Patent Publication Number: US-2019195160-A1

Title: Anomaly diagnosing apparatus and method for air flowmeter

Description:
BACKGROUND 
     The present disclosure relates to an anomaly diagnosing apparatus and an anomaly diagnosing method for an air flowmeter. An air flowmeter is arranged in the intake passage of an internal combustion engine and detects the amount of air. The engine includes a catalyst and an addition valve. The catalyst is arranged in an exhaust passage and has an oxidizing function. The addition valve is arranged upstream of the catalyst in the exhaust passage and adds fuel to exhaust gas. 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, International Publication No. 2011/132678 describes a diagnosing apparatus that determines a deviation rate, which is the deviation between an estimated intake air amount, or an estimated value of the intake air amount, and an intake air amount detected by an air flowmeter. The disclosed diagnosing method determines that there is an anomaly in the air flowmeter if the deviation rate is greater than a reference failure determination value, which is determined in correspondence with the rotation speed of the engine. As described in Paragraph 0038 of the aforementioned document, the estimated intake air amount is calculated based on the rotation speed of the engine and the opening degree of the throttle valve. 
     SUMMARY 
     Examples of the present disclosure will now be described. 
     Example 1 
     An anomaly diagnosing apparatus for an air flowmeter is provided. The air flowmeter is arranged in an intake passage of an internal combustion engine and detects an air amount. The engine includes a catalyst, which is arranged in an exhaust passage and has an oxidizing function, an addition valve, which is arranged upstream of the catalyst in the exhaust passage and adds fuel to exhaust gas, 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 amount estimating process of calculating an estimated air amount, which is an estimated value of an air amount, based on an air-fuel ratio detected by the air-fuel ratio sensor and an injection amount injected by the fuel injection valve; and 
     an upward displacement anomaly determining process of determining that there is an anomaly in which a detected value of the air flowmeter is greater than an actual value if a logical conjunction is true of the condition that the detected value of the air flowmeter is greater than the estimated air amount by a margin greater than or equal to a specified amount and the condition that an amount by which a detected value of the exhaust temperature sensor exceeds a reference value is smaller than or equal to a predetermined amount. 
     Factors that may cause the detected value of the air flowmeter to become greater than the estimated air amount by a margin greater than or equal to the specified amount include not only an anomaly in the air flowmeter but also a stuck-open anomaly of the addition valve, in which the addition valve is stuck open. At the time of a stuck-open anomaly, the fuel added by the addition valve is oxidized by the catalyst and raises the exhaust temperature downstream of the catalyst as compared to a case without a stuck-open anomaly. Therefore, the above-described configuration requires a condition that the extent by which the detected value of the exhaust temperature sensor exceeds the reference value must be smaller than or equal to the predetermined amount. For example, by setting the reference value to the exhaust temperature downstream or upstream of the catalyst in a case without a stuck-open anomaly, erroneous determination of an anomaly in the air flowmeter is restrained in a case with a stuck-open anomaly. 
     Assume a mode in which an estimated air amount is calculated based on a detected value of an air-fuel ratio sensor arranged in the exhaust passage, and the calculated estimated air amount is employed in an internal combustion engine having an addition valve in the exhaust passage, which addition valve adds fuel to exhaust gas. In this mode, if a stuck-open anomaly occurs in the addition valve, the calculated estimated air amount tends to become smaller than the actual value. This may cause erroneous determination that there is an anomaly in which the intake air amount detected by the air flowmeter becomes smaller than the actual intake air amount. The above-described configuration restrains such erroneous determination. 
     Example 2 
     In the anomaly diagnosing apparatus for an air flowmeter of Example 1, the upward displacement anomaly determining process is a process of determining that there is an anomaly in which the detected value of the air flowmeter is greater than an actual value if the logical conjunction remains true for a predetermined period. 
     In the above-described configuration, it is determined that there is an anomaly if the logical conjunction remains true for a predetermined period. This improves the tolerance to noise of such determination, thus enhancing the accuracy of the determination. 
