Patent Publication Number: US-2016238260-A1

Title: Cooking oven having a cooling fan and improved method of controlling the cooling fan of the cooking oven

Description:
The present invention relates to a method of controlling a cooling fan of a cooking oven, in particular a built-in type cooking oven which has a chimney for exhausting steam from a cooking chamber to an outside by the suction effect of the cooling fan. 
     It is customary to install a cooking oven underneath a kitchen counter, in particular between cabinets, and to integrate it with the kitchen furniture. In comparison to a free-standing cooking oven, a built-in cooking oven cannot efficiently radiate off its heat into the kitchen environment. Therefore, a built-in cooking oven is generally provided with a cooling fan which is arranged to intensively ventilate its critical parts. Thus, a built-in cooking oven must be properly ventilated to prevent a breakdown thereof and any hazards that might be caused by its hot parts. 
     In a built-in cooking oven, the cooling fan is additionally utilized for exhausting the steam generated inside the cooking chamber during the cooking process to an outside. 
     A satisfactory completion of the cooking process requires the steam generated in the cooking chamber to be effectively exhausted to an outside. However, the hot ambient air inside the cooking chamber is also discharged together with the exhausted steam. Consequently, a certain amount of thermal energy is dissipated with the discharged hot air. Therefore, an energy consumption of the cooking oven generally increases as the cooking oven starts compensating for the lost thermal energy. 
     WO 2011/080097 A2 discloses an oven with a ventilation device. The oven comprises a cooking chamber and a chimney which extends from the cooking chamber into an exhaust duct. The exhaust duct opens to an outside. The ventilation device has a fan which blows air into the exhaust duct. Thereby, the steam in the cooking chamber is sucked and discharged to an outside. The oven monitors a degree of humidity inside the cooking chamber by utilizing a humidity sensor. The ventilation device causes the cooling fan to blow the ambient air into the exhaust duct when the sensed humidity exceeds a threshold level. 
     Humidity sensors generally measure a capacitance or a resistance of a probe exposed to the cooking environment. Using a humidity sensor for regulating exhaust of steam constitutes in principle an adequate technique. However, humidity sensors have several drawbacks. They are easily contaminated and susceptible to aging. Moreover, a humidity sensor incurs additional costs and renders the cooking oven to become maintenance-intensive. Consequently a customer satisfaction reduces. 
     An objective of the present invention is to provide a method of controlling a built-in cooking oven which overcomes the aforementioned problems of the prior art and which improves an energy efficiency of the cooking oven without compromising a cooking performance and a cooling performance thereof. 
     This objective has been achieved by the method of controlling a cooking oven according to the present invention as defined in claim  1 , and the cooking oven according to the present invention as defined in claim  9 . Further achievements have been attained by the subject-matters respectively defined in the dependent claims. 
     The control method of the present invention comprises: a step of acquiring a user selection of a type of food to be cooked and a user selection of a target temperature to be set for the cooking process; and a step of switching a cooling fan motor on/off based on the acquired user selections. Thereby, the energy consumption of the built-in cooking oven is optimized with respect to the cooking conditions i.e., the type of food and the target temperature. 
     In an embodiment, an on-period and an off-period which are to be used in the on/off switching step are initially derived using a functional relationship which has been pre-established between the target temperature and the on/off-periods. By determining the on-period and the off-period in accordance with the selected target temperature, the on/off switching of the motor can be individually adapted to the thermal conditions which will prevail in a cooking chamber of the cooking oven. The amount of steam generated inside the cooking chamber generally depends on the amount of the food and the type of the food to be cooked. Therefore, in this embodiment the on-period and the off-period which have been initially determined according to the target temperature are subsequently rectified with a respective weighting factor which is specifically preset for the selected type of food to be cooked. By rectifying the on/off-periods, the on/off switching of the motor is further individually adapted to the humidity which will prevail in the cooking environment of the cooking chamber. Thereby, the correct amount of steam can be exhausted to an outside of the cooking chamber without unnecessarily increasing the energy consumption and the cooking duration. Most importantly, the use of any humidity sensor or the like can be dispensed with. 
     In another embodiment, the on-period and the off-period which have been initially determined are not subjected to any rectification, if the user has not selected a type of food via the user interface. In this embodiment, the initially determined on/off-periods which correspond to the selected target temperature are used as default on/off-periods. 
     In another embodiment, the motor is permanently switched off throughout the preheating phase. A substantial amount of the heat which is generated throughout the whole cooking process is generally produced in the preheating phase as the ambient temperature inside the cooking chamber is gradually elevated to target temperature. By inhibiting operation of the cooling fan during the preheating phase energy loss can be prevented. Such inhibition does not impose any risk to the critical parts of the cooking oven since the heat generated in the preheating phase is initially concentrated inside the cooking chamber. Once the target temperature is reached and a steady state is attained, the motor is successively switched on and off. Thereby, the optimal cooking conditions are maintained until termination of the cooking process. 
     In another embodiment, the present control method is applied to a steam-cooking oven which utilizes steam for cooking food. In this embodiment, the motor is switched permanently off throughout the step of cooking the food with steam. Thereby, it is avoided to exhaust the generated steam to an outside which would otherwise impair the steam-cooking process. Moreover, by inhibiting the operation of the cooling fan, the hot ambient air inside the cooking chamber is prevented from being dissipated. Such inhibition does not impose any risk to the critical parts of the cooking oven since the heat generated during the steam-cooking process is generally kept relatively low. For instance the temperature inside the cooking chamber when cooking with steam is typically below 100° C. 
     In another embodiment, the present control method is applied to a steam cooking oven which utilizes steam for cleaning the cooking chamber. In this embodiment, the motor is switched permanently off throughout the step of cleaning the cooking chamber with steam. Thereby, the same benefits as in the previous embodiment are attained. 
     In another embodiment, the present control method is applied to a cooking oven which is suitable for drying food. In this embodiment, the motor is switched permanently on throughout the step of drying the food. Thereby the steam can be rapidly exhausted to an outside. Moreover, the drying process is promoted as the a relative humidity in the cooking chamber is reduced. 
     In another embodiment, the control method is applied to a cooking oven which is provided with an opening/closing unit arranged into a chimney to prevent the steam from escaping to an outside by diffusion and condensing on the critical parts, for example when the motor is switched off and the suction effect of the cooling fan is ceased. In this embodiment, the opening/closing unit is driven concurrently with the motor. Thereby, an uncontrolled discharge of the steam is avoided. Thus, an energy efficiency of the built-in cooking oven is reliably improved. 
     Additional advantages of the control method according to the present invention and the cooking oven according to the present invention will become apparent with the detailed description of the embodiments with reference to the accompanying drawings in which: 
       FIG. 1 —is a schematic perspective view of a cooking oven according to an embodiment of the present invention; 
       FIG. 2 —is a schematic perspective view of a cooking oven according to another embodiment of the present invention; 
       FIG. 3 —is a graph showing a relation between an on-period T on and a target temperature T_set according to an embodiment of the present invention; 
       FIG. 4 —is a graph showing a relation between an off-period T_off and a target temperature T_set according to an embodiment of the present invention. 
    
