Bedding foundation having snap-in place modular wire springs
FIELD OF THE INVENTION 
     This invention relates to bedding foundations, and more particularly, to a box spring style of bedding foundation. 
     BACKGROUND OF THE INVENTION 
     Box springs or bedding foundations have traditionally included coil springs positioned in a vertical orientation so as to provide resilient support for a bedding mattress. In an effort to improve upon these conventional coil spring types of box spring or bedding foundation assemblies, numerous prior art assemblies have been developed which substitute modular wire springs for the more traditional coil springs. &#34;Modular wire&#34; springs is a term of art used to describe springs which derive their resiliency from torsion bars or configurations other than coils. Examples of modular wire springs embodied in box spring assemblies are to be found in U.S. Pat. Nos. 3,825,960; 3,833,948; and 3,835,485. Additionally, some prior art box spring assemblies have been developed which include combinations of coil and modular wire springs, as for example, the box spring assembly shown in U.S. Pat. No. 3,990,121. In those instances wherein modular wire springs and coil springs have been combined in a box spring, the modular wire springs have usually functioned to impart additional firmness to selected areas of the box spring, as for example, around the edge of the box spring or in the center section of the box spring. 
     A limitation of modular wire springs has been the relative smallness of the area of the top rectangular grid supported by the modular wire spring. A larger support area for the rectangular grid would improve the overall support provided by the box spring assembly. 
     One problem associated with some modular wire springs is the lack of resiliency and softness of the support provided by the spring, particularly upon initial deflection of the springs. Modular wire springs are very resilient, i.e., bounce back from deflection, but do not provide the relatively soft support or deflection characteristics achievable by coil springs. What is needed is a spring which has the softness or feel of coil springs in a resilient modular wire spring. 
     It has therefore been an objective of this invention to provide an improved box spring with greater support for a larger area of the top rectangular grid. 
     Still another objective of the present invention has been to provide a modular wire spring that maintains the resiliency of previously known modular wire springs while providing softer resilient support. 
     SUMMARY OF THE INVENTION 
     The improved box spring of this invention comprises a top wire grid and a base frame interconnected by a plurality of modular springs. Each modular spring comprises a flat, horizontal, head section having two parallel edge connector bars attached to opposing ends of a diagonally extending central connector bar by two attachment segments. Each attachment segment has an offset section formed therein. In order to lock the spring within a rectangular pocket of the grid, each edge connector bar passes beneath both a longitudinal and transverse grid wire at one corner of the pocket within which a spring is snap-fit and each offset section of the two attachment segments are urged over parallel longitudinally extending wires of the rectangular pocket. The frictional fit of the attachment segment and the longitudinally extending grid wires over which they are located prevents the flat, horizontal head of the spring from sliding horizontally and inadvertently releasing from the pocket into which it is snap-fit. Since each edge connector bar passes beneath both a transversely and longitudinally extending grid wire at one corner of the grid, the modular spring provides exceptionally good support of the grid at more points along the pocket than prior modular springs. 
     A pair of resilient legs extend downwardly from the flat horizontal head section of each modular spring. Each of the vertical legs comprises at least three parallel horizontal torsion bars interconnected by two edge loops. The edge loops differ substantially in radii so as to impart differing deflection characteristics to the spring. Specifically, one edge loop is substantially larger in radii than the other edge loop of the same leg so that the larger radius loop deflects before the smaller loop and thereby renders the spring initially soft. When the larger radius loop is sufficiently deflected, it becomes harder or more firm and the second smaller radii loop begins to deflect. Thereby, these differing radii loops contribute to the initial softness without loss of resiliency in the bedding foundation constructed according to the principles of the invention. 
    
    
     These and other objects and advantages of the present invention will be more readily apparent from the following description of the drawings, in which: 
     FIG. 1 is a top plan view, partially broken away, of a box spring incorporating the invention of this application. 
     FIG. 2 is a perspective view of one corner portion of the box spring assembly of FIG. 1. 
     FIG. 3 is an enlarged perspective view of one portion of the box spring assembly of FIG. 2. 
     FIG. 4 is a side elevational view of one spring module of the box spring assembly illustrated in FIG. 1. 
     FIG. 5 is a front elevational view of the spring module of FIG. 4. 
