JP2014224504A - Diagnostic device, exhaust purification device and diagnostic method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diagnostic device, an exhaust purification device and a diagnostic method capable of diagnosing appropriateness of a detection value of an NHsensor.SOLUTION: A diagnostic device which diagnoses appropriateness of a detection value of an NHsensor is for an exhaust purification device comprising: a reduction catalyst where exhaust gas discharged from an engine flows therein and NOcontained in the exhaust gas is purified by NH; a reduction agent supply section which supplies an exhaust passage where the exhaust gas flows to the reduction catalyst therethrough with a reduction agent capable of generating the NH; an NOsensor which detects NOflowing out of the reduction catalyst; and the NHsensor which detects the NHflowing out of the reduction catalyst. The diagnostic device has a determination section which determines the appropriateness of the detection value of the NHsensor on the basis of the detection values of the NOsensor and the NHsensor. The determination section determines the appropriateness of the detection value of the NHsensor by comparing the detection values of the NOsensor and the NHsensor when the engine is in a state where fuel is not injected therein.

Description

  The present invention relates to a diagnostic device, an exhaust purification device, and a diagnostic method.

In some cases, exhaust gas discharged from an engine mounted on a vehicle, a ship, or the like includes nitrogen oxides (hereinafter referred to as “NO _x ” (x may be a positive integer)). Examples of the exhaust gas purification device that purifies NO _x contained in the exhaust gas include an SCR (Selective Catalyst Reduction) device (or SCR system) that uses an aqueous urea solution or aqueous ammonia as a reducing agent.

  Under such circumstances, techniques for diagnosing an exhaust gas processing system for processing exhaust gas discharged from an engine have been developed. As a technique for diagnosing an exhaust gas treatment system, for example, a technique described in Patent Document 1 below can be cited.

JP 2008-190529 A

In the exhaust purification device, for example, exhaust gas discharged from the engine (hereinafter simply referred to as “exhaust gas”) purifies NO _x using ammonia (hereinafter sometimes referred to as “NH ₃ ”). Purified by the reducing catalyst. In the exhaust gas purification apparatus, a reduction reaction with NH ₃ and NO _x is promoted by the reduction catalyst, by decomposing the NO _x nitrogen and water, carbon dioxide, NO _x contained in the exhaust gas is purified. For example, aqueous urea solution or ammonia water is used as the reducing agent, it adsorbs NH _3, when the catalyst having the function of promoting the reduction reaction between NH ₃ and NO _x are used as the reducing catalyst, the exhaust gas purifying apparatus, the reduction NH ₃ produced by the decomposition of the agent is adsorbed by the reduction catalyst, and NO _x contained in the exhaust gas flowing into the reduction catalyst reacts with the produced NH ₃ , whereby NO contained in the exhaust gas. _x is purified.

In the exhaust purification device, for example, in order to control the purification of exhaust gas, a nitrogen oxide sensor (hereinafter referred to as “NO _x sensor”) that detects NO _x contained in the exhaust gas after being purified by the reduction catalyst. Is provided in the exhaust passage through which the exhaust gas flowing out from the reduction catalyst passes.

Here, in the exhaust purification apparatus for purifying NO _x contained in the exhaust gas using the NH _3, the amount of NH ₃ that can be adsorbed in the reduction catalyst depends on the temperature of the reduction catalyst. Therefore, in the exhaust purification apparatus for purifying NO _x contained in the exhaust gas using the NH _3, depending on the supply amount of the reducing agent, a portion of the NH ₃ to be generated, may occur flow out from the reduction catalyst. The NO _x sensor also reacts with NH ₃ along with NO _x .

Therefore, in the exhaust purification apparatus for purifying NO _x contained in the exhaust gas using the NH _3, for example, when the detection value of the NO _x sensor is considered to indicate NH ₃ concentration, a detection value of the NO _x sensor used, by the supply of the reducing agent to the reducing catalyst is controlled, while reducing the outflow of NH ₃ from the reduction catalyst (slip NH ₃ from the reducing catalyst), the purification of the NO _x contained in the exhaust gas Is planned.

As described above, in an existing exhaust gas purification apparatus in which an aqueous urea solution or ammonia water is used as a reducing agent, the outflow of NH ₃ from the reduction catalyst is reduced by using the detected value of the NO _x sensor. However, since the NO _x sensor detects the concentrations of NO _x and NH ₃ , it is difficult to accurately detect the concentration of NH ₃ flowing out from the reduction catalyst.

Here, as a method for more accurately detecting the concentration of NH ₃ flowing out from the reduction catalyst, as in the technique described in Patent Document 1, for example, in the exhaust passage through which the exhaust gas flowing out from the reduction catalyst passes, A method of further providing an ammonia sensor for detecting NH ₃ (hereinafter sometimes referred to as “NH ₃ sensor”) may be mentioned. By using the detection value of the NH ₃ sensor, it is expected that the concentration of NH ₃ flowing out from the reduction catalyst can be grasped more accurately than in the case of using the detection value of the NO _x sensor. Therefore, there is a possibility that more precise control can be performed in the exhaust purification device.

However, for example, by an initial failure or aging of the NH ₃ sensor, a detection value of the NH ₃ sensor, the concentration of the actual NH ₃ flowing out of the reduction catalyst may occur different situation. Further, when a situation occurs in which the detected value of the NH ₃ sensor differs from the actual concentration of NH ₃ flowing out from the reduction catalyst, even if an exhaust purification device provided with the NH ₃ sensor is used, the reduction is performed. There is a possibility that the purification rate of NO _x contained in the exhaust gas cannot be improved while reducing the outflow of NH ₃ from the catalyst.

For example, the technique described in Patent Document 1 is based on the assumption that both the detection value of the NO _x sensor and the detection value of the NH ₃ sensor are correct. Therefore, for example, even if the technique disclosed in Patent Document 1 is used, it is not always possible to improve the purification rate of NO _x contained in the exhaust gas while reducing the outflow of NH ₃ from the reduction catalyst. .

  The present invention has been made in view of the above problems, and an object of the present invention is to include ammonia in an exhaust purification device that includes an ammonia sensor and purifies nitrogen oxides contained in exhaust gas using ammonia. It is an object of the present invention to provide a new and improved diagnostic device, exhaust gas purification device, and diagnostic method capable of diagnosing the validity of a detection value of a sensor.

