JP2006023232A - Ammonia gas detector and ammonia gas detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ammonia gas detector constituted so as to precisely detect the ammonia gas component in a gas to be detected by an impedance change type detection element in consideration even of fluctuations in the concentration of moisture contained in the gas to be detected, and an ammonia gas detecting method. <P>SOLUTION: The impedance change type detection element 70 is constituted so as to detect the ammonia gas contained in an exhaust gas on the downstream side of a selective reducing catalyst 14 to generate output voltage. A microcomputer preliminarily stores respective output voltages generated by the detection element 70 when first and second operation conditions are respectively formed and corrects the detection output arbitrarily generated by the detection element 70 on the basis of the predetermined relation set so as to correct a change in the impedance of the detection element 70 corresponding to the concentration of moisture in the exhaust gas between the respective output voltages, which are generated separately from the stored output voltages by the detection element 70 when the first and second operation conditions are respective formed, and the stored output voltages. <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 sensor is adopted as the above-described ammonia sensor, this impedance change type sensor uses a solid acid substance as a sensitive material, and utilizes the hopping conduction action of protons adsorbed on the sensitive material, thereby reducing ammonia. The gas component is configured to be detected.

  Accordingly, when the impedance change type sensor is disposed in the exhaust pipe on the downstream side of the denitration catalyst, the impedance change type sensor is connected to the ammonia on the downstream side of the denitration catalyst under the above-described proton hopping conduction action. The gas component will be detected.

  However, if the concentration of moisture contained in the exhaust gas varies, this variation affects the above-described proton hopping conduction action, thereby varying the characteristics of the impedance variable sensor.

  As a result, the ammonia gas component is not uniquely detected by the impedance change type sensor due to the above-described fluctuation of the moisture concentration, resulting in a problem that the detection accuracy of the sensor is lowered.

  Therefore, in order to cope with the above, the present invention takes into account the variation in the concentration of moisture contained in the gas to be detected, and converts the ammonia gas component in the gas to be detected with an impedance change type detection element. It is an object of the present invention to provide an ammonia gas detection device and an ammonia gas detection method that can detect with high accuracy.

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);
Storage means (81) for storing each detection output (VF1, VF2) generated by each detection element when both detection conditions defined differently are satisfied,
In addition to the detection outputs stored by the storage means, between the detection outputs (VA1, VA2) generated by the detection elements when the two detection conditions are satisfied, and the storage detection outputs of the storage means. The detection output (VN) arbitrarily generated by the detection element is corrected based on a predetermined relationship determined to correct the change in the characteristic of the detection element in accordance with the concentration of moisture in the gas to be detected. Correction means (140),
The correction detection output by the correction means is detected as an output corresponding to the ammonia gas component.

  Thus, based on the above-mentioned predetermined relationship, using each of the memory detection outputs and the detection outputs generated by the detection elements when the two detection conditions are satisfied separately from the respective memory detection outputs, The detection output arbitrarily generated by the detection element is corrected.

  In other words, the characteristic representing the relationship between the ammonia gas component of the detection element and the impedance is corrected based on the above-described predetermined relationship so as not to be affected by fluctuations in the concentration of moisture in the detected gas. Is done. And the detection output arbitrarily generated by the detection element is corrected based on the characteristic representing the relationship between the ammonia gas component corrected in this way and the impedance.

  As a result, a detection output arbitrarily generated by the detection element can be obtained with high accuracy and correction over a long period of time without being affected by fluctuations in the concentration of moisture in the gas to be detected.

According to the first aspect of the present invention, the detection outputs stored in the storage means are VF1 and VF2, and each detection generated by the detection element when each of the detection conditions is satisfied separately from the detection outputs. When the outputs are VA1, VA2, the detection output arbitrarily generated by the detection element is VN, and the correction detection output by the correction means is V,
The predetermined relationship is
V = {VN- (VA1-VF1)} x (ratio between VF1 and VF2 / ratio between VA1 and VA2)
Thus, by being specified, the operational effect of the invention of claim 1 can be achieved more reliably.

In the ammonia gas detection method according to the present invention, according to the description of claim 2,
Using an impedance change type detection element (70) that senses the ammonia gas component in response to the ammonia gas component in the gas to be detected and uses the proton hopping conduction to detect the ammonia gas component according to the impedance and generates a detection output,
Each detection output (VF1, VF2) generated by each detection element when each detection condition defined differently is established is set in advance,
In addition to the set detection outputs, the concentration of moisture in the gas to be detected between the detection outputs (VA1, VA2) generated by the detection elements when the two detection conditions are satisfied and the set detection outputs. A detection output (VN) arbitrarily generated by the detection element is corrected based on a predetermined relationship determined to correct the change in impedance of the detection element according to
This corrected detection output is detected as an output corresponding to the ammonia gas component.

