US3739465A

US3739465A - Method of making an electromagnetic device

Info

Publication number: US3739465A
Application number: US00173592A
Authority: US
Inventors: A Krajc; K Romer; J Schmid
Original assignee: Junkers and Co GmbH
Current assignee: Junkers and Co GmbH
Priority date: 1969-07-05
Filing date: 1971-08-20
Publication date: 1973-06-19
Anticipated expiration: 1990-06-19
Also published as: FR2050513A1; FR2050513B1; NL163319B; ES371125A1; BE741705A; AT290787B; NL6914992A; DE1934163B2; BR6912454D0; GB1287474A; DE1934163A1

Abstract

A bifurcated magnetic core in an electromagnetic device having an armature plate is formed with a fixedly mounted yoke and pair of arms which cooperate with the armature plate and are each provided with a pole surface facing the same. The inherent frequency of the fundamental oscillation of the magnet core prior to application of a winding onto the same is in excess of 25 kilohertz.

Description

United States Patent 1 Riimer et a].

[ June 19, 1973 METHOD OF MAKING AN ELECTROMAGNETIC DEVICE Inventors: Kurt Riimer, Altbach/Neckar; Josef Schmid; Adolf Krajc, both of Wernau/Neckar, all of Germany Assignee: Junkers & Co. Gmbll, I

Wernau/Neckan, Germany Filed: Aug. 20, 1971 Appl. No.: 173,592

Related US. Application Data Division of Ser. No. 883,004, Dec. 8, abandoned.

Foreig p Application Priority Data July 5, 1969 Germany P 19 34 163.0

Int. CL. H02k 15/00, H02k 15/14, H02k 15/16 Field of Search 29/602, 607, 596;

[56] References Cited UNITED STATES PATENTS 3,156,836 11/1964 Koke 310/29 3,039,012 6/1962 Bruninghaus 310/29 Primary ExaminerCharles W. Lanham Assistant Examiner-Carl E. Hall Attorney-Michael S. Striker [57] ABSTRACT 7 Claims, 4 Drawing Figures pmmmq'um sun War 1 w.

METHOD OF MAKING AN ELECTROMAGNETIC DEVICE CROSS REFERENCE TO RELATED APPLICATION This is a division of our copending application Ser. No. 883,004, now abandoned filed on Dec. 8, 1969.

BACKGROUND OF THE INVENTION The present invention relates generally to electromagnetic devices, and more particularly to a method of making an electromagnetic device.

It is known to provide thermoelectric ignition safety devices in certain appliances, particularly in appliances using combustible gas. Such devices comprise an anchor plate cooperating with a plunger and being associated with the free ends of two arms of a bifurcated magnet core whose yoke is fixedly mounted and which carries the magnet winding. There are applications wherein this type of construction is entirely satisfactory. In other applications, however, it has been found that these devices require improvement. The holding power of the electromagnet and the closure time of the ignition safety device which is operated by the electromagnet are of considerable importance in such constructions. Furthermore, the material composition and the manner of annealing are factors which affect the operational efficiency of a magnet insert in such devices.

The most important consideration, however, is the active airgap between the pole surfaces of the magnet core and the abutment surface on the anchor or armature blade because this air gap is to be as small as possible with spacings on the order of for instance less than I being involved. This is difficult to obtain, but it is even more difficult to make the pole surfaces at the free ends of the arms of the magnet core completely planar as well as having them be located in a common plane with one another, a requirement which should ideally be fulfilled in order to assure that, when the electromagnetic device is assembled and it is in operational condition, the abutment surface of the anchor plate and the pole surfaces of the magnet member are as close as possible to being located in a plane common to them all, meaning that all three surfaces should be located in a common plane. The more closely this requirement can be met, the more advantageous is the size of the contact area between the contact surfaces and the surface of the anchor plate, and accordingly more pronounced will be the holding power of the electromagnet.

