Electrical switch

An electrical switch comprises a pair of spaced terminals, fixed in an insulating housing; a metal roller; and, a finger-piece for moving the roller between first and second switching positions engaging only one and both terminals respectively. The one terminal is resiliently flexed to bias the roller against the second terminal in the second switching position. The one terminal comprises a cantilever spring having an upset end protruding into the roller path and providing the fulcrum for an overcenter action biassing the roller in either switching position.

The invention relates to an electrical switch. 
It is desirable to provide an electrical switch which is reliable in 
operation and yet relatively inexpensive to manufacture. 
A known switch comprises a pair of terminals, fixed spaced apart from each 
other in an insulating housing; a metal roller; and, a finger-piece of 
insulating material having a cavity receiving the roller and mounted in 
the housing to move the roller between a first and a second switching 
position in which the roller engages only one and both terminals 
respectively. 
A disadvantage of the known switch is that additional means are required to 
bias the roller against the contacts to ensure a reliable electrical 
connection. 
According to the invention, the one terminal is resilient, the arrangement 
being such that the one terminal is resiliently flexed to bias the roller 
against the terminal in the second switching position. 
Resilient flexure of the one terminal may therefore provide the force 
necessary to establish electrical contact between the roller and both 
terminals in the second switching position obviating need for additional 
biassing means to maintain reliable electrical connection between the 
roller and the contacts. 
The arrangement may be such that the engagement between the roller and the 
or each terminal respectively, traps the roller in the cavity in first and 
second switching positions facilitating simplicity of manufacture and 
assembly of the switch. 
Preferably, increased resilient deformation of the one terminal is produced 
during roller movement providing an overcentre action, biassing the roller 
toward respective switching positions relative to the one terminal. 
The roller may be received as a free fit in the cavity to permit limited 
movement of the roller in the switching direction independently of the 
finger-piece. The switching speed may be increased as the roller may be of 
small mass with consequential reduction in risk of arcing. 
The one terminal may comprise a cantilever spring extending in the 
direction of roller movement and having a transverse roller engaging 
portion protruding into the path of the roller movement and providing the 
fulcrum for the overcentre action. 
Preferably, the finger-piece is mounted in the housing for rocking movement 
to effect switching and includes a channel section portion into which 
roller engaging portions of the terminals extend, the roller being 
received in aligned slots in the channel walls.

The switch comprises an insulating housing 10 a pair of terminals 12 and 13 
respectively, fixed spaced apart in the housing and a metal roller 16 
received in a cavity 15 in a finger-piece 14 mounted in the housing for 
rocking movement to move the roller between a first and a second switching 
position engaging one and both terminals, respectively. 
The housing comprises a base 11 and a cover 41 each moulded in one piece 
from plastics material. The base 11 is of generally channel-section the 
floor of the channel being stepped longitudinally to define a first pair 
of terminal supporting beds 17 and 18, respectively, on opposite sides of 
a central recess 19, and a second pair of beds 21 having transverse slots 
22. The terminal supporting bed 17 is shorter than the bed 18 for reasons 
explained below. The walls of the channel section are rebated to provide 
wire supporting ledges 23. Post portions 24 upstand from a central 
location of each side wall and have apertures 25 towards their upper ends 
providing sockets of a trunnion mounting for the finger-piece. 
The cover 41 has a central aperture 42 for receiving the posts 24 and the 
finger-piece, wire engaging portions 43, and longitudinally extending 
shoulders forming part of wire supporting ledges 23 on opposite sides for 
co-operation with the shoulders on the base to grip wires when the cover 
is mounted on the base. 
Each terminal 12 and 13 is stamped and formed in one piece and has a 
contact portion 26 extending from a wire connecting portion 27. Each 
contact portion comprises a resilient tongue 28 upset and folded 
transversely at its free end to provide a nose 29. Each wire-connecting 
portion 27 comprises a pair of parallel plates 31 and 32 respectively, 
joined together at one end by a web 33 extending transversely from each 
plate, a wire-receiving slot 34 extending through the bight into each 
plate. 
The finger-piece 14 is moulded from plastics material in generally disc 
shape having an internal recess 36 of sectorial cross-section in the disc 
plane and defining a portion of channel axial cross-section. Opposite 
walls 37 of the channel section portion are formed with aligned roller 
receiving slots 38 extending radially into the walls and shoulders 39 and 
40 respectively at opposite circumferential ends. Trunnions 44 extend 
axially from opposite sides of the finger-piece. 
The switch is assembled by mounting the terminals in the base channel so 
that their contact tongues 28 are supported by the beds 17 and 18 and the 
free ends of the plates 32 of the wire connecting portions are 
respectively received in the slots 22. As the bed 17 is shorter than the 
bed 18, the tongue of terminal 12 will provide a cantilever spring arm of 
greater effective length than the tongue of terminal 13 and therefore be 
of greater flexibility than the tongue of terminal 13. 
The roller is then located on the terminal noses and the finger-piece 
applied to the housing base with the trunnions received as a snap-fit in 
aperture 42 so that the roller is located in the slots 38. 
Wires are then aligned with each terminal slot 34 and pushed simultaneously 
into the slots by portions 43 during the application of the cover to the 
base so that the edges of each slot effects permanent electrical 
connection to the conductive wire cores. The beds 21 ensuring that the 
plates 31 and 32 remain parallel during insertion. When provided, 
auxiliary wires are located on ledges 23. The cover can be welded or 
otherwise bonded to the base. The entire assembly may then be inmoulded to 
provide a switch of oval cross-section. 
Operation of the finger-piece moves the roller between first and second 
switching positions in which it engages only the terminal 12 and both 
terminals 12 and 13 respectively. During movement between switch positions 
the roller rides over the nose of terminal 12 increasing the resilient 
deformation of the terminal which biasses the roller to either switch 
position when the roller passes an overcentre condition, increasing the 
speed of switching. It should also be noted that the roller is received as 
a free fit in the slots 38 to permit limited movement in the switching 
direction independent of the finger-piece. This increases the switching 
speed as the inertia of the finger-piece need not be overcome during 
initial stages of engagement between the roller and the terminal 13. A 
self-centering action is also present. Movement of the finger-piece is 
limited by the shoulders 39 and 40 engaging the flow of the base channel. 
The switch described may be manufactured and assembled economically using 
mass production techniques and needs few different parts while providing a 
fast switching action. 
In an alternative example (not shown), the cover member and the base member 
are provided with complementary latching means engageable as a snap fit on 
the application of the cover to the base to force the wires into the 
slots. The base may have resiliently flexible posts upstanding therefrom 
with latching heads at their free ends receivable on flexure of the posts 
in latching apertures provided in the cover. The trunnions are trapped 
between the cover member and the base member instead of being received in 
sockets 25. This facilitates assembly of the switch by mass production 
techniques.