USRE20993E - groot r - Google Patents

Description

'7, 1954 2 Sheets-Sheet 1 a. 9% ttor-neg.

Inventor: Robert W Great, by 7 Jail 1939. R. w. GROUT CENTRIFUGAL SWITCH Original Filed Sept.

Jan. 31, 1939. R. w. GROOT 20,993

CENTRIFUGAL SWITCH Original Filed Sept. 7, 1954 2 Sheets-Sheet 2 Inventor Robert W. Groot,

His Attorn e9.

Reiacued Jan. 31, 1939 Re, 20,993

20,993 common. swrrcn Robert w. Groot, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Original No. 2,084,907, dated June 22; 1937, Serial No. 743,110, September 7, 1934. Application for reissue June 24, 1937, Serial No. 150,147

11 Claims. (Cl. 200-80) My invention relates to centrifugal switches way of making the electrical connections to my and more particularly to improvements in the switch; Fig. is an additional modification showconstruction of such switches. ing the contacts of my switch reversed; Fig. 6 is Centrifugal switches of the so-called center a circuit diagram illustrating an application of contact type, wherein a rotatable member carrymy switch for controlling the speed of a series ing a centrifugally actuated contact which is motorj Fig. '7 is a circuit diagram illustrating an movable along the axis of rotation of the rotatable application of my switch to the armature circuit member and which cooperates with an axially of a shunt motor; Fig. 8 is a circuit diagram positioned stationary contact, have been found illustrating an application of the modified switch 19 difficult to keep in proper operating condition, as shown in Fig. 5 to the field circuit of a shunt it is necessary for the contacts to be extremely motor; Fig. 9 is a perspective view of an additrueand smooth in order to prevent objectionable tional modification of my switch; and Fig. 10 is a contact noise or squealing. As the contacts part sectional view of the switch shown in Fig. 9. naturally tend to pit or burn and become rough in Referring now to the drawings and more parservice, such switches require frequent dressing ticularly to Figs. 1 and 2 thereof, a shaft I, which of the contacts in order to give satisfactory may for example be the shaft of an electric motor service. Accordingly, in my switch the contacts whose speed is controlled by my switch, has are mounted off-center, with the contact surfaces mounted thereon a rotatable member 2 which is in a plane perpendicular to the axis of rotation fastened to the shaft in any suitable manner,

2 of the rotatable member. With such a construcsuch as by a set screw 3; Mounted on rotatable tion, the resultant windage is beneficial to the member 2 are metal collector elements 4 and 5 action of the contacts in that it serves to cool which are preferably circular in shape and which them and to blow out arcs between them. Howare shown as discs, although it will of. course be ever, in order to adjust the setting of the switch obvious to those skilled in the art that conven during its operation, it is usually necessary to tional collector rings may also be employed if de- 25 have an axially movable adjustable means for cosired. Elements 4 and 5 are insulated from the operation with an axially positioned element on member 2 and from each other by suitable inthe rotatable member with the result that wear sulating material, such as hard rubber 6. Coand some noise is produced by these adjustable operating with the-collector discs 4 and 5, respec- 39 members. tively, are brushes 1 and 8 to which the electrical In accordance with my invention, however, 1 connections to the switch may be made. Elecprovide a novel construction in which centrifugal trically connected to metal collector disc 4, and force is utilized to reduce and minimize the force preferably also supported thereby, is an off-center between the stationary and the rotatable elecontact S, which as shown by way of example, is

ments of the adjusting means of the switch so riveted to the disc 4. Supported by the rotatable 35 that under the normal operating speed of the member 2, through the medium of collector disc 5 switch the pressure between the elements of the and metal screw studs I0, is a metal frame or adjusting means is relatively insignificant. plate II which may be made of any suitable mate- An object of my invention is to provide a new rial, such for example, as phosphor bronze. Plate and improved centrifugal switch. H is provided with opposite cutaway portions 40 A further object of my invention is to provide into which project integral fingers l2 and l3. 8. speed adjusting means for centrifugal switches Extensions I4 and I5 are fastened, respectively, with a centrifugal element which serves to reto the fingers l2 and I3 and these extensions duce the wear in the adjusting means. have overlapping. portions in the axis of rotation My invention will be better understood from of the device. -Mounted on finger l3 and exten- 45 the following description taken in connection sion l5 thereof is a contact l6 for cooperation with the accompanying drawings and its scope with the contact 9. Interposed between the overwill be pointed out in the appended claims. lapping extensions I4 and I5 is a compression In the drawingsfin which like reference charspring H which serves to bias the finger i3, carryacters designate similar elements throughout the ing the contact IS, in such a direction as to cause 50 several views, Fig. 1 is a perspective view of one contact l6 normally to engage contact 9. embodiment of my invention; Fig. 2 is a cross- For actuating the contact l5 there is an offsectional view of the switch shown in Fig. 1; Fig. center mounted weight l8 fastened to the finger 3 illustrates a modified speed adjusting means for I3 and plate II.

