US2877323A - Stationary centrifugal switch - Google Patents

Description

March 10, 1959 A. NAHER 2,817,323

STATIONARY CENTRIFUGAL SWITCH Filed March 31,1954

INVENTOR- United States Patent 2,877,323 STATIONARY CENTRIFUGAL SWITCH Arthur Naher, Dunmore, Pa. Application March 31, 1954, Serial No. 419,992 2 Claims. (Cl. 200-159) This invention relates to a new and improved stationary centrifugal switch for use in motors which require a control switching operation to take place in response to the attainment of a specified motor speed.

The centrifugal switch of this invention is particularly designed for use in split-phase and condenser-start singlephase motors. Because the application of a single-phase alternating current to a single stator winding cannot produce a rotating field necessary for developing a starting torque, motors of the above type are provided with an auxiliary or starting winding. This starting winding generates a field out of phase with the stator field, so that the resultant field can produce a starting torque. Once the motor is started, however, the rotor will set up a pulsating field which lags the stator field and which can therefore sustain rotation. When the motor has reached a specified percentage of the ultimate synchronous speed, the energizing circuit for the starting winding is opened by a device such as a centrifugal switch.

Switches which have heretofore performed this function invariably have been located within the motor frame in order to simplify the structure needed. This arrangement was in part unsatisfactory because the easy accumulation of oil, grease and dust upon the switch contacts caused by circulating air currents within the motor frame rendered the contact operation unreliable. Furthermore, the inspection, cleaning, or removal of the contact unit was relatively diflicult and time consuming because the motor housing had to be disassembled in order to have access to any part of the switch.

Accordingly, a principal object of this invention is to provide a centrifugal switch capable of economical manufacture and having a contact unit which can be readily inspected, cleaned or replaced without dismantling the motor, and which is reliable in its contact operation.

The novel centrifugal switch herein features an enclosed switch contact unit which is mounted on the outside of the motor frame. The appropriate making and breaking of the contacts is accomplished by actuating a spring-loaded push rod which extends through the motor frame. When the motor has attained a speed at which the starting winding need no longer be energized, a governor releases a pivotally mounted governor plate having a first end portion which collars the motor rotor shaft. With this operation, the second or opposite end portion of the governor plate forcibly drives the push rod thereby opening the external contacts. This arrangement also provides positive closure of the contacts during the starting period because end play or thrust in the rotor cannot release the governor plate into contact with the push rod. A spring bias applied to the stationary governor plate permits the positive opening of the contacts when the motor attains the specified speed.

A preferred embodiment of the contact unit includes a push-rod actuated contact section which is manually inserted and removed from a female socket section mounted upon the motor frame. The contact actuating push-rod passes through an opening located at the bottom of the socket. Inasmuch as the contact unit is external to the motor frame and therefore readily accessible, the inspection, cleaning and replacement of this unit can be readily accomplished without dismantling the motor frame. Improved contact reliability is also provided by the isolation of the switch contacts from the dirt, oil and grease carried by the circulating air currents within the motor frame.

In order that all of the features and objects'of this invention may be readily understood, reference is herein made to the accompanying drawings wherein:

Figure 1 is a schematic circuit diagram of the energizing circuits for the stator and starting windings of a single-phase motor employing a centrifugal switch;

Figure 2 is a view of a motor incorporating the centrifugal switch of this invention, with a portion of the motor housing and socket section broken away so as to show the position of the switch components prior to the opening of the switch contacts;

Figure 3 shows the structure of Figure 2 with the switch contacts open;

Figure 4 is a section view of the stationary governor plate taken along line 44; and

Figure 5 is an exploded view of the switch contact and socket sections.

In the schematic circuit diagram of Figure 1, stator winding 12 is connected directly to line terminals 10 and 11. Stator winding 12 is properly energized when a single-phase, alternating-current, energizing potential is applied to line terminals 10 and 11. Auxiliary or starting winding 13 is connected to terminals 10 and 11 through a normally closed, centrifugal switch comprising switch contacts 14 and 15 which are electrically connected to one another by contact plate 16. Starting winding 13 is de-energized by operating push rod 17 so as to compress push-rod spring 18 against the body of contact section 19 thereby raising contact plate 16 and opening the connection between switch contacts 14 and 15.

In the application of a centrifugal switch to the usual I motor installation, the switch contacts are normally closed thereby completing the energizing circuit for the starting winding so as to produce a starting torque until the motor has attained a specified percentage of the ultimate rotor speed. At this speed, the centrifugal switch is opened by a mechanism actuated by centrifugal force so as to remove the starting winding from the circuit. In the novel centrifugal switch structure of this invention pushrod 17 extends through motor frame 20 so that the contact unit for the centrifugal switch can be located outside of the motor frame while the actuating mechanism is positioned within the motor frame.

