FR2597583A1 - Control circuit for a domestic cooking oven with an electronic regulation thermostat - Google Patents

Abstract

Control circuit for a domestic cooking oven comprising at least one power circuit 100, characterised in that it further comprises a electronic circuit for regulating the temperature of the oven, the said electronic circuit being composed of at least one electronic thermostat comprising a relay RT, a contact THC, at least one comparator A1 whose output is linked to the relay RT, and whose inputs are subjected respectively to a datum voltage and to the voltage from a temperature probe SF of the oven, so that the said electronic thermostat provides at least one regulation function. Application: manufacture of domestic cooking appliances.

Description

 The present invention relates to a control circuit for a domestic cooking oven of the electric power circuit type.

 Generally, ovens of this type are equipped with at least one control thermostat, a plurality of electrical safety circuits and a multi-position switch for selecting the cooking mode.

 An oven of the above type is manufactured by the applicant under the manufacturer reference 847 and its control circuit, represented in FIG. 1, constitutes the state of the art.

 The main elements are the power circuit (100) and the thermostats (TH1, TH2, TH3, TH4); the entire circuit being known to those skilled in the art. The thermostats (TH1 ... TH4) regulate the temperature of the oven in normal operation, and / or thermal safety.

 In addition, a double winding fan motor (M) for cooling the muffle has two operating speeds: a high speed for starting and the pyrolysis function; a low speed for normal cooking.

The main drawbacks of the circuit in Figure 1 are
- impossibility of modulating the low speed of the fan motor, source of discomfort for the user
- dispersion from one thermostat to another; the accuracy of the usual bulb or stem thermostats is not related to the overall quality of the oven and requires costly testing with rejection of some of the thermostats
- Drift phenomena causing breakdowns and user interventions.

 In order to overcome all these drawbacks, the applicant has replaced the usual thermostats with a circuit with electronic thermostats.

 The present invention relates to a control circuit for a domestic cooking oven comprising at least one power circuit, characterized in that it further comprises an electronic circuit for regulating the temperature of the oven, said electronic circuit being composed at least one electronic thermostat comprising a relay, a contact, at least one comparator, the output of which is connected to the relay and the inputs of which are respectively subjected to a set voltage and to the voltage of an oven temperature probe, so that said electronic thermostat performs at least one regulating function.

In addition, said electronic circuit can include, without limitation, a second comparator, the output of which is in parallel with the output of the first comparator so that the thermostat also provides one by micro-contacts (MC1) and (MC2) of the locking latch. door
- a rectifier circuit (200)
- a control switch (I, II) which comprises a series of contacts (1, la; 2, 2a; ...) whose diagram in FIG. 5 shows in gray4-the closing states and in clear the states d 'opening
- a programmer (PR)
The electronic circuit of Figure 3 mainly comprises
- a supply circuit with rectifier (200)
- a thermal switch (IT) coupled to the resistor (R1) with terminals (A) and (B) also noted in the diagram in Figure 2
- an electronic assembly, connected to the output (24 V) of the rectifier (200), which includes comparators (A1, A2, A3, A4) with their appropriate control circuits.

In particular
- the comparator inputs (Al) are respectively connected to the variable terminal of a setpoint potentiometer (RC) and to a temperature probe (SF) placed in the oven; the output of the comparator (Al) being connected to the relay (RT)
- the comparator inputs (A2) are connected to the probe (SF) and to a fixed resistance bridge; the output of the comparator (A2) is in parallel with the output of the comparator (Al);
- the comparator inputs (A3) are connected, in a rut, in parallel to the probe (SF) and to an input of (Ai), and on the other hand, to a resistance bridge giving a fixed setpoint; the output of the comparator (A3) being in parallel on the pyrolysis circuit and on the relay (RS) of the regulation contact (3206)
- the comparator inputs (A4) are respectively connected to the common point of the transistor (T1) of the pyrolysis circuit and of the potentiometer (RC), and to the common point of the resistance bridge with the fixed input of (A2) the output of the comparator (A4) is connected to the output of the comparator (A3).

 The comparator (Al) has the function of comparing the set temperature of the oven, displayed on the potentiometer (RC), with the temperature detected by the probe (SF) in the oven.

 The comparator (A1) controls the relay (RT) of the contact (THC) according to the information received, via a transistor (T1).

 An indicator can be provided in series with the relay (RT) to inform operation.

 The comparator (A2) has the function of detecting whether the probe (SF) is in short-circuit, and in this case of cutting the supply of the relay (RT).

 The comparator (A3) controls the relay (RS) associated with the safety function contact.

 The inputs of said second comparator are then connected to the oven temperature sensor and to a predetermined resistance bridge.

 The electronic circuit in accordance with the invention may also include, and is not limited to, another electronic thermostat composed at least of a relay, a contact, a comparator whose output is connected to said relay, and whose the inputs are respectively connected to the oven temperature probe and to a fixed safety probe so that the oven does not exceed a critical safety temperature.

