US2942075A - Centrifugal switching device - Google Patents

Description

June 21, 1960 w. E. BUCK CENTRIFUGAL SWITCHING DEVICE Filed Sept. 8, 1958 INVENT OR.

IIIII WILL/1RD E. BUCK ATTORNEYS Fla. 3.

United States Patent CENTRIFUGAL SWITCHING DEVICE Willard E. Buck, P.O. Box 357, Boulder, Colo.

Filed Sept. 8, 1958, Ser. No. 759,677

17 Claims. (Cl. 200-80) This invention relates to speed regulating means and, more specifically, to improvements in centrifugally-operated switching devices of a type particularly adapted for use in controlling the speed of electric motors and the like.

In my United States Patent 2,819,441, for example, I disclose a miniaturized electric motor having a multiplepole rotating armature in which each pole is energized by a separate winding and at least one of said windings includes a switch responsive to centrifugal forces in a manner to cut the winding in and out of the circuit thereby varying the electromotive force and varying the speed. This centrifugal switch element comprises generally a spring arm having one end fixedly attached to a rotatable fly-wheel-like element and the free end thereof provided with a movable contact biased into normallyclosed position against a fixed contact. A weight is preferably affixed to the spring arm intermediatethe ends thereof which enables a heavier spring to be used and provides for much more accurate speed regulation than it is possible to achieve with a light and unweighted spring.

The above described centrifugal switch works quite satisfactorily to control the speed of miniaturized electric motors designed to operate under only small torque loads; however, a need has arisen for small constantspeed motors of greater torque capacity and it has been found that such a switching arrangement is unsuitable for this purpose for several reasons.

mately 30 milliamperes will last as long as a thousand hours; whereas, the same contacts under a current of 300 milliamperes have a life of only 25 hours. High currents cause silver contacts to pit badly because of their metal-transfer tendency which produces a momentary sticking and pronounced speed changes thus preventing them from performing their primary function. Silver contacts require only a light contact pressure which generally results in a marked increase in contact-life; however, they hit together so gently that they become badly oxiglized and will not clean themselves thus causing erratic operation.

'In many relatively high current switching applications, tungsten has been found preferable to silver as a contact material'because it substantially eliminates the metaltransfer problem and the resultant difiiculties with pitting and sticking. Tungsten, on the other hand, also presents certain problems as a switch contact material. Most critical of these is, perhaps, the fact that tungsten requires considerably greater contact pressure than silver or most of the other of the-more common contact-form- ,ing metals. The conventional contact design wherein the mating surfaces comprise relatively large areas is, therefore, unsuitable fortungsten contacts due to the appreciably lowered contact pressure produced thereby. Also, theexpense of tungsten contacts when made in accordance with the ordinary designs is prohibitive for use in flow-cost miniaturized motors. I

First of all, a pair of silver contacts carrying a low current load of approxi- It has no w-been found in accordance with the teaching of the present invention that the aforementioned ditficulties can be overcome by an improved centrifug'allyoperated switching device characterized by a pair of generally cylindrical contacts arranged in crossed relation to provide substantially point contact therebetween. The high loading of the contacts on the point at which they touch one another is sufficient for even tungsten contacts and is ample to break down any oxide film that forms thus keeping them clean. These contacts when made of tungsten provide hundreds of hours of efiicient operation before repairs become necessary even under high current loads. Also, they can be made from short lengths of ordinary tungsten wire at a cost of less than a cent per pair. a

The spring arm that carries the movable contact is also an important and novel feature of the instant centrifugal switching device. This arm holds the movable contact in a manner such that it can both be moved longitudinally and rotated relative to the fixed contact thereby enabling any worn points to be eliminated almost instantly. Thus, the contacts will outlast the motor if repositioned when worn. Also, manufacture and assembly of the switch is greatly simplified.

It is, therefore, the principal object of the present invention to provide an improved centrifugally-operated switching device for use in controlling the speed of miniaturized electric motors.

A second object is the provision of a switch of the class described that includes tungsten contacts capable of carrying high currents for extended periods.

A third objective is to provide a switch that incorporates substantially cylindrical contacts arranged to make point contact with one another thereby producing ample contact pressure to enable the contacts to be made from tungsten.

A fourth objective of the invention is the provision of a novel spring arm that carries the movable contact in a manner such that it can be readily repositioned in relation to the fixed contact should they become worn or pitted.

Another object is to provide a switch that easily is repaired and need never be replaced under normal operating conditions.

Still another objective is to provide a centrifugal switch that is self-cleaning and, therefore, capable of many hours of trouble-free operation even when carrying high currents.