The problem is that when the. pole surfaces on the two arms of the electromagnetic core are being produced, both arms of the magnet member or magnetic core tend to oscillate and therefore counteract the attempt to provide planar surfaces constituting the abutment surfaces. The result is that each individual pole or abutment surface in the end effect is not planar but slightly curved and the planes of the pole surfaces on the respective arms are skew with reference to one another. Thus, even if the abutment surface on the anchor plate is absolutely planar, it is impossible to obtain a lano-parallel abutment between this surface and the pole surfaces on the arms of the magnet core. This, in turn, means that a considerably smaller contact area between the abutment face of the anchor plate and the pole surfaces on the arms of the magnet core must be accepted and in practice this heretofore has always meant that specialists in the field have not decreased the diameter of the electromagnet below a certain minimum size, simply in order to assure that the con tact area which it was possible to attain in view of the aforementioned difficulties would be sufficient to provide the desired holding power of the electromagnet. Attempts to further treat the pole surfaces after annealing were made, but were not successful to any significant extent in improvingthe planar condition of the pole surfaces, because it was again impossible to prevent oscillation of the arms of the magnet core even if the yoke of the core was fixedly held. For this reason the specialists in the field decided that the diameter of an electromagnetic core member with fixedly mountable yoke should not be decreased below 10 mm, and no such decrease has heretofore become known.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to provide an improvement in the above-identified area of art.

More particularly, it is an object of the present invention to provide a method of making an electromagnetic device wherein the area of contact between the pole surfaces and the abutment surface of the anchor plate can be significantly increased with concomitant possibility of decreasing the dimensions of the magnet core without however decreasing the holding power of the electromagnet.

In pursuance of the above objects, and others which will become apparant hereafter, one feature of our invention resides in making an electromagnetic device having an armature plate, a bifurcated magnet core having a fixedly mounted yoke and a pair of arms cooperating with the armature plate and each being provided with a pole surface facing the same, and a winding applied onto the magnet core. In accordance with the invention the inherent frequency of the fundamental oscillation i.e., the natural frequency of vibration of the magnet core prior to application of the winding is in excess of 25 kilohertz (kHz).

Thus, the invention is based on the finding that if the inherent frequency of the fundamental oscillation caused mechanically as by a guiding or lapping wheel of the magnet core with fixedly mounted yoke and prior to application of the winding, is in excess of 25 kHz, the pole surfaces at the free ends of the arms of the magnet core can be produced with such precision that they will be highly planar and also will both be located in one and the same plane rather than being skew with reference to one another, thereby providing a significantly increased area of contact with the abutment surface of the armature plate and permitting an extreme reduction in the dimensions of the electromag netic device without adversely effecting the holding power thereof.

In accordance with the preferred embodiment the inherent frequency of the fundamental oscillation of the non-wound magnet core is preferably on the order of 30 kHz. The inherent frequency of one of the nonwound arms by itself is higher than 30 kHz, preferably on the order of 34 kHz. The volume of one arm is less than mm, preferably smaller than 60 mm. The spacing between the two arms is smaller than the thickness of the arms and preferably the magnet core is extrusion molded from soft-magnetic material.

By resorting to the present invention the dimensions and the weight of a device according to the invention can be reduced to a fraction of the values which heretofore were considered the lower limits by specialists in the field.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic longitudinal section through a thermo-electric ignition safety device utilizing an electromagnetic device made according to the present invention;

FIG. 2 is a fragmentary section through the device illustrated in FIG. 1, on an enlarged scale;

FIG. 3 is a section taken on the line III III of FIG. 2 with the winding having been omitted; and

FIG. 4 is a section taken on the line IVIV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing the drawing in detail it is emphasized that the method of the present invention has been illustrated on the basis of an ignition safety device which is thermo-electrically operated and which in itself is known. The device comprises a housing whose inner wall is provided with a valve seat 1 1 for a valve member 12 of the safety valve. A gas inlet aperture 13 and a gas outlet aperture 14 are provided on the housing 10.

The valve member 12 is connected with a valve stem or plunger 15 and a helically convoluted spring 16 bears upon the valve member 12 urging the same to valve-closing position, as is evident from FIGS. 1 and 2. The free end of the valve stem 15 extends into a mag netic device which is generally identified with reference numeral 20 and more clearly illustrated in FIGS. 2-4.