  According to this, it is possible to provide an ammonia gas detection method that achieves the same function and effect as the first aspect of the invention.

In the second aspect of the invention, the setting detection outputs are VF1 and VF2, and separately from the setting detection outputs, the detection outputs generated by the detection elements when the detection conditions are satisfied are VA1. , VA2, when the detection output arbitrarily generated by the detection element is VN, and the correction detection output is V,
The predetermined relationship is
V = {VN- (VA1-VF1)} x (ratio between VF1 and VF2 / ratio between VA1 and VA2)
Thus, the action and effect of the invention of claim 2 can be achieved more specifically by being specified.

Moreover, in this invention, according to description of Claim 3, in the ammonia gas detection method of Claim 2,
In addition to the setting detection outputs and the setting detection outputs, the self-diagnosis of the detection element is performed based on the detection outputs generated by the detection elements when the detection conditions are satisfied. Features.

  As a result, the operational effect of the invention according to claim 2 can be achieved, and the abnormality countermeasure of the detection element can be taken in a timely manner when diagnosing abnormality of the detection element.

In the ammonia gas detection method according to the present invention, according to the description of claim 4,
Using the impedance change type detection element (70) that detects the ammonia gas component according to the impedance and generates a detection output by using the proton hopping conduction in response to the ammonia gas component in the detection gas,
A detection output (VF1) generated by the detection element when a predetermined detection condition is satisfied is set in advance,
In addition to the set detection output, the impedance of the detection element according to the concentration of moisture in the detected gas is detected between the detection output (VA1) generated by the detection element when the detection condition is satisfied and the set detection output. Based on a predetermined relationship determined to correct the change, the detection output (VN) arbitrarily generated by the detection element is corrected,
This corrected detection output is detected as an output corresponding to the ammonia gas component.

  Thus, unlike the invention according to claim 2, the predetermined relationship is different from the setting detection output when the single detection condition is satisfied and when the single detection condition is satisfied separately from the setting detection output. It is determined based on the detection output generated by the detection element.

  For this reason, the detection output arbitrarily generated by the detection element is not affected by fluctuations in the concentration of moisture in the gas to be detected, based on the predetermined relationship, and easily and practically hinders over a long period of time. It is obtained after correction with no accuracy.

Moreover, in this invention, according to description of Claim 5, in the ammonia gas detection method of Claim 4,
Aside from the setting detection output and the setting detection output, a self-diagnosis is made for the presence or absence of abnormality of the detection element based on the detection output generated by the detection element when the detection condition is satisfied.

  As a result, the operational effect of the invention according to the fourth aspect can be achieved. In addition, when a detection element abnormality is diagnosed, the abnormality countermeasure for the detection element can be taken with good timing.

In the ammonia gas detection method according to the present invention, according to the description of claim 6,
Selection that the nitrogen oxide gas component in the exhaust gas flowing into the exhaust pipe (13) of the diesel engine with the operation of the diesel engine is provided in the exhaust pipe with the ammonia gas component generated in the exhaust gas In a state where the exhaust gas is exhausted together with the exhaust gas while being reduced in the reduction catalyst (14), it is sensitive to the ammonia gas component contained in the exhaust gas on the downstream side of the selective reduction catalyst and utilizes hopping conduction of protons. Using the impedance change type detection element (70) that detects the ammonia gas component according to the impedance and generates a detection output,
Each detection output (VF1, VF2) generated by each detection element when each operating condition of the diesel engine determined to be different from each other is established in advance,
In addition to the setting detection outputs, the concentration of moisture in the exhaust gas is set between the detection outputs (VA1, VA2) generated by the detection elements when the operating conditions are satisfied and the setting detection outputs. The detection output (VN) arbitrarily generated by the detection element is corrected based on a predetermined relationship determined so as to correct the change in impedance of the corresponding detection element,
This corrected detection output is detected as an output corresponding to the ammonia gas component.

  Thus, based on the above-described predetermined relationship, using each of the setting detection outputs, and each of the detection outputs generated by the detection element when each of the operating conditions is satisfied separately from the respective setting detection outputs, The detection output arbitrarily generated by the detection element is corrected.

  In other words, the characteristic representing the relationship between the ammonia gas component of the detection element and the impedance is corrected based on the above-described predetermined relationship so as to eliminate the influence of fluctuations in the concentration of moisture in the exhaust gas. The And the detection output arbitrarily generated by the detection element is corrected based on the characteristic representing the relationship between the ammonia gas component corrected in this way and the impedance.

  As a result, the detection output arbitrarily generated by the detection element is accurately corrected and secured over a long period of time without being affected by fluctuations in the concentration of moisture in the exhaust gas.

