US2859294A - Centrifugal switches - Google Patents

Description

NOV. 4, 1958 R'E HALL i- TAL 2,859294 CENTRIFUGAL swITcHEs Filed Deo. 27, 1955 2 sheets-'sheet 1 INVENTORS mcnmonm E. HALL. "Filename-.K Q-.JoNes Nov. 4, 1958 Filed Dec. 27, 1955 R. E. HALL ETAL CENTRIFUGAL SWITCHES 2 shams-snee*b INVENTORS mcHMoNn E .HALL Finanzamt: R. JONES www United States Patent O CENTRIFUGAL SWITCHES Richard Ernest Hall, Ilford, and Frederick Raymond Jones, Loughton, England, assignors to The Plessey Company Limited, Ilford, England, a British company Application December 27, 1955, Serial No. 555,729

Claims priority, application Great Britain December 29, 1954 6 Claims. (Cl. -200-80) This invention relates to centrifugal switches of the kind used for the automatic starting of induction motors.

In known constructions it is usual for the centrifugal force to operate on a movable member restrained by springs, so that, when the desired speed is reached, this force overcomes the spring tension causing the member to fly outwards to actuate the phase splitting contacts. The energy used to operate these contacts is obtained directly from the centrifugal force available, and for this reason, i. e. because of the fundamental limitations in the amount of this force, the size of contact and the pressure applied has been strictly limited.

The present invention has for an object to provide a centrifugal switch device utilising for the switch operation a force not produced by centrifugal action.

According to the invention the movement under centrifugal action of an actuating element mounted on a rotary body is utilised for producing engagement of said element with a switch operating element mounted in a stationary member so as to operate the switch by utilis ing the momentum of the rotary body.

In one embodiment of this invention, the switch assembly is mounted upon a suitable backing plate. Said switch assembly consists of a knife switch, in which the xed contact is attached to the backing plate and the movable contact is carried by a rocking member pivoted to the backing plate, said member being operatively connected to the backing plate through a toggle spring which imparts a snap-action to the member on passing the dead point. The rocking member is formed with a raised surface and has a rectangular shaped aperture for the purpose hereinafter set forth.

A rotary shaft passing through an enlarged aperture in the backing plate and through the aperture in the rocking member, has keyed thereto a centrifugal ball device consisting of a housing with a radially projecting striker. Said housing moves axially by the centrifugal action of the ball device as hereinafter set forth.

In operation, assuming the device is fitted to an electric motor, the switch contacts are normally closed; starting up the motor the rotor speed increases and the balls are flung outwards, causing the housing to slide along the rotor shaft until the striker hits the face of the aperture in the rocking member throwing it to the opposite side, thus opening the contacts to break the circuit. The movement of the rocking member to open the contacts is limited by a stop on the backing plate. The striker is then free to rotate in the aperture in said member until the motor speed drops when the ball housing will move along the rotor shaft in a reverse direction, thereby striking the opposite inner face of the rectangular aperture in the rocking member closing the contacts.

In order that the invention may be more readily understood, two other embodiments will now be described in more detail with reference to the accompanying drawings.

Figures l and 2 are respectively a perspective and an exploded perspective of one embodiment, while 2,859,294` Patented Nov. 4, 1958 Figures 3 and 4 similarly illustrate another embodiment.

Referring now first to Figures 1 and 2, and assuming the device to be mounted in a single-phase A. C. induction motor to control an auxiliary-phase starting circuit, the slots in the sleeve provide the necessary degree of resilience for an interference fit on the shaft. Pivotted on this sleeve on pivot screws 3 is a bell-crank member 4, carrying a hard steel striker 5, and a weight 6 which also acts as a tie between extremities of the bell-crank. The weighted end of the bell crank is normally held inwards (towards the rotor shaft centre) by a pair of tension springs 7 which hook over the anchorages on 2 and 4. Under the action of centrifugal force, the weight moves outwards against the spring tension, thus moving the striker 5 in an axial direction. The geometry of the bell crank, spring and weight combination Ais such that once the bell crank movement is initiated, a rapid action results i. e. the increase of the centrifugal action as a function of the angular movement of the bell crank is greater than the corresponding increase of the spring action.

Pivotted by a screw 13 on a fixed back plate 8 secured on a carrier plate 9 is a rocking plate 10 -carrying hard steel striking plates 11, 12. These plates are axially spaced, so that as the moving striker 5 moves axially, it engages with one or other of the striking plates, and in moving these radially out o'f its path, also moves the whole rocking plate assembly about its pivot screw 13.

The rocking plate carries an insulating push rod 14 which co-operates with a contact spring 15 carried on the fixed back plate 8 for `co-operation with a fixed contact member 16. Between the plate 8 and the `rocking plate 10 is an over-centre spring member 17 which holds the mechanism either in the contact made or contact broken position. A locking screw 18 engaging a bore 19 in the plate 8 and passing through a slot 20 of plate 10 can be used to lock the device when required in either the contact made or the contact broken position.