    
    
     With reference first to FIGS. 1 and 2, it is seen that the bedding foundation or box spring 5 of this invention includes a box spring assembly 6 over the top of which padding 7 is placed. The box spring assembly 6 and padding 7 are encased in an upholstered covering 8. 
     The box spring assembly 6 of FIG. 2 comprises a wooden base frame 10 upon the top of which there is mounted a plurality of modular wire springs 14 for supporting a top wire grid 16. The top wire grid 16 is intended to resiliently support a mattress, as is conventional in the bedding industry. 
     The base frame 10 is rectangular in configuration and comprises a pair of longitudinally extending side boards 18 (FIG. 2), as well as a pair of transversely extending end boards 20, nailed or otherwise secured to the top of the side boards 18. Additionally, there are a plurality of wooden slats 22 which extend transversely across the rectangular base between the side boards 18. These slats are also nailed or otherwise fixedly secured to the top of the side boards 18. 
     The top wire grid assembly 16 of FIG. 2 comprises a border wire 24 and a wire grid 26. The border wire 24 is formed into a rectangular configuration and overlies the peripheral edge of the rectangular base frame. The wire grid 26 is secured to and located in the plane of the border wire 24, the grid and border wire defining the top plane of the box spring assembly. The wire grid 26 comprises a plurality of spaced, transverse wires 27 and a plurality of spaced, longitudinal wires 28. The transverse wires 27 are arranged in pairs 27a, 27b, and the longitudinal wires 28 are similarly arranged in pairs 28a, 28b. All of the wires 27 and 28 of the wire grid 26 extend between opposite sides and ends, respectively, of the rectangular border wire 24. These grid wires overlie the rows and columns of formed wire springs or modular springs 14 so as to secure the top of those springs 14 against lateral and longitudinal displacement. The edgemost ones of the transverse wires 27 and longitudinal wires 28 lie in close adjacency and parallel to the border wire so as to provide edge support of the border wire from the springs 14 which are snap-fit into pockets of the wire grid defined by these edgemost wires as explained more fully hereinafter. 
     The ends of all the grid wires 27, 28 are hooked around the border wire 24 and are preferably welded to the border wire. The intersections or cross-over points of the transverse wires 27 and the longitudinal wires 28 are preferably welded to provide a matrix of pockets 29 contained within an integral wire top grid. In manufacture, the border wire 24 and the wire grid 26 are all preformed into a top wire grid 16 subassembly. 
     The top wire grid 16 is connected to the wooden frame by the modular wire springs 14. With particular reference to FIGS. 2 and 3, it is seen that each of these modular wire springs 14 comprises a unitary wire spring strip having a flat, horizontal, top section or head 48 and a pair of substantially vertical legs 44, 46. Each vertical leg 44, 46 is formed by a pair of edge loops 40a and 40b, three torsion bars 42a, 42b and 42c, and a vertical connector bar 55. Each vertical leg 44 is a mirror image of the other vertical leg 46 of the spring 14 as shown in FIGS. 3 and 4. The two edge loops 40a and 40b of each vertical leg are interconnected by the middle straight torsion bar 42b. The uppermost edge loop 40a is connected at its upper end to one end of torsion bar 42a. The other end of torsion bar 42a is joined to the vertical connector bar 55 by a sharply radiused curved portion 57 of a vertical segment 55 that joins vertical leg 44 to flat head section 48. The second edge loop 40b is connected at its lower end to the torsion bar 42c. The bottommost torsion bar 42c is connected to the base frame 10 by staples 38. 
     The substantially flat, top section or head 48 of each spring comprises a central connector bar 49 and a pair of parallel edge connector bars 51a and 51b. Attachment segments 53a and 53b connect one end of each edge connector bar to opposite ends of the central connector bar 49. The opposite ends of the edge connector bars 51a and 51b are connected to the vertical connector bars 55 on each of the vertical legs 44 and 46. In the practice of this invention, the attachment segments 53a and 53b each have an inwardly extending offset 50 formed therein. 
     In the preferred practice of this invention, each vertical leg is displaced from a vertical plane by approximately 15° as best illustrated in FIG. 5. In other words, both legs 44, 46 slope inwardly from the edge connector bars 51 toward one another to the point of attachment with the base frame. 