     Example 3 
     In the anomaly diagnosing apparatus for an air flowmeter of Example 1 or 2, the upward displacement anomaly determining process is a process of determining that there is the anomaly based on the estimated air amount, which is calculated through the air amount estimating process, when an adding process of the fuel by the addition valve is not being executed. 
     In the above-described configuration, it is determined that an anomaly has occurred based on the estimated air amount calculated through the air amount estimating process when the adding process is not being executed. It is thus unnecessary to consider the fuel added through the adding process in the air amount estimating process. This decreases the number of parameters that should be considered in the setting of the specified amount. The lowering of the setting accuracy of the specified amount is thus easily restrained. 
     Example 4 
     In the anomaly diagnosing apparatus for an air flowmeter of Example 1 or 2, the air amount estimating process is a process of calculating the estimated air amount based on a fuel amount added to the exhaust gas by the addition valve in addition to the air-fuel ratio detected by the air-fuel ratio sensor and the fuel amount injected by the fuel injection valve. The upward displacement anomaly determining process includes a process of determining that there is the anomaly based on the estimated air amount calculated through the air amount estimating process when the adding process of the fuel is being executed by the addition valve. 
     In the above-described configuration, the estimated air amount is calculated based on the fuel amount added to exhaust gas by the addition valve. Therefore, even when the adding process is being executed, whether there is an anomaly is determined with high accuracy. 
     Example 5 
     In the anomaly diagnosing apparatus for an air flowmeter of any one of Examples 1 to 4, the anomaly diagnosing apparatus is configured to execute an exhaust temperature estimating process of calculating an estimated exhaust temperature, which is an estimated value of an exhaust temperature downstream of the catalyst, based on an operating point of the engine. The reference value is the estimated exhaust temperature. 
     If the addition valve has a stuck-open anomaly, the addition valve leaks fuel and the fuel reacts with oxygen in the catalyst. The exhaust temperature downstream of the catalyst thus tends to rise. A detected value of the exhaust temperature upstream of the catalyst may be used as the “reference value,” with which a detected value of the exhaust temperature detected by the exhaust temperature sensor is compared. However, when, for example, the engine is in a transient operating state, there may be a temperature difference between the upstream side and the downstream side of the catalyst even without a stuck-open anomaly. Therefore, when the temperature upstream of the catalyst is the “reference value,” the temperature difference between the reference value and the downstream exhaust temperature may hamper highly accurate determination that there is no stuck-open anomaly. To solve this problem, the above-described configuration employs the estimated exhaust temperature as the “reference value.” 
     Example 6 
     The anomaly diagnosing apparatus according to any one of Examples 1 to 5 is configured to execute the upward displacement anomaly determining process if a condition is met that the change amount of the air-fuel ratio is smaller than or equal to a predetermined amount. 
     In the above-described configuration, the upward displacement 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 7 
     An anomaly diagnosing method for an air flowmeter is provided that executes the processes according to Examples 1 to 6. 
     Example 8 
     A non-transitory computer readable memory medium is provided that stores a program that causes a processing device to execute the processes described in Examples 1 to 6. 
     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 a first 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 ; 
         FIG. 4  is a timing diagram showing advantages in the engine of  FIG. 1 ; and 
         FIG. 5  is a flowchart representing the procedure of a diagnosing process according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A first embodiment of an anomaly diagnosing apparatus for an air flowmeter will now 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 . 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, which is an estimated value of the exhaust temperature downstream of the oxidation catalyst  22 , based on the rotation speed NE and the injection amount Q, which define the operating point of the engine  10 . The estimated exhaust temperature Texe is determined without considering whether the addition valve  26  has added fuel. That is, if the addition valve  26  adds fuel, the temperature of the exhaust gas downstream of the oxidation catalyst  22  may become higher than the temperature of the exhaust gas discharged from the combustion chambers  16 . Even in this case, the temperature of the exhaust gas downstream of the oxidation catalyst  22  that has become higher is not included in calculation of the estimated exhaust temperature Texe. 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. 
