EP2798907B1

EP2798907B1 - Oven wherein the power of the heater is controlled

Info

Publication number: EP2798907B1
Application number: EP12795776.9A
Authority: EP
Inventors: Mustafa Yuksel
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2011-12-26
Filing date: 2012-11-26
Publication date: 2015-09-16
Anticipated expiration: 2032-11-26
Also published as: WO2013098012A1; EP2798907A1

Description

The present invention relates to an oven wherein the power of the heater is controlled during the heating processes at low temperatures.
In the state of the art, in ovens besides the cooking processes performed at high temperatures, various heating processes such as leavening dough, making yoghurt, drying foodstuffs, thawing frozen foodstuffs, etc. realized at low temperatures are performed. In ovens, the temperature control is provided by activating/deactivating the high-powered heaters, for example changing between 1100 W and 1800 W. The relays that activate/deactivate the heaters are subjected to high-value currents and the lifespan of the relays is decreased. Moreover, an accurate temperature control cannot be provided by activating/deactivating the high-powered heaters. When the high-powered heaters are desired to be operated at low power levels, they can be connected in series by means of the relays, but the desired low power level cannot be obtained.
In the Great Britain Patent Application GB2241615 , an electric oven is disclosed, comprising a heater change-over switch that provides the heaters to be connected in series or parallel and thus provides the power levels thereof to be changed.
The aim of the present invention is the realization of an oven wherein the power of the heaters is precisely controlled during the heating processes at low temperatures.
The oven realized in order to attain the aim of the present invention, explicated in the first claim and the respective claims thereof comprises more than one relay that provides the heaters to be connected in parallel thereby enabling them to be operated at high power levels or provides the heaters to be connected in series thereby enabling them to be operated at low power levels, and also comprises a triac that is connected in series with the heaters connected in series by means of the relays, thus providing a power level much lower than the power level obtained by means of the heaters connected in series.
During the processes requiring lower power such as thawing frozen foodstuffs, making yoghurt, leavening dough, drying foodstuffs, etc., the control unit provides the heaters to be connected in series by means of the relays and activates the triac. During the normal cooking processes requiring high power, the control unit provides at least one of the heaters to be connected in parallel with the mains voltage and deactivates the triac.
In an embodiment of the present invention, in cases requiring low power levels, the triac is activated by means of a triac control relay energized by the control unit.
In another embodiment of the present invention, without using a relay connected to the triac, the control unit directly changes the triac to turned-on (voltage chopping) position, thus activates it or changes the triac to turned-off (conducting the entire voltage without chopping) position and controls it.
In the present invention, the control unit changes the voltage control settings of the triac in variable mains voltage conditions and provides the triac to chop the bigger portion of the voltage at a mains voltage lower than the normal value and to chop the smaller portion of the voltage at a mains voltage higher than the normal value, thereby preventing the heaters from being affected by the variable voltage.
In the oven of the present invention, low power levels are obtained by connecting the heaters in series by means of the relays, and by activating the triac the lowest power level is attained, which cannot be obtained only by connecting the heaters in series. The heater power levels adjusted by the triac are not affected by the variable mains voltage and a precise temperature control can be performed in processes requiring low power.
The oven realized in order to attain the aim of the present invention is illustrated in the attached figures, where:

Figure 1 - is the schematic view of an oven that is not operating wherein the main relay and the relays that control the heaters are not energized.
Figure 2 - is the schematic view of the oven in Figure 1, wherein the triac and the heaters are operated in series by energizing the main relay.
Figure 3 - is the schematic view of an oven that is not operating wherein the main relay, the triac control relay and the relays that control the heaters are not energized.
Figure 4 - is the schematic view of the oven in Figure 3, wherein the triac and the heaters are operated in series by energizing the main relay.

