Patent Publication Number: US-2019195112-A1

Title: Anomaly diagnosing apparatus and method for addition valve

Description:
BACKGROUND 
     The present disclosure relates to an anomaly diagnosing apparatus and an anomaly diagnosing method for an addition valve. An addition valve is arranged in the exhaust passage of an internal combustion engine and adds fuel to exhaust gas. The engine includes an air flowmeter and a catalyst. The air flowmeter is arranged in the intake passage and detects the amount of air. The catalyst is arranged in the exhaust passage and has an oxidizing function. The addition valve is located upstream of the catalyst in the exhaust passage. The engine also includes an air-fuel ratio sensor, an exhaust temperature sensor, and a fuel injection valve. The air-fuel ratio sensor is arranged downstream of the addition valve in the exhaust passage. The exhaust temperature sensor is arranged downstream of the catalyst in the exhaust passage. The fuel injection valve supplies fuel into a combustion chamber. 
     For example, Japanese Laid-Open Patent Publication No. 2009-221939 discloses an anomaly diagnosing apparatus for an addition valve that calculates an estimated air-fuel ratio based on a detected intake air amount, the injection amount from a fuel injection valve, and a fuel addition amount from an addition valve. The apparatus diagnoses whether there is an anomaly in the addition valve based on the difference between a value detected by the air-fuel ratio sensor and the estimated air-fuel ratio. 
     SUMMARY 
     However, if the detected intake air amount is excessively smaller than the actual intake air amount, the above-described apparatus may erroneously determine that there is an anomaly in the addition valve even when the addition valve functions normally. 
     Examples of the present disclosure will now be described. 
     Example 1 
     An anomaly diagnosing apparatus for an addition valve is provided. The addition valve is arranged in an exhaust passage of an internal combustion engine and adds fuel to exhaust gas. The engine includes an air flowmeter, which is arranged in an intake passage and detects an air amount, and a catalyst, which is arranged in the exhaust passage and has an oxidizing function. The addition valve is arranged upstream of the catalyst in the exhaust passage. The engine also includes an air-fuel ratio sensor, which is arranged downstream of the addition valve in the exhaust passage, an exhaust temperature sensor, which is arranged downstream of the catalyst in the exhaust passage, and a fuel injection valve, which supplies fuel into a combustion chamber. 
     The anomaly diagnosing apparatus is configured to execute: 
     an air-fuel ratio estimating process of calculating an estimated air-fuel ration, which is an estimated value of an air-fuel ratio based on an intake air amount detected by the air flowmeter and the sum of a fuel amount injected by the fuel injection valve and a fuel amount added by the addition valve; and 
     a stuck-closed anomaly determining process of determining that there is a stuck-closed anomaly in the addition valve if a logical conjunction is true of a condition that a detected value of the air-fuel ratio sensor is greater than the estimated air fuel-ratio by a margin greater than or equal to a specified amount and a condition that a detected value of the exhaust temperature sensor in a period in which the addition valve adds fuel is smaller than a reference value in that period by a margin greater than or equal to a predetermined amount. 
     Factors that may cause the value detected by the air-fuel ratio sensor to be greater than the estimated air-fuel ratio by a margin greater than or equal to the specified amount include not only a stuck-closed anomaly of the addition valve, in which the addition valve is stuck in a closed state, but also an anomaly in which the air amount detected by the air flowmeter is excessively smaller than the actual air amount. In contrast, if there is a stuck-closed anomaly in the addition valve, the exhaust temperature is not raised by heat of reaction produced by fuel and oxygen in the catalyst due to addition of fuel by the addition valve. Therefore, in the above-described configuration, the condition for determining that there is a stuck-closed anomaly includes a condition that the value detected by the exhaust temperature sensor in the period in which the addition valve adds fuel is smaller than the reference value in that period by a margin greater than or equal to the specific amount. This reduces erroneous determination that there is an anomaly in the addition valve when the air amount detected by the air flowmeter is excessively smaller than the actual air amount. 
     Example 2 
     In the anomaly diagnosing apparatus of Example 1, the stuck-closed anomaly determining process is a process of determining that there is a stuck-closed anomaly if the logical conjunction remains true continuously for a predetermined period. 
     In the above-described configuration, it is determined that there is an anomaly if the logical conjunction remains true continuously for a predetermined period. This improves the tolerance to noise of such determination, thus enhancing the accuracy of determination. 