As is particularly evident from FIG. 2, the device 20 comprises an armature plate 21 which is connected with the valve stem 15 and an electromagnet 22 which is of substantially U-shaped configuration. This electromagnet, or bifurcated magnet core comprises a plate 221 which constitutes its yoke and which is of circular outline, and two

arms

222 and 223 extending from the plate 221 towards the armature plate 21 and having a substantially kidney-shaped cross-section (compare FIG. 3). A peripherally projecting portion 224 is provided on the plate 221 in the region of the base surface thereof and serves in known manner for connecting the magnetic core 22 to a supporting plate 23 through its after the same is introduced into the housing 10, connected with mass of the housing 10. The other end of the winding is identified with reference numeral 241 and is passed through a bore 225 in the plate 221.

A contact member 25 is provided on the plate 23 in known manner, being insulated electrically with reference to the plate 23 and having a bore 251 through which the end portion 241 of the winding 24 extends, the end portion 241 being connected with the member 25 in electrically conductive manner, for instance by soldering or the like. Also connected in known manner to the contact member 25 is the contact 261 of a thermal element 26 shown in FIG. 1. The magnet core 22 and the anchor plate 21 are in a manner which is also known per se by a protective'cap 27 through and into which the valve stem 15 extends. That side of the cap 27 which faces the closure member 12 of the valve serves at the same time as an abutment for the spring 16.

The structural unit consisting of the magnet insert 20 including valve member 12, anchor plate 21, magnet core 22, supporting plate 23 and contact member 25, is inserted into the housing 10 of the device shown in FIG. 1 and is maintained in position by a screw cap 28 which at the same time serves to secure the contact 261 of the thermal element 26.

A pushbutton 29 is shiftably inserted at that end of the housing 10 which is opposite the magnetic insert 20; the pushbutton 29 is rigidly connected with a plunger 291 and is displaceable in the direction towards the valve member 12 of the valve against the oppositely directed biassing force of a return spring 30.

By displacing the pushbutton 29 with the plunger 291 oppositely the force of the spring 30 the valve member 12 can be lifted off its valve seat 11 whereby at the same time the abutment surface of the anchor plate 21 is placed into abutment with the pole surfaces on the

arms

222 and 223 of the magnet core 22 when the gasoperated device which is provided with the ignition safety device illustrated in FIG. 1, is to be put into operation.

The structural details which have heretofore been de scribed are known from the art. In accordance with the present invention, however, the contact area between the pole surfaces on the

arms

222 and 223 of the magnet core 22 and the abutment surface of the anchor blade 21 is significantly increased by assuring when carrying out the present method that the inherent frequency of the fundamental oscillation of the magnet core 22 when the same does not carry the winding and when the yoke constituted by the plate 221 is fixedly mounted is higher than 25 kHz (kilohertz). When this is the case in accordance with the present invention, it has been found that the pole surfaces at the free ends of the

arms

222 and 223 of the magnet core 22 can be produced in such a manner that they will not only be highly planar but'also will be located in a common plane. This means that the slight curvature of each pole surface which heretofore was unavoidable to all intents and purposes, no longer exists and further that the pole surfaces of the

arms

222 and 223 are no longer skew with reference to one another, or at least that this factor is reduced to an acceptable minimum. As a result, the contact area between the pole surfaces of the

arms

222 and 223 on the magnet core 22 and the abutment surface on the anchor plate 21 is significantly increased.

' of the magnet core 22 be on the order of 30 kHz and that the fundamental frequency of one of the arms without the winding alone be higher than 30 kHz,

preferably on the order of 34 kHz. By resorting to the invention as just outlined, the dimensions of the magnet core 22 may be significantly smaller than it was heretofore thought possible by the experts while the device yet provides adequate holding power.

In the illustrated construction the volume of one of the

arms

222 or 223 of the magnet core 22 is less than 70 mm, preferably less than 60 mm Furthermore, the spacing between the two

arms

222 and 223 is smaller than the thickness of an individual arm.

Asa result, the diameter of the magnet core 22 is on the order of 7 mm and the total axial length of the magnet core 22 only insignificantly exceeds this value. This is by contrast with a diameter of 10 mm which heretofore was thought to be the lowermost practicable limit, and because of this reduction in the dimensions the weight of the magnet core is correspondingly decreased and is only approximately one-quarter of the weight heretofore found in the smallest magnet core having a diameter of 10 mm.

It is evident that a reduction in the dimensions of the magnet core 22 permits a corresponding reduction in the dimensions of the anchor plate 21 and that the other parts of the magnetic insert 20 are correspondingly reduced in size so that in a device according to the present invention the outer diameter of the protective cap 27 needs only be approximately 10 mm whereas heretofore in the customary devices having a magnet core with a diameter of 10 mm the outer diameter of the protective cap was 14 mm.

