element for limiting pivoting of said release pawl in said one rotational sense from said blocking position into a freeing position just clearing said stop formation with said stop face. 4. A hinge defined in claim 2 wherein said support surface is above said stop formation and extends at an angle to a radius of the pivot axis of said hinge elements relative to each other. 5. The hinge defined in claim 2 wherein said stop formation and said stop face abut flatly in said forward rest position. 6. The hinge defined in claim 1 wherein said means for locking includes a locking pawl having at least one tooth radially engageable with said positioning means relative to the pivot axis thereof. 7. The hinge defined in claim 1 wherein said other arm is formed with a cutout in part defined by said other surface. 8. The hinge defined in claim 1 wherein said other arm is provided with an adjustable weight. 9. The hinge defined in claim 7 wherein said other arm is generally radial of said pawl axis and formed with a plurality of holes in a row extending generally radially of said pawl axis, said weight being securable in any of said holes. 10. The hinge defined in claim 8 wherein said other arm is formed with an elongated slot extending generally radially of said pawl axis, said weight being securable anywhere along said slot.