EP0924467A1 - Device for controlling the functioning of a domestic burner by detecting the flame - Google Patents

Abstract

A thermocouple (TC) detects the presence of a flame (F) at a gas burner (B). The output signal (Stc) connects to a control unit (COM). This in turn controls an electromechanical valve (AEM) and a gas ignition device (ALL). The valve governs the flow of gas to the burner. The switch on and switch off time for the gas flow are preset in the control unit.

Description

The invention relates to a device for assisting in the management of operation of a domestic burner by flame detection for any type of gas fuel burner present on the appliances domestic gas-fired appliances such as gas stoves gas, gas ovens, hobs.

The burners are the parts of the appliance where the combustion of the mixture between the combustible gas and the air. Some burners are equipped with a device to detect the presence flame and activate the opening and closing of a valve gas inlet. This in particular constitutes security in the event of accidental extinction of the flame which could lead to a gas leak toxic, for example as a result of a strong draft or liquid spilling onto the flame. The most detection device current on household burners includes a thermocouple positioned at the flame and an electromagnet which activates a core for shutting off the gas supply. When the flame is present, the thermocouple heats up, delivering a current which feeds the electromagnet. Beyond a certain threshold, called the catch current, the core is attracted to a position which allows the circulation of gas. At otherwise, if the flame goes out, the current delivered by the thermocouple decreases and when it becomes lower than the catch current, the nucleus moves aside, for example thanks to the action of a spring, and comes to close off the arrival of gas. These devices are simple, space-saving, easy to implement and extremely widespread. Their main drawback is however their inertia both at the time of lighting the flame that at the time of its extinction. It takes several seconds to that in the presence of the flame, the current reaches the current hanging; this therefore requires keeping a valve open gas supply, for example by manual control, during this duration. After extinguishing the flame, it usually takes a few dozen seconds to shut off the gas supply, time during which the gas escapes freely. We can certainly reduce this duration exhaust gas by varying the value of the hanging current. However, this is to the detriment of the time taken to detect the appearance of the flame; indeed, these two time constants are linked.

The device according to the invention provides electronic processing the signal delivered by the thermocouple which makes it possible to detect the presence flame when it first appeared, as well as when it went out, with independent time constants. The burner can thus be activated, with adequate means, at predetermined times independently of each other with respect to the moments of appearance or disappearance of the flame.

More specifically, the invention consists of a device for assisting in the management of the operation of a domestic gas burner, comprising a thermocouple positioned in the vicinity of the flame resulting from the combustion of the gas and delivering an electrical signal s _tc function of the local temperature, means for actuating the burner and a control box, the box processing the electrical signal s _{tc in} order to control said means, characterized in that the box comprises means making it possible to define a second signal, originating from the signal s _tc delivered by the thermocouple, and means for processing these two signals making it possible to detect the presence of the flame in order to actuate the burner at predetermined times independently of one another with respect to the moments of appearance or disappearance of the flame.

The actuating means may include for example a electro-mechanical actuator of a gas inlet valve or a burner ignition device.

The invention makes it possible to control the inertia of the detection device while using standard thermocouples; the device according to the invention is therefore easily adaptable to existing burners. It allows to detect with independent time constants the appearance and the disappearance of the flame.

• la figure 1a, le schéma d'un dispositif selon l'art antérieur et la figure 1b, un chronogramme illustrant un mode de fonctionnement d'un tel dispositif;
• la figure 2, le schéma d'un dispositif selon l'invention;
• la figure 3a, un schéma fonctionnel du boítier de commande d'un exemple de dispositif selon l'invention et la figure 3b, un chronogramme illustrant un mode de fonctionnement d'un tel dispositif;
• les figures 4a et 4b, un schéma fonctionnel et un chronogramme illustrant un autre mode de fonctionnement;

Other advantages and particularities of the invention will appear more clearly on reading the description which follows and the appended figures which represent:

• FIG. 1a, the diagram of a device according to the prior art and FIG. 1b, a timing diagram illustrating an operating mode of such a device;
• Figure 2, the diagram of a device according to the invention;
• Figure 3a, a block diagram of the control unit of an exemplary device according to the invention and Figure 3b, a timing diagram illustrating an operating mode of such a device;
• Figures 4a and 4b, a block diagram and a timing diagram illustrating another mode of operation;

In these figures, the homologous elements are referenced by the same benchmarks.

