US2606981A - Magnetic switching device of the cartridge or plug-type - Google Patents

Description

Aug. 2, 1 5 F. KESSELRING ETAL MAGNETIC SWITCHING DEVICE OF THE CARTRIDGE OR PLUG-TYPE Filed June 28, 1947' 2 SHEETSSHEET 1 IN VE N TORS Fr/2z lfesse/rlny a 04 13/502 716/! Day ler:

ATTOENEX Aug. 12, 1952 F. KESSELRING ET AL 2,606,981

v MAGNETIC SWITCHING DEVICE OF THE CARTRIDGE OR PLUG-TYPE Filed June 28, 1947 2 SHEETS-SHEET 2 1 i 2 I I 31 L 1' u 71 H H I Hr d lr-M 1 +5 w j\ INVENTORS Frz'fz Kessc/rmy and Heinrich Day/er- ATTORNEY Patented Aug. 12, 1952 MAGNETIC SWITCHING DEVICE OF THE CARTRIDGE on PLUG-TYPE Fritz Kesselring, Zollikon/Zurich, and Heinrich Degler, Zurich, Switzerland, assignors to F K G Fritz Kessclring Geratebau Aktiengesellschaft, Bachtobel-Weinfelden,

company Switzerland, a Swiss Application June28, 1947, Serial No. 757,860

In Switzerland July 5, 1946 Our invention relates to magnetic switchin devices of the cartridge or plug-type, i. e. magnetically operated switches whose switch contact means are mounted within an insulating enclosure. Such devices are suitable for closing and opening electric circuits, the insertion of resistance, inductance or capacitance elements into such circuits, and for control, regulating or protective purposes in the various fields of electrical engineering.

It is an object of -the invention to provide magnetically-operated switching devices of the above-mentioned'type which, over those heretofore known, have a highly increased currentinterrupting capacity at comparatively small dimensions so that the current density in the appertaining contact elements may reach unusually high values, for instance in the order of 50 amp./mm. without causing excessive heating of the contact elements. It is also an object of the invention to provide switching devices of the type mentioned that lend themselves readily to performing diversified control operations and that, even when containing several cartridge-type units, require relatively little space as compared with known apparatus of similar performance. Other objects of the invention will be apparent from the following explanation and description,

According to the invention, in one of its aspects, we design and arrange the magnetically-controlled movable switching element, the appertaining magnet poles and stationary contacts within a cartridge-type housing in such a manner that the dissipation of heat from the switching element to the outside of the housing is mainl by heat conduction in the longitudinal direction of the element toward and into the stationary contacts. This makes it possible, with small dimensions of the housing, to achieve the abovementioned high-current'densities without excessive heating, provided the design and material are properly chosen, for instance, so that under steady-state conditions the voltage drop between the stationary contacts is at most about 0.15 volt.

In order to always secure a flow of conducted heat from the switching element to the stationary contact under avoidance of an excessive temperature of the element, it is also. preferable to design the cartridge so that'the switching element does not assume a temperature about 100.

centigrade above that of the stationary contacts. Since, eventually, the heatis' dissipated to the environment, the stationary contacts may be equipped with cooling surfaces such as ribs, vanes or fins. However, it is also possible to give the 9 Claims. (Cl. 200-87) stationary contacts ample dimensions, as regards size and heat conductance, so that they are capable of transferring the heat mainly by conductance to the amply dimensioned current supply conductors. If the current density in these conductors is so low that they heat up only moderately above the ambient temperature, these conductors are readily capable of dissipating the heat produced within the cartridge.

According to another feature of the invention, the switching element with its holding and biasing means, the magnetic pole pieces and also the stationary contacts are all mounted together to form a structural unit. This has the advantage that, for instancebefore inserting these parts into the housing, the switching element and the spring or other biasing means can be properly adjusted so that the subsequentassembling of the parts is facilitated.