The contact member 25 and the valve stem 15 may be unchanged as compared to the known constructions, although it is of course possible to accommodate the dimensions of the contact member 25 to differently-dimensioned contact portions of a thermal element without affecting the intent and scope of the present invention in any manner.

Of course, in making the magnet core it is necessary that the magnet core be so produced that it have the desired inherent frequency of its fundamental oscillation, and that thereupon the contact surfaces be produced on the free ends of the

arms

222 and 223 of the magnet core. Because the resulting contact surfaces are highly planar, and because they are located precisely in a common plane, the area of contact between the pole surfaces or contact surfaces on the

arms

222 and 223 and the abutment surface on the anchor plate 21 is significantly higher than heretofore possible so that despite a decrease in the overall area of the pole surfaces and of the abutment surface of the anchor plate 21 the electromagnetic device still has the desired holding power.

While the present invention has been described herein with reference to its use in an ignition safety device on thermo-electric basis particularly as used in gas-operated appliances and devices, it will be appreciated that the invention is not limited thereto and has a much wider field of applicability.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described with reference to making of an electromagnetic device, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. A method of providing on the arms of a bifurcated magnet core whose yoke is to be fixedly mounted, re-

spective pole surfaces which are highly planar and strictly located in a common plane so as to have a maximum area of contact with a planar abutment surface of an armature plate, said method comprising the steps of forming a bifurcated magnet core blank having a yoke and a pair of arms, from a magnet material having a natural frequency of vibration which is in excess of 25 kHz when said yoke is fixedly mounted; forming on the free ends of said arms by a mechanical metal-working operation pole surfaces which are highly planar and strictly located in a common plane, said natural frequency of vibration of said magnet material of said bifurcated magnet core blank preventing vibration of said bifurcated magnet core blank during said mechanical metal working operation so as not to interfere with said mechanical metal working operation and thus permit obtention of highly planar pole surfaces strictly located in a common plane; and mounting said magnet core with the thus obtained highly planar pole surfaces located in a common plane in such a manner that said pole surfaces extend parallel to and facing said planar abutment surface of said armature plate.

2. A method as defined in claim 1, wherein said material has a natural frequency of vibration which is at least substantially equal to 30 kHz when said yoke is fixedly mounted.

3. A method as defined in claim 1, wherein each of said arms has a natural frequency of vibration which is in excess of 30 kHz when said yoke is fixedly mounted.

4. A method as defined in claim 1, wherein each of said arms has a natural frequency of vibration which is substantially equal to 34 kHz.

5. A method as defined in claim 3, wherein the step of forming said blank comprises providing the latter with said arms so dimensioned as to have respective volumes smaller than mm".

6. A method as defined in claim 1, wherein the step of forming said blank comprises press-molding said blank from said magnetic material.

7. A method as defined in claim 1, wherein the step of forming said blank comprises making the blank with said arms spaced from one another by a distance which is smaller than the thickness of the respective arms.

Claims

1. A method of providing on the arms of a bifurcated magnet core whose yoke is to be fixedly mounted, respective pole surfaces which are highly planar and strictly located in a common plane so as to have a maximum area of contact with a planar abutment surface of an armature plate, said method comprising the steps of forming a bifurcated magnet core blank having a yoke and a pair of arms, from a magnet material having a natural frequency of vibration which is in excess of 25 kHz when said yoke is fixedly mounted; forming on the free ends of said arms by a mechanical metal-working operation pole surfaces which are highly planar and strictly located in a common plane, said natural frequency of vibration of said magnet material of said bifurcated magnet core blank preventing vibration of said bifurcated magnet core blank during said mechanical metal working operation so as not to interfere with said mechanical metal working operation and thus permit obtention of highly planar pole surfaces strictly located in a common plane; and mounting said magnet core with the thus obtained highly planar pole surfaces located in a common plane in such a manner that said pole surfaces extend parallel to and facing said planar abutment surface of said armature plate.

5. A method as defined in claim 3, wherein the step of forming said blank comprises providing the latter with said arms so dimensioned as to have respective volumes smaller than 70 mm3.