    
     The reference signs appearing on the drawings relate to the following technical features.
     1. Cooking oven   2. Cooling fan   3. Cooking chamber   4. Motor   5. Opening/closing unit   6. Duct   

     The control method of the present invention is suitable for controlling a cooking oven ( 1 ) which comprises a cooling fan ( 2 ) for drawing steam from a cooking chamber ( 3 ) into a chimney (not shown) and discharging it to an outside; a motor ( 4 ) for driving the cooling fan ( 2 ); and a user interface (not shown) for allowing a user to select a type of the food to be cooked and a target temperature T_set to be set for the cooking process ( FIGS. 1 and 2 ). 
     The control method of the present invention comprises a step of acquiring the user selection of the type of the food and the target temperature T_set; and a step of switching the motor ( 4 ) on/off based on the acquired user selection. Thereby, the energy consumption of the built-in cooking oven ( 1 ) is optimized with respect to the cooking conditions, in particular with respect to the type of the food and the target temperature. 
     In an embodiment, the control method further comprises: a step of determining on the basis of the selected target temperature T_set, an on-period T_on and an off-period T_off which are to be used in the on/off switching step. In this embodiment, the on-period T_on and the off-period T_off are respectively determined by using the subsequent set of Equations 1 and 2. 
         T _on= a 1( T _set) 2   +a 2  T _set+ a 3   (Eq. 1)
 
