JP4430629B2 - Failure diagnosis method for reducing agent addition valve - Google Patents

Description

  The present invention relates to a technique for diagnosing a failure of an addition valve attached to an exhaust system of an internal combustion engine.

In recent years, an addition valve for adding a reducing agent such as fuel into the exhaust gas is sometimes attached to an exhaust system of an internal combustion engine. As a technique for diagnosing such a failure of the addition valve, the exhaust valve detects the exhaust air / fuel ratio after adding the reducing agent, and compares the exhaust air / fuel ratio with a reference value to diagnose the failure of the addition valve. A method has been proposed (see, for example, Patent Document 1).
JP 2002-38928 A JP 2002-161733 A JP-A-11-62686 JP 2005-54723 A Japanese Patent Laid-Open No. 2003-254048 JP 2003-172185 A

  By the way, the exhaust air-fuel ratio detected after the addition valve has added the reducing agent varies depending on various factors as well as the amount of the reducing agent added from the addition valve. For example, it varies depending on the output error of a sensor or the like that detects the air-fuel ratio of the exhaust or the intake air amount of the internal combustion engine. For this reason, it is not easy to improve the fault diagnosis accuracy by the conventional method described above.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique capable of accurately diagnosing a failure of an addition valve attached to an exhaust system of an internal combustion engine.

  In order to solve the above-described problems, the present invention provides a method for diagnosing a reducing agent addition valve for adding a reducing agent into the exhaust gas of an internal combustion engine, from a post injection from a fuel injection valve of the internal combustion engine and a reducing agent addition valve. When the post-injection is performed, the amount of fuel actually post-injected from the fuel injection valve and when the reducing agent is added are actually added from the reducing agent addition valve. The amount of the reducing agent added is estimated based on the same parameter, and the reducing agent addition valve is diagnosed as malfunctioning on the condition that the difference between the estimated fuel amount and the reducing agent amount is equal to or greater than a predetermined amount. did.

  In such a method, an estimated value of the fuel amount actually injected from the fuel injection valve (hereinafter referred to as an estimated post-injection amount) and an estimated value of the amount of reducing agent actually added from the reducing agent addition valve (hereinafter referred to as “reduced agent amount”) , Referred to as an estimated addition amount) based on the same parameters. If a parameter measurement error or the like occurs at that time, the estimated post-injection amount and the estimated addition amount become values including the same measurement error or the like. As a result, the difference between the estimated post-injection amount and the estimated addition amount is a value in which the above-described measurement error is offset.

  Therefore, if a failure diagnosis of the reducing agent addition valve is performed based on the difference between the estimated post-injection amount and the estimated addition amount, the failure diagnosis of the reducing agent addition valve can be accurately performed even if a parameter measurement error or the like occurs. Can be done.

As a specific method of failure diagnosis, there is exemplified a method of diagnosing that the reducing agent addition valve has failed on the condition that the difference between the estimated post injection amount and the estimated addition amount exceeds a predetermined amount. it can.

  In the failure diagnosis method for the reducing agent addition valve according to the present invention, examples of different timings include different addition periods or different timings in the same addition period.

  The addition period here refers to a period in which fuel or a reducing agent is continuously supplied to the exhaust system (for example, an exhaust purification catalyst) of the internal combustion engine. Therefore, when the different timings described above are different addition periods, only one of the post injection by the fuel injection valve and the reducing agent addition by the reducing agent addition valve is performed in each addition period. Further, when the different timings described above are different timings in the same addition period, both the post injection by the fuel injection valve and the reducing agent addition by the reducing agent addition valve are performed in the same addition period.

  If post injection by the fuel injection valve and reducing agent addition by the reducing agent addition valve are performed at different timings in the same addition period, various conditions such as operating conditions of the internal combustion engine at the time of executing the post injection and at the time of execution of the reducing agent addition It is almost equivalent.

  In this case, the parameter values are unlikely to differ due to factors other than the difference between the actual post-injection amount and the actual reducing agent addition amount. Therefore, it becomes possible to perform failure diagnosis of the reducing agent addition valve more accurately.

  The predetermined amount described above is the difference between the post injection amount (hereinafter referred to as “instructed post injection amount”) instructed to the fuel injection valve and the addition amount (hereinafter referred to as “instruction addition amount”) instructed to the reducing agent addition valve. May be determined on the basis of a difference between the indicated amounts).

  That is, when the difference between the estimated post-injection amount and the estimated addition amount (hereinafter referred to as the estimation difference) is far from the command amount difference, the reducing agent addition valve may be diagnosed as malfunctioning. .

  If the indicated amount difference increases, the magnitude of the error included in the estimated post-injection amount and the estimated addition amount may be different. If the above-described failure diagnosis is performed when the indicated amount difference is substantially zero, the diagnosis accuracy can be further improved.

  In the reducing agent addition valve failure diagnosis method according to the present invention, the parameters used for estimating the estimated post-injection amount and the estimated addition amount are exemplified by measured values of an air-fuel ratio sensor attached to the exhaust passage of the internal combustion engine. Can do.

  When the amount of exhaust discharged from the internal combustion engine (the amount of intake air) and the amount of fuel injected for combustion of the internal combustion engine are equal, the actual post-injection amount and the actual reducing agent addition amount are measured by the air-fuel ratio sensor. Correlate with value.

  Therefore, the amount of exhaust discharged from the internal combustion engine and the amount of fuel injected for combustion of the internal combustion engine when the post injection by the fuel injection valve is performed and when the reducing agent addition by the reducing agent addition valve is performed Are equal, it is possible to diagnose the failure of the reducing agent addition valve by comparing the measured value of the air-fuel ratio sensor at the time of post injection execution with the measured value of the air-fuel ratio sensor at the time of addition of the reducing agent.

On the other hand, the amount of exhaust discharged from the internal combustion engine and the amount of fuel injected for combustion of the internal combustion engine when the post injection by the fuel injection valve is performed and when the reducing agent addition by the reducing agent addition valve is performed Are different from each other as parameters used for estimating the estimated post-injection amount and the estimated addition amount, the measured value of the intake air amount sensor provided in the intake passage of the internal combustion engine, and the air-fuel ratio attached to the exhaust passage of the internal combustion engine The measured value of the sensor and the fuel injection amount provided for combustion of the internal combustion engine can be used.

  In this case, the measured value of the intake air amount sensor is divided by the measured value of the air-fuel ratio sensor when the post-injection from the fuel injection valve is performed and when the reducing agent is added from the reducing agent addition valve. By subtracting the fuel injection amount (fuel injection amount other than post injection) from the result, the estimated post injection amount and the estimated addition amount can be calculated (estimated).

  In the reducing agent addition valve failure diagnosis method according to the present invention, when the measured value of the air-fuel ratio sensor is used to estimate the estimated post-injection amount and the estimated addition amount, the exhaust air-fuel ratio is higher than the stoichiometric air-fuel ratio. The estimated post injection amount and the estimated addition amount may be estimated under the conditions.

