Patent Publication Number: US-2007117058-A1

Title: Control system for the operation of a kitchen oven

Description:
FIELD OF THE INVENTION  
      The present invention refers to a system developed to allow the electronic control of the operating times of a kitchen oven, as a function of the cooking temperature conditions pre-selected by the user. The present control system can be applied to gas or electric ovens, mounted in single cabinets or which are combined with kitchen stoves comprising a cook top provided with one or more burners or heaters.  
     PRIOR ART  
      The instructions provided with the packages of most food products of fast preparation, such as the frozen food products, recommend the consumer to preheat the oven before he/she introduces the food product therein to start cooking. Preheating the kitchen oven is thus an important step in the cooking process.  
      In the known kitchen ovens, the consumer has to use a clock or chronometer, which is provided separate from or incorporated in the cabinet of the oven, in order to be informed by the visual/audible alarm of the clock that the oven is already in the desired operating temperature, which is generally preset by the user in a thermostatic valve or in an also thermostatic energization control.  
      Even in the case the user is informed about the heating time of the oven for each selected temperature level, he/she has to analyze a table indicative of the operating temperature and the preheating time, in order to have the definition of the time to be adjusted in the clock or chronometer. This procedure is laborious and requires certain cares with which the user is not familiar, i.e., different from those procedures directly related to the preparation of the food product. The preheating time has to be calculated and adjusted in an auxiliary device (clock).  
      There are also known the oven operation control systems which use one or more temperature sensors associated with electronic commands, which process the signals received from the sensors, instructing the gas or electric supply adjusting means, as well as visual and audible alarm means associated with timers, to operate as a function of the temperature and time conditions adjusted by the user.  
      This system with electronic sensors allows a precise operational control of the oven to be obtained, without requiring additional cares or procedures from the user, except the simple actuation of the command button of the oven for the position indicative of the desired operating temperature. However, these systems present a high cost, which substantially increases the final cost of the oven or stove associated therewith.  
      There are well known from the art the kitchen ovens comprising a cooking chamber, inside which are mounted at least one heat source in the form of a gas burner or of an electric resistance, and a temperature sensor; and a thermostatic control device, which controls the energization of the heat source, in the form of a thermostatic valve for controlling the gas flow, or in the form of a thermostat, and which is operatively associated with a scale of the oven operating temperatures and with the temperature sensor, in order to adjust the energy supplied to the heat source, as a function of the temperature set in said device upon the activation of the oven and of the temperature sensed by the temperature sensor inside the cooking chamber. This known construction allows the user to control the operating temperature of the oven, upon completion of the preheating phase.  
      Nevertheless, there still persists the difficulty in providing, at a low cost, a control system which is able to determine and automatically inform the user about the end of the preheating phase, with the cooking chamber being in the desired operating temperature.  
     OBJECTS OF THE INVENTION  
      As a function of the limitations related to operation and cost presented by the known control systems, it is an object of the present invention to provide a system of the type exemplified above, which is able to supply the user, by means of a relatively simple construction, with an automatic visual and audible indication that the cooking chamber of the oven has reached the operating temperature which has been set upon the activation of the oven.  
      It is a more specific object of the present invention to provide a control system such as mentioned above, which has its operation automatically started when the user switches on the oven.  
      It is a further object of the present invention to provide a control system as defined above, which can be operatively associated with other functions, such as time control and operational safety of the oven, as well as other heat sources of a stove associated therewith.  
     DISCLOSURE OF THE INVENTION  
      In order to attain the above-mentioned objects, the invention is applied to a control system for the operation of a kitchen oven as defined above, which comprises, besides the usually known control elements, a decoder which is operatively associated with the thermostatic control device in order to produce a digital signal for each temperature preset in the thermostatic control device; and an electronic control module comprising a processing unit, an initial heating timer, a digital display and an audible alarm, operatively associated with each other.  
      The processing unit is connected to the decoder so as to receive therefrom and to process a digital signal indicative of the activation of the oven and of the selected operating temperature, in order to activate the audible alarm when a pre-established initial heating time has elapsed, so that the cooking chamber can reach the selected operating temperature.  