  In addition, 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 operates 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 fuel injection by the fuel injector 12 based on detection outputs of an air-fuel ratio sensor, a rotation speed sensor, and other sensors. Control the 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 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. 2, both the electrodes 72 are provided on the surface of the substrate 71, and each of these 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. Therefore, the heater 77 controls the sensitive film 73 to a constant temperature based on the resistance value (corresponding to the temperature) of the resistance temperature detector 76.

  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 ammonia gas concentration-impedance characteristic correction process of the detection element 70 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. Various processes such as a detection output calculation process of the detection element 70 after the correction process are performed.

  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 output of the air-fuel ratio 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, it is determined whether or not the first operating condition is satisfied. Here, the first operating condition means that the diesel engine is in an operating state at idling speed.

  Therefore, at the present stage, if the rotational speed detected by the rotational speed sensor 82 is the idling rotational speed of the diesel engine, the first operating condition is satisfied. In accordance with this determination, the output voltage generated from the detection element 70 at this stage is input to the microcomputer 81 as the output voltage VA1 in step 101.

  Thereafter, in step 110, it is determined whether or not the second operating condition is satisfied. Here, the second operating condition means that the diesel engine is in an operating state at a rotational speed higher by a predetermined rotational speed than the idling rotational speed. In the first embodiment, the predetermined number of revolutions is determined when the concentration of the ammonia gas component contained in the exhaust gas in the exhaust pipe 13 on the downstream side of the selective reduction catalyst 14 is zero (%). The moisture concentration is set to be different between the first and second operating conditions. In short, the first and second operating conditions are that the concentration of the ammonia gas component contained in the exhaust gas in the exhaust pipe 13 is zero (%) on the downstream side of the selective reduction catalyst 14, and the moisture in the exhaust gas is It is sufficient that the conditions are different from each other.

  At the present stage, if the rotation speed detected by the rotation speed sensor 82 is higher than the idling rotation speed of the diesel engine by the predetermined rotation speed, YES is determined in step 110. With this determination, the output voltage generated from the detection element 70 at the present stage is input to the microcomputer 81 as the output voltage VA2 in step 111.

  When the input processing of both output voltages VA1 and VA2 is completed as described above, output voltage fluctuation ratio calculation processing is performed in the next step 120. This output voltage fluctuation ratio is given by the following equation (1).

VR = (VF1 / VF2) / (VA1 / VA2) (1)
In this formula (1), VR represents the output voltage fluctuation ratio. Further, VF1 and VF2 respectively represent output voltages of the detection element 70, and these output voltages VF1 and VF2 are stored in advance in the ROM of the microcomputer 81 together with the equation (1).

  Here, the output voltage VF1 corresponds to an output voltage (initial value) generated by the detection element 70 at the start of use in a state where the diesel engine is operated under the first operating condition. The output voltage VF2 corresponds to an output voltage (initial value) generated by the detection element 70 at the start of use in a state where the diesel engine is operated under the second operating condition.

  Thus, the output voltage fluctuation ratio VR is obtained by using the expression (1) to the output voltages VA1 and VA2 already input in both steps 101 and 111 and the output voltages VF1 and VF2 stored in the ROM of the microcomputer 81. Based on the calculation.

  When the calculation of the output voltage fluctuation ratio VR is completed in this way, in the next step 130, output voltage input processing is performed. In this input process, an output voltage arbitrarily generated by the detection element 70 upon completion of the process of step 120 is input to the microcomputer 81 as the output voltage VN.

  Thereafter, in step 140, output voltage correction processing is performed. This correction process is performed by calculating the correction voltage V based on the following equation (2).

V = {VN− (VA1−VF1)} × VR (2)
Here, the grounds for introducing this equation (2) will be described. As described above, the detection element 70 is an impedance change type detection element including the sensitive film 73 using proton hopping conduction. In other words, this detection element utilizes the surface conduction of protons on the surface of the sensitive film 73 in detecting the concentration of ammonia gas.

  Therefore, even when the exhaust gas does not contain ammonia gas, if moisture in the exhaust gas adheres to the surface of the sensitive film 73, the proton conductivity changes. In addition, the degree of change in the proton conductivity varies depending on the concentration of moisture in the exhaust gas.

  This means that the ammonia gas concentration-impedance characteristic of the detection element 70 changes due to fluctuations in the concentration of moisture in the exhaust gas. Therefore, when the ammonia gas concentration-impedance characteristic of the detection element 70 changes in this way, the impedance of the detection element 70, that is, the output voltage, varies unambiguously depending on the ammonia gas concentration-impedance characteristic. Arise.

  Therefore, we examined how to eliminate such errors. If the ammonia gas concentration-impedance characteristic is expressed on an orthogonal coordinate plane with the impedance on the horizontal axis and the ammonia gas concentration on the vertical axis, the ammonia gas concentration-impedance characteristic is accompanied by fluctuations in the concentration of moisture in the exhaust gas. It changes on the orthogonal coordinate plane. At this time, a change occurs in the offset of the ammonia gas concentration-impedance characteristic in the horizontal axis direction and the slope of the ammonia gas concentration-impedance characteristic. Therefore, it is necessary to eliminate such changes in the offset and slope of the ammonia gas concentration-impedance characteristic.

