[0001] The present invention relates to a safety switch, in particular for household electrical
appliances and the like, of the type comprising a base body made of an electrically
insulating material, at least one pair of fixed contacts rigidly fastened to the base
body, at least one movable contact adapted to selectively establish and interrupt
an electric continuity between said fixed contacts, and drive means for shifting the
movable contact from an opening position in which there is an electrical discontinuity
between the fixed contacts, to a closing position in which an electrical continuity
exists between said fixed contacts, said drive means comprising at least one operation
push-button and one retention element adapted to hold the push-button to an operative
position corresponding to said contact closing position, against the action of return
spring means.
[0002] More particularly, the invention applies to switches, double-throw switches, changeover
switches and similar components having a relatively reduced bulkiness, of the type
generally used in AC-operated household appliances and the like with values until
16 A and 250 V.
[0003] It is known that switches of the above type are usually comprised of a box-shaped
base body and a pair of fixed contacts integral with said body and adapted to be connected
to respective poles of the electric circuit with which the switch is to be associated.
[0004] Housed in the base body is at least one movable contact provided with operative portions
enabling the electric continuity between the fixed contacts to be selectively established
and interrupted, depending on the respective opening or closing position taken by
the movable contact.
[0005] Shifting of the movable contact between said positions is carried out by drive means
of the conventional type, known per se. Usually, this drive means comprises at least
one operation push-button axially movable against the action of a return spring, and
one flexible retention element or retention spring anchored to the inside of the base
body. The flexible retention element is adapted either to hold the push-button, after
a thrust-and-release action exerted thereon, to an operative position corresponding
to the closing position of the movable contact or to release said push-button upon
the action of the return spring, on the occasion of a new thrust- and-release intervention,
in order to bring the movable contact to an opening position.
[0006] Known switches briefly described above work as cut-out switches in order to complete
and interrupt the electric circuits with which they are associated, only if a manual
operation of same occurs.
[0007] It is also known that, in particular in household appliances, many devices are present
such as pressure switches, thermostats, timers, which are connected to auxiliary circuits
in turn operatively connected to components of said appliances. In no case these devices
act on the cut-out switch of the concerned appliances and therefore, at the end of
an operating cycle controlled by a timer or a programmer for example, said appliances
are still alive.
[0008] If electric leakages occur due to an insulation fault or equipment failure, according
to the known art the intervention of commonly used safety circuit breakers is provided,
which generally cut off the electric supply to the whole installation to which an
apparatus is connected and therefore do not enable detection of which point of the
installation and/or which apparatus has caused a particular current leakage. To solve
this problem, the European Patent Application No. 0 636 893 discloses and claims a
circuit device for displaying leakage currents and capable of identifying without
the intervention of a safety circuit breaker where anomalous current absorptions lower
than a safety threshold occur, both for prevention purposes and for carrying out an
efficient maintenance activity. This circuit device, while being very useful for receiving
precise selective information on the functionality state of installations and apparatus,
has an inherent limit, in that the furnished visual indications can be only used by
an individual and do not cause the automatic intervention of any switch or similar
component.
[0009] Practically, in all the above cases the switches directly applied to household appliances
are exclusively operable by means of manual interventions, whereas the known safety
switches are at the outside of the apparatus and, in addition to being rather bulky,
only work when overcurrents or anomalous leakage currents occur.
[0010] Therefore, in the known art it is still unsolved the technical problem concerning
the availability of a particular switch for household appliances operating under the
normal line voltage and having a compact structure, that is of reduced bulkiness,
which is capable of interrupting the electric continuity between the fixed contacts
provided therein, in connection with precise operating requirements of the apparatus
with which it is associated.
[0011] The technical task of the present invention is substantially to solve the above technical
problem and in particular to provide a safety switch the opening of which, for isolating
an apparatus from the power line supply for example, can be independent of the current
passing therethrough and is subjected to the occurrence of given events previously
established during the design step.
[0012] The technical task mentioned is substantially achieved by a safety switch which is
characterized in that it comprises disengagement means interlocked to a drive signal
from an auxiliary circuit and adapted to selectively intervene on said retention element
so as to release the push-button from said operative position and bring the movable
contact back to said opening position.
[0013] The description of a preferred embodiment of a safety switch according to the invention
is given hereinafter by way of non-limiting example with reference to the accompanying
drawings, in which:
- Fig. 1 is a partially exploded perspective view in split of the safety device according
to the invention;
- Fig. 2 is a longitudinal sectional view of the switch shown in Fig. 1 in an assembled
condition.
[0014] Referring to the drawings, the safety switch according to the invention is generally
identified by reference numeral 1.
[0015] It comprises a box-shaped base body 2 made of an electrically insulating material,
inside which at least two fixed contacts 3 are rigidly secured for connection to the
poles of an electric circuit with which the switch 1 will be associated.
[0016] Housed in the base body 2 is at least one movable contact 4, adapted to selectively
establish an electric continuity or discontinuity between the respective fixed contacts
3, and drive means 5 adapted to shift the movable contact between an opening position
in which the fixed contacts 3 are electrically disconnected, and a closing position
in which an electric continuity exists between the fixed contacts.
