JPH05118542A - Device to detect abnormality in combustion device - Google Patents

Abstract

PURPOSE:To detect malfunction of an oxygen sensor caused by incomplete combustion, etc., and enhance the safety of the combustion device. CONSTITUTION:The abnormality detector of a combustion device caries out the control of an increase or decrease in the quantity of fuel supplied to a burner 2 and, at the same time, a controller 9 is provided which caries out the control of an increase or decrease in the volume of air supplied for combustion based on a value detected by the detector 10 which detects the oxygen concentration in the exhaust gas. The controller 9 judges abnormality if the actual value of the detection does not change towards a reduced oxygen concentration when value of detection of the detector 10 is expected to change towards a reduced oxygen concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention executes control for increasing / decreasing the amount of fuel supplied to a burner, and at the same time, increasing / decreasing the amount of air supplied for combustion based on the detection value of a detecting means for detecting the oxygen concentration in exhaust gas. The invention relates to an abnormality detection device for a combustion device, which is provided with control means for executing

[0002]

2. Description of the Related Art For example, a limiting current type oxygen sensor (hereinafter simply referred to as an oxygen sensor) is used as such oxygen concentration detecting means. This is to detect the oxygen concentration by utilizing the fact that when a DC voltage is applied between the electrodes provided on both sides of a disk-shaped stabilized zirconia, the current that flows with oxygen ions as carriers changes depending on the oxygen concentration. is there.

Based on the output value of the oxygen sensor, the control means determines that the combustion air is insufficient if the oxygen concentration in the exhaust gas is lower than an appropriate value, and increases the air supply amount. On the contrary, if it is higher than the proper value, it is judged that the combustion air is excessive and the air supply amount is reduced. Further, the fuel supply amount to the burner is controlled to increase or decrease so as to reduce the deviation between the set hot water temperature and the detected hot water temperature in the case of a combustion device used for a hot water supply device, for example.

[0004]

However, although the air supply amount is appropriate, the combustibility deteriorates due to local deformation of the burner, local clogging, etc., and unburned components (CO, CO, H ₂ etc.) may be contained in large amounts. The output value of the oxygen sensor (hereinafter,
It is known that the sensor output) will increase.
Then, the control means erroneously determines that the air supply amount is excessive and reduces the air supply amount, so that the incomplete combustion further progresses and it becomes impossible to perform the appropriate air flow control.

As described above, when the increase / decrease control of the air supply amount for combustion is executed based on the oxygen concentration in the exhaust gas detected by using the oxygen sensor, there is a risk that incomplete combustion once becomes unstable. was there. The present invention has been made in view of the above circumstances, and an object thereof is to detect a malfunction of an oxygen sensor due to incomplete combustion and improve the safety of a combustion device.

[0006]

An abnormality detecting device for a combustion apparatus according to the present invention executes an increase / decrease control of a fuel supply amount to a burner and at the same time, based on a detection value of a detecting means for detecting an oxygen concentration in exhaust gas. A control means for executing increase / decrease control of the air supply amount for combustion is provided, and the characteristic configuration is that the control means controls the detection means of the detection means by a change in the fuel supply amount or the air supply amount. When it is predicted that the detected value will change to the oxygen concentration lower side, it is determined to be abnormal if the actual detected value does not change to the oxygen concentration lower side.

[0007]

According to the above characteristic structure, the control means first predicts a case where the detection value of the detection means changes to the oxygen concentration lower side due to the change of the fuel supply amount or the air supply amount.
For example, in a combustion device used for a water heater, when the set hot water temperature is raised or the hot water discharge amount is increased, it is predicted that the fuel supply amount will increase and the oxygen concentration will temporarily decrease. Alternatively, it is expected that the oxygen concentration will temporarily decrease when the air supply amount decreases due to the backwind.

When a change in the detected value toward the oxygen concentration lower side is actually detected, the control means increases the air supply amount in the direction of returning the oxygen concentration to the proper value. However, if incomplete combustion occurs due to the reasons described above and changes to the oxygen concentration increasing side due to the influence of unburned components, or if there is no change, that is, the change to the oxygen concentration decreasing side is not detected unexpectedly. In this case, it is determined to be abnormal, and appropriate processing such as combustion stop is performed.

