Upholstered chair with two-piece shell
BACKGROUND OF THE INVENTION 
     The present invention relates to furniture and, more particularly, to a chair adapted for use in the office environment. 
     Many different types of office chairs are presently available. Such chairs are adapted to a wide variety of tasks and different users. An office chair may include a base structure having a height adjustable pedestal mounted on a caster assembly for easy movement. A tilt or chair control mechanism may be supported on the base, and the back of the chair may tilt with respect to the base. Chairs are also provided which include a fixed base or nontiltable support structure. Side chairs, for example, may include a so-called sled-base. 
     Examples of prior office chairs may be found in commonly owned U.S. Pat. No. 4,390,206 entitled SYCHROTILT CHAIR CONTROL, which issued on Jun. 28, 1984 to Faiks et al; commonly owned U.S. Pat. No. 4,494,795 entitled VARIABLE BACK ADJUSTER FOR CHAIRS, which issued on Jan. 22, 1985 to Roossien and commonly owned U.S. Pat. No. 4,744,603 entitled CHAIR SHELL WITH SELECTIVE BACK STIFFENING, which issued on May 17, 1988 to Knoblock. 
     Prior office chairs have included a one-piece shell which defines both the seat portion and the back portion of the chair. The shell supports the user and is a structural member. The structural shell is, however, flexible so that the seat back portion may tilt or pivot with respect to the seat portion. Various steps are taken in forming the shell to provide the desired strength and tilting action. Since the shell is a one-piece member, force is needed to deform or bend the seat back with respect to the seat portion. This force must be accommodated when designing the chair in order to achieve a particularly desired ride or feel in use. Typical chair controls or tilt mechanisms include an axle connected to a pair of back uprights. The uprights and axle are biased to an upright or first position by a torsion spring. The uprights are moved to a reclined position against the increase in force generated by the torsion spring. The back portion of the one-piece shell is mounted on or secured to the vertical uprights of the chair control mechanism. In such chairs, a cushion assembly and upholstery are secured to the front surface of the shell. The upholstery material is pulled around the edges of the shell and secured to the back surface of the shell by staples or other suitable means. A decorative, non-load bearing outer shell is attached to the inner shell to enclose the back tilt mechanism and the unfinished edges of the upholstery material. 
     Various problems are presented with current office chair constructions. Difficulties are presented with molding the chair shell as an integral one-piece member including a back portion and seat portion. Existing tilt mechanisms including the back uprights and existing upholstery methods necessitate the use of the outer decorative shells or covers. The cover increases the thickness of the side profile of the chair and, hence, has an effect on the chair aesthetics and cost. 
     A need exists for an office chair which is readily adaptable to use with a tilt mechanism and which eliminates, however, the outer decorative shells or covers and the need for the vertical uprights to support the shell back. In addition, a need exists for a chair incorporating an upholstery and cushion assembly integrated with the chair shell to provide a finished appearance while eliminating the need for a decorative outer shell or cover. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the aforementioned needs are met. Essentially, a chair is provided including a base which supports a shell and cushion assembly. In one aspect of the invention, a seat shell is fixed to the base. A separate back shell is mechanically connected to the seat shell through a hinge structure. The separate shell construction eliminates problems heretofore experienced with fabricating the chair shell as a one-piece member defining both the back and seat portions. In addition, the seat shell and back shell may be fabricated from different plastic materials and in different colors. 
     In further aspects of the invention, the back shell is supported for movement between a fully upright and fully reclined position by a tilt mechanism. The tilt mechanism includes side support members which may define the arms for the chair. The support members are secured at one end to the tilt mechanism and biased to an upright position. Opposite ends of the support members are secured to the back shell intermediate the ends of the shell. The arms provide structural support for the shell and guide the back shell through the full range of tilt action. 
