US3217277A - Variable core tuning inductor - Google Patents

Description

Nov. 9, 1965 G, E. GEE ETAL VARIABLE CORE TUNING INDUCTOR Filed June 18, 1962 INVENTORSI 2f E fj@ (2C zdd/ 30 60 so 12o .x50 fao 220 E56/P555 /Pamr/a/v United States Patent O 3,217,277 VARIABLE CORE TUNING INDUCTOR Gordon E. Gee and Ray B. Schrecongost, Park Ridge, Ill., assignors to Hammond Organ Company, Chicago, Ill., a corporation of Delaware Filed June 18, 1962, Ser. No. 203,271 1 Claim. (Cl. 336-135) This invention relates in general to variable core inductors and more particularly relates to an audio frequency ferrite core inductor which is tuned by rotational movement to provide a comparatively linear change in frequency for use in tuning organ oscillators.

One typical previous practice for deriving an audio frequency tone in an organ oscillator involved the use of an iron core tuning inductor. The inductor comprised a core of stacked laminations which was longitudinally reciprocated to vary the gap in the magnetic circuit and therefore the nominal frequency of the associated oscillator. This arrangement was somewhat diicult to adjust precisely, and in addition, since a number of such inductors were mounted in adjacent positions, considerable magnetic interaction might occur unless special preventive techniques were used. The difficulty in adjusting or tuning an inductor of the type described is that its reactance varies in such a manner that minute changes in the air gap result in great changes in oscillator frequency so that precise tuning is diicult to achieve while any subsequent slight misalignment results in a considerable variance in the outo put frequency from what is desired.

Another type of widely used tuning inductor incorporates a so-called ferrite core and cap, with the core being cup-shaped and having a center post about which the coil is mounted. The center post projects toward the cap which is rotatable. The cap is provided with a D-shaped recess, and the post is provided with a similarly shaped portion so that when the cap is rotated, the area of the gap therebtween is altered to vary the frequency of the associated oscillator. This arrangement, however, is subject to wide fluctuations in the amount of frequency variation per increment of rotation of the cap if a substantial percentage range of tuning is to be provided. Thus if a large over all change in frequency is to be provided, the cap must be rotated over an arc which brings the edge of the cap recess into proximity with an edge on the core, resulting in considerable flux leakage and local saturation so that the frequency may change very abruptly in response to slight movement of the cap.

It is therefore an object of the present invention to provide a variable reluctance inductor which may be rotatably adjusted to provide linear percentage frequency changes in the output of an associated oscillator.

It is another object of the present invention to provide a variable reluctance inductor utilizing a rotatable cap element for adjustment, which may be rotated over a considerable arc to provide a large linear change in frequency while at the same time the sensitivity of the inductor is reduced to the point where incremental movement of the cap does not give rise to a large percentage shift in frequency.

Briefly, the objects of the present invention are accomplished by providing a ferrite cup having a center post or core with the coil carried between the core and cup wall. The core has a predetermined shape formed at one end and cooperates with a rotatable ferrite cap element having another predetermined shape formed therein to provide a substantially linear change in the output frequency of the associated oscillator when the cap is rotated relative to the core. Thus the inductive effect is controlled by rotatably varying the area of close proximity between opposing surfaces of the core and cap in such a manner lee that edge areas are not alone maintained in close coupled relationship.

In the drawings:

FIG. 1 is a cross sectional view of one embodiment of the inductor illustrating the relationship between the tuning cup and cap;

FIG. 2 is a front elevational view of the tuning cup;

FIG. 3 is a front elevational view of the cap;

FIG. 4 illustrates another embodiment of the cap;

FIG. 5 is a graph illustrating percentage frequency shifts for various positions of the cap relative to the cup shown in FIG. l; and

FIG. 6 is a graph illustrating percentage frequency shifts for various positions of the cap shown in FIG. 4.

In FIG. l a variable tuning core inductor incorporating the principles of the invention is illustrated by the reference character 10. It comprises a ferrite cup 12 having a center post or core 14 projecting from a back wall 16, and a pair of spaced apart semicircularly shaped walls 18 separated at their edges by narrow slots 50 which are convenient for passing leads to the coil 22 and coaxial with post 14. A bobbin havin a coil 22 is seated in the cup between the core 14 and the walls 18.