[0009]

As described above, according to the present invention, since the malfunction of the oxygen sensor due to the incomplete combustion can be detected and the erroneous control by the control means can be prevented, the combustion device can be made safer. It was

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a water heater will be described below with reference to the drawings. The water heater of this embodiment is configured as shown in FIG. A combustion unit 3 having a burner 2 and a fin-tube type heat exchanger 4 for heating water by its high temperature exhaust are provided in a cylindrical case 1. A discharge side of a fan 5 as a ventilation means for supplying combustion air to the combustion section 3 is connected to the lower end of the cylindrical case 1, and an exhaust passage 6 is connected to the upper end of the cylindrical case 1.

The fuel supply passage 7 to the burner 2 is provided with a gas proportional valve 8 for adjusting the fuel supply amount. The opening of the gas proportional valve 8 is controlled by a combustion controller 9 using a microcomputer. That is,
The proportional valve control circuit 9a in the combustion controller 9 controls the exciting current of the gas proportional valve 8 so as to reduce the deviation between the hot water temperature set by the setting means R and the hot water temperature detected by the hot water temperature detecting means S. Control, and thus the amount of fuel supply.

In order to control the hot water temperature, it is necessary to appropriately control not only the fuel supply amount to the burner 2 but also the combustion air supply amount to the combustion section 3. Therefore, the combustion controller 9 also controls the blowing amount of the fan 5, that is, the rotation speed. Then, in order to monitor whether or not the amount of air supplied to the combustion section 3 is proper, a limiting current type oxygen sensor (hereinafter, simply referred to as an oxygen sensor) 10 as a detection means for detecting the oxygen concentration in the exhaust gas is provided in the exhaust passage. 6 is provided. That is, if the oxygen concentration in the exhaust gas is higher than the proper value, it can be determined that the air supply amount is excessive, and if it is smaller than the proper value, the air supply amount can be determined to be insufficient.

As shown in FIG. 2, the oxygen sensor 10 comprises a sensor element 11, a terminal 12, a terminal block 13 and a mesh cover 14. As shown in FIG. 3, the sensor element 11 is constructed by forming platinum electrodes 11b on both sides of a disk-shaped stabilized zirconia 11a and joining a cap 11d having a small hole 11c on one side thereof.
When a voltage is applied between both electrodes 11b, a current using oxygen ions as carriers flows due to the pumping action.

The inflow of air into the cap 11d is caused by the small hole 1
Since it is limited by 1c, the current becomes almost constant (limit current) in a predetermined voltage range. Since this limiting current changes in proportion to the oxygen concentration in the air, a constant voltage (monitoring voltage) is applied between both electrodes 11b, and the oxygen concentration can be detected from the current value at that time. . or,
Since the pumping action occurs at a high temperature (about 500 ° C.), the heater 11e is provided above the cap 11d.
Is integrally formed, and the sensor element 11 is heated by energizing the heater 11e.

The detected value (current value) of the oxygen sensor 10 is input to the combustion controller 9, and the detected value of the combustion controller 9 is an appropriate value (oxygen concentration target value) determined according to the fuel supply amount to the burner 2. ) Fan 5 to be maintained in
Is controlled to control the amount of air supplied to the combustion unit 3. The relationship between the target oxygen concentration value and the fuel supply amount is obtained in advance by experiments, and is as shown in FIG. 6, for example. The rotation speed of the fan 5 is controlled by the fan control circuit 9b in the combustion controller 9 by changing the voltage applied to the fan motor.

Next, the outline of the control by the combustion controller 9 from the start of combustion to the stop will be described based on the flow charts of FIGS. 4 and 5. As shown in FIG. 4, when the hot water supply plug (not shown) is opened and the water flow switch 15 is turned on, first, the fan 5 is driven to perform pre-purge.
After a while, the gas proportional valve 8 and the like are opened and the burner 2 is ignited.

Next, a combustion control / abnormality detection process is performed. This process will be described later, but as a result of the abnormality detection,
When an abnormality is detected (when the abnormality flag is set), the abnormality lamp (also used as the combustion lamp) 16 provided in the setting means R is blinked to compulsorily stop the combustion. If no abnormality is detected, the water flow switch 15
The combustion control / abnormality detection process is repeated until is turned off. That is, the hot water tap is closed and the water flow switch 15
Is turned off, the gas proportional valve 8 and the like are closed to stop combustion, and the fan 5 is stopped after a few minutes of post-purge.

