Exhaust monitoring device

Abstract

The present application provides an exhaust monitoring device that can properly perform processing based on an output value of a nitrogen oxide sensor. The exhaust monitoring device can acquire an output value of a nitrogen oxide sensor in an exhaust system that includes a three-way catalyst (a first three-way catalyst, a second three-way catalyst) disposed in an exhaust passage of an engine and the nitrogen oxide sensor disposed downstream of the three-way catalyst in the exhaust passage. The exhaust monitoring device acquires a temperature of the three-way catalyst when the output value is acquired. When the temperature of the three-way catalyst is lower than a preheating determination temperature, the exhaust monitoring device determines that the output value is a concentration of nitrogen oxide contained in exhaust gas that has passed through the three-way catalyst. When the temperature of the three-way catalyst is equal to or higher than the preheating determination temperature, the exhaust monitoring device determines that the output value can include a component that reacts with ammonia at the nitrogen oxide sensor.

Description

Technical Field

[0001] This invention relates to an exhaust monitoring device. Background Technology

[0002] Patent Document 1 describes an exhaust monitoring device. This exhaust monitoring device obtains output values ​​from a nitrogen oxide sensor that measures the concentration of nitrogen oxides contained in the exhaust of an engine.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2023-008849

[0004] Sometimes a three-way catalytic converter is installed in the engine's exhaust passage, and a nitrogen oxide sensor measures the concentration of nitrogen oxides in the exhaust gas passing through the catalytic converter. When exhaust gas passes through the catalytic converter, ammonia is sometimes generated on the catalytic converter. The nitrogen oxide sensor reacts with ammonia in addition to nitrogen oxides and outputs a value. Therefore, if the output value of the nitrogen oxide sensor is directly used as the concentration of nitrogen oxides in the exhaust gas passing through the catalytic converter, the processing performed based on the nitrogen oxide sensor's output value cannot be accurately performed. Summary of the Invention

[0005] An exhaust monitoring device that addresses the aforementioned issues is capable of acquiring the output value of a nitrogen oxide sensor in an exhaust system. The exhaust system includes a three-way catalytic converter disposed in the exhaust passage of an engine, and a nitrogen oxide sensor disposed downstream of the three-way catalytic converter in the exhaust passage. When acquiring the output value, the exhaust monitoring device acquires the temperature of the three-way catalytic converter. If the temperature of the three-way catalytic converter is lower than a preheating determination temperature, the exhaust monitoring device determines that the output value represents the concentration of nitrogen oxides in the exhaust gas passing through the three-way catalytic converter. If the temperature of the three-way catalytic converter is higher than the preheating determination temperature, the exhaust monitoring device determines that the output value may contain components resulting from the reaction between the nitrogen oxide sensor and ammonia.

[0006] An exhaust monitoring device that addresses the aforementioned issues can acquire the output value of a nitrogen oxide sensor in an exhaust system comprising: a three-way catalytic converter disposed in the exhaust passage of an engine; and a nitrogen oxide sensor disposed downstream of the three-way catalytic converter in the exhaust passage. When acquiring the output value, the exhaust monitoring device acquires the oxygen storage level of the three-way catalytic converter. If the oxygen storage level of the three-way catalytic converter is above a predetermined amount, the exhaust monitoring device determines that the output value represents the concentration of nitrogen oxides in the exhaust gas passing through the three-way catalytic converter. If the oxygen storage level of the three-way catalytic converter is below the predetermined amount, the exhaust monitoring device determines that the output value may contain components resulting from the reaction of nitrogen oxides with ammonia.

[0007] Invention Effects

[0008] The aforementioned exhaust monitoring device is capable of performing appropriate processing based on the output value of the nitrogen oxide sensor. Attached Figure Description

[0009] Figure 1 This is a schematic diagram showing the configuration of an exhaust system equipped with an exhaust monitoring device according to one embodiment.

[0010] Figure 2 It means Figure 1 The flowchart shows the process by which the exhaust monitoring device performs a series of processes each time it obtains an output value from the nitrogen oxide sensor.

[0011] Figure 3 It means Figure 1 The flowchart shows a series of processes performed by the exhaust monitoring device when it performs additional differentiation judgment only after the first three-way catalytic converter has been preheated.

[0012] Figure 4 It means Figure 1 The flowchart shows the process of a series of procedures performed by the exhaust monitoring device when both the first and second three-way catalytic converters have been preheated.

[0013] Symbol Explanation

[0014] 10-Engine, 11a-First three-way catalytic converter, 11b-Second three-way catalytic converter, 12-Exhaust passage, 13-Intake passage, 14-NOx sensor, 15a-First air-fuel ratio sensor, 15b-Second air-fuel ratio sensor, 15c-Third air-fuel ratio sensor, 16-Air flow meter, 17-Crankshaft angle sensor, 30-Exhaust monitoring device, 31-Processing circuit, 32-Storage device, 40-Exhaust system. Detailed Implementation

[0015] The following is for reference. Figures 1-4 One embodiment of the exhaust monitoring device will be described.

[0016] <Composition of Exhaust System 40>

[0017] like Figure 1 As shown, the exhaust system 40 includes: an engine 10; a first three-way catalytic converter 11a; and a second three-way catalytic converter 11b. The exhaust system 40 is mounted on a vehicle.