     At the top, all of the springs 14 are attached to the grid 16 by having the substantially flat or planar top sections 48 of the springs snap-fit into pockets 29 of the grid defined by intersecting pairs of transverse wires 27a, 27b and longitudinal wires 28a, 28b. To facilitate this snap-fit interconnection of the top sections 48 of the springs 14 within the pockets 29 of the wire grid, it will be noted in FIGS. 2 and 3 that the longitudinal wires 28 pass under the transverse wires 27 at the intersections thereof. It will also be noted that the longitudinal wires of each spring module receiving pocket 29 are bent or offset upwardly between each pair of transversely extending wires. The upward offset is approximately equal to the diameter of the wire from which the spring module is formed. Approximately medially of the upwardly offset portions of the longitudinal wires 28, the wires are bent or offset downwardly for approximately the middle third of the length of pocket defining portion of the longitudinal wires. This downward offset 54 is also equal to approximately the diameter of its module spring wire. Otherwise expressed, the pocket defining portions of each longitudinal wire of the grid is offset upwardly in the outer two thirds of the pocket and offset downwardly in the center one third. 
     When the flat planar head 48 of the springs are snap-fitted into place in the pockets 29 of the grid, each edge connector bar 51a, 51b passes beneath both a transverse wire 27 and longitudinal wire 28 at the intersection of the two wires or at the corner of a pocket. As shown in FIG. 3, edge connector 51b supports or passes beneath wires 27b and 28b at intersection 58b while edge connector 51a passes beneath and supports wires 27a and 28a at intersection 58a at the diagonally opposed corner of rectangular pocket 29. Support of both transverse and longitudinal wires at opposing intersections or corners of the rectangular pockets in grid 16 provides box spring 5 with very good support of the grid of the box spring. 
     To assemble the springs 14 with the grid 16, the flat head section 48 of a spring 14 is snap-fit into a pocket 29 of the grid by first locating one offset 50 of an attachment segment 53 within the indentation or offset 54 of the longitudinal wire 28a which partially defines pocket 29. The central connector bar 49 diagonally extends from one corner of pocket 29 to another in this position. The other offset portion 50 of the other attachment segment 53 is then located beneath the indentation or offset 54 of the opposing longitudinal wire 28b. The offset 50 is then pulled or forced outwardly until the portion 50 of the head snaps over the indentation or offset 54 in the opposing wire 28b to snap-fit flat head 48 of spring 14 into pocket 29 of wire grid 16. The spring is now fixedly attached to the wire grid. 
     In practice, the box spring of FIGS. 1-3 is assembled by first nailing the end boards 20 to the tops of the side boards 18 and by nailing the slats 22 to the tops of these same side boards. The preassembled top wire grid 16 having the springs 14 mounted therein is then fitted over the top of the assembled wooden frame so as to position the bottom section torsion bars 42c of the formed or modular wire springs 14 atop the base frame. The bottom, free end of torsion bars 42c of the wire springs 14 are then stapled to the tops of the end boards 20 and the ends of the slats 22. 
     It is important to note that the edgemost longitudinal and transverse grid wires which partially define the pockets 29 for the edgemost springs 14, are located closely adjacent the border wire 24. In practice, these edgemost grid wires extend parallel to the grid wire but are spaced approximately two centimeters from the border wire 24. The need for this close adjacency positioning of the edgemost grid wires derives from the fact that the border wire is made from such heavy gauge or large diameter wire or rod that it is not suitable for snap-fit connection with the edgemost springs 14. By locating the edgemost grid wires in close adjacency, but spaced from, the border wire, the springs 14 may be snap-fit thereto while still providing vertical edge support for the closely spaced border wire. The edgemost grid wires thus act as an inner border wire extending parallel to, but slightly spaced from, the border wire 24, but of much smaller diameter wire suitable for snap-fit connection with the top flat section of the springs 14. 
     To complete the foundation after completion of the box spring assembly, the fabric pad 7 is overlaid over the top of the wire grid and the complete assembly, including the rectangular wooden frame, the springs, the top wire grid, and the fabric pad, are enclosed within the upholstered covering 8. 
     While we have described only one preferred embodiment of our invention, persons skilled in this art will appreciate changes and modifications which may be made without departing from the spirit of our invention. For example, the relative positioning of the snap-fit modular wire springs in the box spring assembly may be varied without departing from our invention, or those modular wire springs may be mixed with coil springs or other modular springs at selected sites in the assembly. Therefore, we do not intend to be limited except by the scope of the following appended claims.