This is because, when the air-fuel ratio of the exhaust gas becomes lower than the stoichiometric air-fuel ratio due to post injection from the fuel injection valve and reducing agent addition from the reducing agent addition valve, the oxygen storage capacity (so-called O ₂ storage capacity) of the exhaust purification catalyst, exhaust gas Due to various oxidation-reduction reactions (for example, NOx reduction reaction) in the purification catalyst, or a phenomenon in which excess reducing agent / fuel passes through without being oxidized by the exhaust purification catalyst, the actual post injection amount or reducing agent addition amount and empty This is because the correlation with the measured value of the fuel ratio sensor may be lowered.

  The estimated post-injection amount and the estimated addition amount calculated in the failure diagnosis method according to the present invention can be used for the subsequent control of the reducing agent addition valve.

  For example, the subsequent command addition amount may be determined based on the ratio of the estimated post injection amount to the estimated addition amount. Specifically, the target addition amount of the reducing agent addition valve may be corrected based on the ratio of the estimated post injection amount to the estimated addition amount, and the corrected target addition amount may be used as the instruction addition amount.

  In this case, the command addition amount is determined based on the estimated post-injection amount that includes an error equivalent to the estimated addition amount, so even if a measurement error or the like of a parameter used for estimating the estimated addition amount occurs. The actual reducing agent addition amount can be brought close to the target addition amount.

  When it is diagnosed that the reducing agent addition valve is normal in the failure diagnosis method according to the present invention, it is possible to diagnose failures of the exhaust temperature sensor, the intake air amount sensor, and the air-fuel ratio sensor by the following procedure. . Note that the exhaust temperature sensor is disposed in the exhaust passage downstream of the exhaust purification catalyst.

  Since the reducing agent added from the reducing agent addition valve is oxidized in the exhaust purification catalyst, the temperature of the exhaust purification catalyst is raised by the reaction heat at that time. When the temperature of the exhaust purification catalyst increases, the temperature of the exhaust gas flowing out from the exhaust purification catalyst also increases. The amount of increase in exhaust temperature at that time correlates with the amount of reducing agent added from the reducing agent addition valve.

  If the reducing agent addition valve is normal, the increase amount of the exhaust temperature correlates with the indicated addition amount. Therefore, if the increase amount of the exhaust temperature measured by the exhaust temperature sensor does not match the instruction addition amount, it can be considered that the exhaust temperature sensor has failed.

Further, when the reducing agent addition valve is controlled so that the exhaust air-fuel ratio becomes a predetermined air-fuel ratio, the indicated addition amount using the measured value of the intake air sensor, the fuel injection amount of the fuel injection valve, and the above-mentioned predetermined air-fuel ratio as parameters. Is determined. For this reason, if the reducing agent addition valve and the intake air amount sensor are normal, the exhaust air-fuel ratio becomes substantially equal to the predetermined air-fuel ratio. Conversely, if the exhaust air-fuel ratio is far from the predetermined air-fuel ratio, it can be considered that the reducing agent addition valve or the intake air amount sensor has failed.

  Therefore, if the exhaust air-fuel ratio is far from the predetermined air-fuel ratio when the reducing agent addition valve is controlled so that the exhaust air-fuel ratio becomes the predetermined air-fuel ratio, and the reducing agent addition valve is normal, the intake air amount sensor is It can be regarded as malfunctioning.

  Next, if the reducing agent addition valve, the intake air amount sensor, and the air-fuel ratio sensor are normal, the estimated addition amount is substantially equal to the instruction addition amount. On the contrary, if the estimated addition amount is far from the command addition amount, it can be considered that at least one of the reducing agent addition valve, the intake air amount sensor, and the air-fuel ratio sensor has failed.

  Therefore, if the estimated addition amount estimated when the reducing agent addition valve and the intake air amount sensor are normal is far from the indicated addition amount, it can be considered that the air-fuel ratio sensor has failed.

  According to the present invention, it is possible to accurately diagnose a failure of an addition valve attached to an exhaust system of an internal combustion engine.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. In FIG. 1, an internal combustion engine 1 is a compression ignition type internal combustion engine (diesel engine) having four cylinders 2.

  The internal combustion engine 1 includes a fuel injection valve 3 that can inject fuel directly into each cylinder 2 and an intake passage 4 that guides air into each cylinder 2. The air guided from the intake passage 4 into the cylinder 2 is ignited and burned together with the fuel injected from the fuel injection valve 3.

  Gas burned in each cylinder 2 (burned gas) is discharged to the exhaust passage 5. The exhaust discharged into the exhaust passage 5 is purified by an exhaust purification catalyst 6 disposed in the middle of the exhaust passage 5 and then released into the atmosphere.

  Examples of the exhaust purification catalyst 6 include an occlusion reduction type NOx catalyst having oxidation ability and NOx occlusion ability, a particulate filter having oxidation ability and PM trapping ability, a particulate filter carrying the occlusion reduction type NOx catalyst, and the like. be able to.

  A reducing agent addition valve 7 for adding a reducing agent to the exhaust gas flowing through the exhaust passage 5 is attached to the exhaust passage 5 upstream of the exhaust purification catalyst 6. As the reducing agent added to the exhaust gas from the reducing agent addition valve 7, the fuel of the internal combustion engine 1 can be used.

  The operating state of the internal combustion engine 1 is electrically controlled by the ECU 8. At that time, the ECU 8 measures the measured value of the air flow meter (intake amount sensor) 9 disposed in the intake passage 4, the measured value of the exhaust temperature sensor 10 disposed in the exhaust passage 5 downstream of the exhaust purification catalyst 6, and the exhaust purification catalyst. The measured value of the A / F sensor (air-fuel ratio sensor) 11 attached to the exhaust passage 5 downstream from 6, the measured value of the crank position sensor 12 attached to the internal combustion engine 1, the measured value of the accelerator position sensor 13, etc. The fuel injection valve 3 and the reducing agent addition valve 7 are controlled as parameters.

  For example, the ECU 8 adds fuel to the exhaust gas from the reducing agent addition valve 7 when performing a regeneration process for purifying and / or removing NOx or PM occluded or collected by the exhaust purification catalyst 6. Then, NOx and PM occluded or collected by the exhaust purification catalyst 6 are purified and / or removed.

  By the way, when the regeneration processing of the exhaust purification catalyst 6 is performed, if the reducing agent addition valve 7 does not operate as instructed by the ECU 8, there is a possibility that exhaust emission and fuel consumption may be deteriorated.

  When the amount of fuel actually added from the reducing agent addition valve 7 becomes smaller than the addition amount (hereinafter referred to as the indicated addition amount) instructed from the ECU 8 to the reducing agent addition valve 7, the NOx storage capacity of the exhaust purification catalyst 6 becomes smaller. In some cases, the pressure loss of the exhaust purification catalyst 6 becomes excessive or becomes excessive. In such a case, problems such as an increase in the amount of NOx released into the atmosphere and an increase in back pressure are induced. On the other hand, if the amount of fuel actually added from the reducing agent addition valve 7 exceeds the indicated addition amount, excess fuel may be released into the atmosphere, or the exhaust purification catalyst 6 may overheat.

