GB1564637A - Sealed polarised electromechanical relay - Google Patents

Description

(54) A SEALED, POLARISED ELECTROMECHANICAL RELAY (71) We, THOMSON-CSF, a French Body Corporate, of 173, Boulevard Haussmann, 75008 Paris - France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the followmg statement: The present invention relates to the field of polarised electromagnetic relays. Devices of this kind behave in principle like electrically controlled mechanical switches. the motive force for switching being produced by one or more electromagnets.

In the magnetic circuit of these electromagnets a permanent magnet is arranged whose presence has the advantage of making it possible to effect drive in two directions by the simple reversal of the direction of the control current applied to the terminals of the electromagnet or electromagnets.

These relays effect physical contacts and their service life is therefore dependent upon environmental conditions which may bring about a deterioration in the quality of these contacts, for example atmospheric humidity, corrosive atmosphere. dust etcetera.

It is for this reason that these relays are normally arranged in a closed and sealed metallic environment where a chemically neutral atmosphere has been established.

thus maintaning the qualities of the relay which it protects, over a period of time This gives rise to the need to electrically connect the working elements of the relay across the walls of the enclosure and this in turn means the use of terminals which are insulated in relaton to these walls and themselves sealed. For this purpose. wide use is made of lead-through terminals constituted by a segment of wire conductor representing the current lead-through and surrounded at its central part bv a block or "bead" of glass representing the insulator.

The use of this kind of terminal in the wall of the enclosure involves an operation of bonding between the glass of the bead and the metal of the wall so that a perfect seal is achieved provided that perfect compatibility or sealability is obtained between the materials which are to be soldered. Use is normally made of ferromagnetic alloys in order to form that region of the closed enclosure in which the lead-through terminals are located, these alloys having excellent properties of solderabilitv.

A typical relay manufactured in this way is therefore constituted. from the structural point of view, on the one hand by a magnetic circuit comprising one or more permanent magnets, with a fixed yoke and a moving armature to operate the electrical contacts, and on the other hand by one or more electrical circuits in the form of windings which do dutv as drive elements, and. finally. by a closed casing, generally in at least two parts, the walls in one of the parts, being made of ferromagnetic material for the reasons indicated earlier, containing lead-through terminals insulated by glass beads fused to this part.

In practice. as will be explained in more detail later on, the two-part enclosure takes the form of a flat base of plate around whose periphery the insulated lead terminals are arranged, and a hollow cover whose edges are applied against the edge zone of the base where they are soldered in position.

Although this fundamental structure provides satisfactory results in industrial applications on the dimensional scale encountered in electrical engineering work, it has serious drawbacks, such indeed as sometimes to make it impossible to use it, in the increasing number of cases of applications where miniaturisation is essential. for example. applications to printed circuit boards in particular of the hybrid circuit kind. and the situation is even more serious when their simultaneous use with integrated circuits is envisaged.

In this case, it is virtually out of the question to use them unless the volume of the thus miniaturised electromechanical relays is of the same order of magnitude or better still exactly the same, as that of an integrated circuit housed in a standard casing: their field of application then substantially competes with solid-state devices, for example devices of the thyristor kind, since in this area they have the advantages over the latter of a negligible voltage drop at the time of conduction and of perfect insulation between the control circuit and the controlled circuit.

However, satisfying this kind of condition has run up against serious difficulties in the case of composite electromechanical relays of the kind described earlier. This area of difficulty has to do with the appearance of an unwanted parasitic effect which becomes increasingly marked as the dimensions of the relay assembly reduce, namely the development of a magnetic leakage flux crossing between the working magnetic circuit of the relay and the magnetic base of the sealed enclosure.

This kind of effect limits the minimum relay dimensions which are compatible in practice with correct operation, and in addition means that in order to impart sufficient sensitivity to the relay, the electrical windings and magnets have to be oversize.

In fact, dimensional interchangeability with integrated circuits accommodated in housings, is not achieved.

In order to attempt to escape from this restriction. it has been proposed that the base region in which the insulated leadthroughs are located, should be made of an non-magnetic metallic material such as stainless steel or a ferrous alloy containing nickel and chromium.

