Ventilation system for electrical food-cooking appliances comprising a cooking hob and an oven

Abstract: A ventilation system for electrical food-cooking appliances (1) comprising a cooking hob (2) and an oven (3) with a fan (8) positioned in a compartment (9) between the two in order to generate air flow for cooling electronic components (10, 11) controlling the oven operation, in which the fan (8) is of variable speed, its speed being gauged on the basis of the appliance use.

Description: This invention relates to a ventilation system for electrical food-cooking appliances comprising a cooking hob and an oven. The system involves the use of a fan positioned within that space or compartment of the said composite appliance lying between the hob and the oven. The purpose of the fan is to provide air flow through said compartment for increasing the reliability of the electronic components positioned thereat for controlling the hob and oven. US-A-4 886 046 discloses a cooking apparatus including an eye level oven having a vent system for exhausting heated air for cooling electrical control components. US-A-4 549 052 discloses an induction cooking cartridge which includes an internal fan for cooling the various induction heating components. The main object of the invention is to provide a ventilation system which enables the level of ventilation to be adapted to the use of the appliance. A further object of the invention is to provide a ventilation system which enables the annoyance (noise) to the user deriving from unrequired excess ventilation to be reduced. A further object of the present invention is to provide a ventilation system which taking account of the appliance operating conditions gauges to an optimum extent the amount of required additional or extra ventilation on termination of the use of the appliance. These and further objects which will be more apparent from the detailed description given hereinafter are attained by a system in accordance with the teachings contained in the accompanying claims. The invention will be further understood on reading the detailed description of one embodiment thereof given hereinafter by way of non-limiting example and illustrated on the accompanying drawings, in which: Figure 1 is a schematic front view of the composite appliance with some internal parts or components shown by dashed and dotted lines; Figure 2 is an even more schematic partly sectional side view of the composite appliance; Figure 3 is a schematic illustration of the electrical/electronic circuit of the composite appliance; Figure 4 is a simplified partial flow diagram relative to the appliance operation. The appliance shown comprises an outer casing 1 with an electrical cooking hob 2, in particular (in the example) of glass ceramic, an underlying electric oven 3, and a control panel 4 with a series of setting knobs 5a, b, c, d, e and f, the knobs 5a, b being relative to oven setting, and 5c, d, e and f to the cooking hob operation. In this example it is assumed that the cooking hob 2 comprises four conventional heating elements 6a, b, c and d, each being activated by the said knobs (5c, d, e and d), with each of which there is connected in series a safety switch (klixon) which opens the power circuit on reaching a temperature dangerous for the conventional hob plate 2A with which the cooking hob 2 is provided. In this example the knob 5a is used for switching the oven on and off jointly with temperature selection made by the thermostat knob 5b, ie for powering or not powering a resistance element 7A located in the oven, and possibly a fan, not shown, if the oven is of the fan-assisted type. The knob 5b is used to set the required oven temperature. The effective temperature is measured by a sensor 7 positioned within the oven. Within the casing 1 between the oven and cooking hob there is a compartment or interspace 9 in which a variable-speed tangential fan 8 is positioned together with the electronic control and power components for the appliance. These electronic components are an electronic power module 10 and an electronic user interface 11. When in operation, the fan 8 creates within the interspace 9 an air flow along the paths indicated by the arrows of Figure 2, to limit the casing within the compartment 9. The air stream enters the compartment from rear apertures 12 and front apertures 13, strikes the electronic components 10, 11, passes partly through the cooking hob 2 (by entering through suitable holes 14 provided in the lower face of the hob and leaving through central holes facing the suction side of the fan) and discharges to the outside through a delivery duct 16. The power module 10 and the user interface 11 are connected together via a serial communication 20 allowing information relative to the system to be mutually exchanged. The power module 10 is controlled