The operation of this device is as follows:

When the rotor is stationary, the weight will be retracted towards the rotor shaft by the springs 7; consequently the striker 5 will be in a position such that its rotational orbit lies immediately under striking plate 11. The rocking plate 10 will be in an upward position and the contact springs in the contact made position.

When the rotor reaches a predetermined'speed, the weight 6 will overcome the pull of springs 7 and move outward, carrying with it the bell crank assembly and revolving striker 5, whose rotational orbit now lies in the same plane as striking plate 12. The revolving striker therefore engages with the inner face of this striking plate, which is thus moved outwards carrying with it the whole rocking-plate assembly and insulating push rod 14. The push rod is moved away from contact spring 15 which breaks contact with the fixed spring 16, the assembly then being held in the contact broken position by the overcentre spring 17.

When the motor has been switched off and the rotor speed falls, decreasing centrifugal force allows the springs 7 to retract the weight 6 towards the centre of the rotor shaft, and moves the bell crank assembly with its revolving striker 5 to a plane in line with and engage striking plate 11, thereby moving the rocking plate 10 back to the contact made position, where it is held by spring 17 until the next starting sequence.

In the embodiment of Figures 3 and 4 the rotor shaft is fitted with a pair of half-rings or adapters 21 which, when clamped to the shaft by clamp plates 22, 23 and screws 24, form a housing for a pair of 'trip levers or strikers 25, 26, each pivoted on a pin 27.

These strikers are unbalanced about their pivot pins,

. t v 3 and areY formed with blunt projections 25a, 25b, or 26a, 2tb` at each end in such manner that when one projection 25a or 26a moves outward under centrifugal force, the projection 25b or 2.611 at the opposite end of each striker s' retracted inwards, towards the axis 'of the rotor. The strikers are arranged so that, viewed in an axial direction, the heavy ends of the strikers extend in the same direction.

y The geometry of the strikers is such that when one of the extended tips comes into contact with a stationary iat surface (viz: a rocking plate mentioned later), the resulting friction tends to force the striker into the position ofmaximum extension, by over-centre action. The force exerted outwards by the striker is not, therefore, the centrifugal force due to the heavy end of the striker, but is the combined centrifugal force and wedging action due to the over-centre action, and is limited only by the 'stored energy in the rotor and/ or the shear strength of the pivot pins etc. y Fixed t-o the end frame of the motor is a stationary back plate pressing 28 with extensions forming pivoting points for a rocking plate 29 and pivot screws 39. When completely assembled, the rocking plate is arranged to be approximately central in all respects with the striker assembly.

The stationary pressing also forms a platform 31 for attaching a contact spring assembly including a movable contact spring 32 and a stationary contact spring 33. The spring 32 is formed with a corrugation 34, so that in addition to acting as a contact spring, it exerts pressure in an upward direction upon a slotted insulating strip 35 attached to the rocking plate 29 below the pivot centres 36 of the plate 29.

The complete assembly thus forms an over-centre switch, which when moved in one direction slightly more than half its total travel will be moved to the full limit of travel, by the energy stored in the contact spring. Electrical Contact between the two contact springs 32, 33 is thus made or broken by the action of the rocking plate 29.

When the rocking plate is in position over the striker assembly on the rotor shaft, and the rotor is stationary, the rocking plate and switch are in the contact made position. The heavy ends of the strikers are in the retracted position, under the action of springs 38, 39. When the r-otor reaches a predetermined speed, the heavy ends 25a, 26a of the strikers move outwards until one or both of them strike the appropriate flat surface 37 of the rocking plate. One or the other of the strikers, depending on the direction of rotation, will lock over to its fully eX- tended position and move the rocking plate 29 about its pivot pins 30 to the contact broken position. The rocking plate is automatically retained in this position, clear of the revolving strikers, by the over-centre action of the switch spring 32 and remains so whilst the motor is running.

- When the motor has been switched olf and the rotor speed falls, the centrifugal force on the heavy ends 25a, 26a of the strikers gradually decreases, until' this force is overcome by that of retracting springs 38, 39. The heavy ends will then retract and the opposite (light) ends 25b, 2Gb of the strikers extend. When sufficiently extended, these ends contact flat surface 40 of the rocking plate 29. The appropriate striker tip 25b or 26b is forced out in the same manner as for the starting sequence and moves the rocking plate back to its -original contact made position, where it is again held by the over-centre action of the switch spring ready for the starting sequence.

' Due to the provision of two strikers each with an extending and a retracting lobe, the assembly is suitable for a motor of either direction of rotation, or for a reversible motor.

. It should be understood that the embodiments described may be modied in various details without exceeding the scope of the invention. Thus the over-centre action upon thefrocker. member 37, 40 may be provided by a spring 4 v separate from the contact spring 32, thus relieving the latter.

While the switch according to the invention is particularly suited for controlling the starting and phase splitting of induction motors, it could be readily adapted for use as a speed controller on any rotating apparatus requiring speed control or governing by making and breaking an electrical circuit.