FIG. 1a schematically represents an example of a flame detection device according to the prior art for controlling a valve V for the arrival of gas in a burner B. The device comprises a thermocouple TC positioned in the vicinity of the resulting flame F of the combustion of the gas in burner B. The thermocouple is composed of two different metals and placed so that the junction points between the metals are brought to different temperatures in the presence of flame F. This temperature difference is at the origin of the electrical signal delivered by the thermocouple. In known devices, it is the current i _tc delivered by the thermocouple which is used to power an electromagnet EA symbolized in FIG. 1a by a coil. When the current in the electromagnet is greater than a threshold value called latching current, the core N is attracted, this core blocking the valve V of the gas inlet when the current is less than the threshold value. The device described in FIG. 1a further comprises an ALL ignition device for the burner B, triggered manually, capable of operating, for example, by the emission of a train of electrical pulses or by heating near the burner. a glowing wire.

Figure 1b illustrates an operating mode of such a device. The curve 11 represents as a function of the time noted t the presence (noted YES in the figure) or the absence (noted NO) of the flame F. The instant t ₀ represents the moment when the ignition device is actuated . This action is maintained until time t ₁ of appearance of the flame. Between times t ₀ and t ₁ , the valve V is kept open by means different from those used in the device based on the detection of the flame. These means are here called external means. It may for example be a manual control. Curve 11 also shows between instants t ₂ and t ₃ , a momentary and partial extinction of the flame, for example due to the spillage of a liquid on a zone of the flame close to the thermocouple and sufficiently small so that the flame can relight fully and quickly. Finally the instant t ₄ corresponds to the disappearance of the flame. Curve 12 gives, as a function of time t, the current i _tc delivered by the thermocouple during the same period as that represented by curve 11. Depending on the value i _acc of the _latching current, a certain period of time Δt _m , called here rise time or presence detection time, is necessary for the device based on the flame detection to take over from the external means to allow the opening of the valve V. The detection of the presence of the flame which results here by the opening of the valve thanks to the device is represented in FIG. 1b by a quantity Y taking as value 1. The latching current can be reduced to reduce the time Δt _m . But in this case, at the extinction of the flame, the time Δt _d , here called the descent time or extinction detection time, necessary for the current i _{tc to} become lower than the threshold i _acc and therefore that the core N come close the valve V will only be larger; in FIG. 1b, the detection of the extinction of the flame, resulting in the closing of the valve using the device is represented by the quantity Y taking the value 0. Thus for a rise time Δt _m of a few seconds, the descent time Δt _d is typically a few tens of seconds. It can be seen from this example that the times for detecting the presence or extinction of the flame are linked. Between instants t ₂ and t ₃ , corresponding to a momentary extinction of the flame, if this period of time is sufficiently short, the current i _tc has not fallen below the threshold i _acc and the valve therefore remains open, this which is an advantage of the inertia of such a device.

Let us now consider a device according to the invention, a diagram of which is shown in FIG. 2. It also includes a thermocouple TC, which can be the same as those used in the devices of the prior art. The TC thermocouple when subjected to a temperature variation delivers an electrical signal s _tc . The device further comprises means MA for actuating the burner B and a control unit COM. The COM box processes the signal s _{tc in} order to control the means MA which allow the burner to start when they are activated.

