US2897415A - Holding magnet system - Google Patents

Description

July 28, 1959 y HOLDING MAGNETSYSTEM Filed sept; 3o, 1957 F. STCKL INVENTOR EVA/VZ STC/(L.

nited States Patent @Or HOLDING MAGNET SYSTEM Franz Stckl, Vienna, Austria, assigner to 4Optisthe Anstalt C. P. Goetz, Ges. m.b.H., Vienna, Austria yApplication September 30, 1957, Serial No. 687,200

5 Claims. (Cl. 317-4171) This invention relates to a construction of holding magnet with a quick response and suitable in particular for electrical switch-gear.

As a rule electrical switching devices require to have a quick response; i.e. the time lag between the occurrence of the event initiating the switching action, and the actual execution of the switching action, must be as short as possible. In addition, it is also necessary to be able to control high powers with a small expenditure of energy, and the switching action shall be independent of the direction of the passing current.

Those relays hitherto used in which the passage of a current attracts an armature connected with the switching elements or contacts, have only partially satised the above requirements. A quicker response has been obtained by using a very small armature mass, or by applying a very high switching current. In the rst case, the sensitivity of the arrangement is high, but, obviously, only Ivery small powers can be controlled; in the second case, while very high powers can be controlled, the sensitivity is correspondingly lowered. Relays with small armature mass are, for instance, built as polarised relays, and have also been used in sensitive, electrical measuring devices as an overload protection. The useful performance of such relays is low, because the low operating current or applied input can only exert a small force on the armature. A polarized relay has the further disadvantage that its action is dependent on'the direction of the passing current.

Increased useful output in relation to the applied switching current, has been obtained by the use of socalled locking magnets. In these, a spring-loaded armature is held to the pole pieces of the magnet without an air-gap; the input current is applied in such a manner that the resistance to the magnetic flux in the pole pieces is raised'by displacement of the field, to produce practically no ilux in the armature which, consequently, becomes released from the poles. As in this case the rforce acting on the armature is provided by a spring, a very high switching performance can be obtained, with a corresponding increase in the degree of sensitivity of the arrangement. l In relays constructed after this fashion, the armature has the form of a three-armed yoke, with air gaps at two points. These air gaps are bridged by separate armatures. The central arm of the yoke is formed by a permanent bar magnet one pole of which is applied to the part of the yoke frame between the two air gaps, and the other pole is applied to the part of the y'oke frame opposite said air gaps. The input or control windings are fitted on the two outer, remaining arms of the yoke frame.

In such an arrangement it is easily possible `for full contact between the secondary armatures and the yoke to be broken by unequal thermal expansion of the bar magnet and the yoke respectively. In addition, for the same reason or by reason of rough handling, variations may occur in the dimensions of the air gap(s). Con- 2,897,415 Patented July 2e, 1959 ice sequently, the reliable functioning of such relays, is easily disturbed by external causes.

Besides these inconveniences, relays equipped with such locking magnets have the further disadvantage that it is not possible to iind room in the coil windings for any considerable masses of copper.

An object of the present invention is to eliminate these disadvantages. One feature of the invention resides in a holding magnet system having a short response time for the dropping of the armature, comprising a yoke body consisting of two equal, flux-carrying parts having no air gaps and lying one beside the other and separated by a gap of low magnetic permeability, said parts forming a frame comprising two or more arms, one of said parts of said frame carrying (or comprising) a magnet,

and the other part of said frame carrying the armature,

which also bridges the gap between the two parts, andl input windings applied to the arms of the frame forming the yoke body, which arms are neither contacted by the magnet nor by the yoke.

Another feature of the invention resides in that the gap of low magnetic permeability which separates the two parts of the yoke is formed by a layer of nonmagnetic material.

Another feature of the invention resides in the measure to make the parts of the frame which forms the yoke of plates of a magnetic material of low remanence and high permeability.

The accompanying drawing illustrates an exemplary form or embodiment of the invention.

Fig. 1 represents a perspective View of the holding magnet, and

Fig. 2 shows the form and arrangement of the plates of which the yoke frame is constructed.

Fig. 3 shows the way in which the plates are built up.

Fig. 4 shows another embodiment of the invention.

The yoke frame of the holding magnet is indicated by 1 and consists of two, parallel halves 2, 2', each of which is built up of separate plates of a magnetic highly permeable material. The use of a material with a pronounced saturation jump on the magnetisation curve is most suitable. In the illustrated example the yoke frame has approximately the shape of a square. The two halves 2 and 2 are separated by a layer 3 of a nonmagnetic material. The shape of the plates of which the halves 2 and 2 of the yoke frame are constructed is indicated in Fig. 2; the individual plates in this case consist of identical L- parts 4, 4 assembled after the fashion of a transformer core, as is shown in Fig. 3, so that no air gap is formedy because each joint between two plates of a preceding layer will always be bridged by a plate of the following layer.

