ITTO20130259A1 - APPLIANCES WITH SAFETY CIRCUIT - Google Patents

Description

â € œ HOUSEHOLD APPLIANCES WITH SAFETY CIRCUITâ €

DESCRIPTION

[FIELD OF TECHNIQUE]

The present invention relates to a household appliance with a safety circuit.

[ART NOTE]

As is known, household appliances are internally equipped with one or more electrical loads which are suitably powered in order to contribute to the execution of the functions for which the appliance itself is responsible.

By way of example, the heating resistors present in dishwashers and washing machines, which have the task of heating the water used for the washing cycles, can be considered.

Typically such resistors comprise an internal metallic filament, an intermediate coating of electrically insulating material, and an external coating of metallic material. The metal jacket is grounded.

A possible failure of the aforementioned heating resistors occurs when, following a puncture / tearing / breaking of the intermediate coating, the internal filament comes into contact with the external metallic coating. In this circumstance, when the resistor is powered to perform its heating function, the current flowing through the metal filament is entirely dispersed to earth through the aforementioned earth connection.

This can lead to uncontrolled heating of the component, leading to a fire.

According to the state of the art, if the equipment is powered by a network built and maintained according to the safety standards envisaged, a circumstance such as the one briefly described above should be avoided by the security system which is part of the network itself which, following a differential detection on the phase and neutral lines, it recognizes the onset of a dangerous situation and cuts off the power supply to the appliance.

However, there are situations in which, for the most diverse reasons, this safety system does not intervene, or is completely absent.

The known art therefore also provides additional safety systems, mounted directly on board the household appliances.

These additional safety systems are also based on phase-neutral differential detections.

The Applicant has noted that the safety systems which provide a differential type detection are characterized by evident operating drawbacks.

First of all, this type of detection requires the reading of the current flowing in two conductors, so that two detection elements or a single detection element (typically comprising a toroid of ferromagnetic material) of particularly significant dimensions must be used. This clearly increases both the complexity and the costs of creating safety systems of this type, as well as introducing positioning constraints by virtue of the dimensions that the detection element necessarily assumes.

Furthermore, in the case of a single sensing element, the need to be associated with the two phase and neutral conductors places constraints on its positioning, typically being able to be positioned only on the power input of the appliance, thereby creating considerable entity in the design and construction phase of the equipment.

[OBJECTIVES AND SUMMARY OF THE INVENTION]

The aim of the present invention is therefore to provide a household appliance with a safety circuit which allows the drawbacks highlighted above to be overcome.

In particular, the purpose of the invention is to provide a household appliance equipped with an additional safety system with respect to that which the power supply network should be equipped with.

Another object of the invention is to provide a household appliance equipped with an additional safety system that is simple to make.

A further object is to make available a household appliance equipped with a safety system that does not impose particularly stringent constraints, both in the design and construction phases, in terms of flexibility in the positioning of the electrical / electronic components.

These and other purposes are substantially achieved by a household appliance with safety circuit according to what is described in the attached claims.

In particular, according to a first aspect, the subject of the present invention is a household appliance with safety circuit, comprising at least one electric load connected to an electric power supply network, said at least one electric load being associated with an earth connection branch, said appliance also including a safety circuit equipped with:

- a detection element associated with said branch and configured to detect a leakage current flowing in said branch;

- a comparison module configured to compare said leakage current with a preset threshold;

wherein said comparison module is further configured to disconnect said at least one electrical load from said power supply network if said leakage current is greater than said preset threshold.

Preferably, said comparison module is configured to disconnect said at least one electrical load from both a phase line and a neutral line of said power supply network.

Preferably, said household appliance is provided with at least two connection terminals configured to be connected to the phase line and to the neutral line of said power supply network.

Preferably, said at least one electrical load has a first connection via a first switch to one of said connection terminals, and a second connection to the other connection terminal via a second switch.

Preferably, said comparison module is configured to open said first and second circuit breakers if said leakage current is greater than said preset threshold.

Preferably, said at least one electrical load comprises a heating resistor for heating washing water used by said household appliance in at least one washing cycle.

Preferably, said heating resistor comprises an internal metallic filament, an intermediate coating made of electrically insulating material, and an external coating made of metallic material.

Preferably, the earth connection branch of said at least one electrical load is a connection between said outer covering and earth.