The actuating means MA of the burner may include, as illustrated in FIG. 2, an electromechanical actuator AEM allowing the opening or closing of a valve V for the arrival of gas in the burner. The COM box processes the signal s _{tc in} order to control the AEM actuator to trigger the opening or closing of the valve V. The electromechanical actuator AEM can include an electromagnet of the same type as those used in the devices of the prior art, but controlled in this case by the COM control unit. Other types of actuators can be used in the device according to the invention. For example, the actuator may include a piezoelectric device which allows, under the action of an electrical signal, the displacement of a membrane; this membrane coming, for example, to shut off the gas supply at the valve V. Note that a piezoelectric device requires high supply voltages to obtain small displacements, also such an actuator would have been difficult to envisage in a device of the prior art.

The means MA can also include a device ALL ignition of the burner, the COM control unit allowing control the switching on or off of the ignition device. The ignition device can for example as in some devices of the prior art operate by the emission of a train of pulses electric or by heating near the burner of a wire incandescent.

According to the invention, the processing functions performed by the housing COM are such that the activation or deactivation of the means MA can be determined independently with respect to the moments of appearance or disappearance of the flame F. For this, the housing COM of the device according to the invention comprises means making it possible to define a second signal, originating from the signal s _tc delivered by the thermocouple. It further comprises means for processing these two signals making it possible to detect the presence of the flame in order to actuate the burner B at predetermined times independently of one another with respect to the moments of appearance or disappearance of flame F.

An example of such an operating mode of the COM control unit is shown in FIG. 3a. The means making it possible to define the second signal are means 31 for calculating the derivative s' _tc of the electrical signal s _tc delivered by the thermocouple. The means for processing the two signals comprise means 32 for comparing the signal s _tc with a first threshold value s ₁ and means for comparing the derivative s' _tc with a second threshold value s ₂ . The results of these comparisons are called A ₁ and A ₂ respectively. For example, A _{1 is} worth 1 if s _tc is greater than or equal to s ₁ and A _{2 is} worth 1 if s' _tc is greater than or equal to s ₂ . A ₁ and A ₂ are worth 0 otherwise. The processing means also comprise means 34 making it possible to operate a logic function between the quantities A ₁ and A ₂ . In the example chosen in FIG. 3a, this function is a logical OR. The result of this operation is the quantity Y which materializes the flame detection. In the example chosen, Y equals 1 when the presence of the flame is detected, Y equals 0 otherwise. The value of Y determines the activation of the actuation means MA of the burner. To better understand the time response of such a device according to the invention, we can use the example of the timing diagram 11 described in FIG. 1b and repeated in FIG. 3b. At the instant t ₁ of appearance of the flame, it is for example the value of s' _tc which determines the detection of the flame; we set a threshold value s ₂ strictly positive, so that upon ignition of the flame, the variation of heat at the thermocouple almost instantly causes the relationship s' _tc greater than or equal to s ₂ , the quantity A ₂ taking the value 1; it follows that the result Y of the operation between A ₁ and A ₂ also changes to 1, which causes the detection of the flame and therefore the control of the actuation means MA of the burner B with a rise time Δt _m close to 0. In the example chosen, this results in the opening of the valve Y thanks to the electro-mechanical actuator AEM and the automatic shutdown of the ignition device ALL also controlled by the box COM. The derivative s' _tc decreases rapidly but the signal s _tc increases, passing beyond the threshold s ₁ ; s ₁ can be chosen so that, when s' _tc is less than s ₂ , s _tc is greater than s _1, causing the passage to 1 of the quantity A ₁ . Thus, Y is always equal to 1. When the flame is extinguished (time t ₄ ), it is the passage of s _tc below the threshold s ₁ which determines the instant of flame extinction detection (Y passes to 0). This is reflected in the example chosen either by closing the valve V using the AEM actuator (the gas supplying the burner is therefore cut), or by restarting the ALL ignition device in order to relaunch the flame. The choice of s ₁ thus determines the descent time Δt _d ; it is then necessary to find a compromise on the value of s ₁ to reduce the descent time Δt _d while fixing a duration (corresponding on curve 11 to the period between the instants t ₂ and t ₃ ) during which the flame can locally and momentarily turn off without causing the valve V to close or the ignition device to restart; typically, Δt _{d is} worth a few seconds. The threshold s ₁ is advantageously fixed as a function of the family of thermocouples used in order to have a similar response for all of the thermocouples.

