GB2166594A - High sensitivity miniature electro-magnetic relay - Google Patents

Abstract

A miniature highly sensitive low power electro-magnetic relay has a 1-piece yoke (9) having a first limb (9B) extending through the energising winding and a second limb (9A) extending around the winding and parallel to the first limb, and an armature (11) extending within the winding. Energisation of the winding causes attraction of the armature towards the pole face (9C) on the limb (9A) and the attractive force is enhanced by a repelling force from the pole face (9D) of the limb (9B) which extends through the energising winding. This results in a more sensitive, low-power miniature relay, also having a particularly low profile (7.5 mm). <IMAGE>

Description

SPECIFICATION High sensitivity miniature electro-magnetic relay This invention relates two miniature electro-magnetic relays, particularly one with high sensitivity.

Aconventional electro-magnetic relay has a yoke, a winding, and a moveable armature which, when the winding is energised, is attracted towards a pole face on the yoke and this movement is used to actuate one or more moveable contacts to change contact conditions.

It is an object ofthe present invention to increase the force available at least over part ofthe operation of the relay.

According to the present invention there is provided an electro-magnetic relay comprising an energising winding, an armature extending through the winding, and yoke providing a pole face cooperating with one end ofthe armature to attractthe armature towards the pole face on energising the winding to change the electrical condition of contacts associated therewith, characterised in thatthe yoke includes a portion extending through the winding and providing a second pole face which acts to repel the armature on energisation of the winding to enhance the attractive force ofthe first pole face.

In orderthatthe invention can be clearly understood reference will now be made to the accompanying drawings in which Fig. lisa somewhat diagrammatic horizontal section through a miniature DIL relay according to an embodiment of the present invention; Fig 2 shows the armature of the relay of Fig. 1; Fig 3 shows in perspective the armature and comb of the relay of Fig. 1; Fig 4 shows the comb ofthe relay of Fig 1; Figs, 5A and 5B show respectively a plan and side diagrammatic illustration of the base and terminals of the relay of Fig. 1, and Fig 6 is a graph of force versus distance for the relay.

In the embodiment of the invention to be described the dual-in-line package ofthe relay is 10 mm wide, 20 mm long and about8 mum high.The contactforce is in the rangeof4to5gramsandthepowerconsumed by the relay is not more than 200 m.watts.

Referring to Fig. 1,the relay comprises a moulded plastics base 1 having a width of 10 mm and a length of 20 mm. It carries a pair of change over contact sets 2 and 3 comprising fixed contact terminals 2A, 2B, 3A, 3B and moving contact-springs 2C, 3C mounted on terminals 2D, 3D. Also fixed through the base 1 are winding terminals 4 and 5.

The motor unit has a bobbin 6 carrying a winding having connection tags 7 and 8 connected to the winding terminals 4 and 5, respectively, by soldering, during assembly. The motor unit also has a yoke 9 which is an integral 1-piece soft iron strip bent into shape shown butwith the limbs 9A and 9B defining respectivelyfirstand second pole faces 9C, 9D, sprung apartto allowthewound bobbin 6to be slid onto the yoke during manufacture ofthe motor unit The cheeks 6A and 6B of the bobbin are both recessed to receive the yoke 9 and a dovetail arrangement in cheek 6A ca n be used to lock the limb 9A in the position shown in the drawing, at least as a temporary measure until the motor unit is locked in place in the base 1, when stops 1A and 1 B lockthe yoke to provide the desired gap between polefaces9Cand 9D.

Acomb 10, shown in greaterdetail in Figs.3and4, has recesses 1 0A and 108 in the rear face which locate on corresponding projections 1 A and 118 of armature 11 which is located in the bobbin 6. The armature 11 pivots at its inner end 1 C. The shape ofthe armature is shown more clearly in Fig. 2.

The comb 10 has a pushing edge 1 for pushing the contact spring 2C and a pulling edge 1 OD for pulling the contactspring 3C.