by a program based for example on fuzzy or conventional logic, able to estimate the temperature of the conventional glass plate 2A of the cooking hob 2 on the basis of the energy delivered by an individual heating element (6a, b, c, d). This temperature information is used within the power module 10 to adapt the control cycles of the resistance element or elements 6a, b, c and d such as to limit the temperature of the glass plate 2A to a set safety and reliability value. By way of the serial communication 20 this information is transferred to the user interface 11 to enable it to know the temperature conditions of the plate 2A, both when heating and when cooling. By way of this serial communication 20 the user interface 11 transmits to the power module the information relative to the position of the knobs 5c, d, e and f (regarding which of the heating elements 6a, b etc. are switched on and the thermal power which these are required to deliver). The user interface 11 is operationally connected to the knob 5b for analysis of the on/off cycles, in particular for analysis of the on and off periods (duty cycle) executed by the thermostat connected to the sensor 7. This connection enables the user interface 11 to estimate with sufficient approximation (during both heating and cooling) the temperature conditions of the environment surrounding the oven, ie of the compartment 9 in which the power module 10 and the user interface 11 are positioned and in which the temperature is limited by the fan 8. The temperature information received from the cooking hob 2 (or rather from the power module 10) and that estimated for the oven 3 enable the user interface 11 to control the variable-speed fan 8 by adapting it to the real cooling requirements of the compartment 9. Each time the heating element or elements 6a, b... of the cooking hob 2 are switched on by rotating the relative knob or knobs 5c, d, e and f, the user interface 11 acts (Figure 3) on an electronic control section 30 for the fan 8 to regulate its rotational speed on the basis of the thermal power delivered by the heating elements 6a, b ... of the cooking hob 2. In particular, if the total delivered power exceeds a certain value, the fan is regulated to maximum speed. If instead it is below this value, the user interface sets it to a reduced speed. On termination of cooking, when the knob is returned to zero, the power module 10 informs the user interface 11 of the state of cooling of the glass plate 2A, and on the basis of this information the interface decides for how much further time the fan is to operate at a reduced r.p.m. (extra ventilation). This extra ventilation subsequent to the switching-off of the cooking hob eliminates inertial temperature rises which could otherwise occur if the fan were switched off simultaneously with the cooking hob. With regard to the oven, each time it is switched on (rotation of the selection knob 5a to any position other than zero), the fan 8 is forced to operate at maximum r.p.m. under the control, by bypassing through the line 40 (Figure 3), of the electronic control section 30 for the fan 8 which is activated manually by the user interface 11 as stated. When the oven operating temperature is selected (by the knob 5b) the user interface commences its analysis of the on-off cycles of the resistance element 7A. The ambient temperature of the region 9 is deduced from this analysis. On switching off the oven, the bypass 40 is deactivated and the control of the fan 8 returns to the user interface 11 which controls the duration and intensity of the extra ventilation (for the same reasons as those described for the cooking hob 2) on the basis of the overall operating conditions "read", in practice, at the oven resistance element 7A during operation. To obtain the reduced speed or speeds of the fan 8 determined by the user interface 11, the electronic section 30 is used, and which can comprise a triac (or similar electronic switch) connected in series with the motor of the fan 8. The motor can be powered by the mains and be of the single phase induction type. The triac gate receives a square-wave signal (synchronized with zero-zero crossing) with a frequency for example of 5 Hz and a duty cycle variable from 20 to 100% set by the user interface 11. By means of this control, the motor is powered at full mains voltage only during the "on" cycle of the square control wave, whereas during the "off" cycle the motor is disconnected from the mains (and hence not powered). This method of operation can be seen as a continuous very rapid switching on and off of the motor, this on and off switching in combination with the inertia of the motor and of the mechanical part of the fan enabling the fan to run at an r.p.m. less than the rated r.p.m. Again, to ensure that the motor starts under any voltage and temperature