  If the operation of the internal combustion engine 1 is continued in a state where the reducing agent addition valve 7 has failed as described above, various adverse effects are induced. Therefore, it is necessary to accurately diagnose the failure of the reducing agent addition valve 7.

  As a method of diagnosing the failure of the reducing agent addition valve 7, the amount of fuel actually added from the reducing agent addition valve 7 is estimated, and the difference between the estimated amount (estimated addition amount) and the indicated addition amount is larger than a certain value. For example, a method for diagnosing that the reducing agent addition valve 7 has failed has been proposed.

  Here, a method for estimating the amount of fuel added from the reducing agent addition valve 7 will be described with reference to FIG. FIG. 2 is a diagram in which the command addition amount (open / close timing of the reducing agent addition valve 7) sent from the ECU 8 to the reducing agent addition valve 7 and the measured value (A / F) of the A / F sensor 11 are represented on the same time axis. It is.

  In FIG. 2, when the internal combustion engine 1 is in a steady operation state, the ECU 8 starts opening / closing control of the reducing agent addition valve 7 according to a desired instruction addition amount (t1 in FIG. 2). When the reducing agent addition valve 7 starts an opening / closing operation in accordance with an instruction from the ECU 8, fuel is added from the reducing agent addition valve 7 into the exhaust.

  Fuel added to the exhaust gas from the reducing agent addition valve 7 (hereinafter simply referred to as added fuel) reaches the A / F sensor 11 with a transport delay. When the added fuel reaches the A / F sensor 11, the measured value of the A / F sensor 11 starts to decrease from the base A / F (the air-fuel ratio of the air-fuel mixture used for combustion in the internal combustion engine 1) (in FIG. 2). t2).

  When the ECU 8 finishes the opening / closing control of the reducing agent addition valve 7 (t3 in FIG. 2), the measured value of the A / F sensor 11 returns to the base A / F with a delay by the transportation delay of the added fuel (FIG. 2). Middle t4).

  The period from the time when the measured value of the A / F sensor 11 starts to decrease from the base A / F (t2 in FIG. 2) to the time when the measurement value returns to the base A / F (t4 in FIG. 2) (in FIG. 2) The sum of the differences between the base A / F and the measured value of the A / F sensor 11 in the period P) (the area indicated by the hatching in FIG. 2) is the amount of fuel actually added from the reducing agent addition valve 7. Equivalent to.

The area of the portion indicated by the oblique lines in FIG. 2 can be estimated and calculated using the following equation (1).
Qad = Σ (Ga / Maf−Inj) (1)
(Qad is the estimated addition amount, Ga is the measurement value of the air flow meter 9, Maf is the measurement value of the A / F sensor 11, and Inj is the fuel injection amount instructed from the ECU 8 to the fuel injection valve 3)

  By the way, the estimated addition amount Qad obtained by the above-described method includes a measurement error of the A / F sensor 11, a measurement error of the air flow meter 9, an injection amount error of the fuel injection valve 3, and the like. For this reason, although the reducing agent addition valve 7 is normal, the difference between the estimated addition amount Qad and the indicated addition amount becomes larger than a certain value, or the reducing agent addition valve 7 is out of order. A case where the difference between the estimated addition amount Qad and the indicated addition amount is less than a certain value can be considered.

  Therefore, in this embodiment, the ECU 8 causes the fuel injection valve 3 to perform post injection during a fuel addition period that is different from the fuel addition period by the reducing agent addition valve 7 (period t1 to t3 in FIG. 2). The amount of fuel actually post-injected from the fuel injection valve 3 is estimated by the same method as the estimated addition amount Qad. The ECU 8 diagnoses that the reducing agent addition valve 7 is out of order if the difference between the estimated post injection amount (hereinafter referred to as the estimated post injection amount) and the estimated addition amount Qad is larger than a certain value. At this time, the post injection amount instructed from the ECU 8 to the fuel injection valve 3 is substantially the same as the addition amount instructed from the ECU 8 to the reducing agent addition valve 7.

  The estimated post injection amount includes a measurement error of the A / F sensor 11, a measurement error of the air flow meter 9, an injection amount error of the fuel injection valve 3, and the like. Since it is also included in Qad, the difference between the estimated post-injection amount and the estimated addition amount Qad is a value in which the above-described various errors are offset.

  Therefore, when the failure diagnosis of the reducing agent addition valve 7 is performed using the difference between the estimated post injection amount and the estimated addition amount Qad as a parameter, the measurement error of the A / F sensor 11 and the air flow meter 9 and the injection of the fuel injection valve 3 are detected. Even if a quantity error or the like occurs, an accurate fault diagnosis can be performed.

  Hereinafter, the failure diagnosis method for the reducing agent addition valve 7 in this embodiment will be described with reference to the flowchart of FIG. FIG. 3 is a flowchart showing a failure diagnosis routine of the reducing agent addition valve 7. This failure diagnosis routine is a routine that the ECU 8 repeatedly executes every predetermined period.

  In the failure diagnosis routine, the ECU 8 first determines whether or not the value of the failure flag is “0” in S101. The failure flag is a storage area set in advance in the RAM or backup RAM built in the ECU 8, and “1” is written when it is diagnosed that the reducing agent addition valve 7 has failed in this routine, and the reducing agent. “0” is written when the addition valve 7 is diagnosed as normal.

  If an affirmative determination is made in S101 (failure flag = 0), the ECU 8 proceeds to S102 and determines whether a failure diagnosis condition is satisfied. The failure diagnosis condition is that the fuel injection valve 3 is normal, the A / F sensor 11 is activated, and the temperature of the exhaust system (exhaust temperature, temperature of the exhaust purification catalyst 6 etc.) determines the added fuel and post-injected fuel. Conditions such as being in a vaporizable temperature range can be exemplified.

  If an affirmative determination is made in S102, the ECU 8 proceeds to S103 and determines whether or not the value of the post injection flag is “0”. The post-injection flag is a storage area set in advance in the RAM or backup RAM built in the ECU 8, and is “1” when it is diagnosed that the reducing agent addition valve 7 has not failed in the processing of S104 to S115 described later. "And" 0 "are written when a negative determination is made in S101 or S102 described above (see S118).

  When an affirmative determination is made in S103 (post-injection flag = 0), the ECU 8 performs failure diagnosis of the reducing agent addition valve 7 by the conventional method described above in S104 to S107. In S104 to S107, failure diagnosis by the conventional method is performed when the reducing agent addition valve 7 cannot add fuel (the amount of fuel addition is substantially zero) or when the fuel leaks from the reducing agent addition valve 7. This is to detect an obvious failure such as.

  In S104, the ECU 8 controls the reducing agent addition valve 7 so as to add fuel from the reducing agent addition valve 7 into the exhaust.

  In S105, the ECU 8 calculates the integrated value (indicated addition amount) Qads of the fuel addition amount instructed to the reducing agent addition valve 7.

