JP2006023234A - Ammonia gas detector and ammonia gas detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ammonia gas detector constituted so that the detection output of an impedance change type detection element with respect to the ammonia gas component in a gas to be detected is set after the adhesion component of a responsive membrane is removed by the heating of the detection element and the detection output of the detection element is corrected on the basis of the set output to precisely detect the ammonia gas component, and an ammonia gas detecting method. <P>SOLUTION: The impedance change type detection element 70 responds to the ammonia gas component contained in an exhaust gas on the downstream side of a selective reducing catalyst 14 and utilizes the hopping conduction of a proton to detect the ammonia gas component to generate output voltage. A microcomputer sets the output voltage from the detection element 70 as zero point voltage after the heat treatment of the detection element 70 and subsequently calculates the change rate to zero point voltage to correct the output voltage from the detection element 70. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ammonia gas detection device and an ammonia gas detection method using an impedance change type detection element.

  Conventionally, as an example of this type of ammonia gas detection device, for example, there is an ammonia sensor employed in a diesel engine described in Patent Document 1 below. The ammonia sensor is disposed in the exhaust pipe on the downstream side of the denitration catalyst provided in the exhaust pipe of the diesel engine.

  Thus, when the urea component is added to the exhaust gas upstream of the denitration catalyst in the process in which the exhaust gas generated by the operation of the diesel engine is exhausted from the exhaust pipe through the denitration catalyst, the urea component is exhausted. It vaporizes in the gas and becomes an ammonia gas component. Along with this, the nitrogen oxide gas component in the exhaust gas reacts with the ammonia gas component in the denitration catalyst and is reduced and discharged together with the exhaust gas.

Here, since the ammonia gas component is harmful, if the ammonia gas component is discharged without contributing to the reduction of the nitrogen oxide gas component in the denitration catalyst, it leads to air pollution. Therefore, the ammonia gas component is detected by the ammonia sensor on the downstream side of the glass catalyst so as to control the amount of urea component added to the exhaust gas.
JP 2002-266627 A

  By the way, when an impedance change type detection element is used as the above-described ammonia sensor, this impedance change type detection element uses a solid acid substance as a sensitive material and utilizes the hopping conduction action of protons adsorbed on the sensitive material. The ammonia gas component is detected.

  Therefore, when the impedance change type detection element is disposed in the exhaust pipe on the downstream side of the denitration catalyst, the impedance change type detection element is arranged on the downstream side of the denitration catalyst under the proton hopping conduction action described above. In this case, the ammonia gas component is detected.

  However, as described above, the impedance change type detection element detects the ammonia gas component by utilizing the hopping conduction of protons adsorbed on the surface of the sensitive material, so the characteristic of the impedance change type detection element is the surface of the sensitive material. Varies depending on the state of

  In other words, if impurities such as soot, oil, or metal contained in the exhaust gas adhere to the surface of the sensitive material of the impedance change detection element, protons are less likely to be adsorbed on the surface of the sensitive material and hopping occurs. It affects the conduction effect and fluctuates the characteristics of the impedance change detection element.

  As a result, even if the ammonia gas component is detected by the impedance change type detection element, there is a problem that the detection accuracy of the ammonia gas component is lowered.

  Therefore, in order to deal with the above, the present invention removes the adhering component of the sensitive film by heating the impedance change type detection element, and then detects the detection output of the detection element with respect to the ammonia gas component in the detection gas. It is an object of the present invention to provide an ammonia gas detection device and an ammonia gas detection method that detect ammonia gas components accurately by setting and correcting the detection output of the detection element based on the set output.

In solving the above problems, the ammonia gas detection device according to the present invention is, according to the description of claim 1,
Both electrode portions (74) provided on the surface of the substrate (71), and a sensitive film provided on the surface of the substrate via the both electrode portions and sensitive to the ammonia gas component in the gas to be detected and causing proton hopping conduction (73), and an impedance change for detecting the ammonia gas component according to the impedance and generating a detection output based on the characteristic representing the relationship between the ammonia gas component and the impedance between the two electrode portions. An expression detecting element (70);
Heating means (77, 100, 101-104) for heating the detection element;
Setting means (110) for setting the detection output generated by the detection element after heating by the heating means as a zero point output;
Correction means (120, 130) for correcting the detection output arbitrarily generated by the detection element based on the zero point output,
The correction detection output by the correction means is detected as an output corresponding to the ammonia gas component.

  In this way, after removing the adhering impurity component of the sensitive film by heating, the detection output of the detection element for the ammonia gas component in the gas to be detected is set as a zero point output, and the subsequent arbitrary detection output of the detection element is set as above By correcting with the set zero point output, it is possible to provide an ammonia gas detection device capable of accurately detecting an ammonia gas component over a long period of time.

In the ammonia gas detection method according to the present invention, according to the description of claim 2,
Sensing the ammonia gas component in the gas to be detected and utilizing the hopping conduction of protons, the ammonia gas component is detected according to the impedance, and the impedance change type detection element (70) generated as a detection output is heated,
After this heating, the detection output generated by the detection element is set as the zero point output,
The detection output arbitrarily generated by the detection element is corrected based on the zero point output,
This corrected detection output is detected as an output corresponding to the ammonia gas component.

  As a result, it is possible to provide an ammonia gas detection method capable of achieving the same effect as that of the first aspect of the invention.

Moreover, in this invention, according to description of Claim 3, in the ammonia gas detection method of Claim 2,
The detection element includes a sensitive film (73) that is sensitive to the ammonia gas component in the gas to be detected and causes hopping conduction of protons.
The detection element is heated in multiple steps.
The detection output generated by the detection element is set as a zero point output after the plurality of heating operations.