The elements illustrated in the figures are numbered as follows:

1. Oven
2. 102, 202 Heater
3. Control unit
4. Triac
5. Voltage measuring circuit

The oven (1) comprises more than one heater (2, 102, 202) connected to the AC mains voltage and having various power levels different from each other or equal to each other, more than one relay (R1, R2, R3, R4) that is connected between the heaters (2, 102, 202) and the neutral wire (N) or the live wire (L) of the AC mains voltage and that provides the heaters (2, 102, 202) to be connected in parallel thereby enabling them to be operated at high power levels or provides the heaters (2, 102, 202) to be connected in series thereby enabling the power levels thereof to be decreased and a control unit (3) that provides the heaters (2, 102, 202) to be operated at the desired power level by activating/deactivating the relays (R1, R2, R3, R4).
The oven (1) of the present invention comprises a triac (4) that is connected in series with the heaters (2, 102, 202) connected in series with the AC mains voltage by means of the relays (R1, R2, R3, R4) and that provides the heaters (2, 102, 202) to be operated at a power level lower than the power level obtained in the series connection thereof, and the control unit (3) that activates/deactivates the triac (4) depending on the desired power level or controls the triac (4) by changing the voltage chopping settings thereof.
In the oven (1) of the present invention, the control unit (3) enables the heaters (2, 102, 202) to be connected in series by means of the relays (R1, R2, R3, R4) during processes requiring low power level and low temperature such as thawing frozen foodstuffs, making yoghurt, leavening dough, drying foodstuffs, etc. and provides the power level of the heaters (2, 102, 202) to be decreased by activating the triac (4) connected in series with the heaters (2, 102, 202).
When the triac (4) is activated, the total power value of the heaters (2, 102, 202) drops below the power value obtained when the heaters (2, 102, 202) are connected in series. The temperature is prevented from suddenly increasing/decreasing when the current is supplied to the heaters (2, 102, 202) operated at the minimum power level or the current is broke, thus the temperature adjustment of the oven (1) can be performed more precisely. In the oven (1), a less-varying temperature is obtained during processes performed at low temperatures and requiring precise temperature adjustment.
During foodstuff cooking processes requiring high power levels, the control unit (3) enables one or more than one heater (2, 102, 202) to be connected in parallel (not shown in the figures) with the AC mains voltage by means of the relays (R1, R2, R3, R4) and deactivates the triac (4).
In an embodiment of the present invention, the oven (1) comprises a triac (4) control relay (R5) that is connected between the live wire (L) and the triac (4) after the heaters (2, 102, 202), that is energized by the control unit (3) during the heating processes requiring low power level and that provides the triac (4) to be activated by connecting it to the live wire (L) (Figure 4).
In this embodiment, the control unit (3) enables the heaters (2, 102, 202) to be connected in series with the AC mains voltage by means of the relays (R1, R2, R3, R4) when the heaters (2, 102, 202) are required to be operated at a power level lower than the power level obtained in series connection, connects the triac (4) to the live wire (L) by energizing the triac (4) control relay (R5), thereby activates the triac (4). By means of the triac (4) control relay (R5), the triac (4) is provided to be subjected to low level current only when required and no current passes through the triac (4) at high power levels. Thus, the triac (4) is prevented from overheating and costs are lowered by decreasing the dimensions of the heat sink used for cooling the triac (4) or by completely removing the heat sink. During foodstuff cooking processes performed at high temperatures, the control unit (3) enables one or more than one heater (2, 102, 202) to be connected in parallel with the AC mains voltage by means of the relays (R1, R2, R3, R4) and breaks the connection between the triac (4) and the live wire (L) by de-energizing the triac (4) control relay (R5), thus deactivates the triac (4).
In another embodiment of the present invention, the control unit (3) controls the triac (4) by changing the triac (4) to turned-on (conducting by chopping the voltage) position or to turned-off (conducting without chopping the voltage) position with the signals transmitted by means of the gate terminal (G) of the triac (4) (Figure 2).
In this embodiment, the control unit (3) enables the heaters (2, 102, 202) to be connected in series with the AC mains voltage by means of the relays (R1, R2, R3, R4) when the heaters (2, 102, 202) are required to be operated at a power level lower than the power level obtained in series connection during processes such as thawing the frozen foodstuffs, making yoghurt, leavening dough, drying foodstuffs, etc. and provides the triac (4) to be activated by transmitting a signal through the gate terminal (G).
