Precision Snap Switch With Improved One Piece Contact Support and Terminal Member

Precision snap acting switches employing stressed, movable snap members for completing and interrupting electrical circuits are of course well known. Present day designs of such switches typically employ tubular rivets or molded in inserts extending through their mounting bases to provide securement of stationary contacts and terminal members to the base and provide electrical circuit between them and threaded wire terminal screws mounted on an opposite side of the base. Such construction results in electrical joints which if they are not initially firmly secured or otherwise become distorted or loosened in the switch assembly process cause unwanted heating. Such heating necessarily acts as a limitation on the current ratings of such switches. Also such type of construction limits the size of wire terminal securing screws that can be used on such switches thereby making field wiring somewhat difficult.

It is a primary object of the invention to provide an improved terminal and snap blade and contact support construction for precision snap switches which is characterized by a considerable reduction in heat generating electrical joints in facilitating use of larger size wire to terminal securing screws.

A more particular object is to provide such improved construction by employing integral, one piece members which serve both as contact supports and terminal members without any intervening electrical joints.

Other objects and advantages of the invention will hereinafter appear.

FIG. 1 is a view in longitudinal cross section of an electric switch constructed in accordance with the invention.

FIG. 2 is a bottom plan view of the switch of FIG. 1

FIG. 3 is a view in perspective of a contact-terminal member in the switch of FIG. 1.

FIG. 4 is a view like FIG. 3 of another contact-terminal member in the switch of FIG. 1.

FIG. 5 is a view like FIG. 1 of a modified form of switch constructed in accordance with the invention.

FIG. 6 is a bottom plan view of the modified form of switch of FIG. 5.

FIG. 7 is a perspective view of a contact-terminal member and stop member used in the modified form of switch.

Referring to FIGS. 1 to 3 they show a preferred form of normally closed snap-action switch constructed in accordance with the invention. More particularly it comprises a base 10, a cover 12, a combination terminal and pivot member 14, contact-terminal member 16, contact blade 18, and an operating plunger 20.

The base 10 is preferably formed from a phenolic molding material having high electrical insulating characteristics. The terminal-pivot member 14 which is preferably of the form shown in FIG. 3 and formed of brass is secured to the base 10 by a rivet 22 which extends through aligned opening in the upper and lower limbs 14a and 14b the member 18 and base 10. The member 14 has a down turned fulcrum portion 14c that is integral with the upper limb 14a. The outer surface of portion 14c is provided with a fulcrum socket of a shallow V-shaped form having a substantially flat apex in which seats the end of the bowed intermediate finger 18a of the contact blade 18. Such fulcrum socket is preferably like that shown and described in the Richie U.S. Pat. No. 2,182,856.

The left hand end of the blade 18 is secured against the upper side of the boss 10a of base 10 by the rivet 22 and upper limb 14a. Limb 14a is provided with a clearance opening 14d to accommodate a convex hemispherical dimple 18b formed on the blade 18 and the lower end 20a plunger 20 which bears at its lower end against the dimple 18b.

It may be assumed that member 18 has finger portions like the portion 18c which lie on opposite side of the bowed finger 18a. The finger 18a, 18c and the other thereto merge into an integral right hand end portion 18e in which is fixed an electrical contact 23. Contact 23 in the operating position of the switch shown in FIG. 1 bears against the stationary electrical contact 24 secured in the upper limb 16a of a terminal member 16 which is of the form best shown in FIG. 4. The form of the blade 18 is preferable similar to that shown in the Millard U.S. Pat. No. 2,627,754.

The upper and lower limbs 14a and 14b of terminal 14 are interconnected by the integral portion 14e which abuts against the left hand end of the base 10. The lower limb portion 14b is integrally connected with a portion 14f that extends at an angle downwardly therefrom and bears against a complementally angled surface on base 10. The portion 14f in turn is integrally connected with a portion 14g that is generally parallel with the upper limb 14a. Portion 14g has a threaded boss 14h which receives the wire terminal securing screw 28. The right hand end of the portion 14g seats on a shoulder formed on the base 10.

