GB2191039A - Miniature electro-magnetic relay - Google Patents

Abstract

An electromagnetic relay with a DIL footprint has an unmagnetised U- shaped sliding armature (9) with two legs (9a) straddling a pole piece (8a) on the free end of a core (8). In the monostable version (Fig. 1) a pole piece (8e) is magnetically coupled to the yoke limb (8b) via a permanent magnet (M) to provide the relay with a monostable action; a second pole piece (8pc) is also provided on the yoke. Also described is a latching version using two permanent magnets at the pole pieces, (Fig. 2) and an unpolarised version (Fig. 3) having only a single yoke pole piece. The armature (9) includes combs (9d, e) that operate the moving contacts (4a, b) of a pair of contact sets. <IMAGE>

Description

SPECIFICATION Miniature electro-magnetic relay This invention relates to a miniature electromagnetic relay, particularly but not exclusively a polarised relay having a high sensitivity with a DIL footprint.

European Patent Specification 0127309 discloses a monostable (or polarised) relay having a yoke including a core with a coil around the core, the yoke being connected to the core and extending in parallel with the core. An armature includes a permanent magnet and is constrained to be laterally movable between an upstanding pair of legs formed at the free end of the yoke. The relay has movable contacts which are coupled to the armature and the upstanding legs of the yoke have areas of magnetic pole which differ significantly from one another. In the unoperated condition of the relay the permanently magnetised armature is drawn against the larger area pole face by magnetic attraction between the larger area pole face and the armature on the one hand and the exposed end of the core and the leg of the armature on the other hand.When the relay is energised the larger pole piece and the core tip are oppositely magnetised and repel the legs of the armature away until they approach the core tip on the one hand and the smaller area pole piece on the other hand.

The stationary contacts are closed by overcoming the resilient resistance of the movable contact arm. The resilient resistance of the moveable contact arm is effective to restore the armature to the non-operated condition.

The use of a permanently magnetised armature involves a somewhat complicated armature assembly procedure, and the use of a pole piece of significantly smaller area than the other pole, reduces the magnetic efficiency of the relay.

It is an object of the present invention to provide a relay which maintains the advantages of the above mentioned design with regard to miniaturisation but which enables an easier construction and which can improve sensibility in permanently magnetised sensors.

According to the present invention there is provided an electro-magnetic relay comprising a substantially U-shaped yoke having two limbs, a winding on one limb of the U, the free ends of the U-limbs carrying respectively first and second pole pieces and an armature which has two legs lying on respective opposite sides of one of the pole pieces and which is coupled to a spring of a movable contact, therebeing a fixed contact cooperating with the moveable contact for providing an open and a closed contact condition controlled by movement of the armature, said armature being unmagnetised.

According to another aspect of the present invention there is provided a monostable electro-magnetic relay comprising a substantially U-shaped yoke having a winding on one limb of the U, the free ends of the U-limbs carrying first and second pole pieces, there being a third pole piece coupled to the yoke via a permanent magnet and defining with the first and second pole pieces two distinct air gaps, and an armature which has two legs lying in respective ones of the air gaps and which is coupled to a movable contact, there being a fixed contact cooperating with the movable contact for providing an open and a closed contact condition controlled by movement of the armature.

Conveniently the armature is arranged to slide backwards and forwards in guide members integrally moulded with a bobbin on which the energising winding is wound.

In order that the invention can be clearly understood reference will now be made to the accompanying drawing in which: Fig. 1 is a perspective somewhat diagrammatic representation of a monostable polarised miniature electro-magnetic relay according to an embodiment of the present invention; Fig. 2 is similar in construction to Fig. 1, but is a latching version and has an extra magnet and modified pole piece; Fig. 3 is similar in construction to Figs. 1 and 2 but is an unpolarised version with no polarising magnet; Fig. 4 is an end view of Fig. 1 showing just the magnetically operable parts, the base and the comb; Fig. 5 is an end view of Fig. 2, and including some of the parts shown in Fig. 1, and Fig. 6 is an end view of Fig. 3 and showing some of the parts shown in Fig. 1.

Referring to the drawing a base member 1 of moulded plastics material carries external connection terminals such as 2, 3 and 4, terminal 2 being connected to a fixed and normally open contact 2a, contact terminal 3 being connected with a fixed and normally closed contact 3a and contact terminal 4 being connected with a movable spring contact arm 4A having a contact head 4a.

