PATENT ABSTRACT
A chair having a seat and a back rest comprises a fluid-containing cushion in the back rest that provides passive automatically adjustable support for the user&#39;s lumbar region. The cushion can comprise one or more fluid-containing chambers encompassing the areas of the user&#39;s upper back and lumbar regions. As the user leans backs, fluid is forced from the regions adjacent the upper back down to the lumbar region to provide enhanced lumbar support to the user.

PATENT DESCRIPTION
This patent application is related to the patent applications “Chair with Backward and Forward Passive Tilt Capabilities,” application Ser. No. 10/749,008; “Horizontally Adjustable Chair Arm Rest,” application Ser. No. 10/748,537; “Vertically Adjustable Chair Arm Rest,” application Ser. No. 10/749,010; “Chair with Adjustable Seat Depth,” application Ser. No. 10/748,079; and “Chair with Tilt Lock Mechanism,” application Ser. No. 10/749,009; each application being filed on even date herewith and incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     This invention relates to a chair having a seat and a back, wherein the back includes a cushion for providing improved resilience and support. In particular, the invention relates to a chair for office use wherein the back includes a cushion for providing improved resilience and support, which cushion automatically self-adjusts as the back reclines. 
     It is known in the art of office seating design to provide an office chair with a back that adjustably reclines in response to pressure exerted by the user&#39;s back, and then returns to its original position as the user&#39;s back moves forward. Such chairs are typically designed to provide a support for the user&#39;s lumbar region when the back is in the fully upright position. The lumber support can be either fixed or manually adjustable. One difficulty with such prior art chairs is that a fixed lumbar support, or even one that is manually adjustable, may not meet and comfortably support the lumbar regions of users of different heights. Another difficulty with such prior art chairs is that as the user reclines, the position of the user&#39;s lumbar region shifts with respect to the position of the fixed lumbar support in the backrest portion. Thus as the backrest portion reclines, the user&#39;s lumbar region may not receive optimum support over the range of motion of the backrest. 
     It is thus one object of the invention to provide a chair back that includes a cushion for automatically providing resilience and support for a user&#39;s back. 
     It is another object of the invention to provide a chair back that includes a cushion for providing lumbar support that automatically self-adjusts to comfortably support users of different heights. 
     It is still another object of the invention to provide a chair back that includes a cushion for providing adjustable resilience and support that automatically self-adjusts to comfortably support users as the user changes positions against the back, and as the back reclines over different angles of inclination in response to pressure exerted by the user&#39;s back. 
     SUMMARY OF THE INVENTION 
     These and other objects of the invention are met by a chair having a seat and a back, the back being capable of reclining in response to pressure exerted thereon by a user&#39;s back, the chair back including in its interior a cushion for providing automatically self-adjusting resilience and support, the cushion being fluid-containing. The cushion is substantially coextensive with at least that region of the surface of the chair back that engages the user&#39;s lumbar region. The cushion provides automatically varying pressure in response to the variable pressure exerted by different regions of the user&#39;s lumbar region, or other regions of the user&#39;s back that overlay the cushion. The cushion automatically accommodates users of different heights, and automatically self-adjusts to variations in applied pressures as the back reclines through a range of angles. 
     In a preferred embodiment, the cushion comprises two sheets of flexible, air-impermeable plastic film, sealed together so as to define a volume having a lower region and an upper region. The cushion preferably has seams that define a plurality of channels extending generally from the lower region to the upper region when the cushion is installed in a chair back. As the user leans his or her back against the chair back, greater pressure will be exerted against the cushion by the user&#39;s upper back and shoulders than by the user&#39;s lumbar region. This will force fluid from the upper region of the cushion downward toward the lower region, to provide increased resilient lumbar support for the user. The precise location of the increased lumbar support can vary along the length of the channels, so as to provide improved lumbar support as an individual user shifts position in the chair, and for users of different heights. Moreover, as the individual user reclines the backrest, the location of the increased lumbar support can shift in response to variable pressures exerted by different regions of the user&#39;s back, so that the improved chair back automatically provides optimum resilient back support to the user at any angle of inclination. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       The present invention is more readily understood by reference to the figures, wherein 
         FIG. 1  is a diagrammatic, sectional elevation view of a chair having a back of the invention; 
         FIG. 2  is a front elevation view, partially cutaway, of an embodiment of a chair back; 
         FIG. 3  is a sectional plan view of the cushion of  FIG. 2 ; and 
         FIG. 4  is a front elevation view of a another embodiment of a cushion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As illustrated in  FIG. 1 , a chair  10  includes a seat  11  and a back  12  having a forward facing side  14  and a rearward facing side  16 . The back  12  comprises a substantially rigid support member  18 , covered at least on its forward facing side with an upholstery-type covering  20  such as fabric, vinyl or leather. Optionally a pad  22  of foam or other resilient material such as is known in the art, is disposed on the forward facing surface of the support member  18 . 
