US2786913A - Magnetic centrifugal switch - Google Patents

Description

March 1957 H. J. DUURKOOP MAGNETIC CENTRIF'UGAL SWITCH Filed April 20, 1954 iii The present invention relates to a magnetic centrifugal switch.

Switches of this type are used in single-phase dynamoelectric machines for controlling the starting winding; they may also be used for other purposes.

The object of this invention is to provide a magnetic centrifugal switch whose operation is substantially frictionless and noiseless, accurate and reliable and which ensures a perfect instantaneous switching action, resulting in a long life of the contact points, which occupies but little room and which can be readily manufactured.

According to the invention said object is achieved in a centrifugal switch provided with permanently magnetic material, which switch is adapted to interrupt and to close an electric circuit as a result of the change of the magnitude of the magnetic force acting on at least one relatively movable armature included in a magnetic circuit (hereinafter called the magnetic switching circuit) induced by the permanently magnetic material, the change of said force being brought about by a change resulting from centrifugal action in the width of the air gap in a parallel magnetic circuit induced by the same permanently magnetic material as the switching circuit.

When the air gap in the parallel circuit grows smaller a large portion of the magnetic lines of force passes through said circuit, so that, even before the armature in the switching circuit starts moving, a stepwise reduction of the field strength takes place in said switching circuit, so that the force opposing the magnetic attraction, which force may be exerted, for example, by a spring, immediately acquires a great overweight which results in a perfect instantaneous switching action. Upon a subsequent increase of the air gap in the parallel circuit the field strength in the switching circuit will suddenly increase whereupon the armature therein will be instantaneously attracted.

The reduction or the short circuiting of the air gap of the parallel circuit may be caused by centrifugal action and the increase thereof by the opposing force of a spring, or conversely.

According to the invention the most favorable result is obtained if the magnetic lines of force which return in themselves cannot simultaneously pass through all the parts of the two circuits, which is preferably achieved by providing each of the two circuits, which have in common the permanently magnetic material inducing the active field strength, with at least one separate armature. Thus a substantially complete and sudden change-over of all but the total of the lines of force from the one to the other magnetic circuit is possible upon a comparatively small relative displacement of the armature means in the parallel circuit.

The permanent magnetic means may be mounted for movement relatively to the material of the armatures. Preferably, however, only the armatures having a smaller weight, are relatively movable.

According to another feature of the invention the parallel magnetic circuit is preferably conducted via two States Patent ice soft iron rings which are arranged about the axis of rotation and belong to the rotor, which rings are adapted to be short-circuited by one or a plurality of armatures of the parallel circuit. Said rings always guide the lines of force to the zones containing the magnet armatures, so that said armatures may be segment-shaped without waste of magnetic energy. A local arrangement of the permanently magnetic material is also possible.

'Though it is possible to arrange the permanently magnetic material in the stator, said material is preferably enclosed between the rings in the rotor so that said material can be accommodated in a small space where it will have a maximum effect.

The arrangement may be such that the parallel circuit is opened by centrifugal action. Preferably, however, the arrangement is such that said circuit is closed by centrifugal action which causes the most abrupt change over of the lines of force to the other circuit and in consequence the most instantaneous action, which is useful for interrupting the highly inductive circuit of the starting winding of a single-phase motor.

Further features of the invention will appear from the following description of the embodiments which, merely by way of example, are shown in the accompanying drawings, and from the claims.

In said drawings:

Fig. l is a view, partly broken away, of a switch according to the invention as it appears in axial direction from the side where the contact members are located;

Fig. 2 is a view of the rotor portion of said switch as seen from the direction opposite to that indicated with regard to Fig. 1;

Fig. 3 is a sectional view on line IIllIl in Fig. 1;

Fig. 4 is an axial view of another embodiment of the switch according to the invention, one ring being omitted; and

Fig. 5 is a sectional view on line VV in Fig. 4.

