US2357959A - Electromagnet and relay - Google Patents

Description

Sept. l2, 1944.

H. K. KOUYOUMJIAN ELECTROMAGNET AND RELAY Filed April s, 1941 a n ,9M cu we, Qw. vn/ir a a QN Y 0\ 6,45%, wg, l M (o flow Q Q c@ w/ gi? KSQM/ M ATTORNEY Patented Sept. l2, 1944 ELECTROMAGNET AND RELAY Haroutium K. Kouyoumjian, Wakefield, R. I., as-

signor to Ward Leonar d Electric Company, a

corporation of New York Application April 3, 1941, Serial No. 386,672

7 Claims.

This invention relates to time delay relays applicable to various uses, such as opening or closing a control circuit or for actuating any element after a proper time interval and thereby controlling other apparatus in a desired manner.

Certain improvements disclosed herein and not claimed are covered in-my pending application led February 25, 1942, Serial No. 432,228.

One feature of the invention relates to the introduction in the magnetic circuit of the relay coil, or electromagnet, of means for affecting the force or pull exerted by the magnet on the movable element or plunger of the relay. By such means, the force or pull exerted upon the movable element may be modified in such a manner that as the plunger moves further within the coil, the force or pull exerted increases only by a small amount over a wide range of movement of the plunger. In this way. instead of the movemont of the plunger being rapidly accelerated as it passes within the coil, there is imposed upon the plunger a force which gives a. gradual acceleration by small increments. Also by variations in the form and location of the means which modifies the magnetic circuit of the coil or winding, the force exerted upon the plunger may be varied considerably as the plunger moves within the coil, and thereby obtainvariations in the attractive force during the movement of the plunger so as to secure desired particular effects.

Another feature and object of the invention is to provide a form of relay which will give very long periods of time delay where the abnormal condition of the circuit to be controlled departs only slightly from normal conditions and to cause less and less time delay, the greater the departure from' normal conditions. Another object is to provide a relay which will avoid instantaneous response even under extreme departures from normal conditions so that time is ailorded for other devices of the system controlled to function before the relay attains its nal position.

Another object is the provision of means for overcoming undesired operation of the parts due to excessive shocks or jars. Another object is to provide an improved form of construction that will be dependable in operation with the same character of response under similar condiions without the necessity of attention over long periods of time. Other objects and advantages will be understood from the following description and accompanying drawing which illustrates one embodiment of the invention.

Fig. l is a vertical section of the relay; Fig. 2 is a plan view on the line 2-2 of Fig. l; Fig. 3 is a side view of the parts showing the location of the means for modifying the path of the flux of the magnet; Fig. 4 is a. section on the line 4 4 o i' Fig. 3 Fig. 5 is a vertical section of the relay showing the parts in their attracted positions; and Figs. 6, 7, 8 and 9 are explanatory charts.

Before considering the form of structure of the relay, reference is made to Figs. 6 to 9 in order to explain the change of force exerted upon the plunger of a solenoid as the plunger passes within the same to its extreme position, assuming a constant current excitation. In these gures the ordinates represent the force or pull exerted on the plunger and are indicated by the letter F and the abscissas represent the position oi' the plunger from a position where the plunger is about to enter the solenoid to its extreme position and are indicated by the letter P.

Fig. 6 shows the force or pull exerted upon the solenoid core having an air circuit. As the plunger enters the coil the force increases from e. small value rapidly to a maximum value and then rapidly decreases to a small value at which time the end of the plunger has attained the end of the coil. This variation in the attractive force obviously is not suited for most practical purposes.

Fig. '7 shows the effect when an iron-clad solenoid is used. The dotted line shows the effect of the iron magnetic circuit in that it produces a pronounced increase in the attractive force at the latter portion of the movement of the plunger. When this effect is superimposed upon the curve of Fig. 6 it gives the solid line curve of Fig. 'I as the resultant pull. It shows a pronounced increase to a high value and then the curve dips to a lower value and then abruptly increases to a maximum value. Although this is an improved character in the change of force over that of Fig. 6, it is objectionable for most practical purposes owing to the pronounced changes and dip in the curve.