Additional objects of the present invention are to provide a switch responsive to centrifugal forces which is compact, lightweight, simple to manufacture and assemble, inexpensive, and one that is capable of accurate speed regulation in miniature motors.

Other objects will be in part apparent and in part pointed out specifically hereinafter in connection with the description ofthe drawing that follows and in which:

Figure 1 is a diametrical section with portions broken away showing a miniaturized electric motor of the multiple-pole rotating armature type in which the novel centrifugal switch device of the present invention is seen carried by a rotatable fly-wheel-like element;

Figure 2 is a top plan view showing the fly-wheel and centrifugal switch;

Figure 3 is a rear end elevation of the fly-wheel and switch, certain portions thereof having been broken away;

and,

Figure 4 is a fragmentary section taken along line 4-4- of Figure 3 showing the details of the fixed contact mounting.

Referring now to the drawing, and in particular to Figure 1 thereof, it will be seen that the miniaturized electric motor which has been indicated generally by numeral 10 includes a case or housing 12 having a detachable endplate 14 mounted on the open end but insulated therefrom as indicated at numeral 16. The closed end 18 of the housing and endpl-ate 14 are each provided with centrally-located shaft openings 20 and 22, respectively, surrounded by tubular extensions 24 and 26 having inwardly extending annular shoulders 28 and 30 formed therein. O-rings 32 are seated against the shoulders 28 and 30 and each receives shaft bearings 34 and 36. The armature shaft 38 is journalled for rotation within the shaft bearings and contains a multiplepole armature 40 mounted thereon for movement past the permanent magnets 42 carried in diametrically opposed relation on the inside of the housing which are interconncpled by soft iron pole pieces that have been indicated at 44. Axial movement of the shaft 38 and armature 40 relative to the housing 12 and associated elements is prevented by enlarged cylindrical portion 46 and commutator 48 carried by said shaft which bear respectively against bearings 34 and 36.

A fly-wheel-like element 50 formed from an insulating material is mounted on the commutator for rotational movement with the armature. The fly-wheel includes a central opening 52 sized to pass the commutator and an annular recess 54 adapted to abut an annular flange 56 carried by said commutator. As shown, the commutator is recessed in the fly-wheel for the primary purpose of making the unit more compact.

Elongated generally box-like brush holders 53 which are open at their inner ends and closed at the outer ends are positioned in suitable apertures formed between the open end of housing 12 and insulating disk 16. These brush holders are arranged in opposed radial relation with their outer ends electrically connected across a direct current power supply (not shown) by leads 60. Compression springs 62 engage brushes 64 and force the same through the open ends of the brush holders into contact with the commutator, the outer ends of said brushes abutting the closed ends of the brush holders.

Up to this point, the structure which has been described is'largely conventional and a more detailed analysis thereof may be found in my US. patent already mentioned. The improved speed regulating means which forms the subject matter of the present invention, however, will now beset forth in connection with the remaining figures of the drawing with an occasional reference again to Figure 1.

InFigure 3, in particular, it will he noted that the fly-wheel 50 is formed to provide a first notch 65 and a second notch 66 in the peripheral edge thereof separated one from the other by a step or projecting portion 63. The face 70 of step 68 which opens onto first notch 64 is preferably inclined and include a pair of radially spaced substantially parallel openings 72 and 74 that extendchordally into saidstep. A pin-type stop '76 is secured within the outer opening 72' in position to project into notch 64, as shown. The inner opening 74 is intersected by an enlarged transverse opening 78.

Figures 3 and 4 show that. a fixed pin-type contact 80 is located within opening 74 to project intonotch 64 in spaced substantially parallel relation to stop pin 76. Opening '74 is sized such that fixed contact 80 has a rather loose fit therein and may, therefore, be rotated and/or moved longitudinally relative to ,the step 68. A retaining pin 82 is passed into transverse opening 73 and-across the fixed contact 30 as shown in Figure 4. The diameter of retaining pin 82 in relation to transverse opening '78 is such that it will bear against the fixed contact iiilforcing the same-against the wall surrounding opening 74 thereby maintaining said contact in fixed position. Should contact 30 become pitted, worn,

oxidized orotherwise damaged, it is only necessary to withdraw the retainingpin in order to relocate the contact within opening 7.4. xThis operation, of course, :can be performed in a matter of a few seconds and may be 4 repeated as often as is necessary to maintain the motor in first class operating condition. By providing for both rotational and axial movement of contact 82 within opening 74, it can be repositioned and reused over the life of the motor Without replacement.