         T _off= b 1( T _set) 2   +b 2  T _set+ b 3   (Eq. 2)
 
     Herein a 1 =0.01875, a 2 =−5.625, a 3 =465; and b 1 =0.0938, b 2 =−28.125, b3=2325. 
     Graphical representations of the on-period T_on and the off-period T_off with respect to the target temperature T_set are respectively shown in  FIGS. 3 and 4 . By determining the on-period T_on and the off-period T_off in accordance with the selected target temperature T_set, the on/off switching of the motor ( 4 ) is individually adapted to thermal conditions which prevail in the cooking environment of the cooking chamber ( 3 ). In this embodiment, the on period T_on and the off-period T_off are directly calculated by using the target temperature T_set as an input. In an alternative version of this embodiment a look-up table (LUT) is used to readout the on-period T_on and an off-period T_off which correspond to the target temperature T_set. 
     In this embodiment, the control method further comprises: a step of rectifying the determined on-period T_on and the determined off-period T_off respectively with a weighting factor k_on and k_off which are preset for the selected type of food. The above Equations (Eqs. 1 and 2) are rectified to yield the subsequent set of Equations. 3 and 4. 
         T′ _on= k _on( a 1( T _set) 2   +a 2  T _set+ a 3)   (Eq. 3)
 
         T′ _off= k _off( b 1( T _set) 2   +b 2  T _set+ b 3)   (Eq. 4)
 
     Herein a 1 =0.01875, a 2 =−5.625, a 3 =465, and b 1 =0.0938, b 2 =−28.125, b 3 =2325. 
     These constitute reference values. T′_off respectively designate the rectified on-period T_on and the off-period T_off. The coefficients a 1 , a 2 , a 3 , b 1 , b 2 , b 3  should not be construed as limiting the scope of the present invention. In a version of this embodiment, the coefficients used to calculate the on/off periods fall in an interval ranging from a 15% decremented value to a 15% incremented value of the above presented reference values. T′_on and Some exemplary values of the weighting factors k_on and k_off are given in Table. I. The list provided in Table 1 is not exhaustive. In this embodiment, the weighting factors k_on and k_off are readout from a look-up table (LUT). The amount of steam generated inside the cooking chamber ( 3 ) generally depends on the amount of the food and the type of the food. By rectifying the on-period T on and the off-period T_off, the on/off switching of the motor ( 4 ) is further individually adapted to the humidity which prevail in the cooking environment of the cooking chamber ( 3 ). Thereby, the correct amount of steam can be exhausted to an outside of the cooking chamber ( 3 ) without unnecessarily increasing the energy consumption and the cooking duration. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Weighting Factor for 
                 Weighting Factor for 
               
               
                 Type of food 
                 the on-period (k_on) 
                 The off-period (k_off) 
               
               
                   
               
             
            
               
                 Roasted calf meat 
                 0.8 
                 1.2 
               
               
                 Chicken &gt;1600 grams 
                 0.9 
                 1.1 
               
               
                 Biscuits 
                 0.7 
                 1.3 
               
               
                 Beefsteak 
                 0.8 
                 1.2 
               
               
                 Bread 
                 1.1 
                 0.9 
               
               
                 Cake 
                 1.2 
                 0.8 
               
               
                 Meat balls in tomato 
                 1.3 
                 0.7 
               
               
                 sauce 
               
               
                   
               
            
           
         
       
     