     In still further aspects of the present invention, a chair cushion assembly includes a molded foam member covered by an upholstery material such as a fabric. The back shell is formed with an integral attachment flap adjacent an upper edge thereof. The unfinished or frayed edges of the upholstery material are folded over the attachment flap and joined thereto. The attachment flap is then folded against the back surface of the back shell and secured thereto to form a finished edge. In further aspects, the back shell defines channels which extend along the lateral edges thereof. An elongated flexible retention member retains the upholstery in the channel along the lateral edges of the chair. A decorative trim strip may be included to cover the channel. 
     In accordance with the present invention, a chair is provided which may incorporate a tilt mechanism while eliminating the cost of back uprights heretofore used as well as eliminating the need for a separate decorative, non-load bearing cover or outer shell. The chair may be provided in an upholstered version with the upholstery material and cushion assembly readily attached thereto. The back shell may function as a visible outer chair surface. Problems heretofore experienced with mold tooling draw angles and the like resulting from the shape of the one-piece, L-shaped chair shells are eliminated. Molding separate seat and back shells which are mechanically interconnected by a hinge structure also eliminates the energy in the hinge area thereby improving the ride of the chair. A chair incorporating features of the present invention may be manufactured at reduced cost when compared to prior chairs while retaining desired functional advantages. The reduced profile of the chair in accordance with the present invention is aesthetically pleasing. The basic chair construction, including the upholstery and cushion assembly, back shell and seat shell, is adaptable to fixed base, sled base and tilt base mechanisms. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front, perspective view of an office chair in accordance with the present invention; 
     FIG. 2 is a side, elevational view thereof; 
     FIG. 3 is a rear, elevational view thereof; 
     FIG. 4 is a bottom, plan view thereof; 
     FIG. 5 is an exploded, assembly view of a chair in accordance with the present invention; 
     FIG. 6 is a front, elevational view of an arm incorporated in the present invention; 
     FIG. 7 is a cross-sectional view taken generally along line VII--VII of FIG. 6; 
     FIG. 8 is a bottom, plan view of a seat shell incorporated in the present invention; 
     FIG. 9 is a side view of the shell of FIG. 8; 
     FIG. 10 is a cross-sectional view taken generally along line X--X of FIG. 8; 
     FIG. 11 is a front, elevational view of a back shell incorporated in the present invention; 
     FIG. 12 is a side, elevational view of the back shell of FIG. 11; 
     FIG. 13 is a fragmentary, side view taken generally along line XIII--XIII of FIG. 11; 
     FIG. 14 is an enlarged, fragmentary, cross-sectional view illustrating the interconnection between the back shell and seat shell; 
     FIG. 15 is a front, elevational view of the shell and cushion assembly in accordance with the present invention; 
     FIG. 16 is a cross-sectional view taken generally along line XVI--XVI of FIG. 15; 
     FIG. 17 is a cross-sectional view taken generally along line XVII--XVII of FIG. 15; 
     FIG. 18 is a fragmentary view taken generally along line XVIII--XVIII of FIG. 15; 
     FIG. 19 is an enlarged, fragmentary, front view of an upper portion of the back shell in accordance with the present invention; and 
     FIGS. 20, 21 and 22 are fragmentary, cross-sectional views showing the method of attachment of an upholstery and cushion subassembly to the back shell. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A chair in accordance with the present invention is illustrated in FIGS. 1-5 and generally designated by the numeral 10. Chair 10 includes a base 12 having a pedestal 14, arms 16 and casters 18. In the embodiment illustrated, pedestal 14 includes a lower tube 20 which telescopingly receives a height adjustable tube 22. A chair control 26, which includes a tilt mechanism, as described in detail below, is secured to tube 22 of base 12. A shell and cushion assembly 30 defining a front surface 32 is mounted on base 12. Assembly 30 includes a configured back portion 34 and a configured seat portion 36. In the alternative, base 12 could take the form of a fixed base structure without the tilt chair control 26. In addition, assembly 30 could be attached to a sled-base arrangement, as is known in the art. 