In order to achieve the above object, according to a first aspect of the present invention, a reduction catalyst for purifying nitrogen oxides contained in the exhaust gas by using exhaust gas into which exhaust gas exhausted from the engine is introduced; A reducing agent supply unit that supplies a reducing agent capable of generating ammonia to an exhaust passage through which the exhaust gas flows into the reduction catalyst, and a nitrogen oxide that detects nitrogen oxides flowing out from the reduction catalyst A diagnostic device for diagnosing the validity of the detection value of the ammonia sensor in an exhaust gas purification device including an sensor and an ammonia sensor for detecting ammonia flowing out of the reduction catalyst, the detection value of the nitrogen oxide sensor Based on the detection value of the ammonia sensor, a determination unit for determining the validity of the detection value of the ammonia sensor,
The determination unit compares the detection value of the nitrogen oxide sensor with the detection value of the ammonia sensor when the engine is in a no fuel injection state, thereby determining the validity of the detection value of the ammonia sensor. A diagnostic device for determining is provided.

  With this configuration, it is possible to diagnose the validity of the detection value of the ammonia sensor in the exhaust gas purification apparatus that includes the ammonia sensor and purifies nitrogen oxides contained in the exhaust gas using ammonia.

  Further, the determination unit determines that the detection value of the ammonia sensor is valid when the absolute value of the difference between the detection value of the nitrogen oxide sensor and the detection value of the ammonia sensor is equal to or less than a predetermined specified value. When the absolute value is larger than the specified value, it is determined that the detected value of the ammonia sensor is not valid, or when the absolute value is less than the specified value, the detected value of the ammonia sensor is It may be determined that the detection value of the ammonia sensor is not appropriate when the absolute value is equal to or greater than the specified value.

  Moreover, when it is determined that the detection value of the ammonia sensor is not valid, a correction unit that corrects the detection value of the ammonia sensor may be further provided.

  The correction unit calculates a difference value between the detection value of the nitrogen oxide sensor and the detection value of the ammonia sensor and a value obtained by dividing the detection value of the nitrogen oxide sensor by the detection value of the ammonia sensor. The detection value of the ammonia sensor may be corrected using the difference value or the divided value based on whether the difference value varies depending on the ammonia concentration.

  The correction unit corrects the detection value of the ammonia sensor by multiplying the detection value of the ammonia sensor by the divided value when the value of the difference varies depending on the ammonia concentration, and When the value does not change depending on the ammonia concentration, the detected value of the ammonia sensor may be corrected by adding the difference value to the detected value of the ammonia sensor.

  In addition, the determination unit may start determining the validity of the detection value of the ammonia sensor after a predetermined time has elapsed since the engine is in a no fuel injection state.

  Further, the determination unit is configured to detect the detected value of the nitrogen oxide sensor and the ammonia sensor when the engine is in a fuel-free injection state and the reducing agent is not supplied to the reduction catalyst. You may compare with a detected value.

  In order to achieve the above object, according to a second aspect of the present invention, a reduction catalyst that purifies nitrogen oxides contained in the exhaust gas by using exhaust gas flowing in from the engine. A reducing agent supply unit that supplies a reducing agent capable of generating ammonia to an exhaust passage through which the exhaust gas flows into the reduction catalyst; and nitrogen that detects nitrogen oxides flowing out of the reduction catalyst The validity of the detected value of the ammonia sensor is determined based on the oxide sensor, the ammonia sensor that detects ammonia flowing out of the reduction catalyst, and the detected value of the nitrogen oxide sensor and the detected value of the ammonia sensor. A determination unit configured to detect the nitrogen oxide sensor when the engine is in a fuel-free injection state and the ammonia. By comparing the detected value of the capacitors, it determines the validity of the detection value of the ammonia sensor, an exhaust gas purification device is provided.

  With this configuration, it is possible to diagnose the validity of the detection value of the ammonia sensor.

  In order to achieve the above object, according to a third aspect of the present invention, a reduction catalyst that purifies nitrogen oxides contained in the exhaust gas by using exhaust gas that is exhausted from the engine. A reducing agent supply unit that supplies a reducing agent capable of generating ammonia to an exhaust passage through which the exhaust gas flows into the reduction catalyst; and nitrogen that detects nitrogen oxides flowing out of the reduction catalyst A diagnostic method for diagnosing the validity of a detection value of the ammonia sensor in an exhaust gas purification apparatus including an oxide sensor and an ammonia sensor for detecting ammonia flowing out of the reduction catalyst, the detection of the nitrogen oxide sensor Determining the validity of the detected value of the ammonia sensor based on the value and the detected value of the ammonia sensor, The validity of the detected value of the ammonia sensor is determined by comparing the detected value of the nitrogen oxide sensor and the detected value of the ammonia sensor when the engine is in a no fuel injection state. A diagnostic method is provided.

  By using such a method, it is possible to diagnose the validity of the detection value of the ammonia sensor in the exhaust gas purification apparatus that includes the ammonia sensor and purifies nitrogen oxides contained in the exhaust gas using ammonia.

  ADVANTAGE OF THE INVENTION According to this invention, the validity of the detected value of an ammonia sensor can be diagnosed in the exhaust gas purification apparatus which contains an ammonia sensor and purifies the nitrogen oxide contained in exhaust gas using ammonia.

It is a flowchart which shows an example of the process which concerns on the diagnostic method which concerns on embodiment of this invention. It is a flowchart which shows an example of the process which concerns on the diagnostic method which concerns on embodiment of this invention. It is a block diagram which shows an example of a structure of the exhaust gas purification apparatus which concerns on embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

(Diagnostic method according to an embodiment of the present invention)
Before describing an example of the configuration of a diagnostic device according to an embodiment of the present invention and an exhaust purification device according to an embodiment of the present invention, a diagnostic method according to an embodiment of the present invention will be described. Hereinafter, the diagnosis method according to the embodiment of the present invention will be described by taking as an example the case where the diagnosis apparatus according to the embodiment of the present invention performs processing related to the diagnosis method according to the embodiment of the present invention. As will be described later, the exhaust emission control device according to the embodiment of the present invention has the function of the diagnostic device according to the embodiment of the present invention. That is, the exhaust emission control device according to the embodiment of the present invention can also perform the processing related to the diagnostic method according to the embodiment of the present invention described below.

[1] Outline of Diagnosis Method According to Embodiment of Present Invention In an exhaust gas purification device that purifies NO _x contained in exhaust gas using NH ₃ , for example, for the reasons described below, an NO _x sensor and an NH ₃ sensor Are provided in an exhaust passage through which exhaust gas flowing out from the reduction catalyst passes.
· NO _{when x} using the detected value of the sensor for detecting the NH ₃ flowing out from the reduction catalyst, of · NO _x sensor is difficult to accurately detect the concentration of NH ₃ flowing out of the reduction catalyst In some cases, it may be desirable to exclude the detection value from the influence of NH ₃ flowing out from the reduction catalyst.