An aperture or passageway 24 is provided in the center post 14 and back wall 16 for the purpose of enabling the generally circular tuning cap 26 having a central aperture 28 to be rotatably mounted on the cup. The cap 26 is normally engaged flush with the walls 18 and is shown separated therefrom in FIG. l primarily for the purpose of clarity. The coil 22 is thus maintained in a substantially completely shielded environment whereby coupling between adjacent inductors is substantially minimized.

It will be noted that the center post 14 does not extend as far from the back wall 16 as do the walls 18 so that there is a slight air gap between the post 14 and cap 26 to thereby minimize the interaction therebetween and reduce the sensitivity of the assembly. In addition, the center post is provided with a recess or cut away portion 30 defined by the peripheral wall 32 of the center post and a circular wall 34 whose radius extends from the axis passing through point 38 offset from the axis of the center post, as seen in FIG. 2.

The cap 26 is also provided with a recess 40. This recess 40 is crescent shaped and formed by a pair of intersecting radial walls 42 and 44, with wall 42 having its axis of rotation coaxial with the aperture 28 and the wall 44 having its axis offset therefrom as shown by point 46 concentric with point 38. Both of these points lie on a plane passing through a diameter of the cap and core.

In assembling the cup 12 and cap 26 for use, the slots on spacing between cup walls 18 and a pair of spaced apart recesses 51 in the edge of cap 26 are used to align the cap so that a line from point 46 bisecting the recess 40 is aligned at 90 to a similar line bisecting recess 30. This position should normally result in the reluctance of the air gap between the cup and cap being such that the inductance is tuned to a desired audio frequency to be supplied in an organ with the frequency being dependent on the parameters of the coil. However, it often happens that the tolerance of the various components has been exceeded or that characteristics may vary. It therefore becomes necessary to adjust the relative position of the cap and cup so that the relationship between the recesses is changed.

FIG. 5 illustrates characteristic percentage shifts in frequency in the approximate ranges of Z50-450, 500- 825, and 1300-1500 cycles when the cap is rotated relative to the core. From to 60 approximately a 5% linear shift in frequency occurs, while from 90 to 120 a similar linear percentage shift in frequency occurs in the other direction. The 90 axis corresponds to the described assembled relationship between recesses 30 and 40 so that rotation of the cap in either direction from the assembled position will provide slight linear changes in frequency thereby permitting facile adjustment.

FIG. 4 illustrates another cap 52. The cap 52 is similar to cap 26 except that a D-shaped recess 54 is provided therein. The straight leg of the D lies adjacent or parallel to the diameter of the cap, and the radial leg of the recess 54 is coaxial with the center of the cap.

The arrangement shown in FIG. 4 is assembled to the cup 12 in the same manner as described for cap 26 with a line bisecting the straight leg of the D lying at 90 to a line bisecting recess 30. This corresponds to the 90 line indicated by the graph in FIG. 6, and it Will be noted that rotation in either direction results in a substantially linear percentage shift in frequency for frequencies between approximately 1400-1800 cycles as shown in FIG. 5, but with a higher slope.

Thus, having described our invention, but believing the same capable of numerous modifications and adaptations, there is appended hereto a claim which is believed to incorporate the inventive concept.

We claim:

A variable inductor comprising a one piece ferrite cup providing an end wall, a cylindrical post extending upwardly from the end wall, side Wall structure extending upwardly from the end Wall concentric with the post to provide an annular space between the post and the side Wall structure, a coil in said annular space surrounding the post, the upper edge of the side wall structure being at and the upper end of the post having a Hat surface generally parallel to the side wall flat surface, a ferrite cap having a Hat lower face engaging substantially the entire flat upper edge of the side wall structure and overlying the post end, the end of the cylindrical post and the juxtaposed central portion of the cap when the cup and cap are together in alignment forming a pair of opposed generally circular regions, the cap within said region having a D shaped recess having a convex edge occupying substantially half the circular region and the post end having a crescent shaped recess having a convex edge at one side, the convex edge of the crescent shaped recess having the same radius of curvature as the post cylindrical surface, and the convex edges of both recesses having a common center of curvature which is substantially at the common axis of the cup and cap, said cap being rotatable relative to said cup to overlap said recesses to a greater 0r lesser extent.

References Cited by the Examiner UNITED STATES PATENTS JOI-IN F. BURNS, Primary Examiner.

Images