One side of the yoke `frame carries a permanent horseshoe magnet 5, the respective poles whereof make contact with the parts 2 and 2.

On the opposite side of the yoke frame from the permanent magnet 5, is titted the secondary armature 6. This is of semicircular cross-section, in order to offer the most uniform resistance to the magnetic llux. The armature is loaded in they direction of the arrow 9 by a spring 12 and is connected with its nose 13 with an electrical switching spring 14 having a contact tip 15 for actuating the same. The countercontact spring 16 carries a Contact 17.

The actuating coil windings 7, 8 are fitted on the two cross-arms of the yoke frame, being in the example shown connected in series and wound in opposite directions'.

The manner of action of the holding magnet is as follows:

In the rest position, i.e. when no current is passing through the actuating windings 7 and 8, the armature 6 e is held by the magnetic ux (as represented by the arrows of the permanent magnet 5. The force with which this armature is held is relatively great because there is no air gap, or only a very small gap, between the armature and the yoke frame.

If a direct current is passed through the windings 7 and 8, a magnetic flux is thereby produced in the two magnetically- active halves 2, 2 of the yoke frame (as represented by the arrows 11) which can be increased to the saturation point of the magnetic material of these parts, by intensifying the current applied. The magnetic flux in the direction of the arrows 11, has no direct influence on the force with which the armature 6 is held. However, the magnetisation of the yoke frame by the actuating current increases the magnetic resistance of the yoke frame to saturation point, and hence diminishes the intensity of the magnetic ux (represented by the arrows 10) generated by the permanent magnet 5 and passing through the armature; whereby the magnetic force holding the armature 6 is further reduced until said armature can be lifted off by the action of its permanently-attached spring 12.

When the armature is lifted by the spring 12, the nose 13 of the armature will carry the switching spring 14 along and will urge the contact tipi 15 fixed to said switching spring against the contact 17 of the counterspring 16 to close a normally open circuit. Y

The mechanical work performed by the armature 6 can, for instance, be directly used for actuating one or more electrical switch elements or contacts, or any other devices connected with said armature.

After performing the aforesaid motion, the armature 6 does not return of its own accord into the rest position when the current ceases to flo-W through the coil windings 7 and 8. A device (not shown) is provided for returning the armature into the rest position by mechanical, electrical, pneumatic or hydraulic means.

The lifting of the armature 6 takes place independently of the direction of the current passing through the coil windings 7, 8 since only the absolute value of the magnetic induction determines the increase in the magnetic resistance, and not the direction of the magnetic field produced by the current flowing through said coil windings7 and 8.

The magnitude of the magnetic force holding the armature depends on the magnetic induction in the pole pieces and the area of the surface in contact therewith; by correspondingly dimensioning the force of the induction and the area of pole contact, it is possible, even with small geometrical dimensions, to produce great forces and thus great accelerations of the armature 6 during lifting, thereby to obtain a high useful performance of the device.

The sensitivity of the device is determined by the value of the magnetisation current producing magnetic saturation in the parts of the yoke frame. By the use of highlymagnetic, highly-permeable materials, it is possible to make the armature 6 detach itself from the yoke frame already at a low Value of the current flowing through the coil windings 7 and 8. As already stated, the use in this regard of a magnetic material with a pronounced j ump. at the saturation point of the magnetic characterlistic is particularly suitable. The obtainable useful output is 1n a high degree independent of the value of the current passing through the coil windings. In addition to great sensitivity, high useful output, and independence of the direction of the actuating current, the further advantage is afforded that, in spite of the small overall dimensions, ample space is made available for accommodating the coil windings, which are most easily fitted on the yoke frame.

'I'he arrangement of an intermediate layer of a rionmagnetic material between the two halves Z and 2 of the yoke frame also enables a highly-stable form of magnet arrangement, very insensitive to vibration and shocks, to be obtained.

Instead of the embodiment shown, with two coil windings Aconnected in series, it is also possible to use only a' single winding or a number of separate windings connected in different circuits. This will, for instance, enable the dropping of the armature to be made dependent on the simultaneous occurrence of different events, produced by as many, otherwise unrelated circuits.

For these purposes it is of advantage to form the yoke body with a plurality of arms. Such a construction is shown in Fig. 4. Here the yoke body comprises three arms 18, 19, 2t), each of which carries an input winding 21, 22, 23. Each of these three windings may belong to a different circuit so that the holding magnet system may be arranged to respond only when the algebraic sum of the magnetic fluxes produced by the currents flowing through the windings 21, 22, 23 is sufficient to cause the displacement of the lield which is necessary to lift the armature.

The quick response, high sensitivity and mechanical stability of the holding-magnet according to the present invention, make it particularly suitable for use as an overload protection in electrical measuring instruments or electrical measuring circuits.