In assemblingthe relaythe base 1 hasthethrough terminals and contact sets 2,3,4 and 5 formed from a lead frame (such as is described in British Patent Application No.8128565). Then the wound bobbin 6 has the yoke 9 inserted and located and at least temporarily dovetailed at cheek 6A. Then the armature 11 is inserted and the comb 10 fitted on the armature end so that the projections 1 1A and 11B locate in the recesses 1 OA, 1 or, respectively.

The thus completed motor unit is lowered down into the base 1 so that the yoke is locked and the comb engages springs 2C and 3C. Note the comb has sloping edge portions 1 0E, 1 OFto enablethe springs 2C, 3Cto be eased up onto the surfaces 100,108 respectively, and outwardly as the motor unit is lowered in.

A lid 12 (Fig 1) is fitted over the motor unit and onto the base 1 and sealed around its edge with epoxy resin.The lid edge reaches just beyond the bottom of the base to form a shallow well when the relay is upside down, which well is then flooded with epoxy resin to seal the edge of the lid to the base on the one hand and also seal the through-terminals into the base.

Referring nowto Fig. 6 there is shown a graph of force versus distance forthe relay which has been described, explaining how the relay achieved improved sensitivity for an input power not exceeding 200 m.watts and provides a particularly low profile package of approximately 7.5 mm.

Referring to Fig. 6, the graph shows the attractive force applied to an armature and how it changes with armature position as the armature moved from its rest position to a position adjacentthe pole face ofthe yoke. With the normally closed contacts 2B, 2C and 3B, 3C of the change over contact sets closed, and the armature at rest, the attractive force increases as shown by the curve Awhen the relay is energised and as the armature moves across and closes the normally open contacts 2A, 2C and 3A, 3C.

The lever spring force is shown by curve L. This force increases substantially linearly from the point where the normal "undertravel" has been taken up by the armature to the pointwherethe normally closed contacts just open. This occurs at point NC. The curve Lthen changes slope to a more gentle linearslope The drawing(s) originally filed was (were) informal and the print here reproduced is taken from a later filed formal copy.

until the normally open contacts ofthe two change overcontactsets just change to a closed condition at NO.

The curve Lthen proceeds up a steeperslope as the normally-open contacts ofthe relay having been closed, arethen pushed further into contactto achieve the required contact pressure at point C. The slope of this partofthe curve is similarto but not exactlythe same as thefirst partto NC.

Atanypoint along the curveAtheforce dueto the magnetism oftheelectro-magneta has to be greater than the spring force of any ofthe contact springs required to be moved. The effective force on the armature is a combination ofthe attractive force between the end of armature 11 and the poleface 9C on the one hand, as illustrated by curve A, and the force of repulsion between the end ofarmature 11 and the limb, particularlythe end portion 9D, ofthe yoke 9 as illustrated by curve Ron the graph. Curve R combines with curve Ato give the combined curve R+A and itcan be seen thatatall pointsthe force due to the combined curve is greater than the spring force of the contactsprings required to be moved, and illustrated by curve L.

Claims (5)

1. An eiectro-magnetic relaycomprising an ener gising winding, an armature extending through the winding, and a yoke providing a pole face cooperating with one end of the armature to attractthe armature towardsthe pole face on energising the winding to changetheelectrical condition of contacts associated therewith, characterised in that the yoke includes a portion extending through the winding and providing a second pole face which acts to repel the armature on energistion ofthewlndingto enhance the attractive force ofthe first pole face.

2. A relay asclaimed in claim 1, characterised in thatthe yoke consists of a one-piece strip bentto provide a first limb extending through the energising winding and a second limb extending outside the winding butsubstantially parallel to the first limb.

3. A relay asclaimed in claim 1 or2, characterised inthata comb is located on the armature and actuates a first moving contact by pushing and a second moving contact by pulling.

4. A relay as claim in any preceding claim, comprising terminals extending through a base of the relay and wherein the movement of the armature is transverse to the direction ofthe terminals.

5. A miniature electro-magnetic relay substantial ly as herein before described with reference to and as illustrated in the accompanying drawings.