Title:
MEDIUM FREQUENCY TRANSFORMER
United States Patent 3728655


Abstract:
A medium frequency transformer having a single layer flat secondary winding, two flat layers forming a primary winding, and placed face to face, and a plurality of ferrite core members. According to this invention the faces of the secondary winding and of the primary winding layers each include two band shaped zones which are connected at their ends by U-shaped zones. The core members are stacked to form hollow columns embracing the parallel band-shaped zones. A clamping member is mounted at each end of the core stack columns.



Inventors:
REINKE F
Application Number:
05/264456
Publication Date:
04/17/1973
Filing Date:
06/20/1972
Assignee:
AEG-Elotherm GmbH (Remscheid-Hasten, DT)
Primary Class:
Other Classes:
336/183, 336/192, 336/212, 336/232
International Classes:
H01F30/10; (IPC1-7): H01F27/08; H01F27/30
Field of Search:
336/62,183,212,232,210,192,225
View Patent Images:
US Patent References:
3539959TRANSFORMER HAVING SANDWICHED COILS AND COOLING MEANS1970-11-10Wildi
3503026DISC-SHAPED TRANSFORMER1970-03-24Geisel et al.
3419834Electrical coils1968-12-31McKechnie et al.
2847651Coupling transformer for radio frequency heating applications1958-08-12Schamanek
2114186Transformer1938-04-12Hendricks, Jr.
1471096Electrical apparatus1923-10-16Brand
1394044Water-cooled transformer1921-10-18Stephans
1129464N/A1915-02-23Fortescue
1086041N/A1914-02-03Gravell



Primary Examiner:
Kozma, Thomas J.
Claims:
What is claimed

1. In a transformer having a single layer flat secondary winding, two flat layers of a primary winding placed face to face and forming a stack, and

2. A transformer according to claim 1, wherein the primary connections are taken out through one of the clamping members and the secondary connections through the other clamping member.

3. A transformer according to claim 2, wherein the clamping member at the primary terminal end contains two terminal bars which are each electrically connected by a contact bridge to a point of the primary winding layers on an outside face of the winding stack.

4. A transformer according to claim 3, wherein the points that are electrically contacted by the contact bridges are located at least near the extreme ends of the primary winding layers to serve as intermediate taps.

5. A transformer according to claim 4, wherein the overall thickness of the flat secondary winding layer in the region of the connections where the conductors overlap at least does not significantly exceed its thickness elsewhere.

6. A transformer according to claim 5, wherein the secondary winding consists of several hollow section conductors electrically connected in parallel and coiled in one layer.

7. A transformer according to claim 6, wherein the interiors of the hollow section electrically parallel-connected conductors of the secondary winding are at least partly connected in series in so far as the flow of the coolant therethrough is concerned.

8. A transformer according to claim 7 wherein said core members are ferrite.

9. A transformer comprising:

Description:
The invention relates to a transformer, particularly for supplying energy to an inducter for heating workpieces.

For inductively heating metal workpieces, particularly for inductively surface-hardening such workpieces a transformer is normally required to adapt the generator output to the requirements of the inductor. As a matter of convenience, the output side of the transformer is usually connected directly to the inductor. For inductively heating bearing surfaces of crankshafts it has been proposed, for instance in German Patent Specification No. 1 209 137, to make use of a so-called half shell inductor which has one open side and which is associated with a transformer with which it forms a rigid unit. While the crankshaft rotates during inductive heating, this unit rides on the bearing that is to be hardened and participates in its circular movement. If it is desired to heat several bearing surfaces on one crankshaft at the same time the combined transformer-inductor units of course must not foul each other as they move with the cranks. The simplest way this can be ensured is by keeping the overall dimensions of the medium frequency transformers in the direction normal to the crankshaft axis shorter than the center distance between two neighboring bearings that are to be hardened at the same time.