     More specifically, the exhaust temperature estimating process M 26  includes a process of setting a base temperature based on the rotation speed NE and the injection amount Q, which define the operating point of the engine  10 , and a process of causing the estimated exhaust temperature Texe to converge to the 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 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 air flowmeter  50  based on the rotation speed NE, the intake air amount Ga, the air-fuel ratio Af, and the estimated exhaust temperature Texe. 
       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  determines whether a condition for executing anomaly diagnosis for the air flowmeter  50  is met (S 10 ). The diagnosis executing condition includes a condition that the logical conjunction of a condition (i) and a condition (ii) is true. The condition (i) is that the adding process of fuel by the addition valve  26  is not being executed. The condition (ii) is that the change amount ΔAf of the air-fuel ratio Af is smaller than or equal to a specified amount Δth. Specifically, the condition (i) is met when the PM regenerating process is not being executed. 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  calculates an estimated air amount Gae based on the air-fuel ratio Af and the injection amount Q (S 12 ). Specifically, the CPU  42  determines a greater estimated air amount Gae when the air-fuel ratio Af is great than when the air-fuel ratio Af is small. The CPU  42  also determines a greater estimated air amount Gae when the injection amount Q is great than when the injection amount Q is small. Such calculation may be implemented by a process of substituting the product of the integrated value of the injection amount Q in a predetermined period and the air-fuel ratio Af for the estimated air amount Gae. Specifically, the intake air amount Ga is determined in correspondence with the aforementioned predetermined period. In other words, the intake air amount Ga is the amount of the air drawn into the intake passage  12  in the predetermined period. 
     Subsequently, the CPU  42  determines whether the value obtained by subtracting the estimated air amount Gae from the intake air amount Ga is greater than or equal to a specified amount ΔGa1 (S 14 ). This process is a process of determining whether the intake air amount Ga detected by the air flowmeter  50  is excessively greater than the actual air amount. When the CPU  42  determines that the value obtained by subtracting the estimated air amount Gae from the intake air amount Ga is smaller than the specified amount ΔGa1 (S 14 : NO), the CPU  42  initializes an upward displacement determining counter C1 (S 16 ). The upward displacement determining counter C1 counts the duration in which temporary determination that there is an anomaly in which the intake air amount Ga is excessively greater than the actual air amount is maintained. 
     Then, the CPU  42  determines whether the value obtained by adding a specified amount ΔGa2 to the intake air amount Ga is smaller than or equal to the estimated air amount Gae (S 18 ). This is a process of determining whether the intake air amount Ga is excessively smaller than the actual air amount. If the CPU  42  determines that the value obtained by adding the specified amount ΔGa2 to the intake air amount Ga is smaller than or equal to the estimated air amount Gae (S 18 : YES), the CPU  42  increments a downward displacement determining counter C2 (S 20 ). The downward displacement determining counter C2 counts the duration in which temporary determination that there is an anomaly in which the intake air amount Ga is excessively smaller than the actual air amount is maintained. The CPU  42  then determines whether the downward displacement determining counter C2 is greater than or equal to a predetermined value C2th (S 22 ). If the CPU  42  determines that the downward displacement determining counter C2 is greater than or equal to the predetermined value C2th (S 22 : YES), the CPU  42  determines that there is a downward displacement anomaly (S 24 ). The downward displacement anomaly refers to an anomaly in which the intake air amount Ga is excessively smaller than the actual air amount. Then, 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 26 ). 
