Patent ID: 8272691

Claim:
A resilient lower-back supporting device capable of vertical adjustment along with a backrest of a chair, with the resilient lower-back supporting device comprising: a supporting element fixed to the chair and to which the backrest is slidably connected and secured in position; a resilient supporting unit connected between a lower-back supporting portion at a lower end of the backrest and a corresponding position of the supporting element, wherein the resilient supporting unit comprises an outer supporting rod and an inner supporting rod inserted in the outer supporting rod, with the inner and outer supporting rods being extendable and retractable with respect to each other, with the inner supporting rod having a lower end pivotally connected to a predetermined position of the chair, with the outer supporting rod having an upper end pivotally connected to a predetermined position on a back of the backrest; and springs respectively provided where the inner supporting rod and the chair are pivotally connected and where the outer supporting rod and the backrest are pivotally connected, in order to bias the backrest toward a sitter in the chair, wherein the inner supporting rod receives a spring having a lower end attached to the inner supporting rod and an upper end attached to the outer supporting rod.