A medium frequency transformer which is of the required narrow design has already been described in German Gebrauchsmuster No. 66 07 290. This transformer comprises a plurality of disc-shaped secondary and primary winding layers presenting a roughly annular face with the primary and secondary layers -- alternately interleaved -- forming a stack. The primary windings are electrically connected in series and the secondary layers in parallel, and the conductors of the windings are embraced by several frame-like ferrite cores extending radially in the form of a star.

These medium frequency transformers have been very successful. However, in practice it transpires that in such transformers, known as "pancake" transformers, a casing of electrically insulating material is needed for supporting the radial assembly of ferrite cores and that this casing undesirably increases the overall width of the transformer. In order to adapt the inductors that are used in practice to the output of the medium frequency transformer different transformation ratios, i.e. different transformer winding potentials are needed for transmitting the same power without changing the medium frequency output voltage of the generator. Owing to the given induction limit of the ferrite cores the effective total cross section of the cores must therefore likewise vary for different winding potentials.

Assuming that the "width" of the transformer remains roughly the same, this change in the winding potential in the above described "pancake transformers" can in practice be achieved only by varying the number of the ferrite cores that are provided and hence by varying the transformer diameter. For one and the same crankshaft-hardening machine this may mean a relatively large number of different transformer components which impose restrictions upon the numbers of models that can be produced, besides complicating the stock-keeping problem.

It is therefore the object of the present invention to provide a medium frequency transformer comprising a flat single layer secondary winding and two flat layers of primary winding combined in a stack and provided with frame-like cores embracing the conductors of the winding. Preferably the cores are made of ferrite and the overall dimensions of the transformer in a direction normal to the faces of the secondary winding and the layers of the primary winding are small in relation to its overall dimensions in a direction parallel to these faces, thus for different winding potentials transformers with essentially the same components and configuration can be used. Further the smallest overall dimension of the transformer is substantially determined only by the corresponding dimension of the frame-like cores.

According to the invention of this application is achieved that the faces of the secondary winding and of the layers of primary winding each comprise two parallel band-shaped zones which are connected at their ends by U-shaped zones. The frame-like core members are stacked with their side faces abutting to form hollow stacks embracing the parallel band-shaped zones of the faces of the winding respectively winding layers. For securing the stack of magnetic cores a clamping member is provided at each end of the stacks. Preferably, the primary connections are brought out through one of the clamping members and the secondary connections are brought out through the other clamping member.

Moreover, in a preferred embodiment of the invention the clamping member at the primary terminal end contains two connecting bars which are electrically connected by a bridge contact to a point on the primary winding layer forming the outer faces of the stack of windings. These points of contact may be located at the extreme ends of the primary winding layers or optionally one or two turns away from the ends to serve as intermediate taps.

According to another useful aspect of the invention the overall thickness of the flat secondary winding layer in the region of the connections where the conductors overlap does not exceed or does not significantly exceed its thickness elsewhere.

In yet another desirable aspect of the invention the secondary winding consists of several hollow section conductors which are electrically connected in parallel, but contained in one layer. The interiors of the hollow section secondary winding conductors which are electrically connected in parallel are nevertheless preferably at least partly connected in series in so far as the flow of the coolant therethrough is concerned.

Finally the invention also relates to a production size range of such transformers. The transformers are preferably in the range of substantially the same overall dimensions in directions normal to the lengthwise direction of the parallel band-shaped zones of the faces of the windings respectively winding layers. The cores and clamping elements likewise have the same dimensions, but for rising winding potentials the number of cores and the length of the band-shaped zones of the faces of the winding or winding layer are increased.

The invention will be hereinafter more particularly described with reference to the drawings which illustrate a preferred embodiment.

FIGS. 1 and 2 are separate representations of a primary winding and of a secondary winding.

FIGS. 3 and 4 are two views of the fully assembled transformer.

FIG. 5 is a section taken on the line I -- I in FIG. 3.

The transformer winding comprises two primary winding layers 1 (seen best in FIG. 1) which abut the two faces of a secondary winding 2 (shown in FIG. 2) in a manner forming a kind of stack. The conductors of the windings 1 and 2 are embraced by a plurality of frame-like cores 3 (shown in FIG. 5) of ferrite material.

