Box spring assembly with improved stiffness characteristics

A box spring assembly which includes a generally rectangular frame, a plurality of wire springs mounted on the frame and connected to each other so as to yieldably resist downwardly directed bedding loads. Each of the springs has an elongated body portion arranged above the frame and downwardly extending end portions, each of the end portions having an upper section and a lower section which are located in planes that are upright and generally perpendicular to each other with each of the sections being comprised of integral legs arranged in a generally V-formation rotated about ninety degrees and with the included angle between the legs being less than ninety degrees. This construction enables the spring end portions to yieldably resist bedding loads with both bending and torsional stresses thereby enabling increased load-resisting capabilities in the spring end portions with a resulting efficient use of spring wire material.

BACKGROUND 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; and 3,852,838. Box 
spring assemblies of the general type shown in the above list of patents, 
all of which are assigned to 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 of 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. 3,596,299; 3,722,013; 3,825,960; 3,833,948; 3,835,485, 
3,869,740; 3,990,121; and 4,000,531. 
The present invention provides a box spring assembly which utilizes a 
different spring from the formed wire springs utilized in the patented box 
spring assemblies discussed above. The spring in the present box spring 
assembly is a stiffer spring than springs heretofore used, this increased 
stiffness being an inherent feature of the spring achieved by virtue of 
the spring configuration. Furthermore, this increased stiffness is 
achieved without any reduction in the usual height of the box spring 
assembly, and enables the production of firmer box spring assemblies from 
less raw material. 
It is an object of the present invention, therefore, to provide an improved 
box spring assembly having increased resistance to bedding loads and 
requiring a decreased amount of raw material relative to prior art 
structures. 
SUMMARY OF THE INVENTION 
The box spring assembly of this invention consists of a generally 
horizontal rectangular frame and a plurality of wire springs mounted on 
the frame and connected to each other so as to yieldably resist downwardly 
directed bedding loads, each of the springs being formed of spring steel 
wire having an elongated body portion arranged above the frame and 
downwardly extending end portions secured to the frame. Each of the spring 
end portions has an upper section and a lower section which are located in 
planes that are upright and generally perpendicular to each other, each of 
the sections being comprised of integral legs arranged in a generally 
V-formation that is rotated about ninety degrees with respect to the 
horizontal. The included angle between the legs in each of the sections is 
less than ninety degrees so that the legs can be bent toward each other. 
As a result, the included angle between the legs in each section is 
decreased in response to the application of a downwardly directed bedding 
load to the upper end of the end section. 
The end sections are connected so that in response to load, they will twist 
as well as bend and are mounted to the frame by means of a torsion bar. 
This enables the end sections to resist bedding loads by means of both 
tensile and shear stresses induced in the spring end portions. This dual 
capability of the spring end portions to accommodate both shear and 
tensile stresses of substantial magnitudes enables the spring end portions 
to yieldably resist bedding loads with a reduced amount of spring 
material. In addition, each spring imparts increased stiffness to the box 
spring assembly without danger of taking a set, namely, incurring 
permanent deformation in response to load. Increased firmness is 
particularly desirable from a bedding comfort stand-point since the 
comfort qualities of "hard" box spring assemblies are becoming more and 
more appreciated. 
Each spring assembly includes main springs arranged on the frame so that 
the angularly extending end sections are adjacent to the periphery of the 
frame and are secured to the top side of the frame. A conventional 
rectangular border wire is secured to and extends between the end portions 
of the springs at a position overlying the frame and adjacent the 
periphery of the frame. Intermediate springs are mounted on the frame at 
positions spaced from the border wire so as to support the main springs 
intermediate their ends.

