BACKGROUND OF THE INVENTION

Mattress innerspring units are generally formed of a plurality of spring coils arranged in side-by-side relation in parallel rows, with parallel columns also thereby being formed orthogonal to the rows. Border wires typically encircle both the upper and lower per¬ imeters of the innerspring unit formed ^' by the most out¬ board spring coils and are connected to terminal convo- lutions formed on the ends of the spring coils.

It is a common practice to form the terminal convo¬ lution with an enlarged diameter with respect to that ^' of the spirals which are axially inward from the coil ends. This facilitates interengagement of the springs and makes the spring coil more stable in compression- Terminal convolutions of adjacent spring coils in a row< are overlapped, and helical spring coils, referred to as cross-helicals, are then wound along columns to en¬ circle the overlapped convolution portions. These cross- helicals ordinarily have an internal diameter which is slightly larger than the combined diameters of the over¬ lapped terminal convolution portions. Larger diameter helical springs are also often used to attach a border wire to the terminal convolutions. There are some general considerations of manufacture and comfort which underlie the design of any mattress innerspring. For example, considerable effort has been devoted in the industry to the development of terminal

convolutions which facilitate the interengagement of the spring coils as well as their connection to the border wire- For example, terminal convolutions have been developed having offset portions formed thereon 5_ which include a straight part. This enables the spring ends to be secured along a substantial length of the straight part which will "catch" more helical spirals, and thereby provide more stability for the individual coils. Improved stability is always being sought, how-

10. ever.

These efforts have also been directed to find ways to- prevent the spring coils from rotating relative to each- other, and perhaps out of the upper or lower plane of the- unit. A related problem in this area is that of

15- hinging,, where the overlapped portions of coils slip over one another and make noise. Hinging can further occur between coils overlapped with the border ^" wire. Such hinging is obviously desired to be kept at a mini¬ mum in a mattress.

20 Another consideration in mattress design and manu¬ facture is the ability to make innerspring units which have different firmness characteristics suited to an individual's personal preference. This may simply amount to providing several mattress lines having differing

25: firmness, or, in more sophisticated mattresses, provid¬ ing, areas of different firmness in a particular mattress innerspring-.

As may be readily recognized, producing mattresses with different firmness characteristics may be accom-

30 pushed through the use of springs of differing com¬ pression for each mattress firmness, ordinarily achieved by making the various springs out of different wire stock: or in different configurations. The overall lay¬ out or construction of the innerspring unit may also be 5 ^' changed from one mattress firmness to another, such as by changing the coil count and coil arrangement. Use

of heavier wire stock, more springs, different springs or a different layout obviously adds expense to mattress production in terms of parts as well as labor. A primary consideration in making mattresses with different degrees of firmness is therefore to do so in the most efficient and economical manner while still achieving the desired results.

FIELD OF THE INVENTION

This invention relates to spring coils and spring coil assemblies, and particularly to those used in mat¬ tress innersprings.

SUMMARY OF THE INVENTION

The present invention provides a number of innova¬ tions and improvements to spring coils and spring coil assemblies, particularly as adapted for use in a mat¬ tress innerspring unit. The general considerations outlined above take form in the present invention as a spring coil having a firmness that is readily adjusted in manufacture. The invention further includes spring coil and spring assembly features that assure that the spring coils have little or no rotation relative to each other or to a border wire surrounding an inner- spring unit. The invention also comprises various ar¬ rangements of spring coils and cross-helicals that yield innerspring assemblies of different firmness character- isti-cs.

In one aspect of the invention, a spring coil has a spiral coil body and a pair of terminal convolutions. At least one of the terminal convolutions has a C-shaped configuration, which in a present embodiment is comprised of first and second opposed offset portions joined to¬ gether at one end by a third offset portion. The remain¬ ing portion of the terminal convolution is open. All of the offset portions generally lie in the same plane.

The first offset portion has a free end. The second offset portion joins with the spiral coil body via a connecting segment in the form of a gradient arm which extends in the same plane as the terminal convolution. The gradient arm is adjustable in length in manufacture to vary the compression and thereby the firmness of the spring coil. A single basic configuration for the spring coil using a single wire stock can thus be employed to make innerspring units of differing firmness characteris- 1 tics.

Another aspect of the invention is forming the terminal convolution with one or more offset portions that, provide a three point engagement with a border wire when attached thereto with a border wire helical. ^" The. offset portion has a stepped segment formed thereon comprised of a major part that is substantially straight and spaced radially outwardly from the spring coil axis, an angled part extending away from the major part at each end of the major part, and minor straight parts which are substantially in line with each other and parallel to the major straight part and extend outwardly from the angled parts. The stepped offset portion of perimeter spring coils is overlapped with a border wire and: a border wire helical then coiled around the major ^" and minor straight parts to hold the offset portion against rotation about the border wire.