In Figure 1 the numerals 1 and 2 designate the holes by means of which the mounting plate of the stator of the switch may be secured to the inner side of the motor casing. Said mounting plate consists, as seen in Figure 3, of a moulded part 3 of insulating material through which the motor shaft 15 freely passes and on which a metal connecting strip 4 for the current wire is secured by means of rivets 4 and 4", which rivets have been inserted into the plate 3 during the moulding thereof. By means of the two cuphead rivets 9 two flexible metal current conducting strips 5 are secured to the connecting strip 4, to which strips the contact bridge 6 carrying the contact 11 is secured by means of the shouldered rivets 7, to which rivets an annular disc 8 of insulating material is likewise riveted. At the other side of the center of the shaft said annular disc 8 bears on the cup heads of the rivets 9 and is adapted to pivot thereon. The helical draw spring 10 has its one end hooked to the land between two holes in the mounting plate 3 and its other end to the land between two holes in the annular disc 8 and draws said annular disc 8 against the cup heads of the rivets 9 and urges said disc to pivot on the heads of said rivets to thus move the contact 11 via the shouldered rivets 7 and the contact bridge 6 away from the second connecting strip 12 secured to said mounting plate 3 and to thus interrupt the electric circuit. On the annular disc 8, however, a thin segment-shaped soft iron strip 13 is mounted which, together with the soft iron rings 16 and 17 and the permanently magnetic material 18 interposed between said rings, forms the parts of a magnetic circuit in which the strip 13 functions as the relatively movable armature which is magnetically attracted in opposition to the spring 10.

Inasmuch as the movement of said armature 13 controls the electric circuit by interrupting or closing said circuit between the contact 11 and the strip 12, said magnetic circuit is called the switching circuit.

The rings 16, 17 belong to the rotary portion, i. e. to the rotor of the switch. The ring 16 is in pressed fit engagement with the circumference of the hub 14 of nonmagnetic material, which hub in turn is in pressed fit engagement with the circumference of the motor shaft 15, the ring 17 being permanently secured to the ring 16 by means of the magnetic material interposed between said rings. The ring 17 comprises a portion 1" extending in a radial direction to the center of the shaft, the inner edge of said portion 17 having the same diameter as the inner wall of the ring 16. Opposite said inner edge of the portion 17' and the inner wall of the ring 16 there are two soft iron segments 19, the outsides of which segments have the same curvature as the inner edges of the ring 16 and the ring portion 17'.

The relatively movable segments 19 together with the rings 16 and 17 and the material 18 form the parts of a second magnetic circuit which is parallel relatively to the magnetic switching circuit.

The north-south connecting lines between the associated opposite magnet poles of the material 18, which material may also consist of a plurality of separate magnets surrounding the shaft and located between said rings, are radially directed. The lines of force which return in themselves pass-apart from losses due to leakage either via the switching circuit through the armature 13 or via the parallel circuit through one of the armature segments 19. The two routes coincide in the material 13, and in the rings 16, 1'7 they flow to the left or to the right as seen in Figure 3. As a line of force can only once form a closed loop, a line of force can run only according to one or according to the other circuit. Which circuit this will be mainly depends on the ratio between the lengths of the air gaps which are to be bridged in one or in the other magnetic circuit, the magnetic resistance in the circuits approximately increasing proportionally to the increasing length of the air gap.

As the rings 16, 1'7 rotate relatively to the armature 13 an air gap must always be left open between said rings and the armature. The segments 19 rotating along with the rings may, however, completely bear against said rings, so that the magnetic resistance in the parallel circuit will be much smaller than in the switching circuit, as a result of which the major portion of the lines of force will pass through the parallel circuit and the field strength prevailing in the switching circuit will no longer be sufiicient to hold the armature 13 against the action of the spring i and to keep the contact 11 in engagement with the strip 12.