  Therefore, formula (2) was introduced. In this equation (2), VN is the output voltage in step 130 and represents the output voltage actually generated by the detection element 70 after the calculation of the output voltage ratio VR in step 120. VA1 is the output voltage in step 101 and represents the output voltage generated by the detection element 70 when the first operating condition in step 100 is satisfied. VF1 is an output voltage stored in advance in the ROM of the microcomputer 81 and represents an output voltage generated by the detection element 70 at the start of use under the establishment of the first operating condition.

  Therefore, on the right side of Equation (2), {VN− (VA1−VF1)} is to subtract and correct the output voltage VN with the difference between both output voltages (VA1−VF1) when the first operating condition is satisfied. Thus, it serves to correct the offset of the ammonia gas concentration-impedance characteristic.

  In the formula (2), VR is given by the formula (1) as described above. In this equation (1), VF2 is an output voltage stored in advance in the ROM of the microcomputer 81, and the output voltage generated from the detection element 70 at the start of use under the establishment of the second operating condition. To express. VA2 is an output voltage in step 111 and represents an output voltage actually generated from the detection element 70 when the second operating condition in step 110 is satisfied.

  Therefore, in the expression (1), (VF1 / VF2) is a ratio of both output voltages stored in the ROM of the microcomputer 81, and (VA1 / VA2) is each of the first and second operating conditions. It is a ratio of output voltages generated from the detection element 70 as it is established. Therefore, VR = {(VF1 / VF2) / (VA1 / VA2)} corrects the variation in the slope of the ammonia gas concentration-impedance characteristic.

  Therefore, according to Equation (2), VN is corrected to V so that the change in the offset or the slope of the ammonia gas concentration-impedance characteristic is eliminated by multiplying {VN− (VA1−VF1)} by VR. Will be. In other words, the change of the ammonia gas concentration-impedance characteristic according to the fluctuation of the moisture concentration is eliminated by the equation (2).

  From the above, if equation (2) is used, offset correction in the ammonia gas concentration-impedance characteristic and zero point correction in the ammonia gas concentration-impedance characteristic based on this offset correction (impedance value when the ammonia gas concentration is zero) Correction) and the inclination correction of the ammonia gas concentration-impedance characteristic.

  Therefore, in the first embodiment, Expression (2) is introduced and stored in advance in the ROM of the microcomputer 81.

  Accordingly, in step 140, the output voltage VN that has been input in step 130 is corrected to the correction voltage V based on equation (2). Here, since the ammonia gas concentration-impedance characteristic of the detection element 70 is corrected by the equation (2) as described above, the correction voltage V can be obtained accurately over a long period of time.

  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 decreases the concentration of the ammonia gas component in the exhaust gas flowing out from the selective reduction catalyst 14. This control depends on the equation (2) and is therefore performed with high accuracy.

  After step 140, it is determined in step 150 whether or not the diesel engine is stopped. At this stage, if the detected rotational speed of the rotational speed sensor 82 is not zero, the diesel engine is operating, so the determination in step 150 is NO.

  Thereafter, during the determination of NO in step 150, the processes in steps 130 and 140 are repeated in the same manner as described above. For each output voltage VN from the detection element 70 in step 130, in step 140, the correction voltage V is calculated in the same manner as described above based on the equation (2).

  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 decreases the concentration of ammonia gas in the exhaust gas flowing out from the selective reduction catalyst 14.

  As a result, the nitrogen oxidizing gas 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.

  Incidentally, the detection element 70 of the ammonia gas detection device is provided in the exhaust pipe of the diesel engine of the diesel vehicle on the downstream side of the selective reduction catalyst. And the said diesel vehicle was made to drive | work about 1000 (km) on chassis dynamo.

  Thereafter, using the model gas generator, the ammonia gas concentration-impedance characteristics of the detection element 70 after traveling as described above were measured under the following actual measurement conditions.

  However, the actual measurement conditions are as follows.

The gas temperature is 280 (° C.). The control temperature of the detection element 70 is 400 (° C.). The gas composition when the first operating condition is satisfied is 10 (volume%) oxygen (O ₂ ), 5 (volume%) carbon dioxide (CO ₂ ), 1 (volume%) water (H ₂ O). and and nitrogen (N _2).

The gas composition when the second operating condition is satisfied is 10 (vol%) oxygen (O ₂ ), 5 (vol%) carbon dioxide (CO ₂ ), 10 (vol%) water (H ₂ ). O) and nitrogen (N ₂ ).