NH ₃ sensor is provided by the detected value of the NH ₃ sensor is used, the exhaust emission control device, to grasp the concentration of NH ₃ flowing out from the more accurate reduction catalyst than when using the detection value of the NO _x sensor It is expected that it will be possible. Therefore, in the exhaust purification device, for example, control is performed while suppressing the amount of NH ₃ that can be adsorbed in the reduction catalyst using the detection value of the NH ₃ sensor to a value equal to or less than an allowable value, thereby being included in the exhaust gas. There is a possibility that the NO _x purification rate can be further increased. Further, the control using the detected value of the NH ₃ sensor, by enhancing the purification rate of the NO _x contained in the exhaust gas, for example, satisfies the NO _x regulations are expected to become stricter in the future more easily It becomes possible.

However, as described above, for example, an NH ₃ sensor detection value and a concentration of NH ₃ flowing out from the reduction catalyst may be different due to, for example, an initial failure or deterioration with time of the NH ₃ sensor. In addition, when a situation occurs in which the detected value of the NH ₃ sensor and the concentration of NH ₃ flowing out of the reduction catalyst are different, even if an exhaust purification device provided with the NH ₃ sensor is used, There is a possibility that the purification rate of NO _x contained in the exhaust gas cannot be improved while reducing the outflow of NH ₃ .

Therefore, the diagnostic device according to the embodiment of the present invention diagnoses the validity of the detected value of the NH ₃ sensor based on the detected value of the NO _x sensor and the detected value of the NH ₃ sensor (diagnosis process). Imaging apparatus according to the embodiment of the present invention are, for example, when the engine is a fuel non-injection state, the detection value of the NO _x sensor, by comparing the detected value of the NH ₃ sensor, NH ₃ detection sensor Determine the validity of the value.

Here, “when the engine is in the no-fuel injection state” according to the embodiment of the present invention corresponds to, for example, a state where NO _x is not discharged from the engine. The fuel non-injection state according to the embodiment of the present invention occurs in a so-called overrun situation such as a situation where the accelerator is not stepped on when the vehicle is going down a slope.

As described above, the NO _x sensor also reacts to NH ₃ . Further, when the engine is in the no fuel injection state, NO _x is not discharged from the engine. Therefore, the detected value of the NO _x sensor when the engine is in the no fuel injection state indicates the detection result of NH _3. It will be. Furthermore, by using an existing technique for diagnosing the validity of the detection value of the NO _x sensor, it is possible to guarantee that the detection value of the NO _x sensor is appropriate.

Accordingly, imaging apparatus according to the embodiment of the present invention, when the engine is a fuel non-injection state, the detection value of the NO _x sensor, by comparing the detected value of the NH ₃ sensor, NH ₃ detection sensor The validity of the value (for example, whether the detection value of the NH ₃ sensor is valid) can be determined.

Further, the diagnostic apparatus according to the embodiment of the present invention, by diagnosing the validity of the detected value of the NH ₃ sensor, the validity of the detected value of the NH ₃ sensor in the exhaust purification apparatus provided with a NH ₃ sensor is guaranteed .

Therefore, in an exhaust emission control device equipped with an NH ₃ sensor, for example, control is performed while suppressing the amount of NH ₃ that can be adsorbed in the reduction catalyst to a value below an allowable value using a detection value of the NH ₃ sensor that is guaranteed to be valid. Therefore, the purification rate of NO _x contained in the exhaust gas can be further increased. Further, by using the control using the detection value of the NH ₃ sensor that guarantees the validity, the NO _x contained in the exhaust gas is further increased, for example, NO _x that is expected to become severe in the future. You can meet the regulations more easily.

  The diagnostic processing according to the embodiment of the present invention is not limited to the above.

For example, the diagnostic device according to the embodiment of the present invention includes a detection value of an NO _x sensor and an NH ₃ sensor when the engine is in a no fuel injection state and no reducing agent is supplied to the reduction catalyst. The detected value may be compared.

Here, when NH ₃ is detected by the NO _x sensor and the NH ₃ sensor in the case where “the reducing agent is not supplied to the reduction catalyst” according to the embodiment of the present invention, the detected NH ₃ is , Corresponding to NH ₃ naturally flowing out from the reduction catalyst. That is, when comparing the detected value of the NO _x sensor and the detected value of the NH ₃ sensor when the engine is in a fuel-free injection state and the reducing agent is not supplied to the reduction catalyst, the present invention The diagnostic device according to the embodiment determines the validity of the detection value of the NH ₃ sensor based on NH ₃ that naturally flows out from the reduction catalyst. Examples of the case where NH ₃ naturally flows out from the reduction catalyst include a case where the saturated adsorption amount of NH _{3 on} the catalyst decreases due to an increase in the exhaust gas temperature, that is, the catalyst temperature. Note that the diagnostic apparatus according to the embodiment of the present invention, for example, determines the validity of the detection value of the NH ₃ sensor based on NH ₃ intentionally flowing out from the reduction catalyst by supplying a reducing agent to the reduction catalyst. It is also possible to determine.

  Specific examples of the diagnostic processing according to the embodiment of the present invention will be described later.

  Moreover, the process which concerns on the diagnostic method which concerns on embodiment of this invention is not restricted to the said diagnostic process.

For example, the diagnostic device according to the embodiment of the present invention may correct the detected value of the NH ₃ sensor when it is determined that the detected value of the NH ₃ sensor is not appropriate in the diagnostic process (correction process). . A specific example of the correction processing according to the embodiment of the present invention will be described later.

[2] Processing Related to the Diagnosis Method According to the Embodiment of the Present Invention Next, the processing related to the diagnosis method according to the embodiment of the present invention will be described more specifically. In the following, an example of processing related to the diagnostic method according to the embodiment of the present invention will be described by taking as an example the case where the diagnostic device according to the embodiment of the present invention performs processing related to the diagnostic method according to the embodiment of the present invention. explain.

  1A and 1B are flowcharts illustrating an example of processing according to a diagnostic method according to an embodiment of the present invention. Here, the processes of steps S100 to S110 shown in FIG. 1A and the processes of steps S112 to S118 and S128 shown in FIG. 1B correspond to an example of a diagnostic process according to the embodiment of the present invention. Moreover, the process of step S120-S126 shown to FIG. 1B corresponds to an example of the correction process which concerns on embodiment of this invention.