Yet another aspect of the invention contemplates forming the terminal convolution with offset portions terminating in shoulders. The offset portions of adja- cent coils in a row are overlapped, with the overlapped portions then encircled with a cross-helical having an internal diameter which is slightly greater than the combined diameters of the overlapped portions. The helical pitch is matched to the distance between the ^' outsides of the shoulders of at least one of the over-

lapped offset portions such that the cross-helical simul¬ taneously engages the shoulder outsides. The spring coil having its terminal convolution so captured is thereby prevented from rotating. This form of the invention is advantageously further adapted so that the cross-helical also simultaneously engages the inside shoulders of the other of the overlapped offset por¬ tions in each pair as additional fixation against rota¬ tion of the other spring coil. Still another aspect of the invention resides in unique arrangements of spring coil rows and the use of cross-helicals to interengage the coils. In this re¬ spect, the innerspring unit has a length and a width, with the length being longer than the width. The spring coils are arranged in rows extending across the width, with the spring coil columns thereby formed extending along the length. The cross-helicals joining adjacent overlapped spring coils in a row thus extend along the columns. It will be noted that the arrangement of rows across the width of the innerspring unit permits rows to be spaced closer together in certain areas of the unit for more firmness. These areas of increased firm¬ ness would accordingly be constant across the entire width of the mattress. A second set of cross-helical springs is then pro¬ vided which extend along the rows and are coiled about terminal convolution portions other than the overlapped portions. Additional firmness is thus provided for the mattress. This additional firmness from the orthogonally arranged cross-helicals can be concentrated in specific areas of the innerspring unit, such as the middle third for example, or can extend for the entire length. Pro¬ vision of the principal set of cross-helicals along the length of the mattress makes such selective "posturizing" easily accomplished.

A variant on the foregoing use of orthogonal cross- helicals is the formation of a spring assembly with the rows overlapped, such that offset portions of the springs in one row extend into the terminal convolutions of an 5 adjacent row. The second set of cross-helicals (across the width) are then coiled about the overlapped portions of the terminal convolutions of the spring coils in adjacent rows.

It will be noted that a presently preferred form

10 of the invention utilizes a spring coil configuration having an open end offset shape for the terminal convo¬ lution. Three offset portions are provided, two of which are generally segments which are parallel to each other on opposite sides of the coil body. The third

15. offset portion joins the other two, and is provided with the stepped offset segment set forth above for three point border wire engagement. It will thus be •understood that the various aspects or features of the invention can be used alone or in combination, as may

20 be desired.

The foregoing features and advantages of the inven¬ tion will be further understood upon consideration of the' following detailed description of various embodiments of the invention taken in conjunction with the accompany-

25 ing drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a plan view of an end portion of a mat¬ tress innerspring unit incorporating the spring coil of Fig. 2; 30 Fig. 2 is a perspective view of a spring coil embody¬ ing the gradient arm of this invention;

Fig. 3 is an enlarged plan view of a pair of over¬ lapped offset portions encircled by a cross-helical as shown in Fig. 1;

Fig. 4 is a view similar to Fig. 1 illustrating three point engagement of the third offset portion with the border wire;

Fig. 5 is a view similar to Fig. 4 wherein the terminal convolutions of the spring coils have stepped segments on each offset portion;

Fig. 6 is a plan view of a portion of a mattress innerspring unit showing orthogonally laced cross- helicals; Fig. 7 is a view similar to Fig. 1 showing over¬ lapped rows and orthogonally laced cross-helicals;

Fig. 8 is a graph of spring compression related to the length of the gradient arm;

Fig. 9 is a graph of various springs under load; Figs. 10a, 11a and 12a are plan views of terminal convolutions of three spring coils; and

Figs. 10b, lib and 12b are elevational views of the respective terminal convolutions of Figs. 10a, 11a and 12a.

DETAILED DESCRIPTION OF PRESENTLY

PREFERRED EMBODIMENTS OF THE INVENTION

While the invention has found particular applica¬ tion for the innerspring unit of a mattress, and is so described in this environment hereafter, it will be understood that the invention is not limited to this application alone but may find utility in other employ¬ ments.

Referring now to the drawings, Fig. 1 shows an innerspring unit or assembly 10 comprised of spring coils 11 arranged in a rectangular pattern of parallel rows. The rows are shown here extending from right to left as viewed in this drawing, with adjacent rows being spaced apart. These rows extend across the width of the innerspring unit 10. Columns of spring coils 11 (simply referred to as coils hereafter) are thereby

formed which extend along the length (longitudinally) of the innerspring unit 10 and are orthogonal to the rows.