[0018] Engine 10 is a gasoline engine that uses gasoline as fuel.

[0019] The first three-way catalytic converter 11a and the second three-way catalytic converter 11b are three-way catalytic converters installed on the exhaust passage 12 of the engine 10. The second three-way catalytic converter 11b is disposed in the exhaust passage 12 downstream of the first three-way catalytic converter 11a.

[0020] like Figure 1 As shown, the exhaust system 40 includes: a nitrogen oxide sensor 14; a first air-fuel ratio sensor 15a; a second air-fuel ratio sensor 15b; a third air-fuel ratio sensor 15c; an air flow meter 16; and a crankshaft angle sensor 17.

[0021] like Figure 1 As shown, the nitrogen oxide sensor 14 is disposed in the exhaust passage 12 downstream of the second three-way catalytic converter 11b. The nitrogen oxide sensor 14 measures the concentration of nitrogen oxides contained in the exhaust gas passing through the second three-way catalytic converter 11b.

[0022] like Figure 1 As shown, the first air-fuel ratio sensor 15a is disposed in the portion of the exhaust passage 12 between the engine 10 and the first three-way catalytic converter 11a. The first air-fuel ratio sensor 15a measures the air-fuel ratio of the exhaust gas discharged from the engine 10 before reaching the first three-way catalytic converter 11a.

[0023] like Figure 1 As shown, the second air-fuel ratio sensor 15b is disposed in the portion of the exhaust passage 12 between the first three-way catalytic converter 11a and the second three-way catalytic converter 11b. The second air-fuel ratio sensor 15b measures the air-fuel ratio of the exhaust gas passing through the first three-way catalytic converter 11a and before reaching the second three-way catalytic converter 11b.

[0024] like Figure 1 As shown, the third air-fuel ratio sensor 15c is disposed in the exhaust passage 12 downstream of the second three-way catalytic converter 11b. The third air-fuel ratio sensor 15c measures the air-fuel ratio of the exhaust gas passing through the second three-way catalytic converter 11b.

[0025] like Figure 1 As shown, an air flow meter 16 is installed on the intake passage 13 of the engine 10. The air flow meter 16 measures the amount of air drawn into the engine 10.

[0026] like Figure 1 As shown, the crankshaft angle sensor 17 is installed in the engine 10. The crankshaft angle sensor 17 measures the angle of the crankshaft of the engine 10.

[0027] like Figure 1 As shown, the exhaust system 40 includes an exhaust monitoring device 30. (As indicated...) Figure 1As shown, the exhaust monitoring device 30 includes a processing circuit 31 and a storage device 32. The storage device 32 stores programs. The processing circuit 31 performs various processes by executing the programs stored in the storage device 32. The processing circuit 31 includes a processor.

[0028] like Figure 1 As shown, the exhaust monitoring device 30 is communicatively connected to the nitrogen oxide sensor 14, the first air-fuel ratio sensor 15a, the second air-fuel ratio sensor 15b, the third air-fuel ratio sensor 15c, and the air flow meter 16. The exhaust monitoring device 30 can acquire the output values ​​of each sensor through communication.

[0029] like Figure 1 As shown, the exhaust monitoring device 30 is communicatively connected to the crankshaft angle sensor 17. The exhaust monitoring device 30 acquires the output value of the crankshaft angle sensor 17 via communication. Furthermore, the exhaust monitoring device 30 outputs the engine speed 10 per unit time based on the time required for the crankshaft to rotate a specified angle.

[0030] When exhaust gas passes through the three-way catalytic converter, ammonia may sometimes be generated if the converter is preheated and there is little oxygen reacting with hydrogen on the converter. The nitrogen oxide sensor 14 reacts with ammonia in addition to nitrogen oxides and outputs a value. Therefore, the output value of the nitrogen oxide sensor 14 may sometimes represent the concentration of nitrogen oxides in the exhaust gas, and sometimes it may contain an incorrect concentration of components that react with ammonia in the exhaust gas. The exhaust monitoring device 30 determines whether the output value of the nitrogen oxide sensor 14 contains components that react with ammonia.

[0031] <Determination of temperature based on three-way catalytic converter>

[0032] Figure 2 The diagram illustrates a series of processes performed by the exhaust monitoring device 30 when determining whether the output value of the nitrogen oxide sensor 14, based on the temperature of the three-way catalytic converter, contains components that react with ammonia. Figure 2 The series of processes shown are executed by processing circuit 31. Processing circuit 31 executes each time an output value is obtained from nitrogen oxide sensor 14 after the engine 10 starts running. Figure 2 The series of processes shown. In Figure 2 In this context, S represents a step.

[0033] Processing circuit 31 at the beginning Figure 2 During the series of processes shown, process S11 is executed first. In process S11, the processing circuit 31 obtains the temperature of the first three-way catalytic converter 11a.

