Abstract: A shell for a chair in which a bottom shell structure and a backrest shell structure are connected to supporting frame members. The bottom shell structure has a bottom portion and a partial backrest portion that are connected by a curved portion with plural slots. Sideways notches are connected to the extreme left and right slots and extend toward the left and right edges of the shell structure. The edges of the shell adjacent the notches are curved into a U shape. This construction increases the flexibility of the curved portion, while maintaining a significant portion of the unslotted material strength. A separate shell structure is attached to supporting bars and forms the remainder of the backrest support. This separate shell structure has a jagged cross sectional shape where substantially parallel projections and recesses form grooves which extend the length of the backrest shell.

Abstract: A shell for a chair in which a bottom shell structure and a backrest shell structure are connected to supporting frame members such that when a light load is applied to the separate backrest shell the backrest shell will bend to accommodate the load, whereas when a heavy load is applied to the backrest shell the backrest bends and the supporting bars rock backwards. The bottom shell structure has a bottom portion and a partial backrest portion which are integrally formed on the same material and are connected by a curved portion with plural slots. Sideways notches are connected to the extreme left and right slots and extend toward the left and right edges of the shell structure. The edges of the shell adjacent the notches are curved into a U shape. This construction increases the flexibility of the curved portion, while maintaining a significant portion of the unslotted material strength. A separate shell structure is attached to supporting bars and forms the remainder of the backrest support.

Abstract: There is provided an interlocking supporting mechanism for supporting the seat and seat back of a chair, particularly an office chair. In the supporting mechanism a link system is utilized to interlock the seat with the seat back, so that the chair is capable of smoothly moving as a seated person moves.The front portion of a lever member is pivotally connected to the front portion of a frame member which is supported by a fixing member and which extends toward the front portion of the seat. The lever member is attached, with the aid of horizontal shafts on the right-hand and left-hand sides of the seat, to the lower portions of back supporting bars. A spring member is provided between the frame member and the lever member so that the lever member is rocked on the horizontal shafts. A member for receiving the seat includes a front seat-receiving member and a back seat-receiving member.