US2503950A - Centrifugal snap acting mechanism - Google Patents

Description

April 11, 1950 w; JOHNSON 2,503,950

CENTRIFUGAL SNAP ACTING MECHANISM Filed Aug. 30, 1946 2 Sheets-Sheet l INVENTOR. ZZ/MW 5L.

ATTOQNEYS April 11, 1950 w. A. JOHNSON 2,503,950 CENTRIFUGAL SNAP ACTING MECHANISM Filed Aug. so, 1946 2 Sheets-Sheet 2 63 7 as I g 1s 62,

Ill 6 7 P 64 INVENTOR.

ATTOQNEYS Patented Apr. 11, 1950 UNITED STATES PATENT OFFICE CENTRIFUGAL SNAP ACTING MECHANISM Warner A. Johnson, Freeport, 111., assignor to First Industrial Corporation, Wilmington, Del., a corporation of Delaware Application August 30, 1946, Serial No. 693,936

20 Claims. 1

The present invention relates to a snap acting mechanism actuatable by centrifugal force and particularly to such a mechanism of the compact, snap acting precision type which is especially adaptable to use in centrifugal switch mechanisms and the like.

An object of the present invention is to provide a centrifugally actuated snap acting mechanism which is mounted on a rotating member and which is operable by the direct action of centrifugal force upon the over-center snap spring mechanism itself as contrasted with certain conventional mechanisms in which the centrifugal force is employed to lift a set of rotating flyballs which in turn then actuates the snap acting mechanism.

Another object is to provide a centrifugally actuated snap acting switch which may be formed or adjusted to be operated at any preselected speed on acceleration and released at any preselected lower speed on deceleration.

Another object is the provision of a centrifugally actuated snap acting switch in which the operating and release points on acceleration and deceleration respectively may be at different, independently adjustable speeds.

Another object is the provision of a centrifugally actuated snap switch employing a unitary over-center spring construction in which the over-center spring is directly responsive to centrifugal force rather than indirectly through flyballs or the like as above-mentioned.

Other specific objects are the provision of specific means for adjusting or preselecting the operating and release points of an improved centrifugally actuated snap acting switch includ- 1ng-- (a) Provision of a preselected mass upon an actuating or sensitive portion of the over-center spring mechanism;

(b) Adjustment means for varying the positions of the stationary contacts or stops;

(0) Means for varying the spacing of the overcenter spring from the rotational axis, and

((1) Means for varying the angularity of the over-center spring with respect to the rotational axis.

Other objects and advantages will become apparent from the following description in connection with the drawings in which- Figure 1 is a sectional view of a switch embodying several features of the present invention and shown mounted upon a rotatable member;

Fig. 2 is a fragmentary end view of Figure 1;

Fig. 3 is a view of the switchillustrated in Figure 1 shown looking upward into the casing with the cover removed;

Fig. 4 is a fragmentary sectional view, similar to Figure 1, showing modified means which may be employed to preselect the rotational speeds at which the switch operates and releases;

Fig. 5 is an end view of Fig. 4;

Fig. 6 is a sectional side view of a further modified form of the invention;

Fig. 7 is a sectional View of Fig. 6 taken on the line 1 and Fig. 8 is a sectional view of Fig. '7 taken on the line 88.

In the modification shown in Figure 1 the centrifugal switch generally designated I, is mounted on the member generally designated 2 which, in turn is mounted for rotation on the shaft 3.

The switch I has a housing 4 of insulating material, such as Bakelite, consisting of a base 6 and a cover 1. An internally threaded bushing 8 molded integrally with the housing 3 has screws 9 and I2 attached to its inner end and outer ends.

Screw l2 holds terminal tab I 2a in place. Screw 9 holds the U-shaped anchor H (see Fig. 3) and the over-center snap spring system i3 in place.

