JP2502724B2 - Cooking oven - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a burning control method for a cooking oven having a function of burning dirt adhering to a wall surface of a cooking chamber at a high temperature.

2. Description of the Related Art Electric ovens, gas ovens, and microwave ovens are often used that can not only perform normal cooking but also thermally remove food stains accumulated on the storage wall during normal cooking. This decontamination consists of two processes. The first is
It is a process in which food stains are thermally decomposed in a cooking chamber kept at a high cleaning temperature of 440 ° C or higher for 1 to 4 hours. This process produces smoke, odors and gases. The second is a process in which when a cooking chamber atmosphere containing smoke, odor, and gas is exhausted to the ambient atmosphere through the exhaust passage, the oxidation catalyst arranged in the exhaust passage oxidizes smoke, odor, and gas. This dirt removal process is called self-cleaning and is referred to in US Pat. No. 3,428,434, US Pat.
457, U.S. Pat. No. 4,292,501.

Problems to be Solved by the Invention Conventionally, the cleaning temperature has been automatically controlled to 470 ° C. However, the cleaning time is US Pat.
It was determined by the timer settings, as shown in 1,158. The cleaning time is defined as the time from the start of heating until the temperature of the cooking chamber is kept at the cleaning temperature for a period of time and then the temperature of the cooking chamber is lowered to about 300 ° C. by stopping the heating. The cleaning time depends on the cleaning temperature and the amount of food stains. The higher the cleaning temperature, the shorter the cleaning time. However, the cleaning temperature varied from 470 to 30 ° C for each oven. The cleaning time required at the minimum cleaning temperature of 440 ° C is about 1.5 times the cleaning time required at the maximum cleaning temperature of 500 ° C. This indicates that it is difficult to accurately determine the cleaning time for each oven even if the amount of food stains is constant.

Furthermore, the amount of food stains in practical use varies greatly.
In the case of light dirt, it is a sufficient cleaning process to stop the heat supply to the cooking chamber and reduce the cooking chamber temperature immediately after the cooking chamber temperature reaches the cleaning temperature. In this case, a cleaning time of about 1 hour (heating up for about 1/2 hour, cooling for about 1/2 hour) is required. On the other hand,
In the case of heavy dirt, the cooking chamber temperature is kept at the cleaning temperature for about 3 hours. In this case, a cleaning time of about 4 hours (heating up for about 1/2 hour, holding at the cleaning temperature for about 3 hours, cooling for about 1/2 hour) is required. Under practical conditions, there are many intermediate food stains. These facts indicate that even if the cleaning temperature is controlled to be constant, it is difficult to accurately determine the cleaning time for each practical food stain. Since the cleaning time cannot be accurately determined in this way, a large amount of cleaning time is required and wasteful energy is consumed in order to avoid insufficient stain removal.

Therefore, an object of the present invention is to provide a control means capable of automating self-cleaning by automatically and accurately detecting the cleaning time even if the cleaning temperature varies by 470 ± 30 ° C.

Means for Solving the Problems And in order to achieve the above object, the present invention provides a gas sensor in an atmosphere after smoke, odor, or part or all of gas is oxidized by an oxidation catalyst, and the sensor The signal inclination is detected, and the cleaning time is automatically controlled based on the inclination signal.

Action During the self-cleaning process, a large amount of decomposition products including various gases, odors and smoke are generated. Further, when these decomposition products are oxidized by the oxidation catalyst while passing through the exhaust passage to the ambient atmosphere, a large amount of water vapor and carbon dioxide are generated as an oxidation product, and a large amount of oxygen is also consumed as an oxidant. It

In the initial stage self-cleaning process, when food stains accumulated on the storage wall start to decompose, the amounts of decomposition products, oxidation products, and oxygen consumed (hereinafter, simply consumed oxygen amount) increase with heating. However, in the intermediate step of heating for a certain period of time, the amount of food stains decreases with heating due to the progress of thermal decomposition, so that the decomposition products, oxidation products, and oxygen consumption amount decrease. When the food stain is completely decomposed in the final stage except for a small amount of residue, no decomposition products and oxidation products are generated, and oxygen is not consumed either. In the present invention, the gas sensor can detect a change in the oxygen consumption of the oxidation product with respect to the heating time, so that an accurate heating time is required.