  In this manner, by heating the detection element in a plurality of times, it is possible to remove impurities, such as moisture, soot, and oil, attached to the sensitive film much better than when the detection element is continuously heated. The zero point output can be set with higher accuracy. As a result, the function and effect of the invention of claim 2 can be further improved.

Moreover, in this invention, according to description of Claim 4, in the ammonia gas detection method of Claim 2 or 3,
Prior to heating the detection element, the temperature of the detection element or the temperature of the gas to be detected is detected,
The detection element is heated according to the detection temperature.

  Thereby, for example, even if the detection element is wet, even if the detection element is heated under the water, the detection element can be heated well without causing damage. As a result, the operational effects of the invention according to claim 2 or 3 can be further improved.

  Here, the heating of the detection element in accordance with the detection temperature described above is performed, for example, so as to prevent damage due to moisture when the detection element is heated.

  In the present invention, according to the fifth aspect, in the ammonia gas detection method according to any one of the second to fourth aspects, the presence or absence of abnormality of the detection element is determined based on the zero point output. Features.

  Thereby, if the zero point output is fixed to a value in a short circuit state or a disconnection state of the detection element, it is determined that the detection element is abnormal. This means that the deterioration of the detection element can be automatically self-diagnosed while achieving the function and effect of the invention according to any one of claims 2 to 4.

Moreover, in this invention, according to description of Claim 6, in the ammonia gas detection method as described in any one of Claims 2-5,
The detected gas is an exhaust gas that flows into the exhaust pipe (13) of the diesel engine with the operation of the diesel engine, and is an ammonia gas generated in the exhaust gas by its nitrogen oxide gas component An exhaust gas exhausted from the exhaust pipe while being reduced in a selective reduction catalyst (14) provided in the exhaust pipe with a component;
The impedance change type detection element senses the ammonia gas component according to the impedance by sensing the ammonia gas component contained in the exhaust gas on the downstream side of the selective reduction catalyst and utilizing proton hopping conduction. A detecting element that is generated,
Based on the detection output generated by the detection element after the stop of the diesel engine, it is determined whether the detection element needs to be heated again,
When it is determined that the detection element needs to be heated again, the detection element is heated again.

  According to this, during operation of the diesel engine, in a harsh exhaust gas environment including oil components, soot components, and various metal components in addition to various exhaust gas components, from the detection element after the diesel engine is stopped When it is determined that reheating is necessary based on the generated detection output, the detection element is heated again.

  For this reason, it is possible to remove the impurity component adhering again to the sensitive film after the detection element is heated during operation of the diesel engine, and as a result, stable characteristics of the detection element can be maintained when the diesel engine is started next time. Moreover, such an effect can be achieved by providing an ammonia gas detection device that can accurately detect an ammonia gas component in the exhaust gas of a diesel engine over a long period of time.

Moreover, in this invention, according to the description of Claim 7, in the ammonia gas detection method of Claim 6,
After the stop of the diesel engine, the presence or absence of abnormality of the detection element is determined based on the detection output generated by the detection element.

  Thereby, after the stop of the diesel engine, if the detection output is fixed to a value in a short circuit state or a disconnection state of the detection element, it is determined that the detection element is abnormal. This means that the self-diagnosis of the detection element can be automatically diagnosed even after the diesel engine is stopped, while achieving the effect of the invention of the sixth aspect.

  In the invention described in claim 1 or claim 2, the correction is based on, for example, a change rate of the arbitrary detection output with respect to the zero point output or a change amount of the arbitrary detection output with the zero point output. The arbitrary detection output may be corrected.

  Moreover, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

Hereinafter, each embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows a first embodiment in which the present invention is applied to an electronic fuel injection control unit 20 (hereinafter also referred to as ECU 20) mounted on a diesel engine. The diesel engine includes an engine main body 10, and the engine main body 10 sucks an air flow from an intake pipe 11 and mixes the air flow with fuel injected from a fuel injector 12. Then, an air-fuel mixture having an appropriate air-fuel ratio is formed and burned, and is made to flow into the exhaust pipe 13 as exhaust gas. The exhaust gas flowing in in this way passes through the selective reduction catalyst 14 provided in the intermediate part of the exhaust pipe 13 and is discharged from the exhaust pipe 13 into the atmosphere.

In the first embodiment, the selective reduction catalyst 14 is configured with a catalyst that employs ammonia (NH ₃ ) as a reducing agent. Therefore, as described later, when the urea component is added to the exhaust gas in the exhaust pipe 13 on the upstream side of the selective reduction catalyst 14, the added urea component is vaporized in the exhaust gas, and ammonia (NH ₃ ) gas. Become an ingredient. The nitrogen oxide gas component (NOx gas component) contained in the exhaust gas is reduced by the ammonia gas component in the selective reduction catalyst 14 to become a nitrogen component (N ₂ ), which is exhausted from the exhaust pipe 13. It is discharged into the atmosphere together with gas.

  The ECU 20 is operated by being supplied with power from the DC power supply 40 in accordance with the closing of the start key switch 30 of the diesel engine, and a fuel injector based on detection outputs of an air-fuel ratio sensor, a rotational speed sensor, an exhaust temperature sensor, and other sensors. 12 controls the fuel injection amount. Further, the ECU 20 controls the supply amount of the urea component from the urea supply source 60 into the exhaust pipe 13 based on the detection output of the ammonia gas detection device 50.

  The start key switch 30 is closed when the diesel engine is started, and is opened when the diesel engine is stopped. The air-fuel ratio sensor detects the air-fuel ratio of the air-fuel mixture based on the exhaust gas flowing into the exhaust pipe 13. The rotational speed sensor detects the rotational speed of the diesel engine. The exhaust temperature sensor detects the temperature of the exhaust gas flowing from the engine body 10 into the exhaust pipe 13.