  In S106, the ECU 8 substitutes the measured value Ga of the air flow meter 9, the measured value Maf of the A / F sensor 11, and the fuel injection amount Inj instructed from the ECU 8 to the fuel injection valve 3 into the above (1) and estimates. The addition amount Qad is calculated.

  In S107, the ECU 8 determines whether or not the absolute value (= | Qads−Qad |) of the difference between the command addition amount Qads calculated in S105 and the estimated addition amount Qad calculated in S106 is equal to or less than a predetermined value A. Is determined. The predetermined value A described above is a relatively large value, for example, equal to or less than the indicated addition amount Qads.

  If a negative determination is made in S107 (| Qads−Qad |> A), the ECU 8 considers that the reducing agent addition valve 7 is clearly broken and proceeds to S109. In S109, the ECU 8 writes "1" in the above-described failure flag and ends the execution of this routine.

  If an affirmative determination is made in S107 (| Qads−Qad | ≦ A), the ECU 8 proceeds to S108. In S108, the ECU 8 writes "1" in the above-described post injection flag and ends the execution of this routine. When “1” is written in the post injection flag in S108, the ECU 8 makes a negative determination (post injection flag = 1) in S103 at the next execution of this routine.

  If a negative determination is made in S103, the ECU 8 proceeds to S110. In S110, the ECU 8 controls the fuel injection valve 3 so as to perform post injection (for example, fuel injection during the exhaust stroke) separately from the fuel injection that contributes to the combustion of the internal combustion engine 1.

  In S111, the ECU 8 calculates a post-injection amount integrated value (instructed post-injection amount) Qpsts instructed to the fuel injection valve 3.

  In S112, the ECU 8 calculates the estimated post injection amount Qpst. At that time, the ECU 8 calculates the measured value Ga of the air flow meter 9, the measured value Maf of the A / F sensor 11, and the fuel injection amount Inj (excluding post injection) instructed from the ECU 8 to the fuel injection valve 3. ), The estimated post injection amount Qpst is calculated by substituting it into the same equation (Qpst = Σ (Ga / Maf−Inj)).

  In S113, the ECU 8 has an absolute value (= | Qpsts−Qpst |) of a difference between the indicated post injection amount Qpsts calculated in S111 and the estimated post injection amount Qpst calculated in S112 equal to or less than a predetermined value A. It is determined whether or not.

When an affirmative determination is made in S113 (| Qpsts−Qpst | ≦ A), EC
U8 proceeds to S114. In S114, the ECU 8 determines whether or not the command addition amount Qads and the command post injection amount Qpsts are substantially the same amount. Specifically, the ECU 8 determines whether or not the absolute value (= | Qads−Qpsts |) of the difference between the command addition amount Qads and the command post injection amount Qpsts is equal to or less than a predetermined value α.

  If a negative determination is made in S114 (| Qads−Qpsts |> α), in other words, if there is a relatively large difference between the command addition amount Qads and the command post injection amount Qpsts, the ECU 8 End execution.

  If an affirmative determination is made in S114 (| Qads−Qpsts | ≦ α), in other words, if the command addition amount Qads and the command post injection amount Qpsts are substantially the same, the ECU 8 proceeds to S115.

  In S115, the ECU 8 determines whether the absolute value (= | Qad−Qpst |) of the difference between the estimated addition amount Qad calculated in S106 and the estimated post-injection amount Qpst calculated in S112 is greater than a predetermined amount B. Is determined. The predetermined amount B is sufficiently smaller than the predetermined amount A described above.

  If an affirmative determination is made in S115 (| Qad-Qpst |> B), the ECU 8 considers that the reducing agent addition valve 7 has failed and proceeds to S116. In S116, the ECU 8 writes “1” in the above-described failure flag.

  If a negative determination is made in S115 (| Qad−Qpst | ≦ B), the ECU 8 considers that the reducing agent addition valve 7 has not failed and proceeds to S117. In S117, the ECU 8 writes “0” in the above-described failure flag.

  In the failure diagnosis method described above, the estimated addition amount Qad and the estimated post-injection amount Qpst are the same parameters (the measured value of the air flow meter 9, the measured value of the A / F sensor 11, and the ECU 8 instructed to the fuel injection valve 3). Therefore, the estimated addition amount Qad and the estimated post-injection amount Qpst include equivalent errors.

  Therefore, when failure diagnosis of the reducing agent addition valve 7 is performed using the difference between the estimated addition amount Qad and the estimated post-injection amount Qpst as a parameter, accurate failure diagnosis can be performed without considering the above-described error. .

When the estimated post injection amount Qpst and the estimated addition amount Qad are estimated, if the air-fuel ratio of the exhaust gas becomes lower than the stoichiometric air-fuel ratio, the oxygen storage capacity (O ₂ storage capacity) of the exhaust purification catalyst 6 and the exhaust purification catalyst 6 Between the actual post-injection amount or the fuel addition amount and the measured value of the A / F sensor 11 due to various oxidation-reduction reactions (for example, NOx reduction reaction) or the phenomenon that excess fuel passes through the exhaust purification catalyst 6. Correlation may be low.

  Therefore, when the estimated post-injection amount Qpst and the estimated addition amount Qad are estimated, the command post-injection amount Qpsts and The instruction addition amount Qads may be determined.

  If the instruction post injection amount Qpsts and the instruction addition amount Qads are determined in this manner, the correlation between the actual post injection amount and fuel addition amount and the measured value of the A / F sensor 11 is increased, and therefore the estimated post injection amount Qpst and the estimation post injection amount are estimated. The estimation accuracy of the addition amount Qad is also increased. Therefore, the failure diagnosis accuracy of the reducing agent addition valve 7 can be improved.

  Further, since the A / F sensor 11 causes a response delay, it is preferable to make the time during which the exhaust air-fuel ratio is maintained at the weak lean air-fuel ratio as long as possible.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIG. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  In the present embodiment, an example in which the subsequent command addition amount Qads is corrected using the estimated post injection amount Qpst and the estimated addition amount Qad obtained in the failure diagnosis of the first embodiment described above will be described.

  FIG. 4 is a flowchart showing an addition amount correction routine for correcting the instruction addition amount Qads.

  In the addition amount correction routine, the ECU 8 first determines in S201 whether or not the above-described failure diagnosis routine of FIG. 3 has been executed. In other words, it is determined whether or not the estimated post-injection amount Qpst and the estimated addition amount Qad have been calculated.

  If a negative determination is made in S201, the ECU 8 ends the execution of this routine. If an affirmative determination is made in S201, the ECU 8 proceeds to S202.

  In S202, the ECU 8 uses the estimated post-injection amount Qpst, estimated addition amount Qad, commanded post-injection amount Qpsts, and commanded addition amount Qads obtained in the above-described failure diagnosis routine of FIG. A flow rate correction coefficient Kad is calculated.

Specifically, the ECU 8 calculates the flow rate correction coefficient Kad by substituting the estimated post injection amount Qpst, the estimated addition amount Qad, the instruction post injection amount Qpsts, and the instruction addition amount Qads into the following equation (2). To do.
Kad = a * (Qads / Qad) / (Qpsts / Qpst) (2)
(A is a coefficient obtained experimentally in advance)

  In S203, the ECU 8 calculates the target addition amount Qadtrg of the reducing agent addition valve 7 using the NOx occlusion amount of the exhaust purification catalyst 6 and the PM trapping amount as parameters. For this calculation method, a conventionally known method can be used.