     In contrast, if the CPU  42  determines that the value obtained by subtracting the estimated air amount Gae from the intake air amount Ga is greater than or equal to the specified amount ΔGa1 (S 14 : YES), the CPU  42  initializes the downward displacement determining counter C2 (S 27 ). The CPU  42  then determines whether the value obtained by subtracting a predetermined amount ΔTe from the exhaust temperature Tex is smaller than or equal to the estimated exhaust temperature Texe (S 28 ). This is a process of ascertaining that the cause that has brought about a positive determination in S 14  is not a stuck-open anomaly of the addition valve  26 . The stuck-open anomaly refers to a state in which, despite the fact that fuel addition by the addition valve  26  is not being executed, fuel flows from the addition valve  26  into the exhaust gas. In other words, when there is a stuck-open anomaly in the addition valve  26 , fuel flows into exhaust gas from the addition valve  26 . However, such fuel flowing out of the addition valve  26  is not taken into consideration in S 12 . That is, the estimated air amount Gae is calculated in S 12  using the injection amount Q, which is a fuel amount smaller than the total fuel amount (Q+addition amount Ad), which affects the exhaust gas components sensed by the air-fuel ratio sensor  56 . The estimated air amount Gae is thus smaller than the actual value. On the other hand, in the case of a stuck-open anomaly, the fuel from the addition valve  26  reacts with oxygen in the oxidation catalyst  22 . The exhaust temperature downstream of the oxidation catalyst  22  thus becomes high as compared to a case without a stuck-open anomaly. As a result, the exhaust temperature Tex becomes higher than the estimated exhaust temperature Texe, which is obtained assuming that fuel addition by the addition valve  26  is not being executed. Therefore, the predetermined amount ΔTe is set to an assumed upper limit of the amount by which the exhaust temperature Tex exceeds the estimated exhaust temperature Texe due to a calculation error in the estimated exhaust temperature Texe caused by noise or the like, despite the fact that the addition valve  26  operates normally. 
     If the CPU  42  determines that the value obtained by subtracting the predetermined amount ΔTe from the exhaust temperature Tex is smaller than or equal to the estimated exhaust temperature Texe (S 28 : YES), the CPU  42  increments the upward displacement determining counter C1 (S 30 ). The CPU  42  then determines whether the upward displacement determining counter C1 is greater than or equal to a predetermined value C1th (S 32 ). If the CPU  42  determines that the upward displacement determining counter C1 is greater than or equal to the predetermined value C1th (S 32 : YES), the CPU  42  determines that there is an upward displacement anomaly (S 34 ) and carries out S 26 . 
     In contract, if the CPU  42  makes a negative determination in S 18  or S 28 , the CPU  42  initializes the upward displacement determining counter C1 and a downward displacement determining counter C2 (S 36 ). The CPU  42  suspends the series of processes shown in  FIG. 3  when S 26  or S 36  is completed or a negative determination is made in S 10 , S 22 , or S 32 . 
     The operation and advantages of the present embodiment will now be described. 
       FIG. 4  represents changes of the intake air amount Ga, the value obtained by subtracting the estimated air amount Gae from the intake air amount Ga, the value obtained by subtracting the estimated exhaust temperature Texe from the exhaust temperature Tex, and the upward displacement determining counter C1. 
     In the period from a point in time t 1  to a point in time t 2 , the intake air amount Ga is greater than the estimated air amount Gae by a margin greater than or equal to the specified amount ΔGa1. Also, in this period, the absolute value of the difference between the exhaust temperature Tex and the estimated exhaust temperature Texe is small. Therefore, the CPU  42  increments the upward displacement determining counter C1. However, at the point in time t 2 , the exhaust temperature Tex becomes higher than the estimated exhaust temperature Texe by a margin greater than or equal to the predetermined amount ΔTe. This causes the CPU  42  to initialize the upward displacement determining counter C1. Then, continuously following a point in time t 3 , the intake air amount Ga remains greater than the estimated air amount Gae by a margin greater than or equal to the specified amount ΔGa1. Also, the absolute value of the difference between the exhaust temperature Tex and the estimated exhaust temperature Texe remains small. Therefore, the CPU  42  continuously increments the upward displacement determining counter C1. At a point in time t 4 , the upward displacement determining counter C1 reaches the predetermined value C1th, thus causing the CPU  42  to determine that an upward displacement anomaly has occurred. 
       FIG. 4  illustrates a case without a stuck-open anomaly. In a case with a stuck-open anomaly, even when the intake air amount Ga is excessively greater than the estimated air amount Gae, the exhaust temperature Tex is higher than the estimated exhaust temperature Texe by a margin greater than or equal to the predetermined amount ΔTe. The upward displacement determining counter C1 is thus maintained without being incremented. 