     Table. I 
     In another embodiment, the control method further comprises a step of refraining rectifying the on-period T_on and the d off-period T_off which have been determined in the determining step, if the user has not selected a type of food via the user interface. In this embodiment, the control unit utilizes the default values respectively given in the Eqs. 1 and 2 when the user fails to select a type of food via the user interface. 
     In another embodiment, the control method further comprises: a step of preheating the cooking chamber ( 3 ) up to the selected target temperature T_set. In this embodiment, the motor ( 4 ) is permanently switched off throughout the preheating step. A substantial amount of the heat which is generated throughout the entire cooking process is generally produced in the preheating step as the ambient temperature inside the cooking chamber ( 3 ) is gradually increased to the target temperature T_set. By inhibiting an operation of the cooling fan ( 2 ) during the preheating step energy loss can be prevented. Such inhibition does not impose any risk to the critical parts of the cooking oven ( 1 ) since the heat generated in the preheating step is initially concentrated inside the cooking chamber ( 3 ). 
     In this embodiment, the control method further comprises: a step of maintaining the cooking chamber ( 3 ) substantially at the selected target temperature T_set so as to attain a steady state. When steady state is reached, the motor ( 4 ) is successively switched on and off in accordance with the on period T_on and the off period T_off which have been determined/rectified. Thereby, the optimal cooking conditions are maintained throughout the cooking process. 
     In another embodiment, the present control method is applied to a steam cooking oven ( 1 ) which utilizes steam for cooking food. In this embodiment, the control method comprises: a step of generating and supplying steam into the cooking chamber ( 3 ) for cooking the food with steam. In this embodiment, the motor ( 4 ) is switched permanently off throughout the step of cooking the food with steam. Thereby, it is avoided to exhaust the generated steam to an outside which would otherwise impair the cooking process with steam. In addition, by inhibiting the operation of the cooling fan ( 2 ), the hot ambient air inside the cooking oven ( 1 ) is prevented from being discharged. Such inhibition does not impose any risk to the critical parts of the cooking oven ( 1 ), since the heat generated during the cooking process with steam is generally kept at relatively low levels. For instance, the temperature inside the cooking chamber ( 3 ) when cooking with steam typically assumes values below 100° C. 
     In another embodiment, the present control method is applied to a steam cooking oven ( 1 ) which utilizes steam for cleaning the cooking chamber ( 3 ). In this embodiment, the control method further comprises: a step of generating and supplying steam into the cooking chamber ( 3 ) for cleaning the cooking chamber ( 3 ) with steam. In this embodiment, the motor ( 4 ) is switched permanently off throughout the step of cleaning the cooking chamber ( 3 ) with steam. Thereby the same benefits as in the previous embodiment are attained. 
     In another embodiment, the present control method is applied to a cooking oven ( 1 ) which is suitable for drying food. In this embodiment, the control method further comprises: a step of drying the food. In this embodiment, the motor ( 4 ) is switched permanently on throughout the step of drying the food. Thereby the steam can be rapidly exhausted to an outside. Moreover, by virtue of the permanent ventilation, a relative humidity in the cooking chamber ( 3 ) is reduced. This efficiently promotes the drying process. 
     In another embodiment, the control method is applied to a cooking oven ( 1 ) which is provided with an opening/closing unit ( 5 ) arranged into the chimney for preventing the steam from escaping to an outside by diffusion and to condensing on the critical parts, for example when the motor ( 4 ) is switched off and the suction effect of the cooling fan ( 2 ) is ceased ( FIG. 2 ). In this embodiment, the control method further comprises: a step of driving the opening/closing unit ( 5 ) to open or close the chimney in accordance with the on/off switching of the motor ( 4 ). In this embodiment, the opening/closing unit ( 5 ) is driven to an open state when the motor ( 4 ) is switched on. The opening/closing unit ( 5 ) is driven to a closed state when the motor ( 4 ) is switched off. Thereby, an uncontrolled discharge of the steam is avoided. Thus, an energy efficiency of the built-in cooking oven ( 1 ) is reliably improved and the critical parts are protected from condense water. 
