Abstract:
This invention provides a spring assembly for use in a chair tilt control mechanism. The tilt control mechanism is one that can recline and return a backrest for a chair. The spring assembly includes a cylindrical block that has first and second ends and a central bore. A pair of end caps located at each of the first and second ends of the block. Each end cap has a receiving section that can rotate within the central bore of the block. Each end cap also has a hole extending through it that provides a coupling point for the chair backrest. The spring assembly also includes at least one steel coil spring around the block. The spring has one terminal end coupled to the tilt control mechanism and the other end coupled to one of the end caps. The end caps rotate within the block as the chair backrest is reclined or returned. The forced needed to rotate the end caps is a sum of the spring force provided by the spring and the frictional relationship between the block and the end caps.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     TECHNICAL FIELD 
     This invention relates generally to chair control mechanisms, and more particularly to a spring assembly for a chair tilt control mechanism. 
     BACKGROUND OF THE INVENTION 
     Task chairs or office type chairs have evolved greatly over the years to improve the support provided to chair occupants and to provide chairs that better meet the usage needs of modem chair users. Comfort and promotion of ergonomically healthy sitting are among factors considered by occupants when choosing a chair. The development of backrest tilt control mechanisms has enabled chair occupants to adjust the backrest of a chair to their preferred positioning. 
     The spring assemblies associated with chair tilt control mechanisms allow occupants to recline the backrest, and also operate to bias the chair to its upright position when the reclining force is relieved. The spring assemblies are an important component in providing comfort to the user. To allow the users to adjust the chair properly, it is desirable to allow adjustments of the force needed to recline the chair and the force with which the chair returns to an upright position. 
     It is also desirable that more force be necessary in reclining the backrest of the chair than when resisting the biasing force on the backrest that returns it to an upright position. The difference in these forces is termed “dwell.” Dwell is important in meeting the needs of most chair users. With the dwell properly balanced, a user can recline the chair to a desired position and maintain that reclined position with very little effort. Ideally, the mechanism is adjustable so that the weight of the user&#39;s upper body balances the chair in the reclined position. 
     Rubber torsion springs have traditionally been used in the spring assemblies of tilt control mechanisms to achieve the desired dwell in the action of the backrest. In use, the rubber springs are mounted to a rod and energy is stored within the rubber springs as the backrest is reclined. But rubber springs have a limited life due to the inherent limitations of the material. For example, the rubber can break after a long period of use, or the spring characteristics can shift as the rubber ages. Additionally, even new rubber springs can vary due to batch differences in the base rubber material. A mechanism is needed that achieves the desired dwell in the action of the backrest, without the disadvantages of rubber springs. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention is directed to a steel spring assembly for creating dwell when returning the backrest of a chair to an upright position from a reclined position. 
     In one embodiment, the invention provides a spring assembly for use in a chair tilt control mechanism. The tilt control mechanism is one that can recline and return a backrest for a chair. The spring assembly includes a cylindrical block that has first and second ends and a central bore. A pair of end caps is located at each of the first and second ends of the block. Each end cap has a receiving section that can rotate within the central bore of the block. Each end cap also has a hole extending through it that provides a coupling point for the chair backrest. The spring assembly also includes at least one steel coil spring around the block. Each spring has one terminal end coupled to the tilt control mechanism and the other end coupled to one of the end caps. The end caps rotate within the block as the chair backrest is reclined or returned. The force needed to rotate the end caps is a sum of the spring force provided by the spring and the frictional relationship between the block and the end caps. 
     In another embodiment the spring assembly further includes a bearing located within the central bore that can rotate within the central bore of the block. Each end cap has a truncated receiving section that can rotate within the central bore of the block. The bearing and end caps rotate within the block as the chair backrest is reclined or returned. 
     Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views: 
     FIG. 1 is a perspective view of a chair; 
     FIG. 2 is a view of a tilt control mechanism taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a view of the tilt control mechanism similar to FIG. 2 with portions shown in cross-section to reveal details of construction; 
     FIG. 4 is a partial side view of the tilt control mechanism with parts broken-away to reveal details of construction; 
     FIG. 5 is a partial cross-section taken along line  5 — 5  of FIG. 3; 
     FIG. 6 is an exploded view of the spring assembly components of the tilt control mechanism; and 
     FIG. 7 is a view of another embodiment of the tilt control mechanism, similar to FIG. 3, with portions shown in cross-section to reveal details of construction. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention provides a spring assembly for a tilt control mechanism used on chairs. The spring assembly allows an occupant to exert a force on the backrest of the chair to recline the backrest. The spring assembly also biases the chair to an upright position when the reclining force is relieved. As described below, the spring assembly also provides dwell in the action of the backrest without resort to a rubber torsion spring. 