The diagnostic apparatus according to the embodiment of the present invention determines whether or not the NO _x sensor is normal (S100). The process of step S100 corresponds to a process for diagnosing the validity of the detected value of the NO _x sensor. In step S100, the diagnostic apparatus according to the embodiment of the present invention detects the NO _x sensor, such as a process using detection values of various sensors provided in the exhaust purification device such as a NO _x sensor, a pressure sensor, and a temperature sensor. It is determined whether or not the NO _x sensor is normal by performing an arbitrary process capable of diagnosing the validity of the value. Specific examples, diagnostic apparatus according to the embodiment of the present invention, for example, there is no offset of the zero point on the detection value of the NO _x sensor, when the detection value of the NO _x sensor is judged to show a reasonable value Then, it is determined that the NO _x sensor is normal.

If it is not determined in step S100 that the NO _x sensor is normal, the diagnostic device according to the embodiment of the present invention performs processing at the time of abnormality (S102), and relates to the diagnostic method according to the embodiment of the present invention. The process ends. Here, as processing at the time of abnormality in step S102, for example, a user such as a vehicle equipped with an exhaust purification device or a user who manages a vehicle equipped with an exhaust purification device (for example, a manufacturer or sales manufacturer of a vehicle, etc.) And the like) for notifying the abnormality of the NO _x sensor.

Further, when it is determined in step S100 that the NO _x sensor is normal, the diagnostic device according to the embodiment of the present invention determines whether or not the engine is in a no fuel injection state (S104). The diagnostic device according to the embodiment of the present invention determines, for example, whether or not the engine is in a no fuel injection state based on a control state in an ECU (Engine Control Unit) that controls the engine. Here, for example, when the diagnostic device according to the embodiment of the present invention has the function of the ECU, the diagnostic device according to the embodiment of the present invention uses the engine as a fuel based on the control state of the engine in its own device. It is determined whether or not there is no injection state. Further, for example, when the diagnostic device according to the embodiment of the present invention does not have the ECU function, the diagnostic device according to the embodiment of the present invention has a control state transmitted from the external ECU that is an external device. Based on the data shown, it is determined whether or not the engine is in a no fuel injection state.

  If it is not determined in step S104 that the engine is in the no-fuel injection state, the engine is in a normal operation state, and the diagnosis apparatus according to the embodiment of the present invention performs the process related to the diagnosis method according to the embodiment of the present invention. finish.

  When it is determined in step S104 that the engine is in the no fuel injection state, the diagnostic device according to the embodiment of the present invention has passed a predetermined first specified time since it was determined that the fuel is in the no fuel injection state. It is determined whether or not (S106). Here, the first specified time according to the embodiment of the present invention may be a fixed time set in advance, or may be a variable time that can be changed by a user operation or the like.

In step S106, when it is not determined that the first specified time has elapsed since it was determined that the fuel is not injected, the diagnostic device according to the embodiment of the present invention repeats the processing from step S104. In addition, the diagnostic device according to the embodiment of the present invention performs the processing after step S108, the NO _x sensor, when it is determined that the first specified time has elapsed since it was determined in step S106 that there is no fuel injection state. And a process using the detected value of the NH ₃ sensor.

That is, when the diagnosis apparatus according to the embodiment of the present invention performs the process of step S106, in the diagnosis process according to the embodiment of the present invention, a predetermined time (FIG. In the example shown in FIG. 1A and FIG. 1B, after the first specified time) has elapsed, the validity determination of the detected value of the NH ₃ sensor based on the detected value of the NO _x sensor and the detected value of the NH ₃ sensor is started. .

In step S106, when it is determined that the first specified time has elapsed since it is determined that the fuel is not injected, the diagnostic device according to the embodiment of the present invention has a detection value of the NO _x sensor of a predetermined value. It is determined whether or not it is larger than the prescribed value A (S108). Note that the diagnostic device according to the embodiment of the present invention can determine whether or not the detected value of the NO _x sensor is equal to or greater than the specified value A in step S108.

If it is determined in step S108 that the detected value of the NO _x sensor is not greater than the specified value A, the engine is in a normal operation state, and the diagnostic device according to the embodiment of the present invention performs the diagnosis according to the embodiment of the present invention. The process according to the method is terminated. In addition, the diagnostic device according to the embodiment of the present invention performs the processing after step S110, which will be described later, when it is determined in step S108 that the detected value of the NO _x sensor is larger than the specified value A. That is, the specified value A according to the embodiment of the present invention serves as a threshold value for determining whether or not to determine the validity of the detected value of the NH ₃ sensor using the detected value of the NO _x sensor, for example. Fulfill.

Here, the predetermined value A according to the embodiment of the present invention, for example, within the range of measurement accuracy of the NO _x sensor, the NH ₃ determination of validity of the detected value of the sensor using the detected value of the NO _x sensor A value that cannot be set is set. Further, the specified value A according to the embodiment of the present invention may be, for example, a preset fixed value or a variable value that can be changed by a user operation or the like.

If it is determined in step S108 that the detected value of the NO _x sensor is greater than the specified value A, the diagnostic device according to the embodiment of the present invention determines whether the detected value of the NH ₃ sensor is greater than the specified specified value B. It is determined whether or not (S110). Note that imaging apparatus according to the embodiment of the present invention, in step S110, it is also possible to determine whether a detection value of the NH ₃ sensor prescribed value B or more.

If it is not determined in step S110 that the detected value of the NH ₃ sensor is greater than the specified value B, the engine is in a normal operation state, and the diagnostic device according to the embodiment of the present invention performs the diagnosis according to the embodiment of the present invention. The process according to the method is terminated. In addition, the diagnostic device according to the embodiment of the present invention performs processing after step S112 described later when it is determined in step S110 that the detected value of the NH ₃ sensor is larger than the specified value B. That is, the specified value B according to the embodiment of the present invention serves as a threshold value for determining whether or not to determine the validity of the detection value of the NH ₃ sensor using the detection value of the NH ₃ sensor, for example. Fulfill.

Here, the predetermined value B according to an embodiment of the present invention, for example, within the range of measurement accuracy of the NH ₃ sensor, the determination of the validity of the detected value of the NH ₃ sensor using the detected value of the NH ₃ sensor A value that cannot be set is set. Further, the specified value B according to the embodiment of the present invention may be a fixed value set in advance or a variable value that can be changed by a user operation or the like.

When it is determined in step S110 that the detected value of the NH ₃ sensor is greater than the specified value B, the diagnostic device according to the embodiment of the present invention starts processing related to the validity determination of the NH ₃ sensor (S112). ).