The snap spring l3 in this particular case is shown as a modification of that disclosed in the P. K. McGall Patent 1,960,020; however, it will be obvious as the description proceeds that any other type of overcenter spring systems may be employed with satisfactory results. The specific snap spring system herein disclosed may be stamped integrally from a single sheet of thin spring material and is formed to include a pair of compression elements l4 and a tension element l5. One end of the tension element It is formed with an opening for mounting under the head of screw 9, and the anchor ll and spring system l3 are so dimensioned that when assembled, as shown in Figure 1, with the ends of the compression elements l4 pivoted in anchor grooves 24 the elements It will be stressed in compression and element H3 will be stressed in tension. The system will have an axis of maximum stress corresponding to a position where the tension element I6 and the grooves 24 are in substantial alignment, and movement of the tension element It through that axis in either direction will cause it to be moved beyond the axis by snap action. For example, if the tension element I6 were moved outwardly as by centrifugal force, beyond the pivot grooves 24, the spring system would be snapped outward away from its Figure 1 position.

The extent of the force required to move the tension element [6 outward through the abovementioned axis of maximum stress will depend in one respect on the proximity initially of the tension element with that axis. Means for adjusting that initial proximity and, therefore, the force required to snap the spring system outwardly is provided in the adjustable screw 52, threadedly engaged Within the bushing 55 which is molded into the cover plate I. The bushing will usually be a brass insert, although in some cases threads may be formed directly in the cover 7; and the screw 52 will preferably have a tight fit with the bushing 51 to maintain it in adjusted position without the use of a lock nut. Thus, by increasing the pressure of the screw 52 on the tension element It, the latter will be moved initially closer to the pivot groove 24, that is, closer to the position of maximum stress for the spring system. This will lessen the outward force required on the tension element to snap the spring system outward from its Figure 1 position.

Continuing now the description of the modification shown in Figure l, the movable end of the spring system It carries a mobile contact ll. Stationary contact means operably engageable with this mobile contact includes a bushing 22 which is molded into the base it in the same manner as bushing 8, it being internally threaded likewise for reception of screws 2! and 23 which are employed to hold the tab Zia and the terminal member 18, respectively, in place. A set screw 54, locked by nut 56, is threadedly engaged with the terminal member [8, and has a surface 54a engageable with the mobile contact IT. The engaging surfaces of the mobile contact and the set screw 54 will preferably consist of silver or some other highly conductive material to minimize electrical resistance between these parts. The lock screw 54 provides means for adjusting the movable end of the spring system with respect to the axis of maximum stress, just as the screw 52 functions to adjust the spacing of the tension element It from that axis, as will be considered in greater detail.

The switch I is mounted by bolts 26 within radially elongated holes 21 formed in angle brackets 28 mounted on the drum portion 29 of the rotatable member 2. The weight of the switch and bracket is adjustably counterbalanced at a diametrically opposite position by means of the counterbalance 3! having the inward extension 32 threadedly engaged with the drum 29. The counterbalance is fixed in place by means of lock nut 33 which bears on washer 3 5 which is formed to fit the inner contour of the drum 29.

The rotatable member 2 comprises the cylindrical drum portion 29, integral with the disk or spider 36 and the inner cylindrical portion 37 which is attached to the shaft by pin 38. On the projecting end 39 of the cylindrical portion 37? is mounted an insulating ring 4! with an upstanding spacer portion 62 separating a pair of slip rings 43 which are connected by wires a l and 46 to the switch terminal tabs lid and 21a, the slip rings being engageable by leaf spring contacts 42 and 48 to energize or deenergize a suitable electric circuit in response to speed changes of the particular rotating mechanism driving the shaft 3. It will be appreciated that the mechanism shown is more or less diagrammatic and is for the purpose only of affording an adequate disclosure of the principles of the invention.