     With initial reference to FIG. 1, a chair on which the mechanism embodying the principles of the invention can be used is generally indicated by reference numeral  10 . Chair  10  is equipped with a base assembly  12 . Base  12  preferably has a number of castors  14  operably supported on the outer ends of a corresponding number of support legs  16 . Support legs  16  converge to a pedestal column  18 . Column  18  supports a gas cylinder  20  that allows the height of the chair to be adjusted by an occupant, as is known to those of skill in the art. The construction of the base  12  and column  18  is well known to those of skill in the chair industry. 
     With continued reference to FIG. 1, a tilt control mechanism  22  is coupled at one point to gas cylinder  20 . Tilt control mechanism  22  is also coupled to a seat  24  and a chair backrest  26 . Preferably, a pair of armrests  28  is also coupled to tilt control mechanism  22  or seat  24  or back  26 . 
     Having briefly described the basic elements of chair  10 , a more detailed description of the various elements of tilt control mechanism  22  is described below. FIGS. 2,  3 , and  4  show various components of tilt control mechanism  22 . Tilt control mechanism  22  has a base housing or chassis  30 . Chassis  30  is preferably a stamped metal piece that provides the overall structure for holding the various components of the mechanism as described below. Chassis  30  has a pair of spaced-apart sides, each of which has a hole  32 . Hole  32  is used to hold a bearing  34  in place, such as by a press-fit relationship. Bearing  34  is preferably steel and has a hole as well. A bushing  36  is located within the hole of bearing  34 , as best seen in FIG.  4 . The bushing  36  has a polygonal hole formed therein, the importance of which is described below. As seen in the figures, the hole is preferably a hexagonal hole. Bushing  36  has an outer diameter that closely matches the diameter of the hole in the bearing  34 , such that the bushing  36  can rotate relative to the bearing  34 . In a preferred embodiment, bushing  36  is made from a plastic material. The mechanism  22  also includes an elongated rod  38  that is held within the bushings  36 . More specifically, the shape of rod  38  matches the shape of the hole through the bushings  36 . In the preferred embodiment, the shape of rod  38  and the shape of the hole of bushing  36  are hexagonal. Rotation of the rod  38  rotates the bushings  36  within the bearings  34 . 
     Rod  38  is used to hold and operate a spring assembly  40  and to attach tilt control mechanism  22  to the frame of chair  10 . As would be understood by those of skill in the art, only the basic components of the tilt control mechanism  22  that relate to the spring assembly  40  are shown in the figures. Other components, such as a height adjustment mechanism or a tilt lockout mechanism could be incorporated into mechanism  22 , as would be understood by those of skill in the art. Returning to the spring assembly  40 , FIG. 6 most clearly shows the construction, which includes an end cap  42  on each end of the assembly  40 . End caps  42  are preferably made of a metal material, including steel, a sintered metal, a cast metal, or another material of comparable strength. Each end cap  42  has a cap section  44  that extends radially beyond a receiving section  46  that extends axially inward from cap section  44 . Each end cap  42  also has a spring fulcrum section  47 . As best seen in FIG. 4, cap section  44  has a notch  48  formed in a part thereof, the importance of which is described more-fully below. A polygonal hole  51  extends through both cap section  44  and receiving section  46 . Hole  51  is shaped to match the shape of rod  38 . In the preferred embodiment the hole  51  is hexagonal. 
     The spring assembly  40  also includes a block  52 . Block  52  has a hole  54  that extends axially through the entire length of the block  52 . The hole  54  is used to hold the block  52  on the receiving section  46  of the end caps. Each receiving section  46  extends into the hole  54 . The hole  54  has an inner diameter that closely matches the outer diameter of the receiving section  46 . Block  52  also has a pair of raised spring fulcrum sections  56  that are separated by a radially extending spring separator section  58 . As best seen in FIG. 2, spring separator section  58  is preferably shaped to separate a pair of coil springs  60 . 
     In another embodiment best shown in FIG. 7, the spring assembly  40  further includes a bearing  49  located within hole  54  of block  52 . Bearing  49  is able to rotate within hole  54 . In this embodiment each end cap  42  has a truncated receiving section  45  that extends into the hole  54 . A polygonal hole  51  extends through each end cap  42 , including truncated receiving sections  45 . Further, a polygonal hole  53  extends through bearing  49 . Polygonal holes  51  and  53  are shaped to match the shape of rod  38 . In this embodiment, hole  54  is used to hold the block  52  on the bearing  49  and on the truncated receiving sections  45  of the end caps. Hole  54  has an inner diameter that closely matches the outer diameter of the bearing  49 . Preferably, bearing  49  is made of a plastic material. 
     Each coil spring  60  has a longer tail end  62  and a shorter tail end  64 . In-between the tail ends  62  and  64  are a number of spring coils  66 . The short tail  64  has a notch  68  that is located and shaped to mate with the notch  48  in the end cap  42 . As best seen in FIGS. 2 and 6, springs  60  are held in place on block  52  and are separated from one another by spring separator section  58 . Longer tail end  62  and shorter tail end  64  pivot upon fulcrum sections  56  and  47 , respectively, allowing coil spring  60  to coil with minimum restriction. Preferably, springs  60  are made of steel. 
