Chair with zero front rise control

Abstract

A structural support shell for a tilt-back chair has a back portion, a seat portion, and a flexible compression zone extending between the back and seat portions in an integrally molded, one-piece unit. The chair has a base with a recline control and pivoting recline control lever. The seat portion of the shell is fixed to the base and the back portion of the shell is fixed to the recline control lever. The flexible compression zone provides a simplified construction for an ergonomic chair design having an effective axis of rotation between the back portion and seat portion which is located above the seat portion, forward of the back portion, and generally adjacent to the hip joints of a seated user.

Description

BACKGROUND OF THE INVENTION

The present invention relates to seating and more particularly to a chair for general office use.

Many office chairs have a seat portion and a back portion which tilts or reclines relative to a fixed base or support pedestal. This reclining action is accomplished by widely varying approaches, both structurally and philosophically. Relatively simple approaches, which include a chair control and a seat and back joined as a rigid unit, do not consider the natural motions and movement of the human body. The user is required to adapt to the chair. However, one common goal in contemporary design of office seating is the comfort of the user from the perspective of enhancing or at least not degrading the performance of the user in accomplishing the tasks of the office. With such attention directed to the performance of the user, interest has turned to the study of ergonomics in office seating. With the realization and development of ergonomics, a seating designer will endeavor to adapt the chair to follow the natural movement of the user. This can and has lead to sophisticated and complicated constructions which are correspondingly difficult and expensive to manufacture.

Ergonomics has led designers of office seating to focus on the natural and beneficial movements and positioning of a chair user and specifically the user's hips. The hip joints of an average user, seated upright with good posture in a chair, normally lie along an imaginary, generally horizontally oriented axis approximately 3 to 4 inches above the seating surface of the chair and approximately 3 to 5 inches forward of the plane of the chair back. The location of this hip joint axis in side elevational view with respect to a chair is generally referred to as the "H" point. Although the "H" point varies from one individual to another, depending upon the specific physical characteristics of the user, a model or preferred "H" point can be derived empirically, based upon studies of a wide range of different users. The "H" point is significant in ergonomic chair design because a user tends to rotate or roll the pelvis about the "H" point when moving from an upright or task position to a reclined or rest position. Therefore, it is desirable to approximate the "H" point axis in the construction of a chair recline control.

One chair structure responsive to ergonomic chair design and which attempts to approximate the "H" point axis incorporates a synchrotilt-type mechanism. In the synchrotilt mechanism, the seat portion of a chair moves in synchronization with the tilting of the back portion of the chair.

One such chair is disclosed by Linguanotto in U.S. Pat. No. 4,685,730, entitled SEAT, ESPECIALLY WORK SEAT, WITH SEVERAL POSITIONS, issued on Aug. 11, 1987. Linguanotto uses a three-piece seating cushion wherein a front seating portion is pivotally connected to a chair base and to a rear seating portion. The rear seating portion is hingedly connected to a back portion and is supported by a tilt bracket. The tilt bracket is a part of a chair control and is pivotally connected relative to the base. The back portion is also pivotally connected to the bracket.

Another synchrotilt chair is disclosed by Shields in U.S. Pat. No. 4,979,778, entitled SYNCHROTILT CHAIR, issued on Dec. 25, 1990. The Shields chair has separate seat and back portions with the seat portion connected to a chair base, at a front area of the seat portion, by a double pivot link. The seat portion is also pivotally connected to the back. The back portion is connected to a tilt control. When the back reclines, the rear of the seat portion moves rearwardly and downwardly, and the front of the seat portion moves rearwardly and downwardly lowering overall seat height.

Knoblock et al. disclose another synchrotilt chair in U.S. Pat. No. 4,776,633, entitled INTEGRATED CHAIR AND CONTROL, issued on Oct. 11, 1988. Knoblock et al. disclose the use of a structural shell having a seat portion and a back portion for use with a tilt mechanism. The back and seat portions are interconnected for mutual rotation about a common axis located above the seat portion and generally adjacent the hip joints of the seated user. A chair control supports the back and seat portions so that tilting of the back shifts the seat portion and the location of the common axis.