Extending the rows across the width of the unit permits making areas of increased firmness by simply moving rows closer together. The areas of increased firmness are thereby constant across the width of the unit.

With reference now to Fig. 2, the coil 11 has a spiral coil body 11a with terminal convolutions lib and lie formed at each end. The spiral body 11a of the illustrated coil has a fairly constant diameter of about 1.843 in. in this embodiment. The terminal convolutions lib, lie are identical in form, and have a larger dia- meter than the spiral body 11a. The coil has an overall axial length of about 5.00 in. in this embodiment.

The terminal convolutions lib, lie are each formed in an open end offset configuration comprised of three offset portions 12, 13 and 14 and an open end 15. The overall shape for the.,terminal convolution lib, lie is seen to be rectangular. The offset portions 12 and 14 have generally straight segments which are roughly par¬ allel to each other and of approximately the same length. The third offset portion 13 extends between ends of the first and second offset portions 12, 14 and has a stepped segment which will be described in more detail hereafter. All portions of the terminal convolution are approximately in the same plane, which is perpendicular to the axis of the spring coil. These coils 11 are made from a single piece of wire stock, such as 15 gauge (.072) wire, which is first given a spiral body shape and then provided with the desired terminal convolutions.

The coils 11 are positioned so that the offset portions 12 and 14 of adjacent coils in a row overlap. The overlapped offset pairs are then secured together

by spirally rotating a first set of helical coil springs 17 across the rows, i.e. along the columns, so as to interlace the overlapped offset portions. The cross- helicals 17 have an internal diameter which is just slightly greater than the diameter of the overlapped offset portions so that the overlapped relationship is maintained in use. The terminal convolutions lib and lie on both the upper and lower sides of the innerspring unit 10 are thus laced together in this fashion. Pro- viding such long relatively straight segments to the offset portions 12 and 14 enables a significant number of cross-helical turns to be made thereabout, which yields a secure engagement of overlapped offset pairs and greater stability for the coils 11. Offset portions 12-14 at the perimeter of the inner- spring unit 10 are attached to a border wire 18 that extends around this perimeter. A border wire helical spring 19 is used to make this attachment and is spirally wound about the offset portions which are overlapped with the border wire. A border wire 18 is provided for both the upper and lower sides of the innerspring unit. Second offset portion 14 has a free end 14a which is inwardly turned to extend generally perpendicularly to the straight segment of the second offset portion. First offset portion 12 extends into a connecting segment 20 which connects the terminal convolutions lib, lie to the spiral body 11a. This connecting segment 20 extends generally perpendicularly from the end of offset portion 12, and is in the same plane as the terminal convolution. The connecting segment 20 forms what will be re¬ ferred to as a gradient arm for the coil 11. Figs. 10a and 10b, 11a and lib and 12a and 12b illustrate three terminal convolutions with different gradient arm 20 lengths. The compression of the coil 11, and thus the firmness of the coil, can be adjusted within limits by

varying the length of this gradient arm 20. This will be seen with reference to the graph of Fig. 8.

As shown in this graph, a coil having a gradient arm of about 1/4 in. in length (measured from the end of the straight segment of the first offset portion 12 to the bend into the spiral body) had a spring grad¬ ient of 1.45 lbs./in. A like coil 11 with a gradient arm of 5/8 in. in length had a spring gradient of 1.85 lbs./in. From the foregoing it will thus be seen that the compression or firmness of the individual coils can be varied by adjusting the length of the gradient arm 20. This is readily accomplished in manufacture through a relatively uncomplicated adjustment in the coil forming machinery. Spring coils of varying firmness can there¬ fore now be manufactured on the same machine from"the same wire stock in an efficient and cost effective man¬ ner.

A present estimate places the preferred range for the length of the gradient arm 20 at about 3 to 9% of ^• the active material length of the spring coil. The active material length is considered to be that length of material which is free to deflect when a load is applied to the spring. The spiral portion of the coil, exclusive of the gradient arms and terminal convolutions, would thus constitute the active material length for the coils illustrated herein.

Also, while this firmness adjustment feature of the invention has been described in relation to an em- bodiment having particular offset portions, it is con¬ sidered to have applications to other terminal convolu¬ tion configurations.

The spring coil of this invention further provides a firmness that varies under load, i.e. as the coil is deflected. With reference to the graph of Fig. 9, an innerspring units formed with springs of a Bonnell type

exhibited a fairly linear deflection in response to an increasing load (line B). An innerspring unit formed of springs of the type shown in Karpen, U.S. Patent No. 3,533,114 likewise exhibited a fairly linear response to load (line A).

