GB2331402A - A manually resettable relay - Google Patents

Abstract

A manually resettable relay comprises a housing 10 accomodating at least one pair of electrical contacts 12, 14. A ferromagnetic body 26 has a bobbin 40 mounted thereon with a coil 34 wound around the bobbin. A manual reset button 28 is integral with the bobbin and in register with an aperture 36 in the housing. The ferromagnetic body 26 is displaceable in the housing, by pushing the reset button 28, to close the relay. The position of the ferromagnetic body 26 in the housing, and hence the position of the reset button 28 relative to the aperture 36, differs according to whether the relay is open or closed and hence indicates the state of the relay.

Description

1 A MANUALLY RESETTABLE RELAY 2331402 This invention relates to a manually

resettable electro- mechanical relay.

Electro-mechanical relays typically comprise a bobbin on which is wound a coil, a ferromagentic core and plate, and moving contact(s). In general, relays are more commonly closed or opened automatically by the presence or absence of current flow through the coil. However, in some cases, it is desirable to manually close or open the relay, and in such cases, manual reset means must be provided for this operation. In addition, it is desirable to know the state of the relay (closed or open) at any given time, and means for indicating these states are also required for this purpose.

The manual closing operation usually requires the movement of a moving contact from a first (open) position to a second (closed) position where it comes into contact with a fixed contact. This usually requires some form of separate reset button which has to be mechanically coupled to the moving contact. The indicating means usually involves the mechanical coupling of a flag to the moving contact such that the position of the flag indicates the open or closed states.

This usually requires a separate flag indicator which has to be mechanically coupled to the moving contact. In addition, to provide the indicating means in various applications of the relay, it may be necessary to provide a special "window" through which the flag indicator can be seen.

The requirement for a separate reset button and flag indicator impacts adversely on the relay in terms of the number of parts, size, piece part, assembly costs and other factors. In addition, when the flag indicator is mechanically coupled to the moving contacts, it can adversely impact on the movement of the moving contacts.

2 It is the purpose of the present invention to provide an improved relay in which these disadvantages are mitigated in a cost effective manner.

Accordingly, the present invention provides a manually resettable relay comprising a housing accomodating at least one pair of electrical contacts, a ferromagnetic body having a bobbin mounted thereon with a coil wound around the bobbin, and a manual reset member integral with the bobbin and in register with an aperture in the housing, the ferromagnetic body being displaceable in the housing, by pushing the manual reset member, to close the pair of contacts, wherein the oosition of the:Eerromagnetic body in the housing, and hence the position of the reset member relative to the aperture, differs according to whether the pair of contacts is open or closed and hence indicates the state of the relay.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figs. 1A and 1B are schematic front and side views respectively of a relay according to a f-'rst embodiment when the contacts are open; Figs. 2A and 2B are schematic front and side views respectively of the relay of Figs. 1A and 1B when the contacts are being reset to the closed state; Figs. 3A and 3B are schematic front and side views respectively of the relay of Figs. 1A and 1B when the contacts are closed; Fig. 4 shows a bobbin with an integral reset button; and 3 Figs SA and 5B are schematic side views, equivalent to those of Figs. 1B and 3B respectively, of a relay according to a second embodiment of the invention.

References herein to expressions such as clockwise, anticlockwise, upper, lower and the like refer to the orientation of the relay as shown in the figures, and is not to be construed as a limitation on its orientation in use.

Referring now to Figs. 1 to 4 of the drawings, the relay -s accomodated in a housing 10 of which on-Ly one representative outside wall 101 is shown, and includes two pairs of upper and lower contacts 12 and 14. Each contact 12 is located each above a resDective one of the contacts 14. The upper contacts 12 are fixed within the housing 10, whereas the lower contacts 14 are mounted for movement between a first, lower, position (Fig. 1) and a second, upper, position (Fig. 31'. In particular, each contact 14 is mounted near the free end of a respective arm 16 pivotted at one end 18 so that each contact 14 moves from its first to its second position by rotation of the respective arm 16 in an anti-clockwise direction about the pivot 18. The two arms 16 are tied together for common pivotal movement by means (not shown) which extends transversely between the arms and includes a ferromagnetic body 20.

When it is in its first, lower, position each contact 14 is out of engagement with the respective overlying contact 1.2 so that the contact pairs 12, 14 are open (Fig. 1), whereas when it is in its second, upper, position each contact 14 engages the respective overlying contact 12 and the contact pairs 12, 14 are closed (Fig. 3). A tension spring 22 connected between the body 20 and a fixed point 24 inside the housing 10 -resiliently urges the contacts 14 into their first position so that the contact pairs 12, 14 are normaIlly maintained open as seen in Fig. 1. Instead of using a 4 separate tension spring 22 to bias the contacts 14, the arms 16 carrying the contacts 14 could be made of spring material and fixed at their ends 18 so that -he contacts 14 are urged into their first position by the inherent resilience of the arms 16.