Yet another synchrotilt chair is disclosed by Franck et al. in U.S. Pat. No. 4,451,085, entitled CHAIR, issued on May 2, 1984. This chair uses a seat portion and a back portion which are interconnected by a flexible intermediate portion to accommodate changes in angle between the back and seat portions, when the back reclines. The seat portion is pivotally connected to a chair base, near a front edge of the seat portion. The back portion is connected to the chair base by a link which is pivotally connected at the back portion and pivotally connected at the base.

SUMMARY OF THE INVENTION

A chair according to the present invention provides a unique approach to the ergonomic design of reclining chairs by the use of a support shell having an integrally molded seat portion, back portion and a flexible compression zone, between the seat and back portions. In one aspect of the invention, the seat portion is fixed to a chair base and the back portion is fixed to a chair tilt control mechanism. The flexible compression zone flexes and compresses as the back portion reclines relative to the seat portion and chair base.

In another aspect of the invention, the chair is provided with side arms. The side arms are fixed to the back portion of the chair at one end and pivotally connected to the chair base, beneath the seat portion of the chair, at an opposing end. In an another aspect of the invention, outer back and outer seat shells are provided with integrally molded fasteners and the support shell is provided with corresponding apertures for receiving the fasteners so that the outer shells may be fastened to the support shell.

The chair of the present invention provides a simple and unique solution to the ergonomic chair design problem which heretofore has been answered with a myriad of sophisticated and complicated constructions. The chair may be provided with rigid side arms which pivot with the recline of the chair back and do not require any special, flexible materials. Further, the assembly of the chair is simplified by the use of integrally molded fasteners for attaching outer back and outer seat shells to the structural support shell, minimizing the number of components required for assembly and enhancing the ability to disassemble and reassemble the chair for recovering or other maintenance.

These and other objects, advantages and features of the present invention will become apparent upon review of the following specification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a chair according to the present invention;

FIG. 2 is a perspective view of the structural support shell of the chair of FIG. 1;

FIG. 3 is a fragmentary center line sectional view of the chair of FIG. 1;

FIG. 4 is a detail of FIG. 3 showing the flexible compression zone in upright and reclined positions;

FIG. 5 is a fragmentary side elevational view of the chair of FIG. 1 showing the rotation of a side arm between removal and assembled positions;

FIG. 6 is an exploded fragmentary perspective view of a fastener used with the chair of FIG. 1;

FIG. 7 is a sectional view along VII--VII of FIG. 6;

FIG. 8 is an exploded fragmentary perspective view of a pivot arm connector used with the chair of FIG. 1; and

FIG. 9 is an elevational detail view of the connector of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of a chair of the present invention is shown in FIGS. 1-5 and generally designated by the numeral 10. Chair 10 of the present invention includes a chair base 12, structural shell 14, cushion assembly 16, decorative outer seat shell 18, side arms 20, and decorative outer back shell 22 (FIG. 1).

Chair base 12 includes a base pan 24 which provides a fixed structure to which a seat portion 26 of structural shell 14 and side arms 20 are fastened. Pan 24 is preferably a stamped mild steel member and conventionally welded to a chair tilt control 28. Control 28 includes a back support member, bracket or lever.

Control 28 preferably has a housing 31 which is joined to pan 24 and includes a conventional, adjustable torsion spring subassembly 33. Subassembly 33 biases bracket 30 toward an upright or task position, as opposed to a reclined or rest position. Bracket 30 is fixed to the spring subassembly and pivots about an axis "C", as shown in FIG. 3.

Chair base 12 further includes a pedestal or column 32 upon which chair tilt control 28 is conventionally mounted (FIG. 1). Pedestal 32 may include any of a variety of known height adjustment mechanisms. Pedestal 32 preferably extends upward from a five arm base 34. Base 34 is preferably provided with casters 36, but may alternatively be provided with chair glides (not shown).