The upper limb 16a of terminal 16 merges with a short portion 16b that angles downwardly and in turn merges with a horizontal portion 16c. The portion 16c integrally connects with the portion 16d that extends downwardly therefrom at a right angle and bears against the right hand end of base 10. At its lower end portion 16d integrally connects with the portion 16e. Portion 16e integrally connects with a portion 16f that angles downwardly and connects with the lowermost portion 16g. A threaded boss 16h is formed on the portion 16g and receives another wire terminal securing screw 28. A rivet 30 which penetrates aligned openings in the portions 16c and 16e of terminal 16 and in the base 10 secure the terminal 16 on the base.

The cover 12 is provided with an internal downwardly extending boss portion 12a in which is provided with an enlarged recess 12b in which slides an enlarged cylindrical portion 20a of operating plunger 20. The upper shoulder of the portion 20a abuts against the inner end of recess 12b to limit the outward movement of plunger 20. The lower shoulder of portion 20a abuts against the upper surface of portion 14a of member 14 to prevent overstressing of contact blade 18 when plunger 20 is pushed downwardly beyond the normal overtravel needed to assure that blade 18 moves past its overcenter snap position. As best shown in FIG. 2 the cover 12 is secured in place on the base 10 by rectangular projections 10d which interfit within complementally formed openings 12c in the cover.

If plunger 20 is depressed inwardly of cover 12 the blade 18 will move downwardly and the blade fingers 18c and 18d, move with snap action in a well known manner downwardly to separate the contact 23 from stationary contact 24. The bottom surface of contact 23 will then bear against the end of the upwardly extending boss 10b formed on base 10 which acts as a limit stop. If plunger 20 is thereafter released, member 18 being of the astable type will then automatically return with snap action to the operating and contact closed position depicted in FIG. 1.

The important aspects of the present invention reside in the relatively few number of parts and consequent minimization of electrical joints provided by the terminal members 14 and 16. As described they are of integral construction and the only electrical joints made therewith are the terminal screws 28, the blade 18 with member 14 and the stationary contact 24 with terminal 16. Accordingly heat rise due to joint resistance is reduced, and consequently the amperage rating of the switch will be enhanced.

FIGS. 5 to 7 disclose a modified form of switch affording normally open type of switch construction. Parts which are the same as the embodiment of FIGS. 1 to 4 bear identical reference numerals. In this modified version a terminal member 32 and a stop plate 34 take the place of terminal member 16. The base 10 is slightly altered with the boss 10b being removed and a recess 10c provided in its place.

As best shown in FIGS. 5 & 7, terminal 32 is provided with an upper limb 32a that seats on an upper surface of base 10 and merges with a right angle extending stub portion 32b in which is fixed a stationary contact 36. At its opposite end the portion 32a merges with a portion 32c that extends downwardly at a right angle adjacent the right hand end of base 10. The portion 32c in turn merges with a portion 32d that abuts a lower surface on base 10, and the later portion in turn merges with a portion 32e that extends at an angle downwardly and merges with the portion 32f. An integral threaded boss portion 32g is formed on the portion 32f and receives a threaded wire terminal securing screw 28. Terminal 32 is secured on base 10 by a rivet 38 that penetrates aligned openings in the portions 32a and 32d and the base 10.

The stop plate 34 is of the form best shown in FIG. 7 and is secured to the upper end of the raised portion 10d of base 10 by a rivet 40 that penetrates the opening 34a in the plate and an aligned opening in base 10. The plate 34 is thus electrically insulated from the terminal 32.

In the operating position of the switch depicted in FIG. 5, contact 23 bears against the lower surface of stop plate 34 so that the current between terminals 14 and 32 is interrupted. Depressing plunger 20 will result in member 18 moving with snap action to cause contact 23 to complete an electrical circuit between terminal members 14 and 32 through member 18. Release of plunger 20 will of course cause member 18 and contact 23 to return to the normally open position depicted in FIG. 5.