The relay further includes a U-shaped ferromagnetic yoke 206, the free ends of which are indicated at 26A and 26B in Eigs. 1A, 2A and 3A. The yoke 26 is mounted in the housing 10 for 10 vertical movement beween a first, upper, position (Fig. 1) to a second, lower, position (Fig. 2). A moulded plastic bobbin 40 is mounted around one arm of the yoke 26 and a coil 34 is wound around the bobbin 40, such that when a current is passed through the coil 34 a magnetic field is generated 15 within and around the yoke 26. A reset button 28 is moulded integrally with one end of the bobbin 40 and is in register L with an aperture 36 in the housing wall 10'.

A further tension spring 32 connected between the bobbin 40 (or the other arm of the yoke 26) and the interior of the waIl 10' resiliently urges the yoke 26 into its first 1) so that the voke is normallv retained in position (Fig that position. However, by manually depressing the reset button 28 the yoke can be pushed down against the bias of the spring 32 to its second position (Fig. 2), where its free ends 26A and 26B engage the body 20. Similarly to the contacts 14, instead of using a separate tension spring 32 the yoke 26 may be mounted on a spring arm (not shown) which has the necessary inherent resilience to bias -he yoke -into its first position.

The operation of the relay wi'Ll now be described.

Fig. 1 shows the relay and its various components _in an initial open position. The voke 26 is held in its first, upper, position by the spring 32, and the reset button 28 projects through the aperture 36 in the housing wall 10' to stand proud of the housing. The contacts 14 are held in their first, lower, position by the spring 22 so that the contact pairs 12, 14 are open.

If now the reset button 28 is depressed, as shown in Fig. 2, it pushes the yoke 26 downwardly against the bias of t_he spring 32 from its first to its second position and brings the ends 26A, 26B of the yoke into engagement with the body 20 thereby closing a magnetic circuit through 26A-20-26B which holds the body 20 and the yoke 26 together. Where the yoke 26 and body 20 are not permanent magnets, or are insufficiently permanently magnetised to hold the yoke and body together against the bias of the springs 22 and 32, the 15 magnetic holding force can be provided by passing a sufficient current through the coil 34. On the other hand, if the yoke 26 and/or the body 20 are sufficiently permanently magnetised the magnetic holding force may be provided by these alone without the need for a current in the 20 coil.

When the reset button 28 is released, the yoke 26 moves upwardly towards its first, upper, position under the tension of the spring 32, and in so doing entrains and draws with it -the bodv 20, and hence the contacts 14, upwardly against the tension of the sr)ring 22. However, when the contacts 14 come into engagement with the fixed contacts 12, that is, when they are in their second, upper position (Fig. 3) and th-e contact pairs 12, 14 are closed, the yoke 26 is prevented from rising any further with the result that the reset button 28 also stops short of its initial position. As long as the magnetic circuit remains closed, the reset button 28 remains depressed in relation to its initial position and the voke is held in a position intermediate its first, upper, pcs--ion and its second, lower, position.

6 When the magnetic holding force between the yoke 26 and the body 20 is sufficiently reduced or removed, the movable contacts 14 will revert to their first position (Fig. 1) due to the tension of the spring 22, thereby opening the contact pairs 12, 14 and likewise the yoke 26 will revert to its first, upper, position (Fig. 1) due to tension in the spring 32, returning the reset button 28 to its initial position.

If the magnetic holding force is produced by a current passing through the coil 34, the contacts can be opened by removing or reducing the coil current until the magnetic holding force is overcome by the tension of the springs 22 and 32 acting in opposite directions az which point- the body 20, movable contacts 14, voke 26 and reset button 28 w--'-" revert to their inLt'l_al (Fig. 1) positions. On the other hand, if the magnetic holding force is produced by use of a permanent magnet body 20 and/or voke 26, the contacts can be opened by passing a current through the coil 26 such as tc create an opposing magnetic force which reduces the net magnetic holding force to a level which is overcome by the tension of the s-orings 22 and 32 acting in opposite directions.

The tension in 1Che spring 32 exerts an upwards force in opposition to the magnetic holding force between the yoke 26 and the body 20 whereas the tension in the spring 22 exerts downwards force in opposition to the magnetic holding force between the yoke and the bodv. Thus, the two springs 2-'2 and 32 act in combined opposition to the magnetic holding force such as to force the voke 26 to seoaral--e from the body 2,' when the magnetic holding force is reduced.

a we- known that magnetic circuits suffer frorr. resdua' magnetism whereby the magnetic force is not reduced to zero w-ien a magnetis-Jr.g current is removed from the coil. -Lrl addition, the force exerzed by spring tension can weaken over 7 time due to ageing of the spring. As a result of this residual magnetism and the reduction in spring tension due to ageing, there is an increasing risk that the magnetic circuit will not be opened when the magnetising current is reduced to zero. The present embodiment substantially reduces this risk by using two separate spring tensions to act against the magnetic holding force.