Structural shell 14 is a unitary or integral shell having seat portion 26, a back portion 38, and a flexible compression zone 40, extending between the seat and back portions 26, 38, respectively (FIGS. 1 and 2). Structural shell 14 serves to support cushion assembly 16 in a manner that allows a user to move naturally and freely in chair 10 during the performance of a variety of tasks and activities. Structural shell 14 has a generally L-shaped side elevational configuration (FIGS. 1-3), and is constructed of a resilient, semi-rigid, synthetic resin material, which normally retains its molded shape, but permits some flexing. Shell 14 is preferably molded from a polypropylene plastic, but may also be molded from other materials having the above, desirable characteristics. Back portion 38 of structural shell 14 may be selectively stiffened in accordance with the commonly assigned U.S. Pat. No. 4,744,603, entitled CHAIR SHELL WITH SELECTIVE BACK STIFFENING, issued on May 17, 1988 to Knoblock. Structural shell 14 includes two sets of fastener apertures 42, 44, two sets of apertures 48, 50 for receiving threaded fasteners, a series of tabs 52 for engaging the front edge 54 of pan 24 and a series of projecting tabs 56 for engaging the top edge 58 of control arm 30. Shell 14 is fixed at seat portion 26 to pan 28 by fasteners 146. Back portion 38 is fixed to bracket 30 by fasteners 144 (FIG. 3). The shell is in effect suspended hammock-style by the two point attachment. The front is fixed, however, so that there is zero rise of the front when the back is reclined or tilted.

Seat portion 26 of structural shell 14 has a generally concave surface forming a shallow bowl 62 to receive and support the buttocks of a user. Seat portion 26 becomes more planar and rolls off gently toward the forward edge 64 of structural shell 14 to support the rear of the thighs of a user. Shell 14 provides a gentle release of support and avoiding a harsh transition line where the thighs leave the support of the chair 10 at front edge 64.

Back portion 38 also has a complexly curved surface. The upper approximately one-half of back portion 38 has a shallow, transversely concave curvature, providing subtle, wraparound support to the thoracic and shoulder regions of a user. Below the upper concave portion, back portion 38 transitions through a convex area 68 to a concave area 70 near flexible compression zone 40. Each of convex and concave areas 68, 70, respectively, are generally linear transversely with the curvature of convex area 68 formed about an imaginary axis behind back portion 38 and the curvature of concave area 70 formed about an imaginary axis approximating the "H" point of a user (FIG. 3).

Flexible compression zone 40 is a generally concave area transitioning from area 70 of back portion 38 to bowl 62 of seat portion 26 (FIGS. 2 and 3). In the illustrated example, flexible compression zone 40 comprises a plurality of elongated slots 72 through structural shell 14 in a predetermined pattern. Slots 72 selectively relieve structural shell 14 at the flexible compression zone 40 and permit the shell to flex and compress, simulating rotation approximately about an imaginary horizontal axis at the "H" point.

A pair of hinges 74 rotatably interconnect seat portion 26 and back portion 38 (FIG. 2). In the illustrated example, hinges 74 are living hinges, defined by strap-like portions of structural shell 14, integrally molded with the shell, between seat portion 26 and back portion 38. As shown in the illustrated example, hinges 74 are preferably positioned at the outermost periphery of structural shell 14.

A pair of bearing blocks 76 are screw mounted to pan 24 at opposing sides 78, 80 (FIG. 1). Each bearing block 76 has a mounting tab 82 which engages a corresponding mounting slot 84, provided in pan 24 (FIG. 8). A pair or screw holes 86 are also provided in mounting strap 24 and align with screw holes 88, through bearing block 76. Screw holes 88 are sized larger than self-tapping screws 90 so that the screws easily slip into and extend through screw holes 88. Screw holes 86 are sized smaller than screws 90 for engagement with the threads of the screws. Each bearing block 76 is preferably injection molded of an acetal resin thermoplastic or other suitable engineering plastic.

A pin aperture 92 having a cylindrical center portion 94 and keyways 96 extends through bearing block 76 from a front surface 98 through a back surface 100 (FIGS. 8 and 9). Pin aperture 92 is configured to receive a pivot pin 102. Pivot pin 102 includes a cylindrical shaft 104. A pair of ears 106 project perpendicularly from shaft 104 at a terminal end 108. Ears 106 are preferably oriented approximately 180.degree. apart from each other. A tang end 110 of pivot pin 102 is connected at a lower end 112 of a side arm 20. Each side arm 20 is preferably molded around tang 110, which is also preferably knurled to enhance mechanical connection between tang 110 and side arm 20.

Pairs of arcuately shaped camming surfaces 93 are concentrically formed around pin aperture 92 on back surface 100 of bearing block 76 (FIG. 9). Ears 106 engage camming surfaces 93 when pivot pin 102 is inserted through pin aperture 92 and arm 20 is assembled to chair 10 as discussed below. A flat surface 95 projects from back surface 100, between each pair of camming surfaces 93, for engagement with ears 106 after arm 20 has been assembled. Thus, pivot pin 102 and bearing block 76 combine to form a bayonet mount between side arm 20 and base pan 24.