The diagnostic device according to the embodiment of the present invention calculates the absolute value of the difference between the detected value of the NO _x sensor and the detected value of the NH ₃ sensor, and determines whether or not the absolute value is greater than a predetermined specified value C. (S114). Here, the specified value C according to the embodiment of the present invention may be a fixed value set in advance or a variable value that can be changed by a user operation or the like. Note that the diagnostic device according to the embodiment of the present invention determines whether or not the absolute value of the difference between the detected value of the NO _x sensor and the detected value of the NH ₃ sensor is equal to or greater than the specified value C in step S114. It is also possible.

In step S114, when it is not determined that the absolute value of the difference between the detected value of the NO _x sensor and the detected value of the NH ₃ sensor is greater than the specified value C, that is, it is determined that the absolute value is equal to or less than the specified value C. In this case, the diagnostic device according to the embodiment of the present invention determines that the detection value of the NH ₃ sensor is appropriate (S116). And the diagnostic apparatus which concerns on embodiment of this invention performs the process from step S128 mentioned later.

In step S114, when it is determined whether or not the absolute value of the difference between the detected value of the NO _x sensor and the detected value of the NH ₃ sensor is equal to or greater than the specified value C, the diagnosis according to the embodiment of the present invention. The apparatus determines that the detected value of the NH ₃ sensor is appropriate when the absolute value is not determined to be equal to or greater than the specified value C, that is, when the absolute value is determined to be less than the specified value C. .

In Step S114, when it is determined that the absolute value of the difference between the detected value of the NO _x sensor and the detected value of the NH ₃ sensor is larger than the specified value C, the diagnostic device according to the embodiment of the present invention It is determined that the detected value of the NH ₃ sensor is not valid (S118). In step S114, when it is determined whether or not the absolute value of the difference between the detected value of the NO _x sensor and the detected value of the NH ₃ sensor is equal to or greater than the specified value C, the diagnosis according to the embodiment of the present invention. When it is determined that the absolute value is equal to or greater than the specified value C, the apparatus determines that the detection value of the NH ₃ sensor is not valid.

If it is determined in step S118 that the detected value of the NH ₃ sensor is not valid, the diagnostic device according to the embodiment of the present invention determines the difference value between the detected value of the NO _x sensor and the detected value of the NH ₃ sensor ( NO _x value−NH ₃ value (hereinafter may be referred to as “difference value”), and calculation of the correction value f is started (S120). The diagnosis device according to the embodiment of the present invention calculates the difference value and the correction value f, for example, every time the detection value of the NO _x sensor and the detection value of the NH ₃ sensor are acquired. Here, the correction value f according to the embodiment of the present invention is calculated as, for example, a correction value obtained by dividing the detection value of the NO _x sensor by the detection value of the NH ₃ sensor, as shown in Equation 1 below. . In the following Equation 1, the detected value of the NO _x sensor is indicated as “NO _x ”, and the detected value of the NH ₃ sensor is indicated as “NH ₃ ”.

f = NO _x / NH ₃
... (Formula 1)

  For example, the diagnostic device according to the embodiment of the present invention determines whether or not fuel has been injected in the engine after the processing of step 120 is started (S122). The diagnostic device according to the embodiment of the present invention determines whether or not fuel has been injected in the engine based on the control state in the ECU, for example, similarly to the processing in step S104.

If it is determined in step S122 that fuel has been injected in the engine, the diagnostic device according to the embodiment of the present invention performs processing in step S126 described later. Note that NO _x may flow out when fuel injection starts. Therefore, when it is determined in step S122 that fuel has been injected in the engine, the diagnostic device according to the embodiment of the present invention, for example, stops the calculation of the correction value and then performs the process of step S126 described later. Do.

Further, when it is not determined in step S122 that fuel has been injected in the engine, the diagnostic device according to the embodiment of the present invention determines whether or not a predetermined second specified time has elapsed in a state in which fuel is not injected. (S124). The diagnostic device according to the embodiment of the present invention continues to calculate the correction value in order to increase the reliability of the correction value, for example, until fuel injection starts. That is, the diagnostic apparatus according to the embodiment of the present invention calculates correction values in a plurality of NH ₃ concentration states, and checks whether the calculated correction values are approximate values. And the diagnostic apparatus which concerns on embodiment of this invention complete | finishes calculation of a correction value, when 2nd specified time passes. Here, the second specified time according to the embodiment of the present invention may be a fixed time set in advance, or may be a variable time that can be changed by a user operation or the like.

  If it is not determined in step S124 that the second specified time has elapsed in a state where fuel is not injected, the diagnostic device according to the embodiment of the present invention repeats the processing from step S122.

If it is determined in step S122 that fuel has been injected in the engine, or if it is determined in step S124 that the second specified time has elapsed without fuel being injected, the diagnostic device according to the embodiment of the present invention. Corrects the detection value of the NH ₃ sensor (S126). Here, the diagnostic device according to the embodiment of the present invention changes the correction method based on whether or not the difference value (NO _x value−NH ₃ value) changes depending on the NH ₃ concentration in step S126, for example. The detection value of the NH ₃ sensor is corrected.

More specifically, the diagnostic device according to the embodiment of the present invention determines whether or not the difference value varies depending on the NH ₃ concentration, for example, as shown in (a) and (b) below in step S126. The detection value of the NH ₃ sensor is corrected by a corresponding correction method.

Imaging apparatus according to the embodiment of the present invention if (a) the difference value changes by NH ₃ concentration, the detection value of the NH ₃ sensor, by multiplying the correction value f, for correcting the detected value of the NH ₃ sensor.

(B) When the difference value does not change depending on the NH ₃ concentration When the difference value does not change depending on the NH ₃ concentration, it is considered that the detected value of the NH ₃ sensor is offset abnormally. Thus, imaging apparatus according to the embodiment of the present invention, the detection value of the NH ₃ sensor, by adding the differential value, corrects the detected value of the NH ₃ sensor. That is, when the difference value does not change depending on the NH 3 concentration, the difference value serves as a correction value.

For example, in step S126, the diagnostic device according to the embodiment of the present invention corrects the detection value of the NH ₃ sensor, for example, as shown in (a) and (b) above. Needless to say, the method of correcting the detection value of the NH ₃ sensor according to the embodiment of the present invention is not limited to the examples shown in (a) and (b).

When the process of step S116 or the process of step S126 is performed, the diagnostic apparatus according to the embodiment of the present invention ends the process related to the validity determination of the NH ₃ sensor (S128). And the diagnostic apparatus which concerns on embodiment of this invention complete | finishes the process which concerns on the diagnostic method which concerns on embodiment of this invention.

  The diagnosis apparatus according to the embodiment of the present invention performs, for example, the processes shown in FIGS. 1A and 1B as the process related to the diagnosis method according to the embodiment of the present invention. The diagnosis processing according to the embodiment of the present invention is realized by the diagnosis apparatus according to the embodiment of the present invention performing the processing illustrated in FIGS. 1A and 1B, for example.

