US1847012A - Electromagnet - Google Patents

Description

Feb. 23, 1932. M. LAVET 1,847,012

ELECTROMAGNET Filed Oct. 13, 1930 2 Sheet-Sheet l Feb. 23, 1932. M. LAVET 1,847,012

ELECTROMAGNET Filed 001;. 13, 1930 2 Sheets-Sheet 2 mum 72 wwia Patented Feb. 23, 1932 UNITED STATES PATENT OFFICEv name LAVE'I', OI PARIS, FRANCE, ASSIGNOR '10 ETABLISSEHENTS L'EON EATOT, OI PARIS, FRANCE, A CORPORATION OF FRANCE mac-momentum Application fled October 18, 1980, Serial No. 488,502, and in France (lotober 17,

The presentinvention relates'to improvements in electro-magnets (associated or not with electric contacts) and to their application to electric clocks and watches whether self-contained or 0 rated from a distance, provided or not witli triking movements and chimes, andto various other apparatus such as chimes, vibrators, electric twmklers, polarized relays, battery charges, synchronous motors, contactless rotating motors, loud speaker motors, pick u s, etc.

In the industries o electric clocks, telegraphy and wireless, electro-ma ets are employed in many apparatuses w ich have an alternating movement, these being 'rincipall employed for operating ban 5, for win ing up springs, for operating electric contacts, etc.

The requirements for electro-magnets are generally as follows:

1. Good electric efliciency, and small inherent resistances, the latter arising principally from sticking and magnetic attractions from inertia of the parts to be displaced and 5 from mechanical friction.

2. Simple construction and low cost of manufacture.

3. Small weight and reduced overall dimensions of the electro-magnet and reduced consumption, specially for portable time instruments such as clocks etc. and for time receivers disposed in the centre of translucent dials.

4. In several applications, good electrical efficiency must be obtained for a very low supply voltage.

This last quality is in articular sought for electric watches and c ocks which must operate by means of a battery of small size lasting for a very lon time.

In order that the asting power shall be good (for example exceeding two years), it is found that it is advantageous, for given overall dimensions, to use a battery of a single element (1', 5) rather than batteries of three elements (4", 5) like the batteries for pocket lamps. For the same consumption in watt hours, with a very slow rate of discharge, the duration is better. Calculation and experience show that polarized electro-magnets .are found,

automobile watches and give the best results for utilizing the ener of the battery in question than ordinary s3 iron electro-magnets. In all cases, the polarized electro-magnet systems employed hitherto, are bulky, heavy, and costly. Further they comprise strong magnets which give rise to considerable friction and ma etic sticking. This is also caused b the act that the conception of the shapes 0 their various constituent parts does not permit easy assurance of the equality of the widths of air ap, and that in practice relatively large di erences producing lack of balance of the magnetic forces and much reducing the efiiciency particularly when it is a question of producing a relatively small mechanical power, as is the case for the application contemplated.

The present invention relates in the first place to improvements in very small polarized electro-magnets capable of bein housed in the casings of large watches, suc as automobile watches.

The details of construction and the shapes of the constituent parts enable all the members to. be collected into a very restricted space, and permit the maximum use of first class materials in order to obtain a very high electric power of the apparatus.

To obtain this last result, the actual state of the art shows that it is advantageous to employ:

1. A magnet of steel or cobalt such that the ratio between the length and the other dimensions is preferably less than in magnets of horse-shoe type.

2. For the iron parts magnetized by the winding, silicon sheet metal, or electrolytic iron, or any other product having great permeability and very small hysteresis (esgecially certain ferro-nickel alloys when the eld is weak).

3. A winding of high conductivity copper with spires of as small a length as possible disposed to accommodate the maximum volume of copper.

4. Air gaps of large surface and small thickness permittin variation of the reluctance of the de ormable' magnetic cirin relation to the weight explosion motors.

cuits within ve wide limits according to a predetermin law dependent upon the applications.

he magnetic products in questionabovc are very costl and further are only commercial y pro table in certain forms (especially cylindrical rods and thin plates).