Preferably, said at least one electrical load is a plurality of electrical loads, each having a first connection through a respective main switch to one of said connection terminals, and a second connection to the other connection terminal.

Preferably, the second connections of said electrical loads are connected to the respective terminal of said household appliance by means of a common switch.

Preferably, said comparison module is configured to open said main switches and said common switch if said leakage current is greater than said preset threshold.

Preferably, each electrical load has a connection to said ground connection branch.

According to another aspect, the subject of the present invention is a filter for the suppression of electrical disturbances, suitable for use in said household appliance, said filter comprising:

- a first capacitor connected between the connection terminals of said household appliance and suitable for filtering differential mode disturbances;

- a second capacitor and a third capacitor respectively connected between a respective of said connection terminals and an earth node, said second and third capacitors being suitable for filtering disturbances towards earth;

- a detection element associated with an earth connection branch afferent to said earth node, said detection element being configured to detect a leakage current flowing in said branch, said detection element being able to cooperate with a detection module comparison of said household appliance.

According to a further aspect, the object of the present invention is a safety circuit suitable for use in said household appliance.

[BRIEF DESCRIPTION OF THE DRAWINGS]

Some preferred and advantageous embodiments are described by way of non-limiting example, with reference to the attached figures, in which:

- figure 1 shows the block diagram of a first embodiment of a household appliance with safety circuit according to the present invention, in which some parts have been eliminated to better highlight others;

- figure 2 shows the block diagram of a second embodiment of a household appliance with safety circuit according to the present invention, in which some parts have been eliminated to better highlight others;

Figure 3 shows the block diagram of a variant of the embodiment of Figure 2.

[DETAILED DESCRIPTION OF THE INVENTION]

With reference to the accompanying figures, the reference numeral 1 generally indicates a household appliance with safety circuit according to the present invention.

By way of example, the appliance 1 can be a dishwasher or a washing machine.

In general, household appliance 1 is a household appliance in which, for regulatory and / or safety reasons, at least one electrical load is earthed.

Going into greater detail, the household appliance 1 comprises at least one electrical load L1-Ln.

Figure 1 shows an embodiment in which only one electrical load L1 is provided (consisting, as will become clearer in the following, by a heating resistor R).

Figure 2 instead shows an embodiment in which different electrical loads L1-Ln are present.

By way of example, the electrical load L1 of the embodiment of Figure 1 can be one of the electrical loads of the embodiment of Figure 2.

As mentioned, the at least one electrical load L1-Ln is associated with an earth connection branch 10.

In the embodiment of Figure 1, the branch 10 consists of a connection between the electrical load L1 and earth.

In the embodiment of figure 2, the branch 10 is a branch to which connections Y1-Yn direct to earth and coming from each electric load L1-Ln belong.

In particular, the ground connection branch 10 and / or the connections Y1-Yn have one end in contact with a metal part of the at least one electrical load L1-Ln.

In accordance with the invention, the household appliance 1 is equipped with a safety circuit 20.

The safety circuit 20 has the task of disconnecting the at least one electrical load L1-Ln from the power supply network in the event that a leakage current flowing in the branch 10 exceeds a certain threshold.

More particularly, the safety circuit 20 comprises a detection element 30 associated with the ground connection branch 10 and configured to detect a leakage current I flowing therein.

By way of example, the sensing element 30 can be an amperometric transformer or a shunt resistor.

In Figures 1 and 2 the detection element 30 is schematically represented as a toroidal element arranged around the branch 10.

The safety circuit 20 further comprises a comparison module 40 for comparing the leakage current I detected by the detection element 30 with a predetermined threshold.

The preset threshold can be defined both in hardware mode, that is by setting a reference voltage through suitable circuit elements dimensioned in an opportune way, and in software mode, that is by programming a threshold value in a microprocessor that implements said comparison module.

In greater detail, imagining to use an amperometric transformer, equipped with a primary winding associated with the toroid and a secondary winding, the resolution of the measurement can be defined by the number of turns of the secondary.

The maximum measurable flow rate instead depends on the toroid; in particular, the limit is given by the saturation of the torus itself. Advantageously, the saturation limit of the toroid is greater than the predetermined intervention threshold which is set in the comparison module 40.

