Centrifugal switch

A centrifugal switch for effecting an activation or deactivation of an electrical circuit at a predetermined rotational speed of a shaft. The switch comprises magnetic means mounted for rotation about an axis and for sliding movement under the influence of centrifugal force from a starting position adjacent the axis to an operating position radially outwardly therefrom, spring means urging the magnetic means toward the starting position, and electrical switch means operatively responsive to the movement of the magnetic means at a predetermined rotational speed so as to either activate or deactivate an associated electrical circuit.

BACKGROUND OF THE INVENTION 
This invention relates to a centrifugal switch for effecting either an 
activation or deactivation of an electrical circuit. The centrifugal 
switch can be mounted on any suitable shaft for effecting the activation 
or deactivation of an electrical circuit such as for any speed responsive 
or speed sensitive control. Examples of such controls may include 
electrical motor starting circuits, fan switches for heating and air 
conditioning installations, and machine tool clutch circuits. The magnet 
controlled centrifugal switch of this invention is particularly useful in 
combination with a split-phase electrical motor so as to deactivate a 
starting winding thereof at a predetermined rotational speed, and will be 
described hereinafter with particular reference to that environment. 
Heretofore, it has been the practice for centrifugal switches to utilize a 
fly weight type governor in combination with a spring type switch which is 
secured to a housing. To control the opening and closing of an electrical 
circuit at a desired shaft speed, washers or shims were used to fix the 
distal relationship of the switch to the housing. It was previously 
necessary to initially obtain a precise distal relationship between the 
switch and the housing for prior art centrifugal switches to properly 
function at desired shaft speeds. Also, when an electrical motor 
incorporating such a switch was rebuilt, it was necessary to reestablish 
the precise positioning of the switch and governor on the motor shaft or 
the switch would either function improperly or cease to function at all. 
Aslo, due to susceptibility to dirt and grime, it has been the practice to 
position previous centrifugal switches within the housing of the electric 
motor for protection. Furthermore, as the switches were not 
interchangeable from one type of motor to another, it has been necessary 
to stock a variety of different switches for use with the associated 
variety of different electric motors. 
Magnetically-operated centrifugal switches utilizing an attraction between 
opposite poles of two opposing and adjacent magnets for maintaining a 
circuit and relying upon centrifugal force to separate the magnets and 
consequently deactivate a circuit have also heretofore been known and 
used, but this type of switchh can develop an accumulation of dirt or 
grime on the faces of the opposing magnetic poles over time which will 
detrimentally affect the performance of the switch. The 
magnetically-operated centrifugal switch known heretofore has a tendency 
due to the aforesaid accumulation of dirt and grime to activate or 
deactivate an associated circuit prematurely since the centrifugal force 
will then more readily act to separate the opposed magnets thereof. 
The centrifugal switch of the present invention overcomes the problems 
associated with the prior art switches. Dirt or grime on the faces of the 
adjacent and opposing magnets has no significant effect on the performance 
of the centrifugal switch thereby allowing for location either within the 
electric motor housing or even on the shaft external to said housing. 
Furthermore, the inventive switch is of a standardized construction so as 
to fit substantially all electric motors of the same shaft diameter. 
OBJECTS OF THE INVENTION 
In light of the above, an object of the invention is to provide a simple 
and reliable centrifugal switch which at a predetermined rotational speed 
will effect an opening or closing of an associated circuit. 
It is another object of the invention to provide a simple and reliable 
centrifugal switch which can be used in combination with an electric motor 
to effect an opening or closing of an associated circuit, such as opening 
a starting winding circuit, at a predetermined rotational speed of the 
motor. 
It is yet another object of the invention to provide a simple and reliable 
centrifugal switch of standardized construction so as to be capable of 
utilization with a substantial majority of electric motors. 
It is a further object of the invention to provide a simple and reliable 
centrifugal switch which can be mounted on the electric motor shaft either 
outside or inside of any motor housing. 
It is a still further object of the invention to provide a switch assembly 
in which the magnetic elements for operating the switch and the 
functionally related electrical contacts are in a predetermined 
relationship to one another so that the entire switch assembly can be 
utilized in combination with a variety of motors and either within or 
outside of the housing thereof.

