JP2010001846A - Abnormality diagnosis apparatus for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent wrong diagnosis in abnormality diagnosis when fuel having a different alcohol concentration is supplied in an internal combustion engine in which an alcohol-mixed fuel can be used. <P>SOLUTION: An alcohol concentration estimated at previous driving is stored in a backup RAM 39 of an ECU 38. Subsequently, engine control and abnormality diagnosis are performed using provisionally the stored value of the alcohol concentration estimated at the previous driving as an alcohol concentration at the current driving until driving conditions under which the alcohol concentration of fuel can be estimated is obtained after engine start. Then, at a time point when the alcohol concentration at the current driving estimated after the engine start is compared with the alcohol concentration at the previous driving stored in the backup RAM 39, thereby determining that the both are different from each other, processing data (for example, normal/abnormal determination results, data during abnormality diagnosis processing, and learning data) for abnormality diagnosis performed from the engine start to the time point is invalidated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides an internal combustion engine having a function of estimating the property (alcohol concentration or degree of heavy / lightness) of fuel supplied to the internal combustion engine based on the control state of the internal combustion engine that changes due to the influence of the property of the fuel. It is invention regarding the abnormality diagnosis apparatus of this.

In recent years, demands for automobiles equipped with engines (internal combustion engines) that can use gasoline, alcohol, and mixed fuels of both as fuels have increased due to social demands such as reducing CO ₂ emissions and using alternative fuels for oil. is doing. In such an automobile, when fuel with a different alcohol concentration from the previous time is supplied to the fuel tank, the alcohol concentration of the fuel in the fuel tank changes. Since the stoichiometric air-fuel ratio differs between gasoline and alcohol, if the alcohol concentration of the fuel changes, the stoichiometric air-fuel ratio of the fuel also changes. Therefore, it is necessary to change the fuel injection amount (actual air-fuel ratio) according to the alcohol concentration of the fuel. There is.

  Therefore, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2006-152990), an alcohol concentration sensor for detecting the alcohol concentration of the fuel is provided in the middle of the fuel passage from the fuel tank to the fuel injection valve. There is.

  However, since an increase in cost is inevitable if an alcohol concentration sensor is provided, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2007-9903) and Patent Document 3 (Japanese Patent Laid-Open No. 2005-2005) are required to satisfy the demand for cost reduction. 48625), Patent Document 4 (Japanese Patent Laid-Open No. 2008-14160), and the like, the control state of air-fuel ratio feedback control that changes under the influence of the alcohol concentration of the fuel (for example, the air-fuel ratio feedback correction amount, Burned in the internal combustion engine based on any one of air-fuel ratio deviation, ratio of target air-fuel ratio to actual air-fuel ratio, etc.) fuel pressure increase speed at start-up, combustion stability (engine rotation fluctuation), engine torque, etc. There is one that estimates the alcohol concentration of the fuel.

Further, in recent engine control systems that have become electronically controlled, as described in Patent Document 5 (Japanese Patent Laid-Open No. 2008-38785), fuel system abnormality diagnosis, catalyst deterioration diagnosis, and air-fuel ratio control system abnormality A self-diagnosis function for performing various abnormality diagnosis such as diagnosis and combustion state diagnosis (detection of misfire, etc.) is installed.
JP 2006-152990 A JP 2007-9903 A JP-A-2005-48625 Japanese Patent Laid-Open No. 2008-14160 JP 2008-38785 A

However, when the self-diagnosis function as disclosed in Patent Document 5 is mounted on a vehicle equipped with an alcohol concentration estimation apparatus as described in Patent Documents 2 to 4, the following problem occurs.
The fuel system abnormality diagnosis, catalyst deterioration diagnosis, air-fuel ratio control system abnormality diagnosis, combustion state diagnosis, etc. are all parameters that change under the influence of the alcohol concentration of the fuel (for example, excess air ratio = actual air-fuel ratio / theoretical sky). In order to perform each abnormality diagnosis, information on the alcohol concentration of the fuel is required. However, after the internal combustion engine is started, it takes some time until the fuel alcohol concentration can be estimated, so the alcohol concentration of the fuel cannot be estimated for a while after the internal combustion engine is started. For example, when the alcohol concentration of the fuel is estimated based on the control state of the air-fuel ratio feedback control (air-fuel ratio feedback correction amount, air-fuel ratio deviation amount, target air-fuel ratio and actual air-fuel ratio, etc.), the internal combustion engine is started. Thereafter, the alcohol concentration of the fuel cannot be estimated until the exhaust gas sensor (air-fuel ratio sensor, oxygen sensor, etc.) in the exhaust passage is activated and enters an operation state in which air-fuel ratio feedback control can be performed.