     The tension within springs  60  is preferably adjustable with a tension adjustment mechanism  70 . As best seen in FIG. 5, the long tails  62  of springs  60  are held within a receiving bracket or nut  72 . The receiving bracket or nut  72  is threaded onto a threaded rod  74 . Rod  74  terminates at a large bevel gear  76  that mates with a smaller bevel gear  78 . The smaller bevel gear  78  is mounted on the end of a rod  80  that terminates at a handle  82 . By rotating the handle  82 , the user can move the bracket  72  upwardly or downwardly to adjust the initial tension on springs  60 . The tension in springs  60  determines the force necessary to recline the backrest  26  of chair  10 . 
     Spring assembly  40  is held in place within tilt control mechanism  22  by rod  38 . More specifically, springs  60  are placed over the spring fulcrum sections  56  and  47  of block  52  and end caps  42 , respectively. The receiving sections  46  or  45  of the end caps  42  are placed in hole  54  of block  52 . Rod  38  then slides through bushing  36 , into the hole  51  of end caps  42  and out the other bushing  36 . The outwardly extending ends of rod  38  are then coupled to backrest  26 . As would be understood by those of skill in the art, many configurations are available for the attachment of the backrest  26  to the rod  38 . The attachment is made such that reclining the backrest causes rotation of the rod  38 . 
     As shown in FIG. 3, and as discussed above, receiving sections  46  of end caps  42  are placed within hole  54  of block  52 . Preferably, block  52  is made from a material that creates a desired frictional relationship with end caps  42 . The desired relationship creates a frictional force such that dwell is achieved in the action of spring assembly  40 . Again, one such material that may be used for block  52  is nylon in connection with a metal end cap  42 . It will be understood that any materials that create the desired frictional relationship and have properties necessary to maintain the frictional relationship may be chosen for end caps  42  and block  52 . One spring  60  is disposed over spring fulcrum sections,  47  and  56 , with the notch  68  of short tail  64  located within notch  48  of the end cap  42 . The long tail  62  is held within the receiving bracket  72 . 
     In another embodiment as shown in FIG. 7, and as discussed above, truncated receiving sections  45  and bearing  49  are placed within hole  54  of block  52 . It is preferable that block  52  is made from a material that creates a desired frictional relationship with bearing  49 . In another embodiment it is preferable that block  52  is made from a material that creates a desired frictional relationship with end caps  42  and bearing  49 . 
     In operation, a user can adjust the energy in springs  60 , which adjusts the force required to recline backrest  26 . The restoring torque exerted by springs  60  against the rotation of rod  38  can be adjusted by changing the position of the long tails  62 . Rotation of the handle  82  causes the receiving bracket  72  to move linearly along the axis of the rod  74 , which in turn moves tails  62  to the desired radial location. Preferably, the gear ratio of the bevel gears  76 ,  78  is such that a minimal amount of effort is required to adjust springs  60  to vary the initial restoring torque of the springs and, thereby, control the rate at which backrest  26  tilts rearwardly and returns to an upright position. 
     When the user reclines, rod  38  rotates. This rotation causes bushing  36  to rotate within bearing  34  and causes end caps  42  to rotate relative to block  52 . The friction between the end caps  42  and the block  52  adds to the reclining force, such that the force required to recline the backrest is greater than the return force of the backrest. In another embodiment the rotation of rod  38  further causes bearing  49  to rotate relative to block  52 . In this embodiment the friction between bearing  49  and block  52  adds to the reclining force. In another embodiment the friction between both bearing  49  and end caps  42  with block  52  adds to the reclining force. The steel spring assembly  40  can achieve roughly the same reclining force and dwell action as the traditional rubber torsion springs. The springs  60  are more durable than the rubber springs, and offer a more consistent spring assembly. 
     The action of backrest  26  may be adjusted by altering the materials and dimensions of the components of spring assembly  40 . As suggested above, different materials may be used for end caps  42  and block  52  to adjust the frictional relationship between these two components. The desired frictional relationship between end caps  42  and block  52  may also be altered by adjusting the dimensions of these elements. For example, the diameter of receiving section  46  can be altered to provide more or less clearance from block  52 . In addition, the outer diameter of receiving section  46  (FIG.  3 ), or the outer diameter of truncated receiving section  45  and bearing  49  (FIG.  7 ), along with the inner diameter of hole  54  of block  52  may be altered to adjust the amount of force necessary to recline the chair. Springs  60  may also be adjusted to vary their resistance. The dimensions of springs  60  and the number of coils  66  may be altered as desired. Such adjustments are also applicable to the embodiment including bearing  49 . 
     From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.