The invention enables these materials to be used in most favourable conditions and it equally concerns various devices and applications of these systems associated with special electric contacts.

The object of the invention is set out in the followin structional orms w ich have been illustrated by way of example in the attached drawin On t e drawings: Y

Figure 1 shows the usual method of constructing magneto-electric machines ac-' tually known.

Figures 2, 3 and 4 show in projection with parts in section, a polarized electro-magnet provided with improvements constituting the object of the invention.

Figures 5, 6 and 7 are detail views of the constituent members of the electro-magnet.

Figures 8, 9 and 10 are diagrammatic figures showing the effect of the shape of the pole pieces of the movable armature of theelectro-magnet.

Figures 11 and llbis show a modification of the arrangement of the magnet.

Fi ure 12 shows diagrammatically the apphcation of the electro-magnetassociated with an electric contact in an electrically wound clock or watch.

Figure 13 is a dia am of the electric circuit of the system s own in Figure 12.

Figure 14 shows separately the electric contactwhose closure is automatically produced. 7

Figures 15 and 16 show the application of the invention to time receivers operating by means of alternating emissions of the electric current.

The improvements forming the object of the invention relate more particularly to the known t pe of polarized electro-magnet shown in igure 1. This ty e of electro-magnet comprises a magnet provided with heavy polar expansions A an A and a coil wound on an iron armature B rotating about the axis C. The coil is well known under the name of Siemens shuttle. This system is emplo ed as a motor, or as a current generator. n this last application, it is employed very frequently as t eignition magneto for Practice shows that the electro-magnet constructed and proportioned as indicated in Figure 1 does not allow the advantageous production of sensitive electro-magnets and economic manufacture suited to electric clockwork and like applications. This is because when the movable ardescri tions of various conmature of the apparatus of Figure 1 is rotated, very intense forces of magnetic attraction are exerted on this part which tend to rotate the coil in certain directions dependent on the shape ofthe pole pieces. These forces exist when the coil is not traversed by the electric current. They also persist when the coil is energized by a current and they prevent displacement when the current is weak. Displacement is only produced when the current is very intense and, even in this case the driving cou le obtained is irre ular an the electrical e ciency is impaired because the value of the current has to be increased in order that the apparatus may overcome the inherent resistances for the positions airresponding to the minimum driving coup e.

These disadvantages are eliminated with the improved method of construction described with reference to Figures 2, 3 and 4.

According to the invention, the electromagnet consists of a magnet A, preferably of steel or cobalt, and a movable coil whose core N is of electrolytic iron or like metal whose coeflicient of magnetic permeability is very hi h.

The coi is rovided with polar enlargements B and 2 constructed of stamped and bent sheet metal. 'The metal constituting them must be of very high ma etic permeabilit and very weak hysteresis, (for exiti n le 0 silicon sheet or alloy of like properies The shape of the pole pieces is of very great importance, and it may be modified according to the applications. Generally it is desired that the coil be operated by a very weak current and that the driving couple be of a value which is very high and constant over considerable angular displacement. This result is obtained with the shapes and proportions shown in the drawings.

The movable coil pivots in holes cut in the two brass plates C and C These plates are connected together by four iron pillars P P P and P which constitute the fixed pole pieces of the apparatus. These poles are connected magnetically to the magnet by the stain ed angle pieces of sheet iron E and E hese parts E and E are slightly flexible and they bear with heavy pressure on the polar extremities of the magnet and on the pillars P P P and P The use of the flexible parts E and E has the important advantage of permitting very weak reluctance of the joints and strong magnetization of the pillars to be obtained. This result is obtained without the necessity of having an extremely precise spacing of the limbs of the i magnet. The magnets can consequently be less costly than if it was necessary to grind the magnet to a very exact size. The U shape of the parts E and E should also be noted.

The parts E and E are shown separately in employed to parts E and E, also enables a sufiiciently Th large free space to be preserved between the magnet and the movable coil. This space is receive the flexible wires connectin the movable coil with the fixed terminals 0% the circuit. B bending back these connections on themse ves and by makin them of considerable length, the fiexure o t e wire is limited to great flexibility is obtained; also breaka e of the wire in s ite of a large number of displacements of the coil is prevented.