  Therefore, it is conceivable that the memory value of the alcohol concentration estimated during the previous operation is temporarily used as the alcohol concentration during the current operation until the operation state in which the alcohol concentration of the fuel can be estimated after the internal combustion engine is started. When the fuel tank is filled with fuel with a different alcohol concentration from the previous one and the alcohol concentration of the fuel in the fuel tank changes, each abnormality using the wrong alcohol concentration is made until the alcohol concentration can be estimated. Since diagnosis is performed, each abnormality diagnosis may be misdiagnosed. In addition to the case where fuels with different alcohol concentrations are supplied, such a problem is estimated by estimating the fuel heavyness (heavy / lightness) and considering the influence of the fuel heavyness. In the system that executes the abnormality diagnosis of the diagnosis target, the same problem occurs when fuels having different degrees of heavyness are supplied.

  The present invention has been made in consideration of these circumstances, and the object thereof is to prevent misdiagnosis of abnormality diagnosis when fuels having different fuel properties (alcohol concentration or severity) are supplied. An object of the present invention is to provide an internal combustion engine abnormality diagnosis device that can improve the reliability of abnormality diagnosis.

  In order to achieve the above object, the invention according to claim 1 is based on the control state of the internal combustion engine in which the property (alcohol concentration or severity) of the fuel supplied to the internal combustion engine is changed by the influence of the property of the fuel. In the abnormality diagnosis apparatus for an internal combustion engine that performs an abnormality diagnosis of a predetermined diagnosis object in consideration of the influence of the fuel property estimated by the fuel property estimation means, the fuel property estimation means A rewritable nonvolatile storage means for storing the estimated fuel property data is provided, and the fuel property at the time of the current operation estimated by the fuel property estimation means after starting the internal combustion engine is stored in the storage means. Processing data of the abnormality diagnosis (for example, normal / abnormal judgment result, abnormality diagnosis) performed from the time of starting to the time when it is found that they are different from the fuel property at the time Intermediate processing data is obtained by adapted to disabled for diagnostic prevention means erroneous learning data, etc.).

  In this configuration, when it is determined that the fuel property during the current operation, which is estimated after the fuel state can be estimated after the internal combustion engine is started, is different from the fuel property during the previous operation, the fuel tank has different properties. Therefore, it is possible to control that invalidity processing data from the start to the time is invalidated, so that when a fuel with a different property is supplied, Misdiagnosis can be prevented and the reliability of abnormality diagnosis can be improved.

  In this case, as in claim 2, the fuel property estimation means controls air-fuel ratio feedback control executed based on the output of an exhaust gas sensor (air-fuel ratio sensor, oxygen sensor, etc.) installed in the exhaust passage of the internal combustion engine. Means for estimating the fuel property based on the state, and the previous operation stored in the storage means until the exhaust gas sensor is activated after the internal combustion engine is started and the air-fuel ratio feedback control can be executed. It is good also as a structure provided with the means to use a fuel property temporarily as a fuel property at the time of this driving | operation. In this way, if fuel of a different property is not refueled while the vehicle is stopped, the previous fuel property is the same as that of the current operation, even before the fuel state can be estimated after the internal combustion engine is started. Abnormality diagnosis can be performed at an early stage by using fuel property storage data during operation, and both early execution of abnormality diagnosis and prevention of erroneous diagnosis can be achieved.

  By the way, when fuel with a different property from the previous fuel is supplied to the fuel tank, after the internal combustion engine is started, the fuel before refueling remaining in the fuel passage from the fuel tank to the fuel injection valve at first is the fuel injection valve. Until all of the unfueled fuel remaining in the fuel passage is consumed and the fuel after fueling in the fuel tank reaches the fuel injection valve through the fuel passage. Since the subsequent fuel is not injected from the fuel injection valve, the fuel property after refueling cannot be estimated.

  Since it takes some time for the fuel property estimation execution condition to be satisfied after the start, the fuel before refueling remaining in the fuel passage before the fuel property estimation execution condition is satisfied after the start. If all of the fuel is consumed, the property of the fuel after refueling can be estimated at the time when the fuel property estimation execution condition is satisfied. However, if the pre-refueling fuel still remains in the fuel passage when the fuel property estimation execution condition is satisfied after starting, the pre-refueling fuel is injected from the fuel injection valve for a while. As a result, the property of the fuel before refueling is estimated.