Fig. 8 shows by the dotted line the effect of adding to the iron-clad magnet frame an iron plug or core at the end of the solenoid and projecting within it. When this dotted curve is super-imposed on the full line curve of Fig. 7, it gives a resultant curve of the general character shown in full lines in Fig. 8. 'I'his is far more desirable than the curves of Fig. 6 or Fig. 7 because it gives a continuously increasing force as the plunger advances to its final position. However, the increase is so pronounced in value that it results in a rapid acceleration of the plunger' the upper portion of the coil.

which tends to reduce the time interval in passing from one limiting position to the other.

If the full line curve of Fig. 8 could be modifled to avoid the pronounced increase vin the pulling force on theplunger during a considerable period of its travel, it would be highly desirable in reducing the acceleration of the plunger and in prolonging the timeginterval of the movement between extreme positions. This could be accomplished if, in some way, an opposite or negative component could be super-imposed on the full line curve of Fig. 8. Such a negative factor is indicated by the dotted line in Fig. 9; and when the same is super-imposed on the full line curve of Fig. 8, a curve such as the full line in Fig. 9 would be obtained. The first part of the movement is shown as being rather abrupt and then follows a considerable distance of movement over which the pulling force is only slightly increased, followed by an abrupt increase in force 4in movement of the plunger atthe end of the stroke. This character of force exerted is highly desirable for certain uses'and particularly so in time delay relays because of the comparatively slow movement of the plunger during a considerable portion of its stroke, This character of control o f the plunger is obtained in the particular form of relay herein shown and described and it will be appreciated that by changing the position and form of the means for affecting the magnetic circuit, various forms of the force curve can be obtained kfor adaptation to particular requirements.

Referring now to the structure of the relay as shown in Figs. 1" to 5, the solenoid coil I is shown embraced by'an invertedU shaped magnet frame 2 having downwardly projecting legs. The lower ends 2a of the legs are turned inwardly and the upper central portionof the frame is provided with a downwardly extending iron or steel plug or core 3, the lower end of which projects within The upperportion of the core has a screw engagement with the frame and projects upwardly a short distance beyond the same. The magnet'coil or winding I is retained in position against the under side of the magnet frame by a cross-bar Ia of sheet metal which is bent downwardly at its sides and ends and held in position by screws Ib passing through the lower portion of the magnet frame legs. This cross-bar is of non-magnetic metal.

The movable portions of the relay are formed of two main parts, one of which is a hermetically sealed dashpot unit which moves as a whole and the other of which is a movable plunger within `the unit connected with the piston of the dashpot and which serves in the nal portion of its stroke to move the unit as a whole. The plunger 4 of iron or steel is in the form of a tube with an open upper end and a longitudinal slot 4a at one side. It is connected to the piston of the dashpot and provided with an external band 4b to serve as a guide for its upper portion. The plunger is movable within a tube or cylinder 5 of non-magnetic metal and which is covered and sealed at its upper end. This tube extends downwardly and engages by a sealed joint the plate 6 of the dashpot. This plate is sealed to the body I of the dashpot which is shown as having integral therewith the bottom plate of the dashpot. Thus the dashpot and its upwardly extending tube form a hermetically sealed unit which prevents the entrance of any foreign matter and also avoids any evaporation of Oil or other liquid within the unit.

f on the end of the plate II.

ward movement of the piston and plunger;'and

f by small brass pins Ida.

The dashpot is enclosed by a guiding cup 8 closed at its bottom and in which the dashpot unit is freely movable. The retaining cup is provided with an outwardly extending iiange 8a at its upper edge and is secured to the under side of the ends 2a of the magnet frame by the screws Bb. The guiding cup and the dashpot are made of non-magnetic metal, such as brass.

