Limited deflection spring

A spring for a box assembly that is constructed to limit deflection of the spring to a position in which the spring is not overstressed. The limited deflection spring includes a wire body which has a load bearing portion, an upright yieldable portion, and a foot portion. The upright yieldable portion includes a pair of downwardly extending converging connecting bars integral at their upper ends with torsion bars at opposite ends of the load bearing portion. A pair of lower torsion bars are connected to the lower ends of the connecting bars and are spaced inward from a pair of downwardly extending converging wire columns which are connected at their upper ends to the lower torsion bars. As a downward load is applied to the load bearing portion, the wire columns move toward vertical positions in which they limit further deflection of the spring.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates generally to mattress foundation structures and more 
particularly to a box spring assembly of the 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; 4,470,584; and 4,739,977. 
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 standpoint 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. 
The principal objects of this invention are to provide an improved spring 
for box spring assemblies which has limited deflection characteristics to 
avoid overstressing of the spring during loading, reduce points of stress 
concentration, and imparts a "flotation" feel to the box spring assembly 
user which is desirable from a comfort standpoint. 
The spring according to the present invention has a load bearing portion at 
the upper end of an upright yieldable portion. The upright yieldable 
portion comprises a pair of downwardly extending and converging connecting 
bars integral at their upper ends with the load bearing portion, a pair of 
lower torsion bars at the lower end of the connecting bars, and a pair of 
downwardly extending and converging wire columns located at their upper 
ends outwardly of the lower torsion bars. Connecting wire sections join 
the lower torsion bars with the upper ends of the columns. The wire 
columns are spaced inwardly of the load bearing portion at the upper end 
of the spring to reduce the likelihood of metal-to-metal contact during 
deflection with an undesirable "clicking" noise. 
As a downwardly directed load is applied to the load bearing portion, the 
upright columns move toward each other and inward thus causing the upright 
columns to approach a vertical orientation. When the upright columns reach 
a substantially vertical orientation, full deflection is reached. The 
connecting wire sections joining the lower torsion bars with the columns 
are vertically aligned with spaces in the mattress support deck in between 
the metal members which form the deck. Thus the clicking sound associated 
with springs meeting deck members is avoided. 
Additional benefits and advantages of the present invention will become 
apparent to those skilled in the art to which this invention relates and 
from the subsequent description of the preferred embodiment and the 
appended claims taken in conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A box spring assembly utilizing springs in accordance with the present 
invention is shown in FIG. 1 and is generally designated by reference 
numeral 10. Box spring assembly 10 generally consists of a mattress 
support deck 12 supported in a position above and substantially parallel 
to a rectangular box spring frame 14 having a pair of side rails 17 and a 
pair of end rails 18, only one of each being shown in FIG. 1. The frame 14 
also includes a plurality of cross rails 19, only one of which is shown. A 
plurality of deck support springs 16 and cross wire springs 18 support the 
deck 12 on the frame 14. 
A deck support spring 16 comprises a substantially horizontal load bearing 
portion 20 and a pair of downwardly extending yieldable portions 22 and 24 
terminating at their lower ends in a pair of feet 26 and 28. Load bearing 
portion 20 comprises a pair of parallel, spaced apart upper torsion bars 
30 and 32 connected together by an intermediate connecting section 34. 
Intermediate connecting section 34 consists of center bar 36 which is 
parallel to and midway between torsion bars 30 and 32, and connecting bars 
38 and 40 which connect the ends of center bar 36 to the torsion bars 30 
and 32. 
Load bearing portion 20 is positioned in a substantially horizontal plane 
against mattress support deck 12 such that center bar 36 crosses beneath 
the load bearing portion 42 of cross wire spring 18. In addition, the 
upper torsion bars 30 and 32 are positioned parallel to and against a pair 
of adjacent long wires 44 and are clipped thereto by pairs of clips 46. 
Mattress support deck 12 consists of long wires 44 and cross wire springs 
18 positioned in a crisscross fashion with the load bearing portions 42 of 
cross wire springs 18 intersecting long wires 44. Each long wire 44 has a 
plurality of spaced apart notches 45 along its length. Likewise, each load 
bearing portion 42 of cross wire springs 18 has a plurality of spaced 
notches 47. Each of the notches is an upwardly arched deflection in the 
wire member. Notches 45 saddle notches 47 to form intersections 48. 
Notches 47 in turn saddle one of the torsion bars 30 or 32. 
The engaged notches 45 and 47 in long wires 44 and load bearing portions 42 
of cross wire springs 18 respectively prevent sideways movement of the 
wire members at the notched intersections 48 between long wires 44 and the 
load bearing portion 42 of cross wire springs 18. When clips 46 are 
installed around long wires 44 and torsion bars 30 and 32 of deck support 
springs 16, the mattress support deck 12 becomes a fixed wire deck with 
each cross wire spring 18 clamped between notche 45 and a torsion bar 30 
or 32. 