DESCRIPTION OF THE INVENTION 
The centrifugal switch of this invention comprises magnetic means for 
exerting a magnetic field and means mounting said magnetic means for 
rotation about an axis and for sliding movement under the influence of 
centrifugal force from a starting position adjacent the axis to an 
operating position radially outwardly therefrom. Spring means are provided 
for exerting on the magnetic means a force biasing the magnetic means 
toward the starting position and for maintaining the magnetic means at the 
starting position adjacent the axis while stationary. The biasing force of 
the spring means is overcome by the influence of centrifugal force during 
rotation so as to permit the magnetic means to move to the operating 
position. The centrifugal switch has electrical switch means operatively 
responsive to movement of the magnetic means from the starting position to 
the operating position, in the form of a pair of contacts movable to 
closed or open circuit positions and a ferro-magnetic means movable 
axially of the axis of rotation of the magnetic means and cooperating with 
the contacts for maintaining them in one of the closed or open circuit 
positions when the ferro-magnetic means is within the effective influence 
of the magnetic means while in the starting position. The contacts are 
maintained in the other of the closed or open circuit positions when the 
ferro-magnetic means is outside of the effective influence of the magnetic 
means while the magnetic means is positioned in the operating position. 
Referring now more specifically to the drawings, a preferred embodiment of 
a centrifugal switch according to the present invention is shown in FIGS. 
1 through 6 as arranged for use with an electrical motor having a housing 
21 and motor shaft 22 supported for rotation about its axis by bearings 
23. The switch comprises magnetic means, shown in the form of a pair of 
magnets 24 positioned on opposite sides of shaft 22 with their like poles 
adjacent and opposing each other so as to create a repelling force 
therebetween. Means mounting the magnetic means, shown in part in the form 
of an annular, non-magnetic mounting disc 25 having a recessed portion 
providing a channel 27 for receiving portions of the magnets 24 therein 
supports the magnets 24 and provides a guide for predetermined radial 
sliding movement of magnets 24 between the starting position and the 
operating position when acted upon by centrifugal force due to the 
rotation of the mounting disc 25. The mounting means is further shown in 
the form of a rotatably mounted, non-magnetic sleeve member 26 secured to 
shaft 22 which is encircled by magnets 24 and has the annular, 
non-magnetic mounting disc 25 secured thereto so that when shaft 22 
rotates both sleeve 26 and mounting disc 25 rotate therewith. 
Spring means, shown in the form of a pair of springs 28 are affixed to 
magnets 24 so as to urge each of magnets 24 toward the sleeve 26 at which 
the like poles of magnets 24 will be substantially adjacent each other. As 
best illustrated in FIGS. 5 and 6, each of the two spaced apart springs 28 
are positioned on opposite sides of the axis of shaft 22 urging the 
magnets 24 toward each other with one end of each spring 28 connected to 
one of the pair of magnets 24 and the other end of each spring connected 
to the other of the pair of magnets. 
A support member 29 loosely encircles sleeve member 26 and abuts a shoulder 
thereof by any conventional means, not shown, and has spring arm 30 
secured at one end thereto and biased in a direction remote from magnets 
24 and axially of the axis of rotation thereof. As best illustrated in 
FIGS. 2 and 3, the support member 29 is abutted on one side by the 
shoulder of sleeve 26 and by a retaining means 33 which may take the form 
of a snap ring adapted to be positioned in a suitable groove 37 in the 
periphery of sleeve 26. A bracing member 31 is affixed to support member 
29 to maintain the member in a stationary position while shaft 22 rotates 
therethrough. 
The centrifugal switch has electrical switch means in the form of a pair of 
contacts and a ferro-magnetic means. Ferro-magnetic means, shown in the 
form of a disc 32, normally attracted to magnets 24, encircles mounting 
sleeve 26 and is affixed to the other end of spring arm 30 by bridging 
member 32a which extends from the end of the spring arm to the 
ferro-magnetic disc 32 by straddling support member 29. The ferro-magnetic 
disc 32, although normally attracted to magnets 24, is biased by the 
spring arm 30 in a direction away from the magnets 24. A non-magnetic disc 
34 encircles sleeve member 26 and is positioned between magnets 24 and the 
ferro-magnetic disc 32 for preventing mechanical contact therebetween. A 
pair of contacts 35 movable from closed to open circuit position and 
normally contacting each other are secured to proximal opposing sides of 
support member 29 and spring arm 30 for effecting an initially closed 
circuit in the starting window of an associated electric motor through a 
pair of wires 36 which are in electrical contact with the starting winding 
of the electric motor. 