In the present invention, the control unit (3) comprises a voltage measuring circuit (5) that measures the AC mains voltage, changes the value chopping settings of the triac (4) by changing the firing angles thereof with the signals transmitted by means of the gate terminal (G) when the voltage measuring circuit (5) detects that the AC mains voltage is higher or lower than the normal value, thereby preventing the heaters (2, 102, 202) from being affected by the variable AC mains voltage conditions. When the AC mains voltage exceeds the normal value, the control unit (3) provides the current supplied to the heaters (2, 102, 202) from the triac (4) to be decreased and when the AC mains voltage drops below the normal value, provides the current supplied to the heaters (2, 102, 202) from the triac (4) to be increased. By the control unit (3) intervening the operation of the triac (4), the undesired power increase or power decrease in the heaters (2, 102, 202) in variable AC mains voltage conditions are compensated and the power obtained from the heaters (2, 102, 202) is provided to be constant.
In an embodiment of the present invention, the oven (1) comprises a bottom heater (2), an upper heater (102), a grill heater (202), a main relay (R-main) connected to the live wire (L) of the AC mains voltage and providing the heaters (2, 102, 202) to be activated/deactivated, a first relay (R1) that is connected to the normally-closed (NC) contact by not being energized by the control unit (3) when low power level is desired and that provides the bottom heater (2) and the upper heater (102) to be connected in series, a second relay (R2) that is situated between the junction (J1) of the bottom heater (2) and the upper heater (102) and the live wire (L) and that is connected to the normally-open (NO) contact by being energized when low power level is desired, a third relay (R3) that is situated between the junction (J2) of the upper heater (102) and the grill heater (202) and the neutral wire (N), that is connected to the normally-open (NO) contact by not being energized when low power level is desired and that provides the upper heater (102) and the grill heater (202) to be connected in series, and a fourth relay (R4) that situated at one end of the grill heater (202), that is connected to the normally-open (NO) contact by being energized when low power level is desired and that connects the grill heater (202) to the neutral wire (N) (Figure 1, Figure 2, Figure 3, Figure 4).
When the oven (1) is desired to be operated at low power level, the heaters (2, 102, 202) are provided to be connected to the live wire (L) by the main relay (R-main) being energized by the control unit (3), the first relay (R1) is not energized, but the second relay (R2) is energized, and the bottom heater (2) and the upper heater (102) are provided to be connected in series. The third relay (R3) is not energized and the grill heater (202) is provided to be connected in series with the upper heater (102) by breaking the connection between the junction (J2) of the upper heater (102) and the grill heater (202) and the neutral wire (N). The fourth relay (R4) is energized and a connection is provided between the grill heater (202) and the neutral wire (N). The triac (4) is activated by energizing the triac (4) control relay (R5) or by the control unit (3) directly transmitting a signal to the triac (4), and the bottom heater (2) - the upper heater (102) - the grill heater (202) and the triac (4) are provided to be connected in series (Figure 2, Figure 4).
In the oven (1) of the present invention, all the heaters (2, 102, 202) can be controlled independently by being connected in parallel by means of the relays (R1, R2, R3, R4), low power levels are obtained by connecting the bottom heater - the upper heater (2 - 102), the upper heater - the grill heater (102 - 202) or the bottom heater - the upper heater - the grill heater (2 - 102 - 202) in series and a power level lower than the low power level obtained is obtained by activating the triac (4) directly or by means of the triac (4) control relay (R5). For example, in the case that the bottom heater (2) is 1200 W, the upper heater (102) is 1100 W and the grill heater (202) is 1100 W, 600 W of power is obtained when two heaters "(2 - 102) or (102 - 202)" are connected in series, approximately 370 W of power is obtained when three heaters (2 - 102 - 202) are connected in series, and the power drops below 200 W, for example 185 W, by activating the triac (4). The heater (2, 102, 202) power levels adjusted by the triac (4) are not affected by the variable AC mains voltage and a precise temperature control can be performed in processes requiring low power.
It is to be understood that the present invention is not limited by the embodiments disclosed above and a person skilled in the art can easily introduce different embodiments. These should be considered within the scope of the protection postulated by the claims of the present invention.

