Back shell with selective stiffening

Claim 2

A chair comprising: a base; a seat supported on said base; a back support pivotally supported on said base; a control operatively connecting said base and said back support, and selectively controlling rearward tilting of said back support; a cushion assembly shaped to support the back of a user thereon; a shell construction connecting said cushion assembly with said back support, said shell construction comprising: a semi-rigid, resiliently flexible sheet, having forward and rearward surfaces and a back portion shaped to selectively support a back area of an adult user thereon with the cushion assembly being on the forward surface of the shell construction; said back portion having a substantially flat planar shape with a lower area, a central area disposed directly behind a lumbar area of a seated adult user to selectively support the same and an upper area disposed above said central area and generally behind an upper back area and shoulder area of a seated user to selectively support the same and at a location which normally tends to selectively resist movement when the seated user moves his back in a direction having a laterally oriented component; and a plurality of laterally spaced apart first ribs formed integrally with said sheet on the rearward side thereof, and extending generally vertically along the central area of said back portion to stiffen the central area of said back portion in a vertical plane for firm support of at least the lumbar area of the seated user, yet dimensioned to permit at least the upper portion of said back portion to flex in a horizontal plane for improved freedom of movement to the upper back area of the seated user; second ribs formed integrally on the rearward surface of said sheet, and extending across the central area of said back portion in a generally X-shaped pattern and intersecting each other and said first ribs to control horizontal flexing of the upper area of said back portion; and a substantially horizontally oriented rib formed integrally with said sheet on a rearward surface thereof and extending laterally of the back portion, said horizontally oriented rib being positioned at an elevation slightly below the point at which the second ribs intersect each other, and wherein: said back portion has a vertical centerline; and said first-named ribs extend substantially parallel with the vertical centerline of said back portion to rigidify said back portion along said centerline, yet permit integral twisting of said back portion generally about said centerline.

Claim 3

A chair as set forth in claim 1 wherein: said back portion of said sheet includes a marginal edge; and wherein said sheet further includes a third rib formed integrally with said sheet on the rearward side thereof, and extending therealong at a preselected distance inwardly from said back portion marginal edge, and substantially parallel therewith.

Claim 4

A chair comprising: a base; a seat supported on said base; a back support pivotally supported on said base; a control operatively connecting said base and said back support, and selectively controlling rearward tilting of said back support; a cushion assembly shaped to support the back of a user thereon; a shell construction connecting said cushion assembly with said back support, said shell construction comprising: a semi-rigid, resiliently flexible sheet, having forward and rearward surfaces and a back portion shaped to selectively support a back area of an adult user thereon with the cushion assembly being on the forward surface or said sheet; said back portion having a substantially flat planar shape with a lower area, a central area disposed directly behind a lumbar area of a seated adult user to selectively support the same and an upper area disposed above said central area and generally behind an upper back area of a seated user to selectively support the same; and a plurality of first ribs formed integrally with said sheet on the rearward side thereof, and extending generally vertically along the central area of said back portion to stiffen the central area of said back portion in a vertical plane for firm support of at least the lumbar area of the seated user, yet permit at least the upper portion of said back portion to flex in a horizontal plane for improved freedom of movement of the upper back area of the seated user, said upper area being disposed on said back portion at a location which normally tends to selectively resist movement when the seated user moves his back in a direction having a laterally oriented component; and second ribs formed integrally on the rearward surface of said sheet, and extending across the central area of said back portion in a generally X-shaped pattern to control horizontal flexing of the upper area of said back portion, said back portion further including an uppermost edge, said first-named ribs extending along said back portion a predetermined distance which substantially rigidifies said back portion in a vertical plane from said lower area to an uppermost edge of said back portion, said back portion having a vertical centerline, said first-named ribs extending substantially parallel with the vertical centerline of said back portion to rigidify said back portion along said centerline, yet permit lateral twisting of said back portion generally about said centerline, said upper area of said back portion being disposed adjacent to a shoulder area of the seated user, said first-named ribs being spaced laterally apart in a predetermined pattern, said back portion of said sheet including a marginal edge; and wherein said sheet further includes a third rib formed integrally with said sheet on the rearward side thereof, and extending therealong at a preselected distance inwardly from said back portion marginal edge, and substantially parallel therewith; and a fourth rib formed integrally with said sheet on the rearward side thereof, and extending laterally along said back portion between opposite portions of said third rib, said fourth rib being oriented substantially horizontally, and positioned at an elevation slightly below the point at which are said second ribs intersect each other.

Claim 5

A chair comprising: a base; a seat supported on said base; a back support pivotally supported on said base; a control operatively connecting said base and said back support, and selectively controlling rearward tilting of said back support; a cushion assembly shaped to support the back of a user thereon; a shell construction connecting said cushion assembly with said back support, said shell construction comprising: a semi-rigid, resiliently flexible sheet, having forward and rearward surfaces and a back portion shaped to selectively support a back area of an adult user thereon with the cushion assembly being on the forward surface or said sheet; said back portion having a substantially flat planar shape with a lower area, a central area disposed directly behind a lumbar area of a seated adult user to selectively support the same and an upper area disposed above said central area and generally behind an upper back area of a seated user to selectively support the same; and a plurality of first ribs formed integrally with said sheet on the rearward side thereof, and extending generally vertically along the central area of said back portion to stiffen the central area of said back portion in a vertical plane for firm support of at least the lumbar area of the seated user, yet permit at least the upper portion of said back portion to flex in a horizontal plane for improved freedom of movement of the upper back area of the seated user, said upper area being disposed on said back portion at a location which normally tends to selectively resist movement when the seated user moves his back in a direction having a laterally oriented component; and second ribs formed integrally on the rearward surface of said sheet, and extending across the central area of said back portion in a generally X-shaped pattern to control horizontal flexing of the upper area of said back portion, said back portion further including an uppermost edge, said first-named ribs extending along said back portion a predetermined distance which substantially rigidifies said back portion in a vertical plane from said lower area to an uppermost edge of said back portion, said back portion having a vertical centerline, said first-named ribs extending substantially parallel with the vertical centerline of said back portion to rigidify said back portion along said centerline, yet permit lateral twisting of said back portion generally about said centerline, said upper area of said back portion being disposed adjacent to a shoulder area of the seated user, said first-named ribs being spaced laterally apart in a predetermined pattern, said back portion of said sheet including a marginal edge; and wherein said sheet further includes a third rib formed integrally with said sheet on the rearward side thereof, and extending therealong at a preselected distance inwardly from said back portion marginal edge, and substantially parallel therewith; and a fourth rib formed integrally with said sheet on the rearward side thereof, and extending laterally along said back portion between opposite portions of said third rib, said fourth rib being oriented substantially horizontally, and positioned at an elevation slightly below the point at which are said second ribs intersect each other.

Claim 6

A chair as set forth in claim 3 wherein: said second ribs have upper and lower leg portions disposed on opposite sides of the point at which said second ribs intersect each other; and said first-named ribs include uppermost ends disposed adjacent to upper ends of said second ribs, and which extend downwardly therefrom along said back portion.

Claim 7

A chair as set forth in claim 4 wherein: said second ribs comprise two pairs of laterally spaced apart, parallel extending ribs.

Claim 8

A chair as set forth in claim 5 wherein: said lower leg portions of said second ribs intersect said first-named ribs at preselected points, and said first-named and second ribs are integral at said points of intersection.

Claim 9

A chair as set forth in claim 6 wherein said first-named ribs uppermost ends are integral with the upper leg portions of said second ribs.