  As a countermeasure, it is preferable that the estimation of the fuel property is prohibited until a predetermined period has elapsed after the internal combustion engine is started. In this way, it is possible to perform control that prohibits estimation of the fuel property for a while until all of the fuel before refueling remaining in the fuel passage is consumed after the internal combustion engine is started. In this case, it is possible to reliably estimate the properties of the fuel after refueling.

  In this case, the predetermined period is substantially the same or slightly longer in consideration of the time required for all the fuel remaining in the fuel passage from the fuel tank to the fuel injection valve to be injected or the integrated value of the fuel injection amount. What is necessary is just to set to a period. Thereby, a predetermined period can be set to an appropriate period.

  In the present invention, as in claim 5, the alcohol concentration of the fuel may be estimated by the fuel property estimating means, or the heavyness of the fuel may be estimated.

Hereinafter, an embodiment embodying the best mode for carrying out the present invention will be described.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 16 whose opening is adjusted by a motor 15 and a throttle opening sensor 17 for detecting the opening (throttle opening) of the throttle valve 16 are provided on the downstream side of the air flow meter 14.

  Further, a surge tank 18 is provided on the downstream side of the throttle valve 16, and an intake manifold 20 for introducing air into each cylinder of the engine 11 is provided in the surge tank 18. A fuel injection valve 21 for injecting fuel is attached in the vicinity of the intake port of the intake manifold 20 of each cylinder. An ignition plug 22 is attached to the cylinder head of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of the ignition plug 22 of each cylinder.

  On the other hand, the exhaust pipe 23 of the engine 11 is provided with an exhaust gas sensor 24 (air-fuel ratio sensor, oxygen sensor, etc.) for detecting the air-fuel ratio or rich / lean of the exhaust gas. A catalyst 25 such as a three-way catalyst for purifying gas is provided.

  A cooling water temperature sensor 26 that detects the cooling water temperature and a knock sensor 29 that detects knocking are attached to the cylinder block of the engine 11. A crank angle sensor 28 that outputs a pulse signal every time the crankshaft 27 rotates by a predetermined crank angle is attached to the outer peripheral side of the crankshaft 27. Based on the output signal of the crank angle sensor 28, the crank angle and engine The rotation speed is detected.

  The engine 11 can use any of gasoline, alcohol such as ethanol and methanol, and alcohol mixed fuel obtained by mixing alcohol with gasoline as fuel, and any of these gasoline, alcohol, and alcohol mixed fuel can be used in the fuel tank 30. To refuel. A fuel pump 31 that pumps up fuel is provided in the fuel tank 30. The fuel discharged from the fuel pump 31 is sent to the delivery pipe 33 through the fuel pipe 32 and is distributed from the delivery pipe 33 to the fuel injection valve 21 of each cylinder. A fuel filter 34 and a pressure regulator 35 are connected in the vicinity of the fuel pump 31 in the fuel pipe 32, and the discharge pressure of the fuel pump 31 is regulated to a predetermined pressure by the pressure regulator 35, and surplus fuel exceeding that pressure The minute amount is returned into the fuel tank 30 by the fuel return pipe 36.

  Outputs of various sensors such as the exhaust gas sensor 24 described above are input to a control circuit (hereinafter referred to as “ECU”) 38. The ECU 38 is mainly composed of a microcomputer, and executes an air-fuel ratio feedback control program (not shown) stored in a built-in ROM (storage medium), so that the air-fuel ratio is based on the output of the exhaust gas sensor 24. The (fuel injection amount) is feedback controlled to the target air-fuel ratio.

  At that time, considering that there is a relationship that the higher the alcohol concentration of the fuel, the lower the theoretical air-fuel ratio of the fuel, and the more fuel injection amount is required to control the actual air-fuel ratio to the theoretical air-fuel ratio. The ECU 38 controls the engine 11 based on the control state of the air-fuel ratio feedback control (for example, the air-fuel ratio feedback correction amount, the air-fuel ratio deviation amount, the ratio between the target air-fuel ratio and the actual air-fuel ratio) that changes due to the alcohol concentration of the fuel. The alcohol concentration of the fuel burned in the fuel is estimated, and the fuel injection amount is corrected to be increased according to the alcohol concentration of the fuel so that the fuel injection amount increases as the estimated alcohol concentration of the fuel increases. The function of the ECU 38 for estimating the alcohol concentration corresponds to fuel property estimating means in the claims.

