GB2105522A

GB2105522A - Laminated core structure

Info

Publication number: GB2105522A
Application number: GB08126940A
Authority: GB
Inventors: Trevor Bates
Original assignee: General Motors Ltd
Current assignee: General Motors Ltd
Priority date: 1981-09-05
Filing date: 1981-09-05
Publication date: 1983-03-23

Abstract

A laminated core structure 12 for electromagnetic equipment, such as the core of an automobile ignition coil, comprises an cylindrical spiral coil 14 of ferromagnetic material sheet material 16 produced by rolling a rectangular sheet of the ferromagnetic sheet material 16 into a cylindrical spiral shape in such a manner that adjacent turns in the spiral coil are separated from one another by means of an air gap or insulation 18 therebetween. The material may be silicon steel, and may be provided with slits. The structure may be annealed after winding. Two strips may be wound together to form the structure. <IMAGE>

Description

SPECIFICATION Laminated core structure This invention relates to laminated core structures for use in electromagnetic equipment, in particular to laminated core structures for use in ignition coils of automobiles.

Ignition coils for automobiles are customarily manufactured by first winding a secondary winding of fine wire onto a paper former in the shape of a hollow cylinder and then packing the centre of the hollow cylinder with a stack of rectangular lengths of a ferromagnetic sheet material, customarily a specific silicon steel material. The laminated core structure thus formed consists of a relatively large number of rectangular laminations stacked face to face (approximately 19 in a standard ignition coil core) and a lesser number (approximately 6 in a standard ignition coil core) of such laminations stacked with the faces thereof substantially at right angles to the main stack faces in order to fill in the gaps remaining in the hollow centre of the secondary winding of the coil.Such a packing procedure is a time-consuming procedure requiring manual assembly, and is not readily adaptable to automatic assembly procedures.

Moreover, since the rectangular laminations are punched from sheet metal stock, the inherent burrs present on the edges of the rectangular laminates tend to cut through the paper former and break the fine secondary winding, thus causing unacceptably high rates of ignition coil rejection during manufacture thereof.

A laminated core structure according to the present invention, for use in electromagnetic equipment such as ignition coils, is characterised in that the core structure comprises at least one cylindrical spiral coil of ferro-magnetic sheet material arranged in such a manner that, when the core structure is in use in said electromagnetic equipment, eddy currents generated in the core structure are inhibited from passing between adjacent turns in said spiral coil.

One arrangement for achieving this effect is to arrange that adjacent turns in said spiral coil are separated from one another by means of an air gap. Alternatively, an electrically insulating coating may be provided upon one surface of the ferromagnetic sheet material to prevent this passage of eddy currents between adjacent turns of the spiral coil during the use thereof in electromagnetic equipment.

Preferably the laminated core structure comprises at least two spiral coils of ferromagnetic sheet material, one of said coils being nested concentrically within another of said coils.

Alternatively the laminated core structure may comprise at least two spiral coils of ferromagnetic sheet material interleaved with one another by coiling at least two sheets of ferromagnetic sheet material together in the manner of a Swiss roll.

A suitable ferromagnetic sheet material is the silicon steel sheet material customarily used as the sheet metal stock from which the rectangular laminations are punched for use in assembling known ignition coil cores. Advantageously a core structure made from such a silicon steel sheet material is annealed after formation so as to remove any work hardening of the sheet material and to form an oxide layer on the surface of the sheet material which aids in inhibiting eddy current transfer between adjacent turns of the spiral coil during use of the core structure in an ignition coil.

In an alternative embodiment of the invention, the ferromagnetic sheet material used for the core structure has formed therein a series of slits, each of which extends through the thickness of the ferromagnetic sheet material and is aligned, when the ferromagnetic sheet material is coiled to form the core structure, in a direction extending from one end of the core structure to the other end of the core structure. Thus, for example, the ferromagnetic sheet material has a series of substantially parallel slits formed in it, which slits, when the ferromagnetic sheet material is coiled to form the core structure, extend substantially parallel-to the longitudinal axis of the core structure.

