US2751455A - Magnetic centrifugal device - Google Patents

Description

June 19, 1956 K. M. FEIERTAG 2,751,455

MAGNETIC CENTRIFUGAL DEVICE Filed Feb. 23, 1954 ll l 1". 11

[2? V6)? to)" Kar/ M. Fe/ierta g HAS A 27270;")? ey.

MAGNETIC carsrnrruoar DEVICE Karl M. Feiertag, Fort Wayne, ind, assignor to Genera! Electric Sorupany, a corporation of New York Application February 23, 1954, Serial No. 411,671

6 Claims. (Cl. Nil-80) This invention relates to speed responsive apparatus, and more particularly to a magnetic centrifugal device.

There are many applications for speed responsive apparatus; among these is the function of control operable at a predetermined speed. Such a control is often used, for instance, in small single phase alternating current motors which are started with a main winding and a starting winding in parallel, the starting winding being disconnected when the motor attains a certain speed. it has been customary in the past to cause the starting winding to be disconnected by means such as a centrifugal device. Such centrifugal devices have generally consisted of a collar mounted on a shaft, means biasing the collar to close a pair of contacts, and By weight means which is adapted to overcome the biasing means at a predetermined speed to pull the collar along the shaft and open the contacts controlling the starting winding circuit. in order to make the contacts open at a proper predetermined speed it was necessary to devote great care to the longitudinal position of the motor shaft and the attached centrifugal mechanism, since any deviation from the proper position would greatly change the force exerted by the spring and consequently the speed at which the contacts would open. Also, a relatively large number of elements rotatable with the shaft have been needed in previous arrangements.

Another undesirable feature of previous designs has been the fact that rubbing contact was inherent in the arrangement, since a rotating collar was used to mechanically separate a pair of non-rotatable contacts, or else a rotating collar and contact were separated from a stationary contact. This feature of rubbing created wear, and the wear resulted in a change in spring tension and consequently a change in the speed at which the contacts opened.

in specialized types of motors, where the motor is closed to the atmosphere and a particular type of gaseous atmosphere is used in the interior of the motor, it may well be that the gas will prove deleterious to electrical contacts. In previous constructions, wherev the contacts were separated entirely by mechanical means, the exposure of the contacts to the atmosphere could not be avoided to a certain extent. It is proposed in the present invention to avoid by magnetic means the necessity for mechanically moving the contacts, thereby avoiding the rubbing contact, the wear, the consequent sensitivity and, in specialized instances, the harm to the contacts from the atmosphere within the motor.

It is, therefore, an object of this invention to provide improved means operable at a predetermined speed which will incorporate the advantages set forth above.

Further objects and advantages of this invention wil become apparent and the invention will be better understood by reference to the following description and the accompanying drawing, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

nited States Patent "0- Patented June 19, 1956 This invention, in its broadest aspect, provides a substantially circular member of magnetic material movably secured to a rotatable member; the magnetic material is biased to a position which is not vertical to the rotatable member when it is at rest. When the rotatable member comes up to speed the magnetic member will, under the influence of centrifugal force, move to a position in a vertical plane to the axis of rotation of the rotatable part. A permanent magnet is mounted so that when the disc becomes vertical to the rotatable part the magnet is pulled downwardly. A movable contact is adapted to be moved by the magnet so that when the magnet is pulled downwardly the contacts, which are normally closed, will be opened. The magnet will move downwardly toward the magnetic member because of the magnetic attraction which arises between them. Thus, as long as the rotatable part is rotating fast enough to maintain the magnetic member in a plane vertical to the axis of rotation, the magnet will be attracted to the magnetic memher and the contacts will be separated. in a modification of this embodiment, the permanent magnet and the contacts are hermetically enclosed in a non-magnetic housing so that the contacts will not be affected by the atmosphere surrounding this housing.

In the drawing, Figure l is a side view, partly in crosssection and partly cut away, of an electric motor embodying the improved speed sensitive device of this invention;

Figure 2 is an enlarged side view of the improved speed sensitive device shown in Figure 1;

Figure 3 is a front view, partly in cross section, of the improved means shown in Figure 2; and

Figure 4 is a fragmentary front view, partly in cross section, of a modification of the improved speed sensitive means of this invention.

Referring now to Figure l of the drawing, shown a small single phase alternating current of the type having a starting winding (not shown) which is disconnected when a predetermined speed is attained. Motor 1 is enclosed in a housing member 2 of a generally cylindrical shape whose ends are closed by end shields 3 and 4 which are secured to member 2 by any standard means. Motor 1 drives a shaft 5 which is rotatably supported by bearings (not shown) contained within hub 6 of end shield 3- and hub 7 of end shield 4. A casing member 8 having an annular flange 9 may be secured to end shield 4 by any well known means such as threaded members 10 extending through flange a into end shield 4. Shaft 5 extends through end shield 4 into casing member 8 as shown at 11. The improved speed responsive apparatus of this invention is contained Within the casing 8.

