US2084907A - Centrifugal switch - Google Patents

Description

June 22, 1937. R. w. GROOT CENTRIFUGAL SWITCH Filed Sept. 7, 1934 2 Sheets-Sheet 1 Inventor Robert W Go'ot, bld 77/ i @vw-M4 ttor-heg.

June 22, 1937. R. w. GROOT- CENTRIFUGAL SWITCH Filled Sept. 7, 1934 2 Sheets-Sheet 2 Inventor RQbeTt VV. Groot,

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Patented June 22, 1937 v CENTRIFUGAL SWITCH Robert W; Groot, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Application September 7, 1934, Serial No. '743,110

(Cl. 20o-80) 8 Claims.

My invention relates to centrifugal switches and more particularly to improvements in the construction of such switches.

Centrifugal switches of the so-called center contact type, wherein a rotatable member carrying a centrifugally actuated contact which is movable along the axis of rotation of the rotatable member and which cooperates with an axially positioned stationary contact, have been found difficult to keep in proper operating condition, as it is necessary for the contacts to be extremely true and smooth in order to prevent objectionable contact noise or squealing. As the contacts naturally tend to pit or burn and become rough l5 in service, such switches require frequent dress'- ing of the contacts in order to give satisfactory service. Accordingly, in my switch the contacts are mounted olf-center, with the contact surfaces in a plane perpendicular to the axis of rotation of the rotatable member. With such a construction, the resultant windage is benecial to the action of the contacts in that it serves to cool them and to blow out arcs between them. However, in order to adjust the setting of the switch duringY its operation, it is usually necessary to have an axially movable adjustable means for cooperation with an axially positioned element on the rotatable member with the result that wear` and some noise is produced by these adjustable members.

In accordance with my invention, however, I provide anovel construction in which centrifugal force is utilized to reduce and minimize the force between the stationary and the rotatable elements of the adjusting means of the switch so` that under the normal operating speed of the switch the pressure between the elements of the adjusting means is 'relatively insignificant.

An object of my invention is to provide a new and improved centrifugal svwltch.

A further object of my ,invention is to provide a speed adjusting means for centrifugal switches with a centrifugal element which serves to reduce the wear in the adjusting means. My invention will be better understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings, in which like reference characters designate similar elements throughout the several views, Fig. 1 is a perspective view of one embodiment of my invention; Fig. 2 is a crosssectional view of the switch' shown in Fig. 1; Fig. 3 illustrates a modified speed adjusting means for a single speed switch; Fig. 4 illustrates a modified Rill S50 E. 0

Way of making the electrical connections to my switch; Fig. 5 is an additional modification showing the contact of my switch reversed; Fig.,6 is a circuit diagram illustrating an application of my switch for controlling the speed of a series 5 motor; Fig. 7 is a circuit diagram illustrating an application of my switch to the armature circuit of a shunt motor; Fig. 8 is a circuit diagram illustrating an application of the modified switch shown in Fig. 5 to the field circuit of a shunt 10 motor; Fig. 9 is a perspective view of an additional modification of my switch; and Fig. 10 is a part sectional view of the switch shown in Fig. 9.

Referring now tothe drawings and more particularly to Figs. 1 and 2 thereof, a shaft I, which 15 may for example be the shaft of an electric motor whose speed is controlled by my switch, has mounted thereon a rotatable member 2 which is fastened to the shaft in any suitable manner, such as by a set screw 3. Mounted on rotatable 20 member 2 are metal collector elements 4 and 5 which are preferably circular in shape and which are shown as discs, although it will of course be obvious to those skilled in the art that conventional collector ringsY may also be employed if 25 desired. Elements 4 and 5 are insulated from the member 2 and from each other by suitable insulating material, such as hard rubber 6. Cooperating with the collector discs 4 and 5, respectively, are brushes I and 8 to which the elec- 30 trlcal connections to the switch may be made. Electrically connected to metal collector disc 4, and preferably also supported thereby, is an offcenter ycontact 9, which as shown by way of example, is riveted to the disc 4. Supported by the 35 rotatable member 2, through the medium of collector disc 5 and metal screw studs I0, is a metal frame or plate II which may be ,made of any suitable material, such for example, as phosphor bronze. Plate II is provided with opposite cut- 40 away portions into which project integral fingers I2 and I3. Extensions I4 and I5 are fastened, respectively, to the fingers I2 and I3 and these extensions have overlapping portions in the axis l of rotation of the device. Mounted on finger I3 45 and extension I5 thereof is a contact I6 for cooperation with the contact 9. Interposed b'etween the'overlapping extensions I4 and I5 is a compression spring I'I which serves to bias the finger I3, carrying the contact I6, in such a direction as 50 there is provided an adjustment screw I9 which bears against a bearing member, such as a fibre or Bakelite button 20 set in the extension I4. By turning the screw I9 the compression of the biasing spring I1 can be adjusted, thereby adjusting, in a manner to be described more in detail hereinafter, the speed at which the contacts of the switch open.