The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which: Figure 1 shows an isometric view of a known ignition secondary winding and core, with the laminated core partly withdrawn; Figure 2 shows a isometric view of an ignition coil secondary winding and a laminated core structure according to the present invention, with the laminated core structure partly withdrawn; Figure 3 shows an isometric view of the laminated core structure shown in Figure 2; Figure 4 shows a modification of the laminated core structure shown in Figure 3; Figure 5 shows another modification of the laminated core structure shown in Figure 3; and Figures 6 and 7 show, respectively, a plan view of a sheet material portion forming the starting material and an isometric view of a rolled laminated core structure according to another embodiment of the present invention.

Figure 1 shows an isometric view of a portion of a known ignition coil, showing a secondary winding A made on a hollow cylindrical paper former, the hollow centre of which is closely packed with a number of rectangular ferromagnetic metal stampings B, shown partly withdrawn from the secondary winding A.

In contrast, Figure 2 shows an ignition coil secondary winding 10 wound upon a hollow paper former, the hollow centre of which is filled by a laminated core structure 1 2 according to the present invention, also shown partly withdrawn from the secondary winding 10. As can best be seen in Figure 3, the laminated core structure 12 comprises a cylindrical spiral coil 14 of ferro magnetic sheet material 1 6 produced by rolling a rectangular sheet of the ferromagnetic sheet material 1 6 into a cylindrical spiral shape in such a manner that adjacent turns in the spiral coil are separated from one another by means of an air gap 1 8 therebetween.This ensures that, when the core structure 12 is in use in an ignition coil, eddy currents generated in the laminated core structure are inhibited from passing between adjacent turns in said spiral coil 14. Alternatively, one side of the ferro-magnetic sheet 1 6 can be coated with an insulating coating, prior to rolling the material into the spiral coil 14, to prevent the passage of eddy currents between adjacent turns of the spiral coil 14.

The spiral coil 1 4 shown in Figure 3 comprises a rectangular sheet of silicon steel lamination material wound into a cylindrical coil of 3 turns, the outer diameter of which coil is a comfortable fit within the hollow centre of the cylindrical paper former of the ignition coil secondary winding 10 shown in Figure 2. Advantageously, the spiral coil 14 is annealed after formation so as to remove any work-hardening that has occurred in the silicon steel lamination material and to form an oxide layer on the surface of the material which aids in insulating adjacent turns of the spiral coil 14 from one another.

The spiral coil 14 shown in Figure 3 may be produced by a process similar to that used for producing spiral spring roll-pins such as the rollpins used to suspend disc brake pads in sliding caliper disc brake assemblies on motor vehicies.

In such a process, the maximum number of turns produced for each spiral coil is limited to 3 turns.

This results in a spiral coil 14 that is approximately equivalent to a standard ignition coil core of 7 laminations. In order to increase the number of turns in the laminated core structure 12, the modification shown in Figure 4 can be used, in which the laminated core structure 12 is made up of two spiral coils 20, 22, the inner coil 20 of 36 turns being nested concentrically within the outer coil 22, also of 3+ turns. This results in the formation of a laminated core structure 12 comprising effectively of a spiral coil of 7 turns, which is approximately equivalent to a standard ignition coil core of 1 5 laminations.Similarly, if desired, three such spiral coils could be used in such a nested configuration to give a total spiral coil structure of 10 turns, approximately equivalent to 21 laminations of a standard ignition coil core.

An alternative modification of the laminated core structure 1 2 is illustrated in Figure 5, which shows a core structure produced by coiling two sheets 24, 26 of ferromagnetic material together in the manner of a Swiss roll to produce a spiral coil 28 comprising two interleaved spiral coils each of 3 2 turns, which is equivalent to a single 7 turn spiral coil. In forming the laminated core structure shown in Figure 5, it will be advantageous for each of the sheets used to be coated on one side with a layer of electricallyinsulating material so as to prevent any tendency for eddy current transfer to occur between adjacent turns in the spiral coil 28 during use of the coil 28 as an ignition coil core.