The success of this kind of substitution has been compromised in practice by the poor soldering properties of stainless steels of this kind, this giving rise to a high reject rate in manufacture and in the longer term after manufacture due to sealing defects at the glass-metal junctions in the enclosures or casings thus formed.

The invention which forms the object of this patent is not open to these drawbacks.

In principle, the invention assigns to the base (which already, in forming part of the casing, performs a first function of protecting the relay and a second function of supporting insulated lead-through terminals) a third function, that of carrying the working magnetic flux. this kind of combination of functions promoting the attainment of the common, advantageous aim of reducing the geometric dimensions of the relay whilst improving its efficiency.

According to the invention, there is provided a sealed, polirised electroniagnetic relay comprising a two part sealed casing formed respectively by a base equipped with sealed lead-through electrical terminals, and a cover, a plurality of fixed contact elements and moving contact elements, a plurality of electrical control coils, the fixed contact elements, the moving contact elements and the control coils being connected to said terminals, and a magnetic circuit couplcd to the said electrical coils and constituted on the one hand by a fixed part, said fixed part of the magnetic circuit being constituted hy said base, and comprising a three parallel limb structure, namely two lateral limbs, and a central limb made of a permanent magnet linked by a common member, and on the other hand by a moving part, capable of pivoting about an articulation under the control of said coils, said moving part being constituted by a bar forming, with the free end of the two lateral limbs, two air-gaps, and capable of pivoting about its centre, wherein said articulation is constituted by a device of the knife-edge and groove kind, said groove being formed in said bar, and said knife-edge being carried by that of the two ends of the permanent magnet which is located remote from said common member, The invention will be better understood from a consideration of the ensuing description and reference to the attached figures in which: Figure 1 schematically illustrates an electro-magnetic relay of prior art design; Figure 2 illustrates an explanatory diagram of the relay shown in Figure 1; Figure 3 illustrates an electromechanical relay in accordance with the invention Figure 4 illustrates an explanatory diagram of the relay shown in Figure 3.

Viewed in perspective, Figure 1 illustrates an electro-mechanical relay of prior art design.

This relay has a base 1 with flanges 2 to which there can be fitted and soldered the complementary flanges carried by a cover (not shown); a combination of these elements constitutes a sealed protective enclosure or casing. The base carried leadthrough terminals 3 insulated by glass beads 4.

The active part of the relay is attached to the base and is constituted by a magnetic circuit part of which is of moveable design, by an electrical control circuit and by a plurality of controlled contact elements.

The magnetic circuit is constituted by a fixed part of double-U shape 5 and 6, and by a moving part with two arms, 7 and 8, which can pivot about a pivot 9 after the fashion of a rocker, this constituting in association with a fixed part. two elementary closed magne tic circuits.

Two air-gaps 27 and 28 make it possible for the bar to pivot between two limits. In the common arm of the two U-shaped circuit portions, a magnetised bar 20 is arranged.

The electrical circuit is constituted by two coils 10 and 11 whose windings encircle part of each of the two elementary magnetic circuits 5, 7 and 6, 8. The coils can be arranged at 10 and 11 in the fixed part of the magnetic circuit, as shown in Figure 1 in dotted fashion in order to improve clarity.

They may be arranged around the yoke, like the coil 12, also shown in dotted line for the same reason, around the arm 6, the other coil, around the arm 5, having been omitted in order to simplify the illustration.

Finally, the plurality of controlled contact elements has been shown on the one hand in the form of the leaf-springs 13 and 14 which can be operated by the moving bar 7, 8 through the insulated actuators 15 and 16.

attached to it, and on the other hand by the fixed contact springs 17 and 18 arranged opposite the moving end of the springs 13 and 14. The moving bar 7, 8 is maintained in equilibrium at an equal distance from the two fixed parts of the magnetic circuits, the air-gaps 27 and 28 consequently having the same size, under the opposing actions of the two leaf spring contacts 13 and 14 in the absence of any magnetic flux due to the magnetised bar. The operation of this kind of relay can be appreciated from a consideration of Figure 2.

Figure 2 schematically illustrates a relay of the type shown in Figure 1 seen in section, illustration being in the form of an explanatory operating diagram. The same reference numbers have been given to the same elements in the relay and the contacts have been omitted in order to clarify the illustration; the relay can occupy the following two states.