[0034] In the S11 processing, the processing circuit 31 outputs the engine speed of the engine 10 based on the output value of the crankshaft angle sensor 17. Then, the processing circuit 31 estimates the load of the engine 10 based on the engine speed of the engine 10 and the output value of the air flow meter 16. The load of the engine 10 is the ratio of the volume of air actually drawn in during one cycle to the stroke volume of the engine 10 in each cycle. Furthermore, the processing circuit 31 estimates the temperature of the first three-way catalytic converter 11a based on the engine speed of the engine 10 and the load of the engine 10.

[0035] After estimating and obtaining the temperature of the first three-way catalytic converter 11a, the processing circuit 31 proceeds to step S12. In step S12, the processing circuit 31 determines whether the temperature of the first three-way catalytic converter 11a is above the preheating determination temperature. The preheating determination temperature is a threshold used to determine that the preheating of the three-way catalytic converter is complete based on the fact that the temperature of the three-way catalytic converter is above the preheating determination temperature.

[0036] In the process of S12, if the processing circuit 31 determines that the temperature of the first three-way catalytic converter 11a is above the preheating determination temperature (S12: "Yes"), then the process proceeds to S13. In the process of S13, the processing circuit 31 determines that the preheating of the first three-way catalytic converter 11a is complete. Then, the processing circuit 31 proceeds to S15.

[0037] In the process of S12, if the processing circuit 31 determines that the temperature of the first three-way catalytic converter 11a is lower than the preheating determination temperature (S12: "No"), then the process proceeds to S14. In the process of S14, the processing circuit 31 determines that the preheating of the first three-way catalytic converter 11a is not complete. Then, the processing circuit 31 proceeds to S15.

[0038] In the process of S15, the processing circuit 31 obtains the temperature of the second three-way catalytic converter 11b. In the process of S15, the processing circuit 31 estimates the temperature of the second three-way catalytic converter 11b based on the engine speed and engine load of the engine 10, just as in the process of S11.

[0039] After estimating and obtaining the temperature of the second three-way catalytic converter 11b, the processing circuit 31 proceeds to process S16. In the process of S16, the processing circuit 31 determines whether the temperature of the second three-way catalytic converter 11b is above the preheating determination temperature.

[0040] In the process of S16, if the processing circuit 31 determines that the temperature of the second three-way catalytic converter 11b is above the preheating determination temperature (S16: "Yes"), then the process proceeds to S17. In the process of S17, the processing circuit 31 determines that the preheating of the second three-way catalytic converter 11b is complete. Then, the processing circuit 31 proceeds to S19.

[0041] In the process of S16, if the processing circuit 31 determines that the temperature of the second three-way catalytic converter 11b is lower than the preheating determination temperature (S16: "No"), then the process proceeds to S18. In the process of S18, the processing circuit 31 determines that the preheating of the second three-way catalytic converter 11b is not complete. Then, the processing circuit 31 proceeds to S19.

[0042] In the process of S19, the processing circuit 31 determines whether all three-way catalytic converters located upstream of the nitrogen oxide sensor 14 have not completed preheating.

[0043] If processing circuit 31 has performed processing S14 and processing S18, in processing S19, it determines that all three-way catalytic converters located upstream of the nitrogen oxide sensor 14 have not completed preheating. If processing circuit 31 determines in processing S19 that all three-way catalytic converters located upstream of the nitrogen oxide sensor 14 have not completed preheating (S19: "Yes"), then the process proceeds to S20.

[0044] When the preheating of the three-way catalytic converter is complete, ammonia is generated on the three-way catalytic converter. If multiple three-way catalytic converters are not fully preheated, no ammonia will be generated on the three-way catalytic converters. Therefore, if multiple three-way catalytic converters are not fully preheated, the output value of the nitrogen oxide sensor 14 is a value that does not contain components that react with ammonia. In the processing of S20, the processing circuit 31 determines the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter by the output value of the nitrogen oxide sensor 14. Then, the processing circuit 31 ends. Figure 2 The series of processes shown.

[0045] If at least one of the processes S14 and S18 is not executed, in process S19, the processing circuit 31 determines that the condition that all three-way catalytic converters located upstream of the nitrogen oxide sensor 14 have not completed preheating is not met. In process S19, if the processing circuit 31 determines that the condition is not met (S19: "No"), the process proceeds to S21.

[0046] In the process of S21, the processing circuit 31 determines that the output value of the nitrogen oxide sensor 14 may contain components from the reaction between the nitrogen oxide sensor 14 and ammonia. Then, the processing circuit 31 proceeds to S22.

[0047] In the process of S22, the processing circuit 31 determines that an additional differentiation determination should be performed. Then, the processing circuit 31 ends. Figure 2 The series of processes shown.

[0048] Additional differentiation determination refers to determining, from a viewpoint other than the temperature of the three-way catalytic converter, whether the output value of the nitrogen oxide sensor 14 includes the components of the nitrogen oxide sensor 14 reacting with ammonia after the three-way catalytic converter has been preheated.

[0049] The three-way catalytic converter receives exhaust gas from engine 10 and becomes warm; therefore, the upstream three-way catalytic converter in exhaust passage 12 preheats faster. There are two states where the condition that all three-way catalytic converters upstream of the nitrogen oxide sensor 14 have not completed preheating is not met. The first state is where only the first three-way catalytic converter 11a has completed preheating. The second state is where both the first three-way catalytic converter 11a and the second three-way catalytic converter 11b have completed preheating. The additional distinction method changes depending on which of the two states is currently in place.

