US3134057A

US3134057A - Magnetic circuit for the deflection of flux leakage

Info

Publication number: US3134057A
Application number: US57488A
Authority: US
Inventors: Tsunoo Toshihiko; Uruma Mitsuo
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 1960-07-11
Filing date: 1960-09-21
Publication date: 1964-05-19
Anticipated expiration: 1981-05-19

Description

y 1964 TOSHIHIKO TSUNOO ETAL 3,134,057

MAGNETIC CIRCUIT FOR THE DEFLECTION OF FLUX LEAKAGE Filed Sept. 21, 1960 2 Sheets-Sheet 1 y 1964 TOSHIHIKO TSUNOO ETAL 3,134,057

v MAGNETIC CIRCUIT F OR THE DEFLECTION OF FLUX LEAKAGE Filed Sept. 21, 1960 2Sheets-Sheet 2 45 40 A M 4% H54.

:15 40 5 AZ: 4 41 54 F/5 5 164mg 41 4 F/5 5 114 United States Patent 3,134,057 MAGNETIC CIRCUIT FOR THE DEFLECTION GF FLUX LEAKAGE Toshihiko Tsunoo, Amagasaki-shi, and Mitsno Uruma,

Nishinomiya-shi, Japan, assignors to Sunnitomo Kinzoku Kogyo Kahushiki Kaisha, Osaka-shi, Japan, a corporation of Japan Filed Sept. 21, 1960, fier. No. 57,488 Claims priority, application Japan July 11, 1960 Claims. (CL 317-201) This invention relates to a magnetic circuit wherein a small vacant space or a thin non-magnetic material is provided on a permanent magnet, an electromagnet, a yoke or a pole piece at its end face where magnetic fluX leakage occurs, in such a manner that a magnetic pole stands opposite to said end face in the same polarity thereby causing the magnetic pole to repulse and then deflect leakage flux toward the opposite pole of an effective air gap and thus to increase the flux in the air gap.

Magnetic circuits of the type in which a permanent magnet or an electromagnet is used are, in general, arranged to utilize the magnetic flux induced from the two poles of said magnet or accumulated in an air gap through a pole piece or a yoke of soft magnetic material such as soft iron. The magnetic circuit of such type has some disadvantages as described hereinafter.

The nature of the present invention and its advantages will be fully understood from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view showing, by way of example, a conventional magnetic circuit;

FIG. 2 is a similar view showing one embodiment of the present invention;

FIG. 3 illustrates a cross-section of a permanent magnet speaker assembly wherein the magnetic circuit accord ing to the present invention is incorporated;

FIG. 4 is a cross-sectional side view showing the known magnet roller for pressing and drafting;

FIG. 5 is a similar view showing the magnet roller to which the magnetic circuit of the present invention is applied;

FIG. 6 is another similar view showing a part of a modified form of the same.

Referring now to FIG. 1, the conventional magnet circuit generally used for the permanent magnet speaker assembly with a central pillar type magnet comprises a permanent magnet 1, a pole piece 2, a yoke 3 and an annular air gap 4 formed by said pole piece and the yoke, in which gap the flux is-introducedfrom the permanent magnet and accumulated for use. Such magnetic circuit of prior art has a-defect in that a desired accumulation of the effective flux inthe air gap is prevented due to fiuX leakage from the end face of permanent magnet, electromagnet, yoke or pole piece. In the known circuit shown in FIG. 1, the flux induced by the pole piece 2 is deflected 90 at the end face thereof and attracted towards the yoke 3 through the air gap 4 but at the same time a considerable amount of flux is not bent as desired and leaks upwardly from the end face of the pole piece 2. Thus, for making effective use of the flux through the air gap in the magnetic circuit, it is necessary to reduce leakage of the flux in transit to a minimum.