     Chair control 26 includes a housing 42 which is fixed to pedestal tube 22. A pan or chair strap 44 is fixed to housing 42. Housing 42 and pan 44 are fixed with respect to ground. A conventional torsion spring assembly 46 is mounted within housing 42. Assembly 46 includes an axle 48 and coil springs 50. Springs 50 each include an end secured to housing 42 and another end fixed to the axle assembly 46. In accordance with the present invention, support members 52 are secured to the tilt mechanism 46. In the form illustrated in FIGS. 1-4, support members 52 define the arms for the chair. The arms include upper armrest portions 54, a lower inturned end 56 and an upper inturned end 58. End 56 includes a generally circular attachment flange 60. Flange 60 is bolted or otherwise suitably secured to axle 48. Tilt mechanism 46, therefore, resiliently biases the supports or arms 52 to an upright position as illustrated in FIGS. 1, 2, 3 and 5. Ends 58 of the arms 52 are formed with flattened attachment bracket portions 64. Portions 64 are secured to a rear surface of assembly 30. Portions 64 are enclosed by suitable trim caps 68. Suitable arm caps 70 are secured to armrest supports 52. Armrests 52, therefore, form structural members for the chair. The armrests support back portion 32 of assembly 30 and resiliently bias portion 32 to an upright position. As described in more detail below, assembly 30 includes structure permitting back portion 32 to pivot with respect to seat portion 36 and, hence, with respect to base 12. Seat portion 36 of assembly 30 is fixed to pan 44 and, hence, base 42 by suitable fasteners. A decorative cover 72 (FIGS. 4 and 5) is attached to an undersurface of seat portion 36 of assembly 30 to enclose or cover the structural portions of a control housing 42 and pan or strap 44. 
     An alternative, armless version is also illustrated in FIG. 5, wherein generally U-shaped supports 76 are provided for both right and left sides of the chair. U-shaped supports 76 replace support members 52. The supports 76 each include a lower end 78 having an integral attachment flange 80 and an upper end 82 including the back portion attachment bracket 84. Support members 76 function as structural supports supporting back portion 32 of assembly 30 and permitting tilt action of portion 32 with respect to seat portion 36. 
     Assembly 30 in accordance with the present invention includes a seat shell 102, a back shell 104 and a cushion and upholstery subassembly 106. Seat shell 102, as seen in FIGS. 8-10, is a molded structural plastic member. Shell 102 includes a rear edge 112, a forward edge portion 114, lateral sides 116 and a main body portion 118. The undersurface of portion 118 of shell 102 includes suitable reinforcing ribbing 120 to provide structural rigidity. Shell 102 further defines attachment bosses 122 and 124. Seat shell 102 is secured to seat strap 44 at bosses 122 and 124. Suitable fasteners 126 are threaded through pan 44 and into bosses 124. Socket structures 132 (FIGS. 8 and 14) are also defined by seat shell 102 adjacent lateral edges 116 at rear edge 112 thereof. Sockets 132 include a strap 134 formed integral with shell 102 and spaced downwardly therefrom to define an aperture 136. The undersurface of body portion 118 at sockets 132 also defines a stop 138. As described in more detail below, sockets 132 are used to interconnect back shell 104 with seat shell 102. 
     An upholstery attachment flap 142 is molded integrally with shell 102 along front edge 114. Attachment flap 142 is joined to main body portion 118 of shell 102 along an integral, living hinge 144. Hinge 144 extends transversely between lateral edges 116 of shell 102. Flap 142 is formed with integral snaps 148. As explained in more detail below, flap 142 may be folded about hinge 144 towards bottom surface 118 of shell 102. Snaps 148 are snapped into snap apertures 150. 