  The method for estimating the alcohol concentration of the fuel is not limited to the control state of the air-fuel ratio feedback control, but also based on any of the fuel pressure rise speed at the time of start-up, combustion stability (engine rotation fluctuation), engine torque, etc. The concentration may be estimated. In short, the alcohol concentration of the fuel may be estimated based on the control state of the internal combustion engine that changes due to the influence of the alcohol concentration of the fuel.

  The ECU 38 also has various abnormality diagnosis programs (not shown) for performing various abnormality diagnosis such as fuel system abnormality diagnosis, catalyst deterioration diagnosis, air-fuel ratio control system abnormality diagnosis, combustion state diagnosis (detection of misfire, etc.). Execute. Each abnormality diagnosis process is performed using parameters that change under the influence of the alcohol concentration of the fuel (for example, excess air ratio = actual air / fuel ratio / theoretical air / fuel ratio, engine rotation fluctuation, etc.). Accordingly, an abnormality determination threshold value for each abnormality diagnosis is set and each abnormality diagnosis process is executed.

  By the way, when estimating the alcohol concentration of fuel based on the control state of air-fuel ratio feedback control (air-fuel ratio feedback correction amount, air-fuel ratio deviation amount, target air-fuel ratio and actual air-fuel ratio, etc.) Until the exhaust gas sensor 21 is activated and enters an operation state in which air-fuel ratio feedback control can be executed, the alcohol concentration estimation execution condition is not satisfied, and the alcohol concentration of the fuel cannot be estimated.

  Therefore, in this embodiment, the alcohol concentration estimated during engine operation is stored in a rewritable nonvolatile memory such as a backup RAM 39 of the ECU 38 (a rewritable nonvolatile storage means for retaining stored data even when the engine is stopped). The stored alcohol concentration value estimated during the previous operation is temporarily set to the alcohol used during the current operation until the operation state where the alcohol concentration of the fuel can be estimated after the engine is started (the operation state where the alcohol concentration estimation execution condition is satisfied). It is used as a concentration to execute engine control and abnormality diagnosis. As a result, if fuel with a different alcohol concentration is not refueled while the vehicle is stopped, the alcohol in the previous operation, which has the same alcohol concentration as the current operation, even before the operation state is reached after the engine is started Abnormality diagnosis can be performed at an early stage using stored data of concentration, and both early execution of abnormality diagnosis and prevention of misdiagnosis can be achieved.

  However, if the fuel tank 30 is supplied with fuel having a different alcohol concentration from the previous time and the alcohol concentration of the fuel in the fuel tank 30 changes, the incorrect alcohol concentration is set until the alcohol concentration can be estimated. Since each abnormality diagnosis is performed by using this, each abnormality diagnosis may be erroneously diagnosed.

  As a countermeasure, in this embodiment, the ECU 38 executes the misdiagnosis prevention program shown in FIG. 2 to store the alcohol concentration during the current operation estimated after the engine is started in a rewritable nonvolatile memory such as the backup RAM 39. When it is found that the two are different from the alcohol concentration in the previous operation, abnormality diagnosis processing data (for example, normal / abnormal determination result, abnormality diagnosis processing) executed from the time of engine start to that point is determined. Invalidate (reset) intermediate data, learning data, etc.).

  Hereinafter, processing contents of the misdiagnosis prevention program of FIG. 2 will be described. This program is repeatedly executed at a predetermined cycle while the ignition switch is turned on (during the power-on period of the ECU 38), and serves as a false diagnosis prevention means in the claims.

  When this program is started, first, at step 101, it is determined whether or not the exhaust gas sensor 21 has been activated and has reached an operation state in which the alcohol concentration of fuel can be estimated (an operation state in which the alcohol concentration estimation execution condition is satisfied). If the operating state is not yet able to estimate the alcohol concentration, the program is terminated without performing the subsequent processing.

  On the other hand, if it is determined in step 101 that the alcohol concentration can be estimated, the process proceeds to step 102 to determine whether or not the alcohol concentration during the current operation is estimated. If the alcohol concentration is estimated, the program is terminated without performing the subsequent processing.