The housing of switching devices according to the invention consists mainly of insulating material such as pressed material, a tube of woundup materiaL'or for more exacting requirements, of ceramic or vitreous material such as glass, quartz or the like. Since, generally, the magnetic control flux is applied by extraneous means and must enter into the switching device, the insulating housing is preferably designed as a tube whose ends are closed by members of such kind that there is virtually no weakening of the magnetic flux. Iloe closure members may consist of thin plates of insulating material or metal. Preferable are closure members of ferromagnetic sheet material of at most 0.5 mm., especially about 0.1 mm. thickness which lie snug against the magnetic pole pieces in face-to-face relationship and have high specific electric resistance in order to keep eddy-current losses at a minimum.

The foregoing and other objects and features of the invention will be apparent from the following description, in conjunction with the drawing in which Figure 1 illustrates an axial section througha switching unit according to the invention in association withthe appertaining magnetizing yokes and current supply conductors, Figs. 2 to' i show three other embodiments of switching units, and Fig. fiiillustrates a magnetic controldevice according togthe invention which includes a plurality of s'witching'units.v

Referring to Figure 1, the magnetically controlled switchingelement'of the device is denoted by I. This element is mountedonan elastic shaft 2' which forms also the-biasing spring for the switching, element and tends to hold it in the illustrated "position-1' The switching element is disposed between two magnet pole pieces 3 and l. The stationary contacts to cooperate with the switching element are denoted by and 6. They are mounted in metallic sleeves l and 8 which are firmly secured to a tubular insulating enclosure 9. The torsion spring 2 is rigidly secured to this tube so that the switching element l is substantially thermally insulated from all other metal parts with the exception of the stationary contacts 5 and 6. The two ends of the insulating tube 9 are hermetically sealed by thin closure plates ii] and H, for instance, of ferromagnetic metal. The magnetic yokes which supply the control flux 5 are shown at [2 and I 3. It may be necessary to cover the metallic closures lo and H with insulating material for electrically insulating the cartridge from the yokes l2, [3. The additional insulation (not shown) should consist of a material of high insulating strength and good thermal conductivity, and its permissible temperature should be as high as possible. The current Ia to be controlled is applied to the stationary contacts by heavy conductive bars or buses i l and IE. In the illustrated position of switching element l, the current flows from bar [4 to the stationary contact 5, thence through the switching element I to the stationary contact 6 through which it enters into the bar [5. The switching element l is equipped with contact pieces l6 and I7. When the magnetic yokes I 2 Y and i3 are energized to apply the control flux q), the switching element 2 is rotated about its torsion shaft 2 in the counterclockwise direction thereby interrupting the current Ia.

The same switching device, however, may be operated so that the current Ib enters, for in stance, through the yoke [3, the closure plate H and the pole piece 4 to the switching element l and leaves through pole piece 3, closure plate it and yoke l2. This current flow exists when the yokes l2 and I3 are magnetized so that an interruption of the current Ib is effected by terminating the magnetic excitation. In this modification, the stationary contacts 5 and B serve only as insulated stops, or the device may be 1 employed so that the switching element acts as a make and break contact with the efiect that the current Ia is switched in immediately after the interruption of the current In. For the lastmentioned mode of operation, contact pieces I1 and I8 are attached to the respective pole pieces, and contact pieces 19 and 20 are mounted on the switching element I The interior of the enclosure 9 may be filled with a gas 2! which, especially for high voltages, may have elevated pressure of 5 to 10 atmospheres. For certain purposes, however, the interior of the enclosure may be evacuated.

It will be recognized that when a circuit is completed by the switching element I, the heat generated in the element is carried off substantially only by heat conductance from the switching element to the stationary contacts, that is, when the circuit for current Ia is closed, the heat flows from element l to contacts 5, 6 and the metal sleeves 1, 8 to the properly dimensioned conductor bars Id, i5. If the circuit for current Ib is closed, the heat is conducted from element l through the pole pieces 3, 4 to the yokes l2, 13 which are likewise amply dimensioned.

