[0001] The invention relates to an electric plug having two electrically conductive contact
pins connected to cores of a connecting cable and being fastened in end parts of an
elongate bridge piece of electrically insulating synthetic resin, each end part surrounding
one of the contact pins throughout the height of the bridge piece, an electrically
insulating housing being moulded or cast around the bridge piece and an adjacent part
of the connecting cable.
[0002] Such a plug is known from German Patent Specification 2532872. One of the functions
of the bridge piece is to hold the two contact pins in a manner such that they can
resist given mechanical loads. Inspection boards have issued a number of provisions
for safety requirements to be satisfied by a plug. For example, contact pins exposed
to laterally directed forces are allowed to change their relative positions only to
a slight extent. Moreover, the contact pins have to be resistant to a given tensile
and torsional force without getting out of the housing. It is, therefore, important
for the bridge piece to behave like a rigid beam in which the contact pins are firmly
anchored and which itself is firmly anchored in the housing. The bridge piece of the
known plug (see Fig. 2 of German Patent 2532872) is a solid beam which fixedly holds
the contact pins, it is true and which has the required rigidity, but which has the
disadvantage that its manufacture requires a relatively large quantity of expensive
material, for example, glass-filled PA (polyamide), PBT (polybutyl- eneterephthalate)
or PET (polyethylene terephthalate), whilst anchoring in the housing is not to the
optimum. Fig. 1 of said German Patent shows a bridge piece consisting of two parallel
plates one lying above the other, which requires less material, but has the disadvantage
that anchoring of the contact pins in the relatively thin plates is less firm and
the thin plates are more likely to bend than a solid beam.
[0003] The invention has for its object to provide a plug of the kind set forth in the preambule,
the bridge piece of which is at least as rigid as a solid beam, but comprises less
material and is better anchored in the housing.
[0004] The plus embodying the invention is characterized in that an intermediate part of
the bridge piece extending between the two end parts has an I-shaped cross-section
along at least half its length.
[0005] Owing to the 1-section profile of the intermediate part a considerable amount of
material is saved. Moreover, the bridge piece can be made by injection moulding within
a shorter time because the smaller thickness of material in the area of the intermediate
part involves a shorter curing time. Since the intermediate part has an I-cross-section,
it has two recesses along the major part of the length on the sides. When the housing
is being formed, said recesses are filled with material of the housing so that the
bridge piece is firmly anchored in the housing.
[0006] The invention will be described more fully hereinafter with reference to the drawing
showing in
Figure 1 a side elevation of an embodiment of a plug in accordance with the invention,
Figure 2 a cross-sectional view of the bridge piece of the plus taken on the line
II-II in Fig. 1 and
Figure 3 a longitudinal sectional view of the bridge piece taken on the line III-III
in Fig. 1.
[0007] The electric plus shown in Fig. 1 comprises two electrically conductive contact pins
1 fastened in end parts 3 of an elongate bridge piece 5. The bridge piece 5 is made
by injection moulding from a strong, electrically insulating synthetic resin, for
example, glass-filled PA, PBT or PET. The contact pins 1 are embedded along the whole
height of the-bridge piece 5 in the end parts 3. In order to ensure satisfactory anchorage
of the contact pins 1 in the synthetic resin, the contact pins have a thickened part
7 at the areas of the end parts 3. The contact pins are not precisely parallel; they
are at an acute angle to one another so that the connection of the plug with the wall
contact box always has some clamping effect.
[0008] According to the existing safety provisions the angle between the contact pins 1,
when exposed to a lateral force, should not vary beyond given limits. For this purpose
it is necessary for the bridge piece to behave as a rigid beam that can be bent only
with difficulty. On the other hand, for reasons of cost price, the bridge pece 5 should
contain a minimum amount of synthetic resin, since with regard to the high mechanical
requirements this synthetic resin is relatively expensive, whilst moreover curing
a bridge piece having a large volume takes relatively much time, so that the injection
moulding process takes much time. In order to satisfy all these requirements the intermediate
part 9 of the bridge piece 5 extending between the two end parts 3 has an I-shaped
cross-section. A beam having such a cross-section has at least the same resistance
to bending as a solid beam, whilst a considerable amount of material is saved.
[0009] The I-cross-section of the intermediate part 9 is clearly shown in Fig. 2. Along
the two sides of the intermediate part two recesses 11 extend in the direction of
length of said part. From Fig. 3 it is apparent that the depth of these recesses is
constant along almost the entire length of the intermediate part 9. In order to obtain
a gradual transitional area between the intermediate part 9 and the two end parts
3, the depth of the recesses near said end parts progressively diminishes. It will
be obvious that the obtainable saving of cost is higher, the longer are the recesses
11. It has been found that a satisfying saving is already obtained when the recesses
extend along at least half the length of the intermediate part 9.
[0010] The contact pins 1 are provided at one end with connecting sockets 13. Therein the
ends 15 of cores 17 of a connecting cable, from which the insulating jacket is removed,
are fastened, for example, by soldering or crimping. Thus the cores 17 are galvanically
and mechanically connected with the contact pins 1. The bridge piece 5 and the adjacent
part of the connecting cable 19 are surrounded by a housing 21 (shown in broken lines).
The housing 21 may be formed by moulding or casting an electrically insulating synthetic
resin. The requirements for this synthetic resin with respect to resistance to bending
are very mild so that the material may be relatively inexpensive. A suitable synthetic
resin is, for example, soft PVC. During the formation of the housing 21 the synthetic
resin also penetrates into the recesses 11 of the bridge piece 5 so that this bridge
piece is firmly anchored in the housing.
An electric plug comprising two electrically conductive contact pins connected to
the cores of a connecting cable and fastened in ends parts of an elongate bridge piece
of electrically insulating synthetic resin, each end part surrounding one of the contact
pins throughout the height of the bridge piece, an electrically insulating housing
being moulded or cast around the bridge piece and an adjacent part of the connecting
cable, characterized in that an intermediate part of the bridge piece extending between
the two end parts has an I-shaped cross-section along at least half its length.
