Common ground terminal for use with single filament and dual filament wedgebase lamp bulbs

A common ground terminal is adapted for use with wedgebase lamp bulbs of either the single filament of dual filament type in a single filament lamp socket. The common ground terminal has a pair of opposed, upper and lower spring contact arms which biasingly engage opposite sides of a wedgebase when it is inserted into the space between the spring contact arms. The lower spring contact arm has a second spring tab which accommodates the presence of a second contact wire when the dual filament type of wedgebase lamp bulb is used.

BACKGROUND OF THE INVENTION 
This invention relates generally to electrical terminals and more 
specifically to electrical ground terminals for use with wedgebase lamp 
bulbs. 
Wedgebase lamp bulbs may be of the single or dual filament type. The single 
filament type has two contact wires for energizing the filament which 
emerge from the end of the wedgebase and extend over onto opposite flat 
sides of the wedgebase so that there is one contact wire adjacent each 
lateral side of the wedgebase. 
On the other hand the dual filament type has two sets of contact wires for 
energizing the respective two filaments. These four contact wires emerge 
from the end of the wedgebase and extend over onto opposite flat sides of 
the wedgebase so that there is one contact wire on each flat side adjacent 
each lateral side of the wedgebase. This results in a contact area for the 
dual filament lamp bulb which is thicker than the contact area for the 
single filament lamp bulb by the thickness of one contact wire. 
These two types of lamp bulbs are interchangeable in lamp bulb sockets in 
the sense that the dual filament lamp bulb can be used in a lamp socket 
designed for a single filament lamp bulb. In this case, the dual filament 
lamp bulb acts as a single filament lamp bulb. This interchangeability 
requires a common ground terminal which can be used with either the single 
filament lamp bulb with its two contact wires or the dual filament lamp 
bulb with its four contact wires. 
In the past, these common ground terminals have had the drawback that the 
spring contact arms of the common ground terminal are deflected ore by the 
wedgebase of the dual filament lamp bulb because of the added thickness 
which is due to the presence of a second contact wire on the opposite side 
of the wedgebase in the vicinity of each lateral side. Consequently these 
known common ground terminals produce a contact force which varies 
considerably depending upon the type of wedgebase lamp bulb that is being 
used. Moreover these known common ground terminals cannot be designed for 
the optimum contact force with either type lamp bulb because optimizing 
the design for one type introduces the possibility of either exceeding the 
elastic limit of the terminal material or producing an inadequate contact 
force when the other type lamp bulb is used. 
SUMMARY OF THE INVENTION 
The object of this invention is to provide an improved common ground 
terminal for use with wedgebase lamp bulbs which has spring contact arms 
which are deflected so as to produce substantially the same contact force 
regardless of whether the single filament or the dual filament wedgebase 
lamp bulb is being used. 
Another object of this invention is to provide an improved common ground 
terminal for use with wedgebase lamp bulbs which has opposed spring 
contact arms which are deflected substantially the same amount by the 
respective contact areas of the single filament and dual filament 
wedgebase lamp bulbs so that the terminal can be designed to produce an 
optimal contact force. 
Yet another object of this invention is to provide an improved common 
ground terminal for wedgebase lamp bulbs in which one of the opposed 
spring contact arms is in the form of a compound spring which accommodates 
the absence of a second contact wire on the contact area of a wedgebase 
lamp bulb so that the opposed spring contact arms are deflected 
substantially the same amount by the wedgebases of single filament and 
dual filament lamp bulbs. 
Other objects and features of the invention will become apparent to those 
skilled in the art as disclosure is made in the following detailed 
description of a preferred embodiment of the invention which sets forth 
the best mode of the invention contemplated by the inventors and which is 
illustrated in the accompanying sheet(s) of drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawing, FIG. 1 shows a single filament wedgebase lamp 
bulb 10, a dual filament wedgebase lamp bulb 12 and a common ground 
terminal 14 for use with either the lamp bulb 10 or the lamp bulb 12. 
The single filament wedgebase lamp bulb 10 has an evacuated envelope 15 and 
a wedgebase 16. The lamp bulb 10 has a single filament (not shown) which 
is disposed inside the envelope 15 and energized by contact wires 18 and 
20. These contact wires emerge from the end of the wedgebase 16 and extend 
over onto the respective upper and lower sides 22 and 24 of the wedgebase 
16 near its opposite lateral ends 26 and 28. 
The dual filament lamp bulb 12 has an evacuated envelope 30 and a wedgebase 
32 which is the same size as the wedgebase 16 of the single filament lamp 
bulb 10. The lamp bulb 12 has two filaments (not shown) which are disposed 
inside the envelope 30 and energized by two sets or four contact wires 34, 
36, 38 and 40 which emerge from the end of the wedgebase 32. One of the 
filaments is energized by contact wires 34 and 40 which extend over onto 
the respective upper and lower sides 42 and 44 of the wedgebase 32 near 
its opposite lateral ends 46 and 48. As mentioned above the wedgebase 16 
and the wedgebase 32 are exactly the same size. Moreover the location of 
the contact wires 18 and 20 on the wedgebase 16 corresponds exactly to the 
location of the contact wires 34 and 40 on the wedgebase 32. 