The details of construction of the movable coil are shown in the detail views (Figures 5, 6 and 7). The two pivots O and 0 are riveted on two brass parts H and H connected together by two pillars D and D The pivots O and O engage the holes in the lates C and 0,.

e-coil B is wound beforehand on the core which terminates in two threaded rods on which can screw the nuts G nuts permit the whole assembly of the constituent parts of the coil (that is to say, the brass parts H and H the pole pieces B and B and the coil B) to be accomplished. 1'0 this end the outline of the parts H and H, comprises tongues t and shoulders e. The tongues t engage exactly in recesses in the parts 13 and B and all the parts are maintained firmly in well defined emplacements and can be fitted up by suitable manipulations. It should be understood that certain changes may be made within the spirit of the invention. In particular the nuts G and G may be replaced by screws screwing into the core N. 7

'It should be noted that this special method of construction has two particularly important advantages:

1. The play between the cylindrical pole pieces P P P and P and the movable parts B and B depend only upon these parts being produced by stamping. In effect the pivot hole and the three guide holes for the pillars P P P, and P, can be stamped simultaneously in the parts C and C The parts B and B are applied by locking of the nuts G and G on the parts H and H obtained by stamping. It is known that the method of manufacture by stamping enables very large series of parts which are exactly interchangeable being obtained.

This method of construction will thus permit very great accuracy being obtained, particularly in re ard to the play or air gap between the po e pieces. This is very important, for practice shows that very slight differences in the values of the air gaps alter considerably the driving couple as well as the value of the magnetic attractions acting on the coil.

2. The parts constituting the magnetic cirunit are only formed by cylindrical parts of a small value and a cut tapped holes in very thin metal.

and G These P by very thin sheet metal. e coil support is also constituted by very thin stampings. Consequently the maximum space is thus obtained for receiving the electric windin This is particularly important for the pro uction of very small electro-magnets, for theory and practice show that one can only obtain good efiiciency on condition that the coil is made as long as possible. The out in thin sheet metal are diificult to assemble rigidly for one cannot small diameter or the construction shown in 1 sembly is obtained by nuts 1 and G and small screw threaded pillars D and D whereby perfect rigidity is obtained, even if the electro-magnet is given very small dimensions.

When the current is interrupted and the coil is rotated by hand, the magnetic attraction due to the magnet A and acting between pole pieces B and B and the iron pillars P P and P varies according to a certain law which depends on the variation of the total reluctance of the magnetic circuit with the angle of rotation. It is well known that in variable magnetic circuits natural direction of displacement of the movable part is such that it reduces the reluctance of the circuit to a minimum.

In the apparatus shown in Figures 2 to 6, the total reluctance of the magnetic circuit depends mainly on the reluctance of the air gaps, that is to say, on the air spaces bounded by the adjacent parts of the pillars P P P and P and of the pole pieces B and B When the coil rotates, the reluctance of certain air gaps increases and that of other air gaps decreases. This variation depends both on the thickness of the air gap and on its area. Compensation for this variation can be obtained by giving the parts B and B a certain stamped shape and by centering these parts either concentrically with the axis of rotation 0 0 or with a certain degree of eccentricity in order to vary the play or air gap with the angle of rotation.

The shape shown in Figure 6 permits the 0011 provided with iron enlargements B and B to be in neutral equilibrium in the internal magnetic field produced by the magnet A. his coil may be displaced by means of a very weak force. If the coil is brought to any point in its path it remains in position without having any tendency to return or to continue its movement. It should be noted that this result is obtained by shaping the sides of the pole pieces as arcs of circles m ,-n g and m m, g (Figure 6). Further, the angles m m 9 and 92 are slightly directed towards-the centre as is indicated in Figure (ibis. The radius of the points R is slightly smaller than the radius R of the adjacent part of the core of the coil.

