Note: Descriptions are shown in the official language in which they were submitted.
8198
" m ermally or Mechanically A~tuated 5nap Astion
pe Electric Switch"
This invention relates to electric switches incorporating a snap-act-
ing actuator comprising a stressed disc, sheet or strip of resilient sheet mate-
rial (termed an actuator blade) mc~able with a snap-ac~ion between two configura-
tions to control the making and breaking of the switch cont~cts, and a latching
member which when the actuator bl~d~ has snap-acted in one sense to break or
make the switch contacts restrains return movement of a movable contact carrying
member to prevent re-making or re-breaking of the contacts i.e. the resetting of
the switch until said latching member is positively displaced to Fermit return
mcvement of the movable contact carrying member. Such switches will hereinafter
be termed "switches of the kind described". The disc, sheet or strip of resil-
ient material may be made of bimetallic material to provide a thermally-respon-
sive switch or it may be made of suitable spring metal in which case the switch
will be mechanically actuatable. The actuator blade itself may cc)nstitute the
movable contact carrying member, or alternatively, the actuator blade may act
upon a c~ntact carrying or controlling strip of resilient sheet material to make
or break the cantacts.
mermally-responsive switches of the kind described find widespread
use in many areas of technology, particularly for protecting apparatus and
applianoes, such as electric motors or heaters, against c)verheating. The latch-
ing me~ber prevents the occurrenoe of a cycling behaviour in that the switch re-
quires to be reset before any further operation of the apparatus or applianoe
can take pla oe. Otherwise the actuator blade would simply snap back into its
original config~ration only to snap act yet again on further cverheating
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~8~98
and perform cycles indefinitely.
Switches of the kind described are disclosed in United Kingdom Speci-
fication No. 1036127 wherein the latching member is in the form of a spring arm
extending transversely with respect to the actuator blade and movable trans-
versely to the plane of movement of the blade between its latching and unlat-
ching positions. To displace the latching member and reset the switch requires
a movement of the resetting member again transversely to the plane of movement
of the actuator blade. If this resetting member were to be disposed close to
the blade or contacts it would interfere with the operation of the actuator or
the switch terminals, so it was disposed in a location spaced from the actuator.
This however resulted in an undesirable increase in the overall size of the
switch.
A further disadvantage of these known switches is that a substantial
amount of movement of the actuator blade was required in order to release the
latching member to spring into its latching position. This caused manufacturing
difficulties since it needed to be ensured that actuator blades produced all
possessed a sufficient amount of deflection to release the latching member.
It is an object of the invention to provide a switch of the kind des-
cribed which does not have these disadvantages.
According to the invention there is provided an electric switch incor-
porating a snap-acting actuator comprising a stressed member of resilient
sheet material movable with a snap-action between two configurations to control
the making and breaking of the switch contacts, and a latching member which
would if the actuator member has snap-acted in one sense to break or make the
switch contacts restrain return movement of a movable contact carrying member
to prevent re-making or re-breaking of the contacts until said latching member
is positively displaced to permit return movement of the movable contact member,
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~48198
wherein the latching member comprises a spring member having an arm extending
generally transversely to the general plane of the actuator member, said arm
defining an engaging portion for restraining return movement of the movable
contact carrying member, said spring member also having an operating portion
connected with said arm at an angle thereto and extending generally parallel to
said actuator member, said operating portion being movable in a direction
generally transverse to the general plane of the actuator member to cause move-
ment of said engaging portion of said arm in a direction generally parallel to
the general plane of said actuator member to permit return movement of said
movable contact carrying member.
The engaging portion of the arm may engage the actuator member or blade
or the contact carrying member where that member is separate from the actuator
blade.
Thus the movement of the operating portion necessary for resetting the
switch is in the direction of movement of the movable contact carrying member
rather than transversely thereto and the difficulties mentioned earlier do not
arise. Furthermore the operating portion and the engaging portion are inte-
grally combined in a single spring member which is a substantial improvement
in terms of manufacturing cost over previous switches where two or more compon-
ents were provided to perform the same function.
Preferably the spring member is a spring strip and the operating por-
tion is preferably bowed. Thus deflection of the central part of the operating
portion causes the arm to pivot and the engaging portion to move in a direction
substantially parallel to the general planes of the actuator blade and operatingportion. The amount of bowing of the operating portion will preferably be such
that a slight deflection of the operating portion causes a fairly substantial
movement of the engaging portion.
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~48198
A particularly convenient mounting of the spring member to the body of
the switch is effected if the spring member is substantially U-shaped, i.e.,
the angled shape mentioned above with a further arm. In this way a wrap-around
engagement of the spring member with the switch body may be obtained and the
spring member can be mounted in position by means ôf its resilient engagement
with the switch body.
In a preferred embodiment in which the engaging portion engages the
actuator blade and in order to
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~8198
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remove the point(s) of action of the engaging portion
away from the main body of the blade, the latter
is formed with an extension tab adapted to be engaged
by the engaging portion.
S In a preferred embodiment, the engaging portion
of the arm of the spring member can comprise a bifurcated
end of a spring strip which may bear against the
actuator blade at two spaced locations in the latched
postion. This feature enables the tolerances in
the pressed end part of the spring strip to be increased
as the spaced abutments thereby formed accurately
determine the latched position of the blade by preventing
excessive travel of the engaging portion transversely
to the plane of movement of the actuator blade.
