US2929038A - Laminated magnetic core - Google Patents

Description

March 15, 1960 G. SONESSON 2,929,038

LAMINATED MAGNETIC CORE Filed Dec. 10, 1956 INVENTOR. Georg 50112550.

Byuwmd United States Patent '0 LAMINATED MAGNETIC CORE Georg Sonesson, Enskede, Sweden, asslgnor to Allmiinna Svenska Elektriska Aktieb'olaget, Vasteras, Sweden, a corporation of Sweden Application December 10, 1956, Serial No. 627,157

Claims priority, application Sweden December 9, 1955 7 Claims. (Cl. 336-215) Magnetic cores for transductors and other exacting applications should be made with the smallest possible reluctance of the core and the sharpest possible knee of the magnetisation curve. Up to now these two properties have been fulfilled in the best way by wound cores made of magnetic grain-oriented strip material, but these cores required special, expensive arrangements to apply the coils. Attempts to cut a wound core so that normal prefabricated coils can be used have not been successful because the unavoidable air gap often involves a considerable increase in the reluctance.

It is further known that low reluctance and a sharp knee point can be obtained if a core is built by E or U laminations with yokes having the double leg width, because in such a core only overlap joints are present and saturation will occur simultaneously in all parts of the flux path. Such a core cannot be made of grain-oriented material however, which is desirable in order to achieve the best possible magnetic properties, because the E and U laminations cannot be made in such a Way that the magnetic flux Will always follow the direction of the magnetic grain-orientation. The magnetic properties of these cores can never be so good as those of the best Wound cores.

If grain oriented magnetic material is used in a stacked core rectangular laminations must be used in the yoke as well as the leg and overlap joints must be used at all joints. It is necessary to employ overlap joints in order, on the one hand to obtain a low reluctance and on the other hand to prevent the flux from traversing any portion of a lamination across the direction of the grainorientation. The demand that all parts of the core should be saturated simultaneously along the flux path can be fulfilled if the core is made of equally broad laminations in the yoke as well as the leg, but in that case only 50% useful iron area will be obtained in the legs which will involve an unfavourable increase in the average winding length and also in the copper consumption of the windings arranged on the core.

The present invention relates to a magnetic core built from rectangular laminations in the yoke and the leg permitting space factor of iron that is higher than 50%. The characterising feature of the invention is that each leg lamination is joined to a yoke lamination, of mainly the same width, by an overlap joint and that successive overlap joints are staggered.

The sharpest possible knee of the magnetisation curve and the lowest possible reluctance will be obtained by a core according to the invention irrespective of whether or not the laminations are grain-oriented. It is possible, however, by making the core from rectangular laminations to use first class grain-oriented material and at the same time to use pre-wound coils. Owing to the high space factor of the iron, material is saved in both core and windings and simultaneously, if a core according to the invention is used in a transductor, it will permit a corresponding increase in amplification and efliciency.

A great advantage from the manufacturing point of 2,929,038 Patented Mar. 15, 1960 view is that the basic material for a core according to the invention is made of a fully prefabricated strip of the desired width. This strip has only to be cut in lengths corresponding to those of the yoke and legs. If first class core material is used the cutting operation will impair the magnetic properties in a narrow region at the cutting surface. This can easily be compensated for by making the laminations correspondingly longer so that the affected regions protrude beyond the overlap joints. As the laminations are not deformed after the cutting, no deterioration of the magnetic properties of the material will arise and it will not be necessary to anneal the core after it has been staggered.

In the accompanying drawings, Figures 1-3 show joints and the stacking principle of a core and Figures 4 and 5 show two forms, according to the invention.

Figure 1 diagrammatically shows two leg laminations 1 and 2 each one joined by an overlap joint between the yoke laminations 3 and 4 respectively, the latter having mainly the same width as the leg laminations. If the yoke laminations are facing each other according to the figure and are placed on each other in the direction of the arrows, a space is obtained between the leg laminations 1 and 2 which can enclose a third leg lamination 5 with a corresponding yoke lamination 6. When the laminations are pressed together in the direction of the arrows the yoke laminations 4 and 6 will be in line with each other as also will be the yoke lamination 3 and the leg lamination 5. On continued stacking of the core further leg laminations and corresponding yokelaminations are arranged together according to the principle shown and the result will be that three leg laminations will come together and will be separated by an air layer of the thickness of one lamination. The yoke laminations will also form groups of three equally broad laminations. Because one group comprising three leg laminations with corresponding yoke laminations will thus occupy four layers in the core, a space factor of will be obtained in the legs.

In order to obtain a desired higher space factor the principle shown in Fig. 1 can be further developed as indicated in Fig. 2. In this figure two further leg laminations 7, 8 are placed outside the leg laminations 1 and 2 respectively and are longitudinally displaced to allow the corresponding yoke laminations 9 and 10 respectively to be placed in line with the leg laminations 1 and 2 respectively. In order to make the core mechanically stable it is shown in Fig. 2 that the space between the yoke laminations 9 and 10 must be filled up by strips 11 and 12 of non-magnetic material.

