Diagnostic device and diagnostic method for internal combustion engine

Abstract

A diagnostic device and method for an internal combustion engine. An electronic control unit (ECU) diagnoses whether an internal combustion engine has a misfire abnormality based on the misfire frequency of an internal combustion engine that performs fuel cut-off on a specific cylinder, where combustion in a portion of the cylinders is stopped and combustion continues in the remaining cylinders. Furthermore, the ECU performs the following normal recovery diagnostic process: when a misfire abnormality is diagnosed, if the measured value of the misfire frequency falls below a predetermined normal recovery judgment value, the misfire abnormality is diagnosed as eliminated. The normal recovery diagnostic process is configured such that the diagnosis of elimination of the misfire abnormality is not performed during the period of specific cylinder fuel cut-off.

Description

Technical Field

[0001] This disclosure relates to diagnostic devices and methods for internal combustion engines. Background Technology

[0002] In internal combustion engines such as vehicle-mounted internal combustion engines, an increased frequency of misfires, known as misfire anomalies, sometimes occurs due to abnormalities in the fuel system, ignition system, etc. Japanese Patent Application Publication No. 2001-271701 describes a diagnostic device that detects misfires based on rotational variations in the internal combustion engine caused by misfires, and determines a misfire anomaly when the detected frequency of misfires exceeds a certain level. Summary of the Invention

[0003] The problem that the invention aims to solve

[0004] However, there is a situation where, even if a fire anomaly occurs, the anomaly is only temporary and will disappear naturally afterward. Therefore, in diagnostic devices like those described above, sometimes, after a fire anomaly has been identified and the frequency of fires has decreased, a normal recovery determination is made indicating that the fire anomaly has been eliminated.

[0005] On the other hand, in internal combustion engines, sometimes fuel cut-off is implemented for specific cylinders where combustion in a portion of the cylinders stops while combustion continues in the remaining cylinders. In the cylinders where combustion is stopped under such specific fuel cut-off, no misfire occurs because no combustion takes place. Therefore, even if a potential misfire anomaly exists in the cylinder where combustion is stopped, the misfire that should have occurred will not occur during the period of specific cylinder fuel cut-off. Thus, in diagnostic devices like those described above, even if a potential misfire anomaly persists in a portion of the cylinders during the period of specific cylinder fuel cut-off in an internal combustion engine, it is possible to mistakenly determine that the misfire frequency has decreased and the misfire anomaly has been eliminated.

[0006] Technical solutions for solving the problem

[0007] To address the aforementioned issues, a diagnostic device for an internal combustion engine is provided according to a technical solution of this disclosure. The internal combustion engine is configured to perform fuel cutoff on specific cylinders, stopping combustion in a portion of the cylinders and allowing combustion to continue in the remaining cylinders. The diagnostic device is configured to perform the following processes: a misfire anomaly diagnostic process, diagnosing whether the internal combustion engine has a misfire anomaly based on its misfire frequency; and a normal recovery diagnostic process, diagnosing that the misfire anomaly has been eliminated if, when the misfire anomaly is diagnosed, the measured value of the misfire frequency falls below a predetermined normal recovery judgment value. The normal recovery diagnostic process is configured to not perform the diagnosis that the misfire anomaly has been eliminated during the period when the fuel cutoff on the specific cylinder is performed.

[0008] To address the aforementioned issues, according to another technical solution of this disclosure, a diagnostic device for an internal combustion engine is provided. The internal combustion engine is configured to perform fuel cutoff on a specific cylinder, stopping combustion in a portion of the cylinders and allowing combustion to continue in the remaining cylinders. The diagnostic device is configured to perform the following processes: misfire anomaly diagnostic processing, diagnosing whether the internal combustion engine has a misfire anomaly based on its misfire frequency; normal recovery diagnostic processing, diagnosing that the misfire anomaly has been eliminated if the measured value of the misfire frequency falls below a predetermined normal recovery judgment value when the misfire anomaly is diagnosed; and storage processing, storing the operating state of the internal combustion engine at the time the misfire anomaly was diagnosed. The normal recovery diagnostic processing is configured to not perform the diagnosis that the misfire anomaly has been eliminated if the operating state of the internal combustion engine stored in the storage processing is inconsistent with the current operating state of the internal combustion engine. The operating state of the internal combustion engine stored in the storage processing includes whether or not the specific cylinder fuel cutoff has been implemented.

