GB2128407A

GB2128407A - Electromagnetic switch

Info

Publication number: GB2128407A
Application number: GB08322167A
Authority: GB
Inventors: Bernard Dietrich; Tetsuo Mori; Hidetoshi Matsushita
Original assignee: SDS Elektro GmbH; Matsushita Electric Works Ltd
Current assignee: SDS Elektro GmbH; Panasonic Holdings Corp
Priority date: 1982-08-17
Filing date: 1983-08-17
Publication date: 1984-04-26
Also published as: CH661377A5; GB8322167D0; GB2128407B

Abstract

The switch comprises a polarised magnetic drive and a contact apparatus arranged above it including a contact slide (12) of which actuates bridge contacts (13a, 13b) and is operatively connected to return springs (18a, 18b). To enable two or three positions of the contact slide (12) optionally to be obtained without any constructional changes in the switch, the coil former (2) thereof is divided into two spaced, adjacent chambers housing two coils (4, 5), with a permanent magnet arrangement (11) seated between them symmetrically with the longitudinal axis of the coil former (2). The permanent magnet arrangement (11) is polarised at right angles to the longitudinal axis of the coil former and has a central opening to give passage to the armature (8), which is mounted for longitudinal displacement in the hole (3) in the coil former (2). The armature (8) is given a stable centre position by two biased return springs (18a, 18b) although when it is shifted out of its centre position in either direction only one spring or the other continues to be tensioned. <IMAGE>

Description

SPECIFICATION Electromagnetic switch gear This invention relates to an electromagnetic switch gear, including magnetic drive means with a yoke containing a permanent magnet arrangement and surrounding a coil support form, and an armature located in a bore extending through the coil support form, which armature actuates a contact slide by means of a lever, the contact slide being mounted for displacement parallel with the longitudinal axis of the coil form, being operatively connected to two return springs biased in opposite directions, and carrying cushioned bridge contacts, each of which is associated with at least two opposed fixed contacts.

A switch gear of this type is described in the present Applicants' German patent application P 31 38 265.7, in which the armature, which is mounted for tipping movement in the vicinity of one flange on the coil support form, has both ends extending beyond the flanges on the coil form and interacts with pole faces of the yoke, which contains a permanent magnet arrangement, in the form of two bar-type permanent magnets located above and parallel with the coil form. The lever is in engagement with a leaf spring, the other end of which is supported against the casing of the contact apparatus, with the spring being constructed in one part in the mono or bistable embodiment of the switch gear. In the tristable embodiment, however, i.e. with a central position of rest for the contact slide, in which all contacts are open, the spring comprises two leaf springs biased in different directions.Whereas mono and bistable operation of the switch gear has no peculiarities, the direction of movement of the armature and thus the contact slide being determined by the conducting direction in the coil as in any polarised magnetic drive, with tristable operation a throwing pulse of exactly predetermined height and duration is necessary to obtain the centre position, firstly in order to obtain reliable throwing, and secondly to avoid overshooting the centre position. Another factor involved is that the desirable progression of the force of the return spring in dependence on the path of the armature is only approximately achieved by means of the divided leaf spring described.

The invention aims to provide a switch gear of the above type, which can be operated in bistable or tristable mode without any alterations, and which makes no special demands of the switching pulses necessary to reach the particular switch positions.

According to the present invention there is provided electromagnetic switch gear, including magnetic drive means with a yoke containing a permanent magnet arrangement and surrounding a soil support form, an armature located in a bore extending right through the coil form, which armature actuates a contact slide by means of at least one lever, with the contact slide being mounted for displacement parallel with the longitudinal axis of the coil form, being operatively connected to two return springs biased in opposite directions, and carrying cushioned bridge contacts, each of which is associated with at least two opposed fixed contacts, wherein the coil form is divided into two spaced, adjacent chambers housing two wirewound coils, the permanent magnet arrangement lies between the two chambers symmetrical with the longitudinal axis of the coil form and is polarised at right angles to the longitudinal axis of the coil form, the permanent magnet arrangement has an opening for the passage of the armature, substantially corresponding to the diameter of the bore in the coil form, the armature is seated on a non-magnetic guide rod, the two end faces of the armature interact with pole faces of the yoke located in the region of the particular end opening of the bore in the coil form, and the contact slide is operatively connected to both return springs, only in its geometrical centre position, but on leaving this centre position tensions only one of the return springs.