For relieving the force and wear of the adjusting means of the switch I provide another offcenter weight 2I which is fastened by suitable means, such as by riveting, to the finger I2 and plate I I-.

The operation of the switch shown in Figs. 1 and 2 is as follows: In Fig. l the parts are shown in the positions they assume when the switch is at rest. If now the shaft I is rotationally accelerated the centrifugal force on weight I8 will produce a bending movement tending to turn the finger I3 counter-clockwise (asviewed in Fig. 2) about a center approximately at the point where weight I8 is fastened to the arm I3. This is because the centrifugal force on weight I8 is in a radial direction passing through the center of gravity of the weight I8 and the center of gravity is at a distance of approximately half the thickness of the weight I8 from its point of fastening to the arm I3. This distance corresponds to the arm of the bending movement. When a certain critical speed is reached, which speed is determined by the compression of spring I1 and the resilience of arm I3 and the torsional resistance of the portion of plate II to which it is integrally attached, the centrifugal bending moment produced by the weight I8 will be sufficient to cause the contact I5 to move out of engagement with the contact 9, as is shown in Fig. 2. Consequently, an electric circuit from brush 1 through discs 4, contact 9, contact I6, stud I0, disc 5 and brush 8 will be interrupted by the separation of the contacts 9 and I 6.

At the same time that the above described action is taking place, a similar ybending moment is being produced by the Weight 2| on the arm I2 and extension I4, and this bending moment is in such a direction as to cause arm I4 to tend to compress spring I1, thereby relieving most of the pressure or friction between the screw I9 and the button 20. Weight 2| is so proportioned that the bending moment it produces is never surlicient to cause button 20 to leave screw I9, as this of course would change the calibration or setting of the switch. The bending moment produced by weight 2| is merely sufficient to relieve most of the pressure between button 20 and screw I9 so that wear and noise between these two elements is greatly minimized.

Due to the fact that ngers I2 and I3 are inv tegral with the plate I I these fingers are in effect mounted on frictionless hinges and go through their various ranges of movement without causing any wear orl requiring lubrication of any parts.

By screwing adjusting screw I9 inwardly the brought to rest. In this modiiication a screw 22 is passed between extension I4 and the part of the plate II which is opposite thereto and a nut 23 and a locknut 24 are provided thereon on opposite sides of the plate II. By adjusting the distance between plate II and arm I4 the cornpression of spring I1 can be adjusted thereby adjusting the speed setting of the switch in the manner previously described.

In the modification shown in Fig. 4, but a single collector element is employed and current is led into the switch through the adjusting screw I9 and a metal contact member 25 which takes the place of the bre or bakelite button 20. With such a construction, the plate II is mounted directly on the member 2 instead of being mounted indirectly thereon through the interposition of the second collector element 5, as in Figs. 1 and 2.

In the modication shown in Fig. 5, the contacts have been reversed, that is to say, contact I6 is mounted on the other side of extension I5 and nger I3, and contact 9 is mounted for engagement with contact I6 by means of a suitable bracket 26 extending from the collector disc 4 around the arm` I3 and extension I5. With this arrangement of the contacts they are normally open and when the critical speed is attained the flexing of the finger I3 and extension I5 causes the engagement of the contacts. The modification shown in Fig. 5 may obviously be applied either to the switch of Figs. 1 and 2 or to the switch of Fig. 3 or 'to the switch of Fig. 4.