A similar arrangement exists on the far side of the relay see contacts 2b, 3b, 4b and contact spring 4B.

The motor unit of the relay comprises a moulded plastics bobbin 5 having end cheeks 6 and 7 and slid onto one arm 8, in this embodiment the core, of a U-shaped yoke 8 the other limb 8b extending outside the energising winding which will be wound on the bobbin between the cheeks 6 and 7 and extends to carry, at its free end, an upstanding pole piece 8c which in this embodiment has been bent up at right angles to the general plane of the limb 8b of the yoke. The rear end of limb 8b is also bent up to produce an end part 8d which has a central aperture in which the core 8a projects through and has been staked into from the other side. The free end 8a of the core member 8 provides a second pole piece.

A third pole piece 8e is coupled magnetically to the yoke limb 8b via a permanent magnet M which is bonded both to the yoke limb 8b and to the third pole piece 8e by means of resin glue. However bonding is not essential; when magnetised the magnet M holds the parts together. All that is required is a small projection from the end of the bobbin and another from the base to prevent gross mvoement. Pole piece 8e in positioned by two grooves 7a in the end of the bobbin and la in the end of the base 8a and 8c are held likewise.

In the base member 1 the recess la is adapted to fit the yoke member together with its two upstanding pole pieces 8c and 8e secured to the plastics bobbin 5.

The end flange 6 of the bobbin 5 carries connection terminals 6a and 6b which thus project through the casing formed by the base member 1 and closure lid which covers the relay but which is not shown in the drawing.

The arrangement of the connection leads secured to the bobbin is disclosed more fully in and protected by our European Patent 0075393 (A.L. Freeman 7-1-2).

The armature is designated generally by the reference numeral 9 and comprises a Ushaped soft iron member 9a carried by a plastics moulded part which extends to form comb elements 9b and 9c on respective opposite sides of the U member 9a. The comb members 9b and 9c have downwardly extending portions 9d and 9e which embrace movable contact members 4a and its corresponding member on the opposite side.

The base 1 has moulded slide bearers 7a and 7b which support the sliding armature 9.

This can be seen more clearly in Fig. 4 of the drawings.

As shown in the drawing the U-shaped armature part 9a is biassed against the third pole piece 8e and the core pole piece 8a because the permanent magnet M having the north and south poles as shown in the drawing, induces a south pole on pole piece 8e and a north pole on both of pole pieces 8c and core pole piece 8a. Thus the soft iron Ushaped armature part 9a is attracted to the position shown to complete the magnetic circuit between the core pole piece 8a and the third pole piece 8e. Thus the comb members 9d and 9e draw the movable contact springs against the normally closed contacts 3a and 3b.

When the relay is energised via the connection terminals 6a and 6b to induce a south pole on core pole piece 8a and a north pole on first pole piece 8c, the U-shaped soft iron armature part 9a is attracted away from pole piece 8e to complete the magnetic circuit across the pole piece 8c and the core pole piece 8a thus the armature moves to its other position drawing with it the movable contacts 4a and 4b until they make contact with the fixed normally open contacts 2a and 2b.

When the winding is de-energised the armature reverts to the position shown in the drawing for the reasons discussed above.

It is to be understood that the drawing is only schematic and a number of details have been omitted from the drawing for the sake of clarity.

It is to be understood that a number of alternative arrangements could be adopted within the scope of the invention. For example the pole pieces 8c and 8e could be reversed so that the magnet is on the other side of the centre plane containing the core member 8.

The connection terminals 2, 3, 4 and 6 are arranged according to the conventional DIL footprint.

Other versions of the relay are also possible using common parts and these are shown in Figs. 2 and 3. It is to be understood Figs. 2 and 3 are more diagrammatic than Fig. 1 and would be constructed with most of the parts shown in Fig. 1 except where otherwise discussed below. For example a latching version is envisaged in which the pole piece 8c is not integral with the limb 8b of the yoke but instead is magnetically connected to the limb 8b via a permanent magnet in the same way as pole piece 8e. This is shown diagrammatically in Figs. 2 and 5 of the drawings. Yoke 20 carries pole pieces 21, 22 via respective permanent magnets 23, 24. Armature 25 is Ushaped and operates a changeover contact set 26 by moving contact spring 27. A second set and spring on the near side have been omitted for clarity. Otherwise the construction of the relay is very similar to that shown in Fig. 1.The relay will latch into one or other of its tow end positions under the influence of the magnets 23, 24. The pole pieces would be held in the grooves 7a of the bobbin end face as before and the comb 9 would be the same.

