Abstract:
An oven comprises a housing or structure presenting a plurality of inner walls and outer walls, the inner walls defining an oven cavity in which means are provided for cooking foods, the means comprising a grill for browning the foods, the oven also comprising a door for closing the cavity. At least one aperture is present in at least one of the walls of the oven cavity, or in the door, for selective connection to the environment external to the oven, such as to interceptably introduce fresh ambient air into the cavity, controllable interceptor means being provided at the aperture to enable this selectivity in introducing the ambient air into the cavity.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an oven in accordance with the introduction to the main claim. 
     The heating elements positioned in the oven cavity tend to heat both the cavity walls and each item positioned therein by heat transfer by natural convection, by forced convection using a cooking fan, or by irradiation. Heat convection is by heat transfer from the heating elements and from the heated physical parts of the oven to the air present within the oven cavity, and optionally by the operation of a cooking fan. Heat irradiation is by the infrared radiation emitted by the heating surfaces and heated surfaces towards the cooler surfaces, for example those of the food. 
     The cabinet in which the oven is installed is cooled by a cabinet cooling fan, external to the cavity. 
     That heat portion transferred by irradiation is more effective for food browning or grilling than that due to convection. In particular, irradiation enables the heat to penetrate less into the food than the heat transmitted by convection, but facilitates surface browning of the food relative to its degree of internal cooking. 
     2. Description of the Related Art 
     A drawback of known cooking methods is that a food placed in the oven cavity can exceed the point of optimum internal cooking, reached on termination of the cooking process, if it remains in the closed cavity after deactivation of the heating elements present therein. 
     Moreover, after removal of the food from the oven cavity, this latter remains hot for a considerable time period. This condition prevents rapid cleaning of the oven by the user. The condition also delays use of the oven for preparing another food if this requires cooking temperatures less than those used in the previous cooking/cleaning process. 
     There is also the problem that if the oven has been switched off but its cavity and closure door are still hot, persons, in particular children, can suffer burns if they come into contact with it even several minutes after switch-off. 
     The state of the art also comprises ovens in which a condensate exit stack is present, connected between the cavity and the cabinet cooling system (in particular, the ventilation channel), this stack conveying the now heated cooling air to the outside of the oven. A movable closure device is provided on this stack. Such ovens do not enable fresh air to be withdrawn and fed into the oven, i.e. taken directly from the environment outside the oven, as the air flow flows only towards the outside of the cavity (normally entrained by the venturi effect); this flow is in the form of air which is not fresh as it has already been used to cool the cabinet. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an oven which is improved compared with known ovens. 
     A particular object of the invention is to provide an oven which enables a food contained within its cavity to be browned or surface finished while at the same time not involving or considerably limiting any continuation of oven cooking of the food by heat convection, but utilizing to its maximum effect the irradiation of the heating means present within the cavity. 
     Another object is to provide an oven of the aforestated type in which the cavity can be cooled within a very short time, which is in any event less than that of known ovens. 
     A further object is to provide an oven of the aforestated type, the cavity and door of which can be rapidly cooled to ambient temperature after the oven heating elements have been switched off, hence making its presence safer within an environment such as a kitchen. 
     Another object is to provide an oven which, if provided with pyrolysis self-cleaning means, presents rapid cavity cooling to facilitate the final cleaning operations by the user, especially those carried out manually. 
     A further object is to provide an oven of the stated type which has a short cooling time, such that any use of the cooling fan for the cabinet (in which the oven is present) after oven switch-off takes place is for only a limited time, which is shorter than that in known ovens, to hence achieve a noise reduction after termination of food cooking. 
     A further object is to provide an oven of the stated type by which any odours originating from the cooking fumes are eliminated during or on termination of oven use, by preventing their uncontrolled transfer from the cavity to the kitchen, and enabling them to be conveyed into an environment which is external to the oven or to the place where the oven is installed, and/or filtered. 
     Finally, a further object of the present invention is to provide an oven having apertures for air exchange between the cavity closed by the door and the outside, by which suffocation of any living being remained trapped in the oven when closed by its door, whether a child or an animal, in particular when the oven is inactive or no longer used, is prevented. 