In Fig. 6 a series motor 21 having a series field winding 28 is controlled by the switch contacts 9, I6 of the switches shown in either Figs. 1 and 2, or in Fig. 3 or 4. For this purpose it is preferable to connect a regulating resistor 29 across the contacts of the switch and also to connect a discharge capacitor 30 across the contacts for minimizing sparking thereof. With this arrangement, the contacts 9 and I5 are normally in engagement so that when the circuit including the motor 21 is energized from any suitable current source (not shown) the motor comes up to speed and as soon as the critical speedis reached the contacts 9 and I6 open, thereby inserting the resistor 29 in series with the motor which limits the voltage applied thereto so that the motor speed is reduced, but as soon as it falls below the critical speed the contacts close thereby short-circuiting the resistor 29 and the motor again increases in speed. This action, however, is extremely rapid and due to the inertia of the motor there are no sudden changes in speed and it operates at a substantially uniform and constant speed.

In Fig. 7 a shunt motor 3| having a shunt eld winding 32 is controlled by my switch, of the types shown in Fig. 1, 2, 3 or 4, having its contacts 9 and I6 connected in the armature circuit of themotor. With this arrangement the contacts are normally closed so that the motor comes up to speed but when the critical speed is reached the contacts open thereby inserting the resistor 29 in the armature circuit thereby reducing the voltage on the armature with the result that the speed of the motor is decreased. However, as soon as the speed decreases below the critical value the contacts again close as has just been described in connection with Fig. 6, and this results in holding the speed of the motor 1 substantially constant.

In Fig. 8 the shunt motor 3'I is controlled by a switch having its contacts in circuit with the field 32. In order to control the speed of the motor in this manner the contacts must close on overspeed instead of opening on overspeed and consequently a switch having contacts arranged as in Fig. 5 must be employed. With this arrangement the contacts 9, I6 are normally open, thereby causing the eld current to iiow through the resistor 9 and weakening the field of the motor. This causes the motor to tend to operate at overspeed but as soon as the critical speed is reached the contacts close thereby short-circuiting the resistor 29 and. increasing the current to the field 32 thereby reducing the motor speed. This cycle is then repeated rapidly with the result that the average motor speed is held constant.

In the modification shown in Figs. 9 and l0 the plate, or frame, member II has been replaced by two frame members 33 and 34. 'Iheframe 33 is fastened to the collector disc 4 by means of screws 35 threaded into studs 36. I have found that in some cases the hinges produced by the flexing of portions of the' plate or frame II of the. modifications shown in Figs. 1 to 5, inclusive, became distorted and weaved at certain speeds. In order to overcome this I have provided a relatively rigid rod or bar 3l which is mounted in slots in the studs 36, and this rod 3l is adjacent the hinge or exing portion of the frame 33 and thus prevents distortion and weaving. As shown, the frame 33 carries the finger or arm I5 for carrying the movable contact I6. Frame 33 is also provided with an extension 33 for cooperation directly with speed adjusting buttbn 20. With this construction, it is possible to eliminate entirely the helical spring I'I of the previously described modifications and this is sometimes desirable, as I have. found that at times the lhelical spring tends to flutter, and thus upset the speed setting of the switch. In the modification shown in Figs. 9 and 10 the biasing spring for the adjustable contact I6 is formed bythe extension 38, the resilient hinge of the member 33 and the nger I5, all of` which elements are resilient, so that when screw I9 is turned inwardly causing button 20 to push against extension 38, the biasing force on the contact I6 is increased thereby requiring a greater speed of rotation ofthe switch for the centrifugal weight I8 to cause contact I6 to leave the contact 9.l

I have also found that in some cases better contact action is secured if the contacts are placed on the opposite side of the center of the switch from the hinge for the movable contact, and as shown in Figs. 9 and 10, the finger I5 extends beyond the center of rotation of the switch. With the longer lever arm thus produced, a wider and more positive contact opening is secured.

It should also be noted that in the modification shown in Figs. 9 and 10 the contacts have been reversed with respect to the collector discs or elements so that the stationary contact 9 is carried by the. smaller disc 5 while the movable contact I6 is carried by the larger disc 4.