Each side arm 20 is preferably injection molded of a polypropylene plastic or other suitable structural plastic material and is a mirror image replica of the opposing side arm 20 (FIGS. 1 and 5). Each side arm 20 has an upper end 114. An angle bracket 116 is provided at upper end 114 for fastening arm 20 to back portion 38. Angle bracket 116 has a pair of screw holes 118 through a first leg of the bracket for screw attachment of upper end 114 to back portion 38. Angle bracket 116 also has a second leg (not shown) which is integrally molded into upper end 114 of side arm 20.

A plurality of fastener studs 120 are integrally molded with and project from the inner surfaces 122, 124 of outer seat shell 18 and outer back shell 22, respectively (FIG. 1). Outer shells 18, 22 and fastener stud 120 are preferably injection molded of a polypropylene plastic or other suitable structural plastic material. Fastener stud 120 is a generally U-shaped channel member having opposing sidewalls 126 and an interconnecting bight portion 128 (FIGS. 6 and 7). A center stiffening rib 130, which is generally parallel to opposing sidewalls 126 and depends from bight portion 128, may be used to enhance the structural stability of the fastener. As detailed in FIGS. 6 and 7, fastener 120 extends from surface 122 of decorative outer seat shell 18 to a terminal end 132. However, a plurality of fastener studs 120 project from both outer seat shell 18 and outer back shell 22. Fastener 120 has a series of biased teeth 134 formed on an outer surface of bight portion 128, near terminal end 132. Teeth 134 slope away from terminal end 132 so that fastener stud 120 may easily be inserted in an aperture 42 for attaching outer back shell 22 to structural shell 14 and aperture 44 for attaching outer seat shell 18 to structural shell 14 and to resist withdrawal of fastener stud 120.

Each aperture 42, 44 is generally rectangular, corresponding to fastener stud 120. As detailed in FIGS. 6 and 7 with reference to aperture 44, a flexible tab 136 extends into aperture 44 for engagement with teeth 134 when fastener stud 120 is inserted through the aperture. Opposing guide tabs 142 are provided along opposing sides of aperture 44, 42. A thickened edge, forming a wearplate 138, is formed along one side of the aperture 44, opposite tab 136. Wearplate 138 minimizes the potential wear and deformation of aperture 44 from contact with fastener stud 120. A gap 140 is defined between tab 136 and wearplate 138. Gap 140 is slightly less than the depth across sidewalls 126 so that tab 136 is held in a deflected or over center position to resist withdrawal of fastener stud 120 after fastener stud 120 is inserted into aperture 44. Wearplate 138 is particularly important when fastener stud 120 is withdrawn from aperture 44, since tab 136 will toggle over its center position and force fastener stud 120 against wearplate 138 when fastener stud 120 is withdrawn.

Cushion assembly 16 is a molded, upholstered chair cushion comprising an upholstery fabric attached to a sculpted chair cushion and having a perimeter fabric flap 150. Cushion assembly 16 may be formed in accordance with the commonly assigned U.S. Pat. No. 4,718,153, entitled CUSHION MANUFACTURING PROCESS, issued on Jan. 12, 1988 to Armitage et al. Cushion assembly 16 is simply assembled to structural shell 14 by positioning cushion assembly 16 on structural shell 14, wrapping fabric flap 150 around the peripheral edge 152 of structural shell 14 and preferably gluing flap 150 to the back surface of structural shell 14. Flap 150 may be glued to structural shell 14 with any of a variety of upholstery adhesives which are commonly known and used.

Structural shell 14 is assembled to chair base 12 by engaging tabs 52 with front edge 54 of pan 24 and engaging tabs 56 with top edge 58 of recline control lever 30 (FIG. 1). Back portion 38 is fastened and fixed to control lever 30 near top edge 58 by conventional methods and most preferably by self-tapping screws 144 through tabs 56 and lever 30 (FIG. 3). Seat portion 26 is fastened to chair base 12 at opposing sides 78, 80 of base pan 24 by conventional methods and most preferably by self-tapping screws 146.