     A fluid-containing cushion  30 ,  FIGS. 1-3 , is located between the support member  18  and the upholstery cover  20 . An optional pad  32  of foam or other resilient material can be disposed between the cushion  30  and the upholstery cover  20 . The cushion  30  comprises a first layer  34  and a second layer  36 , each of the layers being made of an air-impermeable plastic, the layers being hermetically sealed together about their respective peripheries to form a peripheral seal  38 . The cushion includes a top portion  40 , a bottom portion  42 , a left side portion  44  and a right side portion  46 . The cushion  30  preferably is sized and dimensioned to be substantially co-extensive with at least that region of the chair back  12  that will experience pressure exerted by the back of a user of the chair  10 , extending from the upper back and shoulders down to and including the lumbar region. For ease of reference, the structure of the invention will be discussed in terms of a lower region  50  and an upper region  52 , although it will be appreciated that the actual proportions of the inventive cushion that will serve as lumbar support region and upper back support region, respectively, will depend upon the size and height of the individual user. 
     In a preferred embodiment, the two layers  34 ,  36  of the cushion  30  are further joined by a plurality of seams  54 . The seams  54  together with the peripheral seal  38  define a plurality of channels  56  that generally extend from the lower region  50  to the upper region  52 . The channels can be substantially vertical, as illustrated in the figures, or they can be oriented at different angles. 
     Each channel  56  contains a fluid  58 . The channels are in fluid communication with one another through a plurality of openings  60  in each of the seams  54 . The sizes and locations of the openings  60  can be varied to achieve a desired response. Alternatively, openings  60  can be omitted, and each channel  56  will be completely sealed unto itself. 
     The fluid in the cushion can be air, gas or gas mixtures, liquid, or a flowable gel. The cushion should be only partially filled with fluid, so that the fluid can move from one region of the cushion to another, or from one region in a channel to another, in response to variations in applied pressure caused by movements of the user. 
     In use, when a user of the chair leans against the chair back  12 , the user&#39;s back will be in contact with forward surface  14  and exert pressure thereon. The user&#39;s upper back and shoulders will cause some compression of partially filled channels primarily in upper region  52 , causing fluid to be driven into lower lumbar region  50  where it will provide additional support to the user&#39;s lumbar region, where such support often is most needed. It may be seen that the exact location of the additional lumbar support along the length of channels will be determined automatically by the physical dimensions of each individual user. It is not necessary for an individual user to make manual adjustments to the chair in order to obtain optimum support in the lumbar region. Thus, the fluid support system of the instant invention provides an automatic passive adjustable support of the lumbar region, responsive to each individual user. The inventive system advantageously applies equalized pressure along the user&#39;s back. 
     Moreover, when a user reclines the chair back, the individual&#39;s spinal curvature will change, with the manner and amount of change depending on the individual&#39;s physical dimensions and the angle of inclination of the chair back. The lumbar region of the support member  18  is curved to conform generally to the lumbar region of a user. Generally, the radius of curvature of a user&#39;s back will be smaller than the radius of curvature of a lumbar region of the support member  18 . The space between the user&#39;s lumbar region and the lumbar region of the support member  18  defines a relatively small volume to be filled with fluid. As the chair back reclines, the user&#39;s spinal curvature changes, and in particular the arch of the user&#39;s lumbar region and upper back. The areas of pressure exerted by the user&#39;s back when reclined will vary along the length of the channels. Fluid within the channels will shift away from the areas where pressure is greatest, such as upper region  52  contacted by the user&#39;s upper back and shoulders, and towards the region where pressure is least, such as lower region  50  at the user&#39;s lumbar area. Typically, it is the lumbar region where support is needed most. The shifting of fluid within the channels will happen automatically as the user alternately reclines and straightens the chair back. At the same time, there will be less fluid volume in the cushion in upper region  52 , such that there will be greater stability of the user&#39;s upper back, with no unwanted side-to-side rolling motion. Thus the fluid-containing cushion of the instant invention automatically adjusts to the needs of different individual users, and to the different needs of a single individual as that user assumes different angles of inclination and different positions during the course of ordinary use of the chair. Advantageously, the user will not feel any discontinuity in pressure or support in the lumbar region, regardless of the angle of inclination; i.e., there is no “edge” where lumbar support ends, as can be experienced with systems that employ a discrete mechanical lumbar support member. 
     It will be appreciated that the channels preferably are not filled to their highest capacity. If the pressure in the channels were too high, then the cushion  30  would not yield in response to unevenly applied pressures; i.e., the fluid would not be able to shift from a region of higher applied pressure such as the upper region  52  to a region of lower applied pressure such as the lower or lumbar region  50 . 