The combustion control / abnormality detection process is performed, for example, in FIG.
It becomes like the subroutine shown in. First, the set hot water temperature set by the setting means R and the detected hot water temperature detected by the hot water temperature detecting means S are read. Then, the fuel supply amount (that is, the operation amount of the gas proportional valve 8) is determined based on the deviation between the set hot water temperature and the detected hot water temperature (process (a)).

This fuel supply amount (manipulation amount) is stored in the memory in the combustion controller 9 and compared with the previous value. As a result, if the fuel supply is increasing,
Since it is predicted that the oxygen concentration in the exhaust gas will decrease accordingly, the prediction flag is set. If the fuel supply amount is decreasing or there is no change, the prediction flag is reset. This prediction flag is used in the abnormality detection process described later.

The gas proportional valve 8 is driven by the exciting current corresponding to the fuel supply amount (operation amount), and then the oxygen concentration target is calculated from the relationship between the oxygen concentration target value and the fuel supply amount (see FIG. 6). The value is determined (process (b)). On the other hand, the detection value of the oxygen sensor 10 is read and the actual oxygen concentration in the exhaust gas is detected.

Then, when the above-mentioned prediction flag is set, that is, when the decrease in the oxygen concentration in the exhaust gas is predicted due to the change in the fuel supply amount, the actual detection value of the oxygen sensor 10 decreases (to be exact, , The oxygen concentration is decreasing). If the detected value does not decrease, incomplete combustion occurs and the oxygen sensor 1
Since 0 is considered to be malfunctioning, an abnormality flag is set and the process returns to the main routine of FIG.

Since it is normal when the detected value of the oxygen sensor 10 is lowered, the air supply amount (the operation amount of the fan 5) is determined based on the deviation between the oxygen concentration target value and the detected value. Then, the fan 5 is driven at a voltage corresponding to the air supply amount (operation amount). When the above process ends, the process returns to the main routine.

In the actual process, the oxygen concentration is properly adjusted in consideration of the delay time until the oxygen concentration in the exhaust gas decreases due to the increase in the fuel supply amount and the control delay until the air supply amount increases. A delay time is set for the set / reset of the anticipation flag so that the decrease of the can be detected.

Other examples will be listed below. In the above-mentioned embodiment, when abnormality is detected, the decrease in the oxygen concentration in the exhaust gas is predicted from the change in the fuel supply amount that occurs randomly during the combustion control. The fuel supply amount may be changed by an operation to temporarily generate a state in which a decrease in the oxygen concentration in the exhaust gas is predicted, and the malfunction check of the oxygen sensor may be performed.

The decrease of the oxygen concentration in the exhaust gas can be predicted not only when the fuel supply amount changes, but also the decrease of the oxygen concentration can be predicted from the change of the combustion air supply amount. For example, if the fan drive voltage is temporarily lowered slightly to reduce the air supply amount within the range where incomplete combustion does not occur when the fuel supply amount is constant, naturally the decrease in the oxygen concentration in the exhaust gas is predicted. It is possible to determine whether or not there is a malfunction by checking the detection value of the oxygen sensor of.

Although slightly complicated, it is also possible to predict a decrease in oxygen concentration in exhaust gas from changes in both the fuel supply amount and the air supply amount.

It should be noted that reference numerals are given in the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a water heater according to an embodiment of the present invention.

FIG. 2 is a sectional view of a limiting current type oxygen sensor.

FIG. 3 is a sectional view of a sensor unit.

FIG. 4 is a flowchart showing a process of a combustion controller (control means).

FIG. 5 is a flowchart showing a process of combustion control / abnormality detection.

FIG. 6 is a graph showing the relationship between the fuel supply amount and the oxygen concentration target value.

[Explanation of symbols]

 2 burner 9 control means 10 detection means

Claims (1)

[Claims] 1. An increase / decrease control of a fuel supply amount to a burner (2), and an increase / decrease control of a combustion air supply amount based on a detection value of a detection means (10) for detecting an oxygen concentration in exhaust gas. An abnormality detection device for a combustion apparatus, which is provided with control means (9) for executing the above, wherein the control means (9) detects the detection means (10) based on a change in the fuel supply amount or the air supply amount. An abnormality detection device for a combustion device, which is configured to determine that the value is abnormal if the actual detected value does not change to the oxygen concentration lower side when the value is predicted to change to the oxygen concentration lower side.