Safety switch, in particular for household electrical appliances

Abstract: The described safety switch, in particular for household appliances and the like, comprises at least one pair of fixed contacts (3), at least one movable contact (4) adapted to selectively establish and interrupt an electric continuity between the fixed contacts (3), and disengagement means (9) interlocked to a drive signal from an auxiliary circuit and adapted to selectively intervene so as to release an operation push-button (6) from the operative position in which the movable contact (4) closes the fixed contacts (3).

Description: The present invention relates to a safety switch, in particular for household electrical appliances and the like, of the type. According to the preamble of claim 1, as known from DE-A-2 917 088. More particularly, the invention applied 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. 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. 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. 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. 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. 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. 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 maintenante 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. Practically, in all the above cases the switches directly abolied 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. It is also known from DE-A-2917088 an electrical switch having common drive means for shifting a movable contact from an opening position , in which an electrical discontinuity exists between the fixed contacts, to a closing position in which there is an electrical continuity. More precisely such drive means make use of a cam profile to allow the usual displacement of the contacts. This switch also comprises safety means which can shift the movable contact from the closing position to the opening position in an automatic way. Such safety means comprise a rigid retention element, composed of a rod intergral to a curved support body, hinged to the base body. The rod is adapted to hold the movable contact in the closing position against the action of a spring, allowing the usual working of the switch. In order to maintain the position of the rigid retention element with respect to the base body, the safety means comprise also an anchoring element and a spring both fixed to the base body itself and active on the curved support body, The spring forces the rigid retention element against the anchoring element in order to position the rod. In case of danger a drive signal moves disengagement means which intervene pushing the rigid retention element and over-running the action of said elastic spring. In this situation an end portion of the rod moves in the cam profile along its usual way till a position in which there is no more the holding of the switch button, so to have a trip. When the drive signal stops, the disengagement means come back to the original position and the elastic spring, acting on the curved body, return back the rod to its initial position. In this configuration the electrical switch is ready to be used again. 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. 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. The technical task mentioned is substantially achieved by a safety switch as described in claim 1. 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. Referring to the drawings, the safety switch according to the invention is generally identified by reference numeral 1. 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. Housed in the base body 2 is at least one moveable 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. 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. 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 pushbutton 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. 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. 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. 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. 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. The invention achieves important advantages. 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 from a component of any type for meeting the most various requirements. 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. 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. 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.

Claims: 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), said retention element comprising one end portion (8a) slidable within a cam profile (6a) formed in the operation push-button (6) 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, characterized in that said disengagement means intervene on said retention element for pushing and flexing it according to a direction which is parallel to the longitudinal development of the first end portion (8a) of the retention element itself. 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. 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).

Inventors: GALLONE FLAVIO, GALLONE, FLAVIO
Applicants: SIGNAL LUX SPA, SIGNAL LUX S.P.A.
Application year: 1995
Main classification: H01H13
IPC codes: H01H13, H01H61