Box spring assembly

An improved spring unit for a box spring assembly in which a grid assembly is supported above a frame by a plurality of such spring units. The spring units provide self-limited deflection to prevent them from taking a permanent set after being overloaded. Each unit has two separate legs which support the spring assembly grid assembly to reduce point loadings on the grid assembly. The top portion of the spring spreads out forces over a large area on the grid to further reduce point loading. The configuration of the spring units enables them to be stacked densely without interlacing or twisting. The spring units include a center base bar, a pair of torsion bars extending perpendicularly therefrom, a center torsion bar which is connected to the upper and lower portions of the spring by connecting bars, and a top portion having a torsion bar and a pair of bar members extending in the same horizontal plane.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates generally to mattress foundation structures and more 
particularly to a box spring assembly of a type which utilizes non-coil 
springs. Box spring assemblies of this general type have been known since 
1964, the first such spring assembly being disclosed in U.S. Pat. No. 
3,286,281. Subsequently issued patents disclosing the same general type of 
box spring assembly are: U.S. Pat. Nos. 3,487,480; 3,506,987; 3,574,240; 
3,574,241; 3,665,529; 3,680,157; 3,755,833; 3,824,639; 3,852,838; 
4,060,862; 4,120,058; 4,131,961; 4,195,376; 4,218,790; 4,238,861; 
4,251,892; 4,253,208; 4,339,834; and 4,470,584. Box spring assemblies of 
the general type shown in the above list of patents, all of which are 
owned by the assignee of this application, are advantageous with respect 
to the conventional box spring assemblies using coil springs because they 
provide a desired stiffer foundation for the mattress and contain a 
reduced amount of wire. These box spring assemblies are also advantageous 
from the standpoints of prolonged service life, ease of assembly, and cost 
of manufacture. 
Additional box spring assemblies of this general type are shown in U.S. 
Pat. Nos. 3,546,723; 3,596,299; 3,722,013; 3,825,960; 3,833,948; 
3,835,485; 3,869,740; 3,990,121; and 4,000,531. 
Some current box spring assemblies typically have a wire grid assembly 
which is supported by an array of spring units attached to a supporting 
frame. One approach toward reducing costs of the box spring assembly is to 
minimize the gauge of the wires making up the grid assembly. Grid assembly 
wire diameter, however, is dependent upon the characteristics of the 
spring units on which the grid is supported. Some spring unit types do not 
distribute their loads on the grid assembly but instead exert undesirable 
localized or "point" loads which tend to permanently deform portions of 
the grid assembly when it is subjected to bedding loads. For assemblies 
employing such spring unit types, heavy gauge wire is necessary in the 
grid assembly to resist deformation. 
Accordingly, it is desirable to provide an improved spring module or unit 
which reduces localized loading on the grid assembly. As a means of 
simplifying fabrication, it is further desirable to provide a spring 
module which can be conveniently attached to both the box spring frame 
structure and the grid assembly. Since box spring assemblies may be 
subjected to overload conditions, the spring units should further be 
capable of withstanding such loading without sustaining permanent damage 
or taking a set. Therefore, the springs of a box spring assembly must 
include means for preventing deflection beyond elastic limit. Since large 
numbers of spring modules must be handled and packaged, it is further 
preferable for them to be stackable in a compact manner without 
interlacing or twisting.

DETAILED DESCRIPTION OF THE INVENTION 
A box spring assembly in accordance with this invention is shown in FIG. 1 
and is generally designated by reference number 10. FIG. 1 is a cut-away 
view showing a small portion of box spring assembly 10 and is 
representative of the entire structure which is a repetition of the 
elements shown in the figure. Assembly 10 includes a lower frame or base 
structure 12 conventionally made of interconnected wood members which 
provides a foundation for the remaining components. The frame 12 includes 
side rails 14, which are shown interconnected to form an outside corner, 
and further includes several cross rails 16 which extend laterally across 
the frame 12 and are fastened to side rails 14. 
Grid assembly 18 is positioned above the frame 12 and has a perimeter 
outline shape which corresponds to that of the frame 12. Grid asssembly 18 
includes a heavy gauge border wire 20 outlining its perimeter with a 
number of long wires 22 extending between the ends of assembly 18, and a 
number of cross wires 24 extending between the sides of the assembly and 
intersecting the long wires to define a wire grid. Cross wires 24 and long 
wires 22 are usually welded at their junctions and these wires are wound 
at their ends about the border wire 20 as shown in FIG. 1. 