In the embodiment illustrated in Fig. 2, the switching element I extends horizontally and the stationary contacts 5' and 6 extend vertically and are disposed laterally with respect to the pole .pieces 3 and 4'. The portions of the 4 stationary contacts that extend outside of the enclosure 9 are provided with cooling vanes 22 and 23 respectively. The pole surfaces of the pieces 3 and 4 are slanted so that aside from Maxwells attractive forces, additional attractive forces are efiective due to divergence in permeability. In order to prevent a change in the operating conditions, in particular a variation of the contact distance due to heating enclosure, the coeflicient of thermal elongation of the pole pieces 3. and 4 and of the stationary contacts '5, 6' are so chosen relative to the coefficient of the housing 9 that the relative distances between these parts are substantially independent upon changes in temperature. In other respects, the performance of the device is similar to that shown in Fig. 1 and it will be understood that the special design features mentioned above in connection with Fig. 1 are likewise applicable to switching units of the type shown in Fig. 2.

If the switching devices are to cooperate with an impedance or other electric circuit element, such a circuit element according to another feature of the invention can be structurally combined with the cartridge-type housing. For instance, the housing may be equipped with a holding coil which magnetizes the pole pieces of the cartridge under control by the switching element once the pole pieces are suificiently magnetized from an extraneous source of magnetic flux to initiate the operation. The magnetizing eifect of the holding coil then maintains the switching element in the switched-in position and the switching element is permitted to return to its position of rest only when the current drops below a given small value, for instance 5% or 10% of the rated value. In order to combine such a holding coil with the device, the tubular housing may serve as a carrier for the coil. When using such a combination with direct current, the device closes or opens a circuit in response to a temporary and possibly very short control impulse and then causes the holding coil to produce a magnet field'which maintains the pole pieces sufficiently energized to keep the circuit in the same condition after the termination of the control impulse until some other control efiect occurs to interrupt the holding current. When using a holding coil with alternating current, the device can be used in such a manner that after the interruption of the controlling current, the magnetic energization is continued due to'the efiect of the controlled current until the controlled current approaches its zero passage. The switching function is then delayed accordingly and occurs only at an instantaneous value of the alternating current low enough to prevent damage due to arcs and undue contact consumption.

In cases where the switching unit is applied in order to insert a previously shorted resistor into an electric circuit, this resistor'may be placed on and supported by the insulating housing of the switching unit in the same manner'as mentioned above with reference to holding coils. Such a resistor combination has the advantage of affording minimum inductance of the resistancecircuit, which is of advantage for the prevention of arcs at the switching-in moment. In a similar manner, the switching unit may be combined with an inductive or capacitive circuit element. For instance, the housing or insulating tube of the unit may form part of the casing for a condenser.

For many purposes, it-is of advantage to connect two or more switching elements in electric and magnetic parallel relation to one another. For instance, a relatively large number of switching elements, for instance to 100 and more, can be placed into cartridge-type containers. It is sometimes also of advantage, especially for high voltages, to connect at least two switching elements electrically in series relation within a single housing. These switching elements may also be series-connected in magnetic respects. It is likewise possible to connect them electrically in series but magnetically in parallel.

The above-mentioned features and modifications are exemplified by the embodiment shown in Fig. 3. The device according to Fig. 3 has three switching elements I" arranged in magnetic series relation between the pole pieces 3" and 4". The insulating tube 9", which encloses the switching elements and is sealed at both ends by ferromagnetic plates l0 and H, serves as a spool or carrier for a coil 24, for instance, designed as a holding coil. The magnetic pole pieces 3 and 4" serve as stationary contacts. Additional stationary contacts 25 are disposed between the switching elements in order to provide a definite position for the individual switching elements in the switched-in condition. However, the additional contacts 25 may be omitted and the switching elements designed for directly contacting one another. When a magnetic field impulse of sufiicient strength is applied to the pole pieces, the switch elements I" rotate counter-clockwise and close a circuit which includes the holding coil 24. The controlled current I then produces a magnetic field which maintains the circuit in closed condition regardless of whether or not the control flux from an extraneous source that initiated the performance continues.