     Example 3 
     The anomaly diagnosing apparatus of Example 1 or 2 is configured to further execute an exhaust temperature estimating process of calculating an estimated exhaust temperature, which is an estimated value of the exhaust temperature downstream of the catalyst, based on an operating point of the engine and an addition amount of fuel added by the addition valve. The apparatus is also configured to use the estimated exhaust temperature as the reference value. 
     When the engine is in a transient operating state, for example, there may be a temperature difference between the upstream side and the downstream side of the catalyst. In this case, if the value obtained by adding a predetermined amount to a detected temperature upstream of the catalyst is used as the reference value, it is difficult to highly accurately determine that there is a stuck-closed anomaly based on the difference between the reference value and the exhaust temperature on the downstream side. To solve this problem, the above-described configuration employs the estimated exhaust temperature as the reference value. 
     Example 4 
     The anomaly diagnosing apparatus of Example 3 being configured to execute the stuck-closed anomaly determining process on condition that a change amount of the air-fuel ratio is smaller than or equal to a predetermined amount. 
     In the above-described configuration, the stuck-closed anomaly determining process is executed when the condition is met that the change amount of the air-fuel ratio is smaller than or equal to a predetermined amount. This maximally restrains the factor of noise involved in the determination regarding anomalies. 
     Example 5 
     An anomaly diagnosing method for an addition valve is provided that executes the processes according to Examples 1 to 4. 
     Example 6 
     A non-transitory computer readable memory medium is provided that stores a program that causes a processor to execute the processes described in Examples 1 to 4. 
     Other aspects and advantages of the present disclosure will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be understood by reference to the following description together with the accompanying drawings: 
         FIG. 1  is a diagram showing an anomaly diagnosing apparatus and an internal combustion engine according to one embodiment; 
         FIG. 2  is a block diagram showing part of processes executed by the controller in the internal combustion engine of  FIG. 1 ; 
         FIG. 3  is a flowchart representing the procedure of a diagnosing process in the engine of  FIG. 1 ; and 
         FIG. 4  is a timing diagram showing advantages in the engine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     An anomaly diagnosing apparatus for an addition valve according to one embodiment will hereafter be described with reference to  FIGS. 1 to 4 . 
     As shown in  FIG. 1 , an internal combustion engine  10  is a vehicle-mounted prime mover. The engine  10  draws air through an intake passage  12 , supplying the air into combustion chambers  16  of respective cylinders through a forced induction device  14 . Fuel injection valves  18  inject fuel, such as diesel oil. In each of the combustion chambers  16 , the air-fuel mixture of the air drawn through the intake passage  12  and the fuel is compressed and ignited to be burned. The burned air-fuel mixture is discharged into an exhaust passage  20  as exhaust gas. In the exhaust passage  20 , an oxidation catalyst  22  and a diesel particulate filter (DPF  24 ) are arranged downstream of a forced induction device  14  in this order sequentially from the upstream side. An addition valve  26  is arranged between the forced induction device  14  and the oxidation catalyst  22  to add fuel to the exhaust gas. 
     A fuel pump  30  supplies fuel to the addition valve  26  and a pressure accumulating pipe  32 . The fuel injection valves  18  inject the fuel stored in the pressure accumulating pipe  32  into the combustion chambers  16 . The intake passage  12  and the exhaust passage  20  are connected to each other through an EGR passage  34 . An EGR valve  36  is arranged in the EGR passage  34  to regulate the communication area of the EGR passage  34 . 
     A controller  40  controls the engine  10  and operates operated portions of the engine  10 , including the fuel injection valves  18 , the addition valve  26 , and the EGR valve  36 , to control torque and exhaust gas components, which are controlled amounts of the engine  10 . To control the controlled amounts, the controller  40  refers to an intake air amount Ga, an exhaust temperature Tex between the oxidation catalyst  22  and the DPF  24 , and a differential pressure ΔP between the upstream side and the downstream side of the DPF  24 . The intake air amount Ga is detected by an air flowmeter  50  provided in the intake passage  12 . The exhaust temperature Tex is detected by an exhaust temperature sensor  52 . The differential pressure ΔP is detected by a differential pressure sensor  54 . The controller  40  also refers to an air-fuel ratio Af detected by an air-fuel ratio sensor  56 , an output signal Scr from a crank angle sensor  58 , and an intake manifold pressure Pm detected by an intake manifold pressure sensor  60 . The air-fuel ratio sensor  56  is arranged downstream of the DPF  24 . The intake manifold pressure Pm is the pressure in a section of the intake passage  12  downstream of the forced induction device  14 . The controller  40  further refers to an intake manifold temperature Tin detected by an intake manifold temperature sensor  62  and an accelerator operation amount ACCP. The intake manifold temperature Tin is the temperature in a section of the intake passage  12  downstream of the forced induction device  14 . The accelerator operation amount ACCP is the depression amount of the accelerator pedal and detected by an accelerator sensor  64 . 
