US2582291A - Transformer construction - Google Patents

Description

Jan. 15, 1952 J. G. SOLA 2,582,291

TRANSFORMER CONSTRUCTION Filed Aug. 5, 1948 2 SHEETS-SHEET l IN V EN TOR.

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Jan. 15, 1952 J. G. SOLA 2,582,291

TRANSFORMER CONSTRUCTION File'd Aug. -5, 1948 2 SHEETSSHEET 2 INVENTOR. \27 Joseph 6. 801a Gif 5 Patented Jan. 15,1952

UNITED srA'ras PATENT OFFICE TRANSFORMER CONSTRUCTION Joseph G. Sola, River Forest, Ill. Application August 5, 1948, Serial No. 42,646 a Claims. (01. 175-356) This invention relates to transformers of the pressed-in core type, more particularly to such transformer constructions and methods for reducing noise or hum therein.

Transformers for supplying voltage to lamps of the discharge variety such as fluorescent lamps, for example, must be as free from hum as possible, particularly in areas where the the noise level is low, as in business ofilces.

Transformers of the pressed-in core type are disclosed in two forms respectively in Patent No.

2,346,621, to Joseph G. 8012., for Alternating Current Supply System, and the application Ser. No. 15,701 of Joseph G. Sola, for Transformer, and the core of each transformer includes an outer leg or shell and an inner leg pressed into the shell. These transformers have been subject to a certain amount of hum. In transformers of the character disclosed in the aforementioned application, where the stray field has been largely eliminated and thus the noise consequent thereto, some slight hum has remained. It has been determined that this residual hum is due largely to the fact that all parts of the core did not lie in the same plane. Due to magneto-strictive effects, the interaction of the magnetic fields in the different parts of the core or for other reasons, the core parts tend to vibrate relative to each other which causes humming.

Accordingly, it is a further object of the invention to provide an improved transformer having a, pressed-in type 'core wherein the relative vibration between the various parts of the core is eliminated.

While in the patent and application referred to the transformers disclosed have been shown with fluorescent lamps and operate upon principles utilizing resonant circuits, and the present invention relates to transformers of this character, it has application as well to pressed-in core type transformers generally.

In carrying out the invention in one form, a transformer is provided having a core formed of two parts. The outer part is made of laminations, whose periphery is continuous, stacked together. The inner part is made of laminations stacked together and having a length somewhat less than the distance between the surfaces of the outer part which cooperate with the ends of the inner part. The metallic contact for completing the magnetic circuit is made through the sides of the inner part rather than through the ends.

For a more complete understanding of the invention, reference should be had to the accompanying drawings, in which:

Figure 1 is a top view of one form of well-known transformer not embodying the invention;

Fig. 2 is a sectional view taken substantially along lines 22 of Fig. 1;

Fig. 3 is a top view of a transformer embodying the invention;

Fig. 4 is a sectional view along lines 44 of Fig. 3;

Fig. 5 is an end view of the in Figs. 3 and 4; and

Fig. 6 is a top view of a transformer embodying a modified form of the invention.

Referring to the drawings, there is shown in Figs. 1 and 2 a transformer including a core it having a primary coil II and two secondary coils l2 and I3 thereon, substantially as shown in the application previously referred to.

Core It may comprise a series of stacked onepiece or continuous laminations forming an outer leg or shell l4 and a series of stacked I-shaped laminations forming an inner leg II. In order to have the necessary metal-to-metal contact for a good magnetic circuit, the junctions i6 and I1 between the inner leg and the outer leg must be close. One manner of forming the laminations of outer shell I (outer laminations) is to punch them from a stock of metal of suitable thickness and other dimensions. In this process the windows for the various coils are punched out and in the same or a separate step the central 1- shaped laminations are punched out along lines It and II. This latter step is a simple punching step with no attempt being made to change the length of the I-shaped laminations.

The core is completed by assembling the requisite stack of laminations for outer shell H, by assembling for inner leg IS a stack of I-shaped laminations previously punched out in the forming of laminations for outer shell I, and pressing the inner leg into the outer shell along the same lines it and I! at which the I-shaped laminations were punched. Before pressing inner leg II in, the coils are placed thereon. The I-shaped lamination punched from a particular outer lamination does not necessarily lie within the lamination from which it was punched, inasmuch as in the assembling process the various laminations become shuilled.

Even though the I-shaped laminations forming inner leg ii are punched from the outer laminations forming outer shell H to which the inner leg is finally assembled, the inner leg does not lie in the same plane as the outer shell. If an I- shaped lamination is punched from an outer lamination (say along lines l6, l1) and the I- shaped lamination is placed within the outer lamination at the junctions It and I1, the I- shaped lamination does not lie flat but has a bow in it. Apparently during the punching process the I-shaped lamination becomes somewhat longer than the space from which it is punched. This may be due to a slight burr at the end of the lamination, or possibly the edge along which the shearing took place is not perfectly perpentaken substantially transformer shown dicular to the main surface of the lamination, or it may be that some slight elongation has taken place. In any event, when a series of the I- shaped laminations formed as described are assembled to form inner leg l5 and this leg is then pressed into the outer shell l4 formed of laminations as described, a very tight connection is formed at junctions l6 and I1 and inner leg I5 bows outwardly a substantial distance as may be seen best in Fig. 2. In this figure broken line H! indicates the plane of one side of outer shell M, and line |9 indicates the edge of inner leg I5 when the transformer is formed in the manner described.