  If it is determined in step 102 that the alcohol concentration during the current operation is not estimated, the process proceeds to step 103, where the control state of the air-fuel ratio feedback control (air-fuel ratio feedback correction amount, air-fuel ratio deviation amount, target air-fuel ratio and actual The alcohol concentration of the fuel is estimated based on the ratio to the air-fuel ratio. Thereafter, the process proceeds to step 104, and the alcohol concentration at the previous operation stored in the rewritable nonvolatile memory such as the backup RAM 39 is read.

  Thereafter, the process proceeds to step 105, in which the alcohol concentration during the current operation is compared with the alcohol concentration during the previous operation to determine whether or not the two alcohol concentrations are different, and it is determined that both alcohol concentrations are the same. If this is the case, the program is terminated.

  On the other hand, if it is determined in step 105 above that the alcohol concentration during the current operation is different from the alcohol concentration during the previous operation, it is determined that fuel with a different alcohol concentration has been supplied, and the process proceeds to step 106 to proceed to the engine. Invalidate (reset) the processing data of the abnormality diagnosis executed from the start to that point. At this time, for example, normal / abnormal determination results, data in the middle of abnormality diagnosis processing (RAM value, flag, abnormality counter, etc.), learning data, etc. are invalidated (reset).

  In the present embodiment described above, when it is determined that the alcohol concentration in the current operation estimated after the engine is in an operating state in which the alcohol concentration of the fuel can be estimated after the engine is started is different from the alcohol concentration in the previous operation. When it is determined that fuel with different alcohol concentrations has been supplied to the tank 30 and the processing data of the abnormality diagnosis executed from the time of engine start until that time is invalidated, so fuel with different alcohol concentrations is supplied In addition, erroneous diagnosis of abnormality diagnosis can be prevented, and reliability of abnormality diagnosis can be improved.

  By the way, when the fuel tank 30 is supplied with fuel having a different alcohol concentration from the previous time and the alcohol concentration of the fuel in the fuel tank 30 changes, the fuel from the fuel tank 30 to the fuel injection valve 21 is initially after the engine is started. The fuel before refueling remaining in the passage (fuel pipe 32 and delivery pipe 33) is supplied to the fuel injection valve 21 and injected, and then all the fuel before refueling remaining in the fuel passage is consumed, Since the fuel after refueling in the fuel tank 30 (the fuel whose alcohol concentration has changed due to refueling) reaches the fuel injection valve 21 through the fuel passage, the fuel after refueling is not injected from the fuel injection valve 21. The alcohol concentration of the later fuel cannot be estimated.

  It takes some time for the alcohol concentration estimation execution condition to be satisfied after the engine is started. Therefore, before refueling before the fuel concentration estimation execution condition is satisfied after the engine is started, If all the fuel is consumed, there is no problem because the alcohol concentration of the fuel after refueling can be estimated at the time when the operation state where the alcohol concentration estimation execution condition is satisfied is reached. However, when the pre-refueling fuel still remains in the fuel passage when the alcohol concentration estimation execution condition is satisfied after the engine is started, the pre-refueling fuel is injected from the fuel injection valve 21 for a while. Therefore, the alcohol concentration of the fuel before refueling is estimated.

  As a countermeasure against this, in another embodiment of the present invention, the misdiagnosis prevention program of FIG. 3 is executed until all the fuel remaining in the fuel passage after the engine is started is injected from the fuel injection valve 21. Until the period has passed, the estimation of alcohol concentration is prohibited. The period during which the estimation of the alcohol concentration is prohibited may be set by the elapsed time after engine start in consideration of the volume (fuel amount) of the fuel passage, or by the fuel injection amount integrated value after engine start. Also good.

  The misdiagnosis prevention program of FIG. 3 is obtained by adding the processing of step 100 just before step 101 of the misdiagnosis prevention program of FIG. 2, and the other processes of steps 101 to 106 are the misdiagnosis prevention program of FIG. Is the same.

  The misdiagnosis prevention program shown in FIG. 3 is repeatedly executed at a predetermined cycle during the ignition switch on period (during the power-on period of the ECU 38), and serves as a misdiagnosis prevention means in the claims.

  When this program is started, first, at step 100, it is determined whether or not the elapsed time (or fuel injection amount integrated value) after engine startup has exceeded a predetermined value. Here, the predetermined value is substantially the same or slightly larger in consideration of the time required for all the fuel remaining in the fuel passage to be injected from the fuel injection valve 21 or the integrated value of the fuel injection amount. Is set. If it is determined in step 100 that the elapsed time (or fuel injection amount integrated value) after engine startup does not exceed the predetermined value, this program is terminated without performing the subsequent processing.