With reference to the drawing, the spring assembly of this invention 
indicated generally at 10, is illustrated in FIG. 1 as consisting of a 
generally rectangular horizontally disposed frame 12, usually formed of 
wood, and a wire spring assemblage 14 mounted on the top side of the frame 
12. The frame 12 has side rails 16, end rails 18, and cross rails 20 which 
are secured to and extend between the side rails 16. The cross rails 20 
are shown in the assembly 10 as being formed of metal with spring mounting 
slots 22, but it is to be understood that wooden cross rails can be used 
as an alternative to the metal cross rails 20. 
The spring assemblage 14 consists of a plurality of first main springs 24 
which extend longitudinally of the frame 12 and a plurality of second main 
springs 26, which extend transversely of the main frame 12. The main 
springs 24 and 26 are supported intermediate their ends by intermediate 
springs 28. All of the springs 24, 26, and 28 are formed of spring steel 
wire and are substantially identical in that each has a generally 
horizontal body portion located above the frame 12 and a pair of depending 
end portions which are mounted on the frame 12. Accordingly, only an 
intermediate spring is illustrated in detail in FIGS. 3, 4, and 5 and only 
an intermediate spring will be described in detail hereinafter with like 
numerals indicating like parts on the springs 24, 26, and 28. 
As shown in FIGS. 2, 3, 4, and 5, the spring 28 includes a generally 
horizontal body portion 30 disposed above the frame 12 a distance 
corresponding to the desired height of the box spring assembly 12, this 
height normally being the standard height for box springs in the bedding 
industry. A pair of yieldable end portions 32 extend downwardly from the 
ends of the body portion 30 and are secured to the frame 12. Each of the 
end portions 32 has an upper section 34 and a lower section 36 which are 
located in planes that are upright and generally perpendicular to each 
other, as clearly appears in FIGS. 4 and 5. 
The upper section 34 includes an upper bendable leg 38 that is formed 
integral at its upper end with a horizontal mounting bar 40. The leg 38 is 
inclined downwardly and is formed integrally at its lower end with a leg 
42 that is also bendable and is inclined at an angle of less than ninety 
degrees with respect to the upper leg 38. The upper leg 38 and the lower 
leg 42 are relatively arranged so that the angle therebetween is decreased 
in response to the application of downwardly directed bedding loads, 
indicated by the arrow "F" in FIGS. 3, 4, and 5, to the spring assembly 
10. The bedding load is the load applied to the box spring assembly 10 
when the bed is occupied. 
The lower section 36 of the spring end portion 32 has a bendable upper leg 
44 which extends at its upper end from the lower end of the upper section 
34. The leg 44 is inclined downwardly, as shown in FIG. 4, in the 
undeflected position of the spring. The section 36 also includes a lower 
leg 46 which is reversely inclined relative to the leg 44 and extends 
downwardly from the lower end of the upper leg 44 so that the included 
angle between the legs 44 and 46 is less than ninety degrees to promote 
relative bending to the legs 44 and 46 in response to a vertical load F. 
At its lower end, the leg 46 terminates in a transversely extending 
torsion bar 48 which forms part of a generally U-shape foot 50 at the 
lower end of the spring end portion 32, the foot 50 being retained in 
aligned slots 22 in a cross rail 20. 
The spring assemblage 14 also includes, in addition to the main springs 24 
and 26 and the intermediate springs 28, a border wire 52 which is 
generally rectangular in shape corresponding to the shape of the 
rectangular frame 12, and is spaced a predetermined distance above the 
frame 12. The main springs 24 have their feet 50 secured by conventional 
staples 54 to the end rails 18 while the main springs 26 have their feet 
50 secured to the cross rails 20 by insertion in the slots 22, as 
previously described. Similarly, the intermediate springs 28 are mounted 
on the frame 12 by securing the mounting feet 50 therefor in the slots 22 
in adjacent cross rails 20. 
The mounting bars 40 at the upper ends of the main springs 24 and 26 are 
disposed in a side-by-side relation with the border wire 52 and are 
secured to the border wire 52 by conventional wrap-around-type spring 
clips 56. Each intermediate spring 28 is secured to adjacent main springs 
24 by wrap-around clips 56 extending about the mounting bars 40. The body 
portion 30 in each intermediate spring 28 is irregularly shaped to form 
right angle mounting bars 58 adjacent the mounting bars 40 and these bars 
58 are also secured by clips 56 to adjacent main springs 26. The result is 
a rectangular spring deck consisting of the body portions 30 of the 
springs 24, 26, and 28 and the border wire 52 which is disposed in a 
horizontal plane above the frame 12 and supported on the spring end 
portions 32. The end portions 32 resiliently support the deck so that it 
can yield under bedding loads to accommodate the usual body supporting 
mattress (not shown) so that the mattress will impart the desired degree 
of sleeper comfort to the user. 
In the use of the box spring assembly 10, the loads applied by the mattress 
occupant will be downwardly directed loads such as indicated by the arrow 
F in FIGS. 3-5. The load F acts to compress the spring end portions 32, as 
shown in broken lines in FIGS. 4 and 5. Such movement is resisted by the 
inherent resistance of the spring end portions 32 to being compressed. 
However, limited compression of each of the end portions 32 is achieved by 
movement of the legs 38 and 42 toward each other to reduce the angle 
therebetween and movement of the legs 44 and 46 toward each other to 
reduce the angle between these legs. In addition, the torsion bar 48 is 
twisted and the legs 42 and 44 are twisted with the twisting of these legs 
also causing twisting of the remaining legs 38 and 46. The result is a 
spring end portion 32 in which all of the leg components 38, 42, 44, and 
46 are both bent and twisted without stressing the end portions 32 beyond 
their elastic limits so as to induce a "set" in the spring end portions. 
Each of the legs 38, 42, 44, and 46, in being bent and twisted, has 
tension stresses induced therein by the bending and shear stresses induced 
therein by the twisting. 
In FIG. 6, the stresses in a spring end portion 32 are indicated 
diagramatically by superimposing stress-indicating arrows on a cross 
section of the wire in the end portion 32. Since the shear stresses extend 
transversely of the wire in the spring end portion 32, shear stress is 
indicated by the arrow S. Tensile stress, which extends longitudinally of 
the end portion 32, is indicated by the arrow T. The resultant stress, 
indicated by the arrow R, is less than the sum of the stresses S and T, as 
can be clearly seen from the diagram in FIG. 6. Thus, a given amount of 
spring steel wire in a spring end portion 28 can resist greater loads when 
the loads are a mixture of bending and torsional loads than when the loads 
are either all bending or all torsional loads. Further, the closer the 
bending and torsional loads come to being equal, the higher these loads 
can be without the resultant stress exceeding the elastic limit of the 
spring. As a result, the spring end portions 32 in the assembly 10 perform 
the required function, namely, resilient resistance to bedding load F, 
with a lesser amount of wire than has herefore been the case. This is due 
to the configuration of the spring end portions 28 which deflect as shown 
in broken lines in FIGS. 4 and 5 so that the included angles in the upper 
section 34 and the lower section 36 are reduced. As shown in FIGS. 4 and 
5, the sections 34 and 36 are each in the shape of a V rotated about 
ninety degrees, with the included angle in each case being less than 
ninety degrees. This configuration promotes the desired mixture of bending 
and torsional stresses in the sections 34 and 36. 
From the above description, it is seen that this invention provides an 
improved box spring assembly 10 which will impart the desired degree of 
firmness to a bedding mattress supported on the spring deck formed by the 
springs 24, 26, and 28 and the border wire 52. The frame 12 can be 
structured in a variety of ways to support the spring end portions 32, it 
being primarily necessary that the frame provide a support for the torsion 
bars 48 in the end portions 32 which prevents rotation of the bars 48.