[0050] <Methods for calculating the oxygen storage capacity of a three-way catalytic converter>

[0051] When the air-fuel ratio of the incoming exhaust is lean, the three-way catalytic converter retains oxygen contained in the exhaust; conversely, when the air-fuel ratio of the incoming exhaust is rich, it releases the retained oxygen. The exhaust monitoring device 30 periodically calculates the oxygen storage capacity of the first three-way catalytic converter 11a and the second three-way catalytic converter 11b. In an additional differentiation determination, the exhaust monitoring device 30 determines, based on the oxygen storage capacity of the three-way catalytic converters, whether the output value of the nitrogen oxide sensor 14 contains components from the reaction between the nitrogen oxide sensor 14 and ammonia. The method by which the exhaust monitoring device 30 calculates the oxygen storage capacity of the first three-way catalytic converter 11a and the second three-way catalytic converter 11b will be explained below.

[0052] When calculating the oxygen storage capacity of the three-way catalytic converter, the exhaust monitoring device 30 calculates an update value. The update value represents the amount of oxygen absorbed or released by the three-way catalytic converter from the time the previous oxygen storage capacity was calculated to the time the current oxygen storage capacity is calculated. For example, if the three-way catalytic converter absorbed oxygen from the time the previous oxygen storage capacity was calculated to the time the current oxygen storage capacity is calculated, the update value is positive. Conversely, if the three-way catalytic converter released oxygen from the time the previous oxygen storage capacity was calculated to the time the current oxygen storage capacity is calculated, the update value is negative.

[0053] When calculating the oxygen storage capacity of the first three-way catalytic converter 11a, the exhaust monitoring device 30 first calculates an update value. The exhaust monitoring device 30 calculates the update value based on the air-fuel ratio of the exhaust flowing into the first three-way catalytic converter 11a, the flow rate of the exhaust flowing into the first three-way catalytic converter 11a, and the temperature of the first three-way catalytic converter 11a. The exhaust monitoring device 30 uses the output value of the first air-fuel ratio sensor 15a as the air-fuel ratio of the exhaust flowing into the first three-way catalytic converter 11a. The exhaust monitoring device 30 calculates the exhaust flow rate based on the output value of the air flow meter 16 and uses the calculated flow rate as the exhaust flow rate flowing into the first three-way catalytic converter 11a. The exhaust monitoring device 30 uses... Figure 2 The temperature of the first three-way catalytic converter 11a is calculated in the same way as that of S11. Then, the exhaust monitoring device 30 calculates the current oxygen storage of the first three-way catalytic converter 11a by adding the calculated updated value to the previously calculated oxygen storage of the first three-way catalytic converter 11a.

[0054] When calculating the oxygen storage capacity of the second three-way catalytic converter 11b, the exhaust monitoring device 30 first calculates an update value. The exhaust monitoring device 30 calculates the update value based on the air-fuel ratio of the exhaust flowing into the second three-way catalytic converter 11b, the flow rate of the exhaust flowing into the second three-way catalytic converter 11b, and the temperature of the second three-way catalytic converter 11b. The exhaust monitoring device 30 uses the output value of the second air-fuel ratio sensor 15b as the air-fuel ratio of the exhaust flowing into the second three-way catalytic converter 11b. The exhaust monitoring device 30 calculates the exhaust flow rate based on the output value of the air flow meter 16 and uses the calculated flow rate as the exhaust flow rate flowing into the second three-way catalytic converter 11b. The exhaust monitoring device 30 uses... Figure 2 The temperature of the second three-way catalytic converter 11b is calculated in the same way as that of S15. Then, the exhaust monitoring device 30 calculates the current oxygen storage of the second three-way catalytic converter 11b by adding the calculated updated value to the previously calculated oxygen storage of the second three-way catalytic converter 11b.

[0055] <Additional Distinguishing Decision Only When Preheating of the First Three-Way Catalytic Converter 11a is Completed>

[0056] Figure 3 This illustrates the process by which the exhaust monitoring device 30 performs a series of processes as an additional distinguishing determination when only the preheating of the first three-way catalytic converter 11a is completed. Figure 3 The series of processes shown are executed by processing circuit 31. Processing circuit 31 in... Figure 2 In the series of processes shown, after executing process S13 and process S18, and then after executing process S22, the following process is executed. Figure 3 The series of processes shown. In Figure 3 In this context, S represents a step.

[0057] Processing circuit 31 at the beginning Figure 3 During the series of processes shown, process S31 is executed first. In process S31, processing circuit 31 obtains the current oxygen storage capacity of the first three-way catalytic converter 11a in the manner described above, and determines whether the current oxygen storage capacity of the first three-way catalytic converter 11a is above a predetermined amount. The predetermined amount is a threshold used to determine that the oxygen reacting on the three-way catalytic converter is sufficiently adsorbed based on the oxygen storage capacity of the three-way catalytic converter being above a predetermined amount.

[0058] In process S31, if processing circuit 31 determines that the current oxygen storage capacity of the first three-way catalytic converter 11a is above a predetermined amount (S31: "Yes"), then the process proceeds to S34. In process S34, processing circuit 31 determines the output value of nitrogen oxide sensor 14 as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. Then, processing circuit 31 terminates. Figure 3 The series of processes shown.