[0017] More particularly, the drive means 5 comprises, in a manner known per se, an operation
push-button 6 axially movable against the action of one return spring 7 or equivalent
means and a flexible retention element or retention spring 8 having one end portion
8a slidably guided in a cam profile 6a formed in one side of the operation push-button
6. The cam profile 6a is such shaped that, after a first thrust-and-release intervention
of the push-button 6, said push-button is held to an operative position in which the
movable contact 4 is in a closing position on the fixed contacts 3. Following a new
thrust-and-release intervention of the operation push-button 6, the retention element
8 frees the push-button movement so that the return spring 7 acting thereon will bring
the movable contact 4 to an opening position.
[0018] In an original manner, the switch 1 is comprised of disengagement means 9 adapted
to selectively act on the retention element 8 in order to disengage the push-button
6 from its operative position corresponding to the closing position of the movable
contact 4 and therefore bring said movable contact to the opening position.
[0019] In more detail, the disengagement means 9 comprises a suitably shaped bimetallic
element 10, having an active end 10a in contact with an intermediate portion 8b of
the retention element 8 included between the first end portion 8a and a second anchoring
end portion 8c fitted in the base body 2.
[0020] The bimetallic element 10 has an engagement end 10b integral with the base body 2
and can be thermally deformed so that the active end 10a pushes and flexes the retention
element 8 in order to disengage the push-button 6 from the operative position in which
the electric continuity between the fixed contacts 3 is established by said movable
contact 4.
[0021] The thermal deformation of the bimetallic element 10 is imposed by at least one resistor
11 put into contact with appropriate loops, the shape of which matches that of the
resistor, of a major portion 10c of the bimetallic element 10.
[0022] Activation of the resistor 1 is interlocked to a drive signal coming from any auxiliary
circuit and for example emitted by an electronic control unit. Practically, passage
of current through the resistor 1 and therefore release of the push-button 6 is a
function of the drive signal that can be sent by the operating components of apparatus
such as pressure switches, pressostats, timers, and leakage current detectors.
[0023] The invention achieves important advantages.
[0024] In fact, the safety switch in reference, through the use of simple structural elements
of a low price and reduced bulkiness, can be brought to the opening position by a
signal coming front a component of any type for meeting the most various requirements.
[0025] For example, it can be easily connected to a device for detecting and/or displaying
leakage currents, like the one described in said European Patent Application No. 0
636 893, so as to cause the complete and timely disconnection of the power line from
the corresponding apparatus in the case that, for any reason, an anomalous current
leakage higher than a predetermined threshold should occur inside said apparatus.
If the intervention threshold is set to a lower value than the intervention threshold
of usual safety circuit breakers, a double advantage is achieved, i.e. the presence
of an anomaly is immediately found in the concerned apparatus, and, on the other hand,
this anomaly does not cause the complete disconnection of the power line by the safety
circuit breaker.
[0026] Still by way of example, if the switch in reference is combined with a timer installed
on a coffee-making appliance, a washing machine, a boiler for steam production or
others, disconnection of the appliance from the power line can be achieved after a
given period of time, in order to prevent said appliance from being in operation for
several hours due to a lapse of memory on the part of the user.
[0027] The switch may also be interlocked to an electric signal produced by pressure switches,
thermostats or other detecting devices in order to carry out an immediate disconnection
of the apparatus, on the occurrence of any anomaly.
1. A safety switch, in particular for household electrical appliances and the like, comprising:
- a base body (2) made of electrically insulating material,
- at least one pair of fixed contacts (3) rigidly fastened to the base body (2),
- at least one movable contact (4) adapted to selectively establish and interrupt
an electric continuity between said fixed contacts (3), and
- drive means (5) for shifting the movable contact (4) from an opening position in
which there is an electrical discontinuity between the fixed contacts (3), to a closing
position in which an electrical continuity exists between said fixed contacts (3),
said drive means (5) comprising at least one operation push-button (6) and one retention
element (8) adapted to hold the push-button (6) to an operative position corresponding
to said contact closing position, against the action of return spring means (7), characterized
in that it comprises disengagement means (9) interlocked to a drive signal from an
auxiliary circuit and adapted to selectively intervene on said retention element (8)
so as to release the push-button (6) from said operative position and bring the movable
contact (4) back to said opening position.
2. A switch according to claim 1, characterized in that said disengagement means (9)
comprises:
- at least one bimetallic element (10) having an active end (10a) substantially in
contact with said retention element (8), and
- at least one resistor (11) put into contact with a major portion (8b) of said bimetallic
element (8) and susceptible of being energized by said drive signal.
3. A switch according to claim 2, characterized in that said retention element (8) is
defined by a flexible element comprising:
- one end portion (8a) slidable within a cam profile (6a) formed in the operation
push-button (6), a second anchoring end portion (8c) fitted to said base body (2),
and an intermediate portion (8b) put into contact with the active end (10a) of said
bimetallic element (10).