[1]United States Patent Office 3@162,820 3,162,329 FE,'.ZRCMAGNEiTIC POT-CORE ASSEilkIBLIES Ronald Gordon Wildy, Redhill, .4nd Eric Charles @Sitelling, Ilaywards Heath, Eugland, assignors to Norfh Amer- '6@ ican Philips Conipany, Inc., New Yorl,, N.Y., a corporation of Delaware Filed Nov. 12, 1959, Ser. No. 852,557 Claims priority, apprxcition Great Bi-itiin inoi,. 14,1:958 5 Ci2iiEns. (C.. 3.1,6-83) to The present invention relates,@to an in-iproved asseinbly for ferromagnet-@'c pot-cores. Ferroniagnetic pot-cores are used to provide, in @cori-tbination with a ivind-ing, or windiigs, an inductive or tra@isformer component in electrical circuits and usually com- 1-5- prise ferroniagnetic material sliaped to form an inner core part surrotinded by the winding or V@ndings and ilturtiier ferromagnetic parts to f-orm an enGlosLire for the wi@idings. In order to fagilitate iiianufacture, the wiiidings are tisually wound on a coil former i-ii and around which 20 the ferromagne'tic p,,irts are assembl,--d toi fbrm a potcore. In order to ensure close adlierence to aiiy precalculated electrical cl@iaracteristies of flie pot-core component, it is necessary for the assembled parts to be c.Lrefully aligiied arld el,-imped at aii even ar@d constant pressure. Any 2,4 variation on the physical contact of the vatious ferro- . magnet-'c parts will affeec the reluctaiiee of magnotic@ paths and hence the inductance of the wiiqding within the core par'Ls and it is of the utmost importance, particularly whe.i a quantity of matched pot-core components are to 30 be n-ianufactured, to ensure that iny precate-Lilit,-@d eleetric,il characteristics are n-laintained to close toleraices by carefully controlling the alignment and standzirdising the clamping pressure of the parts. 1?rior to the present invention it has been proposed 35 to provide aii assembly for a pot-core which can be assembled by hand wiffiolit the use of tools in whir-h a cont-,iiner adapted to rec,,eive the pot-core parts, inclules a cioslire plate having li-i-s adapted to lock b-,tyonet fash;on with the housing and a spnng member wi-iirh serves the 40 dual purpose of locking the bayonet fastening and holding the pot-core parts together by exerting a pressure on the outer parts of the core. This known assembly suffers froin the dis,,idvantage that the pressure load exerted by the spriiig is limited to 45 that which cotild be exerted by hand and it can be shown that for the attainment of close electr@, .cal tolerances the loads reqtiired to hold the core parts togetner are quite consid--rable. L-1 this known assembly it is usual to cement the core paits together to obtain stability. This 50 is a relatively expensive i:@Deration and great care is necessary to ensure long term. stability 6@' the compoiients. In arriving at a des-'@red pressure load for particular potcore size it is coiivenient to plot a curve showirig - iiiductance variation against variation o@.'L the applied - pressure 55 load to the core parts. Reference to FIGURE 1 of the accompanying drawiii.-s shows a typical curve A-D obtained for a - pot-core haviiig a diameter of 30 mms. and for which the desired inductance L is obtained at a load of 54 kgs. It will be 60 he relative ' -'oji B noticed that in this case t ilat port -C of the curve A-D corresponds to a load variation from 40 k-s. to 66 kgs. and this will bring about a chan,-e in inductance of only -0.05% and +0.03,7o of the precalculated desired inductance. 65 Pateiited Diac. 22, 1'964 2 Typic@al load@ for differerit pot-cofe di@Lnieters are given in th, f6llowi'ng tabl(@: Po@l-core diameter in nim.: Pr&ssute load@in ka'S. 14 --------- I------------------------ ---- 12 16 ------------ ------------- ------ @--L ---- 14 18 --------------------------------------- 20 I 21 ------------------- ------- 27 25 --------------- ---------------------- 4G 30 ---------- L------------ -------- 54 35 ------------------ --------- 70 From the forego-@ng it will be a]@prec@iated that iii ordet to obtaiii an assembly having clear i@lectr ical toiefarit@es the desired pressur6 load to the core parts; i@ gre@tor , tliah dan, be readily applied by hand Without the use of 'td6ls. I The object of tha present inv6ntion is to pr'ovide a potcore. assembly @vhich caii be re@adily Ass&n@bled solely 'b@Y liand qnd to which a desired @pres ure is applied to th& p<)t-core parts after assembly. Iii one enibodirhdnt of the 1)reseiit inveritioli th@@i@e, i provided a pot-core assembly coni]@tising a sub taiiti@lly tubular cont,,,iner, two or morb fetromagiidtic 'pot-cofe pzirts ciiclosed by tie contaiilejrl an internal aoutindiit provided at one end oi the coiitainer and lockable retaining meaiis I at t@ie oppasite end iiicludihg -d ie@@ilient raember, enaracterized in that nieails @fe pr&vidbd for stressiiig the resilieiit nieiiiber to ilrge and hold ttie pcitcore parts together and 'aga:inst said at-utnient aftot ldcking the retaining means. The str6ssing of the resilieiit liviii I II " I nielliber, which may be in the fOrft-IL Of a Be e spriiig washer, can be effectad by a sctew menber iiige@tted through tlic retaining means. The screw ffeniber coacts with the spring washer to coli-ipress it E@ild thus &g6 the pot-core parts together. The strossing- of this spring washer is effected after the core pqrts have,bi@en @isstrhbled and locked in the container. This asseinbly in the unstr@ssed condition iilay be easily cartied oiit by