GB2069761A - Electromagnetic relays - Google Patents

Abstract

An electromagnetic relay, operable by a current pulse to switch it between stable states, has a solenoid (4) for driving a magnetic core (5), the core being biased as by a tension spring 2 towards one stable state and having latching means (8) for latching with a latching element (17) biased by resilience of a switching arrangement (10 to 16) of the relay. <IMAGE>

Description

SPECIFICATION Relays This invention relates to relays and particularly concerns latching relays.

According to the present invention there is provided a relay comprising switch means, a solenoid, a magnetic core displaceable by energisation of the solenoid between first and second positions, corresponding to two states of the switch means, biasing means for biasing the core towards the first position, and resilient latching means for releasably latching the core in its second position, the arrangement being such that a first current pulse applied to the solenoid can drive the core from the first position to its second, latched, position and a second current pulse applied to the solenoid can apply force to the core to release the latching means and thus permit the biasing means to return the core to its first position.

The latching means may comprise two interlatchable parts one movable with, e.g. carried by, the core and the other being biased by resilience of the switch means. Thus the resilience of the switch means itself can provide the necessary latching pressure, while the latching means could simply be a notched member carried by the core and a latch member carried by, or at least biased by, a resilient element of the switch means. The core could be of rectangular section, e.g. square section, to engage in a former of like shape to guide the core and hold it against rotation.

It will be apparent that it is possible to provide a relay which can be actuated by a single pulse of current to drive the switch means to a stable switching state. The solenoid does not therefore need to be dimensioned to carry current for long durations to hold a switch open or closed.

Moreover, the relay does not require any cam or toggle to maintain a switching condition as it can be implemented by a simple latch and requires only a single motion of the core to produce one stable switching change.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figures 1 and 2 are diagrams of a latching relay; and Figure 3 is a cross-section of another latching relay.

Figures 1 and 2 illustrate the basic form of one embodiment of latching relay which has two stable switching states and which can be switched between these states by a pulse of current.

The relay comprises a plastics former in the form of a hollow, square-section, cylinder 1 across one end of which is a bar 2 to which a spring 3 is attached. The cylinder 1 supports a coil or solenoid 4.

A soft iron core 5 of square cross-section is slidably mounted in the cylinder 1 and is biased to the right (as seen in Figures 1 and 2) by the spring 3.

The left-hand end of the core carries a latching element 6 having a ramp 7 and a shallow latching slot 8.

A spring strip 9 is secured at 10 relative to the cylinder 1 and carries contacts 11 and 12 at its other end. Strip 9 is so formed as to provide a second latching element 17. In the switching state shown in Figure 1, contact 11 makes contact with a contact 13 carried by spring strip 14, but is spaced from a contact 15 carried by spring strip 16.

When coil 4 is energised by a current pulse of sufficient amplitude and duration, core 5 is pulled to the left, being given sufficient momentum to pass through the coil to the position shown in Figure 2. As shown by dotted lines in Figure 1, ramp 7 will meet latching means 17 during this motion, causing strip 9 to rise and subsequently drop into slot 8, in which state contacts 11 and 13 are separated and contacts 12 and 15 touch. This is the second stable switching state of the relay. The tension in spring 3 is insufficient to oppose the resilient force of strip 9 holding element 17 in slot 8.

A further current pulse applied to coil 4 overcomes the resilience of strip 9 and so pulls the core back into the coil, spring 3 ensuring that the first stable position shown in Figure 1 is reattained.

It will be appreciated that this design provides a relay of relatively few parts which can be switched between states by a current pulse and which is therefore suitable for actuation by digital circuits.

Moreover coil 4 need not be designed for high loading, especially as the short duration of the current pulse does not require provision for high heat dissipation. A magnetic return path is also not required. In consequence, this relay can be relatively small, e.g. it might have a total length of 44 mm and a total width of 17 mm, including strip 9 and its contact or contacts. The current pulse can be derived by triac or thyristor control from the mains of which a half-cycle is adequate to change the relay state.

In fact, the masses and resiliences in the relay can be chosen so that during one half-cycle of the mains the core is moved from its first stable position through a symmetrical position relative to the coil, attaining this position substantially at the end of the half-cycle, and then continuing its motion to reach the second stable state substantially at the next mains zero-crossing.

Figure 3 shows a further embodiment of latching relay in which like parts have been given the same numerals as in Figures 1 and 2.

A plastics former 1 has a substantially rectangular section bore 18 in which a soft iron cylinder 5, also of substantially rectangular form, is slidably mounted.

Spring 3 is attached to the cylinder 5 by a rod 19 which engages at its ends in cylinder 5 and passes through a plastics latching element 6.

The latching element 17 is in this case a separate plastics member having a projecting rib 20 and slidably mounted in a rectangular-section boss 21.

Rib 20 prevents element 17 from entering bore 18 beyond substantially the centre of the bore.

The operation of this embodiment is as described in relation to Figures 1 and 2.

Claims (9)

1. A relay comprising switch means, a solenoid, a magnetic core displaceable by energisation of the solenoid between first and second positions, corresponding to two states of the switch means, biasing means for biasing the core towards the first position, and resilient latching means for releasably latching the core in its second position, the arrangement being such that a first current pulse applied to the solenoid can drive the core from the first position to its second, latched, position and a second current pulse applied to the solenoid can apply force to the core to release the latching means and thus permit the biasing means to return the core to its first position.

2. A relay according to claim 1, wherein the latching means comprises two interlatchable elements one movable with the core and the other biased by resilience of the switch means.

3. A relay according to claim 2, and comprising a solenoid former in which the core is displaceable and the switch means comprises a resilient switch element attached to the former and providing said resilience.

4. A relay according to claim 2 or 3, wherein said other element is secured to the switch means.

5. A relay according to claim 2 or 3, wherein said other element is movably mounted separately from the switch means.

6. A relay according to claim 2,3,4 or 5, wherein said one element is a member having a notch to receive the other element.

7. A relay according to claim 6, wherein said one element has a ramp to engage, and thus displace, the other element as the core moves to the second position.

8. A relay according to any one of the preceding claims, wherein the core is of substantially rectangular cross-section and is slidably mounted in a guide of like cross-section to hold the core against significant rotary motion.

9. A relay substantially as hereinbefore described with reference to Figures 1 and 2 or Figure 3 ofthe accompanying drawings.