      The basic construction proposed herein allows the user to be informed about the moment in which the oven is in a pre-selected temperature condition, without requiring any additional operation for activating the oven, such as moving the thermostatic control device toward the open position at the desired temperature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be described below, with reference to the enclosed drawing, given by way of example of a possible embodiment of the present system and in which:  
       FIG. 1  is a schematic diagram of the present control system, applied to a kitchen oven associated with a cook top, and in which the heat sources of both the oven and the cook top are defined by gas burners. 
    
    
     DESCRIPTION OF THE INVENTION  
      As mentioned above and illustrated in the single figure of the enclosed drawing, the present control system is applied to a kitchen oven  10  of the type which comprises a cooking chamber  11 , within which a heat source  20  and a temperature sensor  30  are lodged. The oven  20  can be defined in a single cabinet, or mounted in a cabinet, on which upper portion is defined a stove cook top, comprising one or more heat sources  20  for cooking.  
      The control system of the invention is applied to ovens presenting gas or electric burners and whose operation is determined by a thermostatic control device  40 , external to the cooking chamber and which is operatively associated with an energy source  1 , with the heat source  20  of the cooking chamber  11 , and with the temperature sensor  30 , in order to control the energy supplied to the heat source  20  as a function of the operating temperature to which it has been selectively adjusted and of the temperature detected by the temperature sensor  30 .  
      In the illustrated construction, the heat source  20  is defined by a gas burner and the thermostatic control device is defined by a thermostatic valve, incorporating an electromagnetic obturator  41  and which is connected to a thermocouple  42  mounted close to the heat source  20  so as to be heated by the flame produced by the gas burner in operation, maintaining the electromagnetic obturator  41  in the open condition, to which it has been mechanically manually conducted by the user operating the thermostatic control device  40 .  
      Nevertheless, it should be understood that the heat source  20  could be defined by an electric resistance, in which situation the thermostatic control device  40  consists in a thermostat coupled to the temperature sensor  30 , but without the electromagnetic obturator  41 .  
      Independently of the type of energy supplied to the heat source  20 , the thermostatic control device  40  comprises a driving rod  43 , to which is affixed a knob  44  to be operated by the user, generally by rotation, and which is associated with a scale  45  containing different operating temperatures for the oven  10  which are printed on a control panel (not illustrated) provided in the cabinet of the oven  10  where the knob  44  is located.  
      According to one aspect of the invention, a decoder  50  preferably of the type which uses the Gray Codification, is mounted to the driving rod  43  of the thermostatic control device  40 , or otherwise operatively associated with the latter, in order to produce a digital signal for each temperature of the scale  45  adjusted in said thermostatic control device  40 . Thus, when the user operates the knob  44  to energize the heat source  20 , displacing it to a position corresponding to a chosen operating temperature indicated in the scale  45 , the decoder  50  will be correspondingly displaced, in order to produce, automatically, a digital signal indicative of the operating temperature selected by the user in the thermostatic control device  40 .  
      In order to allow the digital signal produced by the decoder  40  to be used in the determination of the initial heating time of the cooking chamber  11  until the selected operating temperature is reached, the control system further comprises an electronic control module M which is energized by an electric energy source  2  external to the oven  10 . The electronic control module M comprises a processing unit  60 , an initial heating timer Tin, which can be provided in the interior of the processing unit in a time base with adequate precision (for example, the frequency of the AC electric power network, crystal oscillators of the type used in clocks, etc.), a digital display  70 , and an audible alarm  80  operatively associated with each other.  
      The processing unit  60  is connected to the decoder  50  so as to receive therefrom and to process the digital signal indicative of the activation of the oven and of the selected temperature, in order to activate the audible alarm  80 , when a pre-established initial heating time has elapsed, so that the cooking chamber  11  reaches the selected operating temperature.  
      In a preferred constructive form, the processing unit  60  is programmed to indicate, in the display  70 , the selected operating temperature, when the pre-established initial heating time has elapsed in the processing unit  60  as a function of the digital signal received from the decoder  50 .  
      Also a preferred form of processing the signals takes into account the recent historic information about the times elapsed since the activation and deactivation of the oven, allowing to recalculate the remaining time for the preheating, based on a situation in which said oven is already at a temperature superior to that of the environment, thus promoting an effective economy of time and energy to the user.  
      The temperature sensor  30  can take the form of a sensor bulb, directly coupled to the thermostatic control device  40  in order to operate the latter, increasing or decreasing the energy flow (gas or electricity) supplied to the heat source  20 , as a function of the temperature condition sensed by the sensor bulb inside the cooking chamber  11 .  