  In S204, the ECU 8 calculates the command addition amount Qads (= Kad * Qadtrg) by multiplying the target addition amount Qadtrg calculated in S203 by the flow rate correction coefficient Kad calculated in S202.

  In S205, the ECU 8 performs fuel addition from the reducing agent addition valve 7 in accordance with the command addition amount Qads (= Kad * Qadtrg) calculated in S204.

  When the command addition amount Qads is determined based on the estimated post-injection amount Qpst including an error equivalent to the estimated addition amount Qad as described above, parameters used for estimating the estimated addition amount Qad (measurement error of the air flow meter 9, Even when a measurement error of the A / F sensor 11 and an injection amount error of the fuel injection valve 3 occur, the actual fuel addition amount can be brought close to the target addition amount Qadtrg.

<Example 3>
Next, a third embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  In the present embodiment, the air flow meter 9, the exhaust gas temperature sensor 10, and the A / F sensor 11 are provided on condition that the reducing agent addition valve 7 is diagnosed as normal in the failure diagnosis of the first embodiment described above. An example of diagnosing a failure will be described.

  FIG. 5 is a flowchart showing a sensor failure diagnosis routine for diagnosing failures in the air flow meter 9, the exhaust temperature sensor 10, and the A / F sensor 11. In this sensor failure diagnosis routine, the ECU 8 first determines in S301 whether or not the above-described failure diagnosis routine of FIG. 3 has been executed.

  If a negative determination is made in S301, the ECU 8 ends the execution of this routine. If an affirmative determination is made in S301, the ECU 8 proceeds to S302.

  In S302, the ECU 8 determines whether or not the value of the failure flag is “0”. That is, the ECU 8 determines whether or not the reducing agent addition valve 7 has been diagnosed as normal.

  If a negative determination is made in S302 (failure flag = 1), the ECU 8 ends the execution of this routine. If an affirmative determination is made in S302 (failure flag = 0), the ECU 8 proceeds to S303.

  In S <b> 303, the ECU 8 executes failure diagnosis processing for the exhaust temperature sensor 10. Specifically, the ECU 8 monitors the measured value of the exhaust temperature sensor 10 when the fuel addition from the reducing agent addition valve 7 is performed, and obtains the increase ΔT of the measured value.

  When the reducing agent addition valve 7 has normally added fuel, the fuel added from the reducing agent addition valve 7 is oxidized by the exhaust purification catalyst 6. The exhaust purification catalyst 6 is heated by the oxidation reaction heat of the fuel. When the temperature of the exhaust purification catalyst 6 rises, the temperature of the exhaust gas flowing out from the exhaust purification catalyst 6 also rises. The amount of temperature rise at that time increases or decreases in proportion to the amount of fuel added from the reducing agent addition valve 7.

  Therefore, if the amount of increase ΔT in the measured value of the exhaust temperature sensor 10 indicates a value proportional to the command addition amount Qads, it can be considered that the exhaust temperature sensor 10 is normal.

  Therefore, as shown in FIG. 6, the relationship between the increase amount ΔT measured by the normal exhaust temperature sensor 10 and the command addition amount Qads may be obtained experimentally in advance. A region L indicated by diagonal lines in FIG. 6 indicates a range of the increase ΔT that can be measured by the normal exhaust temperature sensor 10. This range is determined based on a measurement error that may occur in the exhaust temperature sensor 10.

  The ECU 8 diagnoses that the exhaust temperature sensor 10 has failed if the increase amount ΔT obtained from the measured value of the exhaust temperature sensor 10 does not fall within the region L determined from the indicated addition amount Qads. If the increase amount ΔT obtained from the measured value falls within the region L determined from the indicated addition amount Qads, it is diagnosed that the exhaust temperature sensor 10 has not failed.

  Here, returning to FIG. 5, the ECU 8 determines whether or not the exhaust temperature sensor 10 is normal in S304. If a negative determination is made in S304, the ECU 8 ends the execution of this routine. On the other hand, if an affirmative determination is made in S304, the ECU 8 proceeds to S305.

In S <b> 305, the ECU 8 executes failure diagnosis processing for the air flow meter 9. In the failure diagnosis process of the air flow meter 9, the ECU 8 first uses the measured value Ga of the air flow meter 9 and the fuel injection amount Inj instructed from the ECU 8 to the fuel injection valve 3 as parameters, and the exhaust air / fuel ratio becomes the stoichiometric air / fuel ratio. The indicated addition amount Qads is calculated. Specifically, the command addition amount Qads is calculated by substituting the measured value Ga of the air flow meter 9 and the fuel injection amount Inj into the following equation (3).
Qads = Ga / 14.7-Ga / Inj (3)

  The ECU 8 controls the reducing agent addition valve 7 according to the instruction addition amount Qads calculated by the above equation (3) and monitors the measurement value Maf of the A / F sensor 11. At that time, if the air flow meter 9 is normal, the measured value Maf of the A / F sensor 11 shows a value substantially equal to the theoretical air-fuel ratio.

  Therefore, if the absolute value (= | Maf-14.7 |) of the difference between the measured value Maf of the A / F sensor 11 and the theoretical air-fuel ratio is less than a predetermined value, it is diagnosed that the air flow meter 9 is normal. Can do. The predetermined value is a value determined based on a measurement error that may occur in the A / F sensor 11 and the air flow meter 9.

  The reason why the command addition amount Qads is determined so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio in the failure diagnosis process of the air flow meter 9 is that the measurement accuracy of the A / F sensor becomes high near the stoichiometric air-fuel ratio.

  Returning to FIG. 5, when the ECU 8 finishes executing the processing of S305, the ECU 8 proceeds to S306 and determines whether or not the air flow meter 9 is normal. If a negative determination is made in S306, the ECU 8 ends the execution of this routine. On the other hand, when a positive determination is made in S306, the ECU 8 proceeds to S307.

  In step S <b> 307, the ECU 8 executes failure diagnosis processing for the A / F sensor 11. In the failure diagnosis process of the A / F sensor 11, the ECU 8 calculates the estimated addition amount Qad when fuel addition from the reducing agent addition valve 7 is performed, and calculates the calculated estimated addition amount Qad and the indicated addition amount Qads. Compare.

  The estimated addition amount Qad estimated when the reducing agent addition valve 7, the air flow meter 9, and the A / F sensor 11 are normal is substantially equal to the instruction addition amount Qads. On the other hand, the estimated addition amount Qad estimated when at least one of the reducing agent addition valve 7, the air flow meter 9, and the A / F sensor 11 is broken shows a value far from the indicated addition amount Qads. If it is diagnosed that the reducing agent addition valve 7 and the air flow meter 9 are normal at the time, it can be considered that the A / F sensor 11 has failed.