After assembling bearing blocks 76 to base pan 24 at opposing sides 78, 80 by inserting mounting tabs 82 through mounting slot 84 and securing block 76 to pan 24 with self-tapping screws 90, as described above, outer seat shell 18 is simply assembled to seat portion 26 of structural shell 14 by aligning and inserting corresponding fastener studs 120 with apertures 44. Two cutouts 148 are provided in outer seat shell 18 so that bearing blocks 76 extend through and below outer seat shell 18.

Side arms 20 are assembled to chair 10 by positioning side arm 20 in assembly or removal position "A" as shown in FIG. 5, aligning pivot pin 102 with pin aperture 92, inserting the pivot pin 102 through the aperture 92 and rotating the side arm 20 generally forward to assembled position "B". With side arm 20 in the assembled position, upper end 114 of side arm 20 may be screw-fastened to back portion 38 by inserting a pair of self-tapping screws through angle bracket 116 and screwing the screws into apertures 48.

As with outer seat shell 18, outer back shell 22 is simply assembled to structural shell 14 by aligning fastening studs 120 with apertures 42 and inserting the studs 120 through the apertures 42.

Chair 10 is easily disassembled by reversing the above described assembly process, as required for reupholstery or maintenance of chair 10. Further, decorative outer seat and back shells 18, 22, respectively, may be used with an upholstery covering as is commonly known or may be used without a covering without affecting the scope of the invention.

In use, back portion 38 of structural shell 14 moves with bracket 30 between an upright position and a reclined or tilted position (FIGS. 3 and 4). As discussed above, seat portion 26 has a generally concave surface forming a shallow bowl 62 to receive and support the buttock of a user. Because of this geometry, the linear distance along support shell 14, from back portion 38 through seat portion 26 is significantly longer through the center of bowl 62 than along the peripheral edges of structural shell 14, through hinges 74 for example. As back portion 38 reclines with lever 30, compression forces develop in a structural shell 14 as indicated by arrows "F" in FIG. 4. As chair 10 reclines, compression forces develop, elongated slots 72 deform and narrow, and flexible compression zone 40 compresses about 1/4 to 3/4 of an inch or about 14% to 43% in response to the compression forces. Conversely, as chair 10 moves from the reclined position to the upright position, the compression forces diminish, elongated slots 72 resume their undeformed configuration, and flexible compression zone 40 expands to resume its uncompressed configuration. The front of seat portion 26 is fixed to the base pan. The front, therefore, does not move during reclining of the chair back. There is zero rise of the chair front. This reduces the thigh compression experienced in prior chairs.

In view of the foregoing description, those of ordinary skill in the art may envision modifications which would not depart from the inventive concepts disclosed herein. Therefore, the above description should be considered that of the preferred embodiment only and that the embodiment shown in the drawings and described above is merely for illustrative purposes. The true spirit and scope of the present invention may be determined by reference to the appended claims.

Claims

1. A chair having a base, a seat portion operatively connected with the base, and a back portion pivotally connected to the base for tilting movement of the back portion between an upright position and a reclined position relative to the seat portion, said chair further comprising:

a pair of side arms, each said side arm having an upper end attached to said back portion and having a lower end pivotally connected with the base so that said side arms pivot with the back portion relative to the base and said seat portion; and

a bayonet mount, including a pivot pin and a bearing block pivotally connecting said lower end of each said side arm with said base, said pivot pin being engageable and disengageable with said bearing block when said side arm is in a first position and said pivot pin being locked with said bearing block when said side arm is rotated from said first position to a second, assembled position.

2. A chair as defined in claim 1 wherein each said pivot pin has a terminal end extending generally toward the lower end of the opposing side arm and has at least one ear projecting perpendicularly from said pivot pin at said terminal end.

3. A chair comprising:

a base;

a recline control lever pivotally connected with said base for moving between an upright position and a reclined position, said lever having a terminal end away from said base;

a one piece structural support shell for receiving and supporting a user, said shell having a seat portion and a back portion, said back portion being fixed to said recline control lever and movable with said recline control lever between the upright and reclined positions, said seat portion being fixed to said base, and said shell further having a flexible compression zone extending between said seat portion and said back portion, said flexible compression zone providing a flexible connection between said seat portion and said back portion for accommodating changes in position between said seat and back portions when said back portion is moved between the upright and reclined positions, said flexible compression zone further providing a compressible zone between said seat portion and said back portion for compressing when said back portion is moved from the upright to the reclined position; and

a pair of opposing side arms, each said side arm having an upper end attached to said back portion and having an opposing, lower end pivotally connected with said base through a bayonet mount, said bayonet mount including a pivot pin and a bearing block said pivot pin being engageable and disengageable with said bearing block when said side arm is in a first position and said pivot pin being locked with said bearing block when said side arm is rotated from said first position to a second, assembled position.

