US3567889A

US3567889A - Knife switch with particularly shaped contact blade

Info

Publication number: US3567889A
Application number: US776102A
Authority: US
Inventors: Charles Franklin Latter
Original assignee: Square D Co Canada Ltd
Current assignee: Schneider Electric Canada Inc
Priority date: 1968-03-20
Filing date: 1968-11-15
Publication date: 1971-03-02
Anticipated expiration: 1988-03-02

Abstract

An edge of a free end portion of the contact blade facing the jaw members of the knife switch has a cutaway portion positioned toward the pivot axis of the blade from the free end of the blade. An outer side edge of the cutaway portion is chamfered and defines one side of an outer nose portion of the blade. The nose portion has a chamfered leading edge disposed at an acute angle with respect to the free end face of the blade.

Description

United States Patent Charles Franklin Latter Inventor Brampton, Ontario, Canada Appl. No. 776,102 Filed Nov. 15, 1968 Patented Mar. 2, 1971 Assignee Square D Company Canada Limited Toronto, Ontario, Canada Priority Mar. 20, 1968 Canada 015,367

KNIFE SWITCH WITH PARTICULARLY SHAPED CONTACT BLADE 3 Claims, 4 Drawing Figs.

US. Cl 200/162, 200/166, 200/144 Int. Cl H0lh 1/42, l-IOlh 21/54 Field of Search 200/162, 166 (E), 166 (B)8, 15, 146 (Cursory), 144 (Cursory) 200/162 ZOO/162 200/166(E) ABSTRACT: An edge of a free end portion of the contact blade facing the jaw members of the knife switch has a cutaway portion positioned toward the pivot axis of the blade from the free end of the blade. An outer side edge of the cutaway portion is chamfered and defines one side of an outer nose portion of the blade. The nose portion has a chamfered leading edge disposed at an acute angle with respect to the free end face of the blade.

PATENTEUIAR 2mm 25 in/5mm CHARLES F LATTER KNIFE SWITCH WITH PARTICULARLY SHAPED CONTACT BLADE This invention relates to electric switches of the knife-blade type, and more particularly to the shape of the free end portion of a pivoted blade of a knife switch and-its cooperative relation with a stationary jaw member comprising a pair of contact jaws.

Most prior knife-switchblades and their cooperating stationary contact jaw members have been designed without giving special consideration to the region or area of contact as the blade enters or is withdrawn from between the contact jaws of the jaw member. Generally, both the blade and the contact jaws are of simple rectangular configuration and the blade enters and is withdrawn from the contact jaws at the outer corner portions thereof nearer the pivot axis of the blade.

The switch blade of the present invention is so shaped that the roots of most arcs that form as the blade is withdrawn from the contact jaws are respectively on the free end face of the blade and the side edges of the contact jaws remote from the pivot axis of the blade, and are not on the edges of the jaws and blade that face each other. This result is obtained because the marginal portion of the blade near the edge which faces the jaw members, when the blade is spaced slightly therefrom, has a cutaway portion positioned inwardly from the free end face of the blade and disposed above the outer portions of the contact jaws at the sides thereof nearer the pivot axis of the blade, and the outer edge of the cutaway portion extends toward the jaw members beyond the plane of the side edge of the blade to define an outer nose portion which faces the jaw members and has a leading edge forming an acute angle with respect to the outer end face of the blade. The pivot axis of the blade is so positioned with respect to the jaw member and the nose portion is so shaped and is so spaced from the pivot axis that, upon swinging movement of the blade to its closed position, the leading edge of the nose portion is parallel to the upper face of the jaw member as the nose portion enters between the jaws at a portion thereof remote from the pivot axis of the blade.

It has been found that less are erosion and beading occurs in the use of switches made in accordance with this invention than occurs in the use of conventional knife switches. This reduction in arc erosion and beading results in a switch of longer life and one that requires less force for operation during its life. Because the last area of contact between the blade and the contact jam member upon withdrawal of the blade is farthest from the pivot axis, the speed of separation is inherently a maximum and the arc is always started in this area. The heat generated by the arc causes it to rise and its roots to move away from the area of last separation. The edge of the blade at the area of entry and withdrawal is chamfered, and the entry force is distributed along the chamfered edges. Since very little arcing takes place in this area, the wear is minimal and the life of the switch thereby extended.

It is an object of this invention to provide a knife-switch blade having its free end portion uniquely shaped to control arcing between the blade and a cooperating jaw member.

Another object is to provide a knife-switch blade provided with a recess and extending relatively narrow nose portion near the outer end thereof so that the nose portion is withdrawn from between the jaws of a cooperating jaw member at an area thereof most remote from a pivot axis of the blade and after a principal contact portion of the blade has been withdrawn.

Other objects and advantages of this invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a side view of a knife switch in accordance with this invention;

FIG. 2 is a view of the knife switch looking from the right in FIG. 1;

FIG. 3 is an enlarged view of the free end portion of a knifeswitch blade shown in FIG. 1; and

FIG. 4 is a view looking from the bottom of FIG. 3.