     The controller  40  includes a CPU  42 , a ROM  44 , and a RAM  46  and controls the aforementioned controlled amounts by executing programs memorized in the ROM  44  by means of the CPU  42 . 
       FIG. 2  shows part of processes executed by the controller  40 . The processes illustrated in  FIG. 2  are implemented by executing programs memorized in the ROM  44  by means of the CPU  42 . 
     An injection amount calculating process M 10  is a process of calculating an injection amount Q injected by each fuel injection valve  18  based on the rotation speed NE and the accelerator operation amount ACCP. An injection valve operating process M 12  is a process of outputting an operating signal MS 1  to each fuel injection valve  18  to operate the fuel injection valve  18  such that the injection amount injected by the fuel injection valve  18  becomes equal to the injection amount Q. 
     A target EGR rate calculating process M 14  is a process of calculating a target EGR rate Regr* as the target of an EGR rate Regr based on the rotation speed NE and the injection amount Q. The EGR rate Regr is a value obtained by dividing the amount of the exhaust gas flowing from the exhaust passage  20  into the intake passage  12  through the EGR passage  34  by the intake air amount Ga. An EGR rate calculating process M 16  is a process of calculating the EGR rate Regr based on the intake air amount Ga, the intake manifold pressure Pm, and the intake manifold temperature Tin. A feedback process M 18  is a process of calculating a command value θegr* for the opening degree of the EGR valve  36  as an operation amount for feedback-controlling the EGR rate Regr to the target EGR rate Regr*. An EGR valve operating process M 20  is a process of outputting an operating signal MS 3  to the EGR valve  36  to operate the EGR valve  36  such that the opening degree θegr of the EGR valve  36  becomes equal to the command value θegr*. 
     An accumulation amount estimating process M 22  is a process of calculating an accumulation amount DPM, which is the amount of particulate matter trapped by the DPF  24 , based on the differential pressure ΔP and the intake air amount Ga. An addition valve operating process M 24  is a process of outputting an operating signal MS 2  to the addition valve  26  to operate the addition valve  26  to add fuel to exhaust gas when the accumulation amount DPM becomes greater than or equal to a predetermined amount, as a PM regenerating process for removing the particulate matter that has been trapped by the DPF  24 . 
     An exhaust temperature estimating process M 26  is a process of calculating an estimated exhaust temperature Texe based on the rotation speed NE and the injection amount Q, which define the operating point of the engine. During the PM regenerating process, the exhaust temperature estimating process M 26  calculates the estimated exhaust temperature Texe with the addition amount Ad of the fuel added by the addition valve  26  taken into condition. This allows the estimated exhaust temperature Texe to represent an estimated exhaust temperature between the oxidation catalyst  22  and the DPF  24 . Specifically, the exhaust temperature estimating process M 26  calculates a greater estimated exhaust temperature Texe when the injection amount Q is great than when the injection amount Q is small. The exhaust temperature estimating process M 26  also calculates a greater estimated exhaust temperature Texe when the addition amount Ad is great than when the addition amount Ad is small. 
     More specifically, the exhaust temperature estimating process M 26  includes a process of setting a base temperature based on the operating point of the engine  10 , a process of correcting the base temperature using an increase correction amount determined based on the addition amount Ad, and a process of causing the estimated exhaust temperature Texe to converge to the corrected base temperature. Specifically, map data having the rotation speed NE and the injection amount Q as input variables and the base temperature as an output variable is stored in the ROM  44 , and the CPU  42  performs map calculation to obtain the base temperature. The map data refers to a data set of discrete values of the input variable and values of the output variable each corresponding to a value of the input variable. When the value of an input variable matches any of the values of the input variable on the map data, the map calculation uses the value of the corresponding output variable on the map data as the calculation result. When the value of the input variable does not match any of the values of the input variable on the map data, the map calculation uses a value obtained by interpolation of multiple values of the output variable included in the map data set as the calculation result. The process of causing the corrected base temperature to converge to the estimated exhaust temperature Texe is a process of updating the estimated exhaust temperature Texe using, for example, an exponential moving average of a current estimated exhaust temperature Texe and a corrected base temperature. 