The gas composition at the time of evaluation of the ammonia gas concentration-impedance characteristic of the detection element 70 is 10 (volume%) oxygen (O ₂ ), 5 (volume%) carbon dioxide (CO ₂ ), and 5 (volume%). Water (H ₂ O), ammonia gas within the range of 0 (ppm) to 100 (ppm), and nitrogen (N ₂ ).

  In the actual measurement by the model gas generator, a 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. Thus, the ammonia gas concentration-impedance characteristic of the detection element 70 was measured while changing the ammonia gas concentration.

Prior to the actual measurement, the ammonia gas concentration-impedance characteristic of the detection element 70 before the traveling of the diesel vehicle was measured in relation to the dependency on water (H ₂ O). Shown with 2 and 3. In FIG. 6, the graph 1 shows the relationship between the ammonia gas concentration and the impedance (output voltage) of the detection element 70 when the water (H ₂ O) 1 (vol%). Graph 2 shows the relationship between the impedance (output voltage) of the detection element 70 and the ammonia gas concentration when water is 5 (volume%). Graph 3 shows the relationship between the impedance (output voltage) of the detection element 70 and the ammonia gas concentration when water is 10 (volume%).

In addition, in relation to the dependency of the ammonia gas concentration-impedance characteristics of the detection element 70 on the diesel vehicle after the traveling of the diesel vehicle in relation to the dependency on water (H ₂ O), in FIG. It is shown. In FIG. 7, a graph 4 shows the relationship between the impedance (output voltage) of the detection element 70 and the ammonia gas concentration when water is 1 (volume%). Graph 5 shows the relationship between the impedance (output voltage) of the detection element 70 and the ammonia gas concentration when water 5 (volume%) is used. Graph 6 shows the relationship between the impedance (output voltage) of the detection element 70 and the ammonia gas concentration when water is 10 (volume%).

6 and FIG. 7, it can be seen that the ammonia gas concentration-impedance characteristic of the detection element 70 depends on water (H ₂ O).

  Next, an actual measurement was performed on the case where the output voltage of the detection element 70 is corrected by the equation (2). Before the traveling of the diesel vehicle, both output voltages VF1 and VF2 of the detection element 70 at the start of use when the first and second operating conditions are satisfied are set in advance. And after the said driving | running | working of the said diesel vehicle, both output voltage VA1, VA2 of the detection element 70 at the time of the said 1st and 2nd operating conditions being satisfied was measured.

  Thereafter, the output voltage ratio VR was calculated using the output voltages VF1, VF2, VA1, and VA2 based on the equation (1). Next, the output voltage VN of the detection element 70 after the traveling of the diesel vehicle was measured. Then, the correction voltage V was calculated according to the output voltage ratio VR and the output voltages VN, VA1, and VF1 based on the equation (2). Thereby, each graph 7-9 shown in FIG. 8 was obtained. In FIG. 8, a graph 7 shows the ammonia gas concentration-impedance characteristic of the detection element 70 before the traveling of the diesel vehicle. Graph 8 shows the ammonia gas concentration-impedance characteristic of detection element 70 after the traveling of the diesel vehicle. Graph 9 shows the ammonia gas concentration-impedance characteristic of the detection element 70 after the correction according to the equation (2).

  Therefore, according to the graphs 7 to 9 in FIG. 8, the ammonia gas concentration-impedance characteristics (see graph 8) of the detection element 70 measured after the traveling of the diesel vehicle are measured before the traveling of the diesel vehicle. It can be seen that the impedance is remarkably increased with respect to the ammonia gas concentration-impedance characteristic (see graph 7) of the detection element 70 by actual measurement. On the other hand, the ammonia gas concentration-impedance characteristic (see graph 9) of the detection element 70 after correction is the ammonia gas concentration-impedance characteristic (see graph 7) of the detection element 70 measured by the diesel vehicle before traveling. It can be seen that this is almost the same.

  Therefore, it can be seen that the water dependency of the ammonia gas concentration-impedance characteristic of the detection element 70 is satisfactorily improved by using the equation (2). That is, the correction voltage V is calculated based on the output voltage VN using the equation (2) in step 140, so that the correction voltage V, and hence the impedance of the detection element 70, changes in the moisture concentration in the exhaust gas. However, it is clear that it is ensured with high accuracy.

  Here, the necessity of correcting the output voltage of the detection element 70 described in the first embodiment will be summarized. When the impedance change type detection element 70 using a sensitive film that causes proton hopping conduction is used as an element for detecting the ammonia gas component, the characteristic of the sensitive film is not only the moisture in the exhaust gas that is the detected gas. Fluctuates easily due to the influence of soot and oil components. For this reason, in order to accurately detect the concentration of the ammonia gas component, it is necessary to correct the output voltage of the impedance change detection element 70.

  However, when the detection element 70 is arranged on the downstream side of the selective reduction catalyst of the diesel engine, an ammonia gas component with an unknown concentration is not supplied around the detection element 70 but an ammonia gas component with an unknown concentration is supplied. Is done. For this reason, it is difficult to correct the output voltage of the detection element 70 using the ammonia gas component.

