Patent ID: 8651575

Claim:
A structure of a seat back with lumbar support for a vehicle, comprising: a seat back; a back frame, which is provided inside the seat back and which supports a headrest; and a lumbar support plate which is positioned inside a perimeter of the back frame in a width direction of the vehicle and which is supported by the back frame movably in a front/rear direction of the vehicle a linking mechanism which normally holds the lumbar support plate at a prescribed position, in the front/rear direction of the vehicle, with respect to the back frame; and a linking release mechanism which permits rearward movement of the lumbar support plate that is in a state of being held at the prescribed position, when a load of a prescribed value or greater is applied to the lumbar support plate; a biasing member that biases the lumbar support plate in the direction of the prescribed position, a handle shaft that can perform a rotating operation and that is provided on one side frame of the back frame, the linking mechanism including: a clutch mechanism that rotates an output member in response to a rotational force from the handle shaft and impedes transmitting rotation of the output member to the handle shaft, and an adjustment member that adjusts a front/rear position of the lumbar support plate with respect to the back frame in relation with rotation of the output member, wherein the adjustment member includes a turning member that turns in synchronization with rotation of the output member, an undulating section formed in the turning member, and the position of the lumbar support plate in the front/rear direction of the vehicle with respect to the back frame is adjustable by turning the turning member, the biasing member includes a torsion bar having one end portion and another end portion in a width direction of the seat back, the linking release mechanism has: a pin member that fits the other end portion of the torsion bar into the turning member swingably about an axis extending in a width direction of the seat back and movably in the width direction of the seat back, a spring member that biases the other end portion of the torsion bar in a direction to make contact with a bottom surface of a recess section of an undulating section, the other end portion of the torsion bar is normally held inside the recess section of the undulating section by a biasing force of the spring member, and the other end portion of the torsion bar is moved in a width direction of the seat back to be away from the recess section of the turning member against the biasing force of the spring member, thereby allowing a rearward movement of the lumbar support plate when a load equal to or greater than a prescribed value is applied to the lumbar support plate.