     A diagnosing process M 28  is a process of diagnosing whether there is an anomaly in the addition valve  26  based on the rotation speed NE, the intake air amount Ga, the air-fuel ratio Af, the estimated exhaust temperature Texe, and the addition amount Ad. 
       FIG. 3  shows the procedure of the diagnosing process M 28 . The process of  FIG. 3  is implemented by executing a program memorized in the ROM  44  by means of the CPU  42  repeatedly, for example, at predetermined cycles. In the following description, the number of each step is represented by the letter S followed by a numeral. 
     In the series of processes shown in  FIG. 3 , the CPU  42  first determines whether a diagnosis executing condition for an anomaly in the addition valve  26  is met (S 10 ). Specifically, the diagnosis executing condition includes, for example, a condition that a change amount ΔAf of the air-fuel ratio Af is smaller than or equal to a predetermined amount Δth. The change amount ΔAf is an amount calculated by the CPU  42  based on time-series data representing the air-fuel ratio Af and also the change amount of the air-fuel ratio Af per unit time. The change amount may be, for example, the value obtained by subtracting the air-fuel ratio Af that has been obtained in the previous control cycle from the air-fuel ratio Af obtained in the current control cycle. Specifically, the air-fuel ratio Af may change when the EGR rate Regr changes, the intake air amount Ga changes due to the change of the EGR rate Regr, or the injection amount Q changes. 
     If the CPU  42  determines that the diagnosis executing condition is met (S 10 : YES), the CPU  42  determines whether an adding process of fuel to exhaust gas by the addition valve  26  is being executed (S 12 ). This process is a process of determining whether the PM regenerating process is being executed. If the CPU  42  determines that the adding process is not being executed (S 12 : NO), the CPU  42  calculates an estimated air-fuel ratio Afe based on the air-fuel ratio Af and the injection amount Q (S 14 ). 
     Specifically, the CPU  42  calculates a greater estimated air-fuel ratio Afe when the intake air amount Ga is great than when the intake air amount Ga is small. Also, the CPU  42  calculates a smaller estimated air-fuel ratio Afe when the injection amount Q is great than when the injection amount Q is small. For example, this process is accomplished by substituting, for the estimated air-fuel ratio Afe, the value obtained by dividing the integrated value of the intake air amount Ga in a predetermined period by the integrated value of the injection amount Q in the predetermined period by means of the CPU  42 . 
     Subsequently, the CPU  42  determines whether the air-fuel ratio Af is smaller than the estimated air-fuel ratio Afe by a margin greater than or equal to a specified amount ΔAf 2  (S 16 ). This process is a process of determining whether there is a stuck-open anomaly. A stuck-open anomaly is an anomaly in which the addition valve  26  is constantly held open without being operated using an operating signal MS 2 . In other words, if there is a stuck-open anomaly in the addition valve  26 , the exhaust components sensed by the air-fuel ratio sensor  56  are influenced by the fuel that has flowed from the addition valve  26  into the exhaust gas. However, the estimated air-fuel ratio Afe is calculated without considering the fuel that has flowed from the addition valve  26  into the exhaust gas and thus becomes greater than the air-fuel ratio Af. Therefore, the specified amount ΔAf 2  is set to a value greater than the maximum amount by which the air-fuel ratio Af becomes smaller than the estimated air-fuel ratio Afe due to an error in calculation of the estimated air-fuel ratio Afe. As a result, when the air-fuel ratio Af is smaller than the estimated air-fuel ratio Afe by a margin greater than or equal to the specified amount ΔAf 2 , it is determined that the fuel is likely to be flowing from the addition valve  26  into the exhaust gas. 