Referring now to Figures 1, 2 and 3, one embodiment f the invention will be described. A substantially round disc-like member 12 is secured to shaft 5 at end 11 by any preferred means. As shown in the present embodiment, this has been effected by providing oppositely disposed keyways 13 in shaft 5, with projections 14 of disc 12 fitting within the keyways so as to hold the disc to the shaft. This relatively simple holding means may be effected by stamping out openings 15 and 16 in the center of the disc, placing the disc over shaft 5, inserting a screw driver (not shown) or some other like tool in the opening 15, and deforming the strip 17 as shown so as to cause projections 14 to enter keyways 13. A leaf spring 18, secured to disc 12 at 19 by any preferred means suchas welding and to shaft 5 by means such as projection 20 extending into and secured within shaft 5, is adapted to bias disc 12 to a canted position when shaft 5 is stationary. Opening 16 in disc 12 is made sufficiently large so that the disc may be canted a considerable amount without interference between it and shaft 5. Disc 1?. is

there is motor 1 further provided with cut away portions 21 at diametrically opposite points on its periphery for a purpose to be hereafter explained.

A terminal board member 22 is secured within casing 8 to end shield 4. This may be effected by any preferred means; in the embodiment shown, threaded members 23, 24 and 25, whose secondary functions will be explained below, have been given the primary function of securing board 22 to end shield 4. A stationary contact 26 is mechanically and electrically secured to a small bracket member 27 which in turn is fastened to board 22 by threaded member 23. A relatively long leaf spring member 28 is firmly secured by nut 29 and screw 30 to a bracket 31 which in turn is fastened to terminal board 22 by threaded members 24. A movable contact member 32 is electrically and mechanically secured to leaf spring 28 and limits the upward movement thereof by engagement with stationary contact 26. Secured to the end of leaf spring 28 by any desired means, such as a nut 33 and a bolt 34, is a permanent magnet 35. The dimensions of the various elements are such that when disc 12 is in a position vertical to the axis of rotation of shaft permanent magnet 35 is directly above the outer periphery of the disc. Downward movement of leaf spring 28 is limited by a stop member 36 which may be secured to or formed integral with bracket 37 which is in turn secured to board 22 by threaded members 25. That part of threaded member 23 which extends into end shield 4 is adapted for use as one electrical terminal and either of threaded members 24 may likewise be adapted for use as a second terminal. Thus, by attaching properly connected leads (not shown) to the start winding (not shown) of the motor, it is possible to cause contacts 26 and 32 to determine whether the start winding will be energized. In the embodiment shown, members 23 and 24 are insulated from end shield 4 to prevent a short in the circuit to the starting winding. It will be apparent, however, that casing 8 may be eliminated and that the improved speed responsive means of this invention may be wholly mounted within housing member 2 and end shields 3 and 4 without departing from the scope of this invention. In such an event, there would be no need for any measures, such as explained hereabove, for preventing short circuits between the terminal members 23 and 24. By the same token, any desired terminal arrangement may be used, since such arrangements are not critical insofar as the invention is concerned.

The operation of the improved mechanism of this invention will now be described. When shaft 5 is brought up r to a predetermined speed of rotation, centrifugal force will overcome the action of spring 18, and disc 12 will move to a vertical position with respect to the axis of rotation of shaft 5, as shown in dotted outline in Figures 2 and 3. When disc 12 is in this position it is directly beneath permanent magnet 35. The magnet therefore tends to attract the magnetic disc toward it. Since the disc is fastened so that no such movement is possible, magnet 35 is pulled down toward the disc taking with it leaf spring 28 and movable contact 32 until its movement is stopped by stop member 36 as shown in dotted outline in Figures 2 and 3. Movement of contact 32 in a downward direction opens the circuit controlled by the contacts 26 and 32 and the start winding of the motor will therefore be deenergized. This state of affairs will continue to exist as long as the speed of rotation of shaft 5 is high enough to keep disc 12 in the vertical position. When the speed of rotation of shaft 5 drops below the predetermined point, spring 18 will return disc 12 to its canted position. Magnetic attraction between the disc and magnet 35 will cease, and spring 28 will return magnet 35 and contact 32 to their upward position where the energization to the start winding will again be completed through contacts 26 and 32.

