Improvements in or relating to relays

Abstract

 A relay includes an electromagnet and an armature (8') for causing a displacement of a pair of spring arms (20') in a respective sense in dependence on energisation or de-energisation of the electromagnet. Each spring arm is arranged to make an electrical connection between one member of a respective set of contact members and, in dependence on the sense of displacement, a selected one of two other members (14',15') in the same set. A trip plate (9') mounted on the armature, acts on both spring arms and has a protrusion (32) which permits pivotal movement of the trip plate relative to the armature: the spring arms are subjected to substantially equal amounts of pressure as they are displaced.
The protrusion may have a convex surface (32) or may comprise a pair of flat surface which meet at an apex to establish a pivot.

Description

[0001] This invention relates to relays and it relates especially, although not exclusively, to miniature relays of the kind used in printed circuit board layouts.

[0002] Figure 5 of our copending British Patent application, Publication No. 2121605 illustrates a side sectional view of a relay. This Figure is shown at Figure 1 of the present application.

[0003] As described in the above-mentioned copending application the relay includes an electromagnetic assembly within a rectangular, plastics material housing 1. The assembly comprises an electromagnet in the form of coil 6 surrounding a magnetic core 2 supported by a yoke 3. The coil is supported on a plastics material bobbin 5 the end portion of which is provided with two protrusions, one at each side of the housing, for anchoring a respective coil lead. One such protrusion is shown at 7. An armature is mounted pivotally on the yoke and a trip plate 9 is mounted fixedly at the end of the armature, remote from the pivot. Two sets of four electrically conductive contact members are provided, one at each side of the housing and each contact member has a terminal pin at one end for connection to a printed circuit board and an electrical contact at the other end. The terminal pins of one set are shown at 18a, 18b, 18c and 18d and the corresponding electrical contacts are shown at 15, 14, 16 and 17 respectively. Contact 17 of each set is connected electrically to a respective lead of coil 6 and electrical power is supplied to the coil via terminal pin 18d to actuate the relay. Pin 18c of each set can be connected electrically to a selected one of pins 18a and 18b in dependence on the position of a respective spring arm 20 which is mounted fixedly on contact 16, at one end, and rests in a normally closed position on contact 15 at Jne other end, thus connecting pin 18c to pin 18a. When electrical power is supplied to the coil to actuate the relay, end 8a of armature 8 is attracted magnetically towards end .2a of core 2 causing the armature to execute a pivotal motion. This movement raises trip plate 9 which, in turn, displaces spring arm 20 and maintains it, in the open position, against contact 14, thus connecting pin 18c to pin 18b. A return spring 10 is provided to lower armature 8, and thus trip plate 9, when coil 6 is denergised allowing spring arm 20 to return to the closed position.

[0004] As shown in the end elevation view of Figure 4 of the above-mentioned copending application the same armature and trip plate are used to act on both spring arms 20 on opposite sides of the housing. In practice it has been found that, under certain operating conditions and after repeated use of the relay one of the spring arms 20 may fail to close its normally open contact on actuation of the relay. It is an object of the present invention to provide a relay wherein the above-described problem is substantially alleviated.

[0005] Accordingly there is provided a relay comprising an electromagnet mounted in a housing, a first set of electrically conductive contact members arranged adjacent to a wall of said housing and a second set of electrically conductive contact members arranged adjacent to the opposite wall of the housing, an armature for causing displacement of a pair of spring arms in a respective sense, dependent on energisation or de-energisation of the electromagnet, each spring arm being arranged to establish an electrical connection between one member in a respective set of contact members and, in dependence on the sense of a displacement caused by the armature, a selected one of two other members in the same set, characterised in that a trip plate is mounted on said armature so as to act on both spring arms and is capable of undergoing a pivotal movement on the armature so as to subject the spring arms, as they are displaced, to substantially equal amounts of pressure.

[0006] In a preferred embodiment, a surface of the trip plate has a protrusion which contacts said armature to allow said pivotal movement. Alternatively, the armature may be provided with a protrusion to permit such pivotal movement.