     If the CPU  42  determines that the air-fuel ratio Af is smaller than the estimated air-fuel ratio Afe by a margin greater than or equal to the specified amount ΔAf 2  (S 16 : YES), the CPU  42  increments the stuck-open anomaly counter C 2  and initializes a stuck-closed anomaly counter C 1  (S 18 ). Then, the CPU  42  determines whether the stuck-open anomaly counter C 2  is greater than or equal to a predetermined value C 2   th  (S 20 ). If the CPU  42  determines that the stuck-open anomaly counter C 2  is greater than or equal to the predetermined value C 2   th  (S 20 : YES), the CPU  42  determines that a stuck-open anomaly has occurred in the addition valve  26  (S 22 ). Also, the CPU  42  operates a warning light  66 , as shown in  FIG. 1 , to execute a notification process of urging the user of the vehicle to order repair service (S 24 ). 
     In contrast, if the CPU  42  determines that the adding process is being executed (S 12 : YES), the CPU  42  calculates the estimated air-fuel ratio Afe based on the intake air amount Ga, the addition amount Ad, and the injection amount Q (S 26 ). Specifically, the CPU  42  calculates a greater estimated air-fuel ratio Afe when the intake air amount Ga is great than when the intake air amount Ga is small. On the other hand, the CPU  42  calculates a smaller estimated air-fuel ratio Afe when the injection amount Q is great than when the injection amount Q is small. The CPU  42  also calculates a smaller estimated air-fuel ratio Afe when the addition amount Ad is great than when the addition amount Ad is small. For example, this process is accomplished by substituting, for the estimated air-fuel ratio Afe, the value obtained by dividing the integrated value of the intake air amount Ga in a predetermined period by the integrated value of the sum of the injection amount Q and the addition amount Ad in the predetermined period by means of the CPU  42 . 
     Next, the CPU  42  determines whether the air-fuel ratio Af exceeds the estimated air-fuel ratio Afe calculated in S 26  by a margin greater than or equal to a specified amount ΔAf 1  (S 28 ). This process determines whether there is a possibility of a stuck-closed anomaly in the addition valve  26 . A stuck-closed anomaly is an anomaly in which, despite the fact that the addition valve  26  is operated to add fuel to exhaust gas, the addition valve  26  actually does not inject fuel and thus cannot add fuel to exhaust gas. The fuel (the addition amount Ad) to be added to the exhaust gas by the addition valve  26  through operation of the addition valve  26  is considered in calculation of the estimated air-fuel ratio Afe. As a result, if there is a stuck-closed anomaly in the addition valve  26 , the estimated air-fuel ratio Afe is smaller than the air-fuel ratio Af. Therefore, the specified amount ΔAf 1  is set to a value greater than the maximum amount by which the air-fuel ratio Af exceeds the estimated air-fuel ratio Afe due to an error in calculation of the estimated air-fuel ratio Afe. This allows for determination that there is a possibility of a stuck-closed anomaly, in which the addition valve  26  cannot add fuel to exhaust gas, in the addition valve  26  when the air-fuel ratio Af is greater than the estimated air-fuel ratio Afe by a margin greater than or equal to the specified amount ΔAf 1 . 
     If the CPU  42  determines that the air-fuel ratio Af exceeds the estimated air-fuel ratio Afe by a margin greater than or equal to the specified amount ΔAf 1  (S 28 : YES), the CPU  42  determines whether the exhaust temperature Tex is smaller than the estimated exhaust temperature Texe by a margin greater than or equal to a predetermined amount ΔTe (S 30 ). This process is carried out to ascertain that the factor that has brought about a positive determination in S 28  is not an anomaly in which the intake air amount Ga detected by the air flowmeter  50  is excessively smaller than the actual intake air amount. In other words, at the time of a stuck-closed anomaly of the addition valve  26 , the adding process cannot add the addition amount Ad of fuel to the exhaust gas. The exhaust temperature downstream of the oxidation catalyst  22  is thus lower than that in a case in which the addition amount Ad of fuel is added to the exhaust gas. Specifically, when the adding process is being executed, the estimated exhaust temperature Texe is determined with an expected rise of the exhaust temperature downstream of the oxidation catalyst  22  caused by the adding process taken into consideration. Therefore, at the time of a stuck-closed anomaly, the exhaust temperature Tex is smaller than the estimated exhaust temperature Texe to a great extent. In contrast, if the intake air amount Ga is excessively smaller than the actual air amount despite the fact that there is no stuck-closed anomaly, the exhaust temperature Tex is expected to be a value approximating the estimated exhaust temperature Texe. Therefore, the predetermined value ΔTe is set to a value greater than the maximum amount by which the exhaust temperature Tex is smaller than the estimated exhaust temperature Texe due to an error in calculation of the estimated exhaust temperature Texe. This allows for determination that there is a stuck-closed anomaly when the exhaust temperature Tex is smaller than the estimated exhaust temperature Texe by a margin greater than or equal to the predetermined amount ΔTe. 
