US3369206A - Electromagnetic telephone relay - Google Patents

Description

Feb. 13, 1968 K. A. LUNDKVIST ELECTROMAGNETIC TELEPHONE RELAY Filed Jan. 6. 1966 INVENTOR.

\(nm. Ann. Lumonvlgr United States Patent 3,369,206 ELECTROMAGNETIC TELEPHONE RELAY Karl Axel Lundkvist, Stockholm, Sweden, assignor to Telefonaktiebolaget L. M. Ericsson, Stockholm,

Sweden a corporation of Sweden F lled Jan. 6, 1966, Ser. No. 519,058 Claims priority, application Sweden, Mar. 10, 1965,

3,151/65 5 Claims. (Cl. 335273 ABSTRACT OF THE DISCLOSURE An electromagnetic relay the core of which is rotatable in the coil of the relay and has at its end facing a pivotal armature of the relay a non-axial or set-oflf portion so shaped that the distance between the pivot axis of the armature and the principal area of a magnetic attraction of said non-axial core portion varies in accordance with the angular position of the core in the coil whereby the relay can be set in accordance with the contact assembly to be controlled by the relay without altering the working angle of the armature and the extent of lifting or lowering of the contact assembly.

In automatic telephone establishments electromagnetic relays of standard design are used. They generally consist of an angular-bent yoke, on which contact spring assemblies, an armature with a residual plate and an iron core with a coil are fastened. The yoke constitutes the frame of the relay and is maintained unchanged independently of the purpose of the relays while the number of contact spring assemblies and the number of contact springs in each assembly are changed within wide limits dependent on the use of the relay. The winding of the coil also varies very much both with regard to electric data and with regard to volume. The residual plate of the armature is likewise changed dependent on the use of the relay. The length of the contact springs, contact distance, contact pressure and the lifting of the movable contact springs are accurately determined magnitudes that are not changed as they have been determined according to a very comprehensive practical and theoretical work. The contact spring assemblies, the yoke and the armature have been the unchangeable standard details of the telephone relay while the iron core, the coil and the residual plate are details that are changed partly with the number of contact springs, partly to adapt the properties of the relay to its use.

A standard relay must in weight and volume be diphone relay are the diameter of the winding wire in the coil and the thickness of the residual plate and also the diameter of the iron core. Sometimes also the diameter of the end of the iron core at the air gap is varied. To vary the winding according to the load of the relay and according to the resistance of the operating circuit is a necessary and natural measure while on the other hand a variation of the dimensions and the appearance of the iron core must be regarded as a deviation from the standardization. Alteration of the thickness of the residual plate may appear acceptable in view of the insignificant size and cost of the detail. In reality also the variation of the residual plate is not desirable as the length of the iron core and the length of the yoke do not coincide at more than one thickness of the residual plate. The armature travel of the relay is likewise changed with the residual plate and increased demands on adjustment possibility for the armature travel and for the lifting of the contact spring assemblies become a necessary consequence.

It has been proposed to construct a telephone relay so, that the length of the lever of the spring load on the armature may be varied. Then the armature travel must be simultaneously varied in order that the movement of the contacts should not be changed. The proposal implies many constructive difiiculties and therefore it has not taken practical shape.

The present invention has for a purpose to reduce in an electromagnetic standard relay with from case to case varying load and working conditions, the need of iron in the magnetic circuit and the need of copper in the relay winding and to bring about with simple means a readjustment of the relation between the levers of the relay armature in view of the intended load.

This is achieved by means of a side-position of the end of the iron core of the coil at the air gap after which by turning the end of the iron core the distance between the working point of the magnetic field on the armature and the axis of rotation of the armature is changed in proportion to the magnitude of the load without change of the angle of rotation of the armature and the lifting of the contact springs.

In order to explain the invention it is assumed that a telephone relay is loaded with that maximum number of contact springs for which the relay is intended and is held in released position and that the relay winding is traversed by a current that produces a magnetic field sufficient for the operation of the relay. When the relay armature releases, it will be attracted against the end of the iron core. Hereby first a number of easily stretched contact springs, so-called under-springs, are actuated which are lifted and make contact with harder stretched contact springs which are to give the contact pressure, and when the armature is a few tenths of a millimetre from the end of the core the armature will pass its critical position, whereby the total contact spring load shall be overcome. Then the spring load rises insignificantly during the last part of the movement of the armature while the magnetic flux increases rapidly and therefore the magnetic flux density in the iron circuit can at least in some part have a chance to approach saturation already when the critical position is reached. If regard is paid to reasonable margins for the operation of the relay both regarding the magnitude of the tractive force and regarding the saturation in the iron, it is possible to determine the cross section area of the iron, the remaining movement of the armature in the critical position and the levers of the armature in such a way that an optimum in' respect to weight and volume for the relay is achieved. The magnetic flux density in the end of the core at the air gap is here indicated by B, the area of the iron core at the core end by A, the magnetic resistance disregarding the remaining movement of the armature in the air gap by m. The spring load is called P, its lifting is called 0 and its lever in relation to the centre of rotation of the armature is indicated by b. The magnetic field at the end of the core becomes B A, its lever on the relay armature is indicated by a, and the remaining movement of the armature in the air gap at the critical position is indicated by d. The cross section of the iron core is assumed to be a circular surface as a round coil gives the smallest copper consumption. The

