Abstract:
A method and an apparatus for operating a gas-powered cooking device including an actuator for moving a closure disposed in the gas feed conduit of a burner to an open state and of igniting gas emitted from the burner by an ignition electrode to form a burner flame, the ignition electrode being connected to an ignition voltage for a predetermined first interval of time, a sensor thermo-conductively connected to the burner flame for generating a sensor voltage for maintaining the closure means in its open state if the sensor voltage attains a predetermined level and of initiating subsequent ignitions after a predetermined interval of time where the predetermined level is not attained within a predetermined further interval of time.

Description:
Priority is claimed to German patent application DE 102 17 008.8, filed Apr. 16, 2002. 
   The invention, in general, relates to a method and apparatus for operating a gas-powered cooking and frying device, and, more particularly, to a method and apparatus of the kind referred to provided with an actuator for moving a valve disposed in the gas feed of the device to an open state, with an ignition electrode for generating an ignition spark for igniting the combustible gas mixture flowing from the burner, with a control unit for electrically connecting the ignition electrode to a source of ignition voltage for a predetermined first interval of time, and with a sensor thermally conductively connected with the flame of the burner, the sensor generating an electrical sensor voltage for maintaining the valve in its open state. 
   BACKGROUND 
   A method is known for operating a gas-powered cooking device in which a rotary knob provided with a keying function is used as an actuator. When actuating the keying function, a closure means structured as a magnetic insert and disposed in a gas feed of a burner is moved from a closed to an open state. This leads to the magnetic insert to be moved from a closed to an open state against the bias of a spring mounted on the magnetic insert. There is provided yet another valve in the gas feed which may be opened by rotating the rotary knob. Only after this has occurred will gas flow from the burner. At the same time, by rotating the rotary knob, a timer in a control unit will be actuated electrically to connect the ignition electrode for a predetermined first interval of time to a source of ignition voltage. The ignition electrode releases an ignition spark for igniting the gas mixture flowing from the burner. A thermo-sensor is arranged in the cooking device in thermo-coupled connection with the flame of the burner to generate an electrical sensor voltage for maintaining the magnetic insert in its open state. If the keying function is no longer actuated and if the electrical sensor voltage is insufficient, the magnetic insert is automatically returned, by the bias of the spring, to its closed state, and the gas feed to the burner is interrupted again. This may happen, for instance, if after ignition the flame of the burner has failed sufficiently to heat the thermo element or if the flame of the burner is extinguished by a draft. In that case, the ignition described about has to be carried out anew. Therefore, one disadvantage of the known method is that every time the burner flame is extinguished the feed of gas is interrupted by the magnetic insert, and renewed manual ignition is necessary. 
   SUMMARY 
   Therefore, it is an aspect of the invention to provide a method of operating a gas-powered cooking or frying device by which following a first manual ignition renewed ignition is performed automatically in case the burner flame has been extinguished. 
   The present invention provides an apparatus and method for operating a gas-powered stove. An actuator is included for moving a valve in the line of a gas feed conduit for a burner to an open state. An ignition electrode generates an ignition source for igniting a combustible mixture emitted by the burner, thereby forming a burner flame. A sensor, connected to the burner flame by heat conductance, generates an electric sensor voltage over a predetermined temporal course to maintain the valve in an open state. Also included is a control unit for electrically connecting the ignition electrode to an ignition voltage for a predetermined first interval of time. The control unit includes an evaluation circuit for processing the electric sensor voltage to connect the ignition electrode to the ignition voltage in response to a switching state dependent on the temporal course of the electric sensor voltage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features which are considered to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, in respect of its structure, construction and lay-out as well as manufacturing techniques, together with other objects and advantages thereof, will be best understood from the following detailed description when read in connection with the appended drawings, in which: 
       FIG. 1  is a block circuit diagram of the device for practicing the method of the invention; and 
       FIG. 2  is a graph exemplarily depicting the course over time of the electric sensor voltage. 
   

   DETAILED DESCRIPTION 
   In addition to the automatic re-ignition after extinction of the burner flame and the operational ease for a user, the advantages derived from the invention include that the sensor, which in the known method serves the sole function of generating, at an existing burner flame, a sufficiently high electric sensor voltage for maintaining a valve in its open state to prevent interruption of gas feed to the burner during operation of the cooking device, additionally functions electrically to connecting the ignition electrode to the source of ignition voltage in dependence of the electric sensor voltage. While it is known instead of the safety arrangement described above i.e. to return the valve to its closed state in case the thermo-element fails to generate a sufficiently high electric sensor voltage, to use an ignition electrode for additionally sensitizing the ionization of air and for initiating a re-ignition in response to this signal. However, a disadvantage of such an arrangement is that in case of an electric power failure no re-ignition can take place, and gas will continue to flow from the burner with a potentially explosive mixture is developing in the room in which the cooking and frying device is installed. 