These shapes and proportions have been ure 7, the asthe proportions indicated determined experimentally. For certain applications it is advantageous to depart from in Figures 6 and (ibis, in order to bring the coil in certain positions. Figures 8, 9 and 10 indicate by way of example the properties of three shapes of the po e pieces B and B If the mean are formed by the pole pieces B and B is relatively small in relation to the distance of P and P as indicated in Figure 8, the mean position shown on this figure is a position of unstable equilibrium. When the current is stopped, the coil tends to be displaced either towards the left or towards the right, so that the pole pieces B and B come opposite to the poles P and P..

or the poles P and P If the mean are formed by the pole pieces B and B is relatively large in relation to the separation between P and P as indicated by Figure 9, the mean position shown on this figure is a position of stable equilibrum. The coil tends of itself to come between the poles P and P under the influence of the magnetic force of attraction due to the magnet.

Figure 10 shows such a shape for the pole pieces B and 13 that the coil tends to be displaced in the direction of the arrow f,. It is sufficient to make the curvature of the pole pieces such as B eccentric. The displacement tends to diminish the play with the pillar P or the air gap. This means may be combined with that of giving a certain stamped shape to the pole pieces B and B The outline may be asymetric. By adopting the proportions of the plan view, Figure 1062's, and by making IR very slightly less than R the result may be obtained that the coil is brought back in the direction f with a very small and constant force, as

if adbalanced part returned by a spring were use The magnet A only having the function of strongly magnetizing the pillars P and P P and P may be disposed in different manners. In particular, it may be placed as shown in Figure 11. To obtain a very high driving force with a weak current, it is desirable to increase the magnetic flux of the magnet and to reduce the reluctance of the magnetic circuit. This double result is obtained by the arrangement shown in Figure llbis which is a sectional view corresponding to Figure 11. It will be seen that two magnets A and A disposed side by side are employed. The length of the pole pieces B and B in the direction parallel to the axis 0 O is increased and this also increases the surface of the air gap and enables a much greater electromagnetic force to be obtained than if the plates C and C were closer together, and than if there were only a single magnet employed.

Actually the manufacturers of power electro-magnets adopt similar forms; The apparatuses are produced by preserving the same proportions and by increasing all the dimensions. Consequently, none of the parts of one model can serve in larger models.

This disadvantage may be avoided by adopting the arrangement'of Fi re llbis. For example the small model wil comprise a single magnet, the next model two magnets, and so on. The whole series can thus be obtained with a ve large number of common parts, which is evidently advantageous in the manufacture in series.

The improved electro-magnet that I have 'ust described may be associated with a nown electric contact system which closes in the oscillations of the coil in a redetermined direction; if the one end 0 the coil is energized in a suitable direction by this contact, and if the coil is returned in the direction opposite to the attraction, the coil tends itself to have a to-and-fro movement. The action is like that of electric trembler bells, with the difference that the alternating moving motor thus produced functions with a much reater efiiciency than that of house bells. he consumption of electricity and the wear of the electric contact is much less than if an electro-magnet of soft iron were employed. The circuit is also much less inductive and there is no tendency for the formation of sparks as strong as those which are produced with the contacts operating non-polarized electro-magnets.

The extent of the displacements can be increased by any known means. The electromagnet described in the present description can then be applied to the production of alternately moving motors for all applications. We will confine ourselves to mentioning the following applications:

The electro-magnet can be employed as a I polarized relay for closing a contact. By giving to the pole pieces the shape of Figure 9, three positions may be obtained; the middle position of rest corresponding to breakage of the circuit and the extreme positions to right and left corresponding to the closure of two distinct contacts.

Employed in an electric bell, the electromagnet may permit extreme reduction of the consumption of current. Such a bell is specially suitable as an electric clock bell provided with a time contact serving, for example, as a morning alarm. The small battery for operating the movement is sufficient for operating the alarm bell.