     Separate back shell 104 is best seen in FIGS. 11, 12 and 13. As shown therein, shell 104 includes a main body portion 162 having a front surface 164 and a rear surface 166. As seen in FIG. 3, rear surface 166 is exposed to view. The surface may be formed with a textured molded surface for aesthetic reasons. In the alternative, a fabric could be glued to the surface. Shell 104 includes lateral edges 167 having structural ribbing 168, a front or lower edge portion 170 and an upper edge portion 172. Shell 104 further defines longitudinally extending channels 174. Channels 174 extend parallel to lateral edges 167 of shell 104. The channels 174 open through rear surface 166 of the shell. 
     An upholstery attachment flap 182 is formed integral with upper edge portion 172 of shell 104. Flap 182 is joined to the main body portion 162 of the shell along an integral living hinge 184. Flap 182, as described in detail below, is foldable rearwardly against rear surface 166 of shell 102. Flap 182 is formed with integral, generally T-shaped snaps 188. As seen in FIG. 19, snaps 188 include wings 190 joined to a central stem portion 192. The T-shaped snaps 188 are dimensioned to be received and retained within a configured slot 194 formed on main body portion 162. Slot 194 includes a stem receiving portion 196. 
     The lower or front edge portion 170 of shell 104 is formed with a pair of outwardly extending attachment tabs 202. Tabs 202 are generally L-shaped in side elevation. Each tab 202 is hingedly joined to body portion 162 at a living hinge 204. As seen in the enlarged view of FIG. 14, tab 202 includes a first end portion 206, a generally vertical transition portion 208 and a second generally horizontal portion 210 which is joined to the main body portion. Attachment tabs 202 are molded integral with shell 104 at the outer lateral edges 167 thereof. 
     Fabricating the seat shell and back shell as separate pieces eliminates problems heretofore experienced with molding an integral one-piece shell. Separating the shell into two separate pieces improves the draw angle of the tooling allowing for better molding conditions. The shells may be molded in different colors. The seat shell, for example, which would be enclosed or not visible may be molded without color pigmentation. The back shell may be molded in any desired color for aesthetic reasons since the rear surface thereof is visible in use. 
     Shell 104 is easily attached to shell 102 by slipping attachment tabs 202 through the attachment apertures 136 formed in the seat shell 102. When shell 102 is fixed to the base 12 at strap 44, the strap, as seen in FIG. 14, engages attachment tab 202. Tab 202 is captured within the socket 134. The tab is sandwiched between the undersurface of shell 102 and the upper surface of pan or strap 44. Attachment strap 134 of shell 102 prevents rearward movement or withdrawal of attachment tab 202 since it engages the generally vertical transition portion 208 thereof. The tab is captured in the socket. The separate shell pieces are easily interconnected without the need for separate fasteners. The simple hinge connection between the tabs 202 and the shell main body portion eliminates the energy at the zone between the back shell and the seat shell. This elimination of energy improves the ride or feel of the chair as it moves from a fully upright to a fully reclined position. 
     The upholstery and cushion subassembly incorporated in the present invention is best seen in FIGS. 15, 16, 17 and 20. As shown therein, the assembly includes an inner molded foam component 232, a foam sheet 234 and an outer upholstery material 236. Upholstery material 236 may be any suitable fabric, leather or other covering material. The upholstery and cushion subassembly is preferably fabricated as a unit with the foam, foam sheet and upholstery bonded together. 
     It is presently preferred that the molded foam and cushion assembly be fabricated in accordance with the process disclosed in commonly owned U.S. Pat. No. 4,718,153 entitled CUSHION MANUFACTURING PROCESS, which issued on Jan. 12, 1988 to Armitage et al. To the extent necessary, this patent is hereby incorporated by reference. The process disclosed therein molds an upholstered chair cushion by placing a sheet of the upholstering material between two dies. Foam material is also positioned between the dies which are moved towards each other to compress the foam in the die cavities to force the upholstery material and foam to conform to the shape of the dies. The foam and upholstery are coated with an air permeable adhesive. Hot vapors are injected into the cavity to shape the foam cushion material and upholstery material generally to the sculpted configuration of the die. 