  The urea supply source 60 selectively reduces the amount of urea component corresponding to the amount of nitrogen oxide gas component in the exhaust gas flowing into the exhaust pipe 13 from the engine body 10 into the exhaust pipe 13 under the control of the ECU 20. Supplied upstream of the catalyst 14.

  The ammonia gas detection device 50 includes an impedance change detection element 70 and a control circuit 80. As shown in FIG. 1, the detection element 70 is disposed in a portion of the exhaust pipe 13 downstream of the selective reduction catalyst 14. As shown in FIGS. 2 and 3, the detection element 70 includes an alumina substrate 71, both electrodes 72, and a sensitive film 73.

  As shown in FIG. 1, both electrodes 72 are provided on the surface of the substrate 71, and each of the electrodes 72 is configured by extending a lead portion 75 from a comb-like electrode portion 74.

Here, the two electrodes 72 are provided on the surface of the substrate 71 so as to intersect with each other in a comb-teeth shape, as shown in FIG. In addition, both the electrode parts 74 are each, for example,
The electrode is composed of 1 (wt%) platinum (Pt) and gold (Au) as the remaining components.

The sensitive film 73 is formed into a thick film by baking the sensitive material paste by screen printing on the center region of the upper half portion shown in FIG. 2 on the surface of the substrate 71 through both comb-like electrode portions 74. ing. The above-mentioned sensitive material paste is further wetted by mixing an organic solvent and a dispersant with a powder of a solid acid substance (for example, a substance containing 10% by weight of WO ₃ and 4YSZ as a remaining component) and adding a binder. Made by mixing.

  Further, as shown in FIG. 3, the detection element 70 includes a resistance temperature detector 76 and a heater 77, and the resistance temperature detector 76 and the heater 77 are built in the substrate 71. The resistance temperature detector 76 is made of a platinum resistor, and the resistance temperature detector 76 is located in the substrate 71 immediately below the sensitive film 73.

  In addition, the heater 77 is formed in a meandering pattern with a sintered body of platinum paste containing alumina, for example, and the heater 77 is lower than the resistance temperature detector 76 in FIG. Built in the substrate 71. The heater 77 is driven by being supplied with power from the DC power supply 40 under the control of the microcomputer 81 to heat the sensitive film 73 via the substrate 71 or the resistance value (temperature) of the resistance temperature detector 76. The sensitive film 73 is maintained at a constant temperature on the basis of (corresponding).

  In the detection element 70 configured as described above, an AC voltage is applied between the electrodes 72 from an AC power source (not shown), whereby the sensitive film 73 forms an impedance between the comb-shaped electrode portions 74. . The impedance changes according to the concentration of the ammonia gas component in the exhaust gas that contacts the outer surface of the sensitive film 73.

  This means that the detection element 70 has an ammonia gas concentration-impedance characteristic that represents the relationship between the concentration of the ammonia gas component and the impedance. Therefore, the detection element 70 detects the concentration of the ammonia gas component in the exhaust gas based on the ammonia gas concentration-impedance characteristic as an output voltage based on the impedance that changes accordingly. Here, this output voltage is proportional to the impedance of the detection element 70 and corresponds to the concentration of the ammonia gas component in the exhaust gas.

  As shown in FIG. 4, the control circuit 80 includes a microcomputer 81. The microcomputer 81 executes a computer program according to the flowchart shown in FIG. During this execution, the detection element 70 is heated, and the output voltage setting process is performed based on the detection output of the rotation speed sensor (hereinafter referred to as the rotation speed sensor 82) of the ECU 20 and the detection output of the detection element 70. And output voltage correction processing and stop determination processing of the diesel engine.

  The microcomputer 81 is powered by the DC power supply 40 when the operation switch 83 is closed. The computer program is stored in advance in the ROM of the microcomputer 81 so as to be readable by the microcomputer.

  In the first embodiment configured as described above, when the start key switch 30 is closed, the diesel engine is in an operating state together with the ECU 20.

  Then, the ECU 20 controls the fuel injection amount by the fuel injector 12 based on the detection outputs of the air-fuel ratio sensor, the exhaust temperature sensor, the rotation speed sensor 82 and other sensors. Therefore, the engine body 10 sucks an air flow from the intake pipe 11, mixes this air flow with the fuel injected from the fuel injector 12, forms an air-fuel mixture with an appropriate air-fuel ratio, and burns it. The gas flows into the exhaust pipe 13. The exhaust gas flowing in in this way passes through the selective reduction catalyst 14 and is discharged from the exhaust pipe 13 into the atmosphere.

  Further, in the ammonia gas detection device 50, when the detection element 70 is powered from the AC power supply and is in an operating state, the impedance of the detection element 70 is downstream of the selective reduction catalyst 14 based on the ammonia gas concentration-impedance characteristic. On the side, the value changes to a value corresponding to the concentration of ammonia gas in the exhaust gas in the exhaust pipe 13. For this reason, an output voltage proportional to the impedance of the changed value is generated from the detection element 70.

  At the present stage, when the operation switch 83 of the control circuit 80 is closed, the microcomputer 81 starts executing the computer program according to the flowchart of FIG. Then, in step 100, heat treatment is performed. In this heat treatment, the heater 77 is driven and supplied with power from the DC power source 40 under the control of the microcomputer 81, and the sensitive film 73 (in other words, through the substrate 71 at a predetermined heating temperature for a predetermined heating time). In this case, the detection element 70) is heated.

  Here, the predetermined heating time is a time sufficient to burn off the impurity component adhering to the outer surface of the sensitive film 73. The predetermined heating temperature is 600 (° C.), for example. Further, the predetermined heating temperature is very high as compared with the detectable temperature of the detection element 70 (for example, 400 (° C.)). For this reason, in the heating state, the output voltage of the detection element 70 is fixed to an abnormal voltage (for example, an upper limit value or a lower limit value of the output voltage). Therefore, the detection element 70 is maintained in a state where it cannot be normally detected.