  Therefore, if the estimated addition amount Qad estimated when the reducing agent addition valve 7 and the air flow meter 9 are normal is far from the command addition amount Qads, it can be diagnosed that the A / F sensor 11 is out of order. .

  Therefore, as shown in FIG. 7, the relationship between the estimated addition amount Qad and the indicated addition amount Qads when the reducing agent addition valve 7, the air flow meter 9, and the A / F sensor 11 are normal is experimentally obtained in advance. You may make it leave. A region G indicated by hatching in FIG. 7 indicates a range that the estimated addition amount Qad can take when the reducing agent addition valve 7, the air flow meter 9, and the A / F sensor 11 are normal. This range is determined based on an addition amount error that may occur in the reducing agent addition valve 7 and a measurement error that may occur in the air flow meter 9 and the A / F sensor 11.

The ECU 8 diagnoses that the A / F sensor 11 is out of order if the estimated addition amount Qad is not within the region G determined from the instruction addition amount Qads.

  As described above, when the ECU 8 executes the sensor failure diagnosis routine, it is possible to accurately diagnose failures of the exhaust temperature sensor 10, the air flow meter 9, and the A / F sensor 11.

<Example 4>
Next, a fourth embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  In the first embodiment described above, an example in which the post injection by the fuel injection valve 3 and the fuel addition by the reducing agent addition valve 7 are performed in different addition periods has been described, but in the present embodiment, the post injection and the fuel addition are the same. An example performed at different timings within the addition period will be described.

FIG. 8 is a timing chart showing the failure diagnosis method in the first embodiment described above.
According to the failure diagnosis method of the first embodiment described above, the fuel injection valve 3 and the reducing agent are used in the addition period (period T1 from t10 to t20 and period T2 from t30 to t40 in FIG. 8). Only one of the addition valves 7 performs post injection or fuel addition.

  On the other hand, in the failure diagnosis method in the present embodiment, as shown in FIG. 9, the fuel injection valve 3 and the reducing agent addition valve 7 perform post injection and fuel addition in one addition period (T10 in FIG. 9). Were repeated alternately.

  At that time, the post-injection amount per time of the fuel injection valve 3 (indicated addition amount in the period A in FIG. 9) and the indicated addition amount per time in the reducing agent addition valve 7 (in the period B in FIG. 9). The instruction post injection amount) is the same amount.

  As described above, when the fuel injection valve 3 and the reducing agent addition valve 7 alternately perform the post injection and the fuel addition within the same addition period, the fuel injection valve 3 performs the post injection and the reducing agent addition valve 7 serves as the fuel. The operating state of the internal combustion engine 1 when the addition is performed (the amount of exhaust discharged from the internal combustion engine 1, the amount of fuel injected for combustion in the internal combustion engine 1), and the state of the exhaust purification catalyst 6 (exhaust purification catalyst) 6 and the amount of fuel consumed by the exhaust purification catalyst 6). For this reason, the actual post injection amount and the actual fuel addition amount correlate with the measured value of the A / F sensor 11.

  For example, when the reducing agent addition valve 7 is normal, the measured value of the A / F sensor 11 is substantially equal between the post injection by the fuel injection valve 3 and the fuel addition by the reducing agent addition valve 7. Show. On the other hand, when the reducing agent addition valve 7 is out of order, the measured value of the A / F sensor 11 is the post injection by the fuel injection valve 3 and the fuel addition by the reducing agent addition valve 7 as shown in FIG. Increases / decreases each time the and are switched.

  Therefore, the ECU 8 calculates the average value of the measured value of the A / F sensor 11 during the period B when the fuel injection valve 3 performs the post-injection and the measured value of the A / F sensor 11 during the period A when the fuel is added by the reducing agent addition valve 7. Each calculation is performed, and if the difference between the average values is equal to or greater than a predetermined amount, it is determined that the reducing agent addition valve 7 has failed.

Specifically, the ECU 8 performs a reduction in a period (a period P in FIG. 10) from the time when the measured value of the A / F sensor 11 starts to decrease from the base A / F to the time when the measured value returns to the base A / F. The measured value of the A / F sensor 11 is read at the timing (period A1, A2, A3 in FIG. 10) when the fuel (added fuel) added from the agent addition valve 7 reaches the A / F sensor 11, and the fuel injection valve The measured value of the A / F sensor 11 is read at the timing (periods B1 and B2 in FIG. 10) when the fuel injected from 3 (hereinafter simply referred to as post-injected fuel) reaches the A / F sensor 11.

  Note that there is a delay in the transport of exhaust gas until the post-injected fuel and the added fuel reach the position of the A / F sensor 11. However, in this embodiment, since the reducing agent addition valve 7 is attached to the exhaust manifold as shown in FIG. 1, the transport delay time until the post-injected fuel reaches the position of the A / F sensor 11 and The transport delay time until the added fuel reaches the position of the A / F sensor 11 is substantially the same.

  Therefore, the ECU 8 adds the time when the transport delay time D has elapsed (tp10, tp30, tp50 in FIG. 10) from the time when the reducing agent addition valve 7 started to add fuel (tp1, tp3, tp5 in FIG. 10). The measured value of the A / F sensor 11 is read assuming that the fuel has reached the A / F sensor 11. That is, the ECU 8 uses the measured value (hereinafter referred to as A / F at the time of fuel addition) of the A / F sensor 11 in one of the periods A1, A2, and A3 (hereinafter referred to as the period An) in FIG. Read.

  Further, the ECU 8 determines that the post-injected fuel is A / A when the transportation delay time D has elapsed (tp20, tp40 in FIG. 10) from the time when the fuel injection valve 3 started the post-injection (tp2, tp4 in FIG. 10). The measured value of the A / F sensor 11 is read assuming that the timing has reached the F sensor 11. That is, the ECU 8 reads the measured value (hereinafter referred to as post-injection A / F) of the A / F sensor 11 in one period (hereinafter referred to as period Bn) of the periods B1 and B2 in FIG.

  The period An and the period Bn are preferably continuous periods. When the period An and the period Bn are continuous from each other, the operating state of the internal combustion engine 1 and the state of the exhaust purification catalyst 6 in the period An and the period Bn are substantially equal. Therefore, the measured value of the A / F sensor 11 is unlikely to be different due to factors other than the difference between the actual fuel addition amount and the actual post injection amount.

  The ECU 8 calculates the average value A / Finj of the fuel addition A / F in the period An and calculates the average value A / Fpst of the post injection A / F in the period Bn. The ECU 8 calculates the absolute value (= | A / Finj−A / Fpst |) of the difference between the average value A / Finj of the A / F during fuel addition and the average value A / Fpst of the post-injection A / F. If the calculated difference is equal to or greater than a certain value, it is determined that the reducing agent addition valve 7 has failed.

  According to the failure diagnosis method described above, reduction is performed using the fuel addition A / F and post-injection A / F as parameters, which are measured under conditions in which the operating state of the internal combustion engine 1 and the state of the exhaust purification catalyst 6 are substantially equivalent. Since the failure diagnosis of the agent addition valve 7 is performed, it is possible to further improve the diagnosis accuracy.