     As has been described, in the present embodiment, not only the difference between the intake air amount Ga and the estimated air amount Gae but also the difference between the exhaust temperature Tex and the estimated exhaust temperature Texe is taken into consideration. This ensures accurate determination regarding the upward displacement anomaly in the air flowmeter  50 , while restraining erroneous determination that there is an upward displacement anomaly due to a stuck-open anomaly. 
     The present embodiment described above further has the following advantages. 
     (1) The condition that the amount by which the exhaust temperature Tex exceeds the estimated exhaust temperature Texe is smaller than or equal to the predetermined amount ΔTe is set as a condition for determining that there is an upward displacement anomaly. This ensures effective determination regarding the upward displacement anomaly while restraining influence by a temperature difference between the upstream side and the downstream side of the oxidation catalyst  22  due to, for example, transient operation of the engine  10 , compared to a case that sets a condition that the difference between the upstream side and the downstream side of the oxidation catalyst  22  is smaller than or equal to a predetermined amount. 
     (2) The diagnosis executing condition includes the condition that the adding process of fuel by the addition valve  26  is not being executed. This makes it unnecessary to consider errors in the addition amount added by the addition valve  26  as a factor of errors in the estimated air amount Gae. The specified amounts ΔGa1, ΔGa2 are thus minimized. Also, since it is unnecessary to consider errors in the addition amount added by the addition valve  26  as a factor of errors in the estimated exhaust temperature Texe, the predetermined amount ΔTe is minimized. 
     (3) 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. 
     Second Embodiment 
     A second embodiment will now be described with reference to  FIG. 5 . The differences from the first embodiment will mainly be discussed. 
     In the second embodiment, during the execution of the adding process, the exhaust temperature estimating process M 26  takes the increasing amount of the exhaust temperature Tex downstream of the oxidation catalyst  22  caused by the fuel addition by the addition valve  26  into consideration in calculation of the estimated exhaust temperature Texe. Such calculation is implemented by correcting, by means of the CPU  42 , the aforementioned base temperature to increase in correspondence with the addition amount Ad added by the addition valve  26 . Specifically, the CPU  42  may determine a greater increasing-correction amount when the addition amount Ad is great than when the addition amount Ad is small. Specifically, the increasing-correction amount may be map-calculated by the CPU  42  with reference to map data in which the addition amount Ad is an input variable and the increasing-correction amount is an output variable. The map data is memorized by the ROM  44  in advance. 
       FIG. 5  represents the procedure of the diagnosing process M 28 . The process shown in  FIG. 3  is implemented by executing a program memorized in the ROM  44  by means of the CPU  42  repeatedly at, for example, predetermined cycles. In  FIG. 5 , the steps that are identical with the corresponding steps shown in  FIG. 3  are given identical step numbers as those given to the corresponding steps of  FIG. 3 . 
     In the series of processes shown in  FIG. 5 , the CPU  42  first determines whether a diagnosis executing condition is met (S 10   a ). The diagnosis executing condition does not include the aforementioned condition (i). If the CPU  42  determines that the diagnosis executing condition is met (S 10   a : YES), the CPU  42  calculates the estimated air amount Gae based on the intake air amount Ga, the addition amount Ad, and the injection amount Q (S 12   a ). Specifically, the CPU  42  determines a greater estimated air amount Gae when the air-fuel ratio Af is great than when the air-fuel ratio Af is small, when the injection amount Q is great than when the injection amount Q is small, and when the addition amount Ad is great than when the addition amount Ad is small. Such calculation may be implemented by, for example, a process of substituting, for the estimated air amount Gae, the product of the sum of the integrated value of the injection amount Q in a predetermined period and the integrated value of the addition amount Ad in the predetermined period and the air-fuel ratio Af. If the addition amount Ad is zero, the same processing as that of S 12  of  FIG. 3  is performed. 
