US2747854A - Snap acting speed responsive device - Google Patents

Description

May 29, 1956 w. K. SCHNEPF SNAP ACTING SPEED RESPONSIVE DEVICE Filed June 27, 1951 6 r .X IN V EN TOR.

W/LL IAN A. SOHA/EPF A7- Toe/V5345 United States Patent SNAP ACTING SPEED RESPONSIVE DEVICE William K. Schnepf, Webster, N. Y., assiguor to General Motors Corporation, Detroit, Mich., a corporatien of Delaware Application June 27, 1951, Serial No. 233,741 6 Claims. (Cl. 264--) This invention relates to centrifugallyoperated switches for use on electric motors and more particularly to centrifugal switches for disconnecting the starting windings of an electric motor.

An object of the present invention is to provide a centrifugal switch which is sturdy and durable and can be produced at low cost. In order to accomplish this object the present invention provides a construction of parts which can be manufactured from sheet metal parts.

In the disclosed embodiment of the invention the centrifugal device which operates the switch comprises five principal parts made of formed sheet metal, namely two auxiliary weight members one on each side of the shaft and two main weight members one on each side of the shaft for pivotally supporting the auxiliary weight member and a bracket mounted on the shaft for pivotally supporting the main weight members upon parallel axes at right angles to the axis of the shaft. All of the weight members are held in inward position toward the motor shaft by two coiled springs each connected with both auxiliary weight members. The main weight members have fingers movable substantially longitudinally of the shaft to move a switch actuator sleeve through which the shaft extends.

Another object of the present invention is to provide, a speed responsive means carried by the shaft for normally holding the switch in closed position and for operating in such a way as to allow the switch to open with a snap action when the speed of the shaft reaches a predetermined value. The speed responsive device also operates reversely to close the switch with a snap action when the speed of the shaft goes below that predetermined value. This object is accomplished in the disclosed form of the present invention by the use of relatively heavy weights and relatively light weights pivotally supported on the heavy weights and both weights are moved.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

Fig. l is a fragmentary longitudinal sectional view of an end member of an electric motor with a centrifugal switch shown in running position, embodying the present invention.

Fig. 2 is a view, on an enlarged scale taken on line 2-2 of Fig. l.

Fig. 3 is a view, looking in the direction of the arrow 3 in Fig. 2, on an enlarged scale showing the centrifugal device holding the switch closed.

Fig. 4 is a fragmentary view of the centrifugal device showing the position of the parts when the centrifugal force is small and the switch is closed.

' Fig. 5 is a view similar to Fig. 4, but showing the positions of the part when the centrifugal force is sulficient to allow the switch to open. a

' Fig. 6-is a side view of one of the weights.

Fig. 7 is a sectional view taken on line 7-7 of Fig. 2.

The centrifugally operated device as illustrated in the drawing for disconnecting the starting winding of an electric motor, not shown, when the motor reaches a predetermined speed comprises an actuating device 26 and a switch 21. The actuating device is carried by a shaft 22 of the rotatable member of the electric motor. The switch 21 may be supported by an end member 23 of the electric motor or other suitable supporting means. In this instance only a fragment of one end member 23 of the motor is shown. The actuating device 20 operates to hold the switch 21 closed until the shaft reaches a predetermined running speed. The position of the actuating device 20 in relation to the switch 21 when the rotatable member has attained running speed is illustrated in Fig. 1. When the rotatable member is stationary, the elements comprising actuating device 20 will be in the positions shown in Fig. 3 and the switch 21 will be closed.

The switch 21 as shown in Fig. 1 has a terminal support or bar 30 of insulating material carrying a stationary contact 31 adapted to be connected with the starter winding of the motor, not shown. This contact is normally engaged by a movable contact 32 carried by a conducting member 33 secured to a block of insulating material 30 attached to the end member 23. The conducting member is bifurcated to provide resilient arms 34 not shown, to straddle the shaft 22. One arm 34 of the conducting member is shown in Figs. 1 and 3. The mid portion of the conducting member 34 has an extension which carries the movable contact 32. The outer ends of the arms 34 are provided with inwardly extending portions 35 which are located in the path of a sliding sleeve 37 of insulating material associated with the centrifugal operating mechanism. The conducting member 33 may be stamped from any suitable material such as bronze and the conducting member is designed so that arms 34 are biased away from the block or the support 30. Brackets or stops 38 are attached to the support 30 to limit the movement of the arms 34 away from the block 30.

