Patent ID: 7500718
Filing Date: 2009-03-10
Classification: A47C

Abstract:
1. In a chair having a base and a seat-back arrangement connected to the base by a tilt control mechanism, said seat-back arrangement comprising a seat assembly and a back assembly which is connected to said tilt control mechanism so as to be tiltable relative to said seat assembly rearwardly from a normal position to a rearwardly tilted position relative to said seat assembly, said tilt control mechanism including a biasing arrangement which generates a restoring force which resists rearward tilting of said back assembly and biases said back assembly towards said normal position, comprising the improvement wherein said tilt control mechanism includes a tilt control housing and a tilt tension arrangement supported on said control housing, said tilt control mechanism comprising a biasing unit which generates said restoring force and comprises an adjustment member which is movable to adjust said restoring force, said tilt tension mechanism including a gear drive mechanism comprising a rotatable drive shaft supported on said control housing which cooperates with said adjustment member such that rotation of said drive shaft about a rotation axis effects movement of said adjustment member, a face gear connected to said drive shaft so as to be rotatable about said rotation axis wherein rotation of said face gear effects a corresponding rotation of said drive shaft, and an actuator shaft which extends sidewardly and is manually rotatable about an actuator axis and cooperates with said face gear such that rotation of said actuator shaft about said actuator axis effects rotation of said face gear, said face gear having said rotation axis, a bearing face and a gear face which is opposite said bearing face and projects radially outwardly from said rotation axis to define a face plane, said gear face having circumferentially adjacent gear teeth extending circumferentially along a gear circumference about said rotation axis which said gear teeth project vertically from said gear face in an engagement direction generally parallel to said rotation axis and transverse to said face plane so as to terminate in said face plane, said gear teeth having a spiral shape in a radial direction extending outwardly from the rotation axis, said actuator shaft including an axially-extending threaded section which overlies said face plane and extends axially along a chordal path that intersects said gear circumference at opposite chord ends thereof and is spaced radially from said rotation axis in non-intersecting relation therewith, said threaded section having spiral threads extending circumferentially thereabout which engage with said gear teeth of said face gear along a portion of said chordal path wherein said spiral threads of said actuator shaft engage a radial extent of each of a plurality of said teeth of said gear face in said face plane extending generally parallel to said gear face, said gear teeth of said face gear each have a radial length that extends parallel to said gear face in said face plane which is perpendicular to said rotation axis such that meshing engagement of a respective radial extent of engagement of said gear teeth and said spiral threads generates a driving force extending circumferentially along the face plane of said gear teeth and axially along said actuator axis to effect rotation of said face gear, said actuator shaft being rotatably supported on said control housing on opposite sides of said threaded section proximate said chord ends and said control housing defining a bearing surface contactingly supporting said bearing face directly opposite said threaded section.