US2799822A - Improved controllable inductance apparatus - Google Patents

Description

July 16, 1957 G. H. DEWITZ I 2,799,822

IMPROVED CONTROLLABLEZ INDUCTANCE APPARATUS Filed July 22, 1952 FIG. 2.

SOURCE OF CONTROLLED CQNTROL CIRCUI T5 p vr INVENTOR GER/ HEB H. QEW/TZ 4:475, fiowlr ir/$14. v ATTORNEW IMPROVED CONTROLLABLE INDUCTANCE APPARATUS Gerhard H. Dewitz, Westport, Conn, assignor to C. G. S. Laboratories, lnc., Stamford, Conn., a corporation of Connecticut Application July 22, 1952, Serial No. 300,196

8 Claims. (Cl. 32389) This invention is in the field of high frequency saturable core magnetic apparatus in which the inductance of a signal winding is controlled electrically by varying the magnitude of a current sent through a control windmg.

In such controllable inductors, sometimes called saturable reactors, the control current acts to regulate the degree of the magnetic saturation of the core and thereby to control the effective inductance of one or more other signal windings wound on the same core. Such a saturable core device using ferromagnetic ceramic core material is described in my copending application, Serial No. 213,548, filed March 2, 1951. That device is provided with a ring core having a rectangular slot or opening through the rim. The controlled winding, called the signal winding, is wound in two portions through this opening and produces flux lines which close around the opening.

According to the present invention the cores are provided with gradually changing or varying cross sectional area in the region of thi signal winding so as to provide control of the degree of saturation of various portions of the core and to regulate the rate at which this saturation occurs. By this means substantially linear control characteristics can be obtained over any desired portion of the operating range and other special characteristics are readily obtained, which have particular application in computing devices.

The present invention will be described as embodied in controllable inductors having ferromagnetic ceramic ring cores. Several embodiments of the invention have been illustrated and described in order to set forth fully the principles of the invention and so that it can be applied readily in each condition of use and to make apparent the various aspects, advantages and objects of the invention.

Figure 1 of the accompanying drawings shows a controllable inductor embodying the present invention;

Figure 2 is a plan view ofthe core of the inductor of Figure 1;

Figure 3 is an enlarged partial elevational view of the core shown in Figure 2.

Other arrangements of the invention are illustrated in Figures 4 to in which the windings have been omitted from the cores in order to illustrate more clearly the differences therebetween.

Figures 4 and 5, respectively, are perspective and front views of inductors in which the cross sectional area of the entire core progressively changes throughout its circumference;

Figures 6 and 7 are perspective and front views, respectively, of a ring core, generally indicated at 14 and having an oval hole therein;

Figure 8 is a perspective view of an inductor having a circular hole in the core through which the signal winding extends;

Figure 9 shows a similar core having a diamond-shaped opening; and

Figure 10 shows a core having a rectangular slot in which the radial thickness of the core decreases gradually from each end of the slot to a minimum at the center of the slot.

The inductor, generally indicated at 2 in Figure 1, includes a ring core 4 of ferromagnetic ceramic material such as is disclosed by Snoeck in U. S. Patents 2,452,529, 2,452,530 and 2,452,531. Other ferromagnetic saturable materials such as Mu-metal, Permalloy, soft iron and the like may be used. However, the ceramic materials offer marked advantages because of their higher Qs, their high permeability and wide operating range, etc. A slot 6 is provided in the core for a purpose to be made clear presently.

The ring core 2 has a first portion of substantially uniform cross sectional area, but between the broken lines 8 and 10 (Figure 3) the cross sectional area of the core gradually decreases and reaches a minimum substantially at the center of the slot 6. This reduction in cross section is obtained by arcuate recesses, generally indicated at 12 and 14, on the top and bottom of the core.

The core 2 carries around its uniform portion a control winding 16, usually having a relatively large number of turns. This winding 16 is connected to a suitable source of control current indicated diagrammatically at 18, and the magnetic saturation of the entire core is controlled by the current flowing through this winding in a manner well known in the art of saturable core magnetic apparatus. This control current produces a flux flowing in a closed loop through the core 10, for instance, this saturating flux may flow in the direction represented by the arrows 20 in Figure 2.

In order to cancel out any undesired magnetic coupling between the control winding 16 and the signal winding 22, the signal winding 22 is formed in two equal sections 22-1 and 222. These winding portions are wound through the slot 6 and around opposite rim portions of the core 4. The two sections 22-1 and 22-2 are connected in series in such manner that flux lines formed by current flowing through the winding 22 close around the slot 6.

Thus, the slot 6 divides the core 4 into two spaced branches and one of the sections of signal winding 22 is wound around each of these branches. The magnetic flux created by the signal winding 22 extends in one or the other direction in a closed loop around the slot 6. All of the saturating flux 20 in the core 4 produced by the control winding 16 extends through the restricted cross sectional areas of the two spaced branches of the core adjacent the slot 6.