The dashpot piston is shown in the form of a circular plate 9 and provided with one or more downward projections 9a for supporting it in its lowest position.. It has a pair of upwardly projecting ears 9b which carry a pin or shaft I0. On this shaft is pivotally mounted a plate I1I to which the plunger 4 is fixed. The plate II extends cross-wise and is slotted at the end opposite its pivotal support so as to freely engage the shank of a pin I2. This pin is fixed at its lower end to the piston 9 and is provided with a head I2a. at its upper end which normally rests These parts assume the position shown in the drawing when the piston is pulled upwardly by the plunger 4 and as there is a slight clearance between the rim of the piston and the main inner wall of the dashpot, the-upward movement of the piston will permit the medium, such as oil, to pass by the rim .of the piston from the upperr portion to the lower portion of the dashpot, as the piston moves upwardly. When, however, the piston is moved downwardly during any portion of its stroke, the pressure of the medium within the dashpot on the under side of. the piston plate will cause it to turn upwardly about the pivot pin I0 and assume an angular relationto the plate I I. This gives a large clearance space between the rim of the piston and the interior wallof the dashpot land thus permits a comparatively lrapid downwhen the piston attairsits lowest po'sition,the parts will again assume the l'relative positions shown in the drawing. l

The lower portion of the cylinder 5 is ernbraced by .a sleeve I3 xed thereto and which has an outwardly turned rim |311 at its upper end.

The tube 5 and sleeve I3 are vembraced by a magnetic plate I4 ofA iron or steel,'the plate being freely movable'axially with relation to the tube and sleeve. This plate, as well shown in Fig. 2, is of rectangular form andextends over and normally rests upon the inturned ends 2a. of the magnet frame, being spacedtherefrom slightly proper relative position lto thewmagnet frame .by a pair of pins I5whichare flxedto .and extend upwardly from'the flange viia'gand .positionedonf opposite sides of one en d ofthe plategfas shown in Fig. 2. A phosphor bronzesprin'gfl having l a central opening is vpositioned between-the flange 'v I3a of the sleeve I3 and thezmagnetic plate Ill'.` f The spring is provided with several ngers which.l extend outwardly over the plate I4, as shownvin Fig. 2. The fingers if@engage-the.'plate Myior yieidingiy holding the same mits normalposition.v The two outwardly extendingngers-"IGbfextend beyond the plate lli andyieldingly engage rrespectively the inner top surfaces of the ends 2a 1 of the magnet frame. A pair of pins I'I- are-fixed .g to and extend upwardly from the plate Iliand pass freely through the body portionof the leaf spring for holding the same in-propcr alignment.

The means for affectingthe flux of the magnet, as already referred to. in connection with Fig. 9, for prolonging the time delayV action of the relay is, in this particular instance, formed of Theplate is kept in two triangular pieces Il of iron or steel. A face view thereof is shown in Fig. 3 and they are positioned on opposite sides of the tube or cylinder l and displaced in an axial direction from the ends oi' the winding and from the-poles of the magnet as shownvln Figs. 1 and 4. The apex oi' these pieces is pointed downwardly and they are xed to and carried by a non-magnetic metal band I9 which encircles the tube 5 and has a threaded engagement therewith. The magnetic pieces I8 are thus magnetically separated from each other. The inner face of the band I9 at opposite sides is cut away, as shown in Fig. 4, to provide recesses for receiving and supporting 'the two triangular magnetic pieces `I8. Adjustability of the pieces I8 upwardly or downwardly is secured by turning the band I5 on the tube 5, a scale being provided, as shown in Fig. 3, for indicating the adjustment of the magnetic pieces.

These magnetic pieces for modifying the ilux of the magnet are thus located within the winding of the relay and although a certain amount of magnetic flux passes directly from `the plug or core 3 to the plunger I in. the usual manner, yet

a certain amount of the ilux will be diverted from the plug through the magnetic pieces and thence to the plunger. It will be noted that these pieces are positioned so that the lower points thereof are about opposite the top of the plunger in its unattracted position,