The transformer as described has been found to have a certain amount of hum, apparently due to the vibration of inner leg l5 relative to the outer shell l4.

Changes in linear dimensions occur when magnetic fields are applied due to magnetostrictive effects. Thus, outer shell l4 and inner leg l5 may contract and expand along their lengths as the flux therethrough varies, thereby causing the inner leg to bow outwardly still further from the position shown in Fig. 2 or possibly allowing it to spring to the straight-line position and even outwardly on the side opposite to lines I8 and |9 depending upon the strengths and phases of the fluxes within the various parts. It may also be that inner leg |5 instead of bowing or vibrating from one side to the other as a whole may vibrate in form having nodes intermediate the ends thereof. Irrespective of how inner leg |5 vibrates or the magnetic effects giving rise thereto, it has been found that the vibration and the incident noise may be prevented by constructing the transformer in a manner illustrated in Figs. 3, 4 and 5, which embody the invention in one form.

Referring to Figs. 3, 4 and 5, there is shown a transformer generally similar to that shown in Figs. 1 and 2 in that the core embodies an outer shell 2| and an inner leg 22 pressed into slots therewithin, coils being assembled thereon as shown. This form of core is constructed of laminations forming outer shell 2| (outer laminations) and I-shaped laminations forming inner leg 22 wherein the I-shaped laminations are punched from corresponding outer laminations. In the punching process the windows for the coils are punched out, and as part of the same step or as a separate step, the I-shaped laminations are punched out along lines 23, 25, 21 and 28 at one end and corresponding lines at the other. The I-shaped laminations are then assembled to form inner leg 22 which is pressed into a corresponding stack of laminations forming outer leg 2| along the lines where punching took place. The I-shaped laminations are punched, however, so that the length between the ends 23 and 24 of inner leg 22 is less than the distance between adjoining edges 25 and 26 of the outer punchings. The I-shaped lamination is sufficiently shorter so that a small air gap may exist between edges 23 and 25, and 24 and 26. This ap need not be large but only sufficient so that when inner leg 22 is pushed into the slots in outer shell 2|, the ends 23 and 24 d not push outwardly against surfaces 25 and 26. Consequently, there is no tendency for inner leg 22 to bow outwardly. Rather, inner leg 22 lies perfectly straight and within the planes defining the sides of outer shell 2| substantially as shown in Fig. 4.

The necessary metal-to-metal contact for producing a good magnetic circuit is produced by having contact alOIlg the lines or sides 21 and 28 at each end of inner leg 22. During the punching operation when the metal is sheared along lines 21 and 28, the width of the I-shaped punchings comes out such that when reassembled to the outer shell metal-to-metal contact is formed along the same surfaces 21 and 28. This is due to phenomena already alluded to in that a burr may form along edges 21 and 28 or possibly some slight elongation occurs therebetween. In any event, when laminations are punched and assembled as described, good metal-to-metal contact is formed along edges 21 and 28, thereby forming the requisite good magnetic circuit.

In the form of transformer shown, the legs of the outer shell may form the return path for flux generated in the inner leg, and thus sufficient area of contact must be provided so as not to im pair the magnetic circuit. Accordingly, the width of the legs of the outer laminations is sufficiently large so that the length of contact between the inner leg and outer shell along both lines 21 and 28 is equal to the width of the inner leg. In the construction shown this necessitates that the legs of the outer shell be somewhat wider than the inner leg in order to leave the strips of metal 29 and 3| for maintaining the continuous periphery of the outer laminations.

The transformer shown being of the character described in the application referred to, increas ing the width of the outer punchings, as shown in Fig. 3, is advantageous in that certain stray field effects are eliminated. In transformers where additional metal in the outer leg is not desired, other constructions of course may be used and still have the present invention embodied therein. Thus, for example, a construction of the form shown in Fig. 6 may be used. In this form of the invention the side legs of the outer laminations have the same total transverse dimension as the inner leg punchings, but the width of the side legs is less than that shown in Fig. 3. Otherwise, the modifications of Figs. 3 and 6 are the same. The construction of the ends in Fig. 6 is such that strips of metal 29 and 3| remain to form the necessary metallic support so that metal-to-metal contact is obtained along edges 21 and 28.

While particular embodiments of the invention have been shown, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of the invention.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. An electromagnetic device core having an outer shell comprising a stack of continuous punchings, and an inner leg comprising a stack of punchings having at each end thereof longitudinal surfaces and transverse surfaces, said shell stack having end members and side members, said end members including slots having longitudinal surfaces and transverse surfaces, each end of said inner leg being within a respective one of said slots with corresponding longitudinal surfaces extending in the same direction and corresponding transverse surfaces extending in the same direction, characterized in that, the transverse surfaces of the ends of said inner leg are spaced away from the transverse surfaces of the corresponding slots and the longitudinal surfaces of the ends of said inner leg engage corresponding longitudinal surfaces of said slots.