conditions, the control signal fed to the triac gate is preceded, at the moment of switch-on, by a continuous activation signal of 5 seconds (indicative value). This prolonged activation at full power enables the motor to start under any operating condition within regulatory limits. The schematic partial flow diagram shown by way of example in Figure 4 further illustrates the invention. When a knob (5c, d, e and f) relative to the cooking hob 2 is set to position 0 (ie the off position of the relative heating element 6a, b, c and d), a check is made to determine whether the estimated (by the power module 10) temperature of the cooking hob glass plate 2A is greater than or equal to a predetermined safety temperature for the cooking hob glass plate 2A. If it is greater the fan is made to further rotate but at reduced speed. If it is less, the fan is switched off (that part of the flow diagram involved up to this point is the right side of Figure 4). In contrast, if the knobs relative to the cooking hob 2 are in an active position (left side of Figure 4), and this position involves a delivered power greater than a value P the fan is rotated at maximum speed, whereas if it does not then the speed is lower. The following advantages are obtained by the aforedescribed system: The described method of operation enables the ventilation required to maintain reliability of the components in the hob to be gauged on the basis of the use of the cooking hob, or likewise for the oven. This gauging of the ventilation is noted by the user as a general reduction in the noise and air flow produced by the appliance, and also concerns the duration and intensity of the extra ventilation. The gauging of the extra ventilation based on temperature estimates obtained by processing the delivered energy enables the desired function to be achieved without the addition of sensors (hence with zero additional cost). An embodiment of the invention has been described in which the cooking hob is of glass ceramic type or the like and has its support surface for the food containers or its hob plate 2A of that material. The invention is however also applicable to appliances in which the cooking hob comprises exposed heating elements rising from a glass ceramic or similar surface. This application is also to be considered as falling within the scope of the present document.

Claims: A ventilation system for electrical food-cooking appliances (1) comprising a cooking hob (2) and an oven (3) with a fan (8) positioned in a compartment (9) between the two in order to generate air flow for cooling electronic components (10, 11) controlling the oven operation, characterised in that the fan (8) is of variable speed, its speed being gauged by one of the electronic components (11) on the basis of the appliance use, without any manual intervention of the user. A system as claimed in claim 1, in which the resting surface of the cooking hob is of glass ceramic or the like, or in which said surface from which the heating elements rise is of glass ceramic or the like, wherein the electronic components (10, 11) comprise a power module (10) for controlling the cooking hob and able to estimate the temperature of the plate (2A) of the cooking hob (2) based on the energy delivered by the cooking hob (2), and a further electronic module (11) dialoging with the power module and arranged to know the operating condition of the oven and to estimate the temperature conditions of the compartment (9) in which the two modules (10, 11) are positioned. A system as claimed in the preceding claims, wherein the second module (11) controls the fan (8) by gauging the real cooling requirements on the basis of the temperature conditions of the compartment (9) and of the cooking hob (2). A system as claimed in the preceding claims, wherein switching-on the oven (3) causes the fan (8) to operate at maximum rotational speed, and setting the operating temperature of the oven (3) results in commencement of analysis of the oven on and off cycles such as to enable the temperature of the compartment (9) to be deduced to allow the second module (11) to set the duration of extra ventilation when the oven (3) is switched off. A system as claimed in the preceding claims, wherein with the motor of the fan (8) there is connected in series a static switch driven by a square wave at frequency less than the mains frequency which powers it, and having a variable duty cycle set by the second module (11).

Inventors: CABRI DAVIDE, FRASNETTI LUCA, SCABURRI ADRIANO, CABRI, DAVIDE, FRASNETTI, LUCA, SCABURRI, ADRIANO, Cabri, Davide, c/o Whirlpool Europe s.r.l., Frasnetti, Luca, c/o Whirlpool Europe S.R.L., Scaburri, Adriano, c/o Whirlpool Europe s.r.l.
Applicants: WHIRLPOOL CO, WHIRLPOOL CORPORATION
Application year: 1998
Main classification: H05B3
IPC codes: H05K7, H05B3, F24C15