A polarised pot magnet system is known from the journal ETZ-A Vol. 86 (1965) Book 11, pages 371 to 375, containing a coil form which is subdivided into two spaced, adjacent chambers, between which an annular permanent magnet is located. The permanent magnet has radial magnetization and an aperture for the passage of the armature. Both end faces of the armature interact with the end faces of the pot shaped yoke, and the armature actuates a bridge contact.

However, this pot magnet system has only one coil with its winding divided between the two chambers, and it can therefore be used only for bistable and possibly monostable operation.

By virtue of the two separate coils in conjunction with the special construction of the two return springs, the switch gear according to the invention, on the other hand, allows for bistable or tristable operation optionally, without any constructional alteration. A bistable action is obtained when current flows through the coils the same way in either direction. The geometrical centre position of the contact slide, in which all contacts are open, is overshot. A tristable action is obtained with current flowing different ways in the two coils. The two coils then each only generate excitations of half the size in opposite directions.These are sufficient to throw the armature reliably out of either of the two end positions, but subsequently, in conjunction with the action of the two return springs, to hold the armature securely in the centre position, where both the electromagnetic and permanent magnetic forces cancel each other out.

In a specially preferred embodiment which is very quick to construct, the yoke merges into two core pieces located inside the coil form, the core pieces being constructed as bearings for the armature guide rod in the region of their pole faces facing towards the armature. This construction also makes it possible to have a particularly small air gap between the permanent magnet arrangement and the armature, since the bending of the armature guide rod as a result of the magnetic forces acting radially on the armature remains slight because the bearings are close beside one another. When the armature is mounted exactly centrally relative to the hole in the permanent magnet, there is no force acting on the armature guide rod, sice the permanent magnetic forces acting radially cancel each other out.In practice however, eccentricity between the armature and the hole in the permanent magnet are to be expected, and may give rise to considerable bending forces on the guide rod of the armature.

In the simplest case the permanent magnet arrangement may comprise one permanent magnet in disc form.

For manufacturing reasons, however, the most preferred embodiment is that where the permanent magnet arrangement comprises two opposed, parallelepipedal permanent magnets, the poles of the permanent magnets facing one another being the same, and the armature being cylindrical but with parallel surfaces in the region of the poles of the permanent magnets.

Similarly the yoke may comprise two halves made of flat profile, lying opposite one another relative to the longitudinal axis of the coil form.

Expensive mounting apparatus, such as is otherwise often necessary when assembling equipment containing biased springs, can be dispensed with in an embodiment, in which the return springs comprise two biased helical compression springs, lying coaxially in a recess in the casing of the contact apparatus, with an entraining lug of the contact slide lying between their facing ends. On movement of the contact slide out of its centre position the lug tensions only one of the return springs, while the other return spring is supported against projections on the casing.

The armature travel and armature force may be adjusted to the travel of the contact slide and the force necessary to operate it, in a simple manner, by having the turn-round lever connected to the end of the armature guide rod and mounted rotatably at a fulcrum, in the manner of a two armed lever.

Embodiments of the switch gear according to the invention are illustrated, by way of example, in diagrammatically simplified form in the accompanying drawings, in which: Figures 1A and 1 B are each a section through the magnetic drive of the switch gear, in the two end positions of the armature corresponding to the line A-A in Figure 2, Figure 2 is a side view in cross-section of the complete switch gear, Figure 3 is a section taken along the line B-B in Figure 2, Figure 4 is a section corresponding to Figure 3 but with a different permanent magnet arrangement.