As the control current through the control winding 16 varies, the magnetic saturation of the core material adjacent the slot 6 varies and thus varies the incremental permeability (or inductance) of the signal winding 22, and this inductance acts to regulate the controlled circuits, diagrammatically shown at 26. If the cross sectional area of the core 4 were constant throughout the flux path associated with the winding 22, all of the core material in this path would be saturated to the same extent at any given instant of time. In the constructions used heretofore the two core branches on either side of the slot operated at all times on corresponding portions of their saturation curves and reached saturation at the same time throughout their entire lengths. With the arrangement shown in Figures 1, 2 and 3, the core portion with the smallest cross-sectional area saturates first and then succeeding portions of the core with larger cross sectional areas are saturated as the control current increases.

The effect of the saturation can be explained best by considering the action of individual portions of the core 4 as the control current increases from zero to a maximum value. The divided signal winding 22 is assumed to be carrying an alternating signal current, at least several times the maximum frequency of the highest frequency components of the control current. The control current may be either alternating or unidirectional as described in the afore-mentioned copending application.

When the control current is zero, there is relatively low reluctance in t.e magnetic path around the slot 6, and consequently the signal winding has maximum effective inductance.

As the control current is increased, the saturation of the core branches on each side of the" slot 6 increases thus causing an increased reluctance to the flow of the signal flux around the slot 6 and hence progressively reducing the inductance in the signal current circuit 26. As the control current is still further increased, the portions of the core 4 having the least cross-sectional area, indicated at 28 in Figure 3, are the first to reach saturation, and the magnetic permeability at these points is reduced substantially to unity or that of air. Initially, the region of this full saturation is confined to a relatively small length of the core. At increasing distances in either direction from the saturated portions of the core, the cross-sectional area of the core increases and the extent of magnetic saturation accordingly decreases. The saturated portions of the core form virtual or imaginary air gaps whose widths increase as the control current is increased.

Because of the gradual change in cross-sectional area of the core adjacent the slot 6, and the consequent spread of the operation throughout the saturation curve, an effect substantially difierent in nature is produced from that which is attained With uniform core dimensions. Thus, if the core has uniform outer dimensions and arectangular slot, all of the core material on each side of the slot operates at any given instant at the same point on the saturation curve of the core material and the entire length of this material reaches saturation at'the same instant, at which time substantially all control over the inductance of the signal winding is lost. Thus, with such a construction no virtual air gap is formed during the time in which any substantial control over the inductance of the signal winding is being exercised.

In addition, this gradual transition in the magnetic saturation of the core branches adjacent the slot 6 along their lengths appears to have a beneficial effect on the hysteresis of the controlled inductance so that it more nearly follows the same path during increase and decrease of the control flux 20. One possible explanation may be as follows: During the time the control current is above a predetermined minimum, the magnetic conditions within the branches adjacent the slot 6 range through the full gamut from substantially full saturation to slight saturation. As the control flux varies above this minimum, there is less efiective change in this range of magnetic conditions within the branches, for any further increase in the control flux increases the effective lengths of the virtual air gaps and substantially the same degree of saturation exists at points in the core which are at a slightly increased distance from the centers 28 of the effective air gaps.

The form of the arcuate recesses 10 and 12 and the size and shape of the slot 6 control the relationship between the minimum control current necessary to cause the initial formation of the effective air gaps and the rate at which these gaps become wider as a function of the control current. By suitably shaping the core portions or branches having reduced crosssectional areas on either side of the slot 6, the inductance of the signal winding 22 can be made a wide variety of desired functions of the control current, and linear operation over relatively wide ranges can be attained readily.

The arrangement described above has particular advantage when the core is formed of ferromagnetic ceramic material. This is because the losses in the core material remain low or actually decrease with increased magnetic saturation, and the reduced core portions can therefore be operated efliciently even though their average magnetic saturation is relatively high.

Thus, by forming the core 4 as described in order to modify the degree of saturation occurring in various portions hereof associated with the signal winding 22, I not only improve the control action characteristics by regulating the relationship between the inductance of the signal winding and apparently reducing the hysteresis effect in the controlled inductance, but also in some instances may actually increase the efficiency by reducing the average losses.

In Figure 4 is shown another embodiment of the present invention, in which the core 30 is tapered or provided with a changing cross-sectional area throughout its total length so that the portion 32 adapted to receive a .control winding similar to the winding 16 shown in Figure 1, has a relatively large cross-sectional area. An elongated slot 34 is proivded in the signal winding portion of the core 36, which has a relatively small crosssectional area. The signal winding is wound through this slot 34 around the two rim portions or core branches 36 formed thereby in a manner similar to the winding 22 shown in Figure 1 so that a current flowing therethrough produces a flux which closes in a loop around the slot 34.