  Hereinafter, the failure diagnosis method according to the present embodiment will be described with reference to FIGS. FIG. 11 is a flowchart showing a failure diagnosis routine of the reducing agent addition valve 7. This failure diagnosis routine is a routine that the ECU 8 repeatedly executes every predetermined period.

  In the failure diagnosis routine, the ECU 8 first determines in S401 whether or not the value of the failure flag is “0”. The failure flag is a storage area set in advance in the RAM or backup RAM built in the ECU 8, and “1” is written when it is diagnosed that the reducing agent addition valve 7 has failed in this routine, and the reducing agent. “0” is written when the addition valve 7 is diagnosed as normal.

  If an affirmative determination is made in S401 (failure flag = 0), the ECU 8 proceeds to S402 and determines whether or not a failure diagnosis condition is satisfied. The failure diagnosis condition is that the fuel injection valve 3 is normal, the A / F sensor 11 is activated, and the temperature of the exhaust system (exhaust temperature, temperature of the exhaust purification catalyst 6 etc.) determines the added fuel and post-injected fuel. Examples of the condition include a temperature range in which vaporization is possible, and the internal combustion engine 1 is in a steady operation state.

  If a negative determination is made in S401 (failure flag = 1) or a negative determination is made in S402, the ECU 8 writes “1” in the diagnostic addition flag in S414, and temporarily ends the execution of this routine. .

  The diagnostic addition flag is a storage area preset in the RAM or backup RAM of the ECU 8, and when the added fuel reaches the A / F sensor 11 in FIG. 10 described above (periods A1, A2, A3). In addition, “1” is written to “0”, and “0” is written when the post-injected fuel reaches the A / F sensor 11 (periods B1 and B2). In addition, as described in the description of S414, “1” is written in the diagnostic addition flag when the failure diagnosis is not performed.

  If an affirmative determination is made in S402, the ECU 8 proceeds to S403 and determines whether or not the value of the diagnostic addition flag is “1”.

  If an affirmative determination is made in S403, the ECU 8 proceeds to S404 and causes the reducing agent addition valve 7 to add fuel for a predetermined period (corresponding to period A in FIG. 9).

  In S405, the ECU 8 measures the measured value (A / F at the time of fuel addition) of the A / F sensor 11 during the period (period An) in which the fuel added from the reducing agent addition valve 7 in S404 reaches the A / F sensor 11. And an average value A / Finj of A / F at the time of fuel addition in the period An is calculated.

  On the other hand, if a negative determination is made in S403, the ECU 8 proceeds to S406 and causes the fuel injection valve 3 to perform post injection for a predetermined period (corresponding to period B in FIG. 9).

  In the present embodiment, the fuel amount post-injected per unit time by the fuel injection valve 3 and the fuel amount added by the reducing agent addition valve 7 per unit time are the same, and the indicated addition amount and the indicated post-injection amount. Are the same amount, the time required for the period A and the period B is the same.

  In S407, the ECU 8 measures the measured value of the A / F sensor 11 during the period (period Bn) in which the fuel post-injected from the fuel injection valve 3 in S406 reaches the A / F sensor 11 (post-injection A / F). And the average value A / Fpst of the post-injection A / F in the period Bn is calculated.

  When the ECU 8 finishes executing the process of S405 or S407, the ECU 8 proceeds to S408. In S408, the ECU 8 executes various flag setting processes according to the subroutine shown in FIG. FIG. 12 is a flowchart showing a subroutine for flag setting processing.

  In FIG. 12, the ECU 8 first increments the value of the counter T by one in S501. The counter T is a counter that counts the execution time of post injection by the fuel injection valve 3 and the execution time of fuel addition by the reducing agent addition valve 7.

In S502, the ECU 8 determines whether or not the value T of the counter T is equal to or longer than a predetermined time. The certain time corresponds to the time required for the period A and the period B described above.

  If a negative determination is made in S502 (T <fixed time), the ECU 8 writes “0” in the failure diagnosis execution flag in S515, and then ends the execution of this routine.

  The failure diagnosis execution flag is a storage area set in advance in the RAM or backup RAM built in the ECU 8, and the average value A / Finj of the fuel injection A / F and the average value A / Fpst of the post injection A / F. "1" is written when both are calculated, and "0" is written when the fault diagnosis is completed.

  If an affirmative determination is made in S502 (T ≧ fixed time), the ECU 8 proceeds to S503, and stores the value of the current diagnostic addition flag in the RAM or backup RAM as the previous diagnostic addition flag.

  In S504, the ECU 8 resets the value of the counter T to “0”.

  In S505, the ECU 8 determines whether or not the value of the previous diagnostic addition flag stored in the RAM or the backup RAM in S503 is “1”.

  If an affirmative determination is made in S505 (diagnosis addition flag = 1), the ECU 8 proceeds to S506 and rewrites the current value of the diagnosis addition flag from “1” to “0”.

  On the other hand, if a negative determination is made in S505 (diagnosis addition flag = 0), the ECU 8 proceeds to S507, and rewrites the current value of the diagnosis addition flag from “0” to “1”.

  The ECU 8 that has completed the processing of S506 or S507 determines whether or not both fuel addition for failure diagnosis and post-injection have been performed in S508 and S509.

  Here, since “1” is written in the addition flag for diagnosis when the failure diagnosis is not performed, the fuel injection is first performed after the fuel addition by the reducing agent addition valve 7 when the failure diagnosis is started. Post injection by the valve 3 is performed.

  Therefore, when both the fuel addition for failure diagnosis and the post-injection are executed at least once, the value of the previous addition flag for diagnosis stored in S503 becomes “0”, and is updated in S506 or S507. The value of the current diagnostic addition flag is “1”.

  Therefore, the ECU 8 determines in S508 and S509 whether or not the previous value of the diagnostic addition flag is “0” and the current value of the diagnostic addition flag is “1”.

  If an affirmative determination is made in both S508 and S509, the ECU 8 considers that fuel addition and post-injection for failure diagnosis have been performed at least once. In other words, if an affirmative determination is made in both S508 and S509, the ECU 8 considers that both the processing of S405 and the processing of S407 have been executed at least once in the failure diagnosis routine of FIG.

  In this case, the ECU 8 proceeds to S510, and rewrites the value of the above-described failure diagnosis execution flag to “1”. Subsequently, in S511, the ECU 8 determines the difference between the average value A / Finj of the fuel addition A / F calculated in S405 and the average value A / Fpst of the post injection A / F calculated in S407. The absolute value ΔA / F (= | A / Finj−A / Fpst |) is calculated.

  In S512, the ECU 8 determines whether or not the value ΔA / F calculated in S511 is equal to or greater than a certain value.

  If an affirmative determination is made in S512 (ΔA / F ≧ a constant value), the ECU 8 writes “1” in the failure diagnosis flag in S513. On the other hand, if a negative determination is made in S512 (ΔA / F <constant value), the ECU 8 writes “0” in the failure diagnosis flag in S514.