  On the other hand, if it is determined in step 100 that the elapsed time (or fuel injection amount integrated value) after starting the engine has exceeded a predetermined value, the processing after step 101 is executed, and the erroneous diagnosis in FIG. The same process as the prevention program is performed, and when it becomes clear that the alcohol concentration during the current operation, which is estimated after the engine is in an operating state in which the alcohol concentration of the fuel can be estimated after starting the engine, is different from the alcohol concentration during the previous operation, It is determined that fuels with different alcohol concentrations have been supplied to the fuel tank 30, and the abnormality diagnosis processing data executed from the time of engine startup until that time is invalidated.

  In the other embodiments described above, the estimation of the alcohol concentration is prohibited until the period until all the fuel remaining in the fuel passage is injected from the fuel injection valve 21 has elapsed. In this case, it is possible to reliably estimate the properties of the fuel after refueling.

  In each of the above-described embodiments, the alcohol concentration of the fuel is estimated. However, the fuel heavyness may be estimated. In this case, the fuel severity during the current operation estimated after the engine has started is different from the fuel operation during the previous operation stored in a rewritable nonvolatile memory such as the backup RAM 39. When it becomes clear, it is sufficient to invalidate the processing data of the abnormality diagnosis executed from the start to the time.

  In addition, the present invention is not limited to the intake port injection type engine as shown in FIG. 1, but includes an in-cylinder injection type engine, and both an intake port injection fuel injection valve and an in-cylinder injection fuel injection valve. It can also be applied to dual-injection engines.

It is a schematic block diagram of the whole engine control system in one Example of this invention. It is a flowchart which shows the flow of a process of the misdiagnosis prevention program of one Example. It is a flowchart which shows the flow of a process of the misdiagnosis prevention program of another Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 14 ... Air flow meter, 15 ... Motor, 16 ... Throttle valve, 17 ... Throttle opening sensor, 21 ... Fuel injection valve, 22 ... Spark plug, 23 ... Exhaust pipe, 24 ... exhaust gas sensor, 25 ... catalyst, 28 ... crank angle sensor, 30 ... fuel tank, 31 ... fuel pump, 34 ... fuel filter, 35 ... pressure regulator, 38 ... ECU (fuel property estimation means, erroneous diagnosis prevention means), 39 ... Backup RAM (rewritable nonvolatile storage means)

Claims (5)

Fuel property estimation means for estimating the property of fuel supplied to the internal combustion engine based on the control state of the internal combustion engine that changes due to the influence of the fuel property, taking into account the influence of the fuel property estimated by the fuel property estimation means In the abnormality diagnosis device for an internal combustion engine that performs abnormality diagnosis of a predetermined diagnosis object,
A rewritable nonvolatile storage means for storing fuel property data estimated by the fuel property estimation means;
Compared with the fuel property at the previous operation stored in the storage means, the fuel property at the current operation estimated by the fuel property estimating means after the internal combustion engine is started is found to be different from the time of starting. An abnormality diagnosis apparatus for an internal combustion engine, comprising: an erroneous diagnosis prevention unit that invalidates the processing data of the abnormality diagnosis executed up to that point.   The fuel property estimation means includes means for estimating fuel property based on a control state of air-fuel ratio feedback control executed based on an output of an exhaust gas sensor installed in an exhaust passage of the internal combustion engine, and the exhaust after the internal combustion engine is started. Means for tentatively using the fuel property at the previous operation stored in the storage means as the fuel property at the current operation until the gas sensor is activated and enters an operation state in which the air-fuel ratio feedback control can be executed. The abnormality diagnosis device for an internal combustion engine according to claim 1, wherein the abnormality diagnosis device is provided.   3. The abnormality diagnosis device for an internal combustion engine according to claim 1, wherein the fuel property estimation means includes means for prohibiting estimation of the fuel property until a predetermined period elapses after the internal combustion engine is started.   The predetermined period is set in consideration of a time required for all the fuel remaining in the fuel passage from the fuel tank to the fuel injection valve to be injected or an integrated value of the fuel injection amount. Item 6. An abnormality diagnosis device for an internal combustion engine according to Item 3.   5. The abnormality diagnosis device for an internal combustion engine according to claim 1, wherein the fuel property estimation means estimates an alcohol concentration of the fuel.

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