[0059] When there is insufficient oxygen to react with hydrogen in the three-way catalytic converter, ammonia is produced in the three-way catalytic converter. Therefore, when the oxygen storage in the three-way catalytic converter is high, the output value of the nitrogen oxide sensor 14 is likely to be a value that does not contain components that have reacted with ammonia. If only the preheating of the first three-way catalytic converter 11a is completed, it is possible that ammonia will only be produced in the first three-way catalytic converter 11a. Therefore, if the first three-way catalytic converter 11a adsorbs a sufficient amount of oxygen, the exhaust gas will not contain ammonia. Figure 3 In the process, the exhaust monitoring device 30 determines the output value of the nitrogen oxide sensor 14 as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter, provided that the oxygen storage capacity of the first three-way catalytic converter 11a is sufficiently ensured.

[0060] In the process of S31, if the processing circuit 31 determines that the current oxygen storage capacity of the first three-way catalytic converter 11a is less than the predetermined amount (S31: "No"), then the process proceeds to S32. In the process of S32, the processing circuit 31 determines whether the air-fuel ratio of the exhaust gas passing through the first three-way catalytic converter 11a is lean based on the output value of the second air-fuel ratio sensor 15b.

[0061] In the process of S32, if the processing circuit 31 determines that the air-fuel ratio of the exhaust gas passing through the first three-way catalytic converter 11a is lean (S32: "Yes"), then the process proceeds to S34. Then, after executing the process of S34, the processing circuit 31 terminates. Figure 3 The series of processes shown.

[0062] When the air-fuel ratio of the exhaust gas passing through the three-way catalytic converter is lean, it is assumed that sufficient oxygen reacts with hydrogen in the three-way catalytic converter. Therefore, the output value of the nitrogen oxide sensor 14, which outputs under the condition that the air-fuel ratio of the exhaust gas passing through the three-way catalytic converter is lean, does not include components that react with ammonia. When the oxygen storage capacity of the first three-way catalytic converter 11a is less than a predetermined amount, the processing circuit 31 determines that the output value of the nitrogen oxide sensor 14 is the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter, even when the air-fuel ratio of the exhaust gas passing through the first three-way catalytic converter 11a is lean, even if the oxygen storage capacity of the first three-way catalytic converter 11a is less than a predetermined amount.

[0063] In the process of S32, if the processing circuit 31 determines that the air-fuel ratio of the exhaust gas passing through the first three-way catalytic converter 11a is rich (S32: "No"), then the process proceeds to S33. In the process of S33, the processing circuit 31 determines that the output value of the nitrogen oxide sensor 14 may contain components from the reaction between the nitrogen oxide sensor 14 and ammonia. Then, the processing circuit 31 terminates. Figure 3 The series of processes shown.

[0064] <Additional Differentiation Judgment When Preheating of Two Three-Way Catalytic Converters is Completed>

[0065] Figure 4 The diagram illustrates a series of processes performed by the exhaust monitoring device 30 as an additional distinguishing determination after both the first three-way catalytic converter 11a and the second three-way catalytic converter 11b have completed preheating. Figure 4 The series of processes shown are executed by processing circuit 31. Processing circuit 31 in... Figure 2 In the series of processes shown, after executing process S13 and process S17, and then after executing process S22, the process is executed... Figure 4 The series of processes shown. In Figure 4 In this context, S represents a step.

[0066] Processing circuit 31 at the beginning Figure 4 During the series of processes shown, process S41 is executed first. In process S41, the processing circuit 31 obtains the current oxygen storage capacity of the second three-way catalytic converter 11b in the manner described above, and determines whether the current oxygen storage capacity of the second three-way catalytic converter 11b is above a predetermined amount.

[0067] In process S41, if processing circuit 31 determines that the current oxygen storage capacity of the second three-way catalytic converter 11b is above a predetermined amount (S41: "Yes"), then the process proceeds to S44. In process S44, processing circuit 31 determines the output value of nitrogen oxide sensor 14 as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. Then, processing circuit 31 terminates. Figure 4 The series of processes shown.

[0068] When both the first three-way catalytic converter 11a and the second three-way catalytic converter 11b have been preheated, ammonia may be generated in both. Even if ammonia is generated in the first three-way catalytic converter 11a, if the second three-way catalytic converter 11b adsorbs a sufficient amount of oxygen, the ammonia will react with oxygen and decompose in the second three-way catalytic converter 11b. Therefore, the exhaust gas passing through the nitrogen oxide sensor 14 will not contain ammonia. Figure 4 In the process, the exhaust monitoring device 30 determines the output value of the nitrogen oxide sensor 14 as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter, provided that the oxygen storage capacity of the second three-way catalytic converter 11b is sufficiently ensured.

[0069] In the process of S41, if the processing circuit 31 determines that the current oxygen storage capacity of the second three-way catalytic converter 11b is less than the predetermined amount (S41: "No"), then the process proceeds to S42. In the process of S42, the processing circuit 31 determines whether the air-fuel ratio of the exhaust gas passing through the second three-way catalytic converter 11b is lean based on the output value of the third air-fuel ratio sensor 15c.