  Thus, when the heating for the predetermined heating time described above is completed, the impurity component adhering to the outer surface of the sensitive film 73 is burned out. Next, when the temperature of the detection element 70 is lowered to the detectable temperature, the detection element 70 is in a state where it can be normally detected.

  Thereafter, in step 110, zero voltage setting processing is performed. In the zero voltage setting process, the output voltage generated by the detection element 70 at the current stage is set as the zero voltage Vz. As described above, since the impurity component is removed from the outer surface of the sensitive film 73 of the detection element 70 by burning, the zero voltage is an accurate voltage.

  Along with the setting process in step 110, an output voltage input process is performed in step 120. In this output voltage input process, the output voltage generated at this stage by the detection element 70 is input to the microcomputer 81 at step 120 as the output voltage Vn.

  Thereafter, in step 130, output voltage correction processing is performed as follows. That is, the correction voltage V is calculated using the following equation (1) based on the input output voltage Vn in step 120 and the zero point voltage Vz in step 110. This means that the output voltage Vn is corrected to the correction voltage V by the equation (1).

V = K {(Vz−Vn) / Vz)} × 100 (%) (1)
However, in Formula (1), K is a positive coefficient. In the equation (1), {(Vz−Vn) / Vz)} × 100 (%) represents a rate of change of the output voltage Vn with respect to the zero voltage Vz. Equation (1) is stored in advance in the ROM of the microcomputer 81.

  When the correction voltage V corrected as described above is input to the ECU 20 as a detection output of the ammonia gas detection device, the urea supply source 60 is controlled by the ECU 20 to supply the urea component into the exhaust pipe 13. Here, the supply amount of the urea component is controlled to an amount that reduces the concentration of the ammonia gas component in the exhaust gas flowing out from the selective reduction catalyst 14 or an amount that does not discharge the ammonia gas component from the selective reduction catalyst 14.

  When the processing in step 130 ends, it is determined in step 140 whether or not the diesel engine is stopped. At this stage, if the rotational speed detected by the rotational speed sensor 82 is not zero, the diesel engine is in operation, so that it is determined as NO in step 140.

  Thereafter, during the determination of NO in step 140, each processing in step 120 and step 130 is repeated in the same manner as described above. Then, for each output voltage Vn from the detection element 70 in step 120, in step 130, the correction voltage V is calculated in the same manner as described above based on the equation (1).

  Each time the correction voltage V is calculated as described above, the correction voltage V is input to the ECU 20. For this reason, the urea supply source 60 is controlled by the ECU 20 based on the correction voltage for each correction voltage that is a detection output of the ammonia gas detection device, and supplies the urea component into the exhaust pipe 13. Here, for each correction voltage, the urea component supply amount is controlled to an amount that reduces the concentration of ammonia gas in the exhaust gas flowing out from the selective reduction catalyst 14 or an amount that does not discharge the ammonia gas component from the selective reduction catalyst 14. Is done.

  As a result, the nitrogen oxide component in the exhaust gas is reduced by the selective reduction catalyst 14 and discharged as a nitrogen component while appropriately reducing the ammonia gas concentration in the exhaust gas discharged from the exhaust pipe 13.

  Next, when the results executed by the microcomputer 81 were measured according to the flowchart of FIG. 5 as described above, the graphs 1 and 2 shown in FIG. 6 were obtained. Here, according to the graph 1, it is shown how the output voltage before correction of the detection element 70 changes with the passage of time. Further, according to graph 2, it is shown how the output voltage after correction of the detection element 70 changes with time.

  In the graph 1, reference numeral 1-1 indicates an output voltage at the time of the heat treatment in step 100, and reference numeral 1-2 indicates that the impurity component adhering to the sensitive film 73 is removed by the heat treatment in step 100 and the output voltage is increased. Shows the correct value. Reference numeral 1-3 denotes a zero voltage set in step 110. In addition, the range of the code | symbol 1-1 to the code | symbol 1-3 shows the range of the state in which an ammonia gas component does not exist in exhaust gas.

  Reference numeral 1-4 indicates an output voltage when the concentration of the ammonia gas component in the exhaust gas increases to 10 (ppm), and reference numeral 1-5 indicates that the concentration of the ammonia gas component in the exhaust gas is 100 ( ppm) shows the output voltage when increased. That is, both reference numerals 1-4 and 1-5 indicate that the output voltage decreases stepwise as the ammonia gas component concentration increases stepwise.

  Reference numeral 1-6 indicates an output voltage when the concentration of the ammonia gas component in the exhaust gas decreases to a value corresponding to the zero voltage indicated by reference numeral 1-3. That is, the range of reference numeral 1-6 indicates a range in which no ammonia gas component is present in the exhaust gas.

  On the other hand, in graph 2, if attention is paid to the time when the time has elapsed from the zero voltage setting time (see reference numeral 1-3), the corrected output voltage is calculated by using the expression (1) in step 130 before correction. It is shown as a value calculated according to the output voltage (corresponding to the output voltage shown in graph 1).

  Here, in the graph 2, reference numeral 2-2 indicates an output voltage after correction corresponding to the output voltage before correction indicated by reference numeral 1-4 in the graph 1, and reference numeral 2-3 indicates reference numeral 1 in the graph 1. The output voltage after correction corresponding to the output voltage before correction indicated by −5 is shown. That is, it can be seen that the corrected output voltage shows a step-like change as the concentration of the ammonia gas component in the exhaust gas increases to 10 (ppm) and to 100 (ppm).

  This is not a step change in the output voltage before correction, but a step change in the output voltage after correction, that is, if the correction voltage calculated using the equation (1) is used, the concentration of the ammonia gas component can be accurately determined. It means that it can be detected well. Therefore, in the first embodiment, the formula (1) is introduced.