What is claimed is:

l. A centrifugal switch device comprising a rotary body, a stationary body relative to which the rotary body can rotate, a switch operating element movably mounted on said stationary body for limited to and fro movement transversely of the peripheral direction of rotation of the rotary body, two switch actuating elements, one for each direction of rotation of the rotary body, mounted for limited pivotal movement on said rotary body under centrifugal force from a position clear of the switch operating element to a position of engagement and respective wedge co-operation with said switch operating element, to move said switch operating element transversely of the peripheral direction of the rotary body, and two reverse switch actuating elements mounted on said rotary member and adapted for action, similar to the said action of the switch actuating elements, when the centrifugal action is a predetermined amount below that at which the said switch actuating element becomes operative.

2. A centrifugal switch device comprising a rotary body, a stationary body relative to which the rotary body can rotate, a switch operating element movably mounted on said stationary body for limited to and fro movement transversely of the peripheral direction of rotation of the rotary body, two switch actuating elements, one for each direction of rotation of the rotary body, mounted for limited pivotal movement on said rotary body under centrifugal force from a position clear of the switch operating element to a position of engagement and respective wedgeV co-operation with said switch operating element, to move said switch operating elements transversely of the peripheral direction of the rotary body, two reverse switch actuating elements mounted on said rotary member and adapted for action, similar to the said action of the switch actuating elements, when the centrifugal action is a predetermined amount, -below that at which the said switch actuating element becomes operative, and an over-centre spring device for biasing the switch operating element and which is so arranged that when it is actuated by either the switch actuating element or the reverse actuating element it will move onto and stay in a position clear of the respective element.

3. A centrifugal switch device comprising a rotary body, a stationary body relative to which the rotary body can rotate, a switch operatingV element movably mounted on said stationary body for limited to and fro movement transversely of the peripheral direction of rotation of the rotary body, two switch actuating elements one for each direction of rotation of the rotary body, mounted for limited pivotal movement on said rotary body under centrifugal force from a position clear of the switch operating element to a position of engagement and respective wedge co-operation with said switch operating element, to move said switch operating elements transversely of the peripheral direction of the rotary body and two reverse switch actuating elements mounted on said rotary member and adapted for action, similar to the said action of the switch actuating elements, when the centrifugal action is a predetermined amount below that at which the said switch actuating element becomes operative, said switch actuating elements and said reverse actuating elements each comprising a lever pivoted on the rotatable body to pivot about a first axis which is parallel to the axis of rotation of the rotatable body, said levers being rigidly connected with each other for joint movement'about a common 5 4. A centrifugal switch device comprising a rotary body, a stationary body relative to which the rotary body can rotate, a switch operating element movably mounted on the stationary body for limited to and fro movement transversely of the peripheral direction of rotation of the rotary body, two switch actuating elements mounted on said rotary body for limited pivotal movement under the action of centrifugal force from a position clear of the switch operating elements to a position of engagement with said switch operating element, the switch operating element having an engagement surface directed substantially parallel to the direction in which the switch actuating elements are moved by said centrifugal force, and being movable away from switch actuating elements in a direction substantially perpendicular to said engagement surface, the direction in which each of the switch actuating elements is guided in the rotary body forming with said engagement surface an angle having a tangent smaller than the coeflcient of friction between said surface and the switch actuating elements.

5. A centrifugal switch device comprising a rotary body, a stationary body relative to which the rotary body can rotate, a switch operating element movably mounted on the stationary body for limited movement transversely of the peripheral direction of rotation of the rotary body, two switch actuating elements mounted on said rotary body for limited pivotal movement under the action of centrifugal force from a position clear of the switch operating elements to a position of engagement with said switch operating elements, the switch operating element having an engagement surface substantially parallel to the direction in which the switch actuating elements are moved by said centrifugal force, and being movable away from the rotary elements in a direcn tion substantially perpendicular to said engagement surface, the directionin which each of the switch actuating elements is guided on the rotary body forming with said engagement surface an angle so small that any initial contact between a switch actuating element and the engagement surface will, due to frictional drag, produce a critical pressure on the engagement surface to cause the switch operating element to execute a switching movement.

6. In a centrifugal switch device, the combination comprising a rotatable body for attachment to a rotatable shaft, a combined forward switch actuating and reverse switch actuating element mounted for pivotal movement in said rotatable member about a first axis parallel to the rotation axis of said rotatable shaft, the combined actuating element comprising two axially spaced levers projecting from the first axis in different radial directions, resilient means for biasing said combined actuating member to a position in which one of sai'd levers projects outwardly of the rotatable body while the other lever projects inwardly, and a centrifugal mass so connected with said two levers as to urge the said combined forward and reverse switch actuating element, when the centrifugal force exceeds a predetermined amount, to a position in which the last mentioned lever projects outwardly and the iirst mentioned lever projects inwardly.

References Cited in the tile of this patent UNITED STATES PATENTS 2,377,830 Von Reppert June 5, 1945 2,483,122 Bower Sept. 27, 1949 2,487,555 Janecky et al. Nov. 8, 1949 2,519,140 Kleiman Aug. 15, 1950 FOREIGN PATENTS 733,564 Great Britain July 13, 1955 733,565 Great Britain July 13, 1955

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