The switch 21 is controlled by the centrifugally responsive mechanism in accordance with the speed of the shaft 22. This mechanism must move the sleeve axially along the shaft without any hesitation to permit the switch to open to disconnect the starting winding at a predetermined speed. This mechanism comprises a bracket 41 made of sheet metal and formed with a tubular portion 42 through which the shaft 22 extends. Various methods, such as welding or brazing may be used to secure the tubular portion to the shaft but in the present instance the tubular portion is press-fitted over a knurled portion 43 provided by the shaft. The bracket 41 includes flat portion 44 located in a plane transverse of the axis of the tubular sleeve portion 41. From the flat portion extends two oppositely disposed horizontal arms 45 and from each arm 45 there extends an angular ear 46. Each horizontal arm is provided with a tab 47 which extends outwardly from the plane of the arms 45 to form stops. The angular arms 46 are each punched out in a manner to provide a transverse elongated slot 48 and a tongue 49 which is bent outwardly from the plane of the ear 46 to provide a bearing surface 46a for a pair of weights 50.

The weights 50 of relatively heavy metal are angular in shape to provide arms 51 and 52. The arm 51 of each weight is channel-shaped to provide flanges 53 each of which is formed with a notch 54 having converging side walls 55 and 56 and a bottom wall 57 (see Fig. 6). It will be noted that the side wall 56 is slightly longer than the side wall 55 the purpose of which being described hereinafter. The arm 52 of the weight 50 is bifurcated to provide fingers or arms 55. These arms are provided with rounded surfaces at their ends and extend loosely into recesses 60 formed in lugs 61 on sliding sleeve 37. There is a clearance between the ends of arms 59' and the bottom of recesses 60 to permit the end 59 to move downwardly to actuate the sleeve 37. The end surfaces of the arms 59 are rounded, thus providing minimum friction when the arms engage wall surfaces provided by the notch 60. In order to support pivotally the weights on the brackets 41 the arms 52 project through the slot 48 in arm 46. Each weight 50 is formed with an opening 62 adjacent the angle of the weights as shown in lower weight in Fig. 3 to receive the tongue 49. By this formation of the opening a knife edge pivot 63 is provided and this edge contacts the bearing surface 46a and affords an axis about which the weights 50 can move.

The main weights t) pivotally support L-shaped auxiliary weights 70. Each weight 70 is formed from a sheet metal stamping of relatively light weight, to form arms 71 and 72. The arm 71 has extended ears 73 on opposite sides thereof and fit into respective notches 54 of the flange 53 of the main weight 50. The cars extend beyond the flanges and are provided with notched portions 74 adapted to receive the hooked ends of springs 75. Referring to Fig. 7, it is pointed out that the notch 74 is provided with a chamfer 74a. This provides almost a knife-edge for engaging the springs 75 to insure positive operation of the device. By this arrangement the spring exerts a force on the weights and 70 which tend to rotate in a counterclockwise direction with respect to the bracket, see Fig. 3. The notches 54 are formed so that the bottom is slightly wider than the Width of the cars 73 to permit the required pivotal movement of the auxiliary weights 70 on the bottom wall of the notch 54.

