JPS63174304A - Magnetic core - Google Patents

Abstract

PURPOSE:To restrain the vibration in the direction of a magnetic path in a gap by increasing the strength against the telescopic motion in the direction of the magnetic path by magnetic striction by laminating magnetic metal thin plates formed in a definite shape in the direction of an axis. CONSTITUTION:Plural magnetic metal thin plates 4 formed in a definite doughnut shape are laminated in the direction of an axis. Ferrite or amorphous metal is used for the magnetic metal. The magnetic metal thin plate 4 is formed in a shape partially provided with a notch for a gap 5. This increases the strength against the telescopic motion in the direction of a magnetic path by magnetic striction and the vibration in the direction of the magnetic path in the gap is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a magnetic core, and more particularly to a magnetic core having a gap in which noise generated at the gap portion is reduced.

(Prior Art) In recent years, in output choke coils and the like in switching power supplies, a magnetic core 1 is used, as shown in FIG.
is often used.

Such a magnetic core has conventionally been manufactured, for example, as follows.

That is, first, magnetic metal ribbons are wound into a predetermined shape and laminated, and then fixed by impregnating adhesive resin or the like into the space between the eyebrows of this wound body.
A gap is formed by cutting with a grindstone with a thin blade of about n.

(Problems to be Solved by the Invention) By the way, when such a conventional magnetic core is used under a condition where the current is periodically turned on and off, such as in an output choke coil in a switching power supply, However, when the switching frequency is an audible frequency such as several kHz, there is a problem in that the core vibrates and generates harsh noise. Also, the switching frequency is 5
Even in the case of a high frequency such as ~10 kHz, if there is a component used at an audible frequency on the secondary side, there is a problem in that the components on the secondary side generate noise, similar to the problem described above.

This noise is generated because the magnetic field applied to the core through the coil causes the core to expand and contract (magnetostriction) in the direction of the magnetic path, and this expansion and contraction movement occurs in the lamination direction at the gap where the magnetic thin plate is free. It is thought that this is because it is converted into vibration.

Conventionally, countermeasures have been taken to address this problem, such as fixing the gap part with resin or creating a space between the magnetic core and the case that houses the magnetic core, which has the effect of reducing the noise level by about 30 dB. However, since the wound body is used as the magnetic core, the structure is weak against expansion and contraction due to magnetostriction, and it has been found that there are limits to fixing with resin when attempting to further reduce noise. In particular, when a Fe-based amorphous metal with large magnetostriction is used as the magnetic metal, or when the switching frequency is as high as 5 to 10 kHz, it is difficult to further reduce the noise. There is a strong demand for a magnetic core with high strength.

The present invention was made to solve these conventional problems, and has a high strength against expansion and contraction due to magnetostriction, which occurs when the coil current is turned on and off at audible or high frequencies. The purpose of the present invention is to provide a magnetic core whose noise level is attenuated as much as possible.

[Structure of the Invention (Problems to be Solved by the Invention) The magnetic core of the present invention is characterized in that a plurality of magnetic metal thin plates formed in a predetermined donut shape are laminated in the axial direction.

The magnetic metal in the present invention is ferrite or has the general formula: M
a M' b xc (In the formula, M represents one or more elements selected from Fe, Co and Ni, and M' is ]l[a, ■a, v
a, ■ Represents one or more elements selected from group a metals, X represents one or more elements selected from B, Si, P, C1Ge, and a+b+c=1.0
．． 6≦a'+b≦0.9.0.005≦b≦0.1.0
．． It is possible to use an amorphous metal represented by the formula (1≦C≦0.3), and Fe-based amorphous metals having a high saturation magnetic flux density are particularly preferred. Moreover, the thickness of this magnetic metal thin plate is preferably in the range of 10 to 40 μm, more preferably in the range of 15 to 30 μm. If the thickness of the magnetic metal thin plate is less than 10 μm, problems may arise in workability during lamination, and if it exceeds 40 μm, it becomes a factor of increased iron loss when used at high frequencies.

The magnetic metal thin plate used in the present invention is formed from the above-mentioned magnetic metal thin plate into a predetermined donut shape by, for example, punching. In addition, at this time, by forming a shape in which a part of the notch serving as a gap is provided, cutting for forming a gap is not necessary after lamination, which is even more effective.

The magnetic core of the present invention is manufactured, for example, as follows.