In all the known systems for rewinding the weights and driving springs of time mechanisms by means of an electro-magnet or of a periodically closed contact, the electromagnet may be replaced by the improved device forming the object of the invention. This change permits reduction of the consumption of electricity and avoidance of 3 is notched and magnets actually employe rapid deterioration of the contact. Further, practice shows that with this device a. batte operating with a single element of 1" is su cient to obtain rewindin With electro- (5 which do not employ a permanent magnet, it is necessary to use batteries of higher voltages.-

There is shown by way of example in Figures 12, 13 and 14, an improved construction for an electrically wound clock or watch comprising the electro-magnet forming the obect of the invention.

The time mechanism shown in the u per comprises a ratchet w eel part of Figure 12 R; which tends to rotate under the action of the pawl arm 1 and of the driving spring 2. f

ThlS arm returns abruptly backwards from time to time under the action of the electromagnet so as to assure continuity of the rotation of the ratchet wheel R in the direction of f This wheel controls the gear chain of the clock and of the watch with the speed of the gearing being regulated by an escapement and a balance wheel. (The principle itself of this rewinding system is well known).

The automatic switch which supplies the electro-magnet at the right time is shown separately in Fi re 14 which consists of a part 3 stamped in thin silicon sheet metal. Any other magnetic product may be employed possessing very weak hysteresis. This part is movable about the axis 0 and is disposed adjacent to the pillars P and P or the pillars P and P or adjacent the extensions of these pillars P and P It is sufiicient for these extensions P a and P to be strongly magnetized.

The part 3 is of the shape shown in Figure 14, the arcs 8 Z 8 t 8 t and 8 t are of spiral sections so that the rotation of the part causes a chan e in the reluctance of the magnetic circuit. 5n the other hand the part provided with fittings preferably shaped as washers, of which one 4 is of insulating material and the other 5 is of non-oxidizing conductin metal. Between these fittings is a conducting pin 6 fast to the movable coil of the electro-magnet. The di-' ameter of the pin 6 is less than the separation of the fittings 4 and 5.

In the position shown in full lines Figure 14 the part 3 is in unstable equilibrium. In effect this part tends to place itself in the magnetic field so as to reduce the reluctance of the magnetic circuit. Consequently, this part tends to rock to left and to right, the parts of the greatest radius tending to approach the magnetized pillars P a and P'..

The parts 3 and the pin 6 are interposed in the electric circuit as shown in Figure 13. One of the ends of the coil B is connected to one of the terminals of the battery, the other end is connected to the pin 6 fixed on a support 7 electrically insulated on the frame of the coil (Figure 12).

. The movable art 3 of the switch ivots on the support w ich is not shown in Figure 12 (for the sake of cleamess). It is connected through the intermediar of a. ve flexible small spiral spring 8 to t e other terminal of the batte V he movement 0 the pawl arm 1 is transmitted to the coil of the electro-magnet ow-' mg to the pm 9 and to the fork 10 solid with the arm 1.

The operation is as follows: (See Figures 12 and 13).

Between the winding actions, the movement of the mechanism is produced by the spring 2. The arm 1 rotates in the direction 1 and the coil rotates in the direction The shape of the pole pieces B and 2 of the electro-magnet must be that of Figures 6 or 10 so that the magnetic attraction of the magnet does not interfere in any way with the movement of the time mechanism. The pin 6 bears on the insulating part 4 and the current is interrupted. When the pin 6 solid with the movable coil reaches the position of unstable equilibrium shown in Figure 14, the contact piece 3 rotates suddenly in the direction f and takes up the position indicated in dotted lines in Figure 14.

The conductin pin 6 comes into contact with the conducting fitting 5. The current passes through the coil as indicated in Figure 13.

The coil of the electro-magnet is then displaced suddenly in the opposite direction f and the pawl arm 1 returns back and cooks the driving spring 2.

But at the end of its travel the pin 6 rotates the contact piece 3, and the fitting 5 suddenly leaves the pin 6 so that the circuit is interrupted. The parts then occupy the position shown in Figure 12, and the operation is repeated.

In this device the abrupt displacement of the movable part of the switch is obtained by avoiding the sprin mechanisms which are usually employed ring which have the disadvantage of acting with considerable friction and of becoming out of order eventually owing to wear of the rubbing parts and jammmg.