  Therefore, for example, by performing the processing shown in FIGS. 1A and 1B, the diagnostic apparatus according to the embodiment of the present invention includes an ammonia sensor, and uses exhaust gas to purify nitrogen oxides contained in the exhaust gas. The validity of the detected value of the ammonia sensor can be diagnosed.

  In addition, the process which concerns on the diagnostic method which concerns on embodiment of this invention is not restricted to the process shown to FIG. 1A and FIG. 1B.

  For example, the diagnostic device according to the embodiment of the present invention may not perform the process of step S106 illustrated in FIG. 1A. Further, for example, the diagnostic device according to the embodiment of the present invention may not perform the process of step S108 and the process of step S110 illustrated in FIG. 1A.

  Further, for example, the diagnostic apparatus according to the embodiment of the present invention may not perform the processing of steps S120 to S126 (an example of the correction processing according to the embodiment of the present invention) illustrated in FIG. 1B.

  Even when the above steps in FIGS. 1A and 1B are not performed, the diagnostic processing according to the embodiment of the present invention is realized. Therefore, even when the above steps in FIGS. 1A and 1B are not performed, the diagnostic device according to the embodiment of the present invention includes an ammonia sensor, and nitrogen oxides contained in exhaust gas using ammonia It is possible to diagnose the validity of the detection value of the ammonia sensor in the exhaust gas purification device that purifies the gas.

(Diagnostic device and exhaust gas purification device according to an embodiment of the present invention)
Next, an example of the configuration of the diagnostic device and the exhaust gas purification device according to the embodiment of the present invention capable of performing the processing according to the above-described diagnostic method according to the embodiment of the present invention will be described.

[I] Exhaust gas purification apparatus according to an embodiment of the present invention FIG. 2 is a block diagram showing an example of a configuration of an exhaust gas purification apparatus 100 according to an embodiment of the present invention. Here, FIG. 2 also shows an engine 200 that combusts fuel and discharges exhaust gas. The engine 200, for example, as such as a diesel engine, and an engine to discharge the exhaust gas containing NO _x.

The exhaust purification apparatus 100 includes, for example, a reduction catalyst 102, a reducing agent supply unit 104, a NO _x sensor 106, an NH ₃ sensor 108, and a control unit 110. The reduction catalyst 102 includes an exhaust passage 112A (exhaust passage through which exhaust gas flows into the reduction catalyst 102) into which exhaust gas discharged from the engine 200 flows, and an exhaust passage 112B through which exhaust gas is discharged from the reduction catalyst 102. And are connected.

  In addition, the exhaust purification apparatus 100 includes a filter (not shown) that reduces PM (Particulate Matter) and soot from exhaust gas, such as DPF (Diesel Particulate Filter), and various sensors (not shown) such as a temperature sensor. May be further provided.

The reduction catalyst 102 receives exhaust gas discharged from the engine 200 and purifies NO _x contained in the exhaust gas using NH ₃ . The reduction catalyst 102 adsorbs NH ₃ produced by decomposition of an aqueous urea solution or ammonia water supplied as a reducing agent, for example, by hydrolysis or thermal decomposition, and is included in the exhaust gas flowing into the NH _3. to promote the reduction reaction with NO _x to be. By reduction reaction with NH ₃ and NO _x is promoted by the reduction catalyst 102, NO _x contained in the exhaust gas flowing the nitrogen and water, carbon dioxide, etc. The, NO _x contained in the exhaust gas Is purified.

Here, examples of the reduction catalyst 102 include any catalyst having a function of promoting a reduction reaction between NH ₃ and NO _x .

The reducing agent supply unit 104 supplies a reducing agent capable of generating NH ₃ to the exhaust passage 112A. When the reducing agent is supplied to the exhaust passage 112 </ b> A, NH ₃ is generated, and the generated NH ₃ flows into the reduction catalyst 102. Examples of the reducing agent according to the embodiment of the present invention, for example, such as urea solution or ammonia water, any aqueous solution capable of generating the NH ₃ and the like by being decomposed.

  The reducing agent supply unit 104 includes, for example, a storage tank 150 that stores the reducing agent, a reducing agent injection valve 152, and a pump 154 that is controlled by a control signal transmitted from the control unit 110 as main components. . The storage tank 150 and the pump 154 are connected by a reducing agent supply passage 156A, and the pump 154 and the reducing agent injection valve 152 are connected by a reducing agent supply passage 156B. The reducing agent supply passage 156B is provided with a circulation passage 158 extending to the storage tank 150. The circulation passage 158 is provided with an orifice 160, and resistance is given to the flow of the reducing agent returned to the storage tank 150 via the circulation passage 158 by the orifice 160, and the pressure in the reducing agent supply passage 156 is increased.

  The reducing agent supply unit 104 has a configuration as shown in FIG. 2, for example, and the operation of the pump 154 and the opening / closing of the reducing agent injection valve 152 are controlled by control signals transmitted from the control unit 110. As a result, the reducing agent is supplied to the reduction catalyst 102.

  In addition, the structure of the reducing agent supply part which concerns on embodiment of this invention is not restricted to the structure shown in FIG.

  For example, the reducing agent supply unit according to the embodiment of the present invention may include a pressure sensor (not shown) that measures the pressure in the reducing agent supply passage 156B. When the pressure sensor (not shown) is provided, the control unit 110 controls the operation of the pump 154 and the opening / closing of the reducing agent injection valve 152 using, for example, a detection value of the pressure sensor (not shown).

  In addition, the reducing agent supply unit according to the embodiment of the present invention may have a known configuration capable of supplying the reducing agent to the reduction catalyst 102.

The NO _x sensor 106 is provided in the exhaust passage 112B and detects NO _x flowing out from the reduction catalyst 102. As the NO _x sensor 106, for example, a known NO _x sensor capable of detecting NO _x and reacting with NH ₃ can be used.

The NH ₃ sensor 108 is provided in the exhaust passage 112B and detects NH ₃ flowing out from the reduction catalyst 102. Examples of the NH ₃ sensor 108 include a known NH ₃ sensor capable of detecting NH ₃ such as an NH ₃ sensor using a solid electrolyte having a property of conducting only one kind of ion.

In the exhaust purification apparatus 100, as shown in FIG. 2, the NO _x sensor 106 and the NH ₃ sensor 108 are provided in the exhaust passage 112B. Here, the NO _x sensor 106 and the NH ₃ sensor 108 are installed, for example, at positions that are not affected by the deviation of the concentration distribution of NH ₃ . Ideally, for example, the concentration of NH ₃ which detect the NO _x sensor 106 and NH ₃ sensor 108, the matching position, NO _x sensor 106 and NH ₃ sensor 108 and is it is desirable installation.