An innerspring unit comprised of spring coils 11 of this invention exhibited a marked non-linear response to load (line C) in contrast to the foregoing innerspring units. The result is that in the initial stage of deflec- tion, the innerspring assembly of this invention offers a first firmness that provides "surface comfort" to an individual. As increased load is imposed on the inner- spring unit, the firmness increases to provide "depth" or "supportive" firmness. A more comfortable mattress is thereby produced.

Referring now to Fig. 3, another feature of this invention resides in matching the pitch of the cross- helicals 17 to the length of the offset portions 12, 14 to lock the coils 11 against rotation relative to one another. To this end, each of the offset portions 12, 14 has a shoulder 25 formed at each end thereof. An inside shoulder 25a and an outside shoulder 25b are thereby presented at each shoulder 25. The pitch (as indicated in Fig. 3) of the helical 17 is selected so that the cross-helical simultaneously engages the out¬ side shoulders 25b of one of a pair of overlapped off¬ set portions, such as the outside shoulders of offset portion 14 in Fig. 3. The offset portion 14, and thus its coil 11, is thereby firmly held against rotation by the cross-helical 17.

The pitch of the cross-helical 17 is also advantage¬ ously selected so that the cross-helical 17 catches the inside shoulders 25a of the other of the pair of over¬ lapped offset portions. As shown in Fig. 3, the over- lapped offset portions 12, 14 are coterminus, and the

cross-helical 17 catches the inside shoulders 25a of offset portion 12. The coil 11 having the offset por¬ tion 12 is thereby further secured against rotation (it being understood that this same coil 11 will have its offset portion 14 held by the next adjacent cross- helical in the manner previously described) .

Another feature of the invention relates to the three point attachment achieved between perimeter coils 11 and the border wire 18. Referring to Figs. 2 and 4 in particular, third offset portion 13 has a stepped segment formed thereon comprised of a major straight part: 13a, angled parts 13b extending from the ends of the major straight part 13a, and minor straight parts 13c extending from the angled parts 13b. The major - straight, part 13a is spaced radially outwardly from the coil body ΪXa and is generally tangential thereto. The minor parts 13c are approximately in line with each other and generally parallel to the major straight part 13a. A border wire helical 19 is wrapped around the overlapped border wire 18 and third offset portion 13 to catch the inboard sides of the minor straight parts 13c and the outboard side of the major straight part 13a.. This yields a three point attachment of the off- -- set portion 13 -with the border wire which is very secure, and which substantially prevents any hinging of the offset portion with the border wire.

As shown in Fig. 5, the terminal convolution of a coil 11 could be provided with such stepped segments on all three of its offset portions 12-14. Three point attachments of the perimeter coils would thus be effected around the entire border wire (although for full effect the- last row of coils may have to be reversed so that the third offset portions thereof are adjacent the border wire) .

Another feature of the invention is the ability to adjust the firmness of the innerspring unit 10 through the addition of a second set of cross-helicals 28 which are orthogonal to the first set 17 to further interlace the coils. As seen in Fig. 6, the cross-helicals 28 extend along the coil rows, that is, they are across the width of the mattress. The cross-helicals 28 are substantially identical to the cross-helicals 17 and are wrapped about the short segments 14a and gradient arms 20 of the terminal convolutions. It will be noted that the cross-helicals 28 could alternatively be wrapped around the third offset portions 13 in a row to the same effect.

The second set of cross-helicals 28 provide extra firmness, and can extend along the entire length of one or both sides of the innerspring unit 10, or can be located in selected segments of the innerspring unit 10 to "posturize" the unit. Such posturizing is readily accomplished due to arranging the springs ^" so that the primary cross-helicals 17 run along the length of the mattress. ,

Fig. 7 illustrates yet another aspect of the inven¬ tion whereby a very firm innerspring unit is produced. Adjacent rows of coils 11 are overlapped so that the third offset portions 13 of one row extend into the open ends 15 of the coils 11 of an adjacent row. A second set of cross-helicals 28 are then wrapped about the "overlapped" major straight portions 13a of one row and the short segments 14a and gradient arms 20 of the other row. A very dense pattern of coils 11 is thereby produced with virtually no gaps existing between coils 11.

Thus, while the invention has been described in connection with certain presently preferred embodiments, those skilled in the art will recognize modifications of structure, arrangement, portions, elements, materials

and components which can be used in the practice of the invention without departing from the principles of this invention. For example, it will be understood that the features of this invention may be used separately or in combination, and are not to be viewed as restricted to application with the types of open end offset springs described herein unless so claimed.