A core according to Fig. 2 will give a space factor in the legs of 83.3%. By arranging further leg laminations, the overlap joints of which are staggered according to the principle shown in Figures 1 and 2, a still higher space factor may be obtained and only the increasing yoke width will put a practical limit on the use of the core.

In practice, an optimum with respect to material consumption will be obtained by a core built of groups of laminations according to Fig. l, where the total yoke width only corresponds to the width of two yoke laminations. Such a core is also advantageous as the joints are compact, which is important when the core is pressed together and'is mounted in an apparatus.

Figure 3 shows a corner of a core of this type. In Fig. 3 the leg laminations 13 are shown filled whereas the yoke laminations are shown as open rectangles.

Figure 4 shows a perspective view of one group of laminations in a two-legged core, having joints according to Fig. 1. Two leg laminations 15, 16 having full leg length, have corresponding yoke laminations 17, 18 at one corner and 19, 20 at the other. The yoke laminations' have mainly the. same. widthas. the. leg. laminations and are placed on top of each other. Said laminations enclose a third leg lamination 21 being two yoke widths shorter. than. they other leg. larninations and having the:

yoke laminations; 22, 23 respectively; Between the leg. lamination 16. andv the leg lamination 21 an air layer will be obtained. The arrows at thecorners show the direction of the magnetic flux path by transitions between leg, laminations and. yoke laminations.

Figure 5. shows a perspective view of a two-legged core being stacked in a modified way but still according; to the principle shown. in Fig, 1. Two yoke laminations 2.4:and. 25 in the. same layer in one corner and 26, 27 in the other. corner, rest against corresponding leg laminations 28. and 29. The leg laminations are one yoke width shorter than the total length of the core. A leg lamination 3.0. of full. length is situated immediately above the leglamination 28. Corresponding yoke laminations: are denoted 31 in one corner and 32 in the other. this figure arrows show the flux transitions between the yoke and leg laminations.

The figures only show the stacking'principle applied to two-legged cores, but it is also applicable for polylegged cores, and insuch cases the yoke laminations may be common to allleg laminations. In such cores it may be necessary to make certain legs'broader than the others and for. this purpose two equally wide leg laminations, level with eachother, may be replaced by one lamination having double width.

In three-legged cores for transductors, the central leg must beat least twice as wide as the outer legs and in these caseszinstead of two equally wide leg laminations level with each. other in the central leg, one lamination, having the desired width, may be used in each layer. In. the same way two. yoke laminations, level with each other, may be replaced by onev lamination.

Owing to the leakage conditions it is often desirable that the yokes should be so dimensioned that they are saturated later than the legs and for this purpose the yoke laminations may be made somewhat broader than the leg laminations.

I claim as my invention:

1. A laminated magnetic core comprising yokes and legs, inthe forrnof rectangular laminations of substantially the same-width,.each of said leg laminations join. ing a yoke lamination to form anoverlap joint, two yoke laminations corresponding to successive leg laminations beingdisplaced one lamination width in relation to each.

Also in other. inthe. longitudinal direction. of the legs when the joint sides of the two leg laminations are facing each other or in the same direction, and the two yoke laminations being equally located longitudinally to the legs when the joint sides of the leg laminations are facing away from each other. i

2. A laminated magnetic core as-claimed in claim 1, in which said core comprises a plurality of groups of laminations, each leg in each group consisting of three leg lam-inations, and said three leg laminations and corresponding yoke laminations being arranged in four layers.

3.. A laminated magnetic core as claimed in claim 2, in which two of said three leg laminations are full length and the third leg lamination is two larnination widths shorter, said two'long leg laminations together with the corresponding'yoke laminations forming a rectangle, and said rectangle enclosing said shorter third leg lamination and its corresponding yoke lamination.

4. A laminated magnetic core as claimed in claim 1, in which every third leg lamination of said core is full length, the interjacent two leg laminations both being one lamination width shorter, the yoke laminations corresponding to a longer leg lamination being arranged on either side of said long leg lamination and in the samelayer asa shorter leg lamination adjacent to the longer lamination, and the four yoke laminations corresponding.

to two interjacent shorter leg laminations being arranged in one layer between said two shorter leg laminations.

5. A laminated magnetic core as claimed in claim 1, in which the leg and yoke laminations of said core protiude beyond the 'overlapjoints corresponding to the length of the region atfected at the cutting of the laminations. 7

6. A laminated magnetic core as claimed in claim 1, in which said core has at least three legs, three leg laminations, each from its own leg, situatedin the same layer, and. having. common yoke. laminations.

7. A laminated magnetic core as claimed in claim 1, in. which said core has laminations of non-magnetic material, said non-magnetic laminations being inserted in the space between the magnetic laminations in the yokes and legs.

References Cited in the file of this patent UNITED STATES PATENTS Granfield Apr. 19, 1949

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