Irreversible adjustment mechanism and a vehicle seat including such a mechanism

An irreversible adjustment mechanism comprising:

• a casing itself comprising a base and a cover;
• an inlet member mounted to pivot relative to the casing about an pivot axis, the inlet member being resiliently urged towards a rest position and being moveable in a first direction from the rest position, over a first angular sector, and in a second direction opposite from the first direction from the rest position, over in a second angular sector;
• an intermediate member mounted to pivot about the pivot axis;
• a drive stage connecting the inlet member to the intermediate member and adapted for:
• positively driving the intermediate member with the inlet member via at least one drive member when the inlet member is moved away from its rest position;
• and
• moving the drive member with the inlet member when said inlet member is returned to its rest position with the drive member rubbing against the intermediate member;
• a blocking surface which is secured to the casing and which is circularly symmetrical about the pivot axis;
• an outlet member which is mounted to pivot about the pivot axis and which is shaped to co-operate with the blocking surface to define at least one pair of wedged-shaped spaces comprising first and second hollow wedge-shaped spaces, the first and second wedged-shaped spaces diverging respectively in the first angular direction and in the second angular direction;
• and
• a locking stage connecting the intermediate member to the outlet member, said locking stage comprising:
• at least one pair of clamping bodies comprising first and second rigid clamping bodies which are disposed in respective ones of the first and second wedge-shaped spaces and which are resiliently urged in respective ones of the first and second angular directions so as to become wedged between the outlet member and the blocking surface;
• at least first and second rigid abutment faces secured to or integral with the intermediate member and which face in respective ones of the first and second angular directions, the first abutment face being adapted to abut against the first clamping body while releasing it when the intermediate member turns in the first angular direction, and the second abutment face being adapted to abut against the second clamping body while releasing it when the intermediate member turns in the second angular direction, the first and second abutment faces having a certain amount of angular clearance relative to the first and second clamping bodies;
• and
• at least first and second thrust faces which are secured to or integral with the outlet member, the first thrust face being adapted to limit the relative movement of the intermediate member relative to the outlet member in the first angular direction after said first abutment face has moved the first clamping body far enough to release it, so as then to cause said outlet member to be driven by the intermediate member, and the second thrust face being adapted to limit the relative movement of the intermediate member relative to the outlet member in the second angular direction after said second abutment face has moved the second clamping body far enough to release it, so as then to cause said outlet member to be driven by the intermediate member;
• wherein the outlet member is secured to a coupling shaft guided in rotation by a guide ring which is fixed to the cover of the casing and in which the coupling shaft is fitted, and wherein the guide ring is held by a plurality of catches belonging to the cover and passing through recesses provided in the inlet member, said inlet member having a central portion which is left visible by the cover of the casing, the catches of said cover being disposed around the central portion of the inlet member, and said central portion being provided with a fixing device for fixing to an actuating member.