U.S. patent number 3,750,069 [Application Number 05/228,086] was granted by the patent office on 1973-07-31 for low reluctance inductor.
This patent grant is currently assigned to Coilcraft, Inc.. Invention is credited to John O. Renskers.
United States Patent |
3,750,069 |
Renskers |
July 31, 1973 |
LOW RELUCTANCE INDUCTOR
Abstract
A closed magnetic circuit, high inductance device characterized
by minimum reluctance and low cost of manufacture.
Inventors: |
Renskers; John O. (Crystal
Lake, IL) |
Assignee: |
Coilcraft, Inc. (Cary,
IL)
|
Family
ID: |
22855727 |
Appl.
No.: |
05/228,086 |
Filed: |
February 22, 1972 |
Current U.S.
Class: |
336/83; 336/192;
336/212 |
Current CPC
Class: |
H01F
17/043 (20130101) |
Current International
Class: |
H01F
17/04 (20060101); H01f 027/24 () |
Field of
Search: |
;336/83,212,192,210,233 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
662,909 |
|
Dec 1951 |
|
GB |
|
897,517 |
|
Mar 1945 |
|
FR |
|
1,564,556 |
|
Jul 1969 |
|
DT |
|
Primary Examiner: Kozma; Thomas J.
Claims
I claim:
1. An inductive device comprising a brittle, sintered cylindrical
core, a winding thereon, and a brittle, sintered shell having side
wall, end walls and a cavity therewithin containing said core and
enclosing said winding, said shell being longitudinally divided on
a plane containing the axis of said core and having arcuate notches
in the free edges of the end walls thereof conforming to and
encompassing the cylindrical ends of said core, said notches being
less than semicircular so that the facing edges of said shell parts
are spaced narrowly apart when said core is contained in said
notches, adhesive means spanning said facing edges of said shell
parts to secure said shell parts together and in direct contact
with said cylindrical ends of said core, said device being
characterized by the absence of adhesive between said core and said
notches.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
As inductors are shrunk to meet the needs of microcircuitry, it is
desirable to make the magnetic circuit of an inductor as perfect as
possible, or in other words, to hold the reluctance to the least
possible figure in order to obtain maximum inductive values. This,
of course, is achieved by a reduction of air gaps to the least
possible extent. As is true with virtually all electronic
components, almost any desired degree of perfection can be attained
if there is no limit on the cost of the component. In consumer
electronics notably, however, cost factors are of prime importance;
the field of circuit element manufacture is highly competitive, as
is the field of the appliances themselves, and volume sales of the
appliances are a direct consequence of low cost in the circuit
elements thereof.
SUMMARY OF THE INVENTION
This invention contemplates an inductor including a core and a
magnetically permeable shell wherein the magnetic circuit achieves
an extremely low reluctance with the least possible air gap at very
little cost.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an inductor incorporating the
present invention;
FIG. 2 is an end elevation of the inductor of FIG. 1;
FIG. 3 is a section taken along the line 3--3 of FIG. 2 looking in
the direction of the arrows;
FIG. 4 is a section taken along the line 4--4 of FIG. 2 looking in
the direction of the arrows;
FIG. 5 is a bottom plan view of the inductor of FIG. 1;
FIG. 6 is a section taken along the line 6--6 of FIG. 4 looking in
the direction of the arrows;
FIG. 7 is a perspective of half of the inductor shell of FIG. 1
divided in an alternative fashion; and
FIG. 8 is a perspective similar to FIG. 7 showing a shell half
formed for a different orientation of the center core.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is directed to a core and shell structure for
an induction device. The material of the structure is preferably a
high resistivity, high permeability material such as a ferrite or
powdered iron, although the shell may be ceramic where low
inductive values are wanted. The induction device 10 includes a
cylindrical core 12 and a shell 14 engaging the ends 16 of the
cylindrical core and providing a cylindrical cavity 18 about the
interior portion 20 of the cylindrical core to accommodate an
induction or transformer winding 22 on the central portion 20 of
the core 12. The shell is divided into two halves substantially on
a plane 24 extending through the axis of the core 12. In other
words, the shell may be regarded as being longitudinally split with
reference to the core 12. The division 24 separates the shell into
a top half 26 and a bottom half 28.
The top half 26 is a plain block with a semicylindrical cavity 30
formed in the underside thereof leaving planar ends 32 having
notches 34 in the free, bottom edges thereof slightly less than
semicircular conforming in radius to the cylindrical core 12.
The bottom half 28 likewise possesses a semicylindrical cavity 36
in the top surface thereof leaving planar ends 38 with, again,
slightly less than semicircular notches 40 formed in the upper edge
thereof to confront the notches 34 in the top half, and, with the
notches 34, to embrace the ends 16 of the cylindrical core 12.
The bottom half 28 has downwardly protruding integral feet 42 at
the corners of the bottom surface 44 thereof. The feet 42 have
transverse grooves 46 therein extending across the feet to the
outside edge of the bottom half 28. Slots 48 are formed in the
bottom of the semicylindrical cavity 36 at each end thereof to
extend through the bottom shell and open between the end pairs of
feet 42.
The bottoms of the feet 42 may be coated with a conductive solder
or conductive cement for attachment to a hybrid microcircuit "thick
film" ceramic plate.
This invention will be best appreciated from some illustrative
dimensions. A commercial model has been disigned wherein the shell
has a length 0.187 inches, a width of 0.125 inches and an overall
height of about 0.125 inches. The core designed to be accommodated
in the notches 34 and 40 is equal in overall length to the shell,
that is 0.187 inches, and has a diameter of 0.032 inches. The
thickness of the end walls of the shell halves is 0.035 inches.