Hereinafter, the present invention will be described with reference to the accompanying drawings. First
The drawing is a block diagram of a cooking oven according to an embodiment of the present invention, which includes a cooking chamber 3 surrounded by a storage wall 1 and a front door 2, an upper electric heating element 4, and a lower electric heating. It comprises an element 5, an exhaust passage 6, an oxidation catalyst 7, a gas sensor 8, a cooking chamber temperature sensor 9 and a controller 10. The gas sensor 8, the upper and lower electric heating elements 4, 5 and the cooking chamber temperature sensor 9 are electrically connected to the controller 10 by leads 11, 12, 13, 14 respectively. The gas sensor 8 is arranged behind the oxidation catalyst 7 in the exhaust passage 6. A heating means consisting of upper and lower electric heating elements 4, 5 supplies heat to the cooking chamber 1.

The control device 10 includes a temperature detecting means 106 for detecting the temperature based on the signal from the cooking chamber temperature sensor 9, and a temperature comparing means 107 for comparing the detected temperature with the cleaning temperature.
Gas concentration gradient signal generating means 101 for generating a gas concentration gradient signal from the signal of the gas sensor 8 and the gradient signal for detecting the point where the gas concentration changes from increasing to decreasing or decreasing to increasing. Code detection means 102
After this change point is detected, a bending point detection means 103 for detecting a bending point where the gas concentration decreases or increases, a timer means 104 for determining a cleaning time based on the output of the bending point, and this timer It is composed of a heater control means 105 for outputting a control signal to the heating means based on the output of the means 104 and the output of the temperature comparison means 107.

During normal cooking, food stains 15 accumulate on the inner surfaces of the storage wall 2 and the front door 3. When it becomes necessary to remove this food stain 15, the cooking chamber temperature, defined as the ambient temperature of the cooking chamber 1, begins to rise from room temperature to a cleaning temperature of about 470 ° C. In the following description, about 1 g and about 20 g of tarred salad oil was randomly applied to the storage wall 2 as light food stain 15 and severe food stain 15, respectively. When the temperature of the cooking chamber reaches about 400 ° C. or higher, the food stain 15 begins to decompose, and a decomposition product 16 is generated. This decomposition product 16
Consists of gases such as methane, ethane, water vapor, carbon monoxide, carbon dioxide, hydrocarbons, odors and smoke. The cooking chamber atmosphere containing the decomposition products 16 is exhausted to the ambient atmosphere through the exhaust passage 6. Since this cooking chamber atmosphere contacts the oxidation catalyst 7, the decomposition products 16 are oxidized by the oxidation catalyst 7, converted into water vapor and carbon dioxide, and oxygen is consumed. As a result, the clean atmosphere 17 free of the dirty decomposition products 16 is exhausted to the ambient atmosphere. Since the gas sensor 8 is arranged behind the oxidation catalyst 7 in the exhaust passage 6, the gas sensor 8 detects the gas component in the clean atmosphere 17. In this embodiment, the cleaning time can be automatically detected by detecting the gas component of the clean atmosphere 17. Since the water vapor and carbon dioxide generated by the oxidation of the decomposition products 16 are present in the clean atmosphere 17, or the oxygen is consumed by the oxidation and the oxygen concentration in the clean atmosphere 17 is reduced, the gas sensor 8 serves as a humidity sensor. , Carbon dioxide sensor and oxygen sensor are desirable.

The gas sensor 8 has an ambient temperature of 300 in the exhaust passage 6.
It is desirable to be placed at a temperature below ℃. Exhaust passage 6
Due to the heat of combustion of the decomposition products 16, the ambient temperature is in the range from a maximum temperature of about 600 ° C. near the oxidation catalyst 7 to a minimum temperature of about 200 ° C. near the outlet of the clean atmosphere 17. The gas sensor 8 is required to operate at a temperature higher than its ambient temperature. When high temperature operation is required, reliability is reduced,
It has many disadvantages such as difficulty in connecting lead wires and thermal oxidation. This indicates that it is desirable that the ambient temperature of the gas sensor 8 is as low as possible. However, the exhaust passage 6
Since the minimum ambient temperature is less than 200 ° C. (temperature near the outlet of the exhaust passage 6), it is desirable that the gas sensor 8 is arranged at a place where the ambient temperature is 300 ° C. or lower in consideration of designing ease of the cooking oven.