      In a preferred form of the invention, the electronic control module M further comprises a timer T which is operatively associated with the processing unit, with the digital display  70 , and with the audible alarm  80  so as to indicate, in the digital display  70 , the time elapsed to be controlled by the user, and to make the audible alarm  70  ring when the time preset in the timer T has elapsed.  
      The present control system may have its electronic control module M comprising an operation timer Top, which is operatively associated with the processing unit  60 , with the digital display  70 , with the audible alarm  80 , and with the thermostatic control device  40 , in order to indicate, in the digital display  70 , the count of an operating time of a heat source  20  preset by the user, making the audible alarm  80  ring and interrupting the energization of the heat source  20  at the end of the time selectively set in the operation timer Top.  
      In the cases in which the heat source  20  takes the form of a gas burner, the electromagnetic obturator  41  is connected to the thermocouple  42  by means of an electronic switch R, generally a normally closed relay, provided in the electronic control module M and which is connected to the processing unit  60  so as to be opened, interrupting the energization of the electromagnetic obturator  41  and blocking the supply of gas to the heat source  20 , upon completion of the time of the operation timer Top selectively adjusted by the user.  
      The electronic control module M can further comprise at least one additional operation timer Tad, which is operatively associated with the processing unit  60 , with the digital display  70 , with the audible alarm  80  and with a control device  90 , connecting the energy source  1  to an additional heat source  20   a  defined in a cook top associated with the oven  10 , the additional operation timer Tad indicating, in the digital display  70 , the count of the operating time of the additional heat source  20   a  adjusted by the user, making the audible alarm  80  ring and interrupting the energization of the additional heat source  20   a  at the end of the time selectively preset in the additional operation timer Tad.  
      In the case in which the additional heat source is a gas burner, and the control device  90  is a valve incorporating an electromagnetic obturator  41 , the present control system further comprises the provision of a thermocouple  42 , associated with the additional heat source  20   a  and which is electrically connected to the electromagnetic obturator  41  by an additional electronic switch Rad, which is normally closed and generally in the form of a relay provided in the electronic control module M and which is connected to the processing unit  60  in order to be opened, interrupting the energization of the electromagnetic obturator  41  and blocking the supply of gas to the additional heat source  20   a , upon completion of the time selectively adjusted by the user in the additional operation timer Tad.  
      In the cases in which the energy used for heating is the electric energy, with the heat sources  20  and  20   a , if existing, being defined by electric resistances, the electromagnetic obturator  41  and the thermocouple  42  are not provided.  
      In this case, the interruption of energy supply to each heat source  20 ,  20   a  is produced by an operation timer associated with the processing unit  60 , in order to instruct the latter to interrupt, through a corresponding electronic switch, the passage of electric energy which supplies the respective heat source.  
      As it can be noted, the present control system allows the user to be informed of the moment in which the cooking chamber  11  of the oven  10  is found at a pre-set operating temperature level, this information being obtained by the selected operating temperature being indicated to the processing unit  70  by the decoder  50 , and also by means of the information stored in the processing unit and which associate, with each operating temperature, an initial heating time which has been previously defined as a function of the constructive characteristics of each oven  10 . Thus, after defining the operating temperature and starting the operation of the oven, the processing unit associates, with the selected operating temperature, an initial heating time to be controlled by the initial timer, so as to activate the audible alarm  80  upon completion of said initial heating time processed in the processing unit  70 .  
      Aiming at guaranteeing an adequate operation of the elements indicative of the temperature status of the oven, the present control system presents, preferably, a means for checking the time elapsed between a last operation of the oven and a new operation being programmed. Therefore, the initial heating time for the cooking chamber  11  is preferably defined by the processing unit  60  also as a function of the time elapsed since the last deactivation of the oven  10  in the thermostatic control device  40  and which is measured by the operation timer Top. Thus, if the operating time elapsed since the last switching-off of the oven  10  is shorter than a determined period of time considered sufficient for a determined cooling degree of the cooking chamber, the initial heating time of the new operation of the oven will be calculated considering a certain residual temperature which is computed as a function of said time interval indicated by the operation timer.  
      While only one embodiment of the present control system has been illustrated herein, it should be understood that changes in the form and arrangement of the elements could be made, without departing from the protective scope defined in the appended claims.