Auxiliary backrest for a chair

Abstract

The auxiliary backrest for a chair includes a support and an auxiliary backrest body. The support has two rails. Each rail is formed by a surrounding wall and a side wall. An open trough is formed within the two rails. The trough has an inlet. The auxiliary backrest body has a back portion with a pair of elastic sheets. Each elastic sheet has a fixing end connected to the back portion and an elastic end corresponding to the two rails. Each elastic end has an insert portion inserted into the trough. A distance between two outer ends of the two insert portions is slightly greater than a width of the trough. When the insert portions are compressedly inserted into the trough, the elastic ends can be held between the rails by the elasticity thereof.

1 . A backrest for a chair, comprising:
 a chair back, being a hollow frame;   a support, mounted in a hollow portion of the chair back, having two rails in a substantially vertical direction, each rail being formed by a surrounding wall and a side wall, an open trough being formed in the two rails, and the trough having an inlet;   an auxiliary backrest body, having a back portion with a pair of elastic sheets and a pad portion for supporting a user's waist or back, each elastic sheet having a fixing end connected to the back portion and an elastic end corresponding to the two rails, and each elastic end having an insert portion inserted into the trough;   wherein a distance between two outer ends of the two insert portions is slightly greater than a width of the trough.   
     
     
         2 . The backrest of  claim 1 , wherein the inlet is provided with a guide plate which is inwardly inclined. 
     
     
         3 . The backrest of  claim 1 , wherein the back portion is formed with two openings for separately allowing the elastic ends to pass through the back portion, and the insert portions project from the back portion. 
     
     
         4 . The backrest of  claim 1 , wherein the support is provided with a positioning aperture between the two rails, the auxiliary backrest body is provided with a protrusion between the two elastic sheets, and the protrusion enters the positioning aperture. 
     
     
         5 . The backrest of  claim 1 , wherein the support is provided with a plurality of positioning apertures arranged in a line between the two rails, the auxiliary backrest body is provided with a protrusion between the two elastic sheets, and the protrusion enters one of the positioning apertures. 
     
     
         6 . The backrest of  claim 4 , wherein the protrusion is of a substantial V-shape. 
     
     
         7 . The backrest of  claim 6 , wherein a bottom of the positioning aperture is of an arced shape. 
     
     
         8 . The backrest of  claim 5 , wherein the protrusion is of a substantial V-shape. 
     
     
         9 . The backrest of  claim 8 , wherein a bottom of each of the positioning apertures is of an arced shape.