A number of identical spring modules or units 26 are provided which are 
positioned between the frame 12 and the grid assembly 18. Details of the 
configuration of spring units 26 are best described with reference to 
FIGS. 2 through 4. Each of the spring units 26 is made from a single piece 
of wire and is comprised generally of a bottom portion 28, a top portion 
30, and a center portion 31. Bottom portion 28 includes base bar 32 formed 
from the center of the wire piece, and base torsion bars 34. 
When spring unit 26 is mounted, base bar 32 extends horizontally and is 
supported by the frame 12. Base torsion bars 34 extend perpendicularly 
from the ends of base bar 32, and lie within the same plane as the base 
bar. Center portion 31 of spring unit 26 includes connecting bars 36 and 
40, and center torsion bar 38. Connecting bars 36 extend upwardly from 
base torsion bars 34 and are oriented in a crossing fashion as viewed in 
FIG. 3. 
Center torsion bars 38 extend horizontally from connecting bars 36, and 
connecting bars 40 extend upwardly to connect center torsion bars 38 with 
top portion 30. Connecting bars 40, like bars 36, form a crossing pattern 
as viewed in FIG. 3. Spring unit top portion 30 includes upper torsion 
bars 42, attaching bars 44, and end bars 46, all of which lie in the same 
horizontal plane. 
As shown in FIG. 1, each of the spring units 26 is mounted on the frame 12 
by staples 50 which engage base bar 32. Spring unit top portion 30 is 
connected to grid assembly 18 by conventional metal clips 45 or other 
fasteners engaging attaching bar 44 and cross wires 24 (or long wires 22). 
Top portion 30 of spring unit 26 preferably defines a rectangular outline 
which is complementary in shape to the outlines formed by the 
intersections of long wires 22 and cross wires 24. Due to this 
configuration, upper torsion bars 42 and attaching bars 44 may be located 
in registry with the wires 22 and 24 such that the forces exerted by 
spring units 26 on grid assembly 18 are distributed, this avoiding 
localized loading on the grid assembly. Moreover, end bars 46 extend at an 
obtuse angle from attaching bars 44 and further tend to distribute loads 
by acting on both wires 22 and 24. Outwardly facing notches or protrusions 
47 formed at the junctures of bars 44 and 46 insure that the bars 42 and 
44 will form a support platform for the grid which is effective even if 
the bars shift slightly during use. By distributing loading on grid 
assembly 18, spring units 26 enable the gauge of wires making up grid 
assembly 18 to be reduced without sacrificing resistance to permanent 
deformation of the grid assembly. 
When spring units 26 are compressed by a load acting downwardly on them, 
torsion bars 34, 38 and 42 are twisted such that they store energy and 
provide resilience. A range of compression of spring unit 26 is provided 
until it reaches the deflected position shown in phantom lines in FIG. 3. 
In this position, center torsion bars 38 fall within the plane of spring 
top portion 30 such that spring unit 26 "bottoms out" and continued 
deflection of the torsion bar elements is resisted. This feature prevents 
excessive stress on the torsion bar elements so that they are permitted to 
deflect only in their range of elastic deformation. Once the spring units 
26 reach the deflected position shown in FIG. 3, the spring is capable of 
withstanding very high column loads before failure. 
Spring unit 26 according to the present invention has an "open top" 
configuration in that the ends of the wire making up the spring unit are 
within top portion 30. Due to this configuration, the spring unit 26 
behaves like a pair of individual spring elements which are joined at base 
bar 32. Such independent support enables spring unit 26 to be 
self-adjusting in nature and capable of responding to contour loading. 
This feature, coupled with the rectangular configuration of the top 
portion 30 of spring unit 26, serve to distribute loadings on grid 
assembly 18, thereby reducing undesirable localized loading. 
Spring units 26 further provide the advantage that the positioning and 
orientation of bars 32 and 34 allows clear access for stapling guns, thus 
facilitating attachment of the spring units to the frame 12. Another 
advantage of spring unit 26 is its "stackability". As is particularly 
evident from FIG. 2, the cross-sectional area swept out by the various 
portions of spring unit 26 increases progressively from bottom to top and 
provides an unobstructed inside cavity outlined by the spring elements. 
This configuration allows a number of spring units 26 to be stacked 
together in a dense form without interlacing or twisting, thus providing 
for efficient packaging and shipping. 
While the above description constitutes the preferred embodiments of the 
present invention, it will be appreciated that the invention is 
susceptible to modification, variation and change without departing from 
the proper scope and fair meaning of the accompanying claims.