Chair

Abstract

A chair includes a seat 5 for sinking backward as a backrest 7 mainly made up of an elastically deformable back shell 71 tilts back, wherein a back support post 6 which is pivoted at its lower end portion on a support base portion 3 disposed below the seat 5 and which supports the back shell 71 includes an upper back frame 61 for supporting a portion of the back shell 71 above a lumbar support portion 71 L of the back shell 71 capable of supporting a lumbar part of a seated person and a lower back frame 62 for supporting a portion near a lower end portion of the back shell 71 , the back frames (the upper back frame 61 and the lower back frame 62 ) are pivoted on each other and the pivot point (third support shaft X 3 ) is set behind the lower end portion of the back shell 71 , and the whole back shell 71 is curved and deformed to protrude the lumbar support portion 71 L relatively forward as the upper back frame 61 tilts back about the pivot point (third support shaft X 3 ) with respect to the lower back frame 62.

1 . A chair including a seat for moving in synchronization with backward tilting operation of a backrest mainly made up of an elastically deformable back shell,
 wherein a back support post which is pivoted at its lower end portion or its portion near the lower end portion on a support base portion disposed below the seat and which supports the back shell includes an upper back frame for supporting a portion of the back shell above a lumbar support portion of the back shell capable of supporting a lumbar part of a seated person and a lower back frame for supporting a lower end portion or a portion near the lower end portion of the back shell, the back frames are pivoted on each other, the pivot point is set behind the lower end portion of the back shell, and the whole back shell is curved and deformed to protrude the lumbar support portion relatively forward as the upper back frame tilts back about the pivot point with respect to the lower back frame.   
     
     
         2 . The chair according to  claim 1 , wherein either one of the upper back frame and the lower back frame has an overhanging portion extending in a predetermined direction from the pivot point and a resilient body for generating a reaction force as the upper back frame tilts back is disposed between the overhanging portion and the other back frame. 
     
     
         3 . The chair according to  claim 1 , wherein a space is formed between the upper back frame and the lumbar support portion of the back shell. 
     
     
         4 . The chair according to  claim 1 , wherein at least one of the upper back frame and the lower back frame supports the back shell while engaged with the back shell for sliding movements in a height direction. 
     
     
         5 . The chair according to  claim 1 , wherein the one back support post including the upper back frame and the lower back frame is disposed at a substantially central portion in a lateral width direction of the back shell. 
     
     
         6 . The chair according to  claim 1 , wherein a deformation trigger means which is more likely to be deformed than portions adjacent to the lumbar support portion is provided to the lumbar support portion of the back shell in order to direct a deformation characteristic of the back shell. 
     
     
         7 . The chair according to  claim 6 , wherein the deformation trigger means comprises one or a plurality of slit(s) extending in the lateral width direction of the back shell. 
     
     
         8 . The chair according to  claim 2 , wherein a space is formed between the upper back frame and the lumbar support portion of the back shell. 
     
     
         9 . The chair according to  claim 2 , wherein at least one of the upper back frame and the lower back frame supports the back shell while engaged with the back shell for sliding movements in a height direction. 
     
     
         10 . The chair according to  claim 3 , wherein at least one of the upper back frame and the lower back frame supports the back shell while engaged with the back shell for sliding movements in a height direction. 
     
     
         11 . The chair according to  claim 2 , wherein the one back support post including the upper back frame and the lower back frame is disposed at a substantially central portion in a lateral width direction of the back shell. 
     
     
         12 . The chair according to  claim 3 , wherein the one back support post including the upper back frame and the lower back frame is disposed at a substantially central portion in a lateral width direction of the back shell. 
     
     
         13 . The chair according to  claim 4 , wherein the one back support post including the upper back frame and the lower back frame is disposed at a substantially central portion in a lateral width direction of the back shell. 
     
     
         14 . The chair according to  claim 2 , wherein a deformation trigger means which is more likely to be deformed than portions adjacent to the lumbar support portion is provided to the lumbar support portion of the back shell in order to direct a deformation characteristic of the back shell. 
     
     
         15 . The chair according to  claim 3 , wherein a deformation trigger means which is more likely to be deformed than portions adjacent to the lumbar support portion is provided to the lumbar support portion of the back shell in order to direct a deformation characteristic of the back shell. 
     
     
         16 . The chair according to  claim 4 , wherein a deformation trigger means which is more likely to be deformed than portions adjacent to the lumbar support portion is provided to the lumbar support portion of the back shell in order to direct a deformation characteristic of the back shell. 
     
     
         17 . The chair according to  claim 5 , wherein a deformation trigger means which is more likely to be deformed than portions adjacent to the lumbar support portion is provided to the lumbar support portion of the back shell in order to direct a deformation characteristic of the back shell.