The operation of this core 30 is different from that of the core 4. For example, as the bias or control flux flowing around the ring core 30 is increased, saturation of the branches 36 is more nearly uniform than the corresponding saturation of the branches of the core 4 during similar operation, because of the more gradual change in cross section thereof.

As the control flux is further increased the branches 36 begin to reach full saturation and virtual air gaps are produced in the central portions thereof. Because of the gradual rate of change of the cross sectional area of the branches 36, the effective air gaps produced therein are varied in width at a proportionately faster rate for any predetermined change in control flux. Thus, the form of the core 30 provides an increased sensitivity of the controlled inductance to changes in the control flux 38. The same maximum control flux produces a much wider effective virtual air gap and consequently .a lower value of controlledinductance than in the case of the core 4.

In Figures 6 and 7 are shown a ring core 40 with an elliptical transverse opening 42 formed therein. As seen in Figure 7, .the opening 42 divides the core 40 into two branches. 44 having varying cross sectional area and adapted to receive the signal winding. The operational characteristics of the core 40 are somewhat similar to the core 4. However, while the variation of the cross sectional area of rim portions 44 is gradual .at regions near the center thereof, the rate of variation of this cross section becomes increasingly greater toward the extreme ends of the hole 42. I have found that the core form shown in Figures 6 and 7 produces an inductance in the signal winding which is substantially a linear function of the magnitude of the control current throughout a wide range of operation.

Figure 8 shows a ring core 46 with a transverse circular opening 48 therein forming a pair of rim portions 50 adapted to receive a control winding similar to the winding 22 shown in Figure l. The operation of' the core 46 is somewhat similar to that of core 40, but because of the relative short length of the branches S0 and the greater average rate of change in the cross sectional area thereof, a smaller change in control current produces a greater proportionate change in controlled inductance. Moreover, the average reluctance of the magnetic control path around the ring 46 is reduced so that a relatively smaller minimum control current produces full saturation of the central portions of the branches 50. Thus, the effective virtual air gaps are produced at a minimum value of control current, resulting in the advantageous control characteristics of this effect, as discussed in connection with Figure 3. The shape of the inductance control curve is regulated even at relatively low values of the control current.

In Figure 9 is shown a ring core 52 having a diamondshaped opening 54 therein forming a pair of core branches 56 adapted to receive a signal winding. The larger dimension of the hole 54 is parallel with the branches 56. These branches or rim portions 56 have a uniformly changing cross sectional area.

In Figure 10, the ring core 58 hasa slot 60 therein forming the two branch magnetic paths 62. A curved recess 64- in the outside surface of the core reduces the cross sectional area of the central segments of the branches 62. An advantage of this form of the core 58 is that the path length for the control flux which flows in the core 58 is a minimum and hence offers a low reluctance to the control flux. Also, this minimum reluctance is obtained in spite of the presence of the large central opening 68 which allows the control winding to have many turns so that a small control current is required for operation.

It is to be understood that the principles set forth above in connection with single ring cores apply equally well to multiple ring core structures using two or more cores.

From the above description it will be apparent that the saturable core magnetic units embodying the present invention are well adapted to attain the ends and objects set forth herein and that the various embodiments of the invention shown herein can be modified so as to produce operating characteristics best suited to the needs of each particualr use.

I claim:

l. A controllable inductance including a closed core of ferromagnetic material having a first closed flux path therein and having a transverse opening therein extending transversely across said first flux path and being elongated in the direction of said first flux path and forming first and second parallel magnetic branches extending along opposite sides of said elongated opening, a control winding around a portion of said core and around a portion of said first flux path for regulating the degree of magnetic saturation of the parallel magnetic branches adjacent said opening, and a signal winding having first and second portions connected in series and both being wound through said opening and respectively around said parallel magnetic branches of said core and leads from the ends thereof connectible to external circuits, the total cross-sectional area of said core decreasing gradually in the vicinity of said elongated opening and having its minimum crosssectional area adjacent the central portions of said parallel magnetic branches, said parallel magnetic branches having a larger cross sectional area at their ends adjacent opposite ends of said transverse opening than in their central portions, whereby the degree of magnetic saturation of said branches progresses from a minimum near the ends thereof to a maximum near their central portions.

2. Improved controllable inductance apparatus including a closed ferromagnetic ring core having a transverse opening therein defining a pair of adjacent branch portions passing on opposite sides of said opening, said opening being elongated in the direction of the circumference of said closed core and extending radially through the rim of said ring core, a control winding carried by said core for regulating the degree of magnetic saturation of said branch portions, and a signal winding divided into two equal portions connected in series, each one of said signal winding portions being wound around one of said adjacent branch portions and both said signal winding portions extending through said elongated opening, said branch portions completing a closed magnetic path around said elongated opening, the reluctance of said closed path being a function of the saturation of said branch portions, said branch portions having a smoothly decreasing crosssectional area from their ends with maximum cross sectional area being at either end of said elongated opening and with minimum area in their central portions.