  Therefore, as described above, in step 130, the output voltage Vn in step 120 is corrected as the correction voltage V based on the equation (1). It can be obtained with high accuracy.

  In particular, when detecting an ammonia component in a harsh gas environment such as exhaust gas of a diesel engine, the correction voltage V obtained as described above is used as a detection output of the ammonia gas detection device, so that the ammonia gas component It is possible to provide an ammonia gas detection device that can detect the detected concentration with high accuracy over a long period of time.

Incidentally, a model gas test was performed on the detection element 70 of the first embodiment, and a test according to the flowchart of FIG. 5 was performed on the detection element 70.
1. Model gas test The test conditions were a gas temperature of 280 (° C.) and a temperature of the detecting element 70 of 400 (° C.). Further, the base gas composition is 10 (vol%) oxygen (O ₂ ), 5 (vol%) carbon dioxide (CO ₂ ), 5 (vol%) water (H ₂ O) and nitrogen (N ₂ ). It was. Moreover, the addition amount of the ammonia component with respect to base gas was 0 (ppm), 20 (ppm), and 100 (ppm).

  Under such test conditions, the detection element 70 is arranged in the model gas generator, and an AC voltage of 2 (Vrms) and 400 (Hz) is applied between both electrodes of the detection element 70 to detect the detection element 70 When the detection characteristics of 70 were examined, a graph 3 shown in FIG. 7 was obtained. However, in FIG. 7, graph 4 shows a stepwise increase in the amount of ammonia added to the base gas in relation to time.

  Here, the graph 3 shows that the output voltage of the detection element 70, in other words, the impedance decreases stepwise in relation to time as the ammonia addition amount in the graph 4 increases stepwise.

  Moreover, the following both tests (1) and (2) were performed based on the base gas composition among the above test conditions.

  That is, in the test (1), the detection element 70 was left for 20 (hours) in an environment having a temperature of 80 (° C.) and a relative humidity of 95 (% RH). In the test (2), the detection element 70 was arranged in the diesel engine of the diesel vehicle in the same manner as in the first embodiment, and the diesel vehicle was run on the chassis dynamo for about 200 (km).

  Then, the impedance (output voltage) of the detection element 70 according to the test (1) and the impedance (output voltage) of the detection element 70 according to the test (2) were examined. In addition, the impedance (output voltage) of the detection element 70 was also examined in the test before performing both tests (1) and (2) (that is, the initial test). As a result, bar graphs 5, 5-1, and 5-2 shown in FIG. 8 were obtained.

  Here, the bar graph 5 shows the initial impedance (output voltage). Moreover, the bar graph 5-1 shows the impedance (output voltage) as a result of the test (1), and the bar graph 5-2 shows the impedance (output voltage) as a result of the test (2).

According to these bar graphs 5, 5-1 and 5-2, it can be seen that the impedance in the tests (1) and (2) is higher than the initial impedance (output voltage).
2. Test According to the Flowchart of FIG. 5 The same processing as that according to the flowchart of FIG. 5 is actually performed under the initial test and both tests (1) and (2), respectively, so that the output voltage of the detection element 70 is obtained. (Impedance) was examined.

  Specifically, under the initial test and test (1), the detection element 70 was heated at 650 (° C.) for 30 (seconds) simultaneously with the application of the AC voltage to the detection element 70. The output voltage generated from the detection element 70 when 90 (seconds) passed after the heating was set to the zero voltage Vz. Next, the output voltage Vn generated from the detection element 70 after the setting of the zero voltage is detected, and the rate of change of the output voltage Vn with respect to the zero voltage Vz is expressed as {(Vz−Vn) / Vz} × 100 (%)}. So calculated.

  Further, under the test (2), simultaneously with the application of the AC voltage to the detection element 70, the detection element 70 is heated at 650 (° C.) for 10 (seconds) at intervals of 10 (seconds). And repeated three times. After that, when 70 (seconds) elapses, the output voltage generated from the detection element 70 is set to the zero point voltage Vz, and then the output voltage Vn generated from the detection element 70 is detected after the setting of the zero point voltage. The change rate of Vn with respect to the zero point voltage Vz was calculated by {(Vz−Vn) / Vz} × 100 (%).

  As a result, the graphs 6, 6-1 and 6-2 shown in FIG. 9 and the graphs 8, 8-1 and 8-2 shown in FIG. 10 were obtained. However, in FIG. 9, an arrow range indicated by reference numeral 7 indicates a time region of only the base gas. An arrow range indicated by reference numeral 7-1 indicates a time region in which 10 (ppm) of ammonia is added to the base gas. Moreover, the arrow range shown with the code | symbol 7-2 shows the time area | region which added 100 ppm of ammonia to base gas.

  In FIG. 9, graphs 6, 6-1, and 6-2 indicate changes in the output voltage Vn (impedance) of the detection element 70 in relation to time. -2 corresponds to the initial test, test (1), and test (2), respectively.

  In FIG. 10, graphs 8, 8-1, and 8-2 show changes in the rate of change of the output voltage Vn in relation to time. These graphs 8, 8-1, and 8-2 These correspond to the initial test, test (1), and test (2), respectively.

  According to each graph shown in FIG. 9, the output voltage (impedance) of the detection element 70 is the same as the output voltage (impedance) shown in each bar graph of FIG. ) Show that they are different from each other. Therefore, it can be understood that the concentration of the ammonia gas component cannot be uniquely detected by using the output voltage Vn of the detection element 70 as it is.