As shown in FIG. 1, each of the cross wire springs 18 includes a torsion 
bar 50 at each end of load bearing portion 42. Torsion bar 50 is secured 
to border 52 by another clip 46. The upright yieldable portion 53 of cross 
wire spring 18 is identical to upright yieldable portions 22 and 24 of 
deck support springs 16 as will be subsequently described. 
Upright yieldable portions 22 and 24 comprise a pair of downwardly 
extending and converging connecting bars 54 and 56 which join one end each 
of the torsion bars 30 and 32 to a pair of horizontal lower torsion bars 
58 and 60 at the lower end of the connecting bars. The lower torsion bars 
58 and 60 extend transversely of the connecting bars 54 and 56. 
Below the lower torsion bars 58 and 60 are a pair of downwardly extending 
and converging wire columns 62 and 64 located with their upper ends 
extending outwardly of lower torsion bars 58 and 60 respectively. Wire 
columns 62 and 64 are connected to lower torsion bars 58 and 60 by 
connecting wire sections 66 and 68. Connecting wire sections 66 and 68 
each have a short straight portion 70 joined with the lower torsion bars 
and a downwardly curved portion 72 joining with the upright columns. 
The combination of the connecting wire sections 66 and 68 and the upright 
columns forms a pair of facing columns of substantially "7" shape which 
spaces wire columns 62 and 64 outward from torsion bars 58 and 60, 
respectively. The connecting wire sections 66 and 68 thereby produce a 
moment arm between the upright columns and the lower torsion bars 58 and 
60 when a load is applied to load bearing portion 20. The positioning of 
the upright wire columns with the connecting wire sections 66 and 68 
directed toward each other transfers part of any downwardly applied load 
on the load bearing portion 20 from the torsion bars through the 
connecting wire sections to the upright columns. This transferred load 
increases as the columns approach a vertical orientation. 
As shown in FIG. 2, the dotted lines represent the fully deflected position 
of the load bearing portion 20 illustrating that connecting bars 54 and 56 
twist downward below the substantially horizontal level of load bearing 
portion 20 in the fully deflected position. The connecting wire sections 
66 and 68, when the spring is fully deflected, remain generally in the 
plane of the load bearing portion 20. As can be seen in FIG. 3, lower 
torsion bars 58 and 60 twistingly deflect downward below load bearing 
portion 20 so as to not engage with the support deck 12 thus preventing 
any clicking sound when spring 16 is fully deflected. 
As shown by the dotted lines in FIG. 2, as load bearing portion 20 moves to 
the fully deflected position, wire columns 62 and 64 move inwardly toward 
each other to substantially vertical spaced apart positions to positively 
limit further deflection. During deflection of a yieldable portion 22, 24 
or 53, however, the deck 12 moves downwardly in a slowly yielding manner 
so as to impart a flotation feel to a user lying on a mattress supported 
on the deck 12. The yieldable portion 22, 24 and 53 are configured so that 
all parts absorb some of the load to thereby eliminate areas of stress 
concentration in which the elastic limit of the wire might be exceeded. 
The connecting wire sections 66 and 68 are vertically aligned with spaces 
in the mattress support deck 12 between the crisscrossed wires 44 and 18 
to absorb shock loads on the deck without metal-to-metal contact. 
The short top or moment arm presented by connecting wire sections 66 and 68 
also transfers some of the load normally absorbed in torsion by lower 
torsion bars 58 and 60 to the wire columns 62 and 64 to prevent the 
torsion bars from exceeding their yield stresses. Accordingly, stresses 
are distributed throughout the spring when full deflection is reached. 
As stated previously and as shown in FIG. 1, the yieldable portions 53 of 
cross wire springs 18 perform in an identical manner to the yieldable 
portions 22 and 24 of deck support springs 16. The only significant 
difference between cross wire springs 18 and deck support spring 16 lies 
in the length of load bearing portion 42 when compared to load bearing 
portion 20 of deck spring 16. Although not shown in the drawing, load 
bearing portion 42 of cross wire spring 18 extends fully across box spring 
assembly 10 therefore spanning multiple pairs of long wires 44. 
At each end of the load bearing portion 42 are torsion bars 50 which are 
coupled via connecting bars 76 to lower torsion bars 78 which in turn join 
upright wire columns 80 via connecting wire sections 82. Upright wire 
columns 80 terminate in foot portions 82 identical to feet 26 and 28. 
Upper torsion bar 50 is clipped via clips 46 to border wire 52. 
As with the deck support spring 16, when cross wire spring 18 is fully 
deflected part of the load is transferred via connecting wire section 82 
to the upright column 80 limiting the full deflection of the spring 18 so 
that the torsion bar yield stresses are not exceeded. Thus the full box 
spring assembly 10 can absorb a higher total loading without reaching or 
exceeding the yield of a torsion bar portion of a spring while allowing 
additional shock absorption capability and eliminating the noisy clicks 
associated with conventional connecting bars contacting the wire grid 
members at full deflection. 
While the above description constitutes the preferred embodiment of the 
present invention, it will be appreciated that the limited deflection 
springs of the present invention are susceptible to modification, 
variation and change without departing from the proper scope and the fair 
meaning of the accompanying claims.