When the coils 10 and 11 are not being supplied with electrical power, the bar 7 rests on one of the two pole faces, and one of the two contacts is made.

The magnetic fluxes developed by the magnet 20 split equally between the two elementary magnetic circuits and their lines of force are indicated by the full-line arrows 30.

When the coils 10 and 11 are supplied with electrical power in directions such that they create oppositely directed magnetic fluxes in the air-gaps 27, 28, the fluxes thus created are added to that already created by the magnet 20 in the open air-gap. and subtracted from that alreadv created in the other air-gap which is closed, so that the bar pivots. The lines of force of the correspond mg magnetic fluxes have been shown in dotted fashion.

The moving bar rotates and the corresponding controlled electrical contacts are closed.

By reversing the direction of application of the voltages to the coils, the symmetry of the structure beings about pivoting of the moving bar in the other direction with closure of the corresponding other electrical contacts.

However, the attractive force exerted on the moving bar by one of the two air-gaps increases as the air-gap size reduces and is maintained after the disconnection of the controlling voltage due to the presence of the permanent magnetic flux developed by the magnet 10. The relay created in this way is therefore a symmetrical, bistable relay.

It should be pointed out that any means used to upset this symmetry, for example the arrangement of a block of nonmagnetic material in one of the air-gaps, would create an asymmetric, monostable relay. In a relay of this kind, control is performed without recourse to any reversal in the direction of application of the voltage; in the absence of any control voltage the bar has a stable or "rest" position once the application of the voltage causes the bar to pivot into a position known as the working position, which it maintains as long as the voltage continues to be applied to the relay.

However, whatever the kind of relay, the design of the known relay in the form of stages these stages being marked (II) in the case of the moving bar and the controlled contacts, (l) in the case of the electrical and magnetic control means and (III) in the case of the sealed supporting and protection means, leads to the appearance of parasitic magnetic fluxes which circulate through the base 1 in accordance with the lines of force shown in chain dotted line. These magnetic losses. as already explained earlier, gives rise to numerous and serious drawbacks.

It should be born in mind, too, that the overall structure of the relay is complex and bulky, involving a multiplicity of expensive components which have to be manufactured and assembled.

Figure 3 illustrates a perspective view of the sealed electromechanical relay in accordance with the invention.

This relay is made up of a base or plate 1 equipped with a flange 2 designed to receive the complementary edge of a cover which has not been shown.

The external part of the base carries the sealed electrical lead-throughs such as 3, electrically insulated by glass "beads" such as 4 fused to the base. Good sealability is achieved bv an appropriate choice of the material of which the base is made, a ferromagnetic metal of the mild steel or ferronickel kind for example.

In the central part of the plate a region 40 in the form of a dished depression is created, leaving only a minimal thickness of metal, whose characteristics in terms ol order of magnitude will be specified later on.

At the centre of the depression, a magnet 20 is attached whose magnetic function is the same as in the case of the relay of known kind described earlier but which at its free end is cut wedge fashion 21.

The relty also incorporates a mobile bar 7. 8 resting upon the wedge formation 21 through the medium of a groove 22 having a section complementary to that of the wedge of the magnet, so that it can pivot, after the fashion of the beam of a baluicc. on its knife edge.

Two coils 31 nnd 32 are arranged rcspectively on the two arms 7 and 8 of the mobile bar. Finally, two electrically insulating actuators 15 and 16 are attached to the ends of the mobile har and henr against fixed leaf springs 13 and 14 supported and electrically connected to the external terminals 3 and 3'.

These springs can make contact with fixed contacts 43 and 44 likewise electrically connected to external terminals.

This kind of relay structure has a certain number of chacteristic advantages.

The first has to do with the fact that here the base 1, which in the prior art designs performs two functions only, on the one hand that of a passive support for the relay and on the other hand that of protection against the environment in association with the cover, has a third function, namely that of carrying the working magnetic flux.

The second advantages features has to do with the fact that the permanent magnet 20, which is indispensable in the polarised relays in order to provide the function of creating an orientated and constant magnetic flux, operates in the case of the relay in accordance with the invention a second function, namely that of mechanically supporting the mobile bar pivot axis, being moreover adapted to this function by virtue of the wedge shaped formation 21 of its extremity in contact with the bar, with which latter it cooperates through a groove 22 of complementary shape.