     If the CPU  42  determines that the exhaust temperature Tex is smaller than the estimated exhaust temperature Texe by a margin greater than or equal to the predetermined amount ΔTe (S 30 : YES), the CPU  42  increments the stuck-closed anomaly counter C 1  and initializes the stuck-open anomaly counter C 2  (S 32 ). Next, the CPU  42  determines whether the stuck-closed anomaly counter C 1  is greater than or equal to a predetermined value C 1   th  (S 34 ). If the CPU  42  determines that the stuck-closed anomaly counter C 1  is greater than or equal to the predetermined value C 1   th  (S 34 : YES), the CPU  42  determines that there is a stuck-closed anomaly in the addition valve  26  (S 36 ) and performs S 24 . 
     If the CPU  42  makes a negative determination in S 16 , S 28 , or S 30 , the CPU  42  initializes the stuck-closed anomaly counter C 1  and the stuck-open anomaly counter C 2  (S 38 ). 
     The CPU  42  suspends the series of processes shown in  FIG. 3  when S 24  or S 38  is completed or if a negative determination is made in S 10 , S 20 , or S 34 . 
     An operation and advantages of the present embodiment will now be described. 
       FIG. 4  shows changes in the value obtained by subtracting the estimated air-fuel ratio Afe from the air-fuel ratio Af, the value obtained by subtracting the exhaust temperature Tex from the estimated exhaust temperature Texe, and the stuck-closed anomaly counter C 1 . 
     At a point in time t 1 , the air-fuel ratio Af exceeds the estimated air-fuel ratio Afe by a margin greater than or equal to the specified amount ΔAf 1 . Also, the difference between the estimated exhaust temperature Texe and the exhaust temperature Tex is relatively small. Therefore, the CPU  42  starts to increment the stuck-closed anomaly counter C 1 . However, at a point in time t 2 , the amount by which the air-fuel ratio Af exceeds the estimated air-fuel ratio Afe becomes smaller than the specified amount ΔAf 1 . This causes the CPU  42  to initialize the stuck-closed anomaly counter C 1 . Then, at a point in time t 3 , the air-fuel ratio Af exceeds the estimated air-fuel ratio Afe by a margin greater than or equal to the specified amount ΔAf 1 . Also, the difference between the estimated exhaust temperature Texe and the exhaust temperature Tex is relatively small. This causes the CPU  42  to restart incrementing the stuck-closed anomaly counter C 1 . At a pint in time t 4 , when the stuck-closed anomaly counter C 1  becomes greater than or equal to the predetermined value C 1   th , the CPU  42  determines that there is a stuck-closed anomaly in the addition valve  26 . Specifically,  FIG. 4  illustrates a case in which the intake air amount Ga detected by the air flowmeter  50  is normal. In a case in which the intake air amount Ga is excessively smaller than the actual air amount and there is no stuck-closed anomaly, the exhaust temperature Tex does not become smaller than the estimated exhaust temperature Texe by a margin greater than or equal to the predetermined amount ΔTe. The stuck-closed anomaly counter C 1  is thus maintained without being incremented. 
     As has been described, in the present embodiment, it is determined that there is a stuck-closed anomaly when the air-fuel ratio Af exceeds the estimated air-fuel ratio Afe by a margin greater than or equal to the specified amount ΔAf 1  and, at the same time, the difference between the estimated exhaust temperature Texe and the exhaust temperature Tex is great. This restrains erroneously determination that there is a stuck-closed anomaly in the addition valve  26  due to the fact that the intake air amount Ga detected by the air flowmeter  50  is excessively smaller than the actual intake air amount. 
     The present embodiment described above further has the following advantages. 
     (1) When the engine  10  is in transient operation, for example, there may be a temperature difference between the upstream side and the downstream side of the oxidation catalyst  22 . Therefore, for example, if the value obtained by adding a predetermined amount to a detected temperature upstream of the oxidation catalyst  22  is used instead of the estimated exhaust temperature Texe, it may become difficult to accurately determine that there is no stuck-closed anomaly. To solve this problem, the present embodiment employs the estimated exhaust temperature Texe to ascertain that the fact that the air-fuel ratio Af has become great is caused not by a stuck-closed anomaly but by an anomaly in which the intake air amount Ga detected by the air flowmeter  50  is excessively smaller than the actual air amount. 