   In a specific embodiment of the invention an electric signal is fed from the actuating means to the control unit to be processed in a second evaluation circuit of the control unit for maintaining the valve, by the second evaluation, in its open state for a predetermined second interval of time depending upon the electric signal. This further improves the ease of operation for a user as a single and short-time actuation of the actuator during an ignition operation is sufficient. Hence, actuation of the actuator up to the point in time at which the valve is maintained in its open state by the electric sensor voltage is no longer necessary. 
   Another embodiment provides for the valve to be maintained in its open state for a second interval of time by an electric holding voltage generated by the control unit and for processing the second interval of time by a safety circuit separate from the control unit and for electrically separating, upon expiration of the second interval of time, the electric holding voltage from the valve for an indefinite third interval of time. The safety of the method is thus improved further as upon expiration of the second interval of time the valve is disconnected from the holding voltage independently of the control unit so that during the third interval of time the valve is maintained in its open state solely by a sufficiently high electric sensor voltage. 
   Another embodiment of the invention provides for the first evaluation circuit of the control unit processing the change over time of the electric sensor voltage. Thus, extinction of the burner flame may be detected in advance and unnecessary re-ignition may be substantially prevented. 
   In yet another embodiment of the invention, the valve is moved to its open state and the electric signal is simultaneously fed to the control unit by the actuator. This provides for improved ease of operation to a consumer. 
   In principle, kind, size, material and number of the actuator may be selected from a wide variety. As a matter of efficiency, the actuator is structured as a rotating dial with an integrated keying function. A touch screen serves as another efficient and useful actuator. 
   In still another embodiment of the invention the valve is provided with a magnetic insert provided with a spring, the bias of which counteracts the magnetic force generated by the electric sensor voltage or electric holding voltage and returns the magnetic insert to its closed state. In this manner, the valve is returned to its closed state whenever the electric sensor voltage or the electric holding voltage is insufficiently high to maintain the valve in its open state. 
   In another embodiment of the invention the control unit is provided with a micro-processor with the first and/or the second evaluation circuit being an integrated circuit of the micro-processor. Micro-processor are advantageous and efficient components requiring little space. 
   The sensor may be a thermo-element in view of the fact that thermo-elements are cost-efficient standard components. 
     FIG. 1  depicts an embodiment of the device for practicing the method in accordance with the invention. The cooking device, which is shown only partially, is provided with actuator  2  structured as a rotary selection switch with an integrated keying function. Alternalitively, actuator  2  may be a touch screen. The actuator  2  cooperates mechanically with valve  4  structured as a magnetic insert. In a state that is not shown, the valve  4  blocks the flow path of a gas feed conduit  6  to a burner  8  and in its shown open state it does not block the flow path. The magnetic insert  4  is provided with a spring which biases the magnetic insert  4  in the direction of the closed state. The actuator  2  is mechanically connected with a valve (not shown) disposed in the gas feed conduit  6 . Further more, a main switch  10  may be actuated by the actuator  2 . The main switch  10  is disposed in a first circuit which is electrically connected to a micro-processor functioning as a control unit  11 . An ignition electrode  12  is arranged in spatial proximity to the burner  8 . Moreover, the ignition electrode  12 , an ignition relay and a source of ignition voltage  14  are arranged in an ignition circuit. The ignition relay is actuated by the control unit  11 . In spatial proximity and in a heat-transfer connection with the flame  16  of the burner  8  there is arranged a sensor  18  structured as a thermo-element. The thermo-element  18  is electrically connected to the magnetic insert  4  and with a first evaluation circuit of the control unit  11 . The magnetic insert  4 , a holding voltage relay and an electric holding voltage generated by the control unit  11  are arranged in a holding voltage circuit. The holding voltage relay may be actuated by the control unit  11 . 
   Hereafter, the function of the method of the invention and of the embodiment of the device for practicing the method will be explained with reference to  FIGS. 1 and 2 . 