     The cooking oven ( 1 ) comprises a cooking chamber ( 3 ) for receiving food to be cooked, a heater for heating the cooking chamber ( 3 ); a chimney for exhausting steam from the cooking chamber ( 3 ) to an outside; a cooling fan ( 2 ) arranged to draw the steam from the cooking chamber ( 3 ) into the chimney and to discharge it to the outside; a motor ( 4 ) for driving the cooling fan ( 2 ); and a control unit for controlling the heater and the motor ( 4 ) ( FIGS. 1 and 2 ). 
     The cooking oven ( 1 ) of the present invention further comprises a user interface for allowing a user to select a type of the food to be cooked and, separately therefrom, a target temperature T_set to be set for the cooking process and outputting the user selection to the control unit. The control unit of the cooking oven ( 1 ) of the present invention is configured to control switching on/off of the motor ( 4 ) based on the type of food and the target temperature T_set selected by the user. Thereby, the user is enabled to arbitrarily adjust the cooking temperature independently of the type of food to be cooked. The cooking oven ( 1 ) optimizes the energy consumption which complies with the user&#39;s selection. 
     In another embodiment, the control unit is further configured to determine on the basis of the selected target temperature T_set an on-period T_on and an off-period T_off to be used in the on/off switching of the motor ( 4 ). In this embodiment, the on-period T on and the off-period T_off are respectively determined by using the above-defined set of Equations 1 and 2. The control unit of the cooking oven ( 1 ) has arithmetic means (not shown) for performing the calculation tasks. The control unit is further configured to rectify the on-period T_on and the off-period T_off respectively with a weighting factor k_on and k_off which are preset for the selected type of food. In this embodiment, the weighting factors k_on and k_off are retrieved from a look-up table (LUT) which is similar to Table I. The look up table is stored in a non-volatile memory (not shown) of the cooking oven ( 1 ). 
     In another embodiment, the control unit is further configured to refrain rectifying the on-period T_on and the off-period T_off if the user has not selected a type of food to be cooked. 
     In another embodiment, the control unit is further configured to permanently switch the motor ( 4 ) off during preheating of the cooking chamber ( 3 ) up to the selected target temperature T_set, and to successively switch the motor ( 4 ) on and off during maintaining the cooking chamber ( 3 ) substantially at the selected target temperature T_set. 
     In another embodiment, the cooking oven ( 1 ) further comprises: a steam generating unit means for generating and supplying steam into the cooking chamber ( 3 ) for cooking the food with steam or for cleaning the cooking chamber ( 3 ) with steam. In this embodiment, the control unit has a mode for cooking the food with steam and/or cleaning the cooking chamber ( 3 ) with steam. The modes can be selected via the user interface. In this embodiment, the control unit is further configured to switch the motor ( 4 ) permanently off when the food is cooked with steam or when the cooking chamber ( 3 ) is cleaned with steam. 
     In another embodiment, the control unit has a mode for drying food. In this embodiment, the control unit is further configured to switch the motor ( 4 ) permanently on during the food drying process. 
     In another embodiment, the cooking device ( 1 ) further comprises an opening/closing unit ( 5 ) arranged into the chimney, to allow or to prevent the steam from escaping from the cooking chamber ( 3 ). In this embodiment, the control unit is further configured to concurrently open the chimney when switching the motor ( 4 ) on, and to concurrently close the chimney when switching the motor ( 4 ) off. 
     In another embodiment, the opening/closing unit ( 5 ) and the motor ( 4 ) are commonly connected to one relay to attain synchronization between the on/off switching of the motor ( 4 ) and the opening/closing of the chimney. 
     In another embodiment, the opening/closing unit ( 5 ) is configured by a flap (not shown). When the motor ( 4 ) is switched off, the flap is lowered so as to obstruct the flow through the chimney. When the motor ( 4 ) is switched on, the flap is raised so as to reopen the chimney. 
     In another embodiment, the chimney is fluidly connected to the cooling fan ( 2 ) by means of a duct ( 6 ) ( FIGS. 1 and 2 ). In this embodiment, the duct ( 6 ) and the chimney are both arranged on an upstream side of the cooling fan ( 2 ). 
     The control method of the present invention improves an energy efficiency of the cooking oven ( 1 ) without compromising a cooking performance and a cooling performance thereof. The correct amount of steam is exhausted in accordance with a selected target temperature and the type of food being cooked.