GB2100070A - Inductor casing - Google Patents

Abstract

A choke for a fluorescent lamp is provided by the assembly of a metal casing 8 around the laminations 2, 3. The casing is then tightened by pressing the casing into recesses formed on the laminations and the casing metal stretched beyond its elastic limit so that in use the metal casing will remain in its deformed state tightly wrapped around the laminations. The additional tightness achieved reduces vibration, obtaining a significant reduction in noise level. <IMAGE>

Description

SPECIFICATION Inductor casing The present invention relates to an inductor and to a method of assembling an inductor.

The casing of an inductor such as a fluorescent lamp choke should preferably be tightly clamped onto the inductor core to avoid inefficient cooling and excessive vibration and noise. British Patent Specification 1 089 976 discloses a laminated core transformer wherein a clamping strap surrounds the limbs of. the core and which is strained against the limbs by a metal tensioning strip forming a closed loop around the two half limbs of the transformer. The metal tensioning strip is situated within a gap separating the two halves of the transformer which gap is maintained by suitable distance pieces within the gap.While this may go some way to providing an improvement in the clamping of the laminations a disadvantage is that the clamping strap or straps is or are only tensioned locally by the tensioning strip, and indeed, it requires the provision of the strip as an additional and permanent means of tensioning.

An object of this invention is to provide a method of assembling an inductor with improved tensioning and an inductor so tensioned. British Patent specification 1559181 (Thorn) discloses a method of assembling an inductor which comprises a core carrying a winding and enclosed in a sheet metal casing.

In the method, the casing is formed in two parts each of which comprises two opposite walls of the casing and a third wall joining the two opposite walls. The side edges of the two opposite walls of each part are shaped to slidingly interengage with the side edges of the two opposite walls of the other part. The two parts are assembled around the core by sliding engagement of the said side edges and the said side edges are thereafter deformed to clamp the two parts together.

According to one aspect of the present invention, there is provided a method of assembling an inductor, the inductor comprising a core including a stack of laminations having one or more recesses therein and a winding around the laminations, the method comprising: looping a metal casting position around the laminations; pressing the metal of the loop into at least one of said recesses thereby stretching the metal of the casing beyond its elastic limit so that the metal of the casing remains substantially in its deformed state in the at least one recess when the pressing force is removed.

Another aspect of the present invention provides an inductor including a core including a stack of laminations and a winding around the laminations, the stack being arranged to have at least one recess, the inductor further including a metal casing portion looped around the laminations and having been tensioned by tensioning means, the casing thereby having been deformed to enter at least one recess and stretched beyond the elastic limit of the casing metal such that it remains substantially in the deformed state in the recess when the tensioning means is removed whereby the casing portion is tightly clamped around the laminations.

It will be clear from the above that the invention in its broadest aspect utilises the casing of an inductor as a means of clamping the laminations together hence obviating the use of a separate and additiona! tensioning strip as required in the prior patent 1 089 976.

For a better understanding of the present invention, reference will now be made by way of example to the accompanying drawing, in which: Figure 1 is an isometric view of an example of a core of an inductor, Figure 2 is a schematic sectional elevation illustrating the invention, Figure 2a shows a detail of Fig. 2, and Figure 3 is a fragmentary view illustrating a modification.

Referring to Fig. 1, the inductor, which is for example a fluorescent lamp choke, comprises in well known manner a core 1 formed of many E-shaped laminations 2 and 3 arranged around a bobbin 4 carrying a winding 5, the laminations being stacked in known manner.

The laminations 2,3 have external projections 6, which define external recesses 7 and 10.

In order to form a casing tightly around the core, a band of sheet mild steel 8 is wrapped tightly around the core as shown in Fig. 2. Its overlapping ends 9 and 9b are then joined together by projection welding at 9a. During this welding step the underlying end 9b is forced into the recess 10 so that the top surface will be generally flush. Due to the projections 6, the band 8 will bridge the recesses 7, as can be seen in the detail view of Fig. 2a, and 10. Thus in order to ensure all slack in the band 8 is taken up and to stress the band beyond the elastic limit of the mild steel, the band is forced (by a mechanical press tool for example as indicated by the arrow A) into the recesses 7 as shown in Fig.