Turning now to Figures 6 and 7 of the, drawings, these figures illustrate another embodiment of the invention, in which a ferromagnetic sheet material stamping 30 used to make the laminated core structure 1 2 is first lanced with a series of parallel slits 32 through the thickness of the ferromagnetic sheet material stamping 30, said slits 32 being at right angles to the longitudinal axis of the stamping 30. The stamping 30 is then rolled into a cylindrical spiral coil 34 as shown in Figure 7,such that adjacent turns in the spiral coil are separated by an air gap 36 and the parallel slits 32 are aligned substantially parallel to the longitudinal axis of the spiral coil 34.The presence of the slits 32 results in a further improvement to the degree of inhibition in the passage of eddy currents through the spiral coil 34 when the spiral coil 34 is used as an ignition coil core. It is not essential that the slits 32 should be parallel to one another, nor that they should be parallel to the longitudinal axis of the spiral coil 34. It is simply more convenient to position these slits 32 in this fashion.

The laminated core structure according to the present invention provides a core structure having electromagnetic properties in an ignition coil of an order and magnitude comparable to those of a standard core structure built up from rectangular lengths of ferromagnetic sheet material. It has the advantages of being more quickly and effectively insertable within the hollow core of a secondary winding during production of an ignition coil, either manually or automatically, and in not having a high incidence of sharp or burred edges which could cut through the paper former of the secondary winding and thus break or short-circuit the secondary winding.

Claims

1. A laminated core structure for use in electromagnetic equipment, characterised in that said core structure comprises at least one cylindrical spiral coil of ferromagnetic sheet material arranged in such a manner that, when the core structure is in use in said electromagnetic equipment, eddy currents generated in the core structure are inhibited from passing between adjacent turns in said spiral coil.

2. A laminated core structure according to claim 1, in which adjacent turns in said spiral, coil are separated from one another by means of an air gap therebetween.

3. A laminated core structure according to claim 1, in which adjacent turns in said spiral coil are separated from one another by means of an electrically insulating coating upon one surface of said ferromagnetic sheet material.

4. A laminated core structure according to any one of the preceding claims, in which said core structure comprises at least two cylindrical spiral coils of ferromagnetic sheet material, one of said coils being nested concentrically within another of said coils.

5. A laminated coil structure according to any one of claims 1, 2 or 3, in which said core structure comprises at least two cylindrical spiral coils of ferromagnetic sheet material interleaved with one another.

6. A laminated coil structure according to any one of the preceding claims, in which the ferromagnetic sheet material is a silicon steel.

7. A laminated coil structure according to any one of the preceding claims, in which the coiled ferromagnetic sheet material is annealed after the core structure has been formed.

8. A laminated coil structure according to any one of the preceding claims, in which the ferromagnetic sheet material has formed therein a series of slits, each of which extends through the thickness of the ferromagnetic sheet material and is aligned when the ferromagnetic sheet material is coiled to form the core structure, in a direction extending from one end of the core structure to the other end of the core structure.

9. A-laminated core structure according to claim 7, in which the slits in the ferromagnetic sheet material are substantially parallel to one another and are aligned, when the ferromagnetic - sheet material is coiled in the core structure, substantially parallel to the longitudinal axis of said core structure.

10. A laminated core structure substantially as hereinbefore particularly described with reference to Figures 2 and 3 of the accompanying drawings.

11. A laminated core structure substantially as hereinbefore particularly described with reference to Figures 2 and 3, as modified in Figure 4, of the accompanying drawings.

1 2. A laminated core structure substantially as hereinbefore particularly described with reference to Figures 2 and 3, as modified in Figure 5, of the accompanying drawings.

1 3. A laminated core structure substantially as hereinbefore particularly described with reference to Figures 6 and 7 of the accompanying drawings.

14. Electromagnetic equipment including a laminated core structure according to any one of claims 1 to 13.

1 5. An ignition coil including a laminated core structures according to any one of claims 1 to 13.