Mattress spring core

A spring core for a mattress consisting of a plurality of side-by-side rows of identically configured helical coil springs each made of a single piece of wire having a central portion of a first radius defining a central spring axis and terminating at opposing ends with unknotted upper and lower end turns disposed in planes substantially perpendicular to the spring axis. The springs are connected with each other at their upper and lower turns by connecting lacing wires. The upper and lower turns are each substantially U-shaped, having a longer relatively straight leg and a shorter arcuate leg located at the free end of each end turn, the legs connected to each other by a base web. The radius of the shorter arcuate leg is substantially less than the first radius of the central portion of each coil spring. All the coil springs are oriented in the same direction, except along an edge region of the spring core.

FIELD OF THE INVENTION 
This invention relates to a spring core for a mattress, and more 
particularly, to a spring core made up of identically formed coil springs 
arranged in side-by-side rows, each coil spring being made of a single 
piece of wire having a central spiral portion terminating in upper and 
lower unknotted end turns with adjacent helical coil springs being joined 
together at their end turns by a helical lacing wire. 
BACKGROUND OF THE INVENTION 
Traditionally, spring cores for mattresses have consisted of a plurality of 
spaced parallel rows of helical coil springs mounted between border wires; 
coil springs adjacent the border wires being attached thereto via helical 
connecting wires, sheet metal clips or other connections. The upper and 
lower end turns of adjacent springs are generally connected to each other 
by helical lacing wires; the helical lacing wires being transverse or 
perpendicular to the columns of coil springs. Coil springs in each row are 
disposed in rectilinear relation to each other so as to form spaced 
parallel rows of springs within the border wires. 
The upper and lower end turns of unknotted coil springs often are made with 
straight portions or legs which abut one another when coils are placed 
next to each other. For example, in U.S. Pat. No. 4,781,360, the end turns 
have deviations or offsets straightening the curved portion of the end 
turn so as to enable adjacent end turns to be laced together. 
Alternatively, the coil end turns may be rectangular with two opposite 
straight legs, as in German Patent No. 3,321,991. Adjacent coil springs 
are connected to each other at their end turns, both upper and lower, by 
helical lacing wire. One leg of a U-turn of an end turn of a coil spring 
is set beside the opposite leg of the U-shaped end turn of the adjacent 
coil spring. The side-by-side legs are laced together with helical lacing 
wire. 
However, when assembled, coil springs of such a spring core may move within 
the lacing wire, causing misalignment or nonparallel alignment of coils in 
adjacent rows of coils. This misalignment causes the coil springs to line 
up improperly. The lines connecting the central axes of the coil springs 
no longer form a 90.degree. angle as they should. This misalignment thus 
changes a rectangular or square spring core into a rhombus. Such an odd 
shape must be then corrected at an additional cost. 
In order to avoid this misalignment problem, spring cores were developed 
having individual coil springs with U-shaped end turns having one leg of a 
greater length than its opposing leg, as in U.S. Pat. No. 4,817,924. Once 
again, adjacent coil springs were connected with helical lacing wire at 
their end turns. However, due to the difference in leg lengths of each 
U-turn, the lacing wire wrapped one more time around the longer leg of the 
U-shaped end turn coil and one less turn around the immediately adjacent 
shorter leg of the adjacent end turn. The different leg lengths bound 
together with helical lacing wire corrected the misalignment or coil 
offset problem. 
In U.S. Pat. No. 4,817,924, the longer leg of each U-shaped end turn is 
disclosed as being spaced further from the central portion of the helical 
spring or the axis of the spring than the distance between the short leg 
and the central portion or axis of the helical spring. The purpose of such 
spacing is to eliminate interference and noise when a load is placed on 
the spring core causing compression of the helical springs. 
When springs are made in accordance with the disclosure of U.S. Pat. No. 
4,817,924, problems may exist during manufacture. For example, because 
both legs of the U-shaped end turns are relatively straight, the coils may 
move or be skewed within the assembly machine dies prior to lacing the 
helical springs together. Movement or improper seating, such as results 
from skewing of the helical springs within the dies causes jambs and 
similar problems when lacing the end turns of the coils together. 
It has therefore been an objective of this invention to eliminate any 
skewing or misalignment problems with end turns of unknotted coils within 
the assembly machine dies of a lacing and assembly machine. 
It has been another objective of this invention to enable end turns which 
are to be assembled together to be more consistently gripped and 
positioned next to one another for lacing during the assembly of coils. 
It has been another objective of this invention to provide a spring core in 
which the top and bottom U-shaped end turns of adjacent coil springs are 
bound together more tightly within or inside helical lacing wires. 
It has been another objective of this invention to provide trouble-free 
manufacturing and assembly of unknotted coil springs by forming a small 
radius on the free end of each end turn of the unknotted coils, thereby 
reducing jambs within the assembly machine and, ultimately, cost of the 
resulting assembled product. 