number of ampere turns required for the operation is indicated by M. Due to the leakage between the iron core and the yoke the magnetic flux density will be greater in the iron core than at the end of the core. The relation between the maximum value of the flux density within the iron core and B is supposed to be a number k valid for critical position of the armature and determined empirically.

If the dispersion of the field in the air gap is neglected, the relations (1), (2) and (3) below are valid. The Equation 1 indicates equilibrium between the moment of the load and of the field on the armature. The Equation 2 indicates the relation between the flux density B and the number of ampere turns. The Equation 3 indicates a mere geometrical relation.

e the absolute permeability for vacuum.

In the above equations are P and determined by the construction of the contact spring assemblies. The maximum fiux density k.B is determined by the properties of the iron. The number k varies somewhat with the air gap d. The value In is composed by the thickness of the residual plate, the magnetic resistance of the iron and by the magnetic resistance is consequence of the surface treatment of the yoke, of the armature and of the iron core.

In a finished relay one cannot alter A, nor can b be altered as has been mentionad above. If the lever b is supposed to be determined there will be obtained out of (1), in case the relay is loaded with a maximum number of contact springs, the relations:

2 .,-P b 2 (4) When the load P decreases, also the lever a and thus the air gap d can be decreased. The value m is determined in practice by the remanence of the iron and by the surface treatment and may here be regarded as a value given in advance, which cannot be varied.

In normal telephone relays both A and a and b are fixed, unchangeable magnitudes. According to Equation 2 the required number of ampere turns M can then be reduced only by a decrease of B, i.e. that the iron volume is utilized completely only at maximum load. On decreasing the load P the need of ampere turns is not diminished in proportion to P but only in the proportion VF. Out of (2) and (4) is namely obtained:

Thus the relay becomes less sensitive at low load when often greater sensitivity is desirable.

From (4) is seen that an increase of a allows the decrease of A, i.e. reduces the need of iron in the relay. When the iron core of the relay coil can be made thinner also the need of copper in the winding decreases at a definite number of ampere turns. From (5) is seen that the increase in M owing to an increased a will be relatively small and can be completely avoided if m can be reduced for example by thinner residual plates.

On an estimation of the dimensions of a relay it is necessary to proceed from an average value for the load and from this determine partly the cross section of the air gap and of the iron circuit, partly the levers a and b of the armature and also the length of the yoke and of the coil. The iron core in the coil is in this connection of course made straight without a side-position of the end of the core at the air gap.

At heavier loads the cross section of the iron becomes insufficient if the length of the lever a is maintained unchanged. According to the invention the end of the iron core is therefore shaped so, that the lever a may be varied upwards and downwards around the average value that corresponds to the lever a at a straight iron core. At a small value on a the relay armature becomes short and light. This is of value in sensitive relays which should be rapid in spite of only small forces being at disposal.

At decreased load only a smaller number of ampere turns is required and the iron circuit becomes utilized unsatisfactorily if the levers a and b and the area A are left unchanged. According to the invention an increased sensitivity is obtained in weakly loaded relays by decreasing the lever a.

In slow-operating relays a large magnetic field is desired but also a low resistance in the copper tube that produces the slow-operation is required. These factors counteract each other at each change of the diameter of the relay core. An increase of the lever a causes however always a better holding and consequently a more eifective slow-operation and therefore the invention comes into use also in slow-operating relays.

At low loads, especially relays with only two contact springs, a great sensitivity is often required, i.e. that the necessary effect on the winding upon operation should be small. If the lever a is decreased by placing the end of the core aside according to the invention, the air gap Will decrease. By increasing the area A of the air gap the flux is increased furthermore and the sensitivity of the relay increases. The flux density B in the air gap will be high in spite of the decreasing of the number of ampere turns. The stray fields may be supposed to decrease with the number of ampere turns. The relative change of the magnitude of the load from average load to low load becomes considerably greater than from average load to maximum load.