The second filament of the dual filament lamp bulb 12 is energized by the 
contact wires 36 and 38 which extend over onto the respective lower and 
upper sides 44 and 42. The contact wires 36 and 38 are still in the 
vicinity of the opposite lateral ends 46 and 48 but are spaced inwardly of 
the contact wires 34 and 40. 
Either contact wire 18 or contact wire 20 may serve as the ground contact 
for the single filament within the lamp bulb 10. The contact wires 34 and 
36, which are near the lateral end 46 of the wedgebase 32, are connected 
to the primary and secondary filaments in the dual filament lamp bulb 12 
respectively. The contact wires 38 and 40 which are near the opposite 
lateral end 48 are connected to the secondary and primary filaments 
respectively. Thus either contact wire 34 or contact wire 40 may serve as 
the ground contact for the primary filament within the lamp bulb 12. 
The common ground terminal 14 is designed to engage either a single contact 
wire, such as the contact wire 18 or contact wire 20 of the single 
filament lamp bulb 10, or one of a pair of laterally spaced contact wires 
on opposite sides of the wedgebase, such as the contact wire 34 of the 
pair of contact wires 34 and 36 or the contact wire 40 of the pair of 
contact wires 38 and 40 of the dual filament lamp bulb 12. 
The common ground terminal 14 comprises a base plate 50 which has a pair of 
vertically spaced support tabs 52 which are integrally connected to 
opposite longitudinal side edges of the base plate 50. The common ground 
terminal further comprises a pair of opposed, upper and lower spring 
contact arms 54 and 56 which are integrally attached to lateral side edges 
of the respective vertically spaced support tabs 52 and extend forwardly 
in cantilever fashion. The spring contact arms 54 and 56 converge toward 
each other in the forward direction so as to biasingly engage opposite 
sides of the wedgebase 16 or 32 when either wedgebase is inserted into the 
space between the spring arms 54 and 56 as shown in FIGS. 2, 3, 4 and 5. 
The lower spring contact arm 56 is in the form of a compound spring which 
has a second spring tab 58 which is formed out of the inward part of the 
spring contact arm 56 which is adjacent to the base plate 50. The spring 
tab 58 extends rearwardly toward the support tab 52 and converges toward 
the upper spring contact arm 54 in the rearward direction. 
The spring tab 58 is designed sot that the common ground terminal 50 
engages the ground contact wires of the wedgebases 16 and 32 with 
substantially the same contact force even though the contact area of the 
wedgebase 32 is thicker due to the presence of a second contact wire 36 or 
38. The spring contact tab 58 accommodates the absence of the second 
contact wire as shown in FIGS. 2 and 3. More specifically, the contact tab 
58 engages the lower side 24 of the wedgebase 16 which in turn deflects 
the lower spring arm 56 outwardly away from the lower side 24 by an amount 
which is about equal to the thickness of the contact wire 18 which is 
clamped between the upper spring contact arm 54 and the upper side 22 of 
the wedgebase 16. Consequently the upper and lower spring contact arms 54 
and 56 are deflected outwardly substantially equal amounts (which are 
equal to a thickness of the contact wire for each) when the wedgebase 16 
of the single filament lamp bulb 10 is inserted into the space between the 
spring contact arms. This applies a predetermined contact force of the 
ground terminal 14 to the contact wire 18 which can be maximized or 
preselected in accordance with the predictable deflection characteristics 
of the spring contact arms 54 and 56. 
On the other hand, the lower spring contact arm 56 (that is, the outward 
portion next to the spring tab 58) accommodates the presence of the second 
contact wire 36 by providing a space for the second contact wire 36 when 
the spring tab 58 engages the lower side 44 when the wedgebase 32 of the 
dual filament lamp bulb 12 is inserted into the space between the upper 
and lower spring contact arms 54 and 56 as shown in FIGS. 4 and 5. In this 
instance the upper and lower spring contact arms 54 and 56 are still 
deflected outwardly by substantially the same equal amounts on each side 
of the wedgebase 32, that is, the thickness of the contact wire 18 on one 
side and the thickness of the contact wire 36 which is accommodated by the 
spring tab 58 on the other side. Consequently the common ground terminal 
14 applies the same predetermined contact force to the ground contact 
wires regardless of whether the terminal 14 is used with the single 
filament lamp bulb 10 or the dual filament lamp bulb 12. 
It should be noted that it is not necessary to establish electrical contact 
with the contact wires 36 or 38 because the single filament lamp socket 
has only one electrical feed which contacts either the contact wire 34 or 
the contact wire 40 when the dual filament lamp bulb 12 is inserted in a 
single filament lamp socket. 
I wish it to be understood that I do not desire to be limited to the exact 
details of construction shown and described, for obvious modifications 
will occur to a person skilled in the art.