As mentioned above, the typical gas sensor 8 is a humidity sensor. Of the many humidity sensors, the absolute humidity sensor is preferred. This is because the ambient temperature of the humidity sensor is as high as 200 to 300 ° C., and the relative humidity in the exhaust passage 6 is so low that it is difficult to measure. Furthermore, since the sensor is preferably arranged in a place where the ambient temperature is 300 ° C. or less, the absolute humidity sensor is
It is desirable to operate at a high temperature of 300 ° C or higher. As a typical absolute humidity sensor, RuO _{2 on} the opposite first and second surfaces
There is a plate-shaped ZrO ₂ -MgO ceramic with an electrode film formed on it. This ZrO ₂ -MgO absolute humidity sensor operates at high temperature of 500-600 ℃.

Using a ZrO ₂ -MgO absolute humidity sensor, the heating time dependence of typical absolute humidity was measured as shown in FIG.
Note that FIG. 2 also shows the heating time dependency of the cooking chamber temperature. The heating time is defined as the heating time after the heating energy is supplied to the cooking chamber 1. The cooking chamber temperature reached and was maintained at a cleaning temperature of about 470 ° C. in about 1/2 hour, as shown by curve A. The cooking chamber temperature sensor 9 was used for this temperature control. For light food stains 15 and heavy food stains 15, the absolute humidity changed with heating time as shown by curves B and C, respectively. Absolute humidity initially increased in both cases, after about 40 minutes and about 80 minutes heating time, about 15 each
A maximum concentration of g / m ³ , about 60 g / m ³ was reached (indicated by points B'and C '). Then the absolute humidity, on the contrary, begins to decrease, after about 1 hour and about 2.5 hours of heating time respectively
An initial absolute humidity of about 10 g / m ³ (indicated by inflection points B ″ and C ″) was reached. The absolute humidity behavior shown by curves B and C results in the following process. When the temperature of the cooking chamber starts to rise, the decomposition rate of the food stain 15 increases with the temperature of the cooking chamber during the initial heating. Since water vaporization occurs due to the catalytic oxidation of the decomposition products 16, the absolute humidity also increases as the decomposition rate of the food soil 15 increases. However, at the cleaning temperature, in the intermediate stage after being heated for a certain time,
On the contrary, the decomposition rate decreases. This also reduces absolute humidity. This is because the amount of food stain 15 decreases with heating time due to the progress of thermal decomposition. In the final heating stage, when the food soil 15 is completely decomposed except for a small amount of residue, steam is no longer generated. As a result, the absolute humidity becomes the initial low absolute humidity.

In this way, the initial heating time corresponding to the bending points B ″ and C ″
t _b may be determined by the signal of the absolute humidity sensor.
After the initial heating time t _b of about 1 hour for light food stains 15 and about 2.5 hours for heavy food stains 15, most of the food stains 15 are removed, but a small amount of residual food stains 15 remains on the storage wall 2. It adhered and was difficult to remove by cooling with a light wipe. However, even for light food stains 15, heavy food stains 15
It was also found that a small amount of residual food stain 15 was completely removed by cooling with light wiping after additional heating for about 1/2 hour. From these facts, it is understood that the cleaning time including the initial heating time t _b and the additional heating time t _b is required to completely remove the food stain 15.

In the case of light food stains 15, a small amount of residual food stains 15 remains on the storage wall 2 and is difficult to remove by cooling with a light wipe, but a small amount of residual food stains 15 does not harm normal practical cooking. Therefore, it is desirable to stop the heating energy to the cooking chamber 1 after the initial heating time t _b of about 1 hour. Of course, as described above, the initial heating time t _b it is clear that is automatically determined from the signal of the absolute humidity sensor. This self-cleaning process adds about 1/2 hour of cooling time, so cleaning time is about 1.
5 hours. However, when it is required to remove a small amount of residual food stains 15 with a light wipe after cooling,
It is desirable to stop heating energy after a heating time including the initial heating time t _b and about 1/2 hour of additional heating time t _a.
In this self-cleaning process, the cleaning time is about 2 hours. For severe food stains 15, the cleaning time can be determined in the same manner as described for light food stains 15.