The resilient frictionless hinge member 34 is mounted on studs 39 by means of screws 40 and for bracing the hinge and preventing distortion thereof there is provided a relatively rigid rod member 4I having eyelets through which the screws 4U are passed.

Although the arm I4 of the speed .adjusting mechanism of my switch is shown mounted on a frictionless resilient hinge in the various modifiv cations of my invention which I have described,

it should be noted that such mounting is not really necessary and that due to the fact that the force for operating the speed adjusting mechanism, which is produced by the screw I 9, is ample to operate this mechanism regardless of any ordinary amount of friction in the hinge, it would be entirely feasible to substitute a conventional hinge for the hinges shown in the various modifications of the speed adjusting means.

While I have shown and described particular embodiments of my invention, it will b-e obvious to those skilled in the art that changes and modifications mayb-e made without departing from my invention, and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

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

1. In a centrifugal switch, a rotatable member carrying a pair of contacts, a biasing spring for one of said contacts carried by said member, means for adjusting the biasing force of said springand centrifugally actuated means carried by said member for reducing the force of said spring on said adjusting means.'

2. In a centrifugal switch, a rotatable member carrying a pair of contacts, a biasing spring for one of said contacts, a movable element carried by said member and bearing against said spring, adjustable means for varying the force of said element against said spring, and a centrifugally actuated weight for varying the force. of said element against said spring in the same direction as said adjustable means whereby the counterforce on said adjustable means is reduced in accordance with increases in the speed of said member.

3. In a centrifugal switch, a rotatable member carrying a pair of contacts, a biasing spring for one of said contacts carried by said member, a normally stationary adjustable member cooperating with said spring for adjusting the biasing force thereof, and centrfugally operated means carried by said rotatable member for reducing the force exerted by said spring on said adjustable member in accordance with increases in speed of said rotatable member.

4. A centrifugal switch comprising, in combination, a. rotatable member, a circular collector element mounted on said member for rotation about an axis perpendicular to said element, a. contact carried by said elementv beyond the center of rotation thereof and having its contact face parallel to the plane of rotation of said element, a

` member moves said finger.

5. A` centrifugal switch comprising, in combination, a rotatable member, a pair of relatively insulated collector discs mounted thereon, a contact attached to one of said discs, a metal frame attached to the other of said discs, said frame having a cut-away portion around an inwardly extending nger, a contact carried by said nger for cooperation with the first mentioned contact, and an off-center weight .attached to said finger for producing a centrifugal force in a direction to move said finger in response to the rotation of said member.

6. In a centrifugal switch, a rotatable member, a circular collector element carried thereby, an off-center contact connected to said element, a metal plate carried by said member, said plate having cut-away portions around two inwardly extending lingers on said plate, a helical compression spring between the inner ends of said fingers, a contact carried by one of said ngers for c0- operation with the rst mentioned contact, and separate centrifugal weights carried by each of said fingers for urging them toward each other in response to rotation of said member.

7. In a centrifugal switch, a rotatable member, a pair of relatively insulated circular collector elements carried thereby, an yoff-center contact carried by one of said elements, a metal frame carried by the other of said elements, said frame having cut-away portions around inwardly extending overlapping metal ngers, a compression spring between the overlapping portions of said fingers, a Contact carried by one of said fingers and cooperating with the rst mentioned Contact, an off-center weight fastened to the contact Carrying lingers for producing a centrifugal force in 20 a direction to flex the contact carrying nger against the compression of said spring, normally stationary means for adjusting the compression of said spring, and an off-center weight fastened to the other finger for producing a centrifugal force in a direction tending to ex the other contact linger against the compression of said spring.

In a centrifugal switch, a rotatable member, a relatively xed Contact carried thereby, a resilient metal frame carried by said member, said frame having a nger carrying a movable Contact for cooperation with said fixed contact, means adjustable along the axis of said rotatable member for flexing said frame and thereby adjusting the setting of said switch, and centrifugally actuated means carried by said member for reducing the force on said adjustable means caused by the exing of said resilient frame.

ROBERT W. GROOT.

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