     These and other objects which will be apparent to the expert of the art are attained by an oven in accordance with the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more apparent from the accompanying drawings, which are provided by way of non-limiting example and in which: 
         FIG. 1  is a schematic perspective view of an oven according to the invention; and 
         FIG. 2  is a section on the line  2 - 2  of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the the figures, an oven comprises a housing or structure  1  presenting side walls  2 ,  3 , a rear wall  4 , an upper wall  5  and a lower wall  6 . These walls define and bound a cavity  8  open at  9  where a door  50  is present to close the cavity  8 . The oven comprises usual heating elements  10  of which only one, the upper element, is visible in  FIG. 1 ; for simplicity, this heating element  10 , usually defined by an electrical resistance element, is shown in proximity to the upper wall  5  of the cavity  8 . 
     The oven also comprises a cooling fan for the cabinet in which the oven is inserted. 
     According to the invention, to improve oven performance and to enable it to quickly cool down after use, at least one aperture  20  is provided in at least one wall (the rear wall  4  in the example) and is connectable selectively (i.e. interruptably and preferably such as to vary its opening cross-section) to the environment external to the oven so as to be able to at least introduce fresh air (at ambient temperature) into the cavity  8 . For this purpose, the aperture can cooperate conjointly with a fan  15  for cooling the cavity  8 . Hence at the rear wall  4  there are positioned the cooling fan  15  for the cavity  8  and a cooking fan (not shown) for ventilating the cavity  8  during food preparation. Food preparation can comprise “oven cooking” achieved by convection-heating (by the elements  10 ) the air within the cavity  8 , and “browning” or surface finishing or grilling, mainly achieved by irradiating the surface of the food in the cavity by means of the element  10 . The cooking fan, together with the oven heating elements, can also be used in the automatic cleaning of the oven (pyrolysis). 
     The cooling fan  15  for the cavity  8  is driven by its own motor  18 , as is the cooking fan, both fan motors being controlled by an oven operation control unit. 
     The cooling fan  15  for the cavity  8  could be located in a different position of the oven cavity  8  than that shown in the drawings, or even in the door  50 . 
     In a preferred embodiment, the cavity cooling function and the air circulation function for convection cooking (by forced air) are performed by the same cooling fan  15 , positioned within the oven cavity  8  and operated by a single motor  18 . 
     With reference to the drawings, the aperture  20  is formed for example within a wall  21  positioned to the rear of the rear wall  4  and connected to the environment external to the oven by a channel or interspace  22  positioned beyond the wall  21  (in the opposite direction to that of the rear wall  4 ), between this latter and a rear outer wall  24  of the oven housing  1 . The interspace  22  can be connected directly to the environment surrounding the oven by an aperture  25  provided in an upper outer wall  26  at the rear of the housing  1 . Alternatively a tube  30  connected to a discharge opening into the environment external to the oven can be connected to the aperture  20 . 
     In a further embodiment, the apertures  20  and  25 , the channel  22  and the tube  30  can be entirely or partially located within the oven door  50 . 
     For each of the aforedescribed methods for connecting the aperture  20  to the outer environment (external to the oven or to the place in which the oven is installed), one or more filters (replaceable or non-replaceable) can be provided to purify the air and/or to eliminate odours, the filters comprising known materials, such as activated carbon, catalysts or materials of equivalent function designed for this purpose. 
     Manually or automatically operable interception means  33  are positioned at the aperture  20  to totally or partially close the aperture as required, to configure a particular surface section of the air interchange conduit between the oven and the outer environment. In the example shown in the figures, these interceptor means  33  are a mobile wall  35  slidable along guides  36  and operated by an actuator  38  controlled by the aforesaid oven control unit. This actuator  38  can however be of any other known type (for example controlled by a stepping electric motor, by a relay device, or by shape memory materials) and be positioned in any preferably heat shielded position of the oven housing  1 , in known manner. 
