US2719193A

US2719193A - Snap acting contactor

Info

Publication number: US2719193A
Application number: US275979A
Authority: US
Inventors: Paul G Frerer
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1948-06-15
Filing date: 1952-03-11
Publication date: 1955-09-27
Anticipated expiration: 1972-09-27

Description

Sept. 27, 1955 P. G. FRERER SNAP ACTING CONTACTOR Original Filed June 15, 1948 INVENTOR. Paul G. Fmrer. BY

ATTORNEY United StatesPatentO SNAP ACTING CON TACTOR Paul G. Frerer, Peru, 11]., assignor to Bendix Aviation Corporation, Baltimore, Md., a corporation of Delaware Original application June 15, 1948, Serial No.- 33,129. Divided and this application March 11, 1952, Serial No. 275,979

2 Claims. (Cl. 200-67) This invention relates generally to improvements in snap acting electrical contactors and more particularly to. an improved snap acting'contactor adapted to be actuated by a thermal control device, and is, a division of my copending application, Serial Number 33,129, filed June 15, 1948, now abandoned.

The invention is embodied as an important component of a so-called primary control unit for domestic oil burner systems. Such controls have a helically formed bi-metal-lic element and are so located. with respect to a furnace that the'bi-metallic element is exposed to hot flue gases arising from the burner. Such primary controls are commonly called stack switches, by virtue of their common location on the stack of the burner. The over-all action of such control units is well known in the art and, suffice to say, for the purpose of describing the subject invention, the bi-metallic element developsa rotary motion on a suitable shaft element in response to changes in temperature of the furnace gases, and this motion is utilized to provide the actuating force for the improved electrical contactor under discussion herein.

Certain of the electrical circuits governed: by primary control units (through their associated contacting devices) include operating loads of such a nature as tend to produce destructivearcs across slowly separating contacts normally encountered in any thermally driven system.

Because of the gradual changes in temperature encountered in practice, the operating characteristics of these contact, or switching, elements must be appropriately modified to insure swift make and break to prevent their early destruction and consequent failure of the system, while yet retaining a simplicity 'of structure lending itself to convenient, economical, large-scale production. In other words, for certain operating loads on circuits governed by primary control units, the switching element actuated by the thermally driven element must be given an appropriate positive snap-action to prevent destructive arcs across the contacts and this action must be provided for with a design compatible with maximum facility of manufacturing accompanied by minimum manufacturing costs, together with appropriate arrangement of parts for maximum ease of installation and service in the field.

Therefore, it is a primary object of the invention to provide a new and novel snap acting electrical contactor of the type utilizing magnetic elements for providing the necessary snap action, and possessing the beneficial charactcristics heretofore enumerated.

The invention will be best understood, and its important advantages readily apparent upon reference to the single sheet of drawings showing the improved contactor in conjunction with the detailed description following.

Referring now to the drawing, there are shown (in perspective) the dotted outlines of fragmentary portions of a pair of thermally driven switch actuators 1 and 2. The portions shown cooperate with the switch assembly to provide the necessary force for governing the action of the electrical contacts. The switch assembly comprises three sets of contacts, or switches 3, 4, and in the position shown, switches 3 and 4 are normally closed and switch 5 is normally open, corresponding to the cold or inactive condition of the associated burner. The other extremities of the switch. actuators are connected to a bi-metallic helix (notvshown) in the manner shown in my aforesaid application Serial Number 33,129 and the action of the arrangement is such that a rise in temperature of the furnace flue gases causes the actuators to rotate, with respect to the flat surface of the drawing, in a counterclockwise direction, and to rotate in a clockwise direction (still with respect to the fiat surface of the drawing) upon a decrease in flue gas temperature. To further clarify the above, the axis of rotation of the'actuators is parallel to the vertical axis of the contactor and lies in a plane below the surface of the drawing.

Thus, it is apparent that a rise in stack temperature causes the actuator 1 to successively open the contacts of switches 3 and 4 and causes the actuator 2 to close the contacts of switch 5. A decrease in stack temperature causes the actuators to reverse in their direction of rotation, permitting closing of the contacts of switches 3 and 4and opening of the contact of switch 5.

The component parts of the switches 3, 4, 5 are assembled' on the insulating base 6. The normally open switch 5 is made upof

contacts

7 and 8 mounted respectively on the

flexible members

9 and 11 having one of theirends anchored to theinsulating block 6 by appropriate screws and spacers. A rigid stop 12 governs the contact carrying member 9, and a dimple 13, formed in the contact carrying member 11, provides a known and reproducible drive point for the associated actuator 2.