For example, as shown in step S114 of FIG. 1B, the exhaust purification device 100 uses the comparison result between the absolute value of the difference between the detected value of the NO _x sensor and the detected value of the NH ₃ sensor and a predetermined specified value C. Based on this, it is possible to determine the validity of the detection value of the NH ₃ sensor. Therefore, even if the concentrations of NH ₃ detected by the NO _x sensor 106 and the NH ₃ sensor 108 do not coincide with each other, the exhaust purification device 100 performs the NH ₃ sensor by the diagnostic processing according to the embodiment of the present invention. The validity of the 108 detected values can be diagnosed.

  The control part 110 is comprised by DCU (Dosing Control Unit) etc., for example, and fulfill | performs the role which controls the exhaust gas purification apparatus 100 whole. For example, when the control unit 110 includes an ECU (or when the DCU has a function of the ECU), the control unit 110 serves to control the engine 200. Here, FIG. 2 shows an example in which the control unit 110 controls the entire exhaust purification device 100 and the engine 200, that is, an example in which the control unit 110 has functions of a DCU and an ECU.

  Moreover, the control part 110 is provided with the determination part 120 and the correction | amendment part 122, for example, and plays the role which performs the process which concerns on the diagnostic method which concerns on embodiment of this invention.

Determination unit 120 plays a leading role in performing the diagnosis process according to the embodiment of the present invention, based on the detected value of the detection value of the NO _x sensor 106 and NH ₃ sensor 108, the detection value of the NH ₃ sensor 108 Diagnose the validity of Determining unit 120, for example, when the engine 200 is a fuel non-injection state, the detection value of the NO _x sensor 106, by comparing the detected value of the NH ₃ sensor 108, the detected value of the NH ₃ sensor 108 Determine validity. The determination unit 120 is, for example, the process of step S100~S110 shown in Figure 1A, and steps S112~S118 shown in Figure 1B, by performing such processing S128, the validity of the detected value of the NH ₃ sensor 108 You may judge.

Correction unit 122 plays a leading role in performing the correction processing according to the embodiment of the present invention, when it is determined that the detected value of the NH ₃ sensor 108 is not valid in the determination unit 120, a NH ₃ sensor 108 Correct the detection value. For example, the correction unit 122 corrects the detection value of the NH ₃ sensor 108 by performing the processing of steps S120 to S126 shown in FIG. 1B.

  The control unit 110 includes, for example, a determination unit 120 and a correction unit 122, thereby leading the processing related to the diagnostic method according to the embodiment of the present invention.

  In addition, the structure of the control part which concerns on embodiment of this invention is not restricted to the structure shown in FIG.

For example, the control unit according to the embodiment of the present invention may be configured not to include the correction unit 122. Even if the configuration does not include the correction unit 122, the control unit according to the embodiment of the present invention can perform the diagnostic processing according to the embodiment of the present invention. Therefore, even if the control unit according to the embodiment of the present invention is configured not to include the correction unit 122, the exhaust purification device according to the embodiment of the present invention diagnoses the validity of the detection value of the NH ₃ sensor 108. Can do.

The exhaust emission control device 100 has, for example, the configuration shown in FIG. 2, and processing related to the diagnostic method according to the embodiment of the present invention (for example, diagnostic processing according to the embodiment of the present invention and correction processing according to the embodiment of the present invention). I do. Therefore, the exhaust emission control device 100 can diagnose the validity of the detection value of the NH ₃ sensor 108 by using, for example, the configuration shown in FIG.

  In addition, the structure of the exhaust gas purification apparatus which concerns on embodiment of this invention is not restricted to the structure shown in FIG.

  For example, the exhaust emission control apparatus according to the embodiment of the present invention individually includes one or both of the determination unit 120 and the correction unit 122 illustrated in FIG. 2 (for example, one of the determination unit 120 and the correction unit 122, Alternatively, both can be realized by a processing circuit separate from the control unit 110).

  Further, as described above, the exhaust gas purification apparatus according to the embodiment of the present invention can be configured not to include the correction unit 122.

[II] Diagnostic Device According to Embodiment of the Present Invention The diagnostic device according to the embodiment of the present invention has, for example, the same configuration as the control unit 110 shown in FIG. 2, and is used in the diagnostic method according to the embodiment of the present invention. Such processing is led. The diagnostic device according to the embodiment of the present invention is, for example, from an exhaust purification device (for example, an exhaust purification device including the reduction catalyst 102, the reducing agent supply unit 104, the NO _x sensor 106, and the NH ₃ sensor 108 shown in FIG. 2). Based on the detected value of the NO _x sensor 106 and the detected value of the NH ₃ sensor 108, processing related to the diagnostic method according to the embodiment of the present invention is performed.

Therefore, the diagnostic device according to the embodiment of the present invention can diagnose the validity of the detection value of the NH ₃ sensor 108 by the configuration described above, for example, similarly to the exhaust gas purification device 100 shown in FIG.

  Note that the configuration of the diagnostic apparatus according to the embodiment of the present invention is not limited to the configuration described above.

  For example, the diagnostic device according to the embodiment of the present invention can have the same configuration as the configuration according to the modified example of the exhaust purification device according to the above-described embodiment of the present invention.

  In addition, the diagnostic device according to the embodiment of the present invention may have the same configuration as the exhaust purification device 100 (including the configuration according to the modification) shown in FIG. That is, the diagnostic device according to the embodiment of the present invention can also function as the exhaust gas purification device according to the embodiment of the present invention.

[III]
As described above, the diagnosis device according to the embodiment of the present invention and the exhaust gas purification device according to the embodiment of the present invention are, for example, the processing of the diagnosis method according to the embodiment of the present invention. Diagnosis processing according to the embodiment is performed.

  Therefore, the diagnostic device according to the embodiment of the present invention and the exhaust gas purification device according to the embodiment of the present invention include an ammonia sensor and an exhaust gas purification device that purifies nitrogen oxides contained in exhaust gas using ammonia. The validity of the detection value of the ammonia sensor can be diagnosed.

Further, by ensuring the validity of the detection value of the NH ₃ sensor, the exhaust purification device according to the embodiment of the present invention (or the exhaust purification device using the diagnosis result in the diagnostic device according to the embodiment of the present invention) is provided. Further, the purification rate of NO _x contained in the exhaust gas can be further increased, and the NO _x regulation that is expected to become stricter in the future can be more easily satisfied.