     The interceptor means  33  can also be formed differently, for example as a plurality of movable bodies defining a closure similar to a “venetian blind” or be defined by several elements movable in different directions or be defined by a fan element or by superposable grids. These means  33  can partially or totally intercept the aperture  20  as required, by a command reaching the actuator  38  from the oven control unit, or by manual action. 
     The size of the cross-section of the aperture  20  through which the air flow communicates with the outside, or of an equivalent plurality of apertures, can have a maximum such that a living being, whether a child or an animal, which can undergo suffocation if accidentally trapped within the oven, is able to breathe, even with the door closed. According to studies and tests carried out, the minimum size of the cross-section must be at least 700 mm 2 , preferably about 750 mm 2 , for example 744.5 mm 2 . 
     By virtue of the invention, fresh ambient air can be introduced into the oven cavity  8 . This can be done either during food preparation, in one or more different steps, or subsequently at the end of this preparation. For example, after attaining the desired “oven cooking” point, the control unit can operate the actuator  38 , in accordance with its own algorithm based for example on the cooking time or on the power and time of activation of the heating elements  10 , such that air can penetrate into the oven cavity  8  before commencement of the food browning stage. This results in a temperature decrease in the cavity and a lesser transfer of heat to the food by convection. Hence there is a substantial reduction in the “oven cooking” process (until it stops), whereas the food continues to receive energy by irradiation (for browning). 
     The flow of air introduced into the cavity can also be increased and controlled by activating the cavity cooling fan  15  and regulating the velocity of this fan. 
     It is also possible to make an optimal calculation of the time required to completely fill the cavity  8  with ambient air, so achieving a complete air change, while still maintaining the heating elements  10  active. This calculation is possible by calculating the flow rate by the following formula:
 
Flow rate (l/s)= A  (m 2 )×vel.air (m/s)×1000  [F1]
 
where:
     A=area of aperture  20     Vel.air=velocity of the air moved by the fan at cavity entry.   The flow rate calculation enables the flow time (time for cavity filling or emptying) to be derived, i.e.
 
Emptying time [s]=[volume of oven cavity (l)]/[flow rate (l/s)]  [F2]
   

     Using this command algorithm which enables an optimal cavity emptying time to be calculated, the control unit, by acting on the actuator  38  of the interceptor means  33  to vary the air passage cross-section of the aperture  20  and/or on the motor  18  of the cooling fan  15  of the cavity  8  to regulate the air velocity in order to control the flow rate, is able to effect air change/introduction for the cavity  8  in accordance with the optimal times in relation to the oven operating method, either for a convective cooking or a browning/grilling process. 
     In other words, knowing the parameters A, vel.air, oven cavity volume and air flow imposed by the fan, the flow time can be regulated to interact with the various cooking and cleaning algorithms, in order to optimize their results. 
     In a similar manner, the hot air can be emptied from the cavity  8  when the oven heating elements are switched off, to shorten the waiting time, for example on termination of pyrolysis before manual cleaning, just as malodorous vapours can be removed from the oven cavity  8  via the aperture  20  by the cooling fan  15  and discharged outside the room. 
     The oven of the invention can also be provided with one or more apertures formed directly in the oven walls  2 ,  3 ,  4 ,  5 ,  6  or in the door  50  and provided with their own elements  33  for varying the areas A of these apertures, which act independently or in combination on the closure or forced ventilation entry, possibly without combined operation with the cooking fan and/or cooling fan  15  for the cavity  8 . 
     Again in this case one or more conduits can be provided, associated or not associated with one or more filters, for intake of fresh air from the outer environment and/or for expelling hot air to the outside. 
     Finally, when the oven is no longer to be used, or each time the oven is in a non-operative condition, i.e. with its cavity at ambient temperature, or when the oven is out of use, the flow interceptor means  33  totally uncover the apertures to enable air change between the cavity closed by the door and the outer environment, these being dimensioned to prevent suffocation of a living being which has accidentally remained trapped in the oven cavity. 
     The oven as formed attains all the objects of the aforegoing invention. 
     A preferred embodiment of the invention has been described. Others are however possible and are to be considered as falling within the scope of the following claims, including the possible combinations of the embodiment variants and/or of the individually described characteristics.