In FIGS. 2 and 3 illustrating the same speaker assembly as in FIG. 1, a magnetic circuit according to the present invention comprises a permanent magnet 1, a pole piece 2, a yoke 3 and air gap 4. On the top end face of the pole piece 2 a non-magnetic material 5 like Bakelite is placed, and a high coercivity permanent magnet 6 such as barium ferrite magnet is so disposed upon said material 5 that its side facing the pole piece 2 becomes the same polarity therewith. Instead of placing said mamagnetic performance.

terial 5, that place may be used as a vacant space (FIG. 3). In FIG. 3, 7 is a voice coil, 8 a cone paper, 9 a damper and 10 a frame.

In operation, the flux liable to leak upwardly from the top end face of the pole piece 2 is repulsed by the flux of the magnet 6 owing to the same polarity, and attracted to the opposite polarity of the yoke 3 to accumulate into the air gap 4 thereby increasing the gap flux density. In addition, the flux of the magnet 6 facing the pole piece 2 is also drawn into the air gap 4. Thus, by these two processes, the gapflux density is increased 10-20% compared with the arrangement shown in FIG. 1.

As a magnetic pole having the same polarity confronting the end face of the magnet 6 where flux leakage occurs, there may be used a high coercivity permanent magnet 6 such as barium ferrite magnet, manganese-bismuthic magnet and alnico magnet. Even a thin plate magnet of the above type can be employed without any loss of For instance, such plate magnet is used in the magnetic circuit for a loudspeaker with advantage that due to its flatness it is conveniently embraced in the moving coil part of the cone paper. As a permanent magnet 1 in the base circuit there is no need for a high coercivity permanent magnet to use, since the magnetic circuit consisting of magnet 1, pole piece 2 and yoke 3 forms practically a closed magnetic circuit so that the magnetic performance of the circuit is not decreased even in the state of repulsion between the magnetic poles of

magnets

6 and 1.

The following Table 1 shows the gap flux density in the magnetic circuit according to the present invention as illustrated in FIG. 2 compared with that in the known circuit (FIG. 1).

wherein the permanent magnet 1 used in the circuit I was a bottle-shaped alnico casting magnet of 17.5 mm. 4: X 13 mm. 4) X 14 mm., while that used in the circuit II was a pillar-shaped alnico casting magnet of 13 mm. x 12 mm. The gap length in both circuits was 0.55 mm. The permanent magnet 6 used in the circuit II was a barium ferrite magnet of 13 mm. (1; X 3 mm. The non-magnetic material 5 used was a Bakelite disc.

As clearly seen from the above table, the gap flux density in the magnetic circuit according to the present invention is much larger than that in prior art.

We have now particularly described an embodiment of the present invention applying to the magnetic circuit using a central pillar type magnet wherein the leakage flux from the end face of the pole piece 2 is repulsed so as to increase the flux in the air gap 4.

Same advantage can be obtained in a similar magnetic circuit using a magnet without a pole piece by disposing a small vacant space or a thin plate of non-magnetic material immediately on the end face of the magnet in such a manner that the same polarities of the magnet and another magnet or its magnetizing coil are facing each other. Also in a magnetic circuit using a ring type magnet or in the base circuit using an electromagnet in place of a permanent magnet, a good magnetic circuit can be easily obtained in similar way.

Another embodiment of the present invention is shown by applying to magnetically attractive rollers generally used for pressing and drafting of fibers, paper and film.

Referring to FIG. 4 illustrating a typical magnetic circuit in the known magnet roller, the roller comprises a permanent magnet 1 having poles in the axial direction, a

yoke 3 connecting to each pole of the magnet 1, an outer casing 11 of non-magnetic material which incorporates the magnet 1 and the yoke 3 into one body, a cot 12, a pole ring 13, said cot and pole ring being put respectively on the round pillar side of the yoke 3, and a non-magnetic cap 14 fitted on the shaft of the yoke 3. The magnetic circuit is formed by a magnetically inductive roller 15 such as a fluted roller cooperating with the magnet roller, thus both rollers being attracted to each other through the .fiux in an air gap'4'therebetween. This circuit however has defect that a considerable amount of magnetic flux leaksfrom; the axial end face of the magnet roller thereby decreasing the flux in the effective air gap and intensifying magnetization around the shaft of the magnet roller.

