GB2166595A - Polarised relay of high sensitivity - Google Patents

Abstract

A polarised miniature electromagnetic relay has two changeover contact sets (12, 13) actuated by a pivotally mounted armature (7) which extends outside the energising winding (2). The energising winding has a fixed soft iron core providing a pole (6) at one end. The armature which is made of sheet metal has bent over end portions (8 and 9), one end portion (8) having mounted on its underside a thin, flat ferrite-loaded plastics magnet (14) which has a low energy and which is effective to polarise the relay. This arrangement has the advantage that two or more such relays can be mounted side by side without the biassing magnets interfering with adjacent relays, and a very compact design can be achieved, in contrast with prior art arrangements using a metal bar magnet. A four-changeover-contact set version is also described (Fig. 2). <IMAGE>

Description

SPECIFICATION Polarised relay of high sensitivity This invention relates to a miniature electromagnetic relay incorporating a permanent magnet.

Permanent-magnet-assisted relays are known and utilise the flux of a permanent magnet to preferentially attract the armature into one rest position. One such relay has a high powersintered magnet located between a pairofyoke members which extend longitudinally of the relay. This provides relatively weak like poles on opposite sides ofthe armature so that in its energised or unenergised state the contact force is enhanced. In orderto polarisethe relay one pole face is made largerthan the other so that the armature undergoes a slightly greater attractive force from the larger pole face and therefore preferentially occupies one rest position onlywhen de energised, the spring forces of the contact springs balancing out and providing a nil netforceonthe armature inthe centre of the armaturetravel.This relay in fact has four sets of changeover contacts but the same applies to a two changeover contact version.

The core ofthis relay extends th rough the energis- ingwinding and isofcircularcrosssection and is fixed; this enables an efficient coil to be provided. The mean turn length ofthe coil is minimised. However the bar magnet is relatively large and can adversely affect neighbouring relays.

It is an object ofthe present invention to provide an improved miniature electromagnetic relay with at least two sets of changeover contacts and utilising a permanent magnetto polarise the relay and enhance the contact force.

According to the present invention there is provided an electromagnetic relay comprising an energising winding, an armature which is actuated on energising the winding to change the condition of contact sets of the relay, a magnetic circuit of magnetic material, and a low energy permanent magnet for polarising the relay, the permanent magnet being located in a gap between the armature and the fixed magnetic circuit of the relay.

In a two changeover contact embodimentthe changeover contacts sets are located at one end ofthe relay and the armature is pivotally mounted at the other end, extends to one end and has a pair of spaced faces between which a core extends, one of the faces having mounted thereon a flat, thin ferrite-loaded plastics magnet.

In a four changeover contact embodiment an additional pair of changeover contact sets are located at the other end ofthe relay and the armature is pivotally mounted halfway between the ends ofthe winding. The armature has a second pair of spaced faces between which the core extends atsaid other end and one ofthe second pair offaces has a second flat thin ferrite loaded plastics magnet mounted thereon to act in conjunction with the first magnet.

Preferably the permanent magnet is protected from mechanical damage buy a protective cover which can be formed by a rivet head of a rivet forsecu ring the magnet in position.

In orderthatthe invention can be clearly understood, reference will now be made to the accompanying drawings, in which: Fig. 1 shows diagrammatically a side view (Fig. 1A) and a plan view (Fig. 1 B) of a two-changeover permanent magnet relay according to a first embodi- mentofthe present invention; Fig. 2 shows somewhat schematically a side view (Fig. 2A) a plan view (Fig. 2B) an end view (Fig. 2C) and a mid way cross section (Fig. 2D) of a four ihangeover permanent magnet relay according to a second embodiment ofthe present invention.

Referring now to Fig. 1 ofthe drawings the relay comprises a bobbin 1 carrying an energising winding 2 and mounted on a base 3 of the relay. External connection terminals such as 4 extend downwardly from the base 3 for making external connection to changeover contact sets and the energising winding ofthe relay.

Fixed through the bobbin 1 is a core 5 having a circular cross section within the bobbin and an enlarged, flat end 6.

An armature 7 is made offlat strip soft iron and, at the left hand end, has a triangular-shaped bent portion 9 and a larger area bent portion 8 (rectangular in this case) between which the end 6 of the core 5 projects.

In the drawings the cross hatching and the straight line hatching are not intended to represent cross sections, ratherto assist identification of the various parts of the relay.

The armature 7 at the opposite end of the relay has a bent down portion 10which is held captive between a pip 11Aon the lid 11 , another pip 3Aon the base 3 and a second pip 11 B on the end wall face ofthe lid 11. This enables the armatureto pivot in a plane perpendicular to the paper in the Fig. 1Aand parallel to the paper in Fig. 1B Two changeover contact sets are provided, indicated generally by the reference numerals 12 and 13 and the bent parts 8 and 9 ofthe armature have respective combs 8A and 9A which move the moveable contact spring 1 2A and 1 3A between the fixed contacts.

If the relay was not polarised then the changeover contact springs 1 2A and 13Awould occupy the positions shown in Fig. 1 B, that is to say, mid way between the fixed contacts 1 2B and 1 2C on the one hand and 13Band l3Contheotherhand.Thusthe system is in balance at the mid position of the armaturetravel.