In another version of the relay the permanent magnet M of Fig. 1 omitted to provide a less sensitive non-polarised version of the relay and this is shown diagrammatically in Figs.

3 and 6 where the yoke 30 has a single upstanding pole piece 31 and a core 32 providing a core pole 33. A U-shaped armature 34 of bent soft iron is constructed and carried in a comb member (not shown) but the same as comb 7 in Fig. 1. A changeover contact set 35 is controlled by the comb through the moveable contact spring 36 similar to spring 4A in Fig. 1 and a second set on the near side would be provided (as in Fig.1) but omitted from Fig. 3 for clarity.

This relay is non-polarised and less sensitive and so it does not matter which way the coil is connected for the relay to operate (unlike the embodiment of Fig. 1 in which energisation must be of the correct electrical polarity to induce the correct magnetic polarity in the yoke). Also in this version the armature will be biassed into one end position by the spring force of the contact springs such as 36 instead of by the permanent magnet force in the magnet M (Fig. 1) or 21 and 22 (Fig. 2).

In Figs. 4, 5 and 6, like reference numerals represent like parts.

Fig. 4 shows an end view of the relay of Fig.1 and shows how the bent armature 9a is held in the moulded plastics comb 9 which is retained against forward movement by the front upper tips of the bearers 7a and 7b and against rearward movement by the bobbin end cheek 7 (not shown in Fig. 4). The armature 9a is shown in its rest (unenergised) position in Fig. 4 and the bearers 7a, 7b embrace the sides of the pole pieces 8c and 8e.

Fig. 5 shows an end view of the relay of Fig.2 incorporating the appropriate parts of Fig. 1. The armature 9a is in its rest position and is the same as in Figs. 1 and 4. So would be the comb although this is not shown in Fig. 5. The base 1 is the same and a lid L is shown which is the same for all three versions of the relay described here.

Fig. 6 shows an end view of the relay of Fig. 3 incorporating the base 1 and lid L. The armature 34 corresponds to armature 9a but is thinner and the comb 34 corresponds to comb 9 except the recess in which the armature is held is slightly narrower to accomodate the thinner armature. A non-magnetic spacer 35 is located on the pole piece 33 to support the armature in the rest position shown and has a thickness which is greater than the gaps 36 and 37 so that when the relay is energised there is a definite net pull on the armature towards the left hand side of the drawing as shown in Fig. 6. The same rest position of the armature could be achieved by other means than the spacer 35, and the contact springs 4A, 4B in this embodiment are set to urge the armature into its desired rest position. For example the fixed contacts 3a, 36 could be sufficient to limit armature movement to the desired position. In the embodiment the gaps 37 and 36 would be about 0.45mm and the spacer 35 (or gap) about 0.7mm. The armature thickness is about 0.6mm and the yoke 33, 8c, 8b about 0.5mm and the core 33 about 0.7mm.

Claims (5)

1. An electro-magnetic relay comprising a substantially U-shaped yoke having two limbs, a winding on one limb of the U, the free ends of the U-limbs carrying respectively first and second pole pieces and an armature which has two legs lying on respective opposite sides of one of the pole pieces and which is coupled to a spring of a movable contact, therebeing a fixed contact cooperating with the moveable contact for providing an open and a closed contact condition controlled by movement of the armature, said armature being unmagnetised.

2. A monostable electro-magnetic relay comprising a substantially U-shaped yoke having a winding on one limb of the U, the free ends of the U-limbs carrying first and second pole pieces, there being a third pole piece coupled to the yoke via a permanent magnet and defining with the first and second pole pieces two distinct air gaps, and an armature which has two legs lying in respective ones of the air gaps and which is coupled to a movable contact, there being a fixed contact cooperating with the movable contact for providing an open and a closed contact condition controlled by movement of the armature.

3. A relay as claimed in claim 1 or 2 wherein the armature is arranged to slide to and fro transversely of the limbs of the Ushaped yoke.

4. A relay as claimed in claim 2, wherein the movable contact spring is biassed by virtue of its inherent resilience, towards a central position intermediate the normally open and normally closed contacts.

5. A monostable electro-magnetic relay substantially as hereinbefore described with reference to and as illustrated in Fig. 1 and Fig. 1 as modified by Fig. 2 or Fig. 3 of the accompanying drawings.