On a relay intended for standardization a residual plate of definite thickness is desired as the length of the relay core has to be adapted to the length of the yoke and the armature cannot lie on the level of the end of the relay core for more than one determined value on the-thickness of the residual plate. If the thickness of the residual plate is determined for a relay loaded with the average number of contact springs, this residual plate can be maintained at all other loads, if the lever a is varied. An adjustment of a implies a levelling between the operation margin of the relay and its release margin. Thus it is suitable that this adjustment may be made continuously and not only step-by-step. The invention may in view of the adjustment of the relay come in to use also for relays with a contact spring load corresponding to the average load.

In the accompanying drawing several preferred embodiments of the invention are shown by way of illustration and not by way of limitation.

In the drawing:

FIG. 1 is a diagrammatic view, partly in section, of a relay set for a heavy load to be controlled;

FIG. 2 is a similar view of the relay but set for a light load to be controlled; and

FIG. 3 is a perspective fragmentary view of a modification of the relay.

In the relay according to FIGS. 1 and 2, a magnetic circuit is formed by the yoke 1, the armature 2 and the iron core 3. A coil 4 is located on the iron core 3 which is turnable in the coil, and a contact spring assembly 5 is mounted on the yoke 1.. The end of the iron core 3 in the air gap is bent to the one side. In FIG. 1 the iron core is turned so that the distance between the end of the core and the yoke 1 is as great as possible. In FIG. 2 the iron core is turned compared with FIG. 1 so that the end of the core is as near to the yoke as possible. All intermediate positions are readily conceivable. Moreover, the end of the core does not need to lie symmetrically in relation to the armature 2. The iron core 3 is potted in a plastic such as Bakelite, so that two end plates 9 are formed and the iron core is insulated from the coil 4. In this way the bent end of the iron core is located inside the fore end plate, so that no extension of the core or loss of coil space arises. As the level of the end of the core runs obliquely to the axis of the bent core part the surface of the end of the core can be made larger than the cross section of the iron core. Dependent on the bending angle of the iron core the size of the pole face may be varied so, that a relay that is effective at all loads is obtained.

The end of the core can also be formed by staving or be be provided with a loose pole piece that can be turned around the iron core of the coil without a simultaneous rotation of the coil itself.

In FIG. 3 is shown a round iron core 8, the end of which has been shaped to an adequate form such as a radial arm 8a. The coil 4 is wound on a loose bobbin and the iron core is extended through the bobbin with the core end 8a protruding therefrom. The back end plate 6 of the bobbin is shaped to carry terminals 7 for connecting the ends and connections of the coil to the bobbin. The iron core can be turned without the coil being turned. The armature and the contact spring assemblies are omitted in order to simplify the figure.

I claim:

1. An electromagnetic relay comprising in combination: a yoke, a rotatably supported elongate core having a nonaxial end portion, a coil encompassing the core permitting rotation thereof, and an armature pivotally mounted adjacent to said nonaxial end portion of the core, the pivot axis of the armature being disposed laterally of said nonaxial core portion, said yoke, core and armature constituting a magnetic circuit including an air gap defined by the armature and the nonaxial end portion, the width of said air gap corresponding to the pivotal position of the armature in reference to the nonaxial end portion of the core, whereby the leverage of the magnetic force attracting the armature toward said nonaxial core portion varies in accordance with the distance between said core portion and the pivot axis of the armature, said distance being a function of the rotational position of the core in the coil; and

a movable load means coacting with the armature to bias the same into the direction away from said nonaxial core portion and to be displaced by the movement of the armature toward and away from said core portion.

2. An electromagnetic relay according to claim 1 Wherein the tip of said nonaxial end portion of the core is located in one plane in all angular positions of the core in the coil whereby the angle of the pivotal movement of the armature and thus the displacement of the load means are the same for all rotational positions of the core.

3. An electromagnetic relay according to claim 1, Wherein said core is a straight core and said nonaxial end portion of the core is a portion bent-off in reference to the center axis of the core.

4. An electromagnetic relay according to claim 3, Wherein the tip of said nonaxial end portion of the core is at a slant in reference to the center axis of the bent-01f core portion, the plane of said slant being normal to the center axis of the straight core portion.

5. An electromagnetic relay according to claim 1, wherein said core is a straight core and said nonaxial end portion of the core is in the form of an arm substantially radially extending from the straight core portion.

References Cited UNITED STATES PATENTS 2,076,658 4/1937 Morgenstern 33528l X 2,294,327 8/1942 Zupa 335281 X 2,588,534 3/1952 Jorgensen 335132 BERNARD A. GILHEANY, Primary Examiner.

G. HARRIS, Assistant Examiner.

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