The functions performed by the COM box can be performed by means of analog or digital electronic functions, by means of software programmed for example on a microcontroller.

The electrical signal s _tc delivered by the thermocouple TC and processed by the control unit COM is for example the voltage measured at the terminals of the thermocouple. This makes the operation of the device more reliable because the signal is then independent of the values of the resistance of electrical connections.

Another example of operation of the COM control unit is illustrated in the operating diagram in FIG. 4a and the timing diagram in FIG. 4b. In this example, the means making it possible to define the second signal are means making it possible to construct from the electrical signal s _tc delivered by the thermocouple TC a signal r _tc (in dotted lines in FIG. 4b) and the means for processing the two signals include means for comparing the signal s _tc and the signal r _tc . The result Y of the comparison makes it possible to determine the detection of the presence of the flame. It is then transmitted to the actuation means MA of the burner to control their activation. In the example chosen, the flame presence detection, corresponding to Y = 1 in FIG. 4b, is obtained when s _tc is greater than r _tc , and the flame extinction detection then corresponding to Y = 0 is obtained otherwise. The quantity Y is sent to the actuation means which can be, to use the previous example, the electromechanical actuator AEM of the valve V and the ignition device ALL. The signal r _tc can for example be constructed as follows. The first step 40 (FIG. 4a) consists in controlling the operation of the burner by the user. It corresponds to time t ₀ on the timing diagram 4b. During the period 41 (FIG. 4a) waiting for the appearance of the flame (Y = 0), the signal r _tc takes a minimum value r _s constant. At the instant t ₁ of appearance of the flame, the signal s _tc begins to increase; when s _tc becomes greater than r _tc (42), Y changes to 1 and the detection of the presence of flame is obtained with a rise time Δt _m which therefore depends on the minimum value r _s . This rise time can be of the order of a second. During the period 43 during which the signal s _tc is increasing or constant, and greater than the sum of the minimum value r _s and a threshold value v _s , the signal r _tc is equal to the difference of the signal s _tc and an offset value s _g . The threshold value can be equal to the offset value, as is substantially the case in Figure 4b. During the period 44 which follows the disappearance of the flame (instant t ₄ ), period during which the signal s _tc is decreasing, the signal r _tc decreases with a predetermined time constant, this constant being greater than that of decrease of the signal s _tc . If s _tc increases again before s _tc has become less than r _tc , r _tc takes the value equal to the difference of the signal s _tc and the offset value s _g . When the signal s _tc becomes lower than the signal r _tc , this causes the flame extinction to be detected (Y = 0) after a period of time corresponding to the descent time Δt _d which depends on the time constant signal r _tc ; typically Δt _{d is} worth a few seconds. According to a first option, the value Y can be maintained at 0 for a duration Δt _b (blocking period 46) corresponding to the time it takes for the signal r _tc to decrease to the minimum value r _s . The blocking period allows, when a new appearance of the flame occurs, to obtain the detection of the presence of the flame and therefore the control of the actuation means MA of the burner with always the same time constant Δt _m . According to another option (shown in dotted lines in FIG. 4a), there is no blocking period and if again, the operation of the burner is controlled by the user (step 40), the detection of extinction flame (Y = 0) is only obtained during the period 45 corresponding to s _tc less than r _tc .

An operating mode such as the one just described can very easily be programmed by means of a microcontroller by example. We can also use an electronic circuit which performs analogically the different functions.

The device according to the invention thus makes it possible to fix so independent rise and fall times and thus reduce significantly the inertia inherent in the devices of the prior art, all using a standard thermocouple. The position of the thermocouple by flame relationship is less critical than in known devices because it is no longer the signal delivered by the thermocouple which feeds directly an actuator; operation is therefore less sensitive to flame temperature. The device according to the invention allows improve safety measures regarding gas leaks due to accidental extinction of the flame. It also makes it easier to put implementation of certain operating modes of the gas burner, such as for example a simmer mode obtained through operation automatic sequential burner.