Figure 5 is a fragmentary section along the line C-C in Figure 2, Figure 6 is a table explaining the tristable operation, Figure 7 is a table explaining the bistable operation, Figure 8 is a graph to illustrate the power/distance ratios of the switch gear, Figure 9 is a sectional view through a switch gear according to another embodiment of the invention, Figure 10 is a sectional view taken on the line D-D of Figure 9, Figure 11 is a sectional view through a switch gear according to a further embodiment of the invention, and Figure 12 is a sectional view similar to that of Figure 1 but through a switch gear according to yet another embodiment of the invention.

In Figures 1 A and 1 B magnetic drive means of the switch gear comprises two halves 1 a and 1 b of a yoke, each of which is in three parts for manufacturing reasons. The two halves surround a coil support form 2, which has a bore or hole 3 extending right through it and which is divided into two chambers, each containing a wire-wound coil of its own (4 or 5 respectively):The yoke halves 1a and 1b extend into the bore 3 in the coil form from both ends, each with a core piece 6 or 7 respectively. The internal end faces of the core pieces form the pole faces interacting with the end faces of a soft magnetic armature 8. The armature is fixedly mounted on a guide rod 9, which is mounted displaceably in bearing surfaces 6a and 7a in the core pieces 6 and 7.The bearing surfaces 6a, 7a are located as far as possible inside the switch gear, that is to say, they are located adjacent the pole faces of the core pieces 6 and 7. The left end of the guide rod 9 reaches beyond the end faces of the yokes 1 a and 1 b and ends in a fork 10. Between the two chambers of the coil form 2 there is a radially polarised permanent magnet 11. Its magnetic flux closes along the flux lines 1 Oa in Figure 1 a when the armature 8 is in the extreme left hand position, and along the lines 1 Ob in Figure 1 b when the armature 8 is in the extreme right hand position.

As shown in Figure 2, the contact apparatus of the switch gear is arranged above the magnetic drive. This comprises a contact slide 12, mounted displaceably in a casing 14 and carrying three contact bridges, each of which comprises two individual bridges 1 3a, 1 3b cushioned against one another. The contact slide 12 is joined to the fork 10 of the armature guide rod 9 by a two armed turn-round lever 15, which is mounted pivotably on a spindle 16. The central position of the armature 8, as illustrated, is maintained by two biased helical compression springs 1 8a, 1 8b.

These are seated in a recess 17 in the casing 4 and their facing ends bear against a lug 12a on the contact slide 12. As will be seen from Figure 5, however, the casing 14 is provided with two projections 1 4a and 1 4b extending into the recess 1 7. The projections 1 4a and 1 4b are spatially at the height of the lug 1 2a in the central position of the contact slide 12. The effect of this is that, when the contact slide 12 moves out of its central position, only one spring 1 8a or 1 8b comes into action as the return spring, while the other spring is out of action.This ensures that the geometrical central position of the contact slide 12 is reliably reached, since in this central position both the permanent magnetic forces and the electromagnetic forces which cause the armature to be thrown intmshve central position armature to be thrown into the central position As will be seen from Figures 3 and 4, the casing 1 4 of the contact apparatus is snapped onto a casing 1 9 surrounding the magnetic drive of the switch gear by its detent lugs 1 4c. The contact bridge 1 3a of the contact slide 12 interacts with two fixed contacts 20 and 21 with connecting screws 20a and 21 a, arranged opposite one another.In the case of Figure 3 the permanent magnet 11 is in the form of a disc magnet with a central aperture for the armature 8 to pass through, and with the polarisation or magnetisation symbolised by the arrows.

In the case of Figure 4 there are instead two permanent magnets 1 a and 1 b which are more favourable from the point of view of manufacturing method. These are arranged opposed one another and polarised so that two poles of the same type are opposite one another relative to the armature 8. To obtain large enough pole faces, the armature 8 is flattened in the region of the permanent magnets 1 a, 11 b; otherwise it is of a cylindrical shape.