The assembly of switches 3 and 4 difiers materially from that. of the switch 5 to economically and conveniently provide for therequired snap action at make and break. The mounting for the elements comprising the switch 4 is shown in. section and will be first discussed. This assembly includes a relatively flexible member 14 and a relatively rigid bracket member 15 secured at one end to the insulation block 6-by suitable screws and spacers, the apertures in the bracket 15 being tapped to accommodate themounting screws. A circular magnet 16, characterized by sufficiently highcoercive force to permit magnetization with diametrically spaced poles, is secured to the free end of the bracket 15. As shown in the illustration, the bracket 15 is provided with an off-set intermediate its length, and the adjustable contact 17 is carried by the bracket 15 from this off-set portion in opposition to a corresponding contact 18 mounted on the flexible member 14. The contact 18 serves also to secure the paramagnetic armature 19 to the flexible spring 14. It should here be noted that for maximum convenience of assembly, it is desired that the paramagnetic armature 19 have a length approximately equal to twice the distance between the center of contact 17 and the far edge of the magnet 16, with the mounting aperture approximately centrally located so that the switch will function properly whatever the orientation of this part. As in the switch 5, the flexible spring or contact carrying member 14 is dimpled at 21 to provide a well-defined drive point for the actuator 1. Since the makeup of the switch 3 may be, and has for purposes of illustration been chosen as, identical to that of the switch 4, a separate description of its assembly is unnecessary and will not be undertaken here.

The switch 4, like switch 3, is normally closed, which is to say that contacts 17 and 18 are in engagement. The spacing of these contacts is so adjusted that in the normally closed position the armature 19 does not mechanically engage the magnet 16, if a low differential of operation is required. This limitation may be dispensed with, however, in many types of service. As the actuator moves to the right in the drawing, it approaches and finally engages the driving dimple 21 on the spring member 14. With continuing movement of the actuator, the armature 19 does not at once move away from the magnet 16 because of the tractive effort exerted thereby. Thus, the initial movement of the actuator 1 after engagement of the driving dimple serves only to deflect the spring 14 and store energy later to be utilized in producing a snap action. The further movement of the actuator 1 continues to deflect the spring 14 until the force built up therein at the magnet 16 equals the tractive effort developed between it and the armature 19. The resulting movement of the armature 19 moves it away from the working face of the magnet 16, rapidly diminishing the magnetic flux to which it is subjected and correspondingly reducing the tractive effort whereupon the energy stored in the deflection of the spring 14 manifests itself by quickly separating contact 18 from the stationary contact 17.

Conversely, as the actuator 1 moves to the left in response to a decrease in temperature of the stack gases, the

' contact carrying spring 14 moves uniformly with it until the armature 19 moves in to a sufliciently Strong field region of the magnet 16, at which time the attraction of the magnet 16 moves it swiftly to the left, carrying with it contact 18 to engage cooperating contact 17 with a quick action. Since the operation of the similar switch 3 is identical in nature, differing only in timing due to the spacing of the contact carrying spring, it is apparent that no further discussion of its action is required.

Thus, from the above, an improved snap acting contactor results from the arrangement of parts described. Differential of operation can easily be adjusted by moving the contact 17 and timing of the switch, in relation to its actuator, can be accomplished by variations in the spacing of the spring member 14 and bracket 15. A positive drive for the switch is provided for by the dimple 21 coacting with the flat blade of actuator 1 and the magnet 16, in cooperation with paramagnetic member 19 and spring member 14, produces the snap action essential to successful operation in connection with the intended operation of the device. The off-set arrangement of bracket 15 permits for an excellent arrangement of the contacts from the standpoint of adjustability, and the design of the paramagnetic member 19 eliminates any possible errors in assembly of this component. All in all, a simple, effective arrangement of parts is availed of to produce an improved snap acting contactor, one that ideally lends itself to convenient, economical, largescale production.

What is claimed and desired to be secured by United States Letters Patent is:

1. A snap-acting electric switch comprising: an anchor block incorporating insulating material, a relatively rigid bracket member fixed at its one extremity to said block and having joined to its opposite extremity a strip of spring material which projects free from its point of jointure with said bracket member, a magnet fixed to one side of said bracket member, a first contact also fixed to said bracket member on the same side as said magnet, a second strip of spring material fixed at its one extremity to said block in spaced insulated relation to said bracket and at its opposite extremity projecting free in spaced substantially parallel relation to said first-named strip, a paramagnetic armature secured to the side of said second strip which faces said magnet for coaction with the latter and a second contact also secured to the same side of said second strip for coaction with said first-named contact, the free projecting extremities of said first and second strips being adapted for engagement by a switch-actuating memher.

2. A snap-acting electric switch comprising: an anchor block incorporating insulating material, a relatively rigid bracket member fixed at its one extremity to said block and formed with an intermediate offset portion and having connected to its opposite extremity a strip of spring material which projects free from its point of connection with said bracket member, a first contact located in the offset portion of said bracket and a magnet piece fixed to said bracket beyond said offset portion and adjacent the point of connection of said strip, a second strip of spring material fixed at its one extremity to said block in spaced insulated relation to said bracket and at its opposite extremity projecting free in spaced substantially parallel relation to said first-named strip, a paramagnetic armature secured to the side of said second strip which faces said magnet for coaction with the latter and a second contact also secured to the same side of said contact strip for coaction with said first-named contact, said armature being of a length equal to substantially twice the distance from the center of said first contact to the far edge of the working face of said magnet, the free extremities of said first and second strips being adapted for engagement by a switch-actuating member.

References Cited in the file of this patent UNITED STATES PATENTS 1,976,954 Mantz Oct. 16, 1934 2,452,425 Berkholder Oct. 26, 1948 FOREIGN PATENTS 874,058 France Apr. 20, 1942