'111e negative or opposing action due to the magnetic pieces may be explained by considering that these pieces are made up of an infinite number of vertical sections and by analyzing the eiect from a polarity stand-point. If the plug 3 be considered a north pole at a selected instant, then the top portions of the magnetic pieces, or sections thereof will have a south polarity, while the lower ends of such considered sections will have a north polarity; and the top portion of the plunger may be considered to have a south polarity. In the position shown in Fig. l, the upper end of the plunger is some distance within the ycoil and the attractive force may be assumed'to be in the region of the right end of the` rst portion of the curve of Fig. 9. As the plunger moves upwardly and approaches the plug 3, the attractive force due to the flux passing from the plug directly to the plunger increases; but during'this movement the north poles at the lower ends of the assumed divided sections of the magnetic pieces I8 exert a gradually increasing downward pull on the south pole or top portion of the plunger. This more or less offsets the in` creasing attractive force directly between ythe plug `3 and the plunger giving as the net result a change in the attractive force represented by the fullline in Fig. 9.

Anotherview-point is to consider the magnetic pieces as a path of leakage iiux from the plug 3 tothe plunger.' In the position shown in Fig. l,

the attractive force rapidly increases, giving a comparatively pronounced upward movement of the plunger in the latter part of its stroke. It is evident that the magnetic pieces form a shunt path for the iiux and this path may be varied for particular requirements by changing the form and the location of the magnetic pieces in relation to the plunger and to the coil to give variable results in the force curve. The particular shape of the magnetic pieces and their location as shown in the drawing results generally in the form of curve shown in Fig. 9.

'I'he operation of the plunger and the movable dashpot unit will now be described. With the parts in the position shown in Fig. l and assuming that suiilcient current is passed through the winding of the relay to raise the plunger from the unattracted position, the nrst effect is that the plunger and piston move upwardly a short distance quite rapidly. This is due to the fact that the lower inside wall of the dashpot is of larger diameter than its central portion which permits the piston to move quite freely until it is opposite the portion o! the inside wal1 of the dashpot of smaller diameter. The liquid medium or oil in the dashpot is then permitted to pass slowly from above the piston around the rim thereof to the lower portion of the piston, owing to the small clearance space between the piston rim and the interior wall of the dashpot. 'I'he dashpot thus exerts considerable retarding eii'ect on the upward movement of the plunger. The dashpot action and the eiect of the introduction of the magnetic pieces I8 result in a very slow upward movement of the plunger, assuming that the current in the winding is maintained slightly above the plck-upvalue. When the plunger is near the upper portion of the stroke, the piston of the dashpot leaves the wall of small diameter in the dashpot and passes into a region where this wall is of larger diameter which greatly reduces its retarding eilect. This permits the plunger to then move rapidly upward in the latter part of its stroke and at that time the lower end of the plunger is slightly above the magnetic plate I4. This results in the. magnetic force exerted by the plunger upon the plate I4 overcoming the attractive force between this plate and the inturned ends of the magnet frame causing the magnetic plate to move upward rapidly a slight distance against the pressure of the portions ISa of the spring I6 and thereby moves the dashpot unit as a whole upwardly to the position shown in Fig. 5. In this upward movement the dashpot is guided by the fixed cup 8. The upward movement of the dashpot unit results in the actuation of the parts controlled by the relay. When the exciting current of the relay is sufficiently reduced or ena. certain amount of. ux passes to the magnetic pieces and thence to the top portion of the plunger'v in aninclined direction and also crosswise. This reduces the net attractive force below what it would be if the magnetic pieces were not present; and as the plunger is drawn upwardly, the 'relative amount of the flux in the v paththrough the magnetic pieces to that in the tlrely removed, the parts will drop to the position shown in Fig, l and during this action, the piston of the relay turns on its pivot, as already explained. so as to permit a comparatively free now of the oil around the piston to the upper portion of the dashpot, thereby permitting a comparatively rapid re-setting action of the parts. The dashpot is preferably filled with oil to near the top of the tube 5 and above the top of the plunger when in its unattracted position. When the plunger moves upwardly, the oil passes from above the plunger through its hollow interior and out through the slot 4a.