In the Figure 6 diagram, at the left hand side below the symbolically indicated coils 4 and 5 with the connections Al, A2 and A3, the possible directions of current flow through the eoils are shown, and to the right thereof the movements of the armature 8 and thus of the contact slide 12 which are initiated thereby in the case of tristable operation. The coils 4 and 5 are assumed to be wound in the same direction. The end of the coil 4 and the beginning of the coil 5 are joined together by the common connection A3. It will be seen that a flow of current in the same direction in both coils, in either direction, brings the armature from the central position to one of the end positions.

Current flowing in opposite directions in the two coils 4 and 5 throws the armature out of either of the two end positions into the centre one. With current flowing in the same direction in both coils, however, the centre position can also be switched through in case of need, that is to say, the armature brought directly from one end position to the other. An important application for such a switch gear with three stable positions, each of which is thus maintained even after cessation of the energisation which brought them about, is the control of electric drives with a reversible direction of rotation, for which so-called reversing contactors of the monostable or bistable type have previously been required. However, a switching action can also be obtained by known measures, where either only the centre position and one end position or only the centre position alone is stable.The armature then returns to the centre position, either from one or both end pOsitions, as soon as the controlling impulse has died away.

Figure 7 is a similar representation of the conditions during bistable operation, where the connection A3 is not required. Instead of a bistable switching action the monostable switching action can again be obtained with known measures. One of the coils may be used as a restraining coil for the non-stable end position.

Figure 8 is a power/distance graph for the switch gear described, optionally with 1, 2 or 3 stable positions.

The path S 1 of the contact slide 12 is to the extreme right hand position and the path S2 into the extreme left hand position is plotted on the abscissa, starting from the centre position, the power is plotted on the ordinate.

The obliquely hatched areas A1/A2 represent the force content of the normal contact compression springs (not drawn in in detail), the limit with new contacts being formed by the lines B3/B2 and by the lines C1/C2 in the case of burnt down contacts.

Thlsis based on the following: Elasticity of new contacts: 1 mm admissible burning down 0.5 mm remaining lift with burnt down contacts 0.5 mm initial contact forces: 3 50 cN=1 50 cN contact forces in end position: 3. 100 cN=300 cN with burnt down contacts: 3. 75 cN=225 cN D 1 /D2 is the force content of the return springs 18a, 18b E1/E2 is the attracting force of the permanent magnet, where El refers to the movement of the armature from the centre position to the right E2 refers to the movement of the armature 8 from the centre position to the left.

The gripping force of the permanent magnet 11 is in each case 700 cN.

F1/F2 is the difference between E1/E2 and the summated curve of B1/B2+D1/D2. The surplus force of the permanent magnet 11 in and before the end position (vertical hatching in graph) leads to the stable end position of the armature and thus of the contact slide 12. An automatic return from one or both end positions to the centre position can be achieved by reducing the force of the permanent magnet, e.g. by means of a distance plate (anti-adhesion piate) mounted on one or both end surfaces of the armature 8.

By having the current flowing in the opposite direction in the coils 4 and 5 to throw the armature from one stable end position to the centre position, the attractive force E1/E2 of the permanent magnet 11 is reduced according to the strength of the energising current, so that the curve G 1/G2 may for example be produced.

Reduction to approximately zero or to change of sign is possible. When the force of the permanent magnet is reduced to G1/G2 there is a resultant H1/H2 with the corresponding force content, shown by vertical hatching. The armature is thrown into the stable centre position.

However, the centre position can be switched through, if both coils are excited in the same direction, whereby the magnetic force curve is shifted to J1/J2 and the following accelerating arise: as far as the centre position the sum of the magnetic force curve J 1 plus the force of the springs 18a, 18b (area Di) and of the contact springs (area Al) is effective. On the centre position the difference between the curve J1 and the spring forces in opposite directions (area D2/A2) is effective In the extreme left hand position J1=1 050 cN--550 cN (spring forces)=500 cN acts as a restraining force. With a permanent magnetic force E2 of 700 cN energisation of both coils can be discontinued. The switch gear holds itself (stable end position).If however the permanent magnetic force El is less than the compressive forces of the particular return spring 1 8a or 1 8b and of the contact springs, then the switch gear drops back to the centre position after disconnecting the coil energisation, that is to say, it takes on the behaviour of a conventional electromagnetic contactor Where both coils 4, 5 are energised in the same direction, on the other hand, there is an initial force surplus for acceleration of 100 cN, starting from the centre position, namely 300 cN less the force of the return springs, which is 200 cN.