     After completing S 12   a , the CPU  42  performs S 14 . If the CPU  42  makes a negative determination in S 10   a , the CPU  42  suspends the process shown in  FIG. 5 . Specifically, in the second embodiment, the predetermined amount ΔTe is set to an assumed upper limit of the amount by which the actual exhaust temperature Tex exceeds the estimated exhaust temperature Texe when the adding process is being executed. As a result, a negative determination is made in S 28  if there is a stuck-open anomaly in the addition valve  26  and the addition amount in this state is greater than the addition amount at the time of the adding process. This restrains erroneous determination that there is an upward displacement anomaly at the time of a stuck-open anomaly. 
     &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 amount estimating process” corresponds to S 12  and S 12   a . The “upward displacement anomaly determining process” corresponds to S 14  and S 28  to S 34 . The “reference value” corresponds to the estimated exhaust temperature Texe. 
     [2] The “predetermined period” corresponds to the period that lasts for the time equal to the value obtained by multiplying the control cycle of the processes of  FIGS. 3 and 5  by the predetermined value C1th. 
     [3] Example 3 corresponds to the fact that the diagnosis executing condition of S 10  includes a condition that “the adding process is in an interrupted state”. 
     [4] The “air amount estimating process” corresponds to S 12   a.    
     [5] The “exhaust temperature estimating process” corresponds to M 26 . 
     [6] Example 6 corresponds to the fact that the diagnosis executing condition of S 10  includes a 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 invention 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 and the load. 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 a 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 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 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 Reference Value 
     For example, as will be described in the section “Regarding Exhaust System,” an exhaust temperature sensor may be arranged upstream of the oxidation catalyst  22 , and, in S 28 , a detected value obtained by the upstream exhaust temperature sensor may be used instead of the estimated exhaust temperature Texe. Specifically, in this case, the predetermined amount ΔTe may be set to the upper limit of the amount by which the downstream exhaust temperature exceeds the upstream exhaust temperature in a case without a stuck-open anomaly of the addition valve  26 . Alternatively, instead of the detected value of the upstream exhaust temperature sensor, an estimated upstream exhaust temperature based on the operating point of the engine  10  may be used to calculate the “reference value”. 
     Regarding Upward Displacement Anomaly Determining Process 
     In the above-described embodiments, it is determined that there is an upward displacement anomaly if the logical conjunction of the condition that the intake air amount Ga is greater than the estimated air amount Gae by a margin greater than or equal to the specified amount ΔGa and the condition that the amount by which the exhaust temperature Tex exceeds the estimated exhaust temperature Texe is smaller than or equal to the predetermined amount ΔTe remains true continuously for a predetermined period. However, the invention is not restricted to this. For example, it may be determined that there is an upward displacement 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 an upward displacement anomaly immediately after the logical conjunction becomes true. 
     Regarding Downward Displacement Anomaly Determining Process 
     In the above-described embodiments, it is determined that there is a downward displacement anomaly if the intake air amount Ga remains smaller than the estimated air amount Gae by a margin greater than or equal to the specified amount ΔGa2 continuously for a predetermined time. However, the invention is not restricted to this. For example, it may be determined that there is a downward displacement anomaly if the intake air amount Ga remains smaller than the estimated air amount Gae by a margin greater than or equal to the specified amount ΔGa2 continuously for a predetermined accumulated time or longer in a specified period. Alternatively, it may be determined that there is a downward displacement anomaly immediately after the intake air amount Ga becomes smaller than the estimated air amount Gae by a margin greater than or equal to the specified amount ΔGa2. 
     Regarding Diagnosis Executing Condition 
     Although the diagnosis executing condition of the first embodiment includes the condition that the adding process is in an interrupted state, the invention is not restricted to this. For example, exclusively for the downward displacement anomaly determining process, the diagnosis executing condition may include a condition that the adding process is in an interrupted state. Also, in the above-described embodiments, it is not essential to use, as a condition, the condition that the change amount ΔAf of the air-fuel ratio Af is smaller than or equal to the predetermined amount Δth. 
     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 . Alternatively, the air-fuel ratio sensor  56  may be arranged downstream of the addition valve  26  and upstream of 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 execution of the downward displacement anomaly determining process based on comparison between the estimated air amount Gae and the intake air amount Ga is not always necessary. Also, the adding process is not restricted to the PM regenerating process.