The spring I6 is for the purpose of vieldingly supporting the unit and for overcoming the effects of vibration and shocks and jars upon the dashpot unit and ls effective against severe upward shocks of the lrelay. It is also for the purpose of aiding the upward movement of the unit when the plungerreaches the latter part of its stroke in its upward movement. The tongues |6b by reason of engaging the ends of the magynet frame and yieldingly supporting the unit,

cushion the effects of upard shocks or movements of the relay by permitting the relay to move upwardly while the dashpot unit remains at rest. The inertia of the dashpot unit tends to maintain it at rest while the spring yields to permit movement of the relay frame with reference to the dashpotunit. The tongues IBa tend to avoid movement of the magnetic plate I4 when the relay is subjected to usual vibrations.

Although oil is a preferable liquid medium for use within the dashpot, the various oils available are subject to a greater or less change of viscosity with changes in temperature and'this is true of many other liquid mediums. Ordinarily the viscosity increases more and more rap- A idly as lower temperatures are approached. It follows that change in ambient temperatures may affect the responsive performance of the relay and in order to overcome this effect, the dashpot, as shown in Figs. 1 and 2, is provided with means for counteracting change in viscosity of the liquid medium. lA hollow screw plug 20 has a threaded engagement at one end with the piston so as to be adjustable therein; and a lock nut 20a serves to hold the screw plug in its adjusted position. Secured t the under side of the piston is a loi-metallic strip 2|, one end of which projects under the plug and almost closes the opening through the plug under normal temperature conditions. The thermostatic strip 2| is spaced from the under side of the piston bya disk 2|a which engages a considerable surface area of the thermostatic strip. The strip and disk 2la are secured to the piston by a screw bolt and washer 2lb which covers a much less area. of the strip than is covered by the disk 2Ia. This character of mounting tends to cause the thermostatic strip to conform in its control of the opening through the plug 20, to compensate for change of viscosity of the liquid. When the relay is used under high temperature conditions, the thermostatic strip will assume a position so as to close or nearly close the lower opening of the plug 20; and its movement toiward the end of the plug is limited by the engagement of the strip against the disk 2 la. When the relay is used under conditions of lower temperatures, the thermostatic strip moves outwardly from the end of the plug 20 and this movement may be considerable because its outward movement is not limited by the disk 2 la but by the holding means 2lb of much smaller size. Thus the control of the opening through the plug 2n may be restricted to a small amount under higher temperatures whereas under lower temperatures the opening may be made considerable to compensate for the high viscosity at the lower temperatures. It follows that the change of viscosity is substantially counter-acted by this device in that it restricts the .passage of the liquid medium from the upper side of the piston to its lower side during its upward movement and when the viscosity of the medium is low, whereas under lower temperatures the opening will be considerably greater and thereby permit more freedom of ow of the medium froiabove the piston to below the piston when the viscosity of the mediumis high.

The parts controlled by the relay are shown mounted on and above the magnet frame. The metal plate 22 rests on top of the magnet and is held in place by a nut 3a on the top portion of the plug 3. A block of insulation '23 is xed to the plate 22. A metal 'frame 24 with upwardly extending ends is xed to the block 23 and carries an axially movable rod 25 having a movable contact 25a at one end and a handle 25b at the other. An angular metal piece 26 supports the fixed contact 26a. The rod 25 has fixed thereto a disk 25e having a beveled edge; and between the hub of the disk and one end of the frame 24 a spring 21 encircles the rod and tends to move the diskoutwardly to separate the contacts.

The edge of the disk 25a is normally engaged by a latch 28 for the purpose of holding the contacts in engagement against the pressure of the spring. The latch is pivotally ymounted on a pin 28a which is supported by ears 24a upturned from the frame 24. A spring 29 encircles the pin and has a portion engaging the base of the frame 24 and another portion engaging the tail of the latch and serves not only to cause the latch to engage the dis'k when re-set by the handle 'but to impose a clockwise moment on the latch tending to keep it in normal engagement with the disk against the effect of vibrations. Also the engagement of the latch with the disk is below the axis of the pin 28a and, due to the pressure of the disk against the latch, another clockwise moment is imposed on the latch tending to keep it in engagement with the disk. A downward projection 28h from the tail portion of the latch limits the upward movement of the latch end when released so it may be engaged readily by the disk in resetting.