Figures 9 and 10 show a different embodiment of the switch gear. The magnetic drive comprises two halves 1 a, 1 b of a yoke surrounding a coil form 2; the coil form has a hole 3 extending right through it and is divided into two chambers, each of which contains its own wire-wound coil 4 and 5 respectively. The yoke halves 1 a and 1 b extend into the bore 3 in the coil form from both ends, each with a core piece 6 or 7 respectively. The internal end surfaces of the core piece form the pole faces which interact with the end faces of a soft magnetic armature 8, joined to a non magnetic, two-part guide rod 9a, 9b. The external ends of the guide rod 9a or 9b are in each case operatively connected to one end of a two-armed turn-round lever 1 spa or 1 sub respectively.The levers 1 5a and 1 sub are mounted to pivot about spindles 1 6a and 1 6b and have their other ends seated in a contact slide.

As compared with the embodiment described at the beginning, e.g. as shown in Figure 2, with only one turn-round lever, which is connected by a fork to a guide rod of the armature, this embodiment has the advantage that the two turnround levers 1 Sa, 1 Sb are loaded exclusively in compression, thus dispensing with the fork and the connection between it and the guide rod.

In this embodiment, furthermore, the returning force is generated not by helical compression springs acting on the contact slide, but by means of two biased retum springs 31 a, 1 3b acting directly on the guide rod 9a, 9b; in Figure 10 these are in the form of leaf springs with their free ends bearing against the casing 1 9 of the switch gear, and with their tops bearing against a stop, in the form of a bolt 32a or 32b respectively, in the inoperative position, to obtain the desired bias.

This has advantages for assembly and for any adjustment that may be necessary, as compared with mounting the return springs in the contact device.

In the embodiment shown in Figures 9 and 10 the permanent magnet flux is generated by two parallelepipedal permanent magnets 33a and 33b, arranged symmetrically of the centre between the yokes 1 a and 1 b and conductors 34a and 34b. Each conductor has a limb which extends between the two chambers of the coil form 2 to near the armature 8.

Figures 11 and 12 show two embodiments of the switch gear, where the permanent magnets 33a, 33b and the conductors 34a, 34b are arranged as in Figures 9 and 10, but additional measures are taken to stabilise the armature 8 in the centre position. One of these measures is to construct those surfaces of the armature 8 and conductors 34a and 34b that are opposite one another in the centre position of the armature 8 as symmetrical pole faces. In the face of Figure 11 the armature 8 has a pole face 8a extending round it and formed by two symmetrical grooves 81,82.

The resultant concentration of magnetic flux passing from the conductors into the armature on the central part of the armature can be further increased as shown in Figure 12. Here the armature 8 is provided in the centre with an annular groove 83, and the conductors 34a and 34b are each constructed with a recess 35a and 35b symmetrical with the groove 83, so that the pole faces which are opposite one another in the centre position of the armature 8 become still narrower and the magnetic fluxes passing over therefore still more concentrated.

A further measure to stabilise the centre position of the armature, which may be used as an alternative or in addition, comprises (Figure 11) wiring the coils 4 and 5 to free running diodes 41 and 51 respectively, connecting the end of the coil 4 to the beginning of the coil 5, and arranging the supply voltage source 60 with one terminal at the connection between the coils 4 and 5, while its other terminal can be connected by a touch contact switch 42 or 52 to the beginning of the coil 4 or the end of the coil 5 respectively. When the armature 8 is thrown out of one of its two possible end positions into the centre position, the return voltage pulse is short circuited by the diodes 41 and so, so that the speed with which the armature 8 returns to its centre position is reduced, and the risk of overshooting the centre position lessened.