On the other hand, according to the respective graphs shown in FIG. 10, the change rate of the output voltage of the detection element 70 is substantially the same without being different from each other in the initial test and both tests (1) and (2). I understand that Therefore, even if the output voltage of the detection element 70 is greatly different from each other in the initial test and the tests (1) and (2), the change rate of the output voltage of the detection element 70 is unambiguous with respect to the concentration of the ammonia gas component. It can be seen that changes. Therefore, it can be seen that the concentration of the ammonia gas component can be detected with high accuracy by using the rate of change of the output voltage of the detection element 70.
(Second Embodiment)
11 and 12 show the main part of the second embodiment of the present invention. In the second embodiment, the flowchart shown in FIG. 12 is adopted instead of the flowchart (see FIG. 5) described in the first embodiment. Accordingly, in the second embodiment, the microcomputer 81 described in the first embodiment is changed to execute the computer program according to the flowchart of FIG.

  In the second embodiment, the exhaust temperature sensor (hereinafter referred to as the exhaust temperature sensor 84) of the ECU 20 described in the first embodiment is connected to a microcomputer 81 as shown in FIG. Other configurations are the same as those in the first embodiment.

  In the second embodiment configured as described above, as described in the first embodiment, in the ammonia gas detection device 50 in the operating state of the diesel engine, the detection element 70 is supplied with power from the AC power source. It shall be in operation.

  In this state, when the operation switch 83 of the control circuit 80 is closed, the microcomputer 81 starts executing the computer program according to the flowchart of FIG. Then, in step 101, exhaust temperature input processing is performed. In this exhaust temperature input process, the exhaust temperature detected by the exhaust temperature sensor 84 is input to the microcomputer 81 in step 101.

  Thereafter, in step 102, it is determined whether or not the detected exhaust gas temperature input in step 101 is less than 100 (° C.). Here, 100 (° C.), which is the determination criterion in step 101, is set on the basis of the following.

  Immediately after starting the diesel engine, moisture such as exhaust condensed water staying in the exhaust pipe 13 is exhausted from the exhaust pipe 13 together with the exhaust gas. If the detection element 70 is wet with moisture such as the exhaust condensed water in the heated state, the detection element 70 is likely to be damaged depending on the heating temperature. Therefore, in the second embodiment, 100 (° C.) is set as the determination criterion in step 102 in consideration of the fact that moisture is less likely to evaporate when the temperature is less than 100 (° C.).

  Therefore, if the detected exhaust temperature is less than 100 (° C.), the moisture covered by the detection element 70 is difficult to evaporate depending on the exhaust temperature. For this reason, it determines with YES in step 102, and a moderate heating process is made in step 103. FIG. In this gentle heating process, the amount of heating by the heater 77 is controlled by the microcomputer 81 so that the detection element 70 is gently heated at a rate of temperature rise that can prevent the thermal damage. Therefore, even if the detection element 70 is wet, the detection element 70 is heated without being damaged by heat.

  Thereafter, when the detected exhaust gas temperature in step 101 rises to 100 (° C.) or higher, NO is determined in step 102. Accordingly, a rapid heating process is performed in step 104. At the present stage, since the detected exhaust temperature is 100 (° C.) or higher, the above-described exhaust condensed water or the like becomes steam, and the moisture adhering to the detection element 70 also evaporates. For this reason, it can avoid that the detection element 70 is damaged due to the water | moisture content by moisture. Therefore, in the rapid heating process, the heating amount by the heater 77 is controlled by the microcomputer 81 so that the detection element 70 is rapidly heated at a rapid temperature increase rate, for example, to 600 (° C.). Accordingly, the detection element 70 is rapidly heated to 600 (° C.).

  As described above, when the detected exhaust temperature of the exhaust temperature sensor 84 rises from a state of less than 100 (° C.) to 100 (° C.) or more, the detection element 70 is performed by the processing from step 101 to step 104. Thus, the detection element 70 can be efficiently heated while preventing the occurrence of thermal damage due to the moisture of the detection element 70 by the slow heating and the subsequent rapid heating.

As a result, the zero point voltage can be set accurately and reliably in step 110. Other processes and effects by the microcomputer 81 are the same as those in the first embodiment.
(Third embodiment)
FIG. 13 shows the main part of the third embodiment of the present invention. In the third embodiment, the flowchart shown in FIG. 13 is employed instead of the flowchart (see FIG. 5) described in the first embodiment. Therefore, in the third embodiment, the microcomputer 81 described in the first embodiment is modified to execute the computer program according to the flowchart of FIG. Other configurations are the same as those in the first embodiment.

  In the third embodiment configured as described above, when the zero point setting process is completed in step 110 as described in the first embodiment, the output voltage input process in step 120 described in the first embodiment is performed. Prior to step 150 (see FIG. 13), it is determined whether or not the detection element 70 is abnormal.

  Here, the abnormality means a state in which the set zero voltage in step 110 is fixed to the upper limit value or the lower limit value of the output voltage of the detection element 70. This is due to the following reason.

  When a short circuit failure occurs in the detection element 70, the set zero voltage is fixed to the lower limit value of the output voltage from the detection element 70. Further, when a disconnection failure occurs in the detection element 70, the set zero voltage is fixed to the upper limit value of the output voltage from the detection element 70. In addition, if the impurity component of soot that is burned out by heating of the detection element 70 remains attached to the outer surface of the sensitive film 73, the set zero voltage is fixed to the upper limit value or the lower limit value of the output voltage. Therefore, in the third embodiment, the fixed state of the set zero voltage as described above is caused by the deterioration of the detection element 70, and is adopted as an abnormality determination criterion in step 150.

  Therefore, if the detection element 70 is abnormal based on the set zero voltage in step 110, YES is determined in step 150. As a result, the microcomputer 81 can automatically perform self-diagnosis that the detection element 70 has the abnormality. As a result, the countermeasure against the abnormality of the detection element 70 can be taken with good timing.

