Electric switch with improved sliding contact holder

An insulating contact holder (26) is reciprocally movable in sliding engagement between flexible stationary contacts (22, 24) to interrupt the circuit therebetween in one position of the holder and to carry a contact (32) into bridging engagement with said stationary contacts in another position of the holder. A wedge formation (40) on the holder separates the stationary contacts a predetermined distance in the circuit interrupting position, and movement therefrom to the bridging position causes said stationary contacts (22, 24) to converge immediately prior to engagement by the bridging contact (32), thereby to relieve the bias in the stationary contacts prior to said bridging engagement to reduce contact bounce. The wedge surfaces (42) are provided with a matte surface for cleaning the stationary contacts.

BACKGROUND OF THE INVENTION 
This invention relates to electric switches and more particularly to snap 
action switches wherein a bridging contact is slidably driven into and out 
of bridging engagement with a pair of flexible stationary contacts. 
U.S. Pat. No. 2,210,037 issued Aug. 6, 1940 to G. J. Meuer discloses a 
switch of the aforementioned type wherein the stationary contacts comprise 
resilient members supported on opposite end walls of the switch housing 
and having free ends overlying each other in spaced apart relationship 
within the central portion of the housing. A bridging contact is mounted 
on a insulating contact holder which is driven by an overcenter toggle 
mechanism for reciprocal sliding movement to carry the contact into and 
out of bridging engagement with the free ends of the stationary contacts. 
The contact holder is blanked, or sheared from a flat sheet of fiberboard 
and the bridging contact is a U-shaped member disposed within a lateral 
slot in the fiberboard contact holder to have the legs of the contact 
disposed horizontally along upper and lower surfaces of the contact 
holder. A rivet is provided through the fiberboard contact holder and the 
outer ends of the legs of the U-shaped bridging contact to maintain the 
contact assembled to the contact holder. Operation of the toggle mechanism 
drives the contact holder and bridging contact to a first position wherein 
the contact is disposed in bridging engagement with and between the upper 
and lower flexible stationary contacts to complete a circuit therebetween. 
Operation of the toggle mechanism to an opposite position drives the 
contact holder and bridging contact in an opposite direction to move the 
contact out of bridging engagement with the stationary contacts and to 
position a portion of the insulating contact holder between the free ends 
of the stationary contacts, thereby interrupting the circuit therebetween. 
Switches of this type have proven to perform very satisfactorily. However, 
the fiberboard contact holder is susceptible to swelling when the switch 
is used in humid, moist atmospheres, is susceptible to erosion from the 
electric arc that occurs upon contact separation, and can become brittle 
with very long life. 
An improvement in the contact holder design is disclosed in U.S. Pat. No. 
3,250,884 issued May 10, 1966 to R. E. Larkin. That contact holder is 
molded of an insulating phenolic resin and has U-shaped contacts which are 
assembled to the sides of the contact holder in lateral recesses as 
opposed to slots. The contacts have off-set legs which extend in the 
direction of motion of the contact holder to attain the desired length, 
and are recessed to be flush with the surface of the holder. The contacts 
are formed of good arc interrupting material and have a high quality 
current conducting material inlaid in the area of bridging engagement with 
the stationary contacts for enhanced performance. That contact holder is 
moisture resistant and less susceptible to arc erosion. Transversely 
disposed serrations are provided in that contact holder which engage the 
stationary contacts in the off position of the switch. Among other 
functions, these serrations provide a mild abraiding of the contacts for 
cleaning residue therefrom during movement of the holder. Testing and 
studies conducted on this switch suggest that the serrations may impart a 
vibration to the resilient stationary contacts during switch operation 
which may result in contact bounce and arcing upon bridging engagement of 
the contacts. 
Switches of the aforementioned type are used extensively in industrial 
grade hand held portable electric tools. In some applications, 
particularly for tools manufactured in Europe, the separation distance 
between stationary contacts in the switch off position is required to be 
greater than presently exists in these switches. A direct solution to this 
requirement is to increase the thickness of the contact holder at the 
point where it engages the stationary contacts in the off position. The 
fiberboard contact holder such as in the aforementioned Meuer patent is 
not readily deformable to produce formations for this purpose, although 
such features can readily be incorporated on a molded contact holder such 
as in the aforementioned Larkin patent. In determining the nature of such 
formations, it has been discovered that particular configurations increase 
the circuit making and breaking performance of switches of this type. 