Has been described above the exhaust gas purifying apparatus as an embodiment of the present invention, embodiments of the present invention, for example, such as a vehicle or a ship, driven by the engine to discharge the exhaust gas containing NO _x, such as a diesel engine It is possible to apply to a moving body.

Moreover, although the diagnostic apparatus was mentioned and demonstrated as embodiment of this invention, embodiment of this invention is not restricted to this form. Diagnostic apparatus as an embodiment of the present invention, for example, such as a vehicle or a ship, it is possible to apply to a moving body driven by the engine to discharge the exhaust gas containing NO _x, such as a diesel engine. The embodiment of the present invention can also be applied to, for example, a DCU, an ECU, or a processing IC (Integrated Circuit) that can be incorporated into the above moving body.

(Program according to an embodiment of the present invention)
A program for causing a computer to function as a diagnostic device according to an embodiment of the present invention or an exhaust purification device according to an embodiment of the present invention (for example, “diagnostic processing according to an embodiment of the present invention” or “the present invention A program capable of executing processing related to the diagnostic method according to the embodiment of the present invention, such as “diagnosis processing according to the embodiment and correction processing according to the embodiment of the present invention”, is executed on the computer Thus, it is possible to diagnose the validity of the detection value of the ammonia sensor in the exhaust gas purification apparatus that includes the ammonia sensor and purifies nitrogen oxides contained in the exhaust gas using ammonia.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the above, it has been shown that a program (computer program) for causing a computer to function as a diagnostic device according to an embodiment of the present invention or an exhaust purification device according to an embodiment of the present invention is provided. The embodiment of the present invention can also provide a recording medium storing the program.

100 exhaust gas purification device 102 reduction catalyst 104 the reducing agent supply unit 106 NO _x sensor 108 NH ₃ sensor 110 control unit 112A, 112B exhaust passage 120 determination unit 122 correction unit 200 Engine

Claims (9)

Exhaust gas discharged from the engine is introduced, and ammonia is generated in a reduction catalyst that purifies nitrogen oxides contained in the exhaust gas using ammonia, and an exhaust passage through which the exhaust gas flows into the reduction catalyst Exhaust gas including a reducing agent supply unit that supplies a reducing agent that can be generated, a nitrogen oxide sensor that detects nitrogen oxides flowing out of the reduction catalyst, and an ammonia sensor that detects ammonia flowing out of the reduction catalyst A diagnostic device for diagnosing the validity of the detection value of the ammonia sensor in a purification device,
Based on the detection value of the nitrogen oxide sensor and the detection value of the ammonia sensor, a determination unit that determines the validity of the detection value of the ammonia sensor,
The determination unit compares the detection value of the nitrogen oxide sensor with the detection value of the ammonia sensor when the engine is in a no fuel injection state, thereby determining the validity of the detection value of the ammonia sensor. A diagnostic device characterized by determining. The determination unit
When the absolute value of the difference between the detected value of the nitrogen oxide sensor and the detected value of the ammonia sensor is not more than a predetermined specified value, it is determined that the detected value of the ammonia sensor is appropriate, and the absolute value is When larger than the specified value, it is determined that the detected value of the ammonia sensor is not valid.
Or
When the absolute value is less than the specified value, it is determined that the detected value of the ammonia sensor is valid, and when the absolute value is equal to or greater than the specified value, the detected value of the ammonia sensor is determined not to be valid. The diagnostic apparatus according to claim 1, wherein:   The diagnostic apparatus according to claim 1, further comprising a correction unit that corrects the detection value of the ammonia sensor when it is determined that the detection value of the ammonia sensor is not valid. The correction unit is
Calculate the difference between the detection value of the nitrogen oxide sensor and the detection value of the ammonia sensor, and the value obtained by dividing the detection value of the nitrogen oxide sensor by the detection value of the ammonia sensor,
The detection value of the ammonia sensor is corrected using the difference value or the divided value based on whether or not the difference value varies depending on the ammonia concentration. The diagnostic device described. The correction unit is
When the value of the difference changes depending on the ammonia concentration, the detection value of the ammonia sensor is corrected by multiplying the detection value of the ammonia sensor by the divided value,
5. The detection value of the ammonia sensor is corrected by adding the difference value to the detection value of the ammonia sensor when the difference value does not change depending on the ammonia concentration. The diagnostic device according to 1.   The said determination part starts the determination of the validity of the detected value of the said ammonia sensor, after predetermined | prescribed time passes after the said engine becomes a fuel non-injection state, It is characterized by the above-mentioned. The diagnostic device according to any one of the above.   The determination unit includes a detection value of the nitrogen oxide sensor and a detection value of the ammonia sensor when the engine is in a no-injection state of fuel and the reducing agent is not supplied to the reduction catalyst. The diagnostic device according to any one of claims 1 to 6, wherein A reduction catalyst for purifying nitrogen oxides contained in the exhaust gas using ammonia and flowing exhaust gas discharged from the engine;
A reducing agent supply unit for supplying a reducing agent capable of generating ammonia into an exhaust passage through which the exhaust gas flows into the reduction catalyst;
A nitrogen oxide sensor for detecting nitrogen oxide flowing out of the reduction catalyst;
An ammonia sensor for detecting ammonia flowing out of the reduction catalyst;
Based on the detection value of the nitrogen oxide sensor and the detection value of the ammonia sensor, a determination unit that determines the validity of the detection value of the ammonia sensor;
With
The determination unit compares the detection value of the nitrogen oxide sensor with the detection value of the ammonia sensor when the engine is in a no fuel injection state, thereby determining the validity of the detection value of the ammonia sensor. An exhaust emission control device characterized by determining. Exhaust gas discharged from the engine is introduced, and ammonia is generated in a reduction catalyst that purifies nitrogen oxides contained in the exhaust gas using ammonia, and an exhaust passage through which the exhaust gas flows into the reduction catalyst Exhaust gas including a reducing agent supply unit that supplies a reducing agent that can be generated, a nitrogen oxide sensor that detects nitrogen oxides flowing out of the reduction catalyst, and an ammonia sensor that detects ammonia flowing out of the reduction catalyst A diagnostic method for diagnosing the validity of a detection value of the ammonia sensor in a purification device,
Determining the validity of the detected value of the ammonia sensor based on the detected value of the nitrogen oxide sensor and the detected value of the ammonia sensor;
In the determining step, the validity of the detected value of the ammonia sensor is compared by comparing the detected value of the nitrogen oxide sensor with the detected value of the ammonia sensor when the engine is in a fuel-free injection state. A diagnostic method characterized in that is determined.

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