  The above-described failure diagnosis flag is a storage area set in advance in the RAM or backup RAM of the ECU 8, and “1” is written when the above-described value ΔA / F is equal to or greater than a certain value. When / F is less than a certain value, “0” is written.

  If a negative determination is made in at least one of S508 and S509, the ECU 8 considers that either one of fuel addition for failure diagnosis or post-injection has never been executed. That is, if a negative determination is made in at least one of S508 and S509, the ECU 8 considers that either the process of S405 or the process of S407 is not yet executed in the failure diagnosis routine of FIG.

  In this case, the ECU 8 proceeds to S515, writes “0” in the above-described failure diagnosis execution flag, and ends the execution of this subroutine.

  Returning to the failure diagnosis routine of FIG. 11, the ECU 8 determines in S409 whether or not the value of the failure diagnosis execution flag is “1”.

  When a negative determination is made in S409 (failure diagnosis execution flag = 0), the ECU 8 has not yet executed either the process of S405 or the process of S407 as described in the description of S515 in FIG. The routine is temporarily terminated.

  If an affirmative determination is made in S409 (failure diagnosis execution flag = 1), the ECU 8 proceeds to S410 and determines whether or not the value of the failure diagnosis flag is “0”. In other words, the ECU 8 determines whether or not a negative determination (ΔA / F <constant value) is made in S512 of FIG.

  When an affirmative determination is made in S410 (failure diagnosis flag = 0), the absolute value ΔA of the difference between the average value A / Finj of the A / F during fuel addition and the average value A / Fpst of the post-injection A / F Since / F is smaller than a certain value, the ECU 8 considers that the reducing agent addition valve 7 has not failed, and writes “0” in the failure flag in S411.

  On the other hand, if a negative determination is made in S410 (failure diagnosis flag = 1), the absolute value of the difference between the average value A / Finj of the A / F during fuel addition and the average value A / Fpst of the post-injection A / F Since ΔA / F is equal to or greater than a certain value, the ECU 8 considers that the reducing agent addition valve 7 has failed, and writes “1” in the failure flag in S412.

  After completing the processing of S411 or S412, the ECU 8 ends the execution of this routine after rewriting the value of the failure diagnosis execution flag from “1” to “0” in S413.

In the failure diagnosis method described above, the actual fuel addition amount of the reducing agent addition valve 7 and the actual post injection amount of the fuel injection valve 3 are estimated based on the same parameter (measured value of the A / F sensor 11). Therefore, it is possible to perform an accurate failure diagnosis.

  Further, in this embodiment, the measured value of the A / F sensor 11 used for estimating the actual fuel addition amount and the measured value of the A / F sensor 11 used for estimating the actual post injection amount are the internal combustion engine 1. Therefore, the measurement of the A / F sensor 11 depends on factors other than the difference between the actual fuel addition amount and the actual post-injection amount. The value is difficult to differ. Therefore, it is possible to further improve the failure diagnosis accuracy of the reducing agent addition valve 7.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. It is a conceptual diagram which shows the estimation method of an estimated addition amount. It is a flowchart which shows the failure diagnosis routine for diagnosing the failure of a reducing agent addition valve. It is a flowchart which shows an addition amount correction | amendment routine. It is a flowchart which shows the sensor failure diagnostic routine for diagnosing the failure of an exhaust temperature sensor, an air flow meter, and an A / F sensor. It is a figure which shows the relationship between increase amount (DELTA) T measured by the normal exhaust temperature sensor, and instruction | indication addition amount Qads. It is a figure which shows the relationship between the estimated addition amount Qad and instruction | indication addition amount Qads when a reducing agent addition valve, an air flow meter, and an A / F sensor are normal. It is a timing chart which shows the failure diagnosis method in the 1st example. It is a 1st timing chart which shows the failure diagnosis method in a 4th Example. It is a 2nd timing chart which shows the failure diagnosis method in a 4th Example. It is a flowchart which shows the failure diagnosis routine in a 4th Example. It is a flowchart which shows the subroutine for a flag setting process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Fuel injection valve 5 ... Exhaust passage 6 ... Exhaust gas purification catalyst 7 ... Reducing agent addition valve 8 ... ECU
9 .... Air flow meter 10 .... Exhaust temperature sensor 11 .... A / F sensor

Claims (9)

In a failure diagnosis method for a reducing agent addition valve for adding a reducing agent to the exhaust gas of an internal combustion engine,
The post-injection from the fuel injection valve of the internal combustion engine and the reducing agent addition from the reducing agent addition valve are performed at different timings,
The amount of fuel post-injected from the fuel injection valve when the post-injection is performed and the amount of reducing agent added from the reducing agent addition valve when the reducing agent addition is performed are estimated based on the same parameter. And
A failure diagnosis method for a reducing agent addition valve, characterized by diagnosing that the reducing agent addition valve is malfunctioning on the condition that a difference between an estimated fuel amount and a reducing agent amount exceeds a predetermined amount.   2. The reducing agent addition valve failure diagnosis method according to claim 1, wherein post injection from the fuel injection valve and reducing agent addition from the reducing agent addition valve are alternately performed within the same addition period.   3. The reducing agent addition valve failure diagnosis method according to claim 1, wherein the parameter is a measured value of an air-fuel ratio sensor attached to an exhaust passage of the internal combustion engine.   3. The parameter according to claim 1, wherein the parameters include a measured value of an intake air amount sensor provided in an intake passage of the internal combustion engine, a measured value of an air-fuel ratio sensor attached to an exhaust passage of the internal combustion engine, and the internal combustion engine. A method for diagnosing a failure of a reducing agent addition valve, characterized in that the fuel injection amount is provided for combustion of the reducing agent.   5. The reducing agent addition valve failure diagnosis method according to claim 3, wherein the parameter detection is performed when the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio.   The failure of the reducing agent addition valve according to any one of claims 1 to 5, wherein the target addition amount of the reducing agent addition valve is corrected based on a ratio between the estimated fuel amount and the reducing agent amount. Diagnostic method.   6. The exhaust passage according to claim 1, wherein when the reducing agent addition valve has been diagnosed as being normal, the reducing agent addition valve is disposed downstream of the exhaust purification catalyst in the exhaust passage. A failure diagnosis method for a reducing agent addition valve, wherein the failure of the exhaust temperature sensor is diagnosed based on the measured value of the exhaust temperature sensor.   The reducing agent is added from the reducing agent addition valve so that the exhaust air-fuel ratio becomes a predetermined air-fuel ratio after the reducing agent addition valve is diagnosed as normal. A failure diagnosis method for a reducing agent addition valve, wherein the failure of the intake air amount sensor is diagnosed by comparing the air-fuel ratio measured by the air-fuel ratio sensor with the predetermined air-fuel ratio. 9. The amount of reducing agent added from the reducing agent addition valve is estimated again when the reducing agent addition valve adds a reducing agent after the intake air amount sensor is diagnosed as normal, and the estimation is performed. A failure diagnosis method for a reducing agent addition valve, wherein the failure of the air-fuel ratio sensor is diagnosed by comparing the reduced amount of the reducing agent with a predetermined reference value.

Images