In practice, any number of switches may be employed on a member such as designated 2 and the wires 44 and 35 will be connected to a mechanism which is operated in response to a certain speed or speeds of the driving shaft 3. For the purpose of illustration, assume a simple case where the shaft 3 is driven by an electric motor and a normally closed switch I is connected by wires 44 and 46 into the motor circuit to deenergize the motor when it reaches a certain speed. As the motor accelerates toward its critical speed, centrifugal force acting on the spring member will move the tension element outward until it is substantially coplanar with the pivot points of the compression elements within the groove 24. This will be the axis or position of maximum stress for the spring system and slightly increased speed will move the tension element beyond this axis whereupon the contact I! will be moved by snap action out of engagement with the stationary contact screw 54 and into engagement with the stop 5'! which will be described, subsequently. This will open the motor circuit and the shaft 3 will decelerate. As the deceleration proceeds, the centrifugal force will decrease, causing the tension element to move inwardly under the bias of the spring which urges it toward a position on the inward side of the pivot grooves 24, as above mentioned, to make it self-returning to the Figure 1 position. When the deceleration has proceeded to the extent that the tension element has once more passed through the axis of maximum stress by stored energy, but from the opposite direction, the contact I? will be snapped from the stop 51 into engagement with the lockscrew 54, whereupon the motor will be reenergized and will pick up speed to repeat the cycle over and over again.

The switch will operate in response to the movement of the tension member of the order of 0.0001 of an inch opposite the pivot grooves and accordingly the actual distance through which the tension member must be deflected to operate the switch is exceedingly small. It should be understood, therefore, that the drawings are intended only to show the general relationship of the parts mentioned.

While the switch illustrated in Figures 1 and 2 is a returning type of switch, that is, the type which will always return to the normal or Figure 1 position when the rotational velocity of the member 2 is low enough, the invention is also readily applicable to the non-returning or reset type of operation by positioning the stop 5? far enough from the stop 5Q so that when the free end of the spring l3 engages the stop 5'? the tension element will remain beyond the pivot grooves 24 and on the outer side of them. The non-returning type of switch would be employed, for example, in testing a piece of equipment where it is desired to bring it up once to a certain speed and then shut oii the equipment entirely.

The speed at which the switch operates, that is snaps outwardly, on acceleration is regulated by the normal spacing of the switch spring I3 inwardly from its axis of maximum stress; that is, in the modification shown the spacing of the tension element it from a line connecting the pivot grooves 24. The adjustable set screws 52 and 54 provide two separate coacting means for effecting different spacing adjustment. Turning the screw 52 outward (that is, outward from the axis of rotation R) moves the tension element [6 closer to the above-mentioned line connecting the pivot grooves 24 and reduces the force needed wer to st re the s ring s stem we s-sates ,outwa d and thus reduces the speed required to snap the eries yste ou ar 9n a lsra e h ther e n o ef t n this adi sim ni s t lpckscrew 4 which can be employed to effect a f ner adjustment at the same time to change the air gap for the switch. That is, turning the lockscrew toward the spring system will move the latter closer to its axisof maximum stress, thereby lowering the force required to move it further outward through that 'axis and hence lowering the required speed for snapping the spring'sys'tem outwardly on acceleration; at the same time this outward movement of the lockscrew 54 will reduce the air gap between it and the mobile contact I! when the latter is in its outward limiting position against the stop 51. In practice, there will be occasions when'it'is d r e to. re uc b h h O erat n pe and h $2 51 ifier n ia tha s, e .d fi r e in icsdh twen that w en t e sw tch 92 an wh n t lose du s sentr fi se ac ion: s may be accomplished in a single operation by the lockscrew 54. There will be other occasions when it is desired to reduce one but increase the other, for example, reducing the speed differential but increasing the rotational speed at which the switch operates. This latter may be carried out by moving lockscrew 54 toward the spring and moving screw 52 away from the spring. There will be still further occasions when it is desired to adjust the switch to raise or lower the operating speed without changing the air gap and this will be readily effected 'by moving only the adjusting screw 52. Thus, it will be apparent that by the use of the two adjusting screws 52 and 54 in combination it will be possible to secure any desired combination of operating speed and air gap. It will also be apparent, however, that in cases where this extremely broad range of adjustment is not required, either 52 or 54 may be employed singly, to minimize the cost of the switch construction.