Two sets of advantageous results accrue from this kind of design the description of which can be followed in Figure 4.

The first set of results relates to the structure itself. The presence of a dished depression 40 in which the magnet 20 and the two coils 31 and 32 can be partially accommodated, considerably reduces the thickness of the relay in relation to the known relay of Figures 1 and 2: in addition, the edges of the depression create the elements of the magnetic circuit whose rightangled relationship to the base of the depression is necessary in order to form the air-gaps 27 and 28. It should be pointed out, too, thit the coils 31 and 32 may cither be fixed lo the base or, and this preferentially, fixed to the mobile bar, moving with the latter due to the flexible nature of the connections between them and the fixed terminals.

Thus, the structure of the relay in accord- ance with the invention not only reducers the dimensions but also gives rise to a reduction in the number of components parts needed by the relay, leading to higher reliability, smaller mass and lower cost.

A second set of advantageous results relate to the relay performance. Figure 4 illustrates the lines of force of the magnetic fluxes circulating in the relay, these having bccii shown in full line in the case where the coils carry no current and in broken line in the case where pivoting has taken place towards the left considered in the figurc, due to the application of a voltage to the terminals of the coils.

It can be seen that the magnetic fluxes close in both cases via the base itself and that the unwanted magnetic leakage effects shown in Figure 2, are not in evidence. The result of this suppression of the leakage fluxes is an improved efficiency on the part of the magnetic circuit, enabling the sizes of the electrical control coils to be reduced and leading to a lower relay power consumption.

Optimizing of the relay characteristic can advantageously include designing the depth of the depression 4(), consistently with an adequate thickness on the part of the wall which constitutes its base, in such a way that the ferro-magnetic material of which it is made is maintained outside its magnetic saturation range.

Taking an order of magnitude offered by way of example, in a typical case of a relay in accordance with the invention this wall has been reduced to a thickness of as little as 0.3 millimetres. in comparison with relays of known kind. it has been possible to arrange the ten output terminals of the bistable relay design at the standard spacing of 2.54 millimetres for direct plugging into a printed circuit.

The thickness of the relay and its fitting in position are therefore no different from the corresponding features of other components used in these circuits, such as cased integrated circuits known in the art by the name "dual-in-line" circuits.