  Incidentally, the concentration of water around the detection element 70 can be estimated from the operating state of the diesel engine. Further, in an impedance change type detection element using a sensitive membrane that causes proton hopping conduction, there is a correlation between the output voltage of the detection element for moisture and the output voltage of the detection element for ammonia gas components.

Therefore, by correcting the output voltage of the detection element with the moisture in the exhaust gas as described above, it is possible to correct the influence of fluctuations in the moisture concentration and to correct the output voltage of the detection element with respect to the concentration of the ammonia gas component. . As a result, according to the first embodiment, the concentration of the ammonia gas component can be accurately detected.
(Second Embodiment)
FIG. 9 shows a main part of the second embodiment of the present invention. In the second embodiment, the flowchart shown in FIG. 9 is employed instead of the flowchart (see FIG. 5) described in the first embodiment. Therefore, in the second 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 second embodiment configured as described above, when the calculation processing of the output voltage ratio VR in step 120 is completed in the same manner as described in the first embodiment, the processing in step 130 described in the first embodiment is completed. Prior to this, in step 121 (see FIG. 9), it is determined whether or not the detection element 70 is abnormal.

  Here, the abnormality is that the output voltage VA1 input in step 101 is abnormally different from the output voltage VF1 stored in the ROM of the microcomputer 81 based on the deterioration of the detection element 70, or step 120. This means that the output voltage VA2 already input is abnormally different from the output voltage VF2 already stored in the ROM of the microcomputer 81 based on the deterioration of the detection element 70.

  Therefore, at this stage, when the output voltage VA1 is abnormally different from the output voltage VF1, or when the output voltage VF2 is abnormally different from the output voltage VA2, the detection element 70 is abnormal. In 121, it is determined YES. As a result, the microcomputer 81 can automatically perform self-diagnosis that the detection element 70 has the abnormality. Thereby, the countermeasure against the abnormality of the detection element 70 can be taken with good timing.

  Further, with the determination of YES in step 121, the microcomputer 81 prohibits the processing of both steps 130 and 140 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 130 and 140 from being performed while the detection element 70 is abnormal.

  On the other hand, in the determination in step 121, when the output voltage VA1 is not abnormally different from the output voltage VF1, or when the output voltage VF2 is not abnormally different from the output voltage VA2, the detection element 70 is normal. For this reason, NO is determined in step 121. 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 121, the processing after step 130 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.
(Third embodiment)
FIG. 10 shows a main part of the third embodiment of the present invention. In the third embodiment, the flowchart shown in FIG. 10 is employed 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. Other configurations are the same as those in the first embodiment.

  In the third embodiment configured as described above, the output voltage VA1 is input from the detection element 70 in step 101 in accordance with the determination of YES in step 100, as in the first embodiment. Next, the input processing of the output voltage is performed in step 130 without performing the processing of both steps 110 and 120 described in the first embodiment. In this input process, the output voltage generated from the detection element 70 upon completion of the process of step 101 is input to the microcomputer 81 as the output voltage VN.

  Thereafter, in step 160, output voltage correction processing is performed. This correction processing is performed by calculating the correction voltage V based on the following equation (3) instead of the equation (2) described in the first embodiment.

V = {VN- (VA1-VF1)} (3)
In the third embodiment, when calculating the correction voltage V, the expression (3) is introduced instead of the expression (2) in order to calculate the correction voltage V easily. Therefore, from this point of view, in the second embodiment, the equation (3) is used to eliminate the offset among the changes in the offset and the slope in the ammonia gas concentration-impedance characteristics described in the first embodiment. ) Has been introduced instead of equation (2).

  Therefore, if Equation (3) is used, offset correction in the ammonia gas concentration-impedance characteristic and zero point correction in the ammonia gas concentration-impedance characteristic based on the offset correction (impedance value when the ammonia gas concentration is zero) Correction). Note that equation (3) is stored in advance in the ROM of the microcomputer 81 instead of equation (2).

  Accordingly, in step 160, the output voltage VN that has been input in step 130 is corrected to the correction voltage V based on equation (3). Here, since the ammonia gas concentration-impedance characteristic of the detection element 70 is corrected by the equation (3) as described above, the correction voltage V can be simply and accurately for practical purposes over a long period of time. can get.

  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. To do. Here, the urea component supply amount is controlled to an amount that decreases the concentration of the ammonia gas component in the exhaust gas flowing out from the selective reduction catalyst 14. This control depends on the equation (3), but the control accuracy can be obtained to such an extent that it can be practically used.

  After the process of step 160, in step 150, it is determined whether or not the diesel engine is stopped, as described in the first embodiment. At this stage, if the detected rotational speed of the rotational speed sensor 82 is not zero, the diesel engine is operating, so the determination in step 150 is NO.