When a carbon dioxide sensor was used instead of the absolute humidity sensor, the same measurement results as in FIG. 2 were obtained. This is natural considering that both humidity and carbon dioxide are mainly generated by the oxidation of the decomposition product 16 of the food stain 15.

Another typical gas sensor is an oxygen sensor. 20
There are a voltaic battery type oxygen sensor and a limiting current type oxygen sensor as an oxygen sensor that operates at a high temperature of 0 ° C. or higher. However, the former requires a reference gas containing a certain amount of oxygen and is not suitable for use. On the other hand, the latter does not require a reference gas and has excellent linearity, which makes it suitable for this application. Since the oxygen sensor is placed at the same position as the absolute humidity sensor, it is desirable that the oxygen sensor also operate at a high temperature of 300 ° C or higher.

A limiting current type oxygen sensor was used to measure the heating time dependence of a typical oxygen concentration during self-cleaning as shown in FIG. Note that FIG. 2 also shows the heating time dependency of the cooking chamber temperature. As shown by the curve D, the cooking chamber temperature was controlled to be almost the same as the cooking chamber temperature shown by the curve A in FIG.

For light food stains 15 and severe food stains 15, the oxygen concentration varied with heating time as shown by curves E and F, respectively. Oxygen concentration is about 21% initially in both cases
From a low concentration to a low concentration and reached a minimum concentration of about 20% and about 11% (indicated by points E'and F ') after heating times of about 40 minutes and about 80 minutes, respectively. . Then the oxygen concentration starts to increase, about 1 hour and about 2.
After heating for 5 hours, the initial concentration (flexion points E ″ and F ″
Reached). The oxygen concentration behavior shown by curves E and F is attributed to a process similar to that described for the absolute humidity sensor of FIG. In other words, the oxygen consumed and the humidity generated result in the same catalytic oxidation of the decomposition products 16. As a result, the curves E and F are symmetrical to the curves B and C in FIG. This means that the cleaning time can be determined by the oxygen sensor by the same means as described above in the case of the absolute humidity sensor.

As shown in FIG. 4, the decomposition product 16 is oxidized in the oxidation catalyst 7, so that the gas sensor 8 may be arranged in the oxidation catalyst 7. In this case, the heating time dependence of absolute humidity or oxygen concentration similar to that shown in FIGS. 2 and 3 is obtained. However, since the temperature inside the oxidation catalyst 7 becomes a high temperature of over 600 ° C., the gas sensor 8 is required to operate at a high temperature of over 600 ° C. or higher. ZrO ₂ -MgO absolute humidity sensor and limiting current type oxygen sensor are 500 to 600 ℃ and 400 to 100, respectively.
Operating at 0 ° C, these sensors are also useful in this arrangement.

FIG. 5 shows a bending point detection method when an absolute humidity sensor is used as the gas sensor 8. In this method, the absolute humidity H is measured by the gas concentration gradient signal generator 101 at a constant time pitch Δt at every sampling time.
The absolute humidity slope signal ΔH is calculated by the formula ΔH = H _m −H _m−1 . Here, H _m is the absolute humidity measured m times. When ΔH = H _m −H _m−1 ≦ 0, the absolute humidity is passing through the maximum absolute humidity shown by point B ′ in FIG. 5 and is changing from an increasing tendency to a decreasing tendency. Found by detector 102. The negative slope signal ΔH is continuously measured, and when it becomes larger than the negative set value ΔH _o as shown in the following equation, that point is the bending point B ′ and the bending detector.
Determined by 103.

ΔH = H _n −H _n−1 ≧ ΔH _o where H _n is the absolute humidity measured at the n-th time, and n >> m.

If you need to remove a small amount of residual food soil 15 after cooling light wiping, additional heating time t _a is set by the timer 105. Typical additional heating time t _a is about 1/2 hour. However, it may be determined an additional heating time t _a from the start of heating associated with the initial heating time t _b required bending point of FIG. 5 B "is obtained. For example, additional heating time t _a is t _a = it is determined as kt _b. where k after a constant. additional heating constant t _a has passed, the heater control circuit 105 stops the heating energy supply to the electrical heating elements 4 and 5.

