US2936352A

US2936352A - Centrifugal switch

Info

Publication number: US2936352A
Application number: US395631A
Authority: US
Inventors: Roger W Patterson
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-12-01
Filing date: 1953-12-01
Publication date: 1960-05-10
Anticipated expiration: 1977-05-10

Description

R. W. PATTERSON CENTRIFUGAL SWITCH Filed Dec. l, 1953 RogerWPale/rson INVENTOR.

Fig

lMay 10, 1960 United States Patent CENTRIFUGAL SWITCH Application December 1, 1953, Serial No. '395,631

2 Claims. (Cl. 200-80) This invention relates to an improved centrifugal switch adapted to control an electrical circuit whenever the speed of rotation of the member to which it is attached reaches a predetermined Value.

Centrifugal switches have been previously known which were intended to attain these same results. However, such switchesjhave been found to be unduly sensitive to acceleration forces and vibration to which the unit may be subjected during its normal course of operation. As a result, the action of such prior art switches is vnot positive and there is found to be a considearble variation in the point at which the switch will be actuated.

It is, therefore, an object of this invention to provide a centrifugal switch which will be actuated at substantially thesame predetermined rate of rotation regardless of the accelerations involved.

A further object is to provide such a switch which will be actuated to make or break the associated electrical circuit quickly and positively regardless of accelerations or vibrations to which it may be subjected at the time when the .predetermined speedof rotation is reached.

A still further object is to provide such a switch which isextremely rugged, of simple construction, and relatively inexpensive to manufacture.

Further objects will become apparent from the following specilication and claims, especially when considered in the light of the accompanying drawing.

Fig. 1 is a perspective view of the centrifugal switch with parts broken away to show the interior construction.

Fig. 2 is an end view of the switch, also with portions broken away to show certain details of the construction.

Fig. 3 is a fragmentary sectional view taken generally in the plane indicated by line 3--3 of Fig. 2.

As best shown in Fig. 1, the `switch includes a shaft 1 having an outwardly extending ilange 2 at the end thereof to which the main switch body 3, of insulating material such as polystyrene, is suitably attached. As shown in Figs. 1 and 2, the body 3 is cylindrical in form and is mounted coaxially with the shaft 1. Suitably secured to the outer periphery of the body 3 lis a cylindrical ring 4 of metal which, as hereinafter described, may conveniently serve as a slip ring for conducting electric current to the switch assembly.

Extending diametrically through the body 3 is a bore 5, one end portion of which is internally threaded, as indicated at 6. A cylindrical guide sleeve 7 is arranged to be screwed into the threaded portion of the bore and is provided at its lower or inner end with an outwardly extending ange 8, the .periphery of which is serrated, as indicated at 9. As will be later described, the radial position of sleeve 7 in bore 5 may be adjusted by screwing it in or out of the bore so as to set the speed at which the switch will be actuated to the desired value. Sleeve 7 is held in its adjusted position by means of a generally L-shaped spring locking member 10, the inner end portion 11 of which extends generally axially inwardly through a suitable slot 12 formed in the body 3 and into engagement with the serrated ange 8 of the sleeve, The

. Patented May 10, j 1960 2 other end of the locking member 10 is secured to the body 3 by means of a bolt 13 which, as shown in Fig. 3, may conveniently extend through the body and into threaded engagement with the ilange 2. Thus, the spring lock and the bolt serve the additional purpose of providing an electrical connection from the switch mechanism to the shaft 1. j

The lower or inner end of the opening through the sleeve 7 is arranged to be closed by a suitable stop member 14 held thereagainst at all times by a compression spring 15. Spring 15 abuts'a-gainst a suitable disk-like member 16 of insulating material, inserted into the lower end of the bore between the spring and the inner periphery of the ring 4.

Slidably guided within sleeve 7 is a metal plunger or weight 17 which is restrained against all but radial movement by means of the bearing surfaces afforded by the inwardly flange 18 on the upper end ofthe sleeve 7 and the outwardly extending ange 19 on the lower end of the plunger 17. A compression spring 20 acting betweenv the

flanges

18 and 19 normally, urges the plunger against the stop 14 and serves to oppose radial outward movement of the plunger 17 under the action of centrifugal force. Plunger 17 is preferably provided at its outer end with a contact button 21 of low resistance contact material.

Ring 4 is provided on its inner periphery with a groove 22 within which is suitably secured a resilient contact member 23 which, as best shown in Fig. 2, extends into position directly opposite, and normally spaced from, the contact button 21 on the plunger 17. Thus when the plunger moves outwardly into engagement with contact member 23, an electrical circuit will be completed from shaft 1, through flange Z, bolt 13, spring lock member 10, sleeve 7, plunger 17, and contact member 23 to the slip ring 4. Suitable brushes (not shown) may be associated with the slipring 4 and the shaft 1 to connect the switch to the external circuit to be controlled.