4. The chair defined in claim 3 wherein each said pivot pin has a terminal end extending generally toward the lower end of the opposing side arm and has at least one ear projecting perpendicularly from said pivot pin at said terminal end.

5. The chair defined in claim 4 wherein:

said bearing blocks are attached to said base on opposing sides of said chair;

each said bearing block has an aperture corresponding to said pivot pins for receiving said pivot pins therethrough;

each said bearing block has a first side for engaging said lower end of said side arm when said pivot pin is inserted through said aperture, said first side being generally perpendicular to said aperture;

each said bearing block has a second side opposite to said first side and generally parallel thereto;

each said bearing block having a thickness defined between said first and second sides so that said ear of said pivot pin will extend beyond and be closely adjacent to said second side when said pivot pin is inserted through said aperture; and

each said second side includes a camming surface corresponding to each said ear of said pivot pin so that each said ear engages said camming surface and said side arm is drawn against said first surface of said bearing block when said side arm is rotated from said first position to said second position.

6. The chair defined in claim 5 wherein said recline control lever has an axis of rotation, each said pivot pin has an axis of rotation and said axes coincide.

7. The chair defined in claim 5 wherein said recline control lever has an axis of rotation, each said pivot pin has an axis of rotation, said pivot pin axes coincide and said pivot pin axes are near said recline control lever axis.

8. The chair defined in claim 3 wherein said chair further includes a plurality of integrally molded-in fasteners for connecting an outer shell with said structural support shell.

9. The chair defined in claim 8 wherein each said fastener includes a stud projecting from an inside surface of the outer shell and said structural support shell includes an aperture corresponding to each said stud for receiving said stud and through which said stud is inserted.

10. The chair defined in claim 9 wherein:

each said stud has a series of biased teeth formed along at least one side of said stud, said teeth being biased to facilitate inserting said stud into said corresponding aperture and to resist withdrawal of said stud from said corresponding aperture;

at least one flexible cantilevered tab projects into said corresponding aperture for engagement with said biased teeth;

each said stud has a thickness from said teeth to a side opposite said teeth; and

said corresponding aperture is dimensioned to define a gap, between said tab and a side of said aperture opposite said tab, which is smaller than said thickness so that an overcenter condition is obtained by said tab for resisting the withdrawal of said stud from said aperture when said stud is inserted through said aperture.

11. The chair defined in claim 10 wherein said side of said aperture which is opposite said tab is thickened to form a surface for engaging said stud and for minimizing wear of said side said aperture.

12. The fastener defined in claim 11 wherein said stud is a generally U-shaped channel member having a bight portion with a pair of generally parallel and spaced sidewalls extending to one side of said bight portion, said stud having a terminal end away from the outer shell, and wherein said biased teeth project from said bight portion in a direction generally opposite to said sidewalls, near said terminal end.

13. A chair comprising:

a base;

a recline control lever pivotally connected with said base for moving between an upright position and a reclined position, said lever having a terminal end away from said base;

a one piece structural support shell for receiving and supporting a user, said shell having a seat portion and a back portion, said back portion being fixed to said recline control lever and movable with said recline control lever between the upright and reclined positions, said seat portion being fixed to said base, and said shell further having a flexible compression zone extending between said seat portion and said back portion, said flexible compression zone providing a flexible connection between said seat portion and said back portion for accommodating changes in position between said seat and back portions when said back portion is moved between the upright and reclined positions, said flexible compression zone further providing a compressible zone between said seat portion and said back portion for compressing when said back portion is moved from the upright to the reclined position; and

a plurality of integrally molded-in fasteners for connecting an outer shell with said structural support shell, each said fastener including a stud projecting from an inside surface of the outer shell and said structural support shell including an aperture corresponding to each said stud for receiving said stud and through which said stud is inserted, said stud having a series of biased teeth formed along at least one side of said stud, said teeth being biased to facilitate inserting said stud into said aperture and to resist withdrawal of said stud from said aperture, said aperture having at least one flexible cantilevered tab projecting into said aperture for engagement with said biased teeth, said stud having a thickness from said teeth to a side opposite said teeth, said aperture being dimensioned to define a gap, between said tab and a side of said aperture opposite said tab, which is smaller than said thickness so that an over center condition is obtained by said tab for resisting the withdrawal of said stud from said aperture when said stud is inserted through said aperture.