The pre-established threshold represents a limit value beyond which there is a concrete danger that a fire could start.

By way of example, the preset threshold can be between 250 mA and 3A.

Therefore, in the event that the leakage current I exceeds the predetermined threshold, the comparison module 40 disconnects the at least one electrical load L1-Ln from the power supply network.

In particular, the comparison module disconnects at least one load L1-Ln both from a phase line P and from a neutral line N of the power supply network. In this way a protection with so-called â € œbipolarâ € disconnection is realized.

Preferably the household appliance 1 has at least two connection terminals T1, T2 configured to be connected to the phase line P and to the neutral line N of the power supply network. The terminals T1, T2 can be part of or included in an electric plug 50, connectable to a socket connected to a power supply network.

An input filter F is associated with the two connection terminals T1, T2 (figures 2, 3), which will be better described later.

As schematically shown in figure 1, the electrical load L1 has a first connection C1 which, through a first switch S1, connects the electrical load L1 itself to one of the two terminals T1, T2, and a second connection C2 which, through a second switch S2, connects the electrical load L1 to the other terminal.

When the comparison module 40 intervenes to disconnect the electrical load L1 from the electrical network, it advantageously opens both the first switch S1 and the second switch S2, so as to implement the aforementioned bipolar disconnection.

As mentioned above, the electrical load L1 schematically represented in figure 1 can be a heating resistor R, used by the household appliance 1 to heat the water used in one or more washing cycles.

In a preferred embodiment, the heating resistor R comprises an internal metallic filament R1, an intermediate coating R2 of electrically insulating material, and an external coating R3 of metallic material.

When, for some reason, the internal metal filament R1 comes into contact with the external coating R3, for example due to a break, a tear and / or a puncture of the intermediate coating R2, a leakage current I of considerable flow flows through the branch 10. entity (for example greater than 250 mA) and, following the reading performed by the sensing element 30, the comparison module 40 intervenes by disconnecting the electrical load L1.

As said, in the embodiment of figure 1, the branch 10 associated with the electrical load L1 is a connection between the external covering R3 and earth.

With reference to the embodiment schematically illustrated in Figure 2, the household appliance 1 comprises a plurality of electrical loads L1-Ln.

By way of example, the electrical loads L1-Ln can comprise a heating resistor R (as in the embodiment of Figure 1), an electric motor forming part of the household appliance 1, etc.

In general, L1-Ln loads are electrical loads that have at least one metal part connected to earth.

In the above example of an electric motor, the metal part connected to earth is represented by the group of metal laminations forming part of the stator.

Preferably, each electrical load L1-Ln is connected to the ground connection branch 10 through a respective connection Y1-Yn.

The ground connections Y1-Yn of all the electrical loads L1-Ln therefore belong to the ground connection branch 10.

Preferably each electrical load L1-Ln has a first connection X1-Xn, through a respective main switch MS1-MSn, to one of the connection terminals T1, T2, and a second connection Z1-Zn to the other connection terminal.

Preferably the second connections Z1-Zn of the electrical loads L1-Ln are connected to the respective terminal T1, T2 of the household appliance 1 by means of a common switch SX.

By way of example, figure 2 shows that the first connections X1-Xn of the loads L1-Ln refer to the second terminal T2, through the main switches MS1-MSn, while the second connections Z1-Zn refer to the first terminal T1 through the SX common switch.

When the comparison module 40 determines that the leakage current I flowing in branch 10 is greater than the predetermined threshold, then it opens both the main switches MS1-MSn and the common switch SX.

As mentioned above, the household appliance 1 is advantageously provided with a filter F (figures 2, 3).

Filter F is a so-called â € œmachine filterâ €, that is, a filter dedicated to the suppression of disturbances entering the appliance from the electrical network, and of disturbances injected into the electrical network by the appliance itself.

Filter F preferably comprises a first class â € œXâ € capacitor C1 connected between the two connection terminals T1, T2.

The first capacitor C1 has the task of eliminating differential mode disturbances.

The filter F preferably comprises a second capacitor C2 and a third capacitor C3, both in class â € œYâ €, respectively connected between the connection terminal T1 and earth, and between the connection terminal T2 and earth.

The second and third capacitors C2, C3 have the task of suppressing ground disturbances.