Spring 20 is so chosen that it will be preloaded when inserted between the flanges Y18 and 19 with the parts in their normal position shown in Fig. l with-the plunger 17 .engaged against the stop 14. Sleeve 7 is so positioned in boreV 5 rthat under normal conditions, the center of gravity of the plunger 17 will be displaced radially outwardly from the axis of the shaft 1 so that, upon rotation of the shaft, the plunger 17 will tend to move radially outwardly by centrifugal action against the action of spring 20. The preloading of spring 20 and the degree of eccentricity of the center of gravity of plunger 17 relative to the axis of the shaft are so related that, until the predetermined desired speed of operation of the switch is reached, radial outward movement of the plunger will be prevented by the spring '20. However, as soon as the predetermined speed is attained, plunger 17 will move radially outwardly and into contact with spring contact member 23 to complete the above-mentioned electrical circuit. The speed of rotation at which the switch will be actuated may be set at the desired point by bodily shifting the sleeve 7 axially of the bore as previously described, thus varying the radial eccentricity of the center j of gravity of the plunger 17 with respect to the axis of the shaft 1.

An important feature of this invention resides in the characteristics of the spring 20. Not only is this spring preloaded, as described above, to prevent movement of the plunger until the desired speed of rotation is attained, but moreover the spring rate of the spring 20 is so related to the mass of the plunger 17 that, upon rotation of the shaft above the predetermined rate, the rate of increase in force exerted by this spring against the plunger due to outward movement thereof will be less than the corresponding rate of increase of the centrifugal force acting thereon as a result of such movement. Thus, the plunger will be held in its normal position until the desired speed is attained and will then suddenly fly radially outwardly into engagement with the spring contact 23. Thus, a snap action will result which will insure a quick and positive closing of the circuit. The spring contact 23 will readily absorb the impact while maintaining the desired positive contact and moreover will follow any slight uctuations in the position of the plunger resulting from vibrations to which the switch unit may be subjected. Similar snap action will be obtained when the speed of rotation again falls below the predetermined speed since, as soon as the plunger begins to move radially inwardly, the centrifugal force will fall off at a more rapid rate than the force exerted by the spring 2t).

Where it is desired that the difference between the speeds of rotation at which the switch will close and open be kept at a minimum, the spring rate should be chosen so that the difference between the force exerted against the plunger by the spring and the centrifugal force increases but slightly as the plunger moves outwardly while still maintaining enough difference to insure the snap action. Obviously, too heavy a spring will entirely prevent the snap action and the plunger would merely move slowly outwardly to a new equilibrium position as the speed increased above the predetermined desired value. On the other hand, too light a spring would give a very strong snap action but would result in an unduly wide difference between the speed at which the switch would close and that at which it would open.

The operation of this switch is believed obvious from the foregoing description. Since all of the movable elements are arranged so that they can move only along a radius, their action will be substantially independent of the rate at which the shaft is accelerating or de-accelerating. Moreover, by adjusting the position of the sleeve, (and as a result, the position of the center of gravity of the plunger) the unit can be accurately adjusted to operate at the desired speed of rotation of the shaft. The novel snap action results in positive opening and closing of the circuit being controlled and, together with the use of the resilient spring contract 23 minimizes any tendency for the contacts to chatter when the unit is subjected to vibration.

hile but one form of the invention has been shown in detail, it is believed obvious that many changes in the specific construction and arrangement of the parts may be made without departing from the principle of operation or the scope of the invention as defined by the appended claims.

l2,936,352 Y r I claim:

l. A centrifugal switch comprising a shaft, a generally cylindrical body member of insulating material rigidly secured to said shaft coaxially therewith, said body being provided with a cylindrical bore extending diametrical- 1y therethrough, a sleeve of conducting material threadedly engaged within said bore, means electrically connecting said sleeve to said shaft, a metal plunger carried within said sleeve with a sliding fit, a stop member slidable within said bore and adapted to abut against the inner end of said sleeve, a ring of conducting material secured to the periphery of said body and covering the opposite ends of said bore, means including a compression spring interposed between said stop member and the inner peripheral wall of said ring for holding said stop against the inner end of said sleeve, a second compression spring surrounding said plunger and acting between said sleeve and said plunger and urging said plunger radially inwardly into a normal position against said stop, said sleeve being so positioned in said bore that when said plunger is in said normal position its center of gravity will be displaced radially from the axis of said body so that upon rotation of said body centrifugal force acting on said plunger will tend to move it radially outwardly from said axis against the action of said second spring, and a resilient contact strap carried by the ring opposite the outer end of said plunger and normally spaced therefrom, said contact being adapted to be directly engaged by said plunger upon a predetermined radial outward movement thereof to complete an electrical circuit from said shaft to said ring.

2. A centrifugal switch as set forth in claim 1 wherein said second spring is preloaded so as to prevent radial movement of said plunger until a predetermined rate of rotation of said body has been reached, said second spring having a spring rate so related to the mass of said plunger that upon rotation of said member above said predetermined rate the rate of increase in force exerted by said second spring against said plunger due to outward movement of said plunger will be less than the corresponding rate of increase of the centrifugal force acting thereon as a result of such movement.

References Cited in the tile of this patent UNITED STATES PATENTS 1,075,987 McMahon Oct. 14, 1913 1,296,138 Taylor Mar. 4, 1919 2,387,788 Wiles Oct. 30, 1945 2,747,854 Schnepf May 29, 1956