 Thus, all of the regulation and safety functions of the power circuit of the oven are ensured by, at most, two contacts1, one of the two contacts at least ensuring several functions.

 In addition, a single oven temperature sensor is used to inform each of the comparators.

The following description of a preferred embodiment of the invention is made with reference to the appended figures for which
- Figure 1 is an electrical diagram of the oven 847 manufactured by the applicant and considered to be the state of the art;
- Figure 2 is a diagram of the electrical circuit according to the invention;
- Figure 3 is a diagram of the electronic circuit according to the invention and associated with the circuit of Figure 2
- Figures 4 and 5 are the contact diagrams of the switches of Figures 1 and 2.

 The preferred non-limiting embodiment of the invention has two parts: the electrical part shown in FIG. 2, the electronic part shown in FIG. 3.

 To facilitate the comparison between the prior art (FIG. 1) and the invention (FIG. 2), the same arrangement of diagrams has been used.

The two circuits have a substantially identical power circuit (100) within the reach of those skilled in the art. The diagram of FIG. 2 further comprises:
- a thermostat contact (THC) for controlling the power circuit ensuring regulation of the oven temperature at the requested setpoint
- a thermostat contact (THR) for limiting the cooking of the oven temperature to 320
- a thermal switch (IT) coupled to a resistor (R1);
- a fan motor (MVe) coupled to a resistor (R2)
- a door locking motor (MVr) switched on or off (THR). The comparator (A3) compares the information received by the probe (SF) and the set point (TF) (320).

 A time delay of two seconds (Tempo 2 S) is, for example, but not limitatively added to the transistor (T5) for the control of (RS).

 The comparator (A4), the transistors (T3, T4), the indicator lights (L2, L3) are part of the pyrolysis circuit.

 For the operation of the switch, reference will be made to French request 82 00 089 from the applicant and, for the operation of the circuit, reference will be made to the description given below.

The operation of the fan during cooking and pyrolysis is as follows; as soon as the switch is in a position other than zero, we have
1) contact closure (2, 2a) (see figure 5)
2) high speed motor supply (MVe), because the resistor (R2), connected in series with (MVe) is short-circuited by the contact (THR) at rest.

 3) after approximately three seconds, the contact (THR) switches, the motor (MVe) is supplied through the resistor (R2), and therefore switches to low speed.

 Said resistance (R2) can be modified as a function of the low speed desired by the user.

 This particular assembly of the ventilation circuit has several functions: it makes it possible to use a single-winding motor, therefore less expensive than the double-winding motor; it makes it possible to set the value of the low speed to a value lower than that of the prior art; it modulates this low speed according to the comfort of the user while ensuring high-speed starting.

 During cooking operation, the power circuit (100) is controlled by the contact (THC) itself controlled by the relay (RT).

 In cooking mode, a set temperature, variable up to 300 for example, is displayed on (RC). The comparator output (Al) is at state 1 if the voltage detected on the oven probe (SF) is lower than that detected on (RC), and the relay (RT) is supplied. Otherwise, the comparator output (Al) is at state 0 and the relay (RT) is cut.

 Electronic thermostat, contact (THC) and relay (RT); here behaves like a control thermostat with variable setpoint temperature.

 In addition, at least one safety device can be provided in the event that the probe (SF) is defective. In the event of a short circuit on the probe (SF), the comparator (A2) switches, interrupts the relay (RT), opens the contact (THC) and the power circuit (100).

 In the event of a contact fault (THC), regulation takes place on the contact (THR) as follows: if the oven probe (SF) detects a temperature above 320 which is the maximum temperature authorized by the manufacturer and the temperature setpoint (TF), then the comparator (A3) switches and supplies the relay (RS).

 The contact (THR) switches, opens the power circuit, while the fan motor (MVe) goes at high speed to cool the oven.

Regulation at 320 is now ensured by the contact (THR) which provides a safety function.

 In the event of a fan failure (MVe) for example, the temperature at the circuit level can reach a critical value, for example (85C +5 C), the power supply to the electronic circuit is cut by the thermal switch (IT).

 The contacts (THC) and (THR) open, the power supply to the electronic circuit being cut off.

 In the event of a mains failure, the oven is restarted when the power returns and on condition that the temperature at the electronics level is below 85 ° C.

 The operation in pyrolysis is described below.

 The contacts (5-5a) and (4-4a) allow the door to be locked. The opening of the micro-contact (MC1) blocks the transistor (Tl) (Figure 3). There is no more cooking information. The comparator (A4) switches and the locking indicator (L2) comes on.

 At the same time, a fixed setpoint, substantially 500 ° C., is applied to the comparator (Al) whatever the value of the potentiometer (RC). The oven temperature is regulated by the electronic thermostat (RT), (THC).

