Redundant seat locking mechanism

Claim 1

In a vehicle seat assembly having a backrest member pivotably moveable with respect to a seat member, a device for controlled adjustment of the inclination of the backrest member with respect to the seat member, said device comprising: (a) a first hinge bracket secured to one of said members and a second hinge bracket secured to the other of said members, wherein the one of said first and second hinge brackets which is secured to the backrest member is pivotally moveable with respect to the other of said first and second hinge brackets; (b) a gear sector means mounted on said second hinge bracket; (c) a gear means mounted on said first hinge bracket in meshing engagement with said gear sector means so as to rotate upon said pivotal movement of the said one of the first and second hinge brackets; (d) a first locking gear affixed to the gear means for rotation therewith; (e) a first locking pawl pivotally mounted on the first hinge bracket for movement between a first position in which the first locking pawl restrainingly engages the first locking gear and a second position in which the locking pawl is removed from said restraining engagement; (f) a second locking pawl pivotally mounted on the first hinge bracket for movement between a first position in which the second locking pawl restrainingly engages the first locking gear and a second position in which the second locking pawl is removed from said restraining engagement; (g) a handle means pivotally mounted on the first hinge bracket so as to be moveable between a first position in which a cam portion of the handle means bears upon a head portion of the first locking pawl so as to urge the first locking pawl into its said first position, and a second position in which said cam portion bears upon a tail portion of the first locking pawl so as to urge the first locking pawl into its said second position; (h) a first spring means mounted on the first hinge bracket so as to be adapted to bias the second locking pawl towards its said first position; (i) a second spring means of greater strength than said first spring means, interconnected between the handle means and the second locking pawl so as to bias the handle means to said first position of said handle means, while at the same time biasing the second locking pawl to its said second position against said biasing of the first spring means, such that, upon failure of the second spring means, the second locking pawl is biased by the first spring means to its first position so as to restrainingly engage the first locking gear, thereby to hold the backrest member against said pivotal movement.