   The cooking device in accordance with the invention is connected to a source of electricity. By actuating the keying function of the actuator  2  the magnetic insert  4  is mechanically moved to its open state ( FIG. 1 ) against the bias of the spring connected to the magnetic insert  4 . The valve in the gas feed conduit  6  is opened by rotating the actuator  2  in a counterclockwise direction. The flow path in the gas feed conduit  6  towards the burner  8  is thus open, and gas will be emitted by the burner  8 . At the same time as the keying function of the actuator  2  is actuated, the main switch  10  in the first control circuit is closed, and an electric signal is fed to the control unit  11 . This causes a first timing member in control unit  11  and the ignition relay to be actuated to connect the ignition electrode  12  for a predetermined interval of time to the ignition voltage  14 . The ignition electrode  12  thus generates ignition sparks for igniting the gas emitting from the burner  8  and generating flame  16  of the burner  8 . Upon expiration of the first interval of time, the ignition relay will again open the ignition circuit. Also, a second time member in the control unit  11  and the holding voltage relay are actuated so that the magnetic insert  4  is electrically connected to the holding voltage for a predetermined second interval of time so that the magnetic insert  4  is maintained in its open state. Thus, only a single and short-time actuation of the keying function of the actuator  2  is required. The thermo-element  18  is heated and the electric sensor voltage is generated by the flame  16  of the burner  8 . Upon expiry of the second interval of time, the holding voltage relay again opens the holding voltage circuit. Provided the electric sensor voltage has reached a sufficiently high value, the magnetic insert  4  will be maintained in its open state by the electric sensor voltage, even after expiry of the second interval of time, so that the electric holding voltage is no longer required. 
   If the burner flame  16  is extinguished at this time, for instance by a draft of air, the electric sensor voltage at the first evaluation circuit of the control unit  11  is changed. In the present example, the evaluation circuit processes the change over time of the electric sensor voltage (see  FIG. 2 ).  FIG. 2  qualitatively depicts an exemplary course over time of the electric sensor voltage. The value of the electric sensor voltage is depicted on the ordinate; the abscissa identifies the time t. The course shown in  FIG. 2  corresponds, from time t 0  to time t 1 , to the course of the electric sensor voltage of the thermo-element  16  at a switched on cooking device and ignited burner flame  16 . It is to be noted that the values shown in the graph are average values since the electric sensor voltage fluctuates within certain limits even during normal operation of the burner  8 . There is a drop in the electric sensor value in the interval of time from t 1 , to t 2 . The first evaluation circuit compares the voltage drop measured in the interval of time t 1 , to t 2  against a predetermined temporal course of the voltage drop which coincides with the extinction of the burner flame  16 . The voltage drop of the example of  FIG. 2  corresponds to the predetermined temporal course of the voltage drop, and the ignition relay is again actuated by the first evaluation circuit of the control unit  11 . The ignition circuit is thus closed and the ignition electrode  12  is again connected to the ignition voltage  14  to generate ignition sparks for igniting the burner flame  16  again. In the mean time, time t 3  has been reached (see  FIG. 2 ). Analogous to the voltage drop, the first evaluation circuit compares the rise in voltage measured during time interval t 3  to t 4  against a predetermined temporal course of the rise in voltage. The rise in voltage of the example of  FIG. 2  corresponds to the predetermined temporal course of the rise in voltage, and the ignition relay is actuated by the first evaluation circuit of the control unit  11  such that the ignition circuit is opened and the ignition electrode  12  is disconnected from the ignition voltage  14 . Upon reaching time t 4  the voltage course will have reached the average value characteristic of normal operation of the burner  8 . The evaluation circuit is structured such that a drop in the voltage of the sensor voltage caused by normal operation of the cooking device, for instance by reducing the gas feed by rotation of the actuator  2  in a counter-clockwise direction, does not result in re-ignition as described above. This may be achieved by utilizing the temporal change in electric sensor voltage which during an intended reduction of the gas flow drops more slowly than it would with an undesired extinction of the burner flame  16 . 
   The described embodiment is additionally provided with a safety circuit which constitutes a safety device electrically connected to the control unit  11 . The safety circuit includes third and fourth timing members and a safety relay. The safety relay opens the holding voltage circuit in response to a signal from the third timing member. The third timing member is actuated after the holding voltage relay has been closed in the manner described supra. Upon expiry of the predetermined second interval of time the safety relay is actuated by the third timing member to open the holding voltage circuit. At the same time the fourth timing member is actuated for clocking a predetermined third interval of time. During the third interval of time the magnetic insert  4  is disconnected from the electrical holding voltage, independent of the control unit  11 . Provided the electric sensor voltage generated by the thermo-element  18  is sufficiently high to maintain the magnetic insert  4  in its open state, the flow path in the gas feed duct  6  remains unimpeded. This is the case as long as the burner flame  16  remains burning. In the present situation, if the burner flame  16  has been extinguished for any reason, the electrical sensor voltage will not be sufficiently high to maintain the magnetic insert  4  in its open state against the bias of its integrated spring. Upon expiry of the third interval of time the safety relay will therefore be actuated again to close the holding voltage circuit. Since the holding voltage relay is otherwise actuated in this manner only for purposes of a first manually initiated ignition during the predetermined second interval of time, the holding voltage circuit remains open until a renewed manually initiated initial ignition.