[0070] In the process of S42, if the processing circuit 31 determines that the air-fuel ratio of the exhaust gas passing through the second three-way catalytic converter 11b is lean (S42: "Yes"), then the process proceeds to S44. Then, after executing the process of S44, the processing circuit 31 terminates. Figure 4 The series of processes shown.

[0071] When the air-fuel ratio of the exhaust gas passing through the second three-way catalytic converter 11b is lean, it is assumed that the oxygen reacting with hydrogen and ammonia in the second three-way catalytic converter 11b is sufficient. Even when the oxygen storage in the second three-way catalytic converter 11b is less than a predetermined amount, the processing circuit 31 determines the output value of the nitrogen oxide sensor 14 as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter, even when the air-fuel ratio of the exhaust gas passing through the second three-way catalytic converter 11b is lean.

[0072] In the process of S42, if the processing circuit 31 determines that the air-fuel ratio of the exhaust gas passing through the second three-way catalytic converter 11b is rich (S42: "No"), then the process proceeds to S43. In the process of S43, the processing circuit 31 determines that the output value of the nitrogen oxide sensor 14 may contain components from the reaction between the nitrogen oxide sensor 14 and ammonia. Then, the processing circuit 31 terminates. Figure 4 The series of processes shown.

[0073] Based on Figure 2 The temperature determination shown and Figure 3 and Figure 4The additional distinction shown indicates that, among these two, the output value deemed potentially containing components that react with ammonia has a higher probability of containing such components. On the other hand, in... Figures 2-4 At any point in the output, the value that determines the concentration of nitrogen oxides in the exhaust gas is the accurate concentration of nitrogen oxides excluding components that react with ammonia.

[0074] The exhaust monitoring device 30 performs processing based on the output value of the nitrogen oxide sensor 14, according to the output value that determines the concentration of nitrogen oxides in the exhaust. For example, if there is a process to display a warning to the user when the concentration of nitrogen oxides in the exhaust exceeds a predetermined value, the processing is performed based on the output value that determines the concentration of nitrogen oxides in the exhaust, thereby appropriately displaying the warning to the user.

[0075] <The function of this implementation method>

[0076] When the preheating of the three-way catalytic converter is complete, ammonia is generated on the three-way catalytic converter. Therefore, the output value of the nitrogen oxide sensor 14, which outputs when the preheating of the three-way catalytic converter is not complete, does not contain the components that react with ammonia.

[0077] The exhaust monitoring device 30 determines, based on the temperature of the three-way catalytic converter, whether the output value of the nitrogen oxide sensor 14 indicates the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. If the engine 10 has processing performed based on the output value of the nitrogen oxide sensor 14, and the exhaust monitoring device 30 performs this processing based on the output value determined to indicate the concentration of nitrogen oxides, then the processing can be performed appropriately.

[0078] <Effects of this implementation method>

[0079] (1) The exhaust monitoring device 30 is able to perform appropriate processing based on the output value of the nitrogen oxide sensor 14.

[0080] (2) The exhaust system 40 has multiple three-way catalytic converters on the exhaust passage 12. When the exhaust monitoring device 30 obtains the output value of the nitrogen oxide sensor 14, it obtains the temperature of all three-way catalytic converters located upstream of the nitrogen oxide sensor 14 in the exhaust passage 12. When the temperature of all three-way catalytic converters located upstream of the nitrogen oxide sensor 14 is lower than the preheating determination temperature, the exhaust monitoring device 30 determines that the output value of the nitrogen oxide sensor 14 is the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converters. When the temperature of at least one of the three-way catalytic converters located upstream of the nitrogen oxide sensor 14 is higher than the preheating determination temperature, the exhaust monitoring device 30 determines that the output value of the nitrogen oxide sensor 14 may contain components that reacted with ammonia.

[0081] If preheating is completed in any one of the multiple three-way catalytic converters, ammonia may be generated in that catalytic converter. Therefore, if all three-way catalytic converters are in a state where preheating is not complete, the output value of the nitrogen oxide sensor 14 does not include components that react with ammonia.

[0082] When the temperature of all three-way catalytic converters located upstream of the nitrogen oxide sensor 14 is lower than the preheating determination temperature, the exhaust monitoring device 30 determines that the output value of the nitrogen oxide sensor 14 is the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converters. Therefore, when multiple three-way catalytic converters are installed on the exhaust passage 12, the exhaust monitoring device 30 can appropriately perform processing based on the output value of the nitrogen oxide sensor 14.

[0083] (3) When there is little oxygen reacting with hydrogen on the three-way catalytic converter, ammonia is produced on the three-way catalytic converter. Therefore, when the oxygen storage in the three-way catalytic converter is high, the output value of the nitrogen oxide sensor 14 is more likely to be a value that does not contain the components that react with ammonia.

[0084] The exhaust monitoring device 30 determines, based on the oxygen storage level in the three-way catalytic converter, whether the output value of the nitrogen oxide sensor 14 indicates the concentration of nitrogen oxides in the exhaust gas passing through the three-way catalytic converter. If the engine 10 performs processing based on the output value of the nitrogen oxide sensor 14, and the exhaust monitoring device 30 performs this processing based on the output value determined to indicate a nitrogen oxide concentration, then this processing can be performed appropriately. Thus, the exhaust monitoring device 30 can appropriately perform the processing based on the output value of the nitrogen oxide sensor 14.