SUMMARY OF THE INVENTION 
The invention of this application which accomplishes these objectives 
comprises a spring core for a mattress made up of a plurality of 
identically configured helical coil springs. Each helical coil spring is 
made of a single piece of wire and has a central portion of a first radius 
defining a central spring axis and terminating in opposing unknotted upper 
and lower generally U-shaped end turns, each disposed in a plane 
substantially perpendicular to the spring axis. The springs are arranged 
in side-by-side rows connected with each other at the upper and lower end 
turns by helical lacing wires. The helical lacing wires run perpendicular 
or transversely to the columns or rows of springs and are arranged in the 
planes of the upper and lower end turns. Each upper and lower end turn is 
substantially U-shaped, having a longer relatively straight leg and a 
shorter arcuate leg connected to each other by a base web. The shorter 
arcuate leg is located at the free unknotted end of each end turn and has 
a radius substantially less than the first radius of the central portion 
of the helical coil spring. Both the long and the short legs of each end 
turn are laterally outwardly spaced from the central portion of the coil 
spring. The spacing between the longer leg of each U-shaped end turn and 
the central portion of the coil spring is less than the corresponding 
spacing between the central portion of the coil spring and the associated 
shorter leg of the same end turn. The corresponding upper and lower end 
turns of each coil spring are rotated approximately 180.degree. in 
relation to each other to dispose the shorter and longer legs of the upper 
end turn of each spring in mirror symmetry to the shorter and longer legs 
respectively of the associated lower end turn. 
Forming the free end of the coil with a relatively small radius enables the 
spring to be easily formed, and subsequently, easily assembled. The radius 
on the smaller leg enables more dimensional stability and enables the 
coils to be tighter within the helical lacing wire. The radius tends to 
spring back to its original shape after the helical passes through the 
lacing jaw, tightening itself against the helical connecting spring. 
These and other objects and advantages of the invention will be more 
apparent from the following description of the drawings in which:

DETAILED DESCRIPTION OF THE INVENTION 
With reference first to FIG. 1, there is illustrated a helical coil spring 
2 having a central spiral portion 4 made up of a plurality of consecutive 
helical loops or revolutions 5 defining a central spring axis 6 and 
terminating in a lower end turn 8 and an upper end turn 12. Lower end turn 
8 is disposed substantially in plane 10 which is substantially 
perpendicular to the central spring axis 6. The upper end turn 12 is 
disposed substantially in plane 14 which is again substantially 
perpendicular to the central spring axis 6. The two end turns 8 and 12 are 
alike so that a description of one end turn will suffice for both. The end 
turns 8 and 12 are aligned relative to the spring axis 6, one on top of 
the other. Each helical coil spring is made of a single piece of wire. The 
active length of the helical coil spring wire which determines the spring 
or resilient property of the coil extends from position 16 of the upper 
end turn down to position 18 of the lower end turn 8. 
Referring to FIG. 2, it will be seen that each end turn is generally 
U-shaped, having a longer relatively straight leg 20 of a length 22 and 
shorter arcuate leg 24 of a length 26. The longer relatively straight leg 
20 and the shorter arcuate leg 24 are connected to each other by a base 
web 27 and a portion of an arcuate section 23, the shorter arcuate leg 24 
and the arcuate section 23 being located on the free unknotted end of each 
of the end turns. The arcuate section 23 and the shorter arcuate leg 24 
both have a common radius R2 which is substantially less than the first 
radius R1 of the central spiral portion of each helical coil spring 2. In 
the preferred embodiment of the invention, the first radius R1 of the 
central portion of each coil spring is approximately 15/16 inch whereas 
the radius R2 of the arcuate section 23 and the shorter arcuate leg of the 
U-shaped end is approximately 5/8 inch. 
Both legs of the U-shaped end turns are laterally spaced from the central 
spiral portion 4 of the helical coil spring 2. Both the shorter arcuate 
leg 24 and the longer relatively straight leg 20 are spaced laterally 
outward from the central portion 4 of the coil spring 2. The spacing D2 
between the longer leg 20 and the central portion 4 of the coil spring is 
less than the corresponding spacing D1 between the central portion 4 of 
the coil spring and the associated shorter arcuate leg 24 of the same end 
turn. These spacings D1 and D2 ensure that even under an extreme load on 
helical circular spring 2 the end turns do not come in contact or clash 
with the central portion 4 of the coil spring. 
Referring to FIG. 2, the central portion 4 of each helical coil spring 
loops upward until it reaches a first bend 30 on the upper end turn 12. 