That is, first, thin magnetic metal plates are formed into a predetermined shape with some notches that will serve as gaps, for example, by punching, and the thin plates are stacked in the axial direction so that the end faces of the notches are aligned and a predetermined thickness is obtained. Then, the glabella is fixed by impregnating the gap with a resin with or without inserting a spacer.

In addition, when using an amorphous metal as the magnetic metal,
Below the crystallization temperature of the amorphous metal, in a thin plate state before the lamination process or after the lamination process so that the laminated structure does not collapse,
Preferably, the heat treatment is performed at a temperature of 300 to 500°C.

In addition, when forming magnetic thin metal plates without providing a notch to serve as a gap portion, the gaps are formed by laminating the sheets and impregnating them with resin, and then partially cutting them as in the conventional method.

(Function) Since the magnetic core of the present invention has a structure in which thin magnetic metal plates formed in a predetermined shape are laminated in the axial direction, it has high strength against expansion and contraction in the magnetic path direction due to magnetostriction, and this is a cause of noise generation. Vibration in the magnetic path direction at the gap portion can be suppressed.

(Example) Next, one embodiment of the present invention will be described.

Example First, a thin plate of Fe7aSi3B+ 1 (atomic %) with a thickness of 25 μm was used, and the outer diameter was 2 as shown in FIG.
A magnetic metal thin plate 4 having a predetermined shape is formed by punching so as to have a donut shape with a width of 6 inches and an inner diameter of 16 mm, and a notch penetrating from the outer periphery to the inner periphery with a width iin to form a gap 5, and then as shown in FIG. So, height 1011
11, and then heat-treated the laminate at 430° C. for 10 minutes in a nitrogen gas atmosphere. Then, after inserting a spacer 6 into the gap 5, a resin was impregnated between the laminated layers using negative pressure to fix the laminated product, thereby producing a magnetic core 3.

In addition, for comparison with the present invention, using the same amorphous metal as in the example, a thin strip of this amorphous metal was wound to have the same shape as in the example, and this wound body was A magnetic core was heat-treated and impregnated with resin under the same conditions as in the example, and then a gap was formed by cutting, and the gap portion was fixed again by resin impregnation (Comparative Example 1), and one that was not fixed (Comparative Example 2). was created.

Using these magnetic cores, create a choke coil,
When a 5 KHz, 3 A sine wave was applied and the noise level was measured, the results shown in the following table were obtained.

As is clear from the table above, the magnetic core according to this example has thin magnetic metal plates laminated in the axial direction, so it has great strength against expansion and contraction in the magnetic path direction due to magnetostriction, which is a factor in noise generation. It is possible to easily suppress the vibrations that occur, thereby significantly reducing the generation of noise. Furthermore, since the notch that will serve as the gap portion is formed at the same time as processing the magnetic thin metal sheet, there is no need to create a gap by cutting the laminate, and problems caused by peeling of the laminate or the occurrence of burrs at the cut portion can be solved. Furthermore, since the gap is already formed at the time of resin impregnation, there is no need for the conventional method of fixing the gap portion by re-impregnating the resin, and this has the effect of reducing the manufacturing process.

[Effects of the Invention] As explained above, according to the magnetic core of the present invention, since the magnetic metal thin plates are laminated in the axial direction, the strength is large against expansion and contraction in the magnetic path direction due to magnetostriction, and this is a cause of noise generation. This makes it possible to easily suppress the vibrations that result, thereby making it possible to significantly reduce the generation of noise.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a magnetic core according to an embodiment of the present invention, FIG. 2 is a plan view showing a magnetic metal thin plate according to an embodiment of the present invention,
FIG. 3 is a perspective view showing a magnetic core manufactured by a conventional method. 3...Magnetic core 4...Magnetic metal thin plate 5...Gap 6...Spacer agent Patent attorney Shi Nori Chika Ken Yukio Yuyama Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) A magnetic core characterized in that a plurality of magnetic metal thin plates formed in a predetermined donut shape are laminated in the axial direction. (2) The magnetic core according to claim 1, wherein the donut-shaped magnetic metal thin plates have a partial notch that serves as a gap portion, and are laminated with the end surfaces of the notches aligned. (3) The magnetic core according to claim 1 or 2, wherein the magnetic thin metal plate is an amorphous magnetic metal.