Attached to the underside of part 8 of the armature is a flat, thin ferrite loaded plastics magnet 14 having the sameshape asthe bent part8 and secured by part8 either by glue or as shown buy a rivet 8a. The head of the rivet8a protectsthemagnetfrom damage bythe armature end 6. An alternative protecting cover could be used ifthe magnet is e.g. glued in place. Both glue and rivet can be used together.

The magnet 14 has a lowenergy, ofthe orderof BHmax = 80uJ. In the particular embodiment shown The drawing(s) originally filed was(were) informal and the print here reproduced is taken from a later filed formal copy.

the magnet has a north pole at its uppersurface in Fig.

1B and a south pole at its lower surface in that Figure.

The thickness ofthe magnet is ofthe order of 0.5 mm.

This magnet is strong enough to bias the armature towards the cooperating face of core end 6so that the rest position ofthe armature would be with the magnet 14 or rivet head againstthe upper surface of the end 6 so thatcontacts 12A and 12C on the one hand and contacts 13Aand i3Contheotherhandare normally closed contacts, and the remaining contacts 12B on the one hand and 13B on the other hand are the normally open contacts.

When the winding 2 is energised, the end 6 becomes a south pole and repels the south pole of magnet 14, so thatthe armature is initially repelled away and begins its travel across the relay. The flux produced by the energising winding in the core smothers any effect ofthe permanent magnetand the ever increasing magneticattraction between the head 6 and the approaching armature part9 attracts the armature into its operated position in which the normally closed contacts are open and the normally open contacts are closed. Inthiscondition part9will engage the underside face of head 6, as viewed in Fig. 1 B.

Upon de-e ergisation ofthe winding 2, the strength ofthe permanent magnet 14 is sufficient to attract part 8 ofthe armature towards the upper surface of head 6 until the permanent magnet 14 engages head 6.

Referring nowto Fig. 2there is shown a four changeover contact relay similar in construction to the relay of Fig.1 1 in many respects, but differing basically in thatthe armature now pivots aboutthe central position of the bobbin, and it operates in a double acting mode in cooperation with both ends of the core of the winding.

In detail the relay comprises a bobbin 21 having an energising winding 22 mounted on a base 23 with external connection terminals such as 24 providing external connection to the changeover contact sets and the energising winding.

Extending within the bobbin 21 is a soft iron core 25 which hasflat poles 26 and 27 at opposite ends ofthe winding. As can be seen in Fig. 2B the poles 26 and 27 have slightly tapering majorfaces. This can be seen in Fig.2B.

An armature 28 made of sheet soft iron has bent up ends 28A and 28B on the left hand side ofthe Figure 2A and 2B, part 28A being larger than part 28B.Atthe other end ofthe relaythe armature has bent up ends 28C and 28D, 28C being largerthan 28D.

Indicating somewhat diagrammatically are four changeover contact sets 29,30,31 and 32.

The moveable contact of each of these contact sets is moved by a respective comb attached to the associated armature end such as 28A, etc. These combs are designated by reference numerals 33,34, 35 and 36.

The armature is pivoted about a pivot point 37 and the mid section of Fig. 2D shows this more clearly. A pivot integrally moulded at 37 on one side of a central cheek2lA ofthe bobbin. Fig. 2C is a section at the mid point of Figs. 2A and 2B, but is not complete and is simplyto showthe pivot detail.

The relay is enclosed by a lid 38 which has a moulded ring 38A in which the pivot 37 fits and this captures the armature 28.

Without any magnetic bias the armature would occupy a central balanced position as shown generalliy in Fig. 2Bwherethemoveablecontactsprings occupy mid positions between the fixed contacts.

However on the undersides ofthe armature ends 28A and 28C are mounted thin, fl at ferrite loaded plastics magnets 39 and 40 a strength similartothe embodiment of Fig. 1 and secured in the sameway. As viewed in Fig. 2B these magnets provide a north pole attheiruppersurfaces and south poles attheir lower surfaces. These magnets, when the winding is not energised, are attracted towards the opposing surfaces ofthe pole faces 26 and 27to produce a normally closed contact at each ofthe four contact sets. When the winding is energised the magneticflux produced bythewindingisarrangedtoprovideasouth poleat pole 26 and a north poleatpoleface27,thus repelling the adjacent magnets 39 and 40 awayfrom the surface ofthe pole faces and providing an ever increasing attractive force towards the armature ends 28B on the one hand and 28D on the other hand.The armature therefore pivots aboutthe pivot 37 until ends 28B and 28D engage the pole faces 26 and 27, respectively. In this end position the normally closed contacts are open andthe normally open contacts are closed in the fourchangeover contact sets.

Claims (5)

1. An electromagnetic relay comprising an energising winding, an armature which is actuated on energising the winding to change the condition of contact sets ofthe relay, a magnetic circuit of magnetic material, and a low energy permanent magnetforpolarisingtherelay,the permanent magnet being located in a gap between the armature and the fixed magnetic circuit of the relay.

2. A relay as claimed in any preceding claim 1, wherein the magnet consists offerrite loaded plastics material.

3. A relay as claimed in claim 2, wherein the armature is pivotally mounted at one end ofthe relay and has two bent up parts between which one end of a core extends, the magnet being secured to one ofthe bent up parts.

4. A relay as claimed in claim 1 or claim 2, wherein the armature is pivotally mounted at or near its mid point, and has at each endthereoftwo bent up parts between which an associated end of a core extends, there being two such low energy magnets, one ateach end ofthe armature and so mounted on a bent up part to cooperate with each other in polarising the relay.

5. A relay substantially as hereinbefore described with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.