WHAT WE CLAIM IS: 1. A sealed. polarised electromagnetic relay, comprising a two part sealed casing formed respectively by a base equipped with sealed lead-through electrical terminals, and a cover, a plurality of fixed contact elements and moving contact elements, a plurality of electrical control coils, the fixed contact elements, the moving contact elements and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. in the form of a dished depression is created, leaving only a minimal thickness of metal, whose characteristics in terms ol order of magnitude will be specified later on. At the centre of the depression, a magnet 20 is attached whose magnetic function is the same as in the case of the relay of known kind described earlier but which at its free end is cut wedge fashion 21. The relty also incorporates a mobile bar 7. 8 resting upon the wedge formation 21 through the medium of a groove 22 having a section complementary to that of the wedge of the magnet, so that it can pivot, after the fashion of the beam of a baluicc. on its knife edge. Two coils 31 nnd 32 are arranged rcspectively on the two arms 7 and 8 of the mobile bar. Finally, two electrically insulating actuators 15 and 16 are attached to the ends of the mobile har and henr against fixed leaf springs 13 and 14 supported and electrically connected to the external terminals 3 and 3'. These springs can make contact with fixed contacts 43 and 44 likewise electrically connected to external terminals. This kind of relay structure has a certain number of chacteristic advantages. The first has to do with the fact that here the base 1, which in the prior art designs performs two functions only, on the one hand that of a passive support for the relay and on the other hand that of protection against the environment in association with the cover, has a third function, namely that of carrying the working magnetic flux. The second advantages features has to do with the fact that the permanent magnet 20, which is indispensable in the polarised relays in order to provide the function of creating an orientated and constant magnetic flux, operates in the case of the relay in accordance with the invention a second function, namely that of mechanically supporting the mobile bar pivot axis, being moreover adapted to this function by virtue of the wedge shaped formation 21 of its extremity in contact with the bar, with which latter it cooperates through a groove 22 of complementary shape. Two sets of advantageous results accrue from this kind of design the description of which can be followed in Figure 4. The first set of results relates to the structure itself. The presence of a dished depression 40 in which the magnet 20 and the two coils 31 and 32 can be partially accommodated, considerably reduces the thickness of the relay in relation to the known relay of Figures 1 and 2: in addition, the edges of the depression create the elements of the magnetic circuit whose rightangled relationship to the base of the depression is necessary in order to form the air-gaps 27 and 28. It should be pointed out, too, thit the coils 31 and 32 may cither be fixed lo the base or, and this preferentially, fixed to the mobile bar, moving with the latter due to the flexible nature of the connections between them and the fixed terminals. Thus, the structure of the relay in accord- ance with the invention not only reducers the dimensions but also gives rise to a reduction in the number of components parts needed by the relay, leading to higher reliability, smaller mass and lower cost. A second set of advantageous results relate to the relay performance. Figure 4 illustrates the lines of force of the magnetic fluxes circulating in the relay, these having bccii shown in full line in the case where the coils carry no current and in broken line in the case where pivoting has taken place towards the left considered in the figurc, due to the application of a voltage to the terminals of the coils. It can be seen that the magnetic fluxes close in both cases via the base itself and that the unwanted magnetic leakage effects shown in Figure 2, are not in evidence. The result of this suppression of the leakage fluxes is an improved efficiency on the part of the magnetic circuit, enabling the sizes of the electrical control coils to be reduced and leading to a lower relay power consumption. Optimizing of the relay characteristic can advantageously include designing the depth of the depression 4(), consistently with an adequate thickness on the part of the wall which constitutes its base, in such a way that the ferro-magnetic material of which it is made is maintained outside its magnetic saturation range. Taking an order of magnitude offered by way of example, in a typical case of a relay in accordance with the invention this wall has been reduced to a thickness of as little as 0.3 millimetres. in comparison with relays of known kind. it has been possible to arrange the ten output terminals of the bistable relay design at the standard spacing of 2.54 millimetres for direct plugging into a printed circuit. The thickness of the relay and its fitting in position are therefore no different from the corresponding features of other components used in these circuits, such as cased integrated circuits known in the art by the name "dual-in-line" circuits. WHAT WE CLAIM IS:

1. A sealed. polarised electromagnetic relay, comprising a two part sealed casing formed respectively by a base equipped with sealed lead-through electrical terminals, and a cover, a plurality of fixed contact elements and moving contact elements, a plurality of electrical control coils, the fixed contact elements, the moving contact elements and

the control coils being connected to said terminals, and a magnetic circuit coupled to said electrical coils and constituted on the one hand by a fixed part, said fixed part of the magnetic circuit being constituted by said base, and comprising a three parallel limb structure, namely two lateral limbs, and a central limb made of a permanent magnet linked by a common member, and on the other hand by a moving part, capable of pivoting about an articulation under the control of said coils, said moving part being constituted by a bar forming, with the free end of the two lateral limbs, two air-gaps, and capable of pivoting about its centre, wherein said articulation is constituted by a device of the knife-edge and groove kind, said groove being formed in said bar, and said knife-edge being carried by that of the two ends of the permanent magnet which is located remote from said common member.

2. An electromagnetic relay as claimed in claim 1, wherein said base contains a depression at its central part, the two said lateral limbs being constituted by the base, at two opposite sides of said depression, and said member by the bottom wall of said depression.

3. An electromagnetic relay as claimed in claim 2, wherein the bottom wall of said depression has in section an area at least equal to that, which, in operation, corresponds to the magnetic saturation state of the material of which it is made.

4. An electromagnetic relay as claimed in claim 1, wherein said plurality of electrical coils is carried by said mobile part of the magnetic circuit.

5. An electromagnetic relay as claimed in claim 2, wherein that said plurality of coils is at least partially included in said depression.

6. An electromagnetic relay as claimed in claim 2, wherein said sealed electrical terminals are fixed on the sides of said depression.

7. An electromagnetic relay substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.