  Thereafter, during the determination of NO in step 150, the processes in steps 130 and 160 are repeated in the same manner as described above. Then, for each output voltage VN from the detection element 70 in step 130, in step 160, the correction voltage V is calculated in the same manner as described above based on equation (3).

  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 decreases the concentration of ammonia gas in the exhaust gas flowing out from the selective reduction catalyst 14.

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 concentration of the ammonia gas component in the exhaust gas discharged from the exhaust pipe 13.
(Fourth embodiment)
FIG. 11 shows the main part of the fourth embodiment of the present invention. In the fourth embodiment, the flowchart shown in FIG. 11 is employed instead of the flowchart (see FIG. 10) described in the third embodiment. Therefore, in the fourth embodiment, the microcomputer 81 described in the third embodiment is changed to execute the computer program according to the flowchart of FIG. Other configurations are the same as those of the third embodiment.

  In the fourth embodiment configured as described above, when the input process of the output voltage VA1 in step 101 is completed in the same manner as described in the third embodiment, the process in step 130 described in the first embodiment is performed. Prior to step 102 (see FIG. 11), it is determined whether or not the detection element 70 is abnormal.

  Here, the abnormality means that the output voltage VA1 already input in step 101 is abnormally different from the output voltage VF1 already stored in the ROM of the microcomputer 81.

  Accordingly, at the present stage, when the output voltage VA1 is abnormally different from the output voltage VF1, the detection element 70 is abnormal, so that it is determined as YES in Step 102. As a result, the microcomputer 81 can automatically perform self-diagnosis that the detection element 70 has the abnormality. As a result, as in the second embodiment, countermeasures against abnormality of the detection element 70 can be taken with good timing.

  In addition, with YES in step 102, the microcomputer 81 prohibits the processing of both steps 130 and 160 described in the third embodiment and advances the computer program to the end step. As a result, similarly to the second embodiment, it is possible to prevent the processing of both steps 130 and 140 from being performed while the detection element 70 is abnormal.

  On the other hand, in the determination in step 102, if the output voltage VA1 is not abnormally different from the output voltage VF1, it is determined NO in step 102 because the detection element 70 is normal. As a result, as in the second embodiment, the microcomputer 81 can automatically make a self-diagnosis that the detection element 70 is normal.

  Further, with the determination of NO in step 102, the processing after step 130 is performed in the same manner as described in the third embodiment. In addition, the other effect in this 4th Embodiment is the same as that of the said 3rd Embodiment.

In carrying out the present invention, the following various modifications are possible without being limited to the above embodiments.
(1) In the determination in step 121 (see FIG. 9) in the second embodiment, any one of the output voltages VA1 and VA2 that have been input in steps 101 and 111 is a disconnection state in the detection element 70 or A value representing a short-circuit state may be adopted as the abnormality.

  In place of this, in the determination at step 121, the output voltage ratio VR calculated at step 120 is a value representing a disconnection state or a short circuit state within the detection element 70 as the abnormality. You may make it employ | adopt.

Alternatively, it may be adopted as the abnormality that any one of the output voltages VA1, VA2 and the output voltage ratio VR deviates from a predetermined allowable range indicating the normality of the detection element 70.
(2) In the determination in step 102 (see FIG. 11) in the fourth embodiment, one of the output voltages VA1 that has been input in step 101 is a value that represents a disconnection state or a short circuit state in the detection element 70. Or that one of the output voltages VF1 and VA1 deviates from a predetermined allowable range representing the normality of the detection element 70 may be adopted as the abnormality.
(3) The first operating condition includes not only that the diesel engine is operating at the idling speed, but also that, for example, the detection output of the air-fuel ratio sensor represents a lean air-fuel ratio. May be.

Further, the second operating condition includes not only that the diesel engine is in an operating state at a rotational speed higher than the idling rotational speed by a predetermined rotational speed, but, for example, the detection output of the air-fuel ratio sensor is on the lean side. It may be added to represent the air-fuel ratio.
(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.

Accordingly, the first and second operating conditions described in the above embodiments are generally grasped as the first and second detection conditions in which the concentration of moisture in the gas to be detected is different. You may do it. Here, the first and second detection conditions are conditions in which the concentration of the ammonia gas component in the gas to be detected is zero (%) and the concentration of moisture in the gas to be detected is different from each other. Say.
(7) The criterion in step 150 in FIG. 5 or FIG. 9 may be based on whether or not a predetermined time has elapsed, for example, instead of whether or not the diesel engine is stopped. In this case, every time it is determined YES in step 150 as the predetermined time elapses, the output voltage ratio VR is cleared in step 151.
(8) Both output voltages VF1 and VF2 are not limited to the ROM of the microcomputer 81, and may be stored in an external memory of the microcomputer 81, for example.
(9) V = {VN− (VA1−VF1)} × F (VR) may be employed instead of the above equation (2). Here, F (VR) is an independent function having the output voltage ratio VR as a dependent variable, and the correction voltage V is the same as that in the expression (2) by multiplication with {VN− (VA1−VF1)}. It is a function that can be calculated with accuracy.
(10) 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.