it is observed that the major part of the lines of force will run according to a cubic curve because the armature 13 is located only opposite a portion of the rings 16, 2'7. The lines of force originating in permanent magnets 13 not located opposite the armature 13 will pass through one of the rings about the shaft to reach the zone opposite the armature and will pass therethrough to subsequently return to their starting point by passing through the other ring about the shaft. The same applies in respect or" the segments which cover only a portion of complete circumference of a circle. This construction, refore, is suited for the use of small and light armae segments and utilizes substantially the total available d strength. The two soft iron segments 15 are each secured in a part of nonn tgnetic material which part 2?; is of such share that it can undergo a rolling motion over the rings 1 during which rolling motion the segments 19 are moved towards and away from the rings. The parts heir nose shaped ends in engagement with a side the square spring vasher 21 rovided with an edge, which washer is urged radially outwardly by the biased spring 22, so that in case the rotor is at a standstill the segments have their ends urged against the support 25 of sound absorbing material, which support is secured to the hub 14. The spring 22 bears with its other end against a nut 24 fitting on the screw 23. By turning the screw 23, which screw is countersunk into the circumference of the hub 14, relatively to the nut 2 the tension of the spring 22 and thus the number of revolutions at which centrifugal force will overcome the force exerted by the spring on the segments 19, can be adjusted.

The operation of the switch as described is as follows.

As as, with an increasing number of revolutions, the centrifugal force of the segments 1.9 overcomes the force of the spring 22, said segments will start moving radially outwards. Because they both cooperate with the same spring washer 21 their relative movement will always be simultaneous and identical. Because the armature 23 is still located close to the rings 16, 17 the segments 19 must already have closely approached said rings if the decrease of the magnetic resistance in the parallel circuit is to be of decisive importance. This, therefore. takes place, in the last stage of the relative movement of the segments 19, in which stage they already have a high speed, which has for its result that the change-over of the main portion of the lines of force from the switching circuit to the parallel circuit takes place very suddenly, so that the force of the spring it) suddenly obtains a great overweight and interrupts the contact between the parts 11 and 12 instantaneously. it subsequently the number of revolutions has sufficiently decreased, the spring 22 will again move the segments 19 inwardly, so that the air gap between the segments 19 and the rings 16, 17 will again become appreciably larger than the air gap between said rings and the armature 13 which armature can effect only a small stroke. The lines of force then again largely pass via the switching circuit, so that the armature 13 is again instantaneously attracted.

Seeing that the force of attraction between the segments 19 and the rings 16, 17 owing to the substantially quadratic influence of the air gap is comparatively very high when said segments bear against the rings and said force is added to the centrifugal force, a special charac teristic is given to the spring 22 so that said spring will exert a suddenly increasing force when said segments closely approach said rings. It is also possible, for example, to use stiff auxiliary springs arranged between the rings, which springs act only on the segments 19 when said segments are located very close to said rings. Furthermore thin antimagnetic intermediate plates or a similar covering of the segments 19, as usual in electro-magnetic relays, may be used. By means of such measures, applied by themselves or in combination, the switching back of the switch may be adjusted to a desired lower number of revolutions.

In Figures 1-3 inclusive a construction is shown in which the armature 13 of the stator is moved in an axial direction under the influence of the magnetic field. it will be clear that if the operation of the switch is to remain the same the armature 13 must each time be able to occupy the same position relatively to the rotor, so that the siaft of the motor may not have any axial play. This is normally the case in motors provided with ball bearings.

In Figures 4 and 5 another embodiment is shown for motors in which the motor shaft has some axial play. in this embodiment the armature 26 of the switching circuit is arranged radially opposite the rings 27, 28 having the magnetic material 29 enclosed between them, which armature also performs a switching action in a radial direction. The armature 26 is somewht broader than the distance "etween the rings, so that a wide axial play is possible without this influencing the operation of the switch.

In this embodiment the operation is otherwise identical to the operation of the first embodiment and is again controlled by armature segments 30 of the parallel circuit which are responsive to the centrifugal force.

The north-south direction of the magnet material 29 is in this case parallel to the shaft.