. a single speed switch; Fig. 4 illustrates a modified For adjusting the speed setting of the switch there is provided an adJustment screw I9 which bears against a bearing member, such as a fibre of Bakelite" button 20 set in the extension I4. By turning the screw I9 the compression of the biasing spring IT can be adjusted, thereby ad justing, 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 oilcenter weight 2| 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 switchis at rest. If now the shaft l is rotationally accelerated the centrifugal force on weight I 9 will produce a bending moment tending to turn the finger l3 counter-clockwise (as viewed in Fig. 2) about a center approximately at the point where weight I 9 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 l8 from its point of fastening to the arm I3. This distance corresponds to the arm of the bending moment. When a certain critical speed is reached, which speed is determined by the compression of spring I! 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-I9 will be sufficient to cause the contact I6 to move out of engagement with the contact 9, as is shown in Fig. 2. Consequently, an electric circuit from brush 1 through disc 4, contact 9, contact I6, stud l9, disc 5 and. brush 9 will be interrupted by the separation or the contacts 9 and It.

At the same time that the above described action is taking place, a similar bending 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 II, thereby relieving most of the pressure or friction between the screw I9 and the button 29. Weight 2| is so proportioned that the bending moment it produces is never sufiicient to cause button 2!] to leave screw I9, as this of course would change the calibration or setting of the switch. The bending moment produced by weight 2I is merely sufficient to relieve most of the pressure between button 29 and screw l9 so that wear and noise between 7 these two elements is greatly minimized.

Due to the fact that fingers I2 and I3 are integral 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 or requiring lubrication of any parts.

By screwing adjusting screw I9 inwardly the compression of spring I1 is increased so that it requires a higher speed of rotation of shaft I to cause the contacts 9 and I6 to separate. Conversely, unscrewing the adjustable screw l9 weakens the compression of spring I! and allows the contacts to open at a lower speed.

The modification shown in Fig. 3 is adapted for constant speed operation and the speed adjusting means is carried on the rotatable member instead of being stationary, so that once the speed is set it cannot be changed unless the switch is brought to rest. In this modification a screw 22 is passed between extension I l and the part of the plate I I which is opposite thereto and a nut 23 and a lock-nut 24 are provided thereon on opposite sides of the plate II. By adjusting the distance between plate II and arm I4 the compression of spring I! 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 fibre or Bakelite button 29. 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 modification shown in Fig. 5, the contacts have been reversed, that is to say, contact IB is mounted on the other side or extension I5 and finger I9, 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 Figs. 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 39 across the contacts for minimizing sparking thereof. With this arrangement, the contacts 9 and I 8 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 speed is reached the contacts 9 and I6 open, thereby inserting the re-.

sistor 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 mot'orBI having a shunt field winding 32 is controlled by my switch, of the types shown in Figs. 1, 2, 3 or 4, having its contacts 9 and I6 connected in the armature circuit of the motor. 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 I substantially constant.

In Fig. 8 the shunt motor 3i 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 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 off-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 fingers, a compression spring between the overlapping portions of said fingers, a contact carried by one of said fingers and cooperating with the first mentioned contact, an off-center weight fastened to the contact carrying fingers for producing a centrifugal force in a direction to flex the contact carrying finger 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 flex the other contact finger against the compression of said spring.

8; In a centrifugal switch, a rotatable member, a relatively fixed contact carried thereby, a resilient metal frame carried by said member, said frame having a finger carrying a movable contact for cooperation with said flxed 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 flexing of said resilient frame.

9. A centrifugal switch adapted by the vibratory engagement of its contacts to maintain the speedof an electric motor substantially constant comprising, in combination, a rotatable member, a contact fixedly mounted off-center on to said rotatable member, a movable centrifugally actuated contact adapted for vibratory engagement with said fixed contact, an arm mounted ofi center on said rotatable member for carrying said movable contact, said arm having an effective pivot on the diametrically opposite side of said member from said fixed contact, resilient means for supporting said am and for biasing said movable contact in a direction opposite to that in which centrifugal force acts to move said movable contact, and a-xially'movable means for adjusting the speed setting of said switch, said adjusting means engaging said resilient means in such a 'manner as to vary adjustably the amount of said bias.

10. A centrifugal switch adapted to govern the speed of an electric motor comprising, in combination, a rotatable insulating member, a pair of collector rings carried by said member, a contact electrically connected to one of said collector rings, said contact being fixedly mounted offcenter relative to said member with its contact face parallel to the plane of rotation of said collector rings, a movable contact for cooperation with said fixedly mounted contact, a resiliently mounted centrifugally actuated arm for carrying said movable contact, said arm extending on the diametrically'opposite side of the axis of rotation of said member from said fixed contact and being electrically connected to the other of said collector rings, means movable along the axis of rotation of said member for adjusting the speed at which centrifugal force actuates said arm to move said movable contact relative to said fixed contact, and resilient connecting means interposed between said arm and said adjusting means.

11. A centrifugal switch adapted to govern automatically the speed of an electric motor comprising, in combination, arotatable insulating member, a pair of collector rings carried thereby, an off-center fixed contact electrically connected to one of said collector rings, said contact being mounted on said switch with its contact face parallel to the plane of rotation of said collector rings, an off-center resilient electrical conducting member electrically connected to the other of said collector rings, said resilient member being mounted on said switch symmetrically with respect to a line passing through said fixed contact and the axis of rotation of said insulating mem-

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