In the embodiment according to Fig. 4, a switching unit 26, inserted between the yokes 21 and 21 is cooled by liquid 28 that serves also as a resistor. These yokes are electrically insulated from the magnetizing core 29 of the control coil 30 and form current conductors for the switching element as well as electrodes for the liquid. If the switching element is normally in open position, the resistance of liquid 28 is normally effective and is shorted when coil 30 is energized; or, if the switching element normally closes the circuit, the liquid resistance is normally shorted and becomes efiective when coil 30 is energized.

If in devices according to the invention, as exemplified by the above-described embodiments, the electrically conductive parts, at which the opening and closing of the circuit occurs, consist of the customary contact materials, these materials insert an element of high magnetic reluctance, equivalent to an air gap, into the ma netic circuit. This reluctance element or air gap must have fairly ample dimensions in order to insure a safe electric contact even when the contact surfaces are partly consumed. The presence of such elements of high reluctance requires an increased amount of ampere turns for controlling the switching element and tends to reduce the contact pressure in the switched-in condition. Therefore, according to another feature of the invention, the stationary contacts and the corresponding contact pieces of the switching element, i. e. the parts denoted by IE, ll, ll, l8, i9, in Fig. 1, are made of ferromagnetic material, for instance nickel, iron, cobalt and ferromagnetic alloys. It is essential that these materials have high relative permeability of at least to 100 up to the expected highest operating temperatures of the device.

If desired, the disappearance of the ferromagnetic condition of these materials when exceeding the so-called Curie temperature may be taken advantage of, for instance, in order to secure an automatic interruption of the current at an excessive temperature of the switching element. Nickel, having a Curie temperature of about 350 C., is well suitable for this purpose. The socalled Hausler alloys with Curie points down to about C. are also applicable.

In order to prevent a change or deterioration of the contacts, especially those of ferromagnetic materials, at least the stationary contacts and the switching element are disposed within a chemically inactive atmosphere, for instance, nitrogen or hydrogen.

The magnetically active parts, that is, the switching element and the pole pieces, are preferably designed so as to have minimum magnetizing losses. Especially the hysteresis and eddycurrent losses should be low if the switching operation is to be performed within intervals of extremely short duration. Therefore, these magnetic parts may be subdivided. For instance, these parts, especially at least the magnet pieces, may be composed of comminuted material.

Switching devices according to the invention are not only applicable for low currents and voltages, for instance, as customary in the communication and measuring fields, but they are likewise advantageous for power purposes. For applications of the latter kind, care should be taken that the elongation or expansion due to the considerable heating effects does not affect the functioning. To this end, the thermal coefficients of expansion of the cooperating parts of the switching cartridge should be chosen in proper relation to one another, for instance, as explained above with reference to Fig. 3. The dis turbing effect of thermal expansion can be minimized in a simple manner if the contact surfaces and pole surfaces are designed so that the tangential planes in the points of engagement of the contacts, as well as the pole surfaces, extend in parallel to the main direction of thermal ex pansion of the switching unit or cartridge. In general, this is tantamount to locating the switching element with its longitudinal axis substantially in parallel to the longitudinal axis of the switching unit in accordance with the embodiments of Figs. 1 and 3.

In order to increase the current-carrying capacity, devices according to the invention may be cooled by a suitable cooling agent. The application of artificial cooling is especially simple if the cartridges or housings are hermetically sealed in accordance with the illustrated embodiments. This permits using a gaseous medium, for instance a flow of air, for cooling purposes. However, the switching units may also be arranged within a stationary or flowing liquid, for instance, in oil or in a water-glycol solution of suiiiciently small conductivity. If desired, the cooling agent may serve as a resistor to be controlled by the switching device. In the latter case, the liquid preferably consists of an electrolyte of the desired conductivity. The'appertaining electrodes should be designed so that the current density remains within permissible limits.

A plurality of switching units or cartridges according to the invention may be connected in parallel, in series, or in'mixed circuit arrangements. In such electric parallel connections, it may be useful, for maintaining a balanced load distribution until the moment of complete interruption, to connect an inductance coil in series with each unit. This coil, if desired, may be c0 bined with the cartridge housing to a structural entity in a manner similar to the embodiment shown in Fig. 3. If units with holding coils are employed, such an inductance coil may consist of at least part of the holding coil.