[0085] (4) The exhaust system 40 has multiple three-way catalytic converters in the exhaust passage 12. When the exhaust monitoring device 30 obtains the output value of the nitrogen oxide sensor 14, it obtains the oxygen storage of the downstream three-way catalytic converter located upstream of the nitrogen oxide sensor 14 in the exhaust passage 12. When the oxygen storage of the downstream three-way catalytic converter is greater than or equal to a predetermined amount, the exhaust monitoring device 30 determines that the output value of the nitrogen oxide sensor 14 is the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. When the oxygen storage of the downstream three-way catalytic converter is less than a predetermined amount, the exhaust monitoring device 30 determines that the output value of the nitrogen oxide sensor 14 may contain components that have reacted with ammonia.

[0086] Ammonia decomposes through reaction with oxygen in a three-way catalytic converter. When multiple three-way catalytic converters are installed in the exhaust passage 12, even if ammonia is generated in the upstream three-way catalytic converter, it is decomposed by the downstream three-way catalytic converter, and the output value of the nitrogen oxide sensor 14 does not contain components that have reacted with ammonia. Therefore, if the oxygen storage capacity of the three-way catalytic converter located upstream of and closest to the nitrogen oxide sensor 14 in the exhaust passage 12 is sufficiently high, the output value of the nitrogen oxide sensor 14 will not contain components that have reacted with ammonia.

[0087] When the oxygen storage capacity of the three-way catalytic converter located upstream and closest to the nitrogen oxide sensor 14 is sufficiently ensured, the exhaust monitoring device 30 determines the output value of the nitrogen oxide sensor 14 as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. Therefore, when multiple three-way catalytic converters are installed on the exhaust passage 12, the exhaust monitoring device 30 can appropriately perform processing based on the output value of the nitrogen oxide sensor 14.

[0088] (5) When the exhaust monitoring device 30 obtains an output value after the three-way catalytic converter has finished preheating, it obtains the air-fuel ratio of the exhaust gas passing through the three-way catalytic converter. When the air-fuel ratio is lean, the exhaust monitoring device 30 determines that the output value of the nitrogen oxide sensor 14 is the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. When the air-fuel ratio is not lean, the exhaust monitoring device 30 determines that the output value of the nitrogen oxide sensor 14 may contain components that react with ammonia.

[0089] When there is insufficient oxygen reacting with hydrogen in the three-way catalytic converter, ammonia is produced in the three-way catalytic converter. When the air-fuel ratio of the exhaust gas passing through the three-way catalytic converter is lean, it is assumed that sufficient oxygen reacts with hydrogen in the three-way catalytic converter. Therefore, the output value of the nitrogen oxide sensor 14, which outputs under the condition of a lean air-fuel ratio in the exhaust gas passing through the three-way catalytic converter, is a value that does not include the components that react with ammonia.

[0090] The exhaust monitoring device 30 determines, based on the air-fuel ratio of the exhaust gas passing through the three-way catalytic converter, whether the output value of the nitrogen oxide sensor 14 indicates the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. If the engine 10 performs processing based on the output value of the nitrogen oxide sensor 14, and the exhaust monitoring device 30 performs this processing based on the output value determined to indicate a nitrogen oxide concentration, then this processing can be performed appropriately. Thus, the exhaust monitoring device 30 can appropriately perform the processing based on the output value of the nitrogen oxide sensor 14.

[0091] <Example of Change>

[0092] The above-described embodiments can be implemented in the following ways. The above-described embodiments and the following modifications can be combined with each other within the scope of technical inconsistency.

[0093] The composition of the exhaust system 40 is not limited to... Figure 1 The exhaust system 40 can have only one three-way catalytic converter or more than three three-way catalytic converters.

[0094] • When the oxygen storage capacity of the three-way catalytic converter is less than the predetermined amount, the exhaust monitoring device 30 can determine that the output value of the nitrogen oxide sensor 14 may contain components that react with ammonia, even if the air-fuel ratio of the exhaust gas passing through the three-way catalytic converter is lean.

[0095] The exhaust monitoring device 30 may acquire the temperature of the three-way catalytic converter in ways not limited to those described above. For example, the exhaust monitoring device 30 may acquire the temperature of the three-way catalytic converter based on the output value of a sensor that measures the temperature of the three-way catalytic converter.

[0096] • The exhaust monitoring device 30 can determine whether the air-fuel ratio passing through the first three-way catalytic converter 11a is lean based on the output value of the O2 sensor located between the first three-way catalytic converter 11a and the second three-way catalytic converter 11b, rather than the output value of the second air-fuel ratio sensor 15b.

[0097] • The exhaust monitoring device 30 can determine whether the air-fuel ratio passing through the second three-way catalytic converter 11b is lean based on the output value of the O2 sensor located downstream of the second three-way catalytic converter 11b, rather than based on the output value of the third air-fuel ratio sensor 15c.