The spring 32, through the bobbin 40 or yoke 26, also acts to move the reset button 28 from its intermediate position (Fig. 3) when the contacts 12, 14 are closed to its initial position (Fig. 1) when the contacts are open. These two positions of the reset button 28 provide an indication whereby the open and closed states of the relay are clearly discernible to the user. In this embod-iment,when the contacts are ocen the reset button 28 is proud of the housing 10 as shown in Fig. 1, whereas when the contacts are closed the reset button is flush with or recessed into the housing 10 as shown in Fig. 3.

The relay is trip free in that holding the reset button 28 (and hence the yoke 26) in the Fig. 3 position when the contact pairs 12, 14 are closed will not prevent the contacts from separating when the magnetic holding force is reduced because the moving contacts 14 are free to move independently of the reset button under this condition.

Figs. 5A and 5B show a relay according to a second embodiment of the invention which differs from the first embodiment only in the provision of a second pair of fixed contacts 50. These additional fixed contacts 50 are each immediatelv below a respective one of the movable contacts 14. When the pairs of contacts 12, 14 are open, Fig. 5A, each contact 1 engages the respective contact 50, so that electrical cont- act is established between the contact pairs 14, 50. However, when the pairs of contacts 12, 14 are closed, Fig. 5B, whicl--,- is 8 brought about in exactly the same manner as described for the first embodiment, each contact 14 disengages the respective contact 50, so that electrical contact is broken between the contact pairs 14, 50. Thus the second embodiment p-rovides a changeover operation whereby when the contact pairs 12, 14 are open the contact pairs 14, 50 are closed and vice versa.

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Claims (8)

1. A manually resettable relay comprising a housing accomodating at least one pair of electrical contacts, a ferromagnetic body having a bobbin mounted thereon with a coil wound around the bobbin, and a manual reset member integral with the bobbin and in register with an aperture in the housing, the ferromagnetic body being displaceable in the housing, by pushing the manual reset member, to close the pair of contacts, wherein the position of the ferromagnetic body in the housing, and hence the position of the reset member relative to the aperture, differs according to whether the pair of contacts is open or closed and hence indicates the state of the relay.

2. A relay as claimed in claim 1, wherein the at least one pair of electrical contacts are normally open contacts of which at least one contact is movable relative to the other contact to open and close the relay, and wherein the housing further accomodates a biassing means urging the first ferromagnetic body into a first position when the contacts are open, the ferromagnetic body being displaceable against the action of the biassing means, by pushing the manual reset member, from the -first position to a second position where the first ferromagnetic body can magnetically entrain a second ferromagnetic body associated with the movable contact and, upon release of the manual reset member, bring the movable contact into engagement with the other contact to close the relay, the first ferromagnetic body being retained in a position intermediate the first and second positions when the relay is closed and only returning to the first position when the relay is open.

3. A relay as claimed in claim 2, wherein the reset member stands proud of the housing in the first position of the first ferromagnetic body and is substantially flush with or recessed into the housing in the intermediate position of the first ferromagnetic body.

4. A relay as claimed in claim 2 or 3, further including a second biassing means urging the movable contact into a first position so as to maintain the contacts normally open, wherein the first ferromagnetic body brings the movable contact into engagement with the other contact against the action of the second biassing means to close the relay, and wherein the first ferromagnetic body is retained in the intermediate position by such engagement preventing return o-f the first ferromagnetic body to its I1J1-rst position, the relay being opened by reducing the magnetic hold-ing force between the and seccnd ferromagnetic bodies sufficiently release the movable contact to permit the movable contact and the first ferromagnet-ic body each to return to its respective first position under the action of the respective biass-'ng means.

5. A relay according to claim 4, wherein the first and second ferromagnetic bodies are unmagnetilsed or insufficiently permanently magnetised to effect entrainment of the second ferromagnetic body, a current being passed through the coil for entraining the second ferromagnetic body and the current being removed or substantially reduced to trip the relay and permit the said one contact to return to the first position.

6. A relay accord-Jng to claim 4, wherein at least one of the first and second ferromagnetic bodies is sufficiently permanently magnetised to effect entra.'nment of the second ferromagnetic body in the absence of a current in the coil, a current being provided in the coil in opposition to the magnetic holding force to open the relay and permit the said one contact to return to the first pos-'tion.

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7. A relay according to any of the claims 2 to 6, including a further electrical contact which is engaged by the movable contact when the said pair of electrical contacts are open and which is disengaged by the movable contact when the said pair of electrical contacts are closed.

8. A manually resettable relay substantially as described hereinbefore with reference to the accompanying drawings and as shown in either Figures 1A, 1B, 2A, 2B, 3A, 3B and 4 of those drawings or in Figures SA and 5B of those drawings.