The first bend 30 connects the longer relatively straight leg 20 to the 
central portion of the coil spring 4. The longer relatively straight leg 
20 terminates in a second bend 31. The longer relatively straight leg 20 
is not perfectly straight but rather is slightly arcuate. The second bend 
31 connects the longer relatively straight leg 20 with the base web 27 
which is slightly curved. At the opposite end of the base web 27 there is 
a third bend 34 with which one end of the arcuate section 23 connects. The 
shorter arcuate leg 24 is bent much more than the longer relatively 
straight leg 20 or the central portion 4 of the helical coil spring 2. The 
shorter arcuate leg 24 has a length 26 which is less than the length of 
its corresponding longer leg 20, length being defined for this purpose as 
the dimension contained within the helical lacing wire 40. At the other 
end of the arcuate section 23 is a fourth bend 36 which connects the 
arcuate section 23 to a straight tail piece 28 having an end 37. The tail 
piece 28 of the top turn is bent downward out of the plane 14 in order to 
avoid puncture of the upholstery which covers the mattress spring core. 
The tail piece 28 of each end turn is also slanted inward towards the 
central spring axis 6. The tail piece 28 of each end turn is bent inwardly 
towards the middle of the spring core in order to avoid puncturing the 
upholstery which covers the spring core. 
The significance of the bent straight tail piece 28 is evident from FIG. 3. 
In FIG. 3, it can be seen that the tail piece 28 is bent at the fourth 
bend 36 inward in the direction of the central spiral portion 4 of the 
coil spring so that it does not fray the upholstery nor contact the 
central portion 4 of the coil spring. 
The lower end turn 8 is formed in an identical manner to the upper end turn 
12 except the lower end turn is rotated approximately 180.degree. in 
relation to the upper end turn 12 to dispose the longer and shorter legs 
of the upper end turn 12 of the coil spring in mirror symmetry to the 
longer and shorter legs, respectively, of the associated lower end turn 8. 
FIGS. 2-5 show the method of interconnection of adjacent coil springs. 
Adjacent coil springs are connected to one another at the upper and lower 
end turns by helical lacing wire 40 as shown in FIG. 3. The helical lacing 
wires 40 attach the longer relatively straight leg 20 of one end turn with 
a corresponding shorter arcuate leg of an adjacent end turn. As can be 
seen in FIG. 2, the helical lacing wire 40 circles the longer leg 20 four 
times but only circles the shorter arcuate leg three times. Such an 
assembly prevents an offset or axial misalignment of the springs during 
formation of the spring core and enables the manufacturer to create a 
rectangular spring core. 
During the assembly lacing process, the shorter arcuate leg of the end 
turn, having a small radius R2 on the free end, is entrapped between a 
pair of opposed lacing jaws or dies which flatten the shorter arcuate leg 
to ease or facilitate the lacing process. Upon the release of the shorter 
arcuate leg by the lacing jaws, the shorter arcuate leg returns to its 
more rounded configuration so that both the longer and shorter legs of 
adjacent end turns press outwardly against the inner surface of the 
helical lacing wire 40, creating a tight fit inside the helical lacing 
wire 40. 
FIG. 5 shows the arrangement in rows and columns of the helical coil 
springs 2. The coil springs 2 are arranged in side-by-side rows 50 and are 
connected with each other at the upper and lower end turns by helical 
lacing wires 40. Helical coil springs 2 are arranged in like orientation 
such that the base web 18 always forms the outer edge of the spring core, 
abutting border wire 52 
In the endmost columns 42 of the spring core the helical coil springs are 
turned around so that the end turn normally at the top is now at the 
bottom. This avoids the problem of having the straight tail piece 28 
facing the edge of the spring core. 
In the central portion of the spring core (other than the endmost column), 
the rows are aligned horizontally so that the central spring axes of 
adjacent coil springs form a horizontal line 44. Likewise, the central 
spring axes of adjacent coil springs form a vertical line 46. The 
connecting lines 44 and 46 intersect at a right angle so that the edge 
sides of the spring core form right angles. Due to the formation of these 
right angles, offset or misalignment is eliminated and no corrections need 
be made. The spring core is surrounded in the top and bottom planes by 
upper and lower border wires 52. A helical connecting spring 60 fastens 
the helical coil springs 2 to the border wires 52 around the edge of the 
spring core. Alternatively, metal clips or other conventional fasteners 
may be used to connect the top and bottom end turns of the endmost coils 
of the spring assembly to the border wires 52. 
By creating the spring core as described above, a sturdy mattress core may 
be easily machine assembled within an assembly machine. Because of the 
unique configuration of the end turns of the unknotted coils, repeated 
accurate positioning of the end turns of coils within the lacing jaws of 
the assembly machine is facilitated and machine jambs because of 
misalignment is minimized. 
While we have described only a single preferred embodiment of our 
invention, we do not intend to be limited except by the scope of the 
appended claims.