Adjusting screw 51 is in a sense the converse of screw 54 in the respect that it provides means for varying the switch release point, that is the rotational speed at which the spring snaps back to the Figure 1 position, on deceleration. The screw 51 is thus an adjustable stop which varies the outward limiting position of the spring systern. In this case, it is engageable with the back of themobile contact I! but in certain other embodiments may satisfactorily engage the spring system at any other position, such as on the tension element H3 or on one of the compression elements it. By moving the screw 51 toward the spring l3, the switch will release or snap to the stationary contact surface 540; at a higher speed; conversely, by moving the screw away from the spring the switch will release at a lower rotational speed.

Another means for preselecting the speed at which the switch is operated and released is by providing means for preselecting the effective mass of the actuating portion of the spring system, the actuating portion of the particular spring system here shown being the tension element l5. One means of accomplishing this is by mounting a separate weight (not shown) On the tension element. By varying the mass of this weight, and by varying its location along the tension element the effect of centrifugal force on the spring system can be varied and the switch can h made to operate and release at higher or lower rotational speeds as desired.

6 An th r me n i nre electine' the s eed at h ch th -W i i Op at and re eas Q mise m an o a in the ha o t e whol D .8 system fro e a o ot tio .I 1 and 2 this means is illustrated as taking Fi the form of radially elongated slots or holes 21 in the brackets 28 which provide for the entire switch to be mounted at the desired distance from the rotational axis R. By increasing the distance of the switch spring l3 from R, the cen trifugal force needed to snap the sp ing will be created at a lower speed; conversely by decreasing the distance from R a higher speed will be needed to create this same centrifugal force. In adjuSting the critical speed in this manner by moving th whole switch it will then be preferable to turn the counterbalance 3| in or out a compensating amount to maintain a balanced condition across the drum 29.

Figs. 4 and 5 illustrate a further means for adjusting the speeds for operating and releasing the switching mechanism. In this case the switch housing has a single bolt 5! molded integral or otherwise fastened on each side. The bolts El are generally engaged within holes 62 in brackets 63 which in turn are mounted upon the drum 29 by screws 64. Washers 65' are provided between the switch casing and the brackets 63. The drum 29 and spider 36 are cut away, as at 61, to provide clearance so the switch may be swiveled within the bracket holes 62 to any angular position desired and then maintained at that angularity by the lock nuts 63. Centrifugal force will be most effective on the switching 'mechanism when the spring mechanism I3 is approximately parallel to the axis of rotation R and when it is swiveled through corresponding amounts of angularity in either direction cen-. trifugal force will be decreasingly eiiective so that higher rotational speeds will be required to operate the switch.

Another modification embodying the above stated principles of the present invention is shown n Fig 6 nd, A u -sh d ho i portion H has in one end thereof a bushing 12- within which is rotatably journaled the shaft like extension [3 of the plate 14, the shaft 13 being held in place by a threaded collar 16. The hQllS': ing portion H has one end threadedly engaged with an outer tubing member 11 which is stationary and is connected to suitable mounting means. Within the tube H is a driving tube 18 removably connected by means of longitudinal slots 19 to the pin 8i in the extension 82, which in this case is formed integral with the plate 14. The other end of the driving tube 18 is connected to a Suitable driving means, for example, the drive shaft of an automobile or truck. A plate 83 of insulating material, such as Bakelite, is mounted by screws 84 to the rotatable plate 14 and has mounted on it the spring system I3 and the counterbalance 86, on opposite sides of the axis of rotation R. The spring system I3 is similar to that disclosed in connection with Figs. 1 and 3, the anchor I I being mounted by screw 81 upon insulating member 88 which is attached to the insulating plate 83 by screw 89. The screw does not extend through the Bakelite plate 83 so that the entire anchor end of the spring system is electrically insulated from the metal plate 14 as well as the rest of the casing. At the freely movable end of the spring system is a contact I! movable between stops 9| and 92 which are mounted to the insulating plate 83 by screws 93 and 94. The screw 93 does not extend 9| is insulated from the rotary metal plate 14 and the rest of the casing. The screw 94 does extend through the insulating plate into threaded engagement with the metal plate 14, as shown in Fig. 8, so that the stop 92 serves the additional purpose of being a stationary contact which is electrically grounded to the casing. An insulating cover 96, also of Bakelite or like material, has an electrically conductive slip rod or bolt 91 mounted at its center. The inner end of the slip rod is engaged by the resilient leaf spring or brush 98 which is held by the anchor screw 81. On the outer end of the slip rod a terminal 99 is connected to a wire 95. The wire 95 leads to the mechanism to be controlled in response to the driving shaft 18, for example, automatic gear shifting mechanism of an automobile or truck, and the circuit is completed by wire 9i) which is grounded to the housing tube 77. The counterbalance 86 is mounted on the insulating plate 83 by screw 85 Within the hole 80 which is elongated to permit the required amount of adjustability.