SUMMARY OF THE INVENTION 
The invention herein disclosed provides an improved insulating contact 
holder for switches wherein the contact holder is slidably disposed 
between a pair of resilient stationary contacts to separate the latter in 
the off position of the switch and to carry a bridging contact into and 
out of bridging engagement with the stationary contacts. The contact 
holder herein disclosed is made from a heat stable nylon material and has 
a wedge formed thereon which increases in thickness away from the bridging 
contact in the direction of movement of the contact holder so as to 
maintain the stationary contacts separated at a predetermined distance in 
the off position of the switch. Movement of the contact holder to the on 
position of the switch causes the stationary contacts first to converge as 
the declining surface of the wedge slides between the stationary contacts 
and thereafter to separate as the stationary contacts ride onto the 
bridging contact to their switch on, bridging contact position. The wedge 
surface is provided with a matte finish to provide mild abraiding for 
cleaning the stationary contacts.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing, a switch embodying this invention is shown in 
FIG. 1 wherein a longitudinal section has been taken through one pole of a 
2-pole switch. The switch comprises an insulating base 2, an insulating 
cover 4 and an actuator superstructure comprising an inverted U-shaped 
channel 6 secured to the base 2 by a pair of screws 8. The channel 6 
serves to pivotally support a shaft 10 on which a toggle lever 12 is 
mounted to extend upwardly through an opening in the channel. A generally 
U-shaped bail 14 is also pivotally mounted between the upright legs of 
channel 6 to depend through an opening in cover 4 into a central cavity in 
base 2. A depending actuator tongue 16 is supported on the bight portion 
of bail 14 and a coil compression spring 18 is disposed between the 
actuator tongue 16 and the toggle lever 12. A cup washer 20 is disposed 
over the upper end of compression spring 18 for engagement by the toggle 
lever 12. A lower stationary contact 22 is supported on the left-hand end 
wall of base 2, the contact 22 having an inwardly extending resilient arm 
which projects toward the center of a central cavity of base 2 near a 
lower wall of that cavity. An upper stationary contact 24 is similarly 
secured on the right-hand end wall of the base 2 and has an inwardly 
extending resilient arm which projects toward the center of the switch 
cavity to overlie the free end of contact 22 in spaced apart relation. The 
contacts 22 and 24 are made of a spring contact material, the lower 
stationary contact 22 being made of a somewhat thicker material stock than 
the upper stationary contact 24 to provide greater rigidity to the lower 
stationary contact 22. Screw terminals are provided adjacent the outer 
ends of the stationary contacts 22 and 24 for connection of the switch 
contacts into an electrical circuit. An insulating sheet 25 is loosely 
disposed on the upper surface of upper stationary contact 24 and confined 
by the central cavity of base 2 to electrically insulate the toggle 
mechanism from the switch contacts. 
A movable contact holder 26 is slidably disposed within the cavity of the 
switch base 2 on a horizontally extending central rib 2a. Contact holder 
26 is positioned between the free ends of the stationary contacts 22 and 
24 to separate these contacts when the switch is in the off position. 
Contact holder 26 is best illustrated in the isometric view of FIG. 3 
wherein it may be seen to comprise essentially a flat, H-shaped member of 
insulating material. This insulating material is preferably heat stable 
nylon such as Vydyne 22H available from Monsanto Chemical Company. Contact 
holder 26 has a slot 28 in the central cross bar portion thereof which 
receives the actuator tongue 16 of the overcenter actuator mechanism for 
the switch. A pair of tranverse lateral slots 30 are provided for 
receiving the bight portion of U-shaped bridging contacts 32 assembled to 
the contact holder such that their legs overlie and extend along the upper 
and lower surfaces of contact holder 26. The free outer ends of the legs 
of bridging contacts 32 are provided with a pair of aligned holes 34 which 
align with holes 36 in contact holder 26 when assembled thereto and rivets 
38 are provided to extend through the contact holder and through the legs 
of the contacts within the holes 34 and 36 to secure the contacts 32 to 
the holder 26. With reference to the orientation of holder 26 in FIG. 3, 
the forward edge of lateral slots 30 define the shallow end of respective 
wedges 40 which are inclined to the right in FIG. 3 and to the left in 
FIGS. 1 and 2. Wedges 40 provide upper and lower ramp surfaces 42 which 
diverge away from the bridging contacts 32 in the direction of movement of 
contact holder 26. Ramp surfaces 42 of the wedges are formed with a 
roughened matte finish by providing an EDM (Electro Discharge Machining) 
surface in the die in which the holder is molded to provide mild abraiding 
for the stationary contacts as the holder 26 is moved therebetween to 
clean the stationary contacts without imparting vibratory motion to the 
contacts. 