Referring to the drawing, there is shown a-knife switch having an insulating base plate 10 carrying a pair of spaced terminal member 11 and 12. Mounted on the terminal member 11 is a conventional bifurcated switch blade support 14 between the legs of which is pivoted, at one end portion, a generally flat, elongated knife blade 15 by means of a pivot shaft 16. Carried by the other terminal member 12 is a conventional stationary contact jaw member 17 defined by a metal frame having a base portion 19, spaced leg portions 20, and inturned and juxtaposed contact jaw portions 21 between which a free end portion of the blade 15 is to be received and which are biased together by the resiliencey of the metal frame and by a delta-shaped spring member 22. In operation, an operator means 23 is moved to cause the blade 15 to swing about the pivot shaft 16 for entry of its free end portion between the inturned contact jaw portions 21 of the jaw member 17 and withdrawal therefrom.

In accordance with this invention the blade 15 includes a straight longitudinal edge 24 facing the jaw member 17, extending generally parallel to the length of the blade from the mounted end portion toward the free end portion, and disposed in a reference plane perpendicular to opposed flat sides of the blade. The blade 15 has a cutaway portion 25 positioned inwardly from a free end face 26 thereof and disposed above the upper extremities of the jaw member 17 at the side thereof nearer the pivot shaft 16 when the blade 15 is in the solid-line position of FIG. 1. The cutaway portion 25 is defined by an inner sloping edge 28, a top edge 29 parallel with the edge 24, and an outer sloping edge 30. The outer edge 30 forms an obtuse angle with the top edge 29 and extends beyond the reference plane of the edge 24 to define, with a leading edge 32 and the end face 26 of the blade 15, an outer nose portion 31. The cutaway portion 25 and the nose portion 31 are thus disposed on opposite sides of the reference plane of the edge 24. The leading edge 32 is preferably less than one-half the width of the jaw portions 21 and is at an acute angle with respect to the outer end face 26.

The pivot shaft 16 for the blade 15 is so positioned with respect to the jaw member 17, and the nose portion 31 is so spaced from the pivot shaft 16, that upon swinging movement of the blade 15 toward its closed position, the leading edge 32 is substantially parallel to the upper face of the jaw member 17 as the nose portion 31 enters between the jaw portions 21, and the entry is at a relatively narrow region of the jaw portions remote from the pivot shaft 16. The completely inserted position of the blade 15 with respect to the jaw member 17 is shown in broken lines in FIG. 1.

Upon withdrawal of the blade 15 from between the jaw portions 21 of the jaw member 17 under load, the top edge 29 of the cutaway portion 25 and a portion of the side edge 30 adjacent the top edge separate from the jaw member 17 first, but no arc is formed because current continues to flow through the nose portion 31. As the nose portion 31 separates from the jaw member 17, an are indicated at 34 forms, rises from the heat in the normal position of the switch, and one of its roots moves along the end face 26 of the blade 15 and the other of its roots moves along outer side edges 35 of the jaw portions 21.

The blade 15 is chamfered equally on both sides along the I I top edge 29 of the cutaway portion 25 as indicated at 29a, along the edge 30 as indicated at 30a, and to a greater extent along the leading edge 32 as indicated at 32a. The chamfering facilitates entry of the blade between the jaw portions 21.

A U-shaped rigid sheet of insulating material 38 may be placed around the jaw member 17 with the inner surface of its bight portion 38a facing the outer side edges 35 of the jawportions 12, and its legs 38b and 380 on opposite side of the jaw member 17. I 7

Although the invention has been described as incorporated in a single-pole knife switch, it is apparent that it can be incorporated in multiple switches with the same advantages.

lclajm: 1. An electric knife switch comprising a stationary contact jaw member, and a generally flat elongated movable contact blade mounted at one end portion for edgewise pivotal movement selectively in one direction to move a free other end portion into engagement with the jaw member and in an opposite direction to disengage the free end portion from the jaw member, the blade having a straight longitudinal edge facing the jaw member, extending generally parallel to the length of the blade from the mounted end portion toward the free end portion, and disposed in a reference plane perpendicular to between the straight longitudinal edge and the projecting nose portion and forming a recess in the blade on the opposite side of the reference plane from the projecting nose portion.

2. An electric knife switch as claimed in claim 1 wherein the projecting nose portion has a straight leading edge which is parallel to a first-engaged portion of the jaw member for initial line contact therewith as the blade is moved into engagement with the jaw member.

3. An electric knife switch as claimed in claim 1 characterized in that a U-shaped sheet of insulating material is positioned adjacent the jaw member and has the inner surface of its bight portion spaced from and facing the side edges of the jaw member facing away from the mounted end portion of the blade and its leg portions spaced from and disposed respectively on opposite sides of the jaw member and extending toward the mounted end portion of the blade.

Claims

1. An electric knife switch comprising a stationary contact jaw member, and a generally flat elongated movable contact blade mounted at one end portion for edgewise pivotal movement selectively in one direction to move a free other end portion into engagement with the jaw member and in an opposite direction to disengage the free end portion from the jaw member, the blade having a straight longitudinal edge facing the jaw member, extending generally parallel to the length of the blade from the mounted end portion toward the free end portion, and disposed in a reference plane perpendicular to the blade, the free end portion of the blade having a projecting nose portion disposed on the side of the reference plane facing the jaw member and engageable with the jaw member at a further end thereof from the mounted end portion of the blade, and the blade having a cutaway portion disposed between the straight longitudinal edge and the projecting nose portion and forming a recess in the blade on the opposite side of the reference plane from the projecting nose portion.