The latch is tripped by a. vertically movable rod 30 of insulating material. This is movable freely through the plug 3 and its upper end is a short distance below the tail of the latch in its normal position. Its lower end is normally a short distance above the top of the tube 5 of the dashpot unit. The rod is held in its normal position by a cross pin 30a through the rod, the cross pin normally resting in the bottom of a vertical slot across the top of the plug 3.

When the dashpot uni't is moved upwardly in the manner already described by the final abrupt movement of the plunger, the rod 30 `will be engaged by the end of the tube 5 and cause the tripping of the latch and the opening of the contacts of the controlled circuit. Instead of opening such a circuit, the parts may obviously be arranged to close a circuit, or t0 open one or more and close one or more, or to actuate a part for a mechanical control.

In various tests made on this relay, it has been found to give a long range of the imposed time delay depending upon the value of the current passed through its winding. When the current was maintained constant at a value slightly above its pick-up value, the delay was prolonged to about two hours. Thus a circuit or apparatus protected by the relay may be permitted to carry an overload current of a few percent for a long time before being finally interrupted by the controlling circuit. A greater overload, however, should be permitted a much shorter time such as an hour, or half hour, or shorter time depending on the overload and this relay functions accordingly. Upon the occurrence of extreme overloads, the relay will respond to effect its control in a few seconds or less. After actuation of the "Sufiicient upward movement parte controlled andthe interruption of the current to the relay winding, the dashpot unit and plunger will return quickly to their unattracted positions in the manner already explained. This action, together with the resetting of the actuated parts, permits the relay to be available quickly for its further protective use.

The setting of the relay may be adjusted readily to change the time delay and response curve by adjusting the magnetic pieces i8 already described. This is done by removing the screws Ib and the guiding cup 8 and then slightly raising the dashpot unit and turning it ninety degrees. The unit may then be withdrawn from the relay and the band i9 turned on the tube for adjusting the magnetic pieces upwardly or downwardly.

This adjustment permits the same relay to be given diiferent ratings within limits such as a plus or minus ten per cent range. Upward adjustment decreases the required value of the pickup current while downward adjustment increases the required value of pick-up current. The adjustment also changes the time delay. I'he control is applicable to overload protection of circuits, the control winding of the relay thus serving as a series coil, such as in motor protection, and is also applicable to various uses where the control winding serves as a shunt coil. In general the force curves are similar in series and shunt uses, although they may differ somewhat in inclination.

Considering further the possible tripping of the relay' when subjected to violent shocks or jars. this may occur due to an upward movement of the tripping rod independently of the cushioning of the movement of the dashpot unit. Such an undesirable action is avoided by the provision of auxiliary counter-acting means. In Fig. 1 there is shown a weight or plunger 3| seated on the plate 22 and housed within the insulating block 23. This weight or mass 3| is provided with an upward projection 3|a of reduced diameter, the top of which is positioned a short distance below the latching end of the latch 28. of the weight 3| is projection Sia to engage of the latch. Thus when any extreme shock or Jar is imposed upon the relay such as to cause the rod 30 to move upwardly and trip the relay, such action is avoided and counter-acted by the weight 3| because it likewise moves upwardly on account of receiving the same shock or jar and thereby holds the latch closed; and as soon as the shock is over, the parts drop to their normal positions. The mass 3| should weight the same or more than the weight of the part or parts to be counter-acted in case they act on opposite sides of the pivot at the same distance from the axis of the latch, so that the moment of the mass will equal or exceed the moment of the part or parts acting on the tail of the latch. If the line of action of the mass is at a less distance from the pivot of the latch than that of the opposing moment, the weight of the mass should be made correspondingly greater than that of the part or parts to be counteracted; and similarly its weight may be made correspondingly less in case its line of action is at a greater distance from the pivot of the latch. That is, the moment of the mass should equal or exceed the moment of the counter-acted parts to insure against undesired tripping of the latch in uses where the relay may be subjected to extreme shocks or jars.

permitted to cause the the bottom of this end Although preferred embodiments ofthe various features of this invention have been shown and described, it. will be understood that various modliications and adaptations thereof may be made without departing from the scope of the invention.