With reference to Figures 2 and 3, it can be seen that an arcuate spring arm'84 of the leaf-type has one end fixedly attached to the periphery of the fly-wheel 50 by means of screw 86. in the specific form shown, the fixed end of arm 84 is mounted on flattened or truncated portion 88 on the edge of the fly-wheel adjacent notch 66 therein. From this point of fixed attachment, arm 84 arches peripherally across notch 66 and step 68 to Where the free end thereof terminates within notch 64. A weight 90 is attached to arm 84 intermediate the ends thereof and on the inside in position to locate within second notch 66 on the edge of the fly-wheel. This weight, of course, upon rotation of the fly-wheel tends to m'ove away from the axis of rotation thereby straightening the arm and lifting the free "end thereof out of notch 64. Opening 92 in the arm between the weight and screw 86 provides a weakened portion that determines the areawhere the bending will take place most easily.

Finally, withreference to Figures 1, 2 and 3, it.will be seen that the free end of arm 84 isprovided'with a longitudinally extending slot 94'of a width to receive stop pin 76 and defining transversely spaced ears 96 and 98 on opposite sides thereof. Each ear includes a sub stantially circular opening 100 near the 'end thereof located such that when the ears are twisted toward one am other, the openings will be in transversely spaced but opposed relation. With the ears thus twisted or sprung, a pin-type movable contact 102'is passed therethrough and between fixed contact 80 and stop pin 76. -Openings 100 have a slightly longer diameterthan movable contact 102; however, they present a generallyelliptically-shaped opening to the contact when the ears are twisted as illustrated, the minor axis of said ellipse being approximately the same as the diameterof the pin-contact. Once the contact is passed through the openings in the cars which have been twisted and sprungtoward one another in opposite directions, the ears tend to spring back into their former collinear positions thus slightly gripping the ends of the Contact 102 and. preventing relative rotational and transverse movement thereof. Here again, movable contact 102 maybe repositioned relative to fixed contact 80 by merely turningand/or moving it axially within openings 100. should it become worn, pitted, oxidized or otherwise damaged. Twisting only one ear in the direction of parallel relation with the other is all that is required to free contact 102for relocation relative to contact 80.

It is important to note that-the substantially cylindrical surfaces offixed and movable contacts 80 and-102' are arranged normal to one another whichprovides point contact therebetween. A gap 104 is provided n ar the fixed end of spring arm 84 between it and the second truncated portion 106 on the periphery of 'fly-wheel'50. Screw 108 is threaded into flattened or truncated portion 106 through arm 34 and is used to adjust the speed at which contacts 80 and 102 separateto open oneof the armature windings, contact 102 b'einglbiase'd' i nto normally-closed position against contact 80. The pressure of the contacts against oneanotheris substantial by reason of the minute area of engagement vtherebetween which easily breaks down any oxide filmthat might otherwise form and also permits tungsten 'wire to be used as acontact material. iv

The switching device just described may be connected in the manner of my Patent 2,819,441 and function in response to centrifugal forces acting thereon. to o'pen the circuit throughone or more 'of the independent armature windings thus providing accuratea'nd constant speed regulation for the motor. Details of the wiring and circuitry may be had by reference to the foregoing patent and need not 'be described'here other" than to point out that a resistance 110 connected as shown across the fixed and movable contacts affords certain advantages by reducing the are which passes between the contacts as they open. Retaining pin 76 cooperates with movable contact 102 to iirnit the outward movement of the spring arm 84.- I I Having thus described the several useful and novel features of the centrifugally-operated switching device of the present invention, it will be seen that the many objects for which it was designed have been achieved. Although but a single specific embodiment of the invention has been illustrated and described in connection with the accompanying drawings, I realize that certain changes and modifications therein may occur to those skilled in the art within the broad teachings found herein; hence, it is my intention that the scope of protection afforded hereby shall be limited only insofar as said limitations are expressly set forth in the appended claims.

What is claimed is:

1. A switching device responsive to centrifugal forces for use in opening and closing electrical circuits at predetermined rotational speeds which comprises, a generally circular tly-wheel formed from an insulating material having at least one notch in the peripheral edge thereof and adapted for rotation about a transverse axis, said fly-wheel including a first opening extending transversely adjacent the notch in spaced relation to the axis of rotation and a second opening within the notch intersecting .the first opening, a fixed contact having a curved surface positioned in the second opening for rotational adjustment about an axis extending in the direction of its length with a portion thereof projecting into the notch, retaining means positioned within the first opening shaped to engage the fixed contact and hold the same in adjusted rotational position within the second opening, an arcuarte spring arm of the leaf type having one end fixedly attached to the periphery of the flywheel at a point angularly spaced from the notch and the other end suspended free above the fixed contact, and a movable contact having a curved surface mounted transversely on the free end of the spring arm, said spring arm biasing the perpendicularly disposed curved surfaces of the fixed and movable contacts into point engagement with one another.