For the purpose of description, Fig. 5, line X-X indicates a center of action of the springs 75. When the shaft 22 of the motor is at rest, as shown in Fig. 3, the weights 70 are urged toward the center of the shaft. When in this position the ears 73 will rest against the side walls of the notch 54 and the force of the springs is such that it will cause arms 52 to hold a collar 76 on the sleeve 37 to abut against the ends 34 to hold the movable contact 32 in engagement with the stationary contact 31. Upon rotation of the shaft 22, the weights 70 will move first. As these weights move outwardly, the ears 73 will rock in slots 54, but the weights 50 remain stationary until the rotatable member reaches the predetermined running speed. When that occurs the ears occupy the position shown in Fig. 4 in which case the other side of the cars 73 will contact the side 56 of the notch 54. When the auxiliary weights 70 are in this position the center lines of action of the springs have shifted from line AA to line B-B and the effective length of the spring 75 is reduced by about .020", as indicated by the space designated by letter S in Fig. 4. When the center line of action of the spring 75 is on the line BB the tension of the springs 75 is reduced, the weights 50 which previously have not rrioved are now under reduced tension. Thus as the running speed of the shaft increases the weights 50 begin to move outwardly by centrifugal force. The weights 50 will pivot about the sharp knife edge 63 causing the arms to act quickly to move the sleeve 37 with snap-like operation at the predetermined running speed and without any hesitancy to allow the switch 21 to open quickly and thereby disconnect the starting windings at that predetermined speed. While the motor shaft is rotating at or about the predetermined speed, the centrifugal force exerted will cause the sleeve 37 to continue to slide along the shaft 22 thus permitting the switch 21 to move to the position shown in Fig. l. The arms of the conducting member will be held against the bracket by the resiliency of the member.

It is pointed out that the force of the springs 75 to hold the weights 50 and toward the motor shaft and thus hold the switch closed is greatest when the center line of action of the spring is on line A-A and as soon as the action line is shifted right of line AA or in other words to line BB the effective length of the spring decreases and the tension of the spring decreases. As this effective length of the spring decreases the tension of springs for holding the weight toward the shaft decreases. By using this combination of centrifugal force and then decreasing the effecting lengths of the springs before the main wcights St) move outwardly these weights will actuate the sleeve 37 along the axis of shaft 22 with a snap-like operation to permit the switch 21 to open quickly and thereby disconnect the starting windings at a predetermined running speed.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In combination with a rotatable shaft and a mem ber supported on said shaft for axial movement relative thereto, a speed responsive device for effecting snap action axial movement ofsaid member at a predeterminedrotational speed of said shaft comprising; a support fixedly mounted on said shaft, a pair of opposed main weights pivotally mounted on said support and operatively con-' nected to said member such that outward pivotal movement of said main weights will effect axial movement of the said member, a pair of auxiliary weights pivotally mounted on said main weights, and spring means connecting portions of said auxiliary weights and opposing outward movement thereof under the urge of centrifugal force due to rotation of said shaft, said spring means being connected with said auxiliary weights so that upon the attainmen't of said predetermined rotational speed of said shaft said auxiliary weights will pivot outwardly a sufficient distance to reduce the tension of said spring means whereby said main weights will instantly pivot outwardly so as to effect snap action axial movement of the said member.

2. A device in accordance with claim 1 wherein said spring means includes a pair of coil springs connected with said auxiliary weights so that a predetermined outward pivotal movement of said auxiliary weights will reduce the effective length of said springs.

3. A device in accordance with claim 1 wherein said main weights are formed with upstanding spaced flanges having aligned notches, and wherein said auxiliary weights are formed with projections that are received in said notches.

4. A device in accordance with claim 3 wherein said spring means comprise a pair of coil springs and wherein the projections on said auxiliary weights are formed with notches which receive the ends of said springs.

5. A device in accordance with claim 1 wherein said auxiliary weights are formed with projections having notches, the bottom surfaces of which are formed with knife-like edges, and wherein said spring means comprises a pair of coil springs, the ends of which are received in said notches whereby a predetermined outward pivotal movement of said auxiliary weights will reduce the effective length of said coil springs so as to reduce the tension thereof.

6. A device in accordance with claim 5 wherein said main weights include spaced flanges having aligned notches Within which the projections of said auxiliary weights are pivotally supported.

References Cited in the file of this patent UNITED STATES PATENTS

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