The cooking chamber temperature is controlled as follows during the self-cleaning process. First of all, heating energy is supplied to the electric heating elements 4 and 5, and the temperature of the cooking chamber is gradually increased. The cooking chamber temperature is measured by the cooking chamber temperature detector 106 to which the signal from the cooking chamber temperature sensor 9 is input. The measured cooking chamber temperature is compared with the set cleaning temperature by the comparator 107. According to the output signal of the comparator 107, the heater control circuit 105 causes the electric heating elements 4,5
Control heating energy supply to the. Heater control circuit 105
It is preferable that the heater current is continuously adjusted by the firing angle method of the thyristor. This continuous control of the heater current is effective in that any small heating power can be obtained. A simple adjustment using an on / off relay is also valid. The cooking chamber temperature, elapsed additional heating time t _a is the supply of heat energy is retained on the cleaning temperature until stopped.

The complex control system described above is implemented using a microcomputer. FIG. 6 shows a flowchart of a microcomputer for realizing the above operation when the absolute humidity sensor is used as the gas sensor 8.

In FIG. 6, the block “Sub |” indicates a normal cooking subroutine, and the block “Sub |” represents the formula ΔH = H _m −H _m-1 (or ΔH
9 shows a subroutine for obtaining an absolute humidity gradient signal ΔH defined by / Δt = (H _m −H _m−1 ) / Δt).

When a self-cleaning process is required, the first button that determines the process is manually selected. Next, the cooking chamber temperature sensor 9 starts measuring the cooking chamber temperature T _c , and heating energy is also supplied to the electric heating elements 4 and 5. Until the cooking chamber temperature T _c exceeds the reference temperature T _o ,
The cooking chamber temperature T _c is repeatedly measured through loop I shown in FIG. This loop process is necessary to eliminate steam malfunctions that are unrelated to the catalytic oxidation of cracked products 16. For example, there is condensed water or water vapor that results from the evaporation of water on the storage wall 2 that happens to fly from the kitchen. Such water evaporates completely by the time the cooking chamber temperature T _c reaches a temperature below 200 ° C., so a typical reference temperature T _o is about 20.
It is desirable to set it to 0 ° C.

When the condition T _c ≧ T _o is satisfied, the operation proceeds to the next step to determine whether the cooking chamber temperature T _c is higher than the cleaning temperature T _s . If T _c <T _s , heating energy is supplied to the electric heating elements 4 and 5, and if T _c ≧ T _s , heating energy is not supplied to the electric heating elements 4 and 5. After both of the processes described above, operation proceeds to the Sub.ltoreq. Block to detect the absolute humidity slope signal .DELTA.H. As shown in FIG. 5, the absolute humidity H is measured at a constant time pitch Δt at each sampling time, and the slope signal Δ defined by the formula ΔH = H _m −H _m−1.
H is obtained by the gas concentration gradient signal generator 101.

In the next process, the sign of the slope signal ΔH is determined by the slope signal sign detector 102. When ΔH> 0, loop I
After a time pitch Δt through I, the step returns to the “Tc Input” step and is repeated until ΔH ≦ 0.

When ΔH ≦ 0 is satisfied, the bending point detector 103 determines whether or not the negative slope signal ΔH is larger than the negative reference slope signal ΔH _{o in the} next process.

When ΔH <ΔH _o , the time pitch Δ passes through Loop III.
After t, the step returns to the “Tc Input” step, and ΔH ≧
Repeat until ΔH _o is obtained. After [Delta] H ≧ [Delta] H _o is first inflection point B, which is defined as the point to be satisfied "is obtained, a timer 104 with a set additional heating time t _a is started operating. After additional heating time t _a, the heater control circuit The supply of heating energy to the electric heating elements 4 and 5 is stopped by 105.

In the above-described embodiment, the cleaning operation based on the bending point B ″ in FIGS. 5 and 6 is shown. However, as another cleaning operation, the maximum absolute humidity point indicated by point B ′ in FIG. 5 is set. based cleaning operation was also effective. For example, in this operation, additional heating time t _a is determined according to the equation t _a = k't _m. here k 'and t _m each is a constant, the maximum absolute humidity from the start of heating Is the heating time required to obtain

On the other hand, as described in FIG. 3, the oxygen sensor is also effective as the gas sensor 8. Since the heating time dependency of oxygen concentration is symmetrical with that of absolute humidity, almost the same process as described in FIGS. 5 and 6 can be used. This process does not consume oxygen, which is unrelated to the catalytic oxidation of the decomposition products 16, and therefore loop I of FIG.
It is not necessary to repeatedly measure the cooking chamber temperature T _c using. This shows that a simpler process is sufficient than the process using absolute humidity and humidity sensor.