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. It is a graph which shows the relationship between the ammonia gas density | concentration of a detection element before driving | running | working of a diesel vehicle, and impedance (output voltage) in the said 1st Embodiment by using the quantity of water as a parameter. It is a graph which shows the relationship between the ammonia gas density | concentration of a detection element and the impedance (output voltage) after driving | running | working of a diesel vehicle in the said 1st Embodiment using the quantity of water as a parameter. It is a graph which shows the ammonia gas concentration-impedance characteristic of the detection element before and behind driving | running | working of a diesel vehicle in the said 1st Embodiment, and the ammonia gas concentration-impedance characteristic of the detection element after correction | amendment. It is a flowchart which shows the principal part of 2nd Embodiment of this invention. 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.

Explanation of symbols

70: Impedance change type detection element 71: Substrate 73: Sensitive film 74: Electrode
81: microcomputer, VA1, VA2, VF1, VF2, VN: output voltage.

Claims (6)

Both electrode portions provided on the surface of the substrate, and a sensitive film provided on the surface of the substrate through the both electrode portions and sensitive to the ammonia gas component in the gas to be detected to cause 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;
Storage means for storing each detection output generated by each of the detection elements when each detection condition established differently is established,
In addition to the detection outputs stored by the storage means, the detection output is generated between the detection outputs generated by the detection elements when the two detection conditions are satisfied and the storage detection outputs of the storage means. Correction means for correcting a detection output arbitrarily generated by the detection element based on a predetermined relationship determined to correct the change in the characteristic of the detection element according to the concentration of moisture in the detection gas; prepare for,
An ammonia gas detection device for detecting a correction detection output by the correction means as an output corresponding to the ammonia gas component. Using an impedance change type detection element that detects the ammonia gas component according to impedance and generates as a detection output by using proton hopping conduction in response to the ammonia gas component in the gas to be detected,
Each detection output generated by each of the detection elements at the time of establishment of both detection conditions set differently from each other in advance,
Separately from the respective set detection outputs, the respective detection outputs generated by the detection elements when the both detection conditions are satisfied and the respective set detection outputs according to the concentration of moisture in the detected gas. Based on a predetermined relationship determined to correct the change in impedance of the detection element, correct the detection output arbitrarily generated by the detection element,
An ammonia gas detection method in which the corrected detection output is detected as an output corresponding to the ammonia gas component.   Separately from the respective setting detection outputs and the respective setting detection outputs, each detection output generated by the detection element when each of the detection conditions is satisfied is self-diagnosed for the presence or absence of an abnormality of the detection element. The ammonia gas detection method according to claim 2. Using an impedance change type detection element that detects the ammonia gas component according to impedance and generates as a detection output by using proton hopping conduction in response to the ammonia gas component in the gas to be detected,
Preset a detection output generated by the detection element when a predetermined detection condition is satisfied,
Apart from the set detection output, a change in impedance of the detection element according to the concentration of moisture in the detected gas between the detection output generated by the detection element when the detection condition is satisfied and the set detection output Is corrected based on a predetermined relationship determined to correct the detection output arbitrarily generated by the detection element,
An ammonia gas detection method in which the corrected detection output is detected as an output corresponding to the ammonia gas component.   In addition to the setting detection output and the setting detection output, the presence or absence of abnormality of the detection element is self-diagnosis based on the detection output generated by the detection element when the detection condition is satisfied. Item 5. The ammonia gas detection method according to Item 4. In the selective reduction catalyst provided in the exhaust pipe, the nitrogen oxide gas component in the exhaust gas flowing into the exhaust pipe of the diesel engine with the operation of the diesel engine is replaced with the ammonia gas component generated in the exhaust gas. In the state where the exhaust gas is discharged from the exhaust pipe together with the exhaust gas while being reduced at the above, the ammonia gas reacts with the ammonia gas component contained in the exhaust gas on the downstream side of the selective reduction catalyst and utilizes hopping conduction of protons, Using an impedance change detection element that detects a component according to impedance and generates a detection output,
Each detection output generated by the detection element when each of the operating conditions of the diesel engine determined to be different from each other is established in advance,
The detection according to the concentration of moisture in the exhaust gas between each detection output generated by the detection element and each setting detection output when each of the operating conditions is satisfied separately from each setting detection output Based on a predetermined relationship determined to correct the change in the impedance of the element, correct the detection output arbitrarily generated by the detection element,
An ammonia gas detection method in which the corrected detection output is detected as an output corresponding to the ammonia gas component.

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