14. The chair defined in claim 13 wherein said side of said aperture opposite said tab is thickened to form a surface for engaging said stud and for minimizing wear of said side of said aperture.

15. The fastener defined in claim 14 wherein said stud is a generally U-shaped channel member having a bight portion with a pair of generally parallel and spaced sidewalls extending to one side of said bight portion, said stud having a terminal end away from the outer shell, and wherein said series of biased teeth project from said bight portion in a direction generally opposite to said sidewalls.

16. A chair having a base, a seat portion operatively connected with the base, and a back portion pivotally connected to the base for tilting movement of the back portion between an upright position and a reclined position relative to the seat portion, said chair further comprising:

a pair of side arms, each said side arm having an upper end attached to said back portion and having a lower end pivotally connected with the base so that said side arms pivot with the back portion relative to the base and said seat portion; and

a bayonet mount at each said lower end of said side arms, said bayonet mount including a pivot pin and a bearing block pivotally connecting said lower end of said side arm with said base;

said pivot pin being engageable and disengageable with said bearing block when said side arm is in a first position; being locked with said bearing block when said side arm is rotated from said first position to a second, assembled position; having a terminal end extending generally toward the lower end of the opposing side arm; and having at least one ear projecting perpendicularly from said pivot pin at said terminal end;

said bearing blocks being attached to said base on opposing sides of said chair; having an aperture corresponding to said pivot pins for receiving said pivot pins therethrough; having a first side for engaging said lower end of said side arm when said pivot pin is inserted through said aperture, said first side being generally perpendicular to said aperture; having a second side opposite to said first side and generally parallel thereto; and having a thickness defined between said first and second sides so that said ear of said pivot pin will extend beyond and be closely adjacent to said second side when said pivot pin is inserted through said aperture;

each said second side including a camming surface corresponding to each said ear of said pivot pin so that each said ear engages said camming surface and said side arm is drawn against said first surface of said bearing block when said side arm is rotated from said first position to said second position.

17. A chair as defined in claim 16 wherein said back portion pivots about an axis of rotation and each said pivot pin rotates about said axis of rotation.

18. A chair as defined in claim 16 wherein said back portion pivots about a first axis of rotation, each said pivot pin rotates about a second axis of rotation, and said second axis of rotation is near said first axis of rotation.

19. In a seating unit having at least a first molded plastic component and a second molded plastic component, the first and second components being fastened to each other, the improvement of a fastener for fastening the first and second components together, comprising:

a stud integrally molded in and projecting from the first component, said stud being a generally U-shaped channel member having a bight portion with a pair of generally parallel and spaced sidewalls extending to one side of said bight portion, said stud having a terminal end away from the first plastic component;

means defining an aperture in the second component for receiving and capturing said stud and through which said stud is inserted for fastening the components together, said stud having a series of biased teeth formed along at least one side of said stud, said teeth being biased to facilitate inserting said stud into said aperture and to resist withdrawal of said stud from said aperture, said biased teeth projecting from said bight portion in a direction generally opposite to said sidewalls, near said terminal end; and

at least one flexible cantilevered tab projecting into said aperture for engagement with said biased teeth, said stud having a thickness from said teeth to a side opposite said teeth, said aperture being dimensioned to define a gap, between said tab and a side of said aperture opposite said tab, said gap being smaller than said thickness so that an over center condition is obtained by said tab for resisting withdrawal of said stud from said aperture when said stud is inserted through said aperture.

20. The fastener defined in claim 19 wherein said stud further includes a stiffening rib and said stiffening rib is generally parallel to said sidewalls and projects from said bight portion in the same direction as said sidewalls.

21. The fastener defined in claim 20 wherein said side of said aperture which is opposite said tab is thickened to form a surface for engaging said stud and for minimizing wear of said side of said aperture.