Each of the primary winding layers 1 consists of a flat copper tube 4 of rectangular cross section coiled to form a single layer pancake winding in such a way that the wider dimension of the copper tube is parallel to the layer. The face of this winding layer comprises two parallel band-shaped zones 5 which are connected at each end by two U-shaped zones 6 and 7 to form the complete face. The external end of the spirally wound layer, which is located in one of the U-shaped zones (6) is bent outwards and provided with a terminal fitting 8 for connection to a coolant circulating system, whereas the inner end is provided with an eyelet-shaped fitting 9. The winding of the second primary winding layer (not shown) viewed from the inside outwards has a pitch contrary to that of the first primary winding layer and it has an external end 10 which is bent in a slightly different manner (indicated by chain lines in FIG. 1) to the end of the first layer. The turns of the primary winding layers are provided with an electrically insulating coating applied by fluidization sintering.

Copper tubes 11 of the secondary winding 2 (FIG. 2) have roughly twice the internal cross section of the conductor tubes 4 of the primary winding and form the single layer secondary winding 2 which has a face consisting of two band-shaped parallel zones 5' and two U-shaped zones 6' and 7' in the same way as the primary winding layers. Secondary winding 2 actually consists of two electrically parallel strands 12 and 13 of two copper tube conductors 11. Each conductor 11, in the U-shaped zone, is connected by a return loop so that they are in series in so far as the circulation therethrough of the coolant is concerned. In the U-shaped zone 7 where the secondary winding is provided with electrical terminals 14 and where the conductors of the winding overlap, the thickness of the conductors is reduced sufficiently for the overall thickness of the winding to be roughly the same as that of the secondary winding in the other zones of its face. For the introduction of the coolant the winding strand 12 incorporates two hollow copper tube lengths provided with coolant connections through which the coolant can be admitted and withdrawn in the direction indicated by arrows 16. The secondary winding is also coated with an insulating film deposited by fluidization sintering in the same way as to the two primary winding layers.

In the completed transformer (FIGS. 3 and 4) the primary winding layers 1 and the secondary winding are combined in a stack. The two primary winding layers 1 are connected at their inner ends by a pipe union 16' (FIG. 3) between their terminal fittings 9 so that they are in series electrically as well as for the circulation therethrough of the coolant. Their outer ends 10 are connected to coolant connections 18 in a clamping member 17 resembling a box. This box 17 also contains, in side-by-side juxtaposition but electrically insulated, two terminal bars 19 which by contact bridges 20 are connected to bright parts of the outside faces of the primary winding layers 1. As will be understood from FIG. 3 that terminal bars 19 may be connected by the contact bridges 20 not only to the outer ends 10 of the primary winding layers 1, but alternatively also to taps at the end of the first respectively second turn. Terminal bars 19 project from the box-like clamping member 17 and their ends, which are of different lengths, carry lugs 21 forming the primary winding terminals of the transformer.

Mounted on the box-shaped clamping member 17 are two stacks of frame-shaped core members 3 of ferrite, each column embracing one of the band-shaped zones 5 of the winding faces. Surmounting these stacks is a second clamping member 22, likewise of box shape, containing the ends of the single layer secondary winding 2 of which the terminal fittings 14 (FIG. 2) are connected to the secondary terminals 23 of the transformer as well as by hollow tube lengths 15 to pipe connectors 24 for the cooling system. The stacks of magnetic ferrite cores 4 are compressed between clamping members 19 and 22 by tie rods 25 and they thus form a unit assembly.

FIG. 5 is a representation on a larger scale in the form of a section taken on the line I -- I in FIG. 3 of the relative positions of the conductors 4 respectively 11 of the primary winding layers 1 and of the secondary winding and of the frame-like ferrite core 3 surrounding the same.

Many changes and modifications in the above embodiments of the invention can of course be made without departing from the scope of the invention. Accordingly, that scope is intended to be limited only by the scope of the appended claims.