Greater importance has come to be attached to the needs for saving of energy in the fields of industrial equipment, home electrical appliances, automotive components, and so forth in recent years. Most of electricity is now generated by domestic power plants, such as a thermal power plant, hydraulic power plant, nuclear power plant, and wind power plant, and those domestic power plants each make use of a rotating electrical machine (generator) that is an electromagnetic application product. Further, driving of rotating electrical machines (motors) accounts for the majority of domestic power consumption. Furthermore, a static electrical machine, such as a transformer, a reactor, for use in transmission of the power, is also an electromagnetic application product. With those electromagnetic application products, a soft magnetic material is used in the iron core thereof, and reduction in loss occurring to the iron core renders it possible to achieve higher efficiency. Further, reduction in cost as well as higher efficiency is required of those electromagnetic application products.
The rotating electrical machine has a basic structure including iron cores made of a soft magnetic material, coils, permanent magnets, and so forth. Loss occurring to a rotating electrical machine falls into two broad categories, that is, iron loss and copper loss. The iron loss is dependent on properties of a soft magnetic material. The copper loss is dependent on a resistance value of the coils, that is, a packing factor, so that the more compact a winding is structured, the less the loss can be rendered. Enhancement in efficiency can be achieved by designing a rotating electrical machine in respect of shape, size, and so forth, such that the loss can be minimized. Changing of properties of material can also contribute to higher efficiency.
The same can be said of a static electrical machine. Iron cores and coils made of a soft magnetic material, making up the static electrical machine, have iron loss and copper loss. The smaller the losses are, the better in efficiency the machine is.
An amorphous metal has low iron-loss characteristics belonging in the top class among soft magnetic materials. Since the amorphous metal is produced by a method for forming an amorphous material by quenching, the amorphous metal can be formed only in the form of a foil strip (in a ribbon-like form) that is small in thickness. For this reason, it has been difficult to render the amorphous metal into the shape of an iron core, and hence, the amorphous metal has not been adopted for the electromagnetic application product described above.
As an example in which the amorphous metal is used for an iron core, a wound iron core can be cited. Because the wound iron core can be made up simply by winding a foil strip, drawbacks of the amorphous metal, such as poor workability, difficulty in handling because of its small thickness, and so forth, can be complemented by the wound iron core. In the case of using a wound iron core as it is, as a motor, without splitting it by cutting, such a configuration as that of an axial gap motor (an axial-gap rotating electrical machine) is suitable for application.
The basic structure of the axial-gap rotating electrical machine includes such a structure as is shown in Japanese Unexamined Patent Application Publication No. 2005-287212. This structure includes a teeth-part and a yoke part, having opposed surfaces contributing to a torque output at only one location in the axial direction. Since magnetic fluxes flow from the teeth-part to the yoke part in the above structure, there is the need for using a soft magnetic material chosen by taking into consideration three-dimensional flow of the magnetic fluxes. In order to meet such requirements, it is necessary to use material of magnetic characteristics having three-dimensional isotropy, such as a dust core, and so forth. However, there is a problem that such material is low in magnetic permeability as compared with a common silicon steel, and so forth, and large in iron loss, so that miniaturization is difficult to implement.
As a method for solving the problem described above, there is a technology whereby an iron core is made up of an amorphous metal by providing opposed surfaces on two planes along the axial direction thereof. A problem with this technology lies in a method for manufacturing an iron core. In the case of manufacturing the iron core, a wound iron core is split by cutting, thereby obtaining iron cores of individual stators. In this case, it is required that the wound iron core is fixedly held and has a high strength so as to be able to withstand the cutting. For this purpose, there is a method for impregnating both the periphery of the wound iron core and a gap between foil strips with resin to obtain strength sufficient for withstanding the cutting. However, in order to implement such a structure, impregnation with resin should be carried out in a vacuum or a reduced-pressure atmosphere, leading to a problem that much time is required to manufacture just one iron core.
An object of the invention is, solving problems with the conventional technology, to provide a high-quality magnetic iron core by concurrently satisfying requirements for enhancement in strength of a wound iron core, particularly, strength of a wound iron core made up of amorphous foil strips, reduction in manufacturing time, and manufacturing cost. Another object of the invention is to provide an electromagnetic application product highly efficient and small in size as an application of the magnetic iron core.