     The cushion of the instant invention can be manufactured of fluid-impermeable plastic films that can be sealed together to form hermetic seals. Such plastic films can include, for example, vinyls, polyurethanes, polyvinyl chlorides, ethylene vinyl acetates, urethane coated membranes, polyolefins, sarans, and engineered multi-layer films. The plastic film selected for the cushion will be practically air-impermeable, having an air transmissibility rate as measured by ASTM D1434 (Standard Test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting) of less than about 100 cm 3 /m 2 /day/atm; preferably less than about 10 cm 3 /m 2 /day/atm; and most preferably less than about 5 cm 3 /m 2 /day/atm. The thickness of the plastic film can be in the range of about 2-20 mil, more preferably about 4-10 mil, and optimally about 4 mil. One particularly preferred material for an air-containing cushion is 4.0 mil Saranex 15, a multi-layer film available from Dow Medical Films and comprising a “Saran®” barrier resin co-extruded between outer layers of polyolefins. The films can be sealed together to form the peripheral seal  38  and seams  54  by known sealing means, such as adhesives, heat sealing, ultrasonic sealing, and RF sealing. Those skilled in the art will be able to select a sealing means suitable for the particular film material being used. A desired amount of air is injected into the various chambers of the cushion during the sealing process by methods known in the art of the manufacture of air-filled bladders. 
     The dimensions of the cushion, and the size, number, and angular orientation of the channels of the cushion, can be varied to accommodate (1) the needs of different users; (2) the design of the chair as a whole, including whether any optional pads of foam or other resilient material are used in front of and/or behind the cushion, and the characteristics of the optional pads; and (3) the different applications for which the chair will be used. The size and number of the openings  60  also can be varied to achieve a desired fluidic response. Further, additional padding such as a foam layer or a gel layer can be interposed between the cushion  30  and the upholstery cover or layer  20 . 
       FIG. 4  illustrates a preferred embodiment of a chair back cushion  100 . The cushion  100  comprises two sheets of plastic film (like that shown in  FIG. 3 ) sealed together with a peripheral seal  102  along a top portion  104 , bottom portion  106 , left side portion  108  and right side portion  110 . The top portion  104  of the cushion  100  includes two parallel, horizontal seals  112 ,  114 , and the bottom portion  106  of the cushion also includes two parallel, horizontal seals  116 ,  118 . Between the two upper seals  112 ,  114  are circular seals  120 ,  122 ,  124 ,  126 ,  128 . Between the two bottom seals  116 ,  118  are three circular seals  130 ,  132 ,  134 . Extending the full vertical length of the cushion are two seams that divide the interior of cushion  100  into a central or center chamber  140  and left and right side chambers  142 ,  144 . The central and side chambers are filled with air. Partial or short middle seams  146 ,  148  in each of the side chambers  142 ,  144  extend vertically from about the upper seals  112 ,  114  down to about the vertical midpoint of the chambers. These partial middle seams  146 ,  148  prevent the side chambers  142 ,  144  from bulging too much at the upper end, and maintain a more uniform pressure level throughout the length of the cushion. The middle seams  146 ,  148  divide each respective left side and right side chambers into two chambers  142   a ,  142   b  and  144   a  and  144   b . It will be understood that middle seams  146 ,  148  could be in the forms of spot welds, i.e., discrete spots where the two layers of cushion  100  are bonded together. Such spots could be arranged in lines or over an area, as long as they serve to moderate expansion of the side chambers  142 ,  141 . In the illustrated embodiment, the middle seams  146 ,  148  terminates in enlarged tear-drop shaped configurations  150 ,  152 , which relieves localized stresses in the plastic sheets. 
     The cushion  100  is about 18 inches high and about 14 inches wide along its top portion  104 . The sides taper inward slightly beginning about six inches from the bottom portion  106 , such that the width of the bottom portion  106  is about 10 inches. The center chamber  140  is pressurized with about 100 cubic centimeters of air, and the side chambers  142 ,  144  are each pressurized with about 300 cubic centimeters of air. Alternatively, an external pump can be provided so that the user can adjust the amount of air in the cushion in accordance with individual preferences. The center chamber  140  is of a generally constant width in a vertical direction and each of the chambers  140 ,  142 ,  144  is sealed from one another by the vertical seams  136 ,  138 . 
     The present invention provides a significant improvement over prior art chair back supports. Unlike foam pads, which simply compress in response to applied pressure, the fluidic support of the present invention redistributes pressure, such that as one part of the cushion compresses, another part expands, to provide additional support where it is needed most. 
     While the novel features of the present invention have been described with respect to particular embodiments, it will be appreciated by those skilled in the art that substitution of materials and modifications as to structure and details can be made without departing from the spirit of the invention.