It will be seen that the necessity for securing disc 12 to shaft 5 so that the disc may pivot results in the fact that the two opposite points on the periphery of the disc which are in line with an extension of the axis on which the disc pivots will remain substantially in the vertical plane when the disc is canted to cause its other parts to be out of axial alignment with magnet 35. Thus, even when the disc is in its canted position these points would be directly beneath magnet 35 if the disc should stop its rotation at a point 90 removed from the position shown in the figures. For this reason, cut-away portions 21 have been provided so that even if the disc should stop in such a position there would be no magnetic material directly beneath magnet 35 to cause contacts 32 and 26 to be separated. When the speed of rotation is such that the disc moves to its vertical position, the location of each of cut away portion 21 directly beneath magnet 35 will be of such short duration that they will have no effect on the magnetic action between disc 12 and magnet 35, and magnet 35 will remain properly in its downward position so long as disc 12 is in a vertical position.

In the modification shown in Figure 4, a board member 38 of insulating material has fastened to it by means of a nut 39 and screw 40 a casing 41 formed of non-magnetic electrically conductive material. Insulation, denoted by numerals 42 and 43, is provided so that casing 41 is entirely insulated from screw 40. The head 44 of screw 40 forms a stationary contact which is adapted to engage with a movable contact 45 in order to close an electrical circuit, as explained in Figures 1, 2 and 3. End 46 of screw 40 is adapted to act as the terminal of the stationary contact 44, and the casing 41 forms the terminal for the movable contact 45. Movable contact 45 is electrically and mechanically secured to a permanent magnet 47 which has an opening 48 formed therein to accommodate a helical spring 49 which is seated at one end on the bottom 50 of casing 41 and at the other end on the top 51 of recess 48. Spring 49 normally biases the permanent magnet 47 and the movable contact 45 upwardly so that contacts 44 and 45 are in engagement to complete the circuit.

As in Figures 1, 2 and 3 a tiltable disc 12 is provided which assumes a vertical position directly beneath magnet 47 at a predetermined speed of rotation. When disc 32 assumes its vertical position as shown in Figure 4 a magnetic attraction arises between it and magnet 47. Since disc 12 does not move upwardly, magnet 47 comes down against the action of spring 49 thereby opening the contacts 44 and 45 and deenergizing the circuit which was completed through them. When disc 12 returns to a canted position away from magnet 47 spring 49 will again close the contacts 44 and 45. Casing 41 is preferably constructed so that the elements within it are hermetically sealed from the outside atmosphere. The embodiment of Figure 4 is particularly useful and desirable where it is necessary that the mechanism be operated in an atmosphere which might have deleterious eifects upon the surfaces of contacts 44 and 45. In such an event, this arrangement permits the contacts to be used with com plete efficiency in such an atmosphere without being affected by it.

It will be seen that this invention provides a speed responsive device wherein the necessity of rubbing contact is completely obviated by eliminating the mechanical operation of the movable contact by a rotating part. In addition, the size of the permanent magnet will normally be such that there is no need whatsover for accurate axial adjustment of the position of disc 12. Because of this, a reliable and precise determination of the speed of actuation is possible without the difliculties of assembly which were previously inherent.

It will be understood that the housing and easing members described hereabove are for purposes of illustration, and may be eliminated or .modified without departing from the scope of the invention.

While this invention has been explained by describing particular embodiments thereof, it will be apparent that improvements and modifications may be made without departing from the scope of the invention as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Speed responsive apparatus comprising a substantially circular member pivotably secured to a rotatable part so as to be rotatable therewith and biased to a canted position with respect to the axis of rotation of said part when said part is at rest, said member being movable to a vertical position by centrifugal force at a predetermined speed of rotation, and magnetic means located substantially in the same plane as said member when the same is in its vertical position and beyond the periphery of said member, said magnetic means being biased away from said member and being susceptible to magnetic force between it and said member to overcome said bias and move toward said member when it is in its vertical position, said member having a pair of diametrically opposite peripheral cut-away portions located in line with the pivotal axis of said member thereby to preclude movement of said magnetic means toward said member below said predetermined speed of rotation.

2. Speed responsive apparatus comprising a substantially circular member pivotably secured to a rotatable part so as to be rotatable therewith, spring means biasing said member to a canted position with respect to the axis of rotation of said part when said part is at rest, said member being movable to a vertical position by centrifugal force at a predetermined speed of rotation, a permanent magnet located substantially in the same plane as said member when the same is in its vertical position and beyond the periphery of said member, second spring means biasing said magnet away from said member, said magnet being susceptible to magnetic attraction between it and said member to overcome said second spring means when said member is in its vertical position, stop means associated with said magnet to limit its travel toward said member, said member having a pair of diametrically opposite peripheral cut-away portions located in line with the pivotal axis of said member thereby to preclude movement of said permanent magnet toward said member below said predetermined speed of rotation.