Claims

An oven (1) for cooking, comprising more than one heater (2, 102, 202) connected to the AC mains voltage and having various power levels, more than one relay (R1, R2, R3, R4) that provides the heaters (2,102,202) to be connected in parallel thereby enabling them to be operated at high power levels or provides the heaters (2, 102,202) to be connected in series thereby enabling the power levels thereof to be decreased and a control unit (3) that provides the heaters (2, 102, 202) to be operated at the desired power level by activating/deactivating the relays (R1, R2, R3, R4), characterized by a triac (4) that is connected in series with the heaters (2, 102,202) connected in series with the AC mains voltage by means of the relays (R1, R2, R3, R4) and that provides the heaters (2, 102, 202) to be operated at a power level lower than the power level obtained in the series connection thereof, and the control unit (3) that controls the triac (4) depending on the desired power level,
further characterized in that the control unit (3) comprises a voltage measuring circuit (5) measuring the AC mains voltage and that, when the AC mains voltage exceeds the normal value, provides the current supplied to the heaters (2, 102, 202) from the triac (4) to be decreased by decreasing the voltage chopping setting of the triac (4) and that, when the AC mains voltage drops below the normal value, provides the current supplied to the heaters (2, 102, 202) from the triac (4) to be increased by increasing the voltage chopping setting of the triac (4).
An oven (1) as in Claim 1, characterized by the control unit (3) that enables the heaters (2, 102,202) to be connected in series by means of the relays (R1, R2, R3, R4) and that activates the triac (4) connected in series with the heaters (2, 102,202) during processes requiring low temperature
An oven (1) as in Claim 1 or 2, characterized by a triac (4) control relay (R5) that is connected between the live wire (L) and the triac (4) after the heaters (2, 102, 202), that is energized by the control unit (3) during the heating processes requiring low power level and that provides the triac (4) to be activated by connecting it to the live wire (L).
An oven (1) as in Claim 1 or 2, characterized by the control unit (3) that controls the triac (4) by changing the triac (4) to turned-on (conducting by chopping the voltage) position or to turned-off (conducting without chopping the voltage) position with the signals transmitted by means of the gate terminal (G) of the triac (4).
An oven (1) as in any one of the above claims, characterized by a bottom heater (2), an upper heater (102), a grill heater (202), a main relay (R-main) connected to the live wire (L) of the AC mains voltage and providing the heaters (2, 102, 202) to be activated/deactivated, a first relay (R1) that is connected to the normally-closed (NC) contact by not being energized by the control unit (3) when low power level is desired and that provides the bottom heater (2) and the upper heater (102) to be connected in series, a second relay (R2) that is situated between the junction (J1) of the bottom heater (2) and the upper heater (102) and the live wire (L) and that is connected to the normally-open (NO) contact by being energized when low power level is desired, a third relay (R3) that is situated between the junction (J2) of the upper heater (102) and the grill heater (202) and the neutral wire (N), that is connected to the normally-open (NO) contact by not being energized when low power level is desired and that provides the upper heater (102) and the grill heater (202) to be connected in series, and a fourth relay (R4) that is situated at one end of the grill heater (202), that is connected to the normally-open (NO) contact by being energized when low power level is desired and that connects the grill heater (202) to the neutral wire (N).