In the variant of figure 3, the sensing element 30 is integrated in the filter F.

In particular, in the variant of figure 3, the connections Y1-Yn coming from the electric loads L1-Ln refer to the earth node N, to which the second and third capacitors C2, C3 are also connected; from the ground node N then develops the ground connection branch 10 on which the detection element 30 operates.

The invention achieves important advantages.

First of all, the household appliance according to the invention is equipped with an additional safety with respect to the system that each power supply network should provide.

Furthermore, the safety circuit present in the household appliance according to the invention is simple and economical to produce.

In addition to the above, the safety circuit can be mounted inside the appliance according to the invention with extreme flexibility, particularly with reference to the arrangement of the sensing element.

Claims (14)

CLAIMS 1. Household appliance with safety circuit, comprising at least one electric load (L1-Ln) connected to an electric power supply network, said at least one electric load (L1-Ln) being associated with an earth connection branch (10), called household appliance (1) further comprising a safety circuit (20) provided with: - a detection element (30) associated with said branch (10) and configured to detect a leakage current (I) flowing in said branch (10); - a comparison module (40) configured to compare said leakage current (I) with a preset threshold; wherein said comparison module (40) is further configured to disconnect said at least one electrical load (L1-Ln) from said power supply network if said leakage current (I) is greater than said preset threshold. 2. Appliance according to claim 1 wherein said comparison module (40) is configured to disconnect said at least one electrical load (L1-Ln) both from a phase line (P) and from a neutral line (N) , of said power supply network. 3. Household appliance according to any one of the preceding claims provided with at least two connection terminals (T1, T2) configured to be connected to the phase line (P) and to the neutral line (N) of said power supply network. 4. Household appliance according to claim 3 wherein said at least one electrical load (L1-Ln) has a first connection (C1) through a first switch (S1) to one of said connection terminals (T1, T2), and a second connection (C2) to the other connection terminal via a second switch (S2). 5. Household appliance according to claim 4 wherein said comparison module (40) is configured to open said first and second switches (S1, S2) if said leakage current (I) is greater than said preset threshold. Household appliance according to any one of the preceding claims, wherein said at least one electrical load (L1-Ln) comprises a heating resistor (R) for heating washing water used by said household appliance (1) in at least one washing cycle. 7. Household appliance according to claim 6 wherein said heating resistor (R) comprises an internal metallic filament (R1), an intermediate coating (R2) of electrically insulating material, and an external coating (R3) of metallic material. 8. Household appliance according to claim 7 wherein the branch (10) for connection to the ground of said at least one electrical load (L1-Ln) is a connection between said external coating (R3) and ground. 9. Household appliance according to any one of the preceding claims, in which said at least one electrical load (L1-Ln) is a plurality of electrical loads, each having a first connection (X1-Xn) through a respective main switch (MS1-MSn) to one of said connection terminals (T1, T2), and a second connection (Z1-Zn) to the other connection terminal. 10. Household appliance according to claim 9 wherein the second connections (Z1-Zn) of said electrical loads (L1-Ln) are connected to the respective terminal (T1, T2) of said household appliance (1) by means of a common switch (SX). 11. Household appliance according to claim 10 wherein said comparison module (40) is configured to open said main switches (MS1-MSn) and said common switch (SX) if said leakage current (I) is greater than said threshold preset. A household appliance according to any one of claims 9 to 11, in which each electrical load (L1-Ln) has a connection (Y1-Yn) to said earth connection branch (10). 13. Filter (F) for the suppression of electrical disturbances, suitable for use in a household appliance (1) according to any one of the preceding claims, said filter (F) comprising: - a first capacitor (C1) connected between connection terminals (T1, T2) of said household appliance (1) and suitable for filtering differential mode disturbances; - a second capacitor (C2) and a third capacitor (C3), respectively connected between a respective of said connection terminals (T1, T2) and an earth node (N), said second and third capacitor (C2, C3) being suitable for filtering ground disturbances; - a detection element (30) associated with an earth connection branch (10) afferent to said earth node (N), said detection element (30) being configured to detect a leakage current (I) flowing in said branch (10), said detection element (30) being able to cooperate with a comparison module (40) of said household appliance (1). 14. Safety circuit (20) suitable for use in the household appliance (1) according to any one of claims 1 to 12.