[0007] Specific embodiments of the present invention are now described, by way of example only, by reference to the remaining Figures of the accompanying drawings of which Figure 2 shows an end elevation view of a relay,

Figures 3a and 3b show respective end elevation and perspective views of the trip plate shown in Figure 2,

Figure 4 shows a perspective view of the end of the armature on which the trip plate of Figures 3a and 3b is mounted,

Figure 5 shows an end elevation view of another form of trip plate,

Figure 6a shows an end elevation sectional view of an alternative form of trip plate and armature,

Figures 6b and 6c show perspective views of the trip plate and armature respectively, and

Figures 7a and 7b respectively show perspective views of a yet further form of armature and trip plate.

[0008] The electromagnetic assembly (not shown in Figure 2), the armature 8' and the electrical contacts, shown by way of example at 14' and 15', are constructed, and assembled in the housing (shown schematically at 1') as described in our copending British Patent application , Publication No. 2121605.

[0009] The trip plate 9', however, is mounted freely on the armature 8' and, as shown in Figures 2 and 3, is provided at surface 31 thereof, which contact the armature, with a protrusion in the form of a dome 32. This allows the trip plate to pivot on the armature thereby to offset any pressure difference to which the spring arms 20' may otherwise be subjected. The trip plate is held in place lengthwise on the armature partly by the downward force of spring arms 20' and partly by providing slots in the armature. as shown at S in Figure 4, and/or in the trip plate. Figure 5 shows an alternative form of trip plate in which a protrusion 51 is formed by a pair of flat surfaces 52, 53 which are inclined to one another and meet at an apex A to form a pivot.

[0010] As shown in Figure 6a, instead of providing a protrusion on the trip plate it may be provided on the armature. In the illustrated example the protrusion is in the form of a hemispherical done 61 which seats in a complementary depression 62 in the underside of the trip plate. Perspective views of the armature and trip plate are shown in Figures 6b and 6c respectively. As shown in the perspective views of Figure 7a the end 71 of the armature 70 may be shaped to fit snugly within a complementary channel 72 formed in the. trip plate of Figure 7b. Again this serves to hold the trip plate in place on the armature.

[0011] In an alternative embodiment a trip plate, in accordance with any one of the above described examples, is provided with grooves in opposite side edges. In an initial stage of assembly the plate is mounted slidably on the spring arms, an edge of each arm being received in a respective groove. By upending the relay the trip plate is allowed to slide along the spring arms, thus tending to bring the arms into substantial alignment.

[0012] This arrangement permits relative movement of the trip plate on the armature to equalise pressure on the spring arms while also maintaining the spring arms in substantial alignment.

Claims

₁. A relay comprising electromagnet (6, 2, 3) mounted in a housing (1), a first set of electrically conductive contact members arranged adjacent to a wall of said housing and a second set of electrically conductive contact members arranged adjacent to the opposite wall of the housing, an armature (8' ) for causing displacement of a pair of spring arms (20') in a respective sense, dependent on energisation or de-energisation of the electromagnet, each spring arm being arranged to establish an eleconical connection between one member (16) in a respective set of contact members and, in dependence on the sense of a displacement caused by the armature, a selected one of two other members (14', 15') in the same set, characterised in that a trip plate (9') is mounted on said armature (8) so as to act on both spring arms and is capable of undergoing a pivotal movement on the armature so as to subject the spring arms (20'), as they are displaced, to substantially equal amounts of pressure.

2. A relay according to Claim 1 characterised in that a surface (31') of said trip plate (9') has a protrusion (32') which contacts said armature (8') to allow said pivotal movement.

3. A relay according to Claim 1 characterised in that said armature (8') has a protrusion (61') which contacts the trip plate (9') to allow pivotal movement.

4. A relay according to Claim 2 or Claim 3 characterised in that said protrusion (32') has a generally convex surface.

5. A relay according to Claim 2 or Claim 3 characterised in that said protrusion (51) comprises a pair of generally flat surface (52, 53) which meet at an apex (A) to establish a pivot.

6. A relay according to any one of claims 1 to 5 characterised in that said armature and/or trip plate is provided with means for locating the trip plate on the armature.

7. A relay according to any one of Claims 1 to 6 characterised in that said trip plate is mounted slidably on said sprung arms.

Drawing