The invention may be applied to time receivers in which the advance of the hands is controlled by spaced impulses sent out by a master clock.

The electro-magnet forming the object of the invention is particularly suitable for time receivers operating by means of impulses of alternating directions, in which an endeavour is made to reduce the overall dimensions. This result is particularly desirable to obtain in the case of hand controlling mechanisms which are placed behind trans lucent dials lit from behind by means of electric lamps. The construction of such clocks may be simplified by fixing the mechanism it is then necessary to reduce to the. limit the dimensions of t e mechanism, so that the shadow which it produces on the centre of the dial does not adversely affect the visibility of the hands.

Figures 15 and 6 show by way of example how the invention may be applied to the construction of such a time mechanism. The frame of the coil is provided with a control finger 11 which engages in the fork arm 12 solid with the support 13 on which are articulated pawls 14 and 15 acting on the ratchet wheel 16. It is advantageous to adopt pole pieces of such sha' s that that armature of the coil tends to be inclined to left or to ri ht, as has been explained with reference to igure 8.

After each emission of current, the coil remains in place and the magnetic attractions which prevail cause one or other of the pawls 14 or 15 to bear on the locking sto s 16 and 17. Thus the hands are maintaine in lace. Owing to the arrangement shown in 1 are 16, a ratchet wheel 16 may be emplo ed aving a relatively large diameter an all the members may be grouped in a very reduced area corresponding to the external shape of the magnet.

Various modifications may be made in the mechanism described within the spirit of the invention. In particular, instead of the permanent magnet, an electro-magnet ma be employed having a winding energized y a continuous or rectified current.

The special shape of the pole pieces which enable the magnetic attraction to be varied with the position of the movable parts according to a selected law can be applied to other types of polarized electro-magnets, and in particular to those which comprise a movable soft iron armature polarized by a permanent magnet, and displaced in re ation to other iron parts which are temporarily magnetized, owing to coils of electric wire traversed by intermittent currents.

What I claim is 1. Polarized electro-magnet comprising a movable armature carrying an energizing coil provided with polar enlargements consisting of stamped and bent ieces of sheet metal of high permeability and low hysteresis, which armature oscillates in a field of a permanent magnet whose pole pieces consist of cylindrical iron illars connected to the polar extremities o the ma et by concave sheet metal plates held resillently between the polar extremities of the magnet and the pillars, and whose concavity is sufficient to accommodate the connections of the coil.

2. Electro-magnet according to claim 1, in which the movable armature consists of two thin plates which are non-magnetic and carry the pivots connected by cross bars, on which the pole pieces of the coil are fitted, these parts having apertures for the passa e of the ends of the core of the coil, assemb y being obtained b means of nuts screwed externall on the en s of the core, this armature osci latgng in the field of the permanent magnet.-

olarized electro-magnet according to claim 1, in which the polar enlargements of the armature are shaped as cylindrical surfaces having as axis the axis of rotation of the coil and limited to an arc of small length relatively to the spacing of two adjacent polar 1pillars of diflerent polarity.

4. olarized electro-magnet according to claim 1, in which the polar enlargements of the armature are shaped as cylindrical surfaces having as axis the axis of rotation of the coil and extending for an arc of considerable length and, in the position of equilibrium of the coil projecting considerably on either side of those of their points which are nearest to the polar pillars.

5. Polarized electro-magnet according to claim 1, in which the polar enlargements of the armature are shaped as surfaces comprising at the centre a cylindrical part having as axls the axis of rotation of the coil limited to an arc of small length relatively to the space between two adjacent olar pillars of different olarity, connected to cylindrical surfaces 0 much smaller radius which in the position of equilibrium of the coil project considerably on either eide of those of their points which are nearest to the polar pillars.

6. Device according to claim 1, in which several identical ermanent magnets are disposed side by si e and in which the coil is given a length in the direction of its axis of rotation corresponding to the number of magnets employed.

In testimony whereof I have aflixed my signature.

MARIUS LAVET.

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