Note: Descriptions are shown in the official language in which they were submitted.
761~
Many telephone sets contain a circuit board having
conducting paths on one 'ace and a host of components, connected
into an electrical circuit by the conducting paths, mounted on
the board on the opposite face. The components include a
transformer characterized, typically, by a pair of overlapping
coils of shellac-coated 34 gauge copper wire. Surface turns of
the outer transformer coil are normally exposed within the
telephone sub-set and, on occasion, have fallen victim to a
screw driver during repair or installation. Transformer wire
is even more vulnerable where it extends from the coils to
outlying terminals since single unsupported filaments of wire
may be suspended in mid-air.
We propose a removable shield tailored to fit
conventional transformer structures and functioning to prevent
damage to the associated transformer wire.
According to one aspect of the invention, for
telecommunication apparatus a transformer and shield assembly
comprises:
a transformer having coils wound on a bobbin
having a central former extending between first and second flanges,
electrical input and output wire of said coils passing adjacent
said first flange; and
a demountable shield having a cap, at least one
side extending from said cap to at least partially cover
transformer coil wire on said former, and a flange projecting
outwardly from said each side to at least partially cover
transformer coil input and output wire.
The bobbin flanges and the former can be generally
rectangular and the shield can have, for example, two opposed
sides extending adjacent opposite side~ of the bobbin.
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The transformer ca~ further comprise a stack of
laminations extending adjacent an outer surface of said flange,
said cap being planar and rectangular and having depending
~alls fitting closely over said laminations.
Each of the shield sides can have an outwardly
extending web and a two-part side wall one part of the side wall
uniting the web and the flange and the other part of the side wall
projecting from, and being spring deflectable relative, the
flange.
Each of said other side parts can have a free
end formed with an inwardly projecting lug, preferably ramp-shaped.
Both the web and the flange of each shield side can be inclined
relative to the plane of the cap.
The shield can be moulded in ABS plastic.
We would now refer the reader to the attached
pictures in which Figures 1 to 3 are respectively a plan view,
a vertical section and a horizontal section of one embodiment
of shield, Figure 4 is a perspective view of a circuit board
supporting a shield-transformer assembly with a part of the
shield cut away to illustrate the positional relationship of the
shield to the transformer; and Figure 5 is a perspective view
of the shield with part cut away.
Referring in detail to Figure 4 and 5 only, there
is shown part of a board 1. On its top surface are mounted
electrical components - transformer 2, resistor 3 and terminal
posts 4, for example, and on its bottom surface are solder
interconnections (not shown) to establish an electrical circuit
including the components. The transformer is conventionally
formed by winding primary and secondary coils of enamel coated
copper wire of 34 gauge onto a bobbin having a central former 5
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and outer flanges 6 and 7, the flanges being square. Mounted on
the board 1 is a stack of laminations 8 of rectangular configuration;
the laminations have a cross span 9 of cuboid form. As can be
seen in the drawings input and output lengths 12 of transformer
wire extend from the coils to terminals 10 formed at the upper
ends of stakes 11 which are connected into the electrical circuit
by the solder interconnections.
Demountably mounted on the transformer is a
shield 13 moulded in ABS plastics. The shield has a rectangular
cap 14 dimensioned to fit closely over cross span 9. Projecting
outwardly, and then downwardly, from two opposite edges of the cap
are shield sides ~each having a web 16, a side wall 17, a
free-standing columnar projection 18 and an inclined flange 19.
Webs 16 extend a top face of the cap 14 to the width of flange 7.
Side walls 17 contact the edge o~ flange 7 and screen a major
part of the transformer wire on two sides, a major part of the
transformer wire on the other two sides being screened by the
laminations 8.
On assembly, the inclined flange 19 integral with
the bottom edge of each side wall 17, co~ers the input and output
transformer wire lengths 12. Each projection 18 lies in the
plane of its neighbouring side wall 17 and extends upwardly from
one end of respective flanges 19, the two projections 18 being at
diametrically opposite sides of a shield. When in place, an upper
tip of each projection 18 locates under and hard by a corner of the
flange 7, projecting from an inner surFace of the tip is a ramp 20.
To attach the shield 13, it is hand guided to a
horizontal orientation resembling that of Figure 4 and then pressed
downwardly into place over the transformer 2. The ramps 20 initially
function as camming surfaces to deflect the tips of projections 18
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outwardly. This allows the shield to be pushed down at a position
determined by the fit of cross span 9 in cap 14. Then, when the
shield is in place, the natural resilience of the projections 18
restores the tips to their rest position under the flange 7; in
this position they function to lock the shield against inadvertent
removal.
In order, deliberately, to detach the shield, for
example, during repair, the repairer hooks a thumb tip between the
laminations 8 and the most accessible projection 18 and outwardly
deflects the projection to release it from its locking engagement
with the flange 7. As the ramp 20 is released, the cap 14 lifts
slightly away from the cross span 9 to allow the shield to be
easily manipulated to release the other ramp 20. In fact, we have
determined that in the embodiment illustrated, sufficient spring
energy is stored in the shield as one projection 18 is being
released, that the shield 13 recoils completely from the transformer
2.
In an alternative embodiment, (not shown) the
columnar projection 18 is integral with its neighbouring sidewall
17 and the whole side is torsionally flexed as the shield is
pressed down onto the transformer.
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