  Further, with the determination of YES in step 150, the microcomputer 81 prohibits the processing of both steps 120 and 130 described in the first embodiment and advances the computer program to the end step. Thereby, it is possible to prevent the processing of both steps 120 and 130 from being performed while the detection element 70 is abnormal.

  On the other hand, if the set zero voltage in step 110 is not fixed to the upper limit value or the lower limit value of the output voltage, the detection element 70 is normal, and therefore, NO is determined in step 150. As a result, the microcomputer 81 can automatically make a self-diagnosis that the detection element 70 is normal.

Further, with the determination of NO in step 150, the processing after step 120 is performed in the same manner as described in the first embodiment. In addition, the other effect in this 2nd Embodiment is the same as that of the said 1st Embodiment.
(Fourth embodiment)
FIG. 14 shows a main part of the fourth embodiment of the present invention. In the fourth embodiment, the flowchart shown in FIG. 14 is employed instead of the flowchart (see FIG. 5) described in the first embodiment. Therefore, in the fourth embodiment, the microcomputer 81 described in the first embodiment is changed to execute the computer program according to the flowchart of FIG. Other configurations are the same as those in the first embodiment.

  In the fourth embodiment configured as described above, as in the first embodiment, if YES is determined in step 140, processing in steps 160 to 180 (see FIG. 14) is performed. Here, the reason why these steps 160 to 180 are introduced in the fourth embodiment will be described.

  The exhaust gas discharged from the diesel engine through the exhaust pipe 13 during its operation is placed in a harsh gas environment containing impurity components such as oil components, soot components and various metal components in addition to various exhaust gas components. Therefore, even if the heat treatment is performed once in step 100 as described in the first embodiment, the impurity component easily adheres to the outer surface of the sensitive film 73 of the detection element 70 after that.

  When the impurity component adheres to the sensitive film 73 again as described above, the characteristics of the detection element 70 change as described in the first embodiment. Therefore, steps 160 to 170 are introduced.

  Therefore, if the diesel engine is stopped because the detected rotational speed of the rotational speed sensor 82 is zero, it is determined as YES in step 140 as in the first embodiment. Accordingly, in step 160, an output voltage input process is performed. In this output voltage input process, the output voltage generated by the detection element 70 at this stage is input to the microcomputer 81 in step 160.

  Next, at step 170, it is determined whether or not there is an output fluctuation. Here, if the output voltage generated from the detection element 70 is fixed to the upper limit value or the lower limit value immediately after the diesel engine is stopped, the output voltage is determined in step 120 before determining YES in step 140. It fluctuates from the output voltage. Therefore, it is determined YES in step 170 because there is an output fluctuation.

Thereafter, in step 180, heat treatment is performed. This heat treatment is a heat treatment performed again separately from step 100, but the detection element 70 is heated by the heater 77 as in the heat treatment in step 100. Thereby, the impurity component adhering to the outer surface of the sensitive film 73 of the detection element 70 after the heat treatment in step 100 is removed by burning. As a result, stable characteristics of the detection element can be maintained. Moreover, such an effect can be achieved by providing an ammonia gas detection device that can accurately detect an ammonia gas component in the exhaust gas of a diesel engine over a long period of time. Other functions and effects are the same as those of the first embodiment.
(Fifth embodiment)
FIG. 15 shows an essential part of the fifth embodiment of the present invention. In the fifth embodiment, the flowchart shown in FIG. 15 is employed instead of the flowchart (see FIG. 14) described in the fourth embodiment. Therefore, in the fifth embodiment, the microcomputer 81 described in the fourth embodiment is modified to execute the computer program according to the flowchart of FIG. Other configurations are the same as those in the fourth embodiment.

  In the fifth embodiment configured as described above, when the zero point setting process is completed in step 110 as described in the fourth embodiment, the output voltage input process in step 120 described in the fourth embodiment is performed. Prior to step 190 (see FIG. 15), it is determined whether or not the detection element 70 is abnormal. Here, the abnormality refers to a state in which the set zero voltage in step 110 is fixed to the upper limit value or the lower limit value of the output voltage of the detection element 70 as described in the third embodiment.

  Therefore, if the detection element 70 is abnormal based on the set zero voltage in step 110, YES is determined in step 190. As a result, the microcomputer 81 can automatically self-diagnose that the detection element 70 has the abnormality under the prohibition of the processing after step 120. As a result, the countermeasure against the abnormality of the detection element 70 can be taken with good timing.

  On the other hand, if the set zero voltage in step 110 is not fixed to the upper limit value or the lower limit value of the output voltage, the detection element 70 is normal, and therefore NO is determined in step 190. As a result, the microcomputer 81 can automatically make a self-diagnosis that the detection element 70 is normal. Other functions and effects are the same as those of the fourth embodiment.