     The cushion subassembly in accordance with the present invention and as illustrated, for example, in FIGS. 16, 17 and 20 is formed with unfinished edges 242. Edge 242 may be frayed from cutting of the fabric or upholstery material. Edge 242 is attached to the shell assembly including back shell 104 and seat shell 102 by folding the edge over and onto fabric attachment flap 182 of shell 104. The unfinished edge 242 is attached to the rear surface of flap 182 by an adhesive or by suitable staples. As shown in FIGS. 21 and 22, flap 182 is then folded downwardly about integral hinge 184 until the snap fasteners 188 are received in apertures 194. The upholstery material 236 will be pulled over upper edge 172 of the back shell. The frayed edges of the fabric are hidden between flap 182 and a rear surface of the shell. As seen in FIG. 3, the attachment flap provides a finished appearance for the upholstery. 
     Prior to folding flap 182 over to secure the upholstery thereto, lateral edges 248 of the upholstery and cushion assembly are positioned within channels 174 defined by shell 104 (FIG. 17). The lateral edge portions of the fabric are retained within channels 174 by an elongated, flexible extrusion 288. Extrusion 288 is dimensioned to be press-fitted into the channel 174 to firmly retain and clamp the fabric edges to the chair shell 104 within the channel. The extrusions 288 are formed with a configured channel 286 adapted to receive a barbed end 289 of a trim extrusion 290. Extrusion 290 covers extrusion 288 and channel 174 to provide a pleasing finished appearance to the rear surface of the chair back (FIG. 3). Once the lateral edges have been secured within the channel 174, top flap 182 is folded over to complete the rear appearance of the upholstery and shell combination. 
     A forward edge 304 of the upholstery and cushion subassembly is folded over and secured to upholstery attachment flap 142 of seat shell 102. The upholstery material and foam is secured to flap 142 with adhesive or suitable staples. Flap 142 is then folded downwardly about its living hinge 144 until snaps 148 are received in snap apertures 150 defined by shell 102. This provides a finished appearance at the front edge of the seat shell. Lateral edges 308 of the fabric along the seat portion of the chair are similarly folded over against the undersurface of seat shell 102 and secured by suitable staples before flap 142 is secured. The undersurface of the chair is not normally visible in use. The undersurface may, however, be covered by a decorative shell 72, as seen in FIG. 4, to further complete the finished appearance of the chair. 
     The chair in accordance with the present invention offers significant advantages over prior chair constructions. Plastic shells may be employed for the back portion and seat portion. Problems heretofore experienced with molding such shells are, however, eliminated due to their fabrication as separate pieces and subsequent mechanical interconnection through a living hinge arrangement. Improved mold conditions are achieved and cost is reduced. The ride of the chair may be improved also by elimination of energy at the interface or zone between the back and seat portion of the chair. The shells are easily interconnected due to the tab and slot or socket arrangement with the tabs being readily captured by attachment of the seat to the base pan structure. The back shell may be fabricated in an aesthetically pleasing color. The attachment channels along the lateral sides of the back shell and the attachment flaps on the back shell and seat shell readily secure an upholstery and cushion subassembly to the shells. A finished edge is provided. Separate decorative outer shells or covers heretofore used to finish off the appearance of the chair and hide the cut or frayed fabric edges are eliminated. The separate tilt uprights for mounting the back portion of the chair on the base and the need for separate decorative covers are also eliminated through the use of the structural arms and tilt mechanism in accordance with the present invention. The resulting chair has a significantly reduced profile when compared to prior chairs incorporating a tilt mechanism with back uprights. The advantages of an adjustable chair including a tilt control for comfort are obtained at a significantly reduced cost from that heretofore available or achievable. The chair is relatively easily manufactured and assembled and should provide reliable operation in use. 
     In view of the above description, those of ordinary skill in the art may envision various modifications which would not depart from the inventive concepts disclosed herein. It is expressly intended, therefore, that the above description should be considered as only that of the preferred embodiment. The true spirit and scope of the present invention may be determined by reference to the appended claims.