As shown in FIG. 5, in the magnetic circuit according to the present invention for the magnet roller having the same structure with that shown in FIG. 4, a high coercivity magnet piece 6 such as barium ferrite magnet is fitted .on the axial end face of the pole ring 13 in such a way that the same polarities are facing each other in order to is so arranged as to leave a space between the end face of the pole ring 13 and the opposing magnet piece 6 of high coercivity. The separator is formed of a flange portion 16 of the non-magnetic cap 14 covering the axial end face of the pole ring 13. Instead of the arrangement that the same polarities stand close to each other as shown in FIG. 5, there is thus provided a proper space between the same polarities so that the flux from the permanent magnet 1 is more advantageously repulsed and effectively deflected into the air gap 4.

Tests of the magnetic circuit were conducted on a magnet roller of 28 mm. in outer diameter and 126 mm. in length wherein a permanent magnet of 25 mm. in outer diameter and 50 mm. in length (l3 13,500 gausses, H 650 oersteds) and as a pole piece forming the air gap, a pole ring of 27.6 mm. in outer diameter, 18 mm. in inner diameter and 8 mm. in length were used. The result was that the attractive power was 7.2 kg. on the fluted roller in the magnetic circuit shown in FIG. 4, while on the other hand, in the magnetic circuit shown in FIG. 5 wherein a high coercivity magnet piece of 27 mm. in outer diameter, 17 mm. in width and 3 mm. in length (B 3,500 gausses, H

4 2,800 oersteds) was fitted, the attractive power was 8.3 kg., 15% higher than in FIG. 4.

The present invention provides a magnetic circuit which excels as one used for loudspeakers and magnet rollers, and also for acoustic machines, meters and vibrators.

We claim:

1. A magnetic circuit comprising: an axially polarized central magnet, including first and second end portions; a magnetic pole piece in contact with one end portion of said central magnet and axially extending therefrom; a yoke including a central portion in contact with the second end portion of said central magnet, a side portion spaced from and extending parallel to said central magnet and said magnetic pole piece, and a top portion extending laterally toward said magnetic pole piece to provide an annular gap between the top portion of said yoke and said magnetic pole piece; a second magnet of high coercivity axially displaced from said magnetic pole piece to provide a second gap between said magnetic pole piece and said second magnet, said second magnet being magnetically polarized with respect to the polarization of said first magnet to force the leakage flux in said second gap from said central magnet to the top portion of said yoke via said annular gap.

2. The magnetic circuit of claim 1, wherein said first magnet is a permanent magnet.

3. The magnetic circuit of claim 1 including a spacer of non-magnetic material interposed between said magnetic pole piece and said second magnet to define said second gap. 7

4. The magnetic circuit of claim 1 including a voice coil disposed about said magnetic pole piece and a cone fixed to said voice coil.

5. A magnetic roller comprising a cylindrical magnet which is axially polarized, cylindrical yokes fixed to each end of said cylindrical magnet, annular pole rings fixed to said cylindrical yokes and having diameters less than said cylindrical yokes, a magnetically inductive roller including an outer surface disposed parallel and adjacent the peripheral surfaces of said cylindrical magnet, said cylindrical yokes and said annular pole pieces whereby a material to be rolled is insertable in the gap between said outer surface and said peripheral surfaces, magnet pieces having high coercivity fixed to said annular pole rings, said magnetic pieces being polarized with respect to said cylindrical magnet to force the axial flux from the ends of said annular pole rings radially toward said magnetically inductive roller.

References Cited in the file of this patent 7 UNITED STATES PATENTS 2,585,714 Wrobel et al Feb. 12, 1952 2,698,917 Van Urk et al Jan. 4, 1955 2,895,092 Cluwen July 14, 1959 2,993,152 Pierce et al July 18, 1961 3,067,366 Hofman Dec. 4, 1962 FOREIGN PATENTS 670,667 Great Britain Apr. 23, 1952