What is claimed is:

l. In combination in a magnetic structure, a magnetic circuit including a permanent magnetic, an armature, a yoke, and electrical coils on the yoke, the yoke comprising two identical yoke parts each having the form of a closed frame including two crosspieces and at least two arms connecting said crosspieces, said yoke parts lying parallel one beside the other, a zone of low magnetic permeability separating lsaid parts, said yoke parts having two outside surfaces each of which extends perpendicular to tlie plane of the frame and each of which lies in a single plane with the corresponding surface of the other yoke part, said permanent magnet forming a source of magnetic ux and engaging said yoke in one of the planes thus formed, said magnet having two poles each of which lies on said outside surface of one of said yoke parts, the armature engaging in its rest position said yoke in the other of the planes thus formed and bridging the gap between the two yoke parts, and at least one electrical coil for displacing the magnetic ux in the yoke situated on the arms connecting the crosspieces.

2. A holding magnet `system having a short response time for the dropping of the armature, including a permanent magnet, an armature, and a yoke, the yoke cornprising two identical yoke parts, each of said yoke parts having the form of a closed frame comprising two crosspieces and at least two arms connecting said crosspieces, said yoke parts lying parallel one beside the other, a nonmagnetic zone separating said parts, said yoke parts having two outside surfaces each of which extends perpendicular to the plane of the frame and each of which lies in a single plane with the corresponding surface of the other yoke part, said permanent magnet forming a source of magnetic flux and engaging said yoke in one of the planes thus formed, said magnet having two poles each of which lies on said outside 4surface of one of said yoke parts, the armature engaging in its rest position said yoke in the other of the planes thus formed and bridging the gap between the two yoke parts, and at least one electrical coil for displacing the magnetic flux in the yoke situated on the arms connecting the crosspieces.

3. A holding magnet system having a short response time for the dropping of the armature, including a permanent magnet, an armature, and a yoke, the yoke comprising two identical yoke parts, each of said yoke parts having the form of a closed frame comprising two crosspieces and at least two arms connecting said crosspieces, said yoke parts consisting of laminations of a material of low magnetic remanence and high permeability, said yoke parts lying parallel one beside the other, a zone of low magnetic permeability separating said parts, said yoke parts having two outside surfaces each of which extends perpendicular to the plane of the frame and each of which lies in a single plane with the corresponding surface of the other yoke part, said permanent magnet forming a source of magnetic ux and engaging said yoke in one of the planes thus formed, said magnet having two poles each of which lies on said outside surface of one of said yoke parts, the armature engaging in its rest position said yoke in the other of the planes thus formed and bridging the gap between the two yoke parts, and at least one electrical coil for displacing the magnetic lluX in the yoke situated on the arms connecting the crosspieces.

4. A holding magnet system having a short response time for the dropping of the armature, including a permanent magnet, an armature, and a yoke, the yoke comprising two identical yoke parts, each of said yoke parts having the form of a closed frame comprising two crosspieces and at least two arms connecting Said crosspieces, said yoke parts lying parallel one beside the other, said yoke parts consisting of laminations of a material of low magnetic remanence and high permeability, said yoke parts lying parallel one beside the other and being separated by a nonmagnetic zone, said yoke parts having two outside surfaces each of which extends perpendicular to the plane of the frame and each of which lies in a single plane with the corresponding surface of the other yoke parts, said permanent magnet forming a source of magnetic ux and engaging said yoke in one of the planes thus formed, said magnet having two poles each of which lies on said outside surface of one of said yoke parts, the armature engaging in its rest position said yoke in the other of the planes thus formed and bridging the gap between the two yoke parts, and at least one electrical coil for displacing the magnetic flux in the yoke situated on the arms connecting the crosspieces.

5. A holding magnet system having a short response time for the dropping of the armature, including a permanent magnet, an armature, a yoke, and electrical coils on the yoke, the yoke comprising two identical yoke parts, each of said yoke parts having the form of a closed frame comprising two crosspieces and at least two arms connecting said crosspieces, said yoke parts lying parallel one beside the other and being separated by a zone of low magnetic permeability, said yoke parts having two outside surfaces each of which extends perpendicular to the plane of the frame and each of which Ilies in a single plane with the corresponding surface of the other yoke part, said permanent magnet forming a source of magnetic flux and engaging said yoke in one of the planes thus formed, said magnet having two poles each of which lies on said outside surface of one of said yoke parts, the armature engaging in its rest position said yoke in the other of the planes thus formed and bridging the gap between the two yoke parts, and at least one electrical coil for displacing the magnetic ux in the yoke situated on the arms connecting the crosspieces, said coils belonging to different electrical circuits.

References Cited in the le of this patent UNITED STATES PATENTS 2,275,839 Boehme l M ar. 1o, 1942

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