The bifurcations may for example comprise two
spaced ears forme2 at the end of the engaging portion
of the spring strip. The ears may be bent out of
the general plane of the arm towards the main body
of the blade so as to prevent excessive movement
of the blade thus decreasing fatigue of the blade
and increasing the operating life of the blade.
As an alternative to the end of the spring
strip being bifurcated, the arm of the spring may
have a slot therein, an extension tab of the actuator
blade entering the slot in the latched position.
The tab then rests against one edge of the slot in
the latched position, an opposite edge of the slot
serving to prevent excessive movement of the blade.
In order that the invention may be readily
understood two embodiments thereof will now be described
by way of example with reference to the accompanying
drawings in which:-
Fig. 1 shows a longitudinal section through
a switch according to the invention,
Fig. 2 is a plan view of the switch of Fig. 1,
Fig. 3 is a plan view of a second embodiment
of a switch according to the invention, and
Fig. 4 is a section through the embodiment
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~8198
of Fig. 3.
In Fig. 1 there is shown a moulded plastics
switch body 1 having terminals 2, 14 extending therefrom.
One terminal 2 is connected to a switch contact 3
and the other terminal 14 is connected to the tongue
4 of a movable contact carrying member in the form
of a known snap acting bimetallic actuator blade
22 which is mounted by means of the said tongue to
the switch body 1. The bridge portion 5 of the actuator
blade carries a movable contact 6.
A latching spring member in the form of a U-
shaped copper alloy spring strip 7 is sprung around
and then engaged to the switch body 1. The left
hand arm 8 is formed with a flange 9 which engages
lS about a shoulder on the switch body and serves to
retain the spring strip on the body. The right hand
arm or actuator blade engaging portion l0 is formed
with a bifurcated actuator blade engaging end 11,
and is resiliently biased in an anti clockwise direction
to engage the actuator blade. The bridge or operating
portion 12 of the U-shaped spring member is slightly
bowed and it will be seen that upward pressure on
this operating part will cause arm 10 to pivot clockwise
(Fig. 1) and the end 11 will withdraw from the blade.
From Fig. 2 will be seen the extension tab
13 on the blade against which the end of the arm
10 engages, the arm 10 therefore being well spaced
from contacts 3, 6. The tab 13 includes a narrow
end portion 15 having a shoulder 16 on each side
thereof. In the latched position of the switch,
the portion 15 enters the gap between ears 17 of
the bifurcated portion 11, and the shoulders 16 bear
against the ears 17, thus preventing further anti-
clockwise movement of the arm 10.
On reaching a predetermined temperature the
blade snaps throug~ to open the contacts 3, 6 and
this raising of the bridge portion 5 causes the arm
10 to deflect under its own resilience in an anti-
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clockwise direction and the portion 15 to engage
the gap between the ears 17 and restrain the blade
from snapping through to its original configuration
on a drop in temperature.
To reset the blade, upward pressure is applied
to bowed portion 12, causing the end 11 of arm 10
to move substantially parallel to the general plane
of the blade and allow the latter to remake the contacts
3, 6. This pressure can be applied by a simple button,
by rotation of a coarsely threaded member, or lateral
movement of a wedge or otherwise.
In a modified embodiment, the bifurcated end
11 of the arm 10 comprises two ears which are bent
out of the plane of arm 10 towards the main body
lS of the blade, i.e. ta the left as seen in Fig. 1.
When the blade snap acts to open the contacts, excessive
travel of the actuator blade is prevented by engagement
with the ears.
The embodiment of Figs 3 and 4 is similar to
that of Figs. 1 and 2 and identical parts have been
given the same reference numerals. The features
common to the two embodiments will not be further
described.
In place of the bifurcated end 11 of the arm
10, the spring strip 7 has a rectangular slot 18
therethrough which the portion 15 of the tab 13 enters
in the latched position of the switch. Thus, when
the bimetallic actuator moves to break the contacts
3, 6, the portion 15 enters the slot 18 and further
movement of the actuator is prevented by engagement
of the portion 15 with the edge of the slot 18 which
is shown as being uppermost in Fig. 4. Excessive
actuator movement resulting in fatigue of the actuator
is thus prevented. This feature can be enhanced
by deformation of the portion of the arm 10 above
the slot 18 towards the main body of the blade.
When the blade attempts to remake the contacts 3,
6, for example upon cooling, this is prevented by
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engagement of the portion 15 with the edge of the
slot which is shown as being lowermost in Fig. 4.
In addition, the embodiment of Figs. 3 and
~ shows a reset slide member 19. The slide member
19 is biassed leftwardly as shown in the Figures
by means of a coil spring 20. The member 19 includes
a cam portion 21. When the slide member 19 is pushed
rightwardly as shown in the Figures into the position
indicated by broken lines in Fig. 4, against the
force of the spring 20, the cam portion 21 exerts
an upwardly directed force against the bowed portion
12 of the spring member 7, thus rotating the arm
10 of the spring member 7 in the anti-clockwise direction
as shown in Fig. 4, thus allowing the actuator to
make the contacts 3, 6. Once this has been done,
and the member 19 is released, it returns to the
illustrated position under the force of the spring
20.