 As soon as the oven temperature is above 320 C, the comparator (A3) switches, the pyrolysis indicator (L3) lights up and the relay (RS) switches the contact (THR). The engine (MVe) is then at high speed and the contact (II, 5, 5a) supplies the heating elements.

 At the end of programming, the oven cools, the temperature drops below 300 ° C, the contact (THR) toggles enabling unlocking as soon as the switch leaves the pyrolysis position.

 Note that depending on the position of the switch in the zero position (see Figure 5), the electronic thermostat is supplied by the contacts (MC1) and (II, 1, la) until opening (MC1).

 The thermal switch (IT) ensures in pyrolysis mode the same safety function as in cooking mode and in addition prohibits resetting.

 A current of about 2 mA remains in the power supply through the resistor (R1). This resistor (R1) placed below the thermal switch (IT) will maintain the said thermal switch (IT) at a temperature above 85 C.

 Resetting the switch and waiting for one to two minutes will authorize restarting in cooking or pyrolysis.

 The process is identical for a power cut of more than three minutes, the temperature at the thermal switch quickly exceeding 85 C.

The achievements of the invention are numerous
- marked reduction in dispersion and drift
- improved precision and elimination of overlapping of the thermostat ranges
- only two contacts replace the four contacts of the oven 847
- no increase in the cost price of the whole
- accumulation of functions: regulation at a setpoint temperature kills (500)) and regulation at a variable setpoint temperature (Up to 300> by a single oven temperature sensor, safety at 320 '.

- possible reduction of the low fan speed with single winding motor
- ease of control at the end of the chain and time savings: the probes are replaced by suitable resistors to simulate temperatures; the operation lasts a few minutes. Previously, a rise in temperature was necessary to control the bulbs and the power circuit; o
- memorization of mains failure by replacing the thermal fuse with a thermal switch associated with a resistor.

 For the wiring of the invention and the components not described above, reference is made to the appended figures which are sufficient for the reproduction of the invention by a person skilled in the art.

 Of course, the adjustment values indicated above are not limiting and the cabling itself may have variant embodiments, without thereby departing from the field of technical equivalents of the invention.

 For example, a delay capacitor can be added to the input of the transistor (T2); in operation, the relay time delay (RT) is greater than that of the relay (RS) being, for example, 1 to 2 seconds.

 Throughout the text, description, claims and descriptive abstract, it will be understood that the terms "domestic cooking oven" means any domestic cooking enclosure, whether it is a built-in or built-in enclosure, a stove enclosure ... , said cooking chamber being equipped with pyrolysis cleaning. The invention is not limited to multifunction speakers, but also applies to the whole range of the manufacturer: conventional ovens, fan-assisted, etc., by modifying the power circuit and the switch.

Claims (8)

 1) Control circuit for a domestic cooking chamber comprising at least one power circuit (100), characterized in that it further comprises an electronic circuit for regulating the temperature of the oven, said electronic circuit being composed of less than an electronic thermostat comprising a relay (RT), a contact (THC), at least one comparator (Al) whose output is connected to the relay (RT), and whose inputs are respectively subjected to a setpoint voltage and at the voltage of a temperature probe (SF) of the oven, so that the said electronic thermostat performs at least one regulation function.  2) control circuit for a domestic cooking chamber according to claim 1, characterized in that said electronic circuit further comprises a comparator (A2) whose output is in parallel with the output of the comparator (A1) so that the electronic thermostat also provides a safety function. The inputs of said comparator (A2) then being connected to the oven temperature sensor (SF) and to a predetermined resistance bridge.  3) Control circuit for a domestic cooking enclosure according to any one of the preceding claims, characterized in that the electronic circuit further comprises an electronic thermostat composed at least of a relay (RS), of a contact (THR) , a comparator (A3) whose inputs are respectively connected to the temperature probe (SF) and to a setpoint bridge (TF) giving a fixed safety value.  4) Control circuit for a domestic cooking enclosure according to any one of the preceding claims, characterized in that it comprises a thermal switch (IT) associated with a resistor (R1) connected to the power supply of the electronic circuit to ensure a thermal safety function and a fault memory function.  5) Control circuit for a domestic cooking enclosure according to claim 1, characterized in that the comparator setpoint temperature (Al) is fixed in pyrolysis operation and variable in cooking operation.  6) control circuit for a domestic cooking enclosure according to any one of the preceding claims, characterized in that it controls a fan motor (MVe) in series with a resistor (R2), said resistor (R2) being in parallel on a contact (THR) of an electronic thermostat.  7) Control circuit for a domestic cooking enclosure according to any one of the preceding claims, characterized in that it includes a relay delay (RT) composed of a capacitor mount on the input of the transistor (T2).  8) Control circuit for a domestic cooking enclosure according to any one of the preceding claims, characterized in that it includes a relay time delay (RS) composed of a capacitor mount on the input of the transistor (T5).