     (2) The diagnosis executing condition includes the condition that the change amount ΔAf of the air-fuel ratio Af is smaller than or equal to the predetermined amount Δth. This maximally restrains a factor of noise involved in anomaly determination. 
     &lt;Correspondence&gt; 
     The correspondence between the items in the above-described embodiments and the items described in the above SUMMARY is as follows. Below, the correspondence is shown for each of the numbers in the examples described in the above SUMMARY. 
     [1] The “catalyst” corresponds to the oxidation catalyst  22 . The “anomaly diagnosing apparatus” corresponds to the controller  40 . The “air-fuel ratio estimating process” corresponds to S 26 . The “stuck-closed anomaly determining process” corresponds to S 28  to S 36 . The “reference value” corresponds to the estimated exhaust temperature Texe. 
     [2] The “predetermined period” corresponds to a period that lasts for a length corresponding to the value obtained by multiplying the control cycle of the process of  FIG. 3  by the predetermined value C 1   th.    
     [4] Example 4 corresponds to the fact that the diagnosis executing condition in S 10  includes the condition that the change amount ΔAf of the air-fuel ratio Af is smaller than or equal to the predetermined amount Δth. 
     OTHER EMBODIMENTS 
     The above-described embodiments may be modified as follows. The above-described embodiments and the following modifications can be combined as long as the combined modifications remain technically consistent with each other. 
     Regarding Exhaust Temperature Estimating Process 
     In the above-described embodiments, the estimated exhaust temperature Texe is calculated based on the rotation speed NE and the injection amount Q, which define the operating point of the internal combustion engine  10 . However, the configuration is not restricted to this. For example, the accelerator operation amount ACCP may be used instead of the injection amount Q as load. Alternatively, for example, the estimated exhaust temperature Texe may be calculated based on the air-fuel ratio Af in addition to the rotation speed NE, the load, and the addition amount Ad. Such calculation is implemented by, for example, a process of correcting the base temperature, which is determined in correspondence with the rotation speed NE and the load, by the increase correction amount, and an air-fuel ratio correction amount determined in correspondence with the air-fuel ratio and then causing the estimated exhaust temperature Texe to converge to the corrected base temperature. Specifically, the air-fuel ratio correction amount may be map-calculated by the CPU  42  with reference to map data in which the air-fuel ratio is an input variable and the air-fuel ratio correction amount is an output variable. The map data is memorized in the ROM  44  in advance. 
     The process of causing the estimated exhaust temperature Texe to converge to the base temperature, which is determined in correspondence with the operating point, is not restricted to the exponential moving average process. The process may be, for example, a process of setting an output value of a low-pass filter, such as a first-order lag filter or a second-order lag filter, in which the base temperature is an input may be set as the estimated exhaust temperature Texe. 
     Regarding Diagnosis Executing Condition 
     In the present embodiment, the diagnosis executing condition for the stuck-open anomaly determining process includes the condition that the adding process is in an interrupted state. However, the present configuration is not restricted to this. 
     Also, it is not always necessary to set the change amount ΔAf of the air-fuel ratio Af being smaller than the predetermined amount Δth as a condition. 
     Regarding Air-Fuel Ratio Estimating Process 
     If the adding process being not executed is excluded from the diagnosis executing condition for the stuck-open anomaly determining process as has been described in “Regarding Diagnosis Executing Condition,” for example, the estimated air-fuel ratio Afe calculated in S 26  may be used in S 16 . 
     Regarding Reference Value 
     In the present embodiment, the estimated exhaust temperature Texe is set as the “reference value” when the adding process is being executed. However, the configuration is not restricted to this. For example, a sensor may be provided to detect an upstream exhaust temperature that is the exhaust temperature upstream of the oxidation catalyst  22 . In this case, the value obtained by adding a predetermined amount to a detected upstream exhaust temperature may be set as the “reference value”. Alternatively, instead of the detected upstream exhaust temperature, an estimated upstream exhaust temperature based on the operating point of the engine  10  may be used to calculate the “reference value”. 