As viewed in FIG. 1, when the toggle lever 12 is moved to its right-hand 
position, the overcenter toggle linkage (bail 14, spring 18 and actuator 
tongue 16) causes actuator tongue 16 to drive contact holder 26 to its 
right-hand position within the cavity of switch base 2. This position is 
determined by engagement of the central web of contact holder 26 with 
upstanding portions of the switch base at the respective ends of the 
central cavity. In the right-hand position it can be seen that the wide 
end of the wedge portions 40 is disposed between the upper and lower 
stationary contacts 24 and 22, respectively, to maintain these contacts 
separated at a predetermined spacing. The resiliency and initial spacing 
of stationary contacts 22 and 24 maintains them continuously biased into 
contact with the upper and lower surfaces of contact holder 26. The wedge 
40 acts in opposition to the bias of the stationary contacts to cam them 
apart, thereby introducing a mild stress to the stationary contacts in the 
off position. 
Movement of the toggle lever 12 to the left-hand position with respect to 
the orientation in FIG. 1 will cause the toggle mechanism to slide the 
contact holder 26 to its left-hand position, thereby driving contacts 32 
into bridging engagement between stationary contacts 22 and 24. Lower 
contact 22 is formed to project slightly above the plane of central rib 2a 
to insure good contact pressure with the lower leg of bridging contact 32. 
As a result, as seen in FIG. 1, the contact holder assembly rides up onto 
the lower stationary contacts 22 in moving toward the left-hand position. 
With reference to FIG. 2, as the contact holder 26 moves to the left, the 
ramp surfaces 42 of wedge 40 move in a direction to permit the stationary 
contacts 22 and 24 to converge until the contacts 32 abut the stationary 
contacts at the base of the wedge adjacent slots 30 as shown in solid 
lines in FIG. 2. Thereafter the continued leftward movement of holder 26 
carries the bridging contact 32 fully between the stationary contacts 22 
and 24 to the position shown in dot-dash lines FIG. 2. The relative 
movement between the stationary and movable contacts is such that the 
stationary contacts may be described as riding up the curvature of the 
bight portion of briging contact 32 and onto the flat surfaces of the 
upper and lower legs of contact 32. It will be appreciated that the speed 
with which the holder 26 moves causes the bridging contact 32 to abruptly 
drive stationary contacts 22 and 24 apart when moving to bridging 
engagement therewith and that momentum imparted to the stationary contacts 
may carry the respective stationary contact temporarily off the flat 
surface of the bridging contact 32 at the point of transition from 
curvature to flat surface, i.e. contact bounce occurs. This contact bounce 
creates undesirable arcing between the stationary and movable contacts. 
However, it has been found that less contact bounce occurs on contact 
holders having the wedge 40 preceding the bridging contact in movement to 
the on position. The convergence of the stationary contacts 22 and 24 as 
the inclined ramp surfaces 42 of the wedge 40 are moved from between the 
stationary contacts reduces or relaxes the minimal stress (originally 
applied to the stationary contacts by the wedge 40) immediately prior to 
their separation by the bridging contact 32, and the harmonics of this 
action minimize the contact bounce. Moreover, on movement of the bridging 
contact 32 out of engagement with the stationary contacts 22 and 24, the 
ramp surfaces 42 engage the stationary contacts as the latter converge 
downward along the curved portion of contact 32 and begin to separate the 
contacts immediately as the wider portion of the wedge 40 is driven 
therebetween. This action reduces any arc that is formed between the 
contacts at separation. 
While the electric switch with improved sliding contact holder of this 
invention has been disclosed in a single preferred embodiment herein, it 
is to be understood that the invention is susceptible to various 
modifications without departing from the scope of the appended claims.