Other optional functions can be implemented easily thanks to the device according to the invention. For example, the device may include means for blocking the general operation of the domestic appliance on which the burner is located. These means are activated by the COM control unit when an abnormal presence flame on the burner is detected; for example when the flame is detected while the gas supply valve is closed. This blockage may consist, for example, of a temporary impossibility for the user to have access to the controls of the device. The device according to the invention may also include display means, controlled by the control unit (COM), and allowing inform the user about the presence or extinction detection of flame.

Claims (10)

Aid device for managing the operation of a domestic gas burner (B), comprising a thermocouple (TC) positioned in the vicinity of the flame (F) resulting from the combustion of the gas and delivering an electrical signal s _tc function of the local temperature, actuation means (MA) of the burner (B) and a control box (COM), the box (COM) processing the electrical signal s _{tc in} order to control said means (MA), characterized in that the housing (COM) comprises means making it possible to define a second signal, coming from the signal s _tc delivered by the thermocouple, and means for processing these two signals making it possible to detect the presence of the flame in order to actuate the burner (B ) at predetermined times independently of one another with respect to the moments of appearance or disappearance of the flame (F). Device according to claim 1, characterized in that the means making it possible to define the second signal are means for calculating (31) the derivative s' _tc of the signal s _tc , and in that the means for processing the two signals are means for comparing (32) the signal s _tc with a first predetermined threshold value (s ₁ ), means for comparing (33) the signal s' _tc with a second predetermined threshold value (s ₂ ) and means allowing from the results of said comparisons to detect the presence of the flame. Device according to claim 2, characterized in that the means making it possible to detect the presence of the flame are means (34) making it possible to carry out a logical OR function between the result A of the comparison between the signal s _tc and the first threshold ( s ₁ ) and the result B of the comparison between the derivative s' _tc and the second threshold (s ₂ ), the detection of the presence of the flame being determined by the result Y of said function. Device according to Claim 1, characterized in that the means making it possible to define the second signal are means making it possible to construct from the signal s _tc a signal r _tc and the means for processing the two signals comprise means for comparing the signal s _tc with the signal r _tc , the detection of the presence of the flame being determined by the result Y of said comparison, the signal r _tc being constructed so that it is worth a constant minimum value (r _s ) during the period (41) of waiting for the appearance of the flame, it is equal to the difference of the signal s _tc and of an offset value (s _g ) during the period (43) during which the signal s _tc is increasing or constant, and greater than the sum of the minimum value (r _s ) and a threshold value (v _s ), it decreases with a predetermined time constant during the period (44) during which the signal s _tc is decreasing, said constant being greater than that of decrease of the signal s _tc . Device according to claim 4, characterized in that the housing (COM) further comprises means allowing the blocking of the actuating means (MA) during the period (46) which follows the disappearance of the flame and during which the signal r _tc is still greater than said minimum value (r _s ). Device according to any one of the claims previous, characterized in that the housing (COM) comprises a microcontroller allowing programming of at least some of the functions necessary for processing the two signals and for controlling actuation means (MA). Device according to any one of the claims previous, characterized in that the actuating means (MA) include an electromechanical actuator (AEM) of a valve (V) gas inlet in the burner (B), the housing (COM) thus allowing control the opening or closing of said valve (V). Device according to any one of the claims previous, characterized in that the actuating means (MA) include an ignition device (ALL) of the burner (B), the housing (COM) thus making it possible to control the starting or stopping of said ignition device. Device according to any one of the claims previous, characterized in that it further comprises means for blocking of the general functioning of the domestic appliance on which finds the burner (B), said means being activated by the housing command (COM) when an abnormal presence of the flame on the burner (B) is detected. Device according to any one of the claims previous, characterized in that it further comprises means display controlled by the control box (COM) and allowing to inform the user about the detection of the presence of the flame.

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