In carrying out the present invention, the following various modifications are possible without being limited to the above embodiments.
(1) In the output voltage correction process in step 130, the output voltage Vn may be corrected based on the amount of change between the set zero voltage and the output voltage Vn in step 110 without using Equation (1). .
(2) The detection element 70 may be heated not by the heater 77 but by a heating element separate from the detection element 70.
(3) In step 150 or 190, the set zero voltage in step 110 may be compared with a predetermined threshold set in advance to determine whether or not the detection element 70 is abnormal. Further, instead of the set zero voltage, a self-diagnosis may be performed by comparing an arbitrary output voltage of the detection element 70 with a predetermined threshold value set in advance.
(4) Both electrodes 72 are not limited to those having comb-like electrode portions, and may have electrode portions having various shapes such as simple strip-like electrode portions.
(5) The ammonia gas detection device described in each of the above embodiments is not limited to the diesel engine, and may be applied to, for example, an exhaust gas system of a gas turbine of a power plant.
(6) The ammonia gas detection device described in each of the above embodiments is not limited to the exhaust gas of the diesel engine, and may be applied to detection of the concentration of the ammonia gas component contained in various detection gases.
(7) In the second embodiment, instead of the exhaust temperature detected by the exhaust temperature sensor 84, the temperature detected by the resistance temperature detector 76 of the detection element 70 is adopted as the element temperature. Even if it is determined whether or not the temperature is less than 100 (° C.), the same effect as the second embodiment can be achieved.
(8) In the heat treatment in step 100, the detection element 70 may be heated in a plurality of times. Specifically, the detection element 70 is intermittently heated by dividing the predetermined heating time into a plurality of times. According to this, impurities such as moisture, soot and oil attached to the sensitive film 73 can be removed more satisfactorily than when the detection element 70 is continuously heated during the predetermined heating time. As a result, the zero-point voltage is set in step 110 with higher accuracy, and the operational effects of the above embodiments can be further improved.
(9) The detection element 70 may be housed in an appropriate casing, and may be disposed in the downstream portion of the selective reduction catalyst 14 in the exhaust pipe 13 via the casing. The casing has a structure in which the sensitive film of the detection element 70 is exposed in the exhaust gas.
(10) The presence or absence of deterioration of the selective reduction catalyst 14 may be determined using the correction voltage V calculated in each of the above embodiments. Further, when the selective reduction catalyst 14 is inactive, it may be determined whether or not the urea water having the optimum concentration is supplied from the urea supply source 60 using the correction voltage V.

1 is a block diagram illustrating an example in which a first embodiment of the present invention is applied to a diesel engine. It is a top view of the detection element of FIG. FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. It is a detailed block diagram of the control circuit of FIG. It is a flowchart which shows the effect | action of the microcomputer of FIG. 4 is a graph showing temporal changes in output voltage before and after correction of the detection element using the amount of ammonia gas component added as a parameter in the first embodiment. It is each graph which shows the time change of the output voltage (impedance) of a detection element, and ammonia addition amount in the said 1st Embodiment. It is each bar graph which shows the output voltage (impedance) of the detection element in an initial test and both tests (1) and (2) in the said 1st Embodiment. In the said 1st Embodiment, it is each graph which shows the time change of the output voltage (impedance) of the initial stage test and both tests (1) and (2) which made the addition amount of ammonia a parameter. FIG. 6 is a graph illustrating the initial test using the amount of ammonia added as a parameter in the first embodiment and the change rate of the output voltage of the detection element in both tests (1) and (2) in relation to time. FIG. It is a block diagram which shows the principal part of 2nd Embodiment of this invention. It is a flowchart showing the computer program performed by the microcomputer in the said 2nd Embodiment. It is a flowchart which shows the principal part of 3rd Embodiment of this invention. It is a flowchart which shows the principal part of 4th Embodiment of this invention. It is a flowchart which shows the principal part of 5th Embodiment of this invention.

Explanation of symbols

13 ... exhaust pipe, 14 ... selective reduction catalyst, 70 ... impedance change type detection element,
71 ... Substrate, 73 ... Sensitive film, 74 ... Electrode part, 77 ... Heater,
81: Microcomputer.

Claims (7)

Both electrode portions provided on the surface of the substrate, and a sensitive film that is provided on the outer surface of the substrate via the both electrode portions and is sensitive to the ammonia gas component in the gas to be detected and causes proton hopping conduction, Based on the characteristic representing the relationship between the ammonia gas component and the impedance between the two electrode parts, an impedance change type detection element that detects the ammonia gas component according to the impedance and generates a detection output;
Heating means for heating the detection element;
Setting means for setting the detection output generated by the detection element after heating by the heating means as a zero point output;
Correction means for correcting the detection output arbitrarily generated by the detection element based on the zero point output,
An ammonia gas detection device for detecting a correction detection output by the correction means as an output corresponding to the ammonia gas component. Sensing the ammonia gas component in the gas to be detected and utilizing the hopping conduction of protons, the ammonia gas component is detected according to the impedance and the impedance change type detection element generated as a detection output is heated,
After this heating, the detection output generated by the detection element is set as a zero point output,
A detection output arbitrarily generated by the detection element is corrected based on the zero point output,
An ammonia gas detection method in which the corrected detection output is detected as an output corresponding to the ammonia gas component. The detection element includes a sensitive film that is sensitive to an ammonia gas component in a gas to be detected and causes proton hopping conduction;
Performing heating of the detection element in a plurality of times,
3. The ammonia gas detection method according to claim 2, wherein a detection output generated by the detection element is set as a zero point output after the plurality of times of heating. Prior to heating the detection element, the temperature of the detection element or the temperature of the gas to be detected is detected,
The ammonia gas detection method according to claim 2, wherein the detection element is heated according to the detection temperature.   5. The ammonia gas detection method according to claim 2, wherein the presence or absence of abnormality of the detection element is determined based on the zero point output. The detected gas is an exhaust gas that flows into the exhaust pipe of the diesel engine with the operation of the diesel engine, and with the nitrogen oxide gas component, with the ammonia gas component generated in the exhaust gas, Exhaust gas discharged from the exhaust pipe while being reduced in the selective reduction catalyst provided in the exhaust pipe,
The impedance change type detection element detects and detects the ammonia gas component according to the impedance using the proton hopping conduction in response to the ammonia gas component contained in the exhaust gas on the downstream side of the selective reduction catalyst. A detection element generated as an output,
Based on the detection output generated by the detection element after the diesel engine stops, determine whether the detection element needs to be heated again,
6. The ammonia gas detection method according to claim 2, wherein when it is determined that the detection element needs to be heated again, the detection element is heated again.   The ammonia gas detection method according to claim 6, wherein after the diesel engine is stopped, the presence or absence of abnormality of the detection element is determined based on a detection output generated by the detection element.

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