Switching devices as eXemplified by the abovedescribed embodiments may be used as individual apparatus or, according to another feature of the invention, several switching units or car tridges appertaining to electrically separate current paths are subjected to a common magnetic control flux. For instance, a single control coil may produce the controlling magnetic flux for the plurality of cartridges, while the magnetic return path extends through the individual units. As a rule, a magnet core surrounded. by the control coil represents the source of the magnetic control flux, this source having a small magnetic reluctance as compared with that of the several switching units controlled thereby. However, the control coil may also immediately act upon one of the cartridges, while other cartridges form the magnetic return path or part thereof. If desired, more than one control coil may be provided to jointly act on the magnetically associated cartridges.

In devices of the just-mentioned type, the switching units or cartridges may be assigned for response to respectively different values of an electric current. To this end, the different units may be rated to respond to respectively diiferent critical currents. For the same purpose, however, several SWitChing units may have the same critical current value while means extraneous to the units proper are provided to make the equally rated units respond to respectively diiferent current values. Such a different response of substantially equally rated units is ob tained, for instance, by inserting magnetic resistance or reluctance into the magnetic circuit of one or several of the units. Different reluctance in the magnetic circuit can be obtained by providing air gaps of different width. For certain purposes, a simultaneous response of several or all switching units of such a multiple device is desirable.

In general, the different units or cartridges appertaining to the device are magnetically parallel-connected in order to maintain the controlling ampere turns at a minimum. There are cases, however, in which it is preferable to arrang the cartridges at least partly in a magnetic series connection.

Depending upon the operating conditions, the magnetic control flux is unidirectional or variable. When operating with alternating current, the control flux can be prevented from dropping to zero by providing two or more phase-displaced control fluxes. These fluxes may stem from separate current sources. In mose cases, however, a phase-displaced flux is more simply obtained with the aid of short-circuit windings. Such a winding may be common for a number of switching units, although it is also possible to assign a short-circuited winding to each.

For many cases of application, the switching device for the main current is advantageously combined with an auxiliary switching device for the control currents, the auxiliary device being also subject to the control flux. It may be of advantage to equip the auxiliary switching device also with switching units which, as a rule, may have smaller dimensions and may be rated for a smaller switching capacity than those of the main device.

If the current in one of the separate circuits to be controlled by the switching device is above the current value permissible for one switchin unit, two or more units may b electrically parallelconnected. For operating with high voltages, it may be similarly of advantage to electrically series-connect two or more units.

The above-mentioned features relating to a multiple unit device according to the invention re exemplified by the embodiment illustrated in Fig. 5. The core 3! of the magnetic field structure shown in this figure is equipped with a control coil 32 and also with a short-circuited winding 32, which permits energizing the control coil with alternating current while preventing the magnetic control flux induced in core 3| from dropping to zero due to the current zero passages of the energizing control current, The cor 3| is joined with two yokes 33 and 3d. The yokes extend in parallel to each other and form extended pole surfaces between which three cartridge-type switching units 35, 3B and iii are inserted. As apparent from the sectional illustration of cartridge 35, each cartridge has two magnet pole pieces 38 and 3t, a movable switching element 49, and an insulating tubular body 41. In detail, the cartridges are designed in accordance with the features of the invention represented in Figs. 1, 2 and 3. Each cartridge is shown to be equipped with a holding coil 42, 63 and 54 respectively, arranged on the insulating enclosure of the cartridge, as explained in the loregoing with reference to Fig. 3. The magnetic field system is equipped with auxiliary yo'xes Al and 8 for controlling an auxiliary switching device denoted, as a whole, by 25. The auxiliary device is composed of three switching cartridges, all denoted by $6. The switching cartridges 35, 36 and 37 are electrically insulated from the yokes 33 and 34 by insulating strips 49 and 58.