In operation, the outer tube Ti, casing 1!, and

cover 96 carrying the slip rod 91 will be stationary. Rotation of the driving shaft 18 at increasing speeds will accelerate the switch carrying plate 83 to the point that centrifugal force will efiect the snap action movement of the contact This contact 92, spring system I3, anchor Ii, spring leaf 98, slip rod 91, and conducting wire 95. When the rotatable parts decelerate, the spring system will snap the contact I! back to its normal position against the stop 9|. The operating point of the Fig. 6 switch on acceleration may be preselected by adjustably varying the position of the stop 9! about the screw 93; and the release point on deceleration may be preselected by locking the stationary contact 92 in various positions about the screw 94.

Thus, it will be obvious that I have provided a snap acting centrifugally actuated mechanism which is highly flexible in application and may be advantageously employed in switches as well as a variety of other uses. While particular forms of the present invention have been shown it will be apparent that minor changes therein will readily suggest themselves to others skilled in the art without departing from the spirit and scope of the invention. Having thus described the invention, what is claimed as new is:

1. In a centrifugally actuated snap acting switch, a snap spring system mounted upon a rotatable member and spaced from the rotational axis thereof, said spring system having a part stressed in tension and another part associated therewith stressed in compression, a contact carried by said spring system, said system being movable through a position of maximum stress between limiting positions of lesser stress defined by stops, at least one of said stops being a stationary contact engageable with said carried contact, said spring system being movable by centrifugal force from one of said limiting positions through said position of maximum stress upon acceleration of said rotatable member to a certain speed to move said carried contact by snap action between said stops, and means for preselecting said certain speed comprising variable means for preloading a portion of said spring sys- 8 tem at a position remote from said carried contact.

2. In a centrifugally actuated snap acting switch, a snap spring system having a compression element and a tension element mounted upon a rotatable member, said spring system being movable through a position of maximum stress between normal and abnormal limiting positions of lesser stress defined by stops, at least one of said stops comprising a contact engageable with a contact carried by said spring system, said spring system being movable from said normal to said abnormal position in a snap action manner by centrifugal force upon acceleration of said rotatable member through a preselected speed range and movable from said abnormal to said normal position in a snap action manner by stored energy therewithin upon deceleration through a preselected speed range, one of said stops being movable for adjustment of the stored energy required to move said spring system from said abnormal to said normal positions on deceleration.

3. In a centrifugally actuated snap acting switch, a snap spring system having an element stressed in compression and an element stressed in tension, said elements being operably associated with one another for movement through an unstable position of maximum stress between limiting positions of lower stress defined by stops, one of said stops comprising a contact engageable with a contact carried by one of said elements, rotatable means for mounting said snap spring system and said stops and for applying centrifugal force to said spring system to move it through said position of maximum stress to cause said carried contact to be moved between stops by snap action, and adjustable mounting means for said system adjustable to vary the angularity of said spring system with respect to said axis of rotation whereby the effect of centrifugal force on said system can be preselected to move said snap spring system at a preselected rotational speed of said rotatable means.