3. Speed responsive apparatus for controlling an electrical circuit comprising a disc-like member pivotably secured to a rotatable shaft so as to be rotatable therewith, spring means biasing said member to a canted position with respect to the axis of rotation of said shaft when said shaft is at rest, said member being movable to a vertical position by centrifugal force at a predetermined speed of rotation, a permanent magnet located substantially in the same plane as said member when the same is in its vertical position and beyond the periphery of said member, a leaf spring immovably secured at one end and secured to said magnet at the other end, said leaf spring being arranged to bias said magnet away from said member, said magnet being susceptible to magnetic attraction between it and said member to overcome the bias of said leaf spring when said member is in its vertical position, contact means controlling said circuit and operable to open said circuit when the bias of said leaf spring is overcome, a stop member positioned between said disc member and said leaf spring to limit the travel of said magnet toward said disc member, said member having a pair of diametrically opposite peripheral cutaway portions located in line with the pivotal axis of said member thereby to preclude movement of said magnet toward said member below said predetermined speed of rotation.

4. Speed responsive apparatus for controlling an electrical circuit comprising a disclike member pivotably secured to a rotatable shaft so as to be rotatable therewith, a leaf spring engaging said shaft at one end and secured to said member at the other end thereby to bias said member to a canted position with respect to the axis of rotation of said shaft when said shaft is at rest, said member being movable to a vertical position by centrifugal force at a predetermined speed of rotation, permanent magnet located substantially in the same plane as said member when the same is in its vertical position and beyond the periphery of said member, a second leaf spring immovably secured at one end and secured to said magnet at the other end, said second leaf spring being arranged to bias said magnet away from said member, said magnet being susceptible to magnetic attraction between it and said member to overcome the bias of said second leaf spring when said member is in its vertical position, a first electrical contact secured to said second leaf spring intermediate its ends, a second electrical contact immovably arranged to engage said first contact when said magnet is biased away from said member and thereby complete said electrical circuit, said first contact being arranged to move away from said second contact when said magnet moves toward said member thereby to disconnect said electrical circuit, a stop member arranged between said disc member and said second leaf spring thereby to limit the travel of said magnet and said second leaf spring toward said disc member, said disc member having a pair of diametrically opposite peripheral cutaway portions located in line with the pivotal axis of said disc member thereby to preclude movement of said magnet toward said disc member below said predetermined speed of rotation.

5. Speed responsive apparatus for controlling an electrical circuit comprising a disc-like member pivotably secured to a rotatable shaft so as to be rotatable therewith, a leaf spring engaging said shaft at one end and secured to said member at the other end thereby to bias said member to a canted position with respect to the axis of rotation of said shaft when said shaft is at rest, said member being movable to a vertical position by centrifugal force at a predetermined speed of rotation, a permanent magnet located substantially in the same plane as said member when the same is in its vertical position and beyond the periphery of said member, an electrically conductive non-magnetic casing hermetically enclosing said magnet, a coil spring seated at one end against an inner surface of said casing and at the other end against said magnet thereby to bias said magnet away from said member, a first electrical contact secured to said magnet, a second electrical contact mechanically secured to and electrically insulated from said casing, said first contact being arranged to engage said second contact when said magnet is in biased position thereby to complete said electrical circuit, said magnet being susceptible to magnetic attraction between it and said member to overcome the bias of said coil spring when said member is in its vertical position whereby said magnet moves toward said member and said first contact separates from said second contact to break said circuit.

6. Speed responsive apparatus for controlling an electrical circuit comprising a disc-like member pivotably secured to a rotatable shaft so as to be rotatable therewith, spring means biasing said member to a canted position with respect to the axis of rotation of said shaft when said shaft is at rest, said member being movable to a vertical position by centrifugal force at a predetermined speed of rotation, a permanent magnet located substantially in the same plane as said member when the same is in its vertical position and beyond the periphery of said member, an electrically conductive non-magnetic casing hermetically inclosing said magnet, electrically conductive means within said casing in contact with said casing and with said magnet arranged to bias said magnet away from said member, an electrical contact within said casing and electrically insulated therefrom, said magnet being susceptible to magnetic attraction between it and References Cited in the file of this patent said member tr overcame said biasing means when said UNITED STATES PATENTS member is in its vertical position whereby said magnet 6 moves towards said member, said magnet being arranged ,754 et July 1937 to control electrical engagement of said contact and said 5 21215294 Sept- 1940 casing.

Images