EFFECTS OF THE INVENTION As described above, as is apparent from the examples, the present invention detects water vapor generated when a decomposition product of food stains is oxidized by an oxidation catalyst, carbon dioxide or oxygen consumed by a sensor, and detects those gases. Since the cleaning time is judged by the density gradient signal generating means, its sign detecting means, and the inflection point detecting means, and the energy supply to the heating means is controlled based on this judgment result, the cleaning temperature varies. However, the cleaning time can be automatically and accurately determined. Therefore, the self-cleaning can be automated, and a sufficient cleaning effect can be obtained with the minimum energy and time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a cooking oven according to an embodiment of the present invention, and FIG. 2 is a diagram showing heating time dependence of typical absolute humidity and cooking chamber temperature during a self-cleaning process,
FIG. 3 is a diagram showing heating time dependence of typical oxygen concentration and cooking chamber temperature during the self-cleaning process, and FIG.
FIG. 6 is a configuration diagram of another embodiment of the oven of the present invention, FIG. 5 is a diagram showing the heating time dependency of absolute humidity for explaining the principle and operation of the present invention for determining a bending point, and FIG. 6 is a cleaning process. It is a flow chart which shows an example of time control operation. 1 ... Cooking room, 2 ... Storage wall, 3 ... Front door, 4, 5 ...
Heater, 6 ... Exhaust passage, 7 ... Oxidation catalyst, 8 ... Gas sensor, 9 ... Cooking room temperature sensor, 101 ... Gas concentration gradient signal generating means, 102 ... Inclination signal sign detecting means, 103
...... Bending point detection means, 104 ...... timer means, 105 ...... heater control means, 106 ...... temperature detection means, 107 ...... temperature comparison means.

Claims (6)

(57) [Claims] 1. A cooking chamber surrounded by a storage wall and a front door, heating means for supplying heat to the cooking chamber, and a cooking chamber containing smoke, odor, and gas generated by decomposition of food stains during self-cleaning. An exhaust passage through which the atmosphere is exhausted to the ambient atmosphere, an oxidation catalyst arranged in the exhaust passage, and an atmosphere after a part or all of the smoke, odor, and gas is oxidized by the oxidation catalyst. A gas sensor disposed in the cooking chamber, a cooking chamber temperature sensor disposed in or near the cooking chamber, a temperature detection unit that detects a temperature based on a signal from the cooking chamber temperature sensor, and a temperature detection unit that detects the temperature. Temperature comparing means for comparing the temperature and the cleaning temperature, gas concentration gradient signal generating means for generating a gas concentration gradient signal from the signal of the gas sensor, and change from increase in gas concentration to decrease A code detection unit of the tilt signal for detecting a point at which changes to increase that point or from a decrease,
After the change point is detected, a bending point detecting means for detecting a bending point where the gas concentration decreases or increases, a timer means for determining a cleaning time based on the bending point output, and an output of the timer means and A cooking oven, comprising: heater control circuit means for outputting a control signal to the heating means based on the output of the temperature comparison means. 2. A gas concentration gradient signal generator configured to sample a gas concentration signal at a certain sampling time pitch to generate a gas concentration gradient signal between gas concentrations at adjacent sampling times, and a gas. Claims: A bending point detector configured to detect when a concentration gradient signal exceeds a reference gradient, and timer means configured to include an additional heating time after detection of the bending point. A cooking oven according to the item 1). 3. The cooking oven according to claim 1, wherein the gas sensor is an oxygen sensor. 4. The cooking oven according to claim 2, wherein the oxygen sensor is a limiting current type oxygen sensor. 5. The cooking oven according to claim 1, wherein the gas sensor is an absolute humidity sensor. 6. The cooking oven according to claim 1, wherein the gas sensor is a carbon dioxide sensor.