4. In a centrifugally actuated snap acting switch, a snap spring system having a compression element and a tension element mounted upon a rotatable member, said spring system being movable through a position of maximum stress between normal and abnormal limiting positions of lesser stress defined by stops, at least one of said stops comprising a contact engageable with a movable contact carried by said spring system, said spring system being movable from said normal to said abnormal position in a snap action manner by centrifugal force upon rotation of said rotatable member above one certain speed and movable from said abnormal to said normal position in a snap action manner by stored energy therein when the rotation of said rotatable member drops below a second certain speed, one of said stops being movable to preselect said one certain speed, and the other of said stops being movable to preselect said second certain speed.

5. In a centrifugally actuated mechanism, a rotatable member rotatable about an axis in combination with a snap spring system mounted on said rotatable member to be spaced from the axis of rotation and having an axis of unstable equilibrium, said snap spring system having a portion movable generally outwardly from the axis of rotation between preselected positions by snap action and a second portion movable generally outwardly from said axis of rotation through said axis of unstable equilibrium to 11 preselected value, and means for adjusting one of the radial positions of said actuated portion.

16. In a centrifugally actuated snap acting mechanism, a snap spring system arranged to be mounted on a rotatable member, said spring system having an actuated portion movable radially by snap action between preselected positions to actuate the spring system and an actuating portion movable radially between preselected positions, said actuating portion shaped and positioned to be moved between its preselected positions when the speed of rotation of said member attains a preselected value, and means for adjusting one of the positions of said actuated portion for adjusting the preselected value of speed at which the spring system is actuated.

17. In a centrifugally actuated mechanism, a rotatable member, spaced stops mounted on said member at different distances from the axis of rotation of said member, at least one of said stops being adjustable radially, a, sprin system mounted on said rotatable member spaced from the axis of rotation thereof, said spring system having a tension portion having an end rigid with said rotatable member and having an opposite end in spaced relation to said rigid end and a compression portion having an end interconnected with said opposite end of the tension portion and forming therewith an end free to move radially between said stops with a snap action, and means for mounting the opposite end of the compression portion, said tension and compression portions forming a snap spring system having an axis of unstable equilibrium,

one of said portions shaped and positioned to be moved through said axis of unstable equilibrium when the speed of rotation of said rotatable member exceeds a preselected speed to move said free end radially between said stops with a snap action.

18. In the combination with claim 17, means for adjusting the initial radial position of said one portion to preselect the speed of rotation at which said portion moves through the axis of unstable equilibrium to actuate the spring system.

19. In a centrifugally actuated mechanism, a member rotatable about a fixed axis of rotation, a snap spring system spaced from the axis of rotation of said member having a first portion movable radially between preselected positions by a snap action and a second portion movable radially to actuate said snap spring system when the centrifugal forces acting on said second portion exceeds a preselected value, bracket means mounted on said member, and means acting between said bracket means and said spring system for mounting said spring system and adjustable to permit variations in the angular position of the snap spring system with respect to the axis of rotation.

20. In a centrifugally actuated mechanism, the combination of a support rotatable about an axis, a snap spring system mounted on an axial face of said support at a distance from said axis and having an axis of unstable equilibrium, said snap spring system having a portion movable :between preselected positions by a snap action and a second portion movable away from said axis of rotation through said axis of unstable equilibrium to actuate said snap spring system when the centrifugal force acting on said second portion exceeds a preselected value and stops on said axial face of the support and defining said opposed positions, one of said stops being adjustable to preselect the speed at which the centrifugal force moves the second portion through said axis of unstable equilibrium.

WARNER A. JOHNSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,682,424 Schiesser Aug. 28, 1928 1,713,148 Schild May 14, 1929 1,722,117 Suter July 23, 1929 2,113,645 Bone Apr. 12, 1938 2,172,673 Eaton Sept. 12, 1939 2,416,973 Wright Mar. 4, 1947

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