The switching device according to Fig. 5 may be applied for the following purpose. If the control coil 3| is energized by a control current of a given value ii, the switching cartridge 35 is supposed to respond and to close its circuit so that a current I1 flows in the appertaining circuit connections. At the same time, one of the auxiliary cartridges 4% is to operate, If the controlling current in coil 32 is increased to a given value isthe current I2 previously flowing in the circuit of cartridge 35 is to be interrupted for instance, and this occurrence is to be transmitted to a central station by the response of an appertaining control switch. When the current in coil 3i assumes a still higher value is, the current I3 is supposed to be switched-in by the cartridge 3?. It will be understood from the explanation given in the foregoing that the just exemplified mode of operation is readily achieved by designin the switching elements of cartridges 35 and 37 as make contacts and the switching element of cartridge 35 as a break contact, and by rating the critical currents of the three cartridges correspondingly.

This example will show that multiple switching devices according to the invention lend themselves readily for a large variety of applications. For instance, sucha device can be applied as an alternating-current relay, especially for multiphase current, with the result that complicated relay control schemes can be carried out with simplified'relay devices'that require considerably less space than theseparate relaysheretofore customary for such purposes. Forinstance, if in a control system a number of separate circuits are to be-switchedsimultaneously, all these circuits can be controlled by respective switching units or cartridges which aresubjectedto the control flux of a single control coil. For startingschemes, a multiple device according to-the invention maybe used t o perform a given sequence of control actions in response to a progressive change of the control current. Similar advantages ar obtained in remote control and measuring systems, for regulating purposes and also for rectification, inversion,"orother translation of electric current or voltage in which a controlled switching or commutation between circuits is required. An essential advantage of such devices lies in the fact that a virtually unlimited variety of control actions can be performed with small control energies and that the particular requirements can readily be satisfied by selecting proper combinations of control coils and switching units. 7

It will-be understood from the foregoing disclosure by those skilled in the art that the invention permits various alterations and modifications and can be embodied in devices other than those specifically shown and described without departing from the gist of -the invention and within its essential features asset forth in the claims attached hereto.

We claim:

1. A switching device, comprising an insulating housing, two magnet pole pieces having respective pole faces spaced from each other within said housing, said pole pieces extending from within to substantially the outside of said housing, a magnetizable rigid switching member pivoted at its center-between said pole' pieces for rotational movement toward said two pole faces and away therefrom respectively, spring means for biasing said member away from said pole faces, and two stationary contact structures extending from without to within said housing and having in said housing respective contact faces bridged by said member in one of said positions, said contact structures having at all points between said contact faces and the outside of said housing a conductive cross section larger than that engageable by said member.

2. A switching device, comprising an insulating tubular housing, two magnet pole pieces disposed in the two axial ends respectively of said housing so as to substantially close said housing ends, said pole pieces being axially spaced from each other and having two respective pole faces within said housing and two outer faces at said axial ends respectively of said housing, a magnetizable rigid switching member disposed in said housing between said pole pieces and pivotally connected wtih said housing for angular movement toward and away respectively from said pole faces, said member extending substantially in the axial direction of said housing, biasing means for normally holding said member away from said pole faces, and electric contact means including said member to be closed and open depending upon the position of said member.

3. A switching device, comprising an insulating tubular housing, two rigid magnetic pole pieces attached to said housing at the respective ends thereof and having respective pole faces spaced from each other withinsaid housing, said pole pieces being magnetically and electro-conductive- 1y accessible outside said housing, a rigid switching member revolvably mounted in said housing between said pole pieces so as to be movable between two positions toward said pole faces and away therefrom respectively, said member having biasing means tending to holdit away from said pole faces and consisting substantially of ferromagnetic material to be movable toward said pole faces when magnetized thereby, and two rigid parts of electric contact material integral with said respective pole pieces and electrically engageable by said'member to be bridged thereby. 4. A switching device, comprising an insulating housing, two magnet pole pieces attached to said housing at opposite sides respectively and having respective pole faces within said housing, two stationary rigid contact structures extending fromwithout to within said housing and having respective contact faces within said housing, an elongated rigid and magnetizable' switching member pivoted about its center withinsaid housing between said pole pieces and movable between two angular positions, said member having a air of faces engageable with said pole faces when said member is in one position and having a pair of faces engageable with said contact faces when said member is in the other position, said member being biased toward said other position and magnectically controllable by said pole pieces to move to said one position, all said faces extending substantially parallel to the longitudinal direction of said member.