Claims

1. Electromagnetic switch gear, including magnetic drive means with a yoke containing a permanent magnet arrangement, and surrounding a coil support form, an armature located in a bore extending right through the coil form, which armature actuates a contact slide by means of at least one lever, with the contact slide being mounted for displacement parallel with the longitudinal axis of the coil form, being operatively connected to two return spring biased in opposite directions, and carrying cushioned bridge contacts, each of which is associated with at least two opposed fixed contacts, wherein the coil form is divided into two spaced, adjacent chambers housing two wire-wound coils, the permanent magnet arrangement lies between the two chambers symmetrical with the longitudinal axis of the coil form and is polarised at right angles to the longitudinal axis of the coil form, the permanent magnet arrangement has an opening for the passage of the armature, substantially corresponding to the diameter of the bore in the coil form, the armature is seated on a non-magnetic guide rod, the two end faces of the armature interact with pole faces of the yoke located in the region of the particular end opening of the bore in the coil form, and the contact slide is operatively connected to both return springs, only in its geometrical centre position, but on leaving this centre position tensions only one of the return springs.

2. Switch gear according to claim 1, wherein the yoke merges into two core pieces located inside the coil form, the core pieces being constructed as bearings for the armature guide rod in the region of their pole faces facing towards the armature.

3. Switch gear according to claim 1 or claim 2, wherein the permanent magnet arrangement is a permanent magnet in disc form.

4. Switch gear according to claim 1 or claim 2, wherein the permanent magnet arrangement comprises two opposed parallelepipedal permanent magnets, the poles of the permanent magnets which face towards one another being of the same type, and the armature being cylindrical with parallel surfaces in the region of the poles of the permanent magnets.

5. Switch gear according to any one of claims 1 to 4, wherein the yoke comprises two halves of flat profile, located opposite one another with respect to the longitudinal axis of the coil form.

6. Switch gear according to any one of claims 1 to 5, wherein the return springs comprise two biased helical compression springs located coaxially in a recess in the casing of the contact apparatus, with an entraining rod of the contact slide located between the facing ends of the springs, the arrangement being such that when the contact slide moves out of its centre position, the lug tensions only one of the return springs, while the other return spring is supported against projections on the casing.

7. Switch gear according to any one of claims 1 to 6, wherein the lever is linked to the end of the armature guide rod and is pivotally mounted on a fulcrum in the manner of a two-armed lever.

8. Switch gear according to any one of claims 1 to 5, wherein the return springs comprise two biased leaf springs, each of which interacts with one end of the armature guide rod, has both ends supported against the casing of the switch gear, and has its top lying against a stop in the central position of the armature.

9. Switch gear according to any one of claims 1 to 7, wherein two symmetrical levers are provided, each of which is pivotally mounted intermediate its ends on a fulcrum, has one end operatively connected to one end of the armature guide rod, and has the other end operatively connected to the contact slide.

10. Switch gear according to claim 1 or claim 2, wherin the permanent magnet arrangement comprises two parallelepipedal permanent magnets which are located symmetrically opposite one another relative to the armature, each of which magnets has one pole face lying against the yoke and the other pole face lying against a conductor which extends between the two chambers of the coil form to adjacent the armature.

11. Switch gear according to claim 10, wherein the opposing surfaces of the conductors and armature are in the form of symmetrical pole faces.

1 2. Switch gear according to any one of claims 1 to 11, including a free-running diode connected in parallel with each of the wire-wound coils, the end of one coil being connected to the beginning of the other coil, one terminal of a current source being located at this connection, and the other terminal of the current source being connected to the beginning of one coil via a first switch, and to the end of the other coil via a second switch.

1 3. Electromagnetic switch gear substantially as hereinbefore described with reference to Figures 1A, B to 3 and 5, Figure 4, Figures 6 to 8, Figures 9 and 10, Figure 11 or Figure 12 of the -accompanying drawings.