2. Stretching the mild steel beyond its elastic limit in this fashion ensures that the casing material will remain tightly clamped around the laminations in the deformed state.

In practice it has been found preferable not to force the band into recess 1 0a although it is possible to do so. However it is desirable to force it into all four of recesses 7.

Very briefly the method of assembling the inductor comprises: 1. Wrapping the metal casing around the laminations and forming the corners tightly; 2. Clamping the sides (at xxx, see Fig. 2) and projection welding the overlapping ends, 3. Reclamping the sides (at xxx, see Fig. 2) and applying press tools simultaneously to press the casing into the four corner recesses.

Due to relative movement between the clamps and the sides of the casing some tool marks may appear on the sides of the casing but these are not detrimental to the performance of the inductor.

Instead of providing projections 6 on the laminations to define the recesses 7, the recesses may be defined in otherwise plain edges of the laminations as shown at 11 in Fig. 3.

The preferred material for the band 8 is mild steel. However, other suitable materials will be apparent to those skilled in the art; aluminium for example.

The laminations are made in the required shape by means known in the art such as stamping them. Alternatively recesses can be formed by a suitable arrangement of the laminations.

The described example of the invention provides a casing for four sides of the inductor. The other two sides may be covered by bending extensions of the casing at both ends, interlocked in such a manner that they do not touch the coil. Alternatively, the coil could be covered by plastics mouldings, one at either end.

The described example of the invention provides a tightly fitting casing which is posttensioned and thus aids efficient cooling and the reduction of vibration and noise.

Claims (14)

1. A method of assembling an inductor, the inductor comprising a core including a stack of laminations having one or more recesses therein and a winding around the laminations, the method comprising: looping a metal casting position around the laminations; pressing the metal of the loop into at least one of said recesses thereby stretching the metal of the casing beyond its elastic limit so that the metal of the casing remains substantially in its deformed state in the at least one recess when the pressing force is removed.

2. A method according to Claim 1 wherein the loop is formed from a length of sheet metal which has its ends joined together.

3. A method according to Claim 2 wherein the joint is located within a recess.

4. A method according to Claim 2 wherein the joining is effected by welding.

5. A method according to Claim 4 wherein the welding is projection welding.

6. A method according to Claim 1 wherein the lamination stack has a number of recesses and wherein press tools are arranged to press the casing into the recesses.

7. A method according to Claim 6 wherein the press tools are arranged to press the casing metal substantially simultaneously into the recesses.

8. A method of assembling an inductor substantially as herein described with reference to the accompanying drawings.

9. An inductor comprising a choke for a fluorescent lamp made in accordance with any of the preceding claims.

10. An inductor including a core including a stack of laminations and a winding around the laminations, the stack being arranged to have at least one recess, the inductor further including a metal casing portion looped around the laminations and having been tensioned by tensioning means, the casing thereby having been deformed to enter at least one recess and stretched beyond the elastic limit of the casing metal such that it remains substantially in the deformed state in the recess when the tensioning means is removed whereby the casing portion is tightly clamped around the laminations.

11. An inductor according to Claim 10 wherein the loop is formed from a length of sheet metal having the ends thereof joined together.

1 2. An inductor according to Claim 11 wherein the ends overlap.

1 3. An inductor according to Claims 11 or 1 2 wherein the join of the ends is situated in a recess.

14. An inductor according to Claims 11, 1 2 and 1 3 wherein the joining is effected by welding.

1 5. An inductor according to Claim 14 wherein the welding is projection welding.

1 6. An inductor according to any of Claims 10, to 1 5 comprising a choke for a fluorescent lamp.

1 7. An inductor substantially as described herein and with reference to the accompanying drawings.