Figure 2 shows the application of a centrifugal switch to a motor having a rotor 36. Components corresponding in function and operation to those previously described with reference to Figure 1 are identified by the same numerals. It will be noted that a socket 22 for receiving the switch contact unit is mounted upon motor frame 20 so that the switch contact unit is located on the outside of the motor. The details of the switch contact unit and socket are best shown in Figure 5. The contact section comprises a body 19 having two switch contact pins 14 and 15 extending therethrough. The portion of these pins projecting from the left surface of body 19 are normally electrically connected to one another by contact plate 16. When the Contact section is inserted within socket 22, the portion of contact pins 14 and 15 projecting from the right surface of body 19 contact socket pins 23 and 24, respectively. Pin springs 25 and 26 firmly contact socket pins 23 and 24 to contact pins 14 and 15. The left portion of the push-rod 17 is rigidly attached to the center portion of contact plate 16, and the right portion of push-rod 17 extends through a circular antenna 3 opening in the bottom of socket 22 so as to project into the motor interior. As is shown in Figure 5, guide pm 28 positioned in body 19 mates with a set of socket guide slots 27 so that the contact section can be mechanically locked to the socket section.

As is best shown in Figure 4, stationary governor plate 30 is formed with a collar hole 35 sufliciently large so that rotor shaft 36 can pass therethrough without contacting governor plate 35. As is shown in Figure 2, the lower end portion of governor plate 38 is spaced slightly from the right end portion of push-rod 17 when the motor is stopped or rotating at a speed less than the specified speed for which the centrifugal switch is to operate. Bracket 32 which is welded to one surface of stationary governor plate 30 is pivotally coupled to bracket 33 by pin 34. Bracket 33 is welded to the interior of motor housing 20.

The application of a spring force by U-spring 31 tends to pivot the upper portion of governor plate to the right and the lower portion of governor plate 30 to the left. Contact between governor plate 30 and the right portion of push-rod 17 during all times wherein the motor is stopped or rotating at a speed less than the speed at Which the centrifugal switch is to operate is prevented by the application of a force to the governor plate collar by governor spool 37, which overcomes the closing force exerted by U-spring 31.

With the application of an energizing current to line terminals and 11, stator winding 12 and starting winding 13 are energized with consequent rotation of rotor 36. The centrifugal force exerted upon arms 38 of the governor at the specified rotor speed, cause the arms to snap outwardly in opposition to the force exerted by spring 39, thereby withdrawing spool 37 to the right and causing the governor plate to contact the right hand portion of push-rod 17. The application of this force to push-rod 17 compresses push-rod spring 18 and removes contact plate 16 from contact pins 14 and so that the energizing circuit for the starting Winding is opened.

It is to be understood that the above-described structural arrangement is illustrative of the principles of this invention. Numerous other arrangements may be devised by those skilled in the art to which this invention pertains without departing from the scope of the invention.

Having thus described the invention, what is claimed as new and desired to be secured by Letters-Patent is:

1. An electrical switch unit comprising a housing defining a cylindrical socket closed at one end, relatively spaced socket pins axially disposed through the said closed end of said socket, a cylindrical body removably coaxially disposed in said socket and having axially extending switch contact pins fixed therethrough in endwise abutting engagement with the respective socket pins, a push rod slidable axially through said body and having an actuating end slidably disposed through said closed end of the socket, a contact plate carried by said push rod adjacent the end of said body remote from the closed end of said socket, and in axial registry with both said contact pins, and spring means normally urging said push rod in an axial direction to cause engagement between said contact plate and said contact pins, whereby axial pressure on said actuating end of the push rod will open the switch.

2. The combination of claim 1 wherein said body includes radially projecting guide pins, said socket being formed with circumferential guide slots for reception of said pins, said socket pins being axially slidably disposed through said closed end of the socket, and spring means coacting between said socket pins and said closed end for maintaining said socket pins in engagement with the respective contact pins and for exerting a thrusting force against said body to maintain its said guide pins in frictional engagement with the edges of said guide slots.

References Cited in the file of this patent UNITED STATES PATENTS 1,368,617 Everett Feb. 15, 1921 1,586,506 Berg May 25, 1926 1,790,330 Smith Ian. 27, 1931 1,873,484 Rosine Aug. 23, 1932 1,928,691 Huddleson Oct. 3, 1933 2,057,525 Horning Oct. 13, 1936 2,083,411 Swanson June 8, 1937 2,346,341 Werner Apr. 11, 1944 2,394,283 Yost Feb. 5, 1946 2,452,807 Thompson Nov. 2, 1948 FOREIGN PATENTS 483,019 Great Britain Apr. 11, 1938 891,286 Germany Mar. 15, 1954

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