haiid withoift the use of tools and the screw hiehiber rr@ay bia provided with a; slot so that a screwdriver, which m@,y be@@ a rudinientary@ screwdriv-,r such as the edgi,- of a coin, can be used to scr@w the moi,@iber a aiiist the spr@ing washer. An abutment may be positioned along thif, scre'W @mefhber to limit to a predetermined distan@e, the compres ion of the spring washer. The compression is selected so that the desired load is applied to the cote parts irresi@&ctive of diniensionalvariations 6f the Yari6us paris, Of the asgembly witliin their re@pective tolera-@ices. One embodim6nt of the present in-@6ntibil will now be described with reference to- the accoirip'anying dizigtqriimatic dirawings in whirhFIG'URE 2 is an' exploded View of 0, com @@lete pbt@tbre assenably and FIGURE 3 shows a part sbctiong viewof the asserii@ bled po'L-core shown in FIGURE 2. The complete p6t-core assei-nbly ,qs @hown Oill how be described in the order in which the various component parts are assembled. Referring to FIGURE 2 a pot-core container 1, which n-lay for example be of brass tubing, is provided with inwardly disposed longitudinal ribs 3 the upper ends of which have b,-en cut out to form slbts 4 whereas an abutment comprising inwardly turned edges 2 is provided at the lower end. Apertures 5 are also provided a,t the lower edge which may be used for the passage of leads from an inner coil winding. An insulating terminal base 6 wbich when inserted in the con-
[2]3 tainer I rests against the turned in edge 2 is provided with keyways 9 which engage the ribs 3 and an inner recessed portion 7 is provided with terrninals 8. Reference numeral 10 indicates one half of a ferromagnetic pot-core having an inner ring core 12 the central hollow portion having a threaded spigot 13 for the insertion of a trinimer plug 16. Keyways I][ are provided on the outer shell of the pot-core 10 which are adapted to engage the ribs 3 when inserted in the container I and also to provide access for terminal leads. A coff former 14, which may for example be made of moulded plastic, is adapted to fit into the inner recess 18 of the pol-core half 10, and slots 15 are provided to allow terminal leads to be taken froni a winding to be wound round the coil former 14. The trimmer plug 16 may also for example be made of plastic material and have a sleeve of ferromagnetic material 17, adjustment,of the trimmer plug 16 being effected by screwing it in or out ol' the inner ring core 12. The second half of the ferromagnetic pot-core 19 is substantially the same as that of the first half 10 with the exception that a through central aperttire 20 is provided for the insertion of the tritnmer plug 16 and keyways 21 are provided to engage the container ribs 3. A Bellville spring washer 22 having a central aperturg 23 is positioned on top of the second half of the pot-core 19. The aperture 23 allows for the insertion of a trimming tool for adjustment of the trimmer plug 16. A retaining plate 24 having cut outs correspondin.a to the container ribs 3 is adapted to be inserted at a level of the container height which will permit the cut outs 25 to be rotated through the container slots 4. A pair of slots in the container wall allows the locking of the plate 24 by bending the tab 32 thus formed inwardly into one of the cut outs 25 in the retaining plate 24. The retaining plate 24 is provided with a central threaded aperture 26 which receives a screw member 27. In order to apply pressure to the assembly the screw member 27 is screwed into the retaining plate aperture 26 so that the screw member 27 depresses the Bellville spring washer 22 until lan abutment 28 prevents further insertion by coacting against the retaining plate 24. By location of the screw abutment 28 a preicalculated pressure may be applied to the whole -assembly and it has been found, for example, that an assembly having a pot-core of about 30 mm. diameter a force of about 54 kgs' is desirable and at that load the tolerance in electrical characteristics is much improved ovet other known assemblies. A secondary screw thread 29 on the opposite end of screw member 27 provides, together with nut 31, a means for mounting the assembly on a chassis. In FIGURE 3 a pot-core assembly having the same c I omponent reference as in FIGURE Z is shown where the container I has been partly cut away to show the internal dis osition of the winding coil former 14 and the two halves of the pot-core 19 and 10 clamped together under the,depressed Bellville spring washer 22, the screw member 27 having been screwed in until the abutment 28 abuts against the retaining plate 24. The tr . immer @lug 16 having the ferromagnetic sleeve 17 is shown inserted in the central column 30 and @djustm ent being obtained by screwing the trimmer plug 16 cqaxially, along the threaded spigot 13. : Although the assem-bly shown in FFGURES I and 2 has provision for the termination of in.iernal leads by use of the terminals 4 8 fixed to the depressed portion 7 of the insulated base 6, the assembly is readily adaptable for use with "flying leads" in that leads emanating from the coil former 14 may be passed through the bobbin slots 15, core keyways 11 and out through the aperture 5 in the container 1. It may be envisaged that the assembly is also readily adaptable to form a plugin unit where terminals 8 inay protrude externally in the form of pins adapted to plug into a suitable socket. 10 What is