2. The switching device as set forth in claim 1 in which the free end of the spring arm is longitudinally slotted to define a pair of cars each of which includes an opening therethrough, said ears being twisted in opposite directions to locate said ear openings in transversely aligned relation and in position to receive the movable contact which is inserted therein.

3. The switching device as set forth in claim 1 in which the retaining means comprises a pin having a tapered inner end operative to wedge the fixed contact within the second opening.

4. The switching device as set forth in claim 1 in which the medial portion of the spring arm lies in spaced relation to the peripheral edge of the fly-wheel to provide a gap therebetween, and in which adjustment means operatively interconnect the spring arm and fly-wheel in a manner to provide for varying the width of the gap.

5. The switching device as set forth in claim 1 in which the fly-wheel is formed to provide a second notch in the peripheral edge thereof angularly spaced from the first-mentioned notch in the direction of the fixed end of the spring arm, and in which a weight is attached to the medial portion of the spring arm in position to enter the second notch when the contacts close.

6. The switching device as set forth in claim 1 in which stop means are carried by the fiy-wheel extending into the notch in spaced relation to the fixed contact and on the opposite side of the movable contact from said fixed contact, and in which the .slot in the free end 6 of the spring arm is sized and located to receive the stop means,

7. The switching device as set forth in'claim 1 in which a resistance element is electrically connected between the fixed contact and the fixed end of the spring arm carrying the movable contact.

8. A switching device responsive to centrifugal forces for use in opening and closing electrical circuits at predetermined rotational speeds which comprises, a generally circular fly-wheel formed from an insulating material having at least one notch in the peripheral edge thereof and adapted for rotation about a transverse axis, a fixed contact attached to the fly-wheel with a portion thereof projecting into the notch in spaced substantially perpendicular relation to the axis of rotation, an arcuate spring arm of the leaf type having one end fixedly attached to the periphery of the fly-wheel at a point spaced angularly from the notch and the other end suspended free above the fixed contact, the free end of said arm being slotted longitudinally to define a pair of cars each of which includes an opening therethrough, said ears being twisted in opposite directions to locate said ear openings in transversely aligned relation, and a movable contact having a curved surface mounted within the transversely aligned ear openings, said spring arm biasing the perpendicularly disposed curved surfaces of the fixed and movable contacts into point engagement with one another.

9. The switching device as set forth in claim 8 in which the retaining means comprises a pin having a tapered inner end operative to wedge the fixed contact within the second opening.

10. The switching device as set forth in claim 8 in which the medial portion of the spring arm lies in spaced relation to the peripheral edge of the fiy-wheel to provide a gap therebetween, and in which adjustment means operatively interconnect the spring arm and fly-wheel in a manner to provide for varying the width of the gap.

11. The switching device as set forth in claim 8 in which the fly-wheel is formed to provide a second notch in the peripheral edge thereof angularly spaced from the first-mentioned notch in the direction of the fixed end of the spring arm, and in which a weight is attached to the medial portion of the spring arm in position to enter the second notch when the contacts close.

12. The switching device as set forth in claim 8 in which stop means are carried by the fly-wheel extending into the notch in spaced relation to the fixed contact and on the opposite side of the movable contact from, said fixed contact, and in which the slot in the free end of the spring arm is sized and located to receive the stop:

means.

13. The switching device as set forth in claim '8 in which a resistance element is electrically connected be tween the fixed contact and the fixed end of the spring arm carrying the movable contact.

14. A switching device for use in opening and closing electrical circuitsvwhich comprises, a generally cylindrical fixed contact formed from an electrical conductor and adapted to be connected to one side of an electrical circuit, a movable switch arm formed from an electrical conducting material having one end adapted for connection to the other side of the electrical circuit, and a generally cylindrical movable contact formed from an electrical conductor attached to the other end of the switch arm for adjustable rotational movement about an axis extending in the direction of its length and in crossed relation to the fixed contact for movement into substantially point engagement therewith.

15. The switching device as set forth in claim 14 in which the fixed contact is mounted for rotational movement relative to the movable contact.

16. The switching device as set forth in claim 14 in which at least one of the contacts is mounted for longitudinal movement relative to the other.

17. The switching device as set forth in claim 14 in 7. which the switch arm is formed from spring metal and the 'contactwarrying'encl thereof is providedwitlf'a pair of ears arranged in side-b'y-side relation, each of said ears including an aperture therethrough sizedand located to receive and hold the movable'contact when said ears are sprung and twisted in opposite directions tolocate said apertures in opposed relation.

' UNITED spares PATENTS Welch Apr. 27, 1954 Fisher July 17, 1 956 Tountellot Nov. 26, 1957 Buck Jan. 7, 1958

Images