3. Improved controllable inductance apparatus including a closed ferromagnetic core having a first fiux path therein and an elliptical opening therein with its elongated dimension parallel to the direction of said first flux path and defining a pair of branch portions passing along opposite sides of said elliptical opening, a first winding carried by said core and spaced from said opening, said first winding encircling said first flux path, said elliptical opening causing said branch portions to have a progressively decreasing cross-sectional area from their ends toward their central portions, the minimum cross-sectional area of said branch portions being near the center portion of said elliptical opening and a second winding having two equal winding portions connected in series with each other and each extending through said opening and around one of said core branches and being connectible to external circuits.

4. A ferromagnetic ceramic ring core defining a large central opening and having a curved body portion curved around said large central opening and a pair of spaced branch portions between the ends of said body portion, said branch portions passing along opposite sides of and defining an elongated transverse opening extending through said ring core and connecting with said central opening, said opening being elongated in a direction parallel with said branch portions, a controlwinding on said body portion and arranged to carry a control current for regulating the degree of magnetic saturation of said branch portions, said branch portions completing a closed magnetic path around said transverse opening whose reluctance is controlled by the current flowing in said control winding, a central portion in each of said branch portions, said branch portions having a progressively reduced cross-sectional area from the ends of said body portion toward said central portions, whereby the relative magnetic saturation of the central portions of said branches caused by flux flowing through said body portion exceeds the saturation of the ends of said branches, and a signal winding divided into two equal parts connected in series and both extending through said elongated opening, one of said equal winding parts being wound around one of said branch portions and the other being wound around the other of said branch portions, said signal winding having terminals connectible to external circuits.

5. A controllable inductance comprising magnetically permeable core apparatus substantially completely defining a closed magnetic flux path and including magnetically permeable core means defining an elongated opening which is elongated in a direction substantially parallel with said magnetic flux path and which converges toward pointed ends, a pair of generally parallel branch portions extending along opposite sides of said elongated opening, said opening being elongated in a direction substantially parallel with the longitudinal axes of said branch portions, said branch portions having central parts of smaller cross sectional area than their ends, the ends of each branch portion having progressively larger cross sectional area in a direction away from their central parts, the central region of said opening being wider than said pointed ends, a signal winding having first and second portions connected in series and wound through said opening and respectively around said opposite branch portions with leads therefrom connectible to external circuits, and magnetic control means for controlling the magnetic saturation of said parallel branches.

6. A controllable inductance as claimed in claim 5 and wherein the pointed ends of said elongated opening are triangular in appearance.

7. A controllable inductance comprising magnetically permeable core apparatus substantially completely defining a closed magnetic flux path and including magnetically permeable core means having a transverse opening therein extending transverse to said flux path and elongated in the direction of said flux path and a pair of parallel branch portions passing on opposite sides of said opening and forming, said opening being elongated in the direction of the longitudinal axes of said branch portions, said branch portions completing a magnetic path around said transverse opening whose reluctance is controlled by the magnetic saturation of said branch portions, said branch portions having reduced cross sectional areas near their central regions and tapering toward larger cross sectional areas at each end, a signal winding having first and second portions connected in series and wound through said elongated opening and respectively around said branch portions and leads therefrom connectible to external circuits, and magnetic control means for controlling the magnetic saturation of said parallel branches.

8. A controllable inductance comprising magnetically permeable core apparatus substantially completely defining a closed flux path and including core means defining a transverse opening therein extending transverse to said flux path and being elongated in the direction of said flux path and having a pair of parallel branch portions of magnetically permeable material passing along opposite sides of said elongated opening an bo h ng lud a flux path, said branch portions having a smaller cross sectional area near their central regions than at either end, theends of each branch portion being tapered to increase in crosspsectional area toward the ends, the outer surfaces of each of said branch portions having recesses therein with the deepest areas of the recesses lying adjacent to the central regions of said branches a signal winding having first and second portions connected in series and wound through said opening and respectively around said opposite branch portions with leads therefrom connectible to external circuits, and magnetic control means for controlling the magnetic saturation of said parallel branches.

References Cited in the fileof this patent UNITED STATES PATENTS 1,722,167 Wilson July 23, 1929 2,241,912 Kersten et a1. May 13, 1941 2,284,406 DEntremont May 26, 1942 2,332,879 Weis Oct. 26, 19.43 2,452,529 Snoek Oct. 26, 1948 2,755,446 Gabor July 17, I956

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