I claim:

l. An electromagnet having a movable magnetic plunger, and a plurality of magnetic elements positioned in circumferential relationship to each other and spaced uniformly from each other Within the winding of the magnet and between the interior of the winding and path of movement of the plunger and displaced in an axial direction from the poles of the magnet and from the ends of the winding for affecting the iiux through the plunger upon the movement of the plunger from its unattracted position to its attracted position, said magnetic elements having their side edges tapered in a converging direction toward the unattracted position of the plunger.

2. An electromagnet having a movable magnetic plunger, a plurality of magnetic elements V positioned in circumferential relationship to each other and spaced uniformly from each other Within the winding of the magnet and between the interior of the winding and path of movement of the plunger and displaced in an axial direction from the poles of the magnet and from the ends of the winding for affecting the flux through the plunger upon the movement of the plunger from its unattracted position to its attracted position, and a non-magnetic ring for supporting and magnetically separating the magnetic elements.

3. An electromagnet having a movable magnetic plunger, a plurality of magnetic elements positioned in circumferential relationship to each other and spaced uniformly from each other within the winding of the magnet and between the interior of the winding and path of movement oi' the plunger and displaced in an axial direction from the poles of the magnet and from the ends of the winding for affecting the ilux through the plunger upon the movement of the plunger from its unattracted position to its attracted position, a non-magnetic ring for supporting and magnetically separating the magnetic elements, and means whereby said ring may be adjusted in the direction of the axis of said winding.

4. An electromagnet having a solenoid winding, a hermetically sealed movable dashpot unit having an upper cylindrical portion of non-magnetic material extending within the winding, a movable magnetic plungel within said unit and adapted to move within said cylindrical portion, said plunger being connected to the piston of the dashpot and movable within said cylindrical portion when controlled by said winding for effecting the movement of said unit when the plunger nears its limit of travel in the attracted position, and a magnetic element supported on the outside of said cylindrical portion within the winding of the magnet for aifecting the flux through the plunger upon the movement of the plunger from its unattracted position to its attracted position.

5. An electromagnet having a solenoid winding, a hermetically sealed movable dashpot unit having an upper cylindrical portion of non-magnetic material extending within the winding, a movable magnetic plunger within said unit and adapted to move within said cylindrical portion,

said plunger being connected to the piston of the dashpot and movable within said cylindrical porl tion when controlled by said winding for effecting the movement of said unit whenftheplunger nears its limit of travel inthe attractedpo'sition, i

a magneticr element supported on the outside of said cylindrical portion within the winding of the magnet for affecting the 'ux through the plunger upon the movement of the plunger from its unattracted position toits attracted-position, n'

said magnetic element being tapered in a converging direction towards the unattracted position of said plunger.

magnet for affecting the ilux through' the plunger upon the'movementof the-plungerfrom its unattractedy position vto its attracted" position,v and means whereby -saidl magneticy elements-r mayzbe adjusted along said cylindrical'portion in1an axial direction.` H

7. An electromagnet having amagnetirame and afwinding,ia'movablesealed unitlfhavingr a l6. An electromagnet'fhaving a solenoid windelements positioned in circumferential relationn ship to each other andy spaced uniformly from reach other and-supported on the outside-ofsaid cylindrical portion within the winding of'the portion extending within said Winding and'normally having a predetermined unattractedazposition lin relation to saidv winding, v,a magnetic plunger movable -within saidrunitvfrom its( normal position toits fullyfattracted 4position `.Within said `cylindrical n portion, :an .aauxiliaryfmovable magnetic element for forming la'by-path` for a portion of the fluxof said magnet tosaidplunger when the latter is in its normal .postion,zsaidiunit and saidelernent being actuated :upon the-plungi er attaining a position :near its'fully attracted position and causingsaidv element to move from its normal` position to a position to increasev4 the reluctance of said by-path,-andsyieldable'means extending between' said unit 'and "said -frame for yieldingly supportingA said 'unit and between said vunitvand said magneticVVV element for yieldingly `holding said element in itsnormalposition.

HARoU'rIUM K. KOUYOUMJIVAN.

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