     Regarding Stuck-Closed Anomaly Determining Process 
     In the illustrated embodiment, it is determined that there is a stuck-closed anomaly if the logical conjunction remains true continuously for a predetermined period of the condition that the air-fuel ratio Af is greater than the estimated air fuel-ratio Afe by a margin greater than or equal to the specified amount ΔAf 1  and the condition that the exhaust temperature Tex is smaller than the estimated exhaust temperature Texe by a margin greater than or equal to the predetermined amount ΔTe. However, the configuration is not restricted to this. For example, it may be determined that there is a stuck-closed anomaly if the above-described logical conjunction remains true for a predetermined accumulated time or longer in a specified period. Alternatively, for example, it may be determined that there is a stuck-closed anomaly immediately after the logical conjunction becomes true. 
     Regarding Stuck-Open Anomaly Determining Process 
     As has been described in “Regarding Diagnosis Executing Condition,” for example, the diagnosis executing condition for the stuck-open anomaly determining process may exclude the condition that the adding process is not being executed. In this case, as has been described in “Regarding Air-Fuel Ratio Estimating Process,” the stuck-open anomaly determining process may be carried out by using, in S 16 , the estimated air-fuel ratio Afe calculated in S 26 . In other words, if the addition amount caused by a stuck-open anomaly is greater than the addition amount brought about by the adding process, a positive determination is made in S 16 . This allows for detection of a stuck-open anomaly. Specifically, in this case, the specified amount ΔAf 2  may be set to a value greater than the maximum absolute value of the difference between the air-fuel ratio Af and the estimated air-fuel ratio Afe when the addition amount Ad of fuel is added. 
     Regarding Adding Process 
     The adding process is not restricted to the PM regenerating process. For example, even when the accumulation amount DPM is small, the adding process may be executed exclusively for the stuck-closed anomaly diagnosis. 
     Regarding Notification Process 
     In the above-described embodiments, the process of operating a device that outputs visual information (the warning light  66 ) is used, by way of example, as the notification process of issuing a notification about the existence of an anomaly. However, the invention is not restricted to this. For example, the notification process may be a process of operating a device that outputs auditory information, such as warning sound. In other words, any suitable notifying device may be employed as long as the notifying device outputs at least either auditory or visual information. 
     Regarding Exhaust System 
     In the above-described embodiments, the addition valve  26  is provided upstream of the oxidation catalyst  22 , while the exhaust temperature sensor  52  and the air-fuel ratio sensor  56  are provided downstream of the oxidation catalyst  22 . However, the invention is not restricted to this. For example, the oxidation catalyst  22  may be omitted and replaced by an oxidation catalyst arranged in the DPF  24 . In this configuration, the addition valve  26  may be provided upstream of the DPF  24  while the exhaust temperature sensor  52  and the air-fuel ratio sensor  56  may be provided downstream of the DPF  24 . Also, for example, the air-fuel ratio sensor  56  may be arranged between the addition valve  26  and the oxidation catalyst  22 . 
     Regarding Anomaly Diagnosing Apparatus 
     The anomaly diagnosing apparatus is not limited to an apparatus that includes the CPU  42  and the ROM  44  and executes software processing. For example, at least part of the processes executed by the software in the above-described embodiment may be executed by hardware circuits dedicated to execution of these processes (such as ASIC). That is, the anomaly diagnosing apparatus may be modified as long as it has any one of the following configurations (a) to (c). (a) A configuration including a processor that executes all of the above-described processes according to programs and a program storage device such as a ROM (including a non-transitory computer readable medium) that stores the programs. (b) A configuration including a processor and a program storage device that execute part of the above-described processes according to the programs and a dedicated hardware circuit that executes the remaining processes. (c) A configuration including a dedicated hardware circuit that executes all of the above-described processes. A plurality of software processing circuits each including a processor and a program storage device and a plurality of dedicated hardware circuits may be provided. That is, the above processes may be executed in any manner as long as the processes are executed by processing circuitry that includes at least one of a set of one or more software processing circuits and a set of one or more dedicated hardware circuits. 
     OTHER EMBODIMENTS 
     The internal combustion engine is not limited to a four-cylinder engine. For example, an in-line six-cylinder engine may be used. The stuck-open anomaly determining process does not necessarily have to be executed based on the comparison between the estimated air-fuel ratio Afe and the air-fuel ratio Af.