' 2. An electromagnetic device core having an outer shell comprising a stack of continuous punchings, and an inner leg comprising a stack of punchings, said shell stack having end members and side members, said end members each having a slot within each of which is a respective end of said inner leg, the longitudinal dimension of said inner leg defining an axis, said slots and the respective ends of said inner leg therein each having adjacent longitudinal surfaces parallel to said axis, said slots and the respective ends of said inner leg therein having ad- .iacent surfaces transverse to said axis, characterized in that, the corresponding transverse surfaces of said slots and of the ends of said inner leg are spaced from each other, and corresponding longitudinal surfaces of said slots and of the ends of said inner leg engage each other.

3. An electromagnetic device core having an outer shell comprising a stack of continuous punchings, and an inner leg including a stack of punchings, said shell stack having end members and side members, said end members each having a slot within each of which is a respective end of said inner leg, the longitudinal dimension of said inner leg defining an axis, said slots and the respective ends of said inner leg therein each having adjacent longitudinal surfaces parallel to said axis, said slots and the respective ends of said inner leg therein having adjacent surfaces including components transverse to said axis, characterized in that, the transverse components of the corresponding surfaces of said slots and of the ends of said inner leg are spaced from each other, and the corresponding longitudinal surfaces of said slots and of the ends of said inner leg engage each other.

4. An electromagnetic device core having an outer shell comprising a stack of continuous punchings, and an inner leg including a stack of punchings, said shell stack having end members and side members, said end members each having a slot within each of which is a respective end of said inner leg, the longitudinal dimension of said inner leg defining an axis, said slots and the respective ends of said inner leg therein each having adjacent longitudinal surfaces parallel to said axis, said slots and the respective ends of said inner leg therein having adiacent surfaces transverse to said axis, characteriaed in that, the corresponding transverse surfaces of said slots and of the ends of said inner ice are spaced from each other, and correspondl' longitudinal surfaces of said slots and of the endsof said inner leg engage each other, the area of engagement of said longitudinal surfaces at each end of said inner leg being substantially ebdualtothecross-sectionalareaofsaidinner 6. An electromagnetic device core having an outer shell comprising a stack of continuous punchings having end members and side members, and an inner leg including a stackof punchingasaid end members each having a slot within each of which is a respective end of said inner leg, the longitudinal dimension of said innerlegdeilninganaxis,saidslotsandthe.respective ends of said inner leg therein each having; adjacent longitudinal surfaces parallel to said axis, said slots and the respective ends of said inner leg therein having adjacent surfaces transverse to said axis. characterised in that.

- 6 said inner leg is less than the distance between the corresponding transverse surfaces of said slots, and corresponding longitudinal surfaces of said slots and the ends of said inner leg engage each other.

6. An electromagnetic device core comprising, an outer shell including a stack of continuous punchings having end members and side members, and an inner leg including a stack of punchings, the longitudinal dimension of said inner leg defining an axis, said end members each including a substantially rectangular slot having side surfaces parallel to said axis and end surfaces perpendicular to said axis, said inner leg having ends including side surfaces parallel to said axis and end surfaces perpendicular to said axis, the said ends of said inner leg being within respective ones of said slots, the parallel side surfaces of said slots and of the ends of said inner leg being in engagement, and the length of said inner leg being less than the distance between the perpendicular surfaces of said slots.

7. An electromagnetic device core comprising. an outer shell including a stack of continuous punchings having end members and side members, and an inner leg including a stack of punchings, the longitudinal dimension of said inner leg defining an axis, said end members each including a substantially rectangular slot having side surfaces parallel to said axis and end surfaces perpendicular to said axis, said inner leg having ends including side surfaces parallel to said axis and end surfaces perpendicular to said axis, the said ends of said inner leg being within respective ones of said slots, the parallel side surfaces of said slots and of the said ends of said inner leg being in engagement with each other, the cross section of the said end members of said shell being greater than one-half of the cross section of said inner leg, the area of engagement of said side surfaces of said inner leg with said slots being substantially equal to the cross section of said inner leg, and the length of said inner leg being less than the distance between the perpendicular surfaces of said slots.

8. A lamination layer for an electromagnetic device core comprising an outer punching continuous in periphery and having end members and side members, and an inner punching, said end members each including a substantially rectangular slot having longitudinal edges and transverse edges, said inner punching having longitudinal edges at its ends and transverse edges at its ends, said inner punching Lving with each of its ends in a respective one of said rectangular slots, there being a gap between the transverse edges of said inner leg and the respective slot at each end of said inner leg, and the longitudinal edges of said inner punching adiacent the ends thereof engaging the longitudinal edges of said slots.

JOSEPH G. BOLA.

REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number

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