In the stator the mounting plate 31 of insulating material is secured to the motor casing 34 by means of screws 32, 33, the motor shaft 35 being supported in the journal bearing 36 of said motor casing. The armature 26 is pivoted to the mounting plate 31 by means of the journal 37 and is moved away from the rotor rings 27, 28 by the helical spring 38, when the magnetic parallel circuit is closed. An insulating part 40 is secured to the armature 26 by means of a rivet 39, the contact finger 41 being firmly secured in said insulating part, which finger is connected with the connecting strip 43 by a flexible cord 42 and at its other end carries a silver contact 44 which, together with the contact 45 on the connecting strip 46, closes or interrupts the circuit.

In Figure 4 the ring 28 is not shown so that the arrangement of the magnetic material 29 consisting of six separate permanent magnets clearly appears therefrom. Said magnets are bonded to the rings 27, 28 by means of an ethoxylene resin, said rings themselves being connected to each other and to the hub 49 of non-magnetic material by means of two round studs 47 and two square studs 48.

Two identical nylon parts 51 pivot on the edges 50 of the studs 48, the armature segments 30 being firmly secured to said nylon parts 51 by means of screws 52. Weights 53 are riveted to said segments, said weights being chosen in relation to the number of revolutions at which the switching is to take place. The two nylon parts 51 are interconnected by a thin steel strip 54 held by the screws 52, which strip is kept under tension by the spring washer 56 loaded by the spring 55, so that the parts 51 bear against the hub 49 when the segments 30 do not bear against the rings 27, 28 under the influence of centrifugal action. The spring 55 bears with its one end against the nut 58 on the adjusting screw 57. Said screw 57 is countersunk in the hub 49 and has its other end guided in a bridge piece 59 connected to the studs 48. The screw 57 passes through a hole in the strip 54, so that said strip cannot shift and the movements of the segments 30 will always be symmetrical.

The operation of the embodiments shown by way of example is identical in principle. Various other embodiments are possible without departing from the scope of this invention. Thus it is possible e. g. in the first embodiment to provide the segments 19 on the outside of rings similar to the rings 16, 17 so that the operation is reversed, but remains the same in principle. It is also possible, for example, to arrange the permanently magnetic material in the stator and to employ e. g. rings similar to the rings 28, 27 of the second embodiment in conjunction with the segments 30 only for closing the magnetic parallel circuit, while the permanently magnetic material may be provided only locally and not about the shaft.

I claim:

1. A centrifugal switch comprising a movable armature, an electric circuit-controlling device position to be actuated by said armature upon movement thereof, at least one permanent magnet for inducing in the flux path through said armature a magnetic flux for moving said armature, and at least one centrifugally-responsive movable secondary armature for changing the magnetic reluctance in a parallel magnetic flux path to cause the magnetic flux in the first-named flux path to change.

2. A centrifugal switch comprising a movable armature, an electric circuit-controlling device positioned to be actuated by said armature upon movement thereof, at least one permanent magnet enclosed between iron rings for inducing in the flux path through said rings and said armature a magnetic flux for moving said armature, and at least one centrifugally-responsive movable secondary armature for changing the magnetic reluctance in a parallel magnetic flux path to cause the magnetic flux in the first-named flux path to change.

3. A centrifugal switch having a rotor portion and a stator portion and comprising a movable armature, an electric circuit-controlling device positioned to be actuated by said armature, at least one permanent magnet enclosed between iron rings mounted in the rotor portion to induce in the flux path through said rings and said armature a magnetic flux for moving 'said armature, and at least one centrifugally-responsive radially-movable secondary armature for changing the magnetic reluctance in a parallel magnetic flux path to cause the magnetic flux in the first-named flux path to change.

4. A centrifugal switch comprising a movable armature, an electric circuit-controlling device positioned to be actuated by said armature, at least one permanent magnet enclosed between iron rings mounted in the rotor portion to induce in the flux path through said rings and said armature a magnetic fiux for moving said armature, and two centrifugally-responsive radially-movable secondary armatures coupled as a pair with a common spring means acting against centrifugal force for changing the magnetic reluctance in a parallel magnetic flux path to cause the magnetic flux in the first-named flux path to change.

References Cited in the file of this patent UNITED STATES PATENTS

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