5. A switching device, comprising an insulating housing, two ferromagnetic and. electrically conductive pole structures insulated from each other and extending from without to within said housing, said structures having respective pole faces spaced from each other within said housing and having respective portions accessible at the outside of said housing for supplying magnetic flux and electric current, contact pieces of electrically good conductive material disposed on said respective pole faces, a magnetizable and electrically conductive armature member disposed within said housing and magnetically movable toward said pole faces, said member when so moved being in electric bridging engagement with said two contact pieces, spring means disposed in said housing, said armature member being rigid throughout and being mounted on said spring means, said spring means having relative to said member a biasing force directed away from said pole faces for disengaging said member from said structures and being the only mechanical support of said member.

6. A switching device, comprising an insulating housing, two ferromagnetic and electrically conductive pole structures insulated from each other and extending from without to within said housing, said structures having respective pole faces spaced from each other within said housing and having respective portions accessible at the outside of said housing for supplying magnetic flux and electric current, each of said pole structures having a piece of electric contact material disposed on said pole face in face-to-face contact therewith, a rigid and electrically conductive armature member movably disposed in said housing, biasing spring means connected with said member to bias it away from said pole faces, said member being magnetically movable toward said pole faces due to said flux and being engageable with said two pieces of contact material to electrically bridge said structures.

7. A switching device, comprising an insulating housing, two magnetically and'electri'caily conductive structures extending from within said housing to the outside of said housing and having respective faces spaced from each other Within said housing, said structures being electrically insulated from each other and being accessible from the outside of said housing for passing magnetic flux and electric current through said structures, a magnetizable and electrically conductive switching member disposed in said housing and being movable into bridging engagement with said two faces and away therefrom to electrically interconnect and disconnect said two structures, a biasing spring connected with said member in said housing for biasing said member away from said faces, each of said structures having at all points between said'face and the outside of said housing an electrically conductive cross section larger than the area of contact engagement with said member.

8. A switching device, comprising an insulating housing, twomagnetically and electrically conductive structures extending from within said housing to the outside of said housing and having respective pole .face's spaced from each other within said housing, said structures being electrically insulated from each other and having respective portions magnetically and electrically accessible from the outside of said housing for passing magnetic flux and electric current through said structures, a magn'etizable and electrically conductive member being rigid throughout and being disposed in said housing, a biasing spring means connected with said member for biasing it away from said two pole faces, said member being mechanically supported only by said spring means and being movable due to said flux into bridging engagement with said two structures of said respective pole faces to then electrically interconnect said structures, each of said structures having at all points between said pole face and the outside of said housing an electrically conductive cross sect-ion larger than the area of contact engagement with-said member.

9.11 switching device, comprising-a plurality of individual devices according to claim 7 connected in magnetic and electric parallel relation to each other and having a common magnetic field structure outside of said respective housings and a common control coil on said field structure, said field structure having two yoke portions in magnetic engagement with said respective two structures of each of said individual devices.

FRITZ KESSELRING.

HEINRICH DEGLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 604,682 Moore May 24, 1898 684,378 Potter Oct. 8, 1901 1,185,240 Petersen May 30, 1916 1,510,341 Proctor Sept. 30, 1924 1,783,279 Burnham Dec. 2, 1930 2,060,235 Miller 1 Nov. 10, 1936 2,080,356 Haslev May 11, 1937 2,187,115 Ellwood et a1. Jan. 16, 1940 2,234,982 Ross Mar. 18, 1941 2,264,124 Schreiner i Nov. 25., 1941 2,277,215 7 Ellwood Mar. 24, 1942 2,342,781 Aamodt Feb. 29, 1944 2,378,986 Dickten, Jr June 26, 1945 2,445,401 Langer July 20, 1948 2,481,003 Curtis Sept. 6, 1949 2,521,723 Hubbell 1 Sept. 12, 1950 V FOREIGN PATENTS Number Country Date 451,596 Germany Oct. '28, 1927

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