The inductive device illustrated will be formed in the following
fashion. The shell halves 10 and 28 will be molded and sintered or
fired with the notches formed. The core pins 12 will be molded and
sintered and trued to the formed notch diameter by centerless
grinding, probably on a batch basis to conform to the lots of shell
halves. Since the core extends to the external surface of the shell
and is cylindrical and of uniform diameter over its length, it will
be appreciated that its length is not critical as long as the
necessary minimum is provided.
The notches and shell half edges are interrelated such that, in the
dimensionally specified embodiment described, the center of the
notch arc is 0.001 of an inch outside the line of the facing edge
such that if the two halves conform exactly to specification and
are assembled on opposite sides of a core 12, there will be a 0.002
separation between the shell halves. The tolerance assigned to the
outward displacement of the center of the arc in the above
embodiment actually is .+-. 0.001 inches. Thus, combined notches
describing a complete circle is a limiting case, and in practice,
there is always a positive gap existing between the shell halves
when closed on a core.
In view of the smallness of the unit, the coil or transformer will
probably be wound directly upon the core 12 although, of course,
there is always the possibility that the coil may be wound on a
tubular form to encompass the core. In view of the likelihood of
direct winding, the extension of the core to the exterior of the
shell provides some elongation of the core for greater ease of
handling.
The core with the coil on it will be situated in the arcuate
notches 40 of the bottom half and the leads of the winding extended
through the slots 48 and bent over to lodge within the grooves 46
in the feet 42 of the bottom half and soldered therewithin. The
leads thus become conductively connected to the conductive material
deposited on the bottom of the feet but are recessed into the
surface of the feet allowing the feet to make broad contact with
the appropriate pads on the thick film for connection thereto.
A polymerizing cement such as epoxy or polyester will be applied to
the facing edges of the shell halves to span the separation imposed
by the core. The two shell halves are then pressed together to
obtain a pressure bearing of the arcuate notches against the core
12 and the adhesive cured. The adhesive is preferably not applied
in the area of the notches to avoid an adhesive film which
necessarily has some thickness and thus enlarges the air gap to
that extent.
An optional shell structure or method of making the shell is
illustrated in FIG. 7. Here, the shell is vertically instead of
horizontally divided. Thus, two identical shell halves 50 are
employed to make up the whole shell 14. In this situation, the line
of division separates the slots 48 into open-ended notches 52.
FIG. 8 shows a shell structure designed to have the center core
thereof extending perpendicularly to the mounting structure. In
this situation, the shell halves 56 have the feet 58 formed on the
bottom end walls 60 and the divided slots for the passage of coil
leads to the feet again present as notches 62 in that same bottom
end wall.
Although the shell halves of FIGS. 7 and 8 might appear to be
adaptable to a simple compression molding, in actuality, the feet
present difficulties. Accordingly, the feet are best formed by
molding ribs to extend to the parting line of the shell halves,
firing, and grinding off the inner ends of the ribs to leave the
outer ends to constitute the feet. The grinding operation, while an
additional step in manufacture, is simple and non-precise and,
therefore, inexpensive.
The separation of the slots into the facing notches 52 or 62 may
readily facilitate assembly of the complete inductor. Laying the
leads of the winding of the inductor in open notches may in many
cases be a simpler and quicker procedure than threading them
through the slots 48 of the principal described form, and thus
offset the added expense of the shell halves incurred from the
grinding operation, above.
Some of the advantages of this invention have been set forth above.
Others going directly to the matter of improved permeability of the
whole magnetic circuit or minimal reluctance are first that the
division of the shell into the two halves is axial or longitudinal
with respect to the core rather than transverse to the axis
thereof. Thus, the fact of the division of the shell into halves
imposes no air gap reluctance in itself to the development of flux
therewithin. The division is parallel to the lines of force.
Second, the formation of the arcuate notches to less than a
semicircle provides for direct and positive contact between the
shell halves and the cores to reduce the air gap to an absolute
minimum. It will be appreciated that this device as described
interposes not even an adhesive film therebetween. The curing of
the adhesive while the shell halves are held under pressure results
in an effective frictional binding of the ends of the core between
the shell halves.
Third, the containment of the ends of the cylindrical core between
the notches in the shell halves results in a maximum of confronting
surfaces of area of gap, so minimizing reluctance.
These advantages of this invention will be best understood by
consideration of alternative forms presently employed. One of these
is the center post type pot core closed either by a plate or by a
second opposing similar pot core. This configuration has the
advantage of only two air gaps in the magnetic circuit, as does the
present invention. The confronting area of the center post air gap
in either case is .pi. r.sup.2 whereas with the contained core end
of the present invention the area is .pi. dh. In order to obtain
the same gap area from the center post pot core configuration as is
present in the specified inductor above, the center post would have
to be four times the diameter of the center core of the present
invention, or be equal in diameter to the given shell itself.
Other problems pertain. The center post pot core requires jig
grinding to obtain true aligned surfaces which is expensive.
Adhesive or dirt enlarges the width of the gap. Avoidance of
adhesive requires an outside clamp, adding substantially to the
cost.
A second existant option is a pair of facing cup cores with holes
in their bottoms and a cylindrical center core contained in the
holes to give the .pi. dh gap area. This structure, however,
imposes first, a third air gap. Second, there is the conflict of
tolerances. The minimum diameter of the holes must be at least
equal to the maximum diameter of the center core, so the normal
assembly will include a gap of positive width between the core and
holes.
* * * * *