Background One common technique of manufacturing spring mat- tresses is the one known as the pocket technique.

According to this technique, the springs are enclosed in pockets, i. e. they are enclosed individually by a cover- ing material. Owing to this arrangement, the springs become individually resilient, such that each spring may flex separately without affecting neighbouring springs, which increases the user's comfort, since the load will be distributed more evenly across the surface that receives the load.

In order to enhance the comfort further, two super- posed layers of pocket springs are used in some cases, i. e. a structure, which in principle consists of two joined-together pocket spring mattresses. In this type of mattress the load exerted on the mattress by the user is distributed further, and the mattress is felt as more comfortable.

One problem found in this type of mattresses is, however, that they are complex and time-consuming to manufacture and that in addition thereto, much material is required, since in principle it is necessary not only to manufacture two pocket spring mattresses of conven- tional type but in addition thereto, to join the two mattresses together.

A further problem encountered in this type of mat- tresses is that only the springs in the uppermost layer are individually resilient. Because of the material of

the covers, the force exerted on the lower-layer springs by the lower parts of the loaded upper-layer springs is distributed over the upper layer, and from there it is distributed over several springs in the lower layer. This detracts from the individual resilience of the bottom- layer springs and consequently this layer contributes only marginally to the comfort of the mattress.

Object of the Invention One object of the present invention thus is to pro- vide a spring mattress of the kind defined in the intro- duction hereto, and to suggest a method of manufacturing said mattress, wherein the disadvantages referred to above are completely or at least partly eliminated.

This object is achieved by a spring mattress and a manufacturing method therefor as defined in the appended claims.

Brief Description of the Drawings In the accompanying drawings: Fig 1 is a partly broken, perspective view of a mattress in accordance with the invention ; Fig 2 is a lateral partly broken view of a first side of the mattress of Fig 1; and Fig 3 is a schematic view of the cover of the mattress of Fig 1 as seen from another side and without springs having been inserted.

Description of Preferred Embodiments As appears from Figs 1 and 2, a spring mattress in accordance with the invention comprises two layers of springs, the springs of both layers being essentially in alignment with one another in such a manner that the springs of the upper layer 1 are positioned essentially straight above the corresponding springs of the lower layer 2.

The springs are enclosed in covers, the facing ends of which preferably consisting of a common partition wall. In this manner the covers form a common external cover 4 around one pair of springs and one partition wall 3, which is joined to the external cover.

Preferably, the cover is made from a textile mate- rial and advantageously it is of a type that may be welded, but also other types of material, such as various kinds of plastic materials, may be used.

The extension of the partition wall between the junctions 5 to the external cover exceeds that of the springs abutting against said portions. Owing to this arrangement, the part of the partition wall, against which the springs abut, is movable between an upper and a lower end position without affecting the external cover at the areas of junction of the partition wall to the external cover. In this manner, the springs in the two layers may flex individually between these end positions within the area of extension inside the cover.

More specifically, in the spring mattress in accord- ance with this embodiment, the springs in the lower layer are more strongly biased than those in the upper layer.

Consequently, the lower springs will urge the partition wall upwards, to the upper position thereof, which is illustrated in Figs 1 and 2, when there is no load on the mattress. Upon increasing load on the mattress only the springs of the upper layer will be compressed initially.

At a predetermined threshold value of the force exerted by the upper springs on the lower springs, also the lower springs will eventually be compressed and be individually resilient up to the point, at which the partition wall reaches its lower end position (not shown). In this manner, the mattress is given a soft upper layer, which distributes the load across the entire surface of contact between the user's body and the mattress, and a harder lower layer adapted to take the load exerted for example by the user's buttock and shoulder regions while at the

same time all springs at least to some extent are indi- vidually resilient. In this manner, the mattress serves to straighten out the user's spine while at the same time the supporting/carrying force is distributed so as to prevent blockage of the circulation of the blood. As a result, the mattress is imparted excellent qualities of comfort and is felt as very comfortable.

The above mattress preferably is manufactured by applying a piece of material in such a manner that it extends between one pair of springs, whereby the portion of the material that thus extends between the springs will form the partition wall 3. The material ends 6 and 7, respectively, externally of the springs, are then carried round their respective spring of the pair and are attached to the piece of material on the opposite side in overlap areas 8 and 9, respectively, as clearly illus- trated in Fig 2. The external cover and the partition wall thus are formed from the same continuous piece of material, which saves material and also makes possible rational manufacture of the mattresses.

The remaining sides, i. e. those in parallel with the plane of the drawing of Fig 2, are thereafter joined together so as to completely enclose the springs inside the cover. This step preferably is effected by welding or gluing.

Preferably, the same piece of material also is used to encase several pairs of springs, as illustrated in Fig 2. The welding between neighbouring springs preferably is carried out in such a manner as to ensure that there will be more material between the lateral interconnecting joints at the middle of the external cover, i. e. in the area where the springs of the pair abut against one another, than at the top and bottom regions of the external cover. This is illustrated schematically in Fig 3, showing the material of the cover at right angles to (the plane of) Fig 2 but without springs. Attachment lines 10a, b and lla, b are arranged between neighbouring

external covers, the weld seams at the top and bottom splitting into two seam parts that are directed away from one another with a gradually growing spacing between them upwards and downwards. In this manner it is ensured that the distance between two lateral attachment lines lOb, lla of one and the same external cover along the material of the cover is longer at the middle of the external cover, i. e. in the area of the partition wall 3, than at the top and bottom, respectively. This arrangement con- tributes to the movability of the partition wall 3 in the lengthwise direction of the springs relative to the external cover.

As already mentioned, the covers inclosing a spring pair preferably are disposed in successive rows, which are then attached to one another, side by side, as indi- cated in Fig 2. Preferably, the rows are attached in two or three vertically spaced attachment points 12 opposite each spring. A larger or smaller number of attachment points is, of course, possible. It is likewise possible to provide for a longer line of attachment extending essentially in parallel with the longitudinal direction of the springs, instead of using several shorter attach- ment points.

Interconnection of rows may be effected by welding or gluing, in the same way as the previous attachment within individual rows. However, as an alternative, staples or clips may be used, as also Velcro tape or other fastening means.

The invention has been described herein by way of one embodiment. Several varieties of the invention are, however, possible. For instance, it is not necessary to manufacture the partition wall and the external cover from the same piece of material but the external cover could be manufactured separately, whereupon the partition wall is attached in at least some points to the inner face of the cover. The partition wall need not in this case be a full wall but could be configured as a smaller

bridge extending between diametrically opposite points on the external cover. Another alternative embodiment, which produces a larger longitudinal range of individual resil- ience but which requires more material, is to arrange a separate cover that encloses one of the springs of the pair of springs and thereafter apply a larger external cover around both springs of the pair. In addition, it is not either necessary first to arrange the external covers in rows and then join together these rows to form mat- tresses, but separate external covers could be joined together directly to form a mattress.

Advantageously, the springs are all of the same type, i. e. they have identical wire thickness and essentially identical resilience properties, the dif- ference in resilience properties in the springs cf the two layers being achieved by biasing the springs dif- ferently. However, it is of course equally possible to use different types of springs. In addition, the springs are shown having tapering ends. This configuration is not, however, necessary but alternatively the springs could have the same diameter size throughout or even be formed with diameters of increasing size towards the ends, i. e. they could be of the spring type known as double-cone springs.

These and other obvious varieties must be regarded to be within the scope of protection of the invention as the latter is defined in the appended claims.