[0098] Furthermore, when the nitrogen oxide sensor 14 is configured to measure the air-fuel ratio of the exhaust gas, the exhaust monitoring device 30 can determine whether the air-fuel ratio passing through the second three-way catalytic converter 11b is lean based on the air-fuel ratio of the exhaust gas output by the nitrogen oxide sensor 14. In this case, the exhaust system 40 does not need to have a sensor measuring the air-fuel ratio in addition to the nitrogen oxide sensor 14 installed downstream of the second three-way catalytic converter 11b.

[0099] ·exist Figure 4 In the additional distinguishing determination shown, if the oxygen storage capacity of at least one of the first three-way catalytic converter 11a and the second three-way catalytic converter 11b is less than a predetermined amount, it can also be determined that the output value of the nitrogen oxide sensor 14 may contain components that react with ammonia.

[0100] ·exist Figure 2In the series of processes shown, the exhaust monitoring device 30 may not perform additional differentiation determination after determining that the output value of the nitrogen oxide sensor 14 may contain components that react with ammonia.

[0101] • The exhaust monitoring device 30 can determine whether the output value of the nitrogen oxide sensor 14 contains components from the reaction between the nitrogen oxide sensor 14 and ammonia based on the relationship between the oxygen storage capacity of the three-way catalytic converter and a predetermined quantity, without having to perform a determination based on the temperature of the three-way catalytic converter.

[0102] • In the additional differentiation determination, the exhaust monitoring device 30 can determine whether the output value of the nitrogen oxide sensor 14 contains the components of the nitrogen oxide sensor 14 reacting with ammonia based on whether the air-fuel ratio of the exhaust gas passing through the three-way catalytic converter is lean, without having to confirm the relationship between the oxygen storage capacity of the three-way catalytic converter and the predetermined amount.

Claims

1. An exhaust monitoring device, characterized in that, The exhaust monitoring device is able to acquire the output value of the nitrogen oxide sensor in the exhaust system. The exhaust system includes: The three-way catalytic converter is located in the engine's exhaust passage; and A nitrogen oxide sensor is disposed downstream of the three-way catalytic converter in the exhaust passage. When the exhaust monitoring device receives the output value, it also receives the temperature of the three-way catalytic converter. When the temperature of the three-way catalytic converter is lower than the preheating determination temperature, the exhaust monitoring device determines the output value as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. When the temperature of the three-way catalytic converter is above the preheating determination temperature, the exhaust monitoring device determines that the output value may contain components that react with ammonia as described by the nitrogen oxide sensor.

2. The exhaust monitoring device according to claim 1, characterized in that, The exhaust system has multiple three-way catalytic converters in the exhaust passage. When the exhaust monitoring device acquires the output value, it acquires the temperature of all the three-way catalytic converters located upstream of the nitrogen oxide sensor in the exhaust channel. When the temperature of all the three-way catalytic converters located upstream of the nitrogen oxide sensor is lower than the preheating determination temperature, the exhaust monitoring device determines that the output value is the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converters. If at least one of the three-way catalytic converters located upstream of the nitrogen oxide sensor has a temperature above the preheating determination temperature, the exhaust monitoring device determines that the output value may contain components from the reaction between the nitrogen oxide sensor and ammonia.

3. An exhaust monitoring device, characterized in that, The exhaust monitoring device is able to acquire the output value of the nitrogen oxide sensor in the exhaust system. The exhaust system includes: The three-way catalytic converter is located in the engine's exhaust passage; and A nitrogen oxide sensor is disposed downstream of the three-way catalytic converter in the exhaust passage. When the exhaust monitoring device receives the output value, it obtains the oxygen storage capacity of the three-way catalytic converter. When the oxygen storage capacity of the three-way catalytic converter is above a predetermined amount, the exhaust monitoring device determines the output value as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. When the oxygen storage capacity of the three-way catalytic converter is less than the predetermined amount, the exhaust monitoring device determines that the output value may contain components from the reaction between the nitrogen oxide sensor and ammonia.

4. The exhaust monitoring device according to claim 3, characterized in that, The exhaust system has multiple three-way catalytic converters in the exhaust passage. When the exhaust monitoring device acquires the output value, it acquires the oxygen storage capacity of the downstream three-way catalytic converter located upstream of the nitrogen oxide sensor in the exhaust channel. When the oxygen storage capacity of the three-way catalytic converter located at the downstream end is above the predetermined amount, the exhaust monitoring device determines the output value as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. When the oxygen storage capacity of the three-way catalytic converter located at the downstream end is less than the predetermined amount, the exhaust monitoring device determines that the output value may contain components from the reaction between the nitrogen oxide sensor and ammonia.

5. The exhaust monitoring device according to any one of claims 1 to 4, characterized in that, When the exhaust monitoring device obtains the output value after the three-way catalytic converter has finished preheating, it obtains the air-fuel ratio of the exhaust gas passing through the three-way catalytic converter. When the air-fuel ratio is lean, the exhaust monitoring device determines the output value as the concentration of nitrogen oxides contained in the exhaust gas passing through the three-way catalytic converter. When the air-fuel ratio is not lean, the exhaust monitoring device determines that the output value may contain components that have reacted with ammonia as described by the nitrogen oxide sensor.

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