To secure bracing member 31 so as to prevent rotation of support member 29 
with shaft 22, a motor housing bolt 38 is utilized. 
Referring now more specifically to FIG. 5, the magnets 24 are there shown 
in their starting position on opposite sides of and substantially adjacent 
sleeve member 26 with springs 28 urgingly engaging magnets 24 and 
overcoming the repelling force of the opposing and adjacent like magnetic 
poles. FIG. 6 illustrates the magnets 24 forced into their operating 
position by the centrifugal force created by rotation of shaft 22 and 
sleeve 26 and mounting disc 25 secured thereto. The centrifugal force 
created by this rotation is sufficient to overcome the urging of pair of 
springs 28 and to force magnets 24 to slide radially outward along the 
path of the guiding channel 27 within mounting disc 25. 
Preferably, sleeve member 26, annular disc 25, disc 34, and support member 
29 are constructed of non-magnetic materials with support member 29 and 
disc 34 constructed of plastic. 
In operation, the centrifugal switch of the present invention operates to 
disconnect the starting winding circuit of an electric motor at a 
predetermined rotational speed, for example eighty percent of the 1,725 
revolutions per minute speed of a typical electric motor. 
When a typical split-phase electric motor is activated, motor shaft 22 
begins rotating and thereby also rotates sleeve member 26 and mounting 
disc 25 affixed to the shaft. At a predetermined speed the centrifugal 
force on magnets 24 overcomes the urging of the pair of springs 28 and 
allows magnets 24 to slide radially outward within the guiding channel 27 
of mounting disc 25 from a starting position radially adjacent sleeve 26 
(FIG. 5) to an operating position radially remote therefrom (FIG. 6). When 
the magnets 24 are in the operating position, the ferro-magnetic disc 32 
which is normally attracted to magnets 24 is urged in a direction remote 
therefrom along the axis of rotation of shaft 22 by spring arm 30 which 
overcomes the relatively diminished magnetic influence on ferro-magnetic 
disc 32. As magnets 24 and the associated ferro-magnetic disc 32 move from 
the starting position, illustrated in FIGS. 5 and 3, respectively, to the 
operating position illustrated in FIGS. 6 and 4, respectively, electrical 
contacts 35 are separated by the associated movement of the bridge member 
32a and the connected spring arm 30 which disconnects the starting winding 
circuit of the associated electrical motor. When the starting winding of 
the electric motor is disconnected after the motor has substantially 
achieved operating rotational speed, the motor thereafter continues to 
operate on its main winding. 
In order to accommodate electric motors of varying shaft sizes, it is 
foreseen that the inventive centrifugal switch could be constructed with 
sleeve members 26 accommodating typical standard motor shaft sizes, for 
example 3/8", 1/2", 5/8", 3/4", 1" and greater. Also, to accommodate the 
functioning of the centrifugal switch over a range of predetermined 
percentages of the normal rotational speed of electrical motors, magnets 
24 can be constructed of varying weights and the springs 28 can be 
constructed with varying tension. For example, by varying the weight of 
magnets 24 and tension of springs 28 the centrifugal switch can be 
constructed so as to activate at ninety percent of normal rotational speed 
of the motor as opposed to eighty percent. 
It will be thus seen that there is provided, as described herebefore, a 
simple and reliable centrifugal switch which at a predetermined rotational 
speed will effect an opening or closing of an associated circuit. More 
specifically, a centrifugal switch is provided for disconnecting the 
starting winding of an associated split-phase electric motor at a 
predetermined rotational speed thereof. 
In the drawing and specification, there has been set forth a preferred 
embodiment of the invention, and although specific terms are employed, 
they are used in a generic and descriptive sense only and not for purposes 
of limitation.