[0009] To address the aforementioned issues, according to another technical solution of this disclosure, a diagnostic method for an internal combustion engine is provided. The internal combustion engine is configured to perform fuel cutoff on specific cylinders, stopping combustion in a portion of the cylinders while continuing combustion in the remaining cylinders. The diagnostic method comprises: diagnosing whether the internal combustion engine has a misfire abnormality based on the misfire frequency; and, when the misfire abnormality is diagnosed, diagnosing that the misfire abnormality has been eliminated if the measured value of the misfire frequency falls below a predetermined normal recovery threshold. In this diagnostic method, the diagnosis of elimination of the misfire abnormality is not performed during the implementation of the fuel cutoff on the specific cylinders. Attached Figure Description

[0010] Figure 1 This is a schematic diagram showing the configuration of a first embodiment of a diagnostic device for an internal combustion engine.

[0011] Figure 2 This is a flowchart of the fire fault diagnosis routine executed by the diagnostic device of the first embodiment.

[0012] Figure 3 This is a flowchart of the normal recovery diagnostic routine executed by the diagnostic device of the first embodiment.

[0013] Figure 4 This is a flowchart of a misfire anomaly diagnosis routine executed in the second embodiment of the diagnostic device for an internal combustion engine.

[0014] Figure 5 This is a flowchart of the normal recovery diagnostic routine executed by the diagnostic device of the second embodiment. Detailed Implementation

[0015] (First Embodiment)

[0016] The following is for reference Figures 1-3 The first embodiment of the diagnostic device for an internal combustion engine will be described in detail.

[0017] <Composition of Diagnostic Devices>

[0018] First, refer to Figure 1 The configuration of the diagnostic device in this embodiment will be described.

[0019] like Figure 1 As shown, the internal combustion engine 10 using the diagnostic device of this embodiment has a plurality of cylinders 11. In the internal combustion engine 10, each cylinder 11 is provided with: an injector 12 for injecting fuel that is burned in the cylinder 11; and an ignition device 13 for igniting the fuel introduced into the cylinder 11. Additionally, the internal combustion engine 10 is provided with a throttle valve 14 for adjusting the amount of intake air flowing into each cylinder 11. Each cylinder 11 of the internal combustion engine 10 is individually labeled with a cylinder number.

[0020] The internal combustion engine 10 is controlled by an electronic control unit 20. The electronic control unit 20 includes a processing unit 21 for performing operations to control the internal combustion engine 10, and a storage unit 22 for storing control programs and data. Various sensors for monitoring the operating status of the internal combustion engine 10 are connected to the electronic control unit 20. These sensors include an air flow meter 23, a crankshaft angle sensor 24, and a coolant temperature sensor 25. The air flow meter 23 detects the intake air volume of the internal combustion engine 10. The crankshaft angle sensor 24 detects the rotational phase of the crankshaft, which serves as the output shaft of the internal combustion engine 10. The coolant temperature sensor 25 detects the temperature of the coolant in the internal combustion engine 10. The electronic control unit 20 controls the internal combustion engine 10 based on the sensor readings. The control of the internal combustion engine 10 is achieved through controlling the fuel injection quantity of the injector 12, controlling the ignition timing of the ignition device 13, and controlling the opening of the throttle valve 14. Furthermore, the electronic control unit 20 is connected to a warning light 26 for notifying the driver of the occurrence of a fire malfunction in the event of a fire malfunction.

[0021] <Specific cylinder fuel cut-off>

[0022] The electronic control unit 20 implements specific cylinder fuel cutoff as part of the control of the internal combustion engine 10. Specific cylinder fuel cutoff involves stopping combustion in a portion of the cylinders 11 of the internal combustion engine 10 while continuing combustion in the remaining cylinders 11. During specific cylinder fuel cutoff, the electronic control unit 20 stops fuel injection from the injector 12 and ignition from the ignition device 13 in the cylinder 11 where combustion has stopped. Alternatively, ignition can continue in the cylinder 11 where combustion has stopped, allowing unburned fuel remaining in the cylinder 11 to burn.

[0023] When fuel is cut off in a specific cylinder, fresh air is discharged directly from the cylinder 11 where combustion has stopped to the exhaust passage. Therefore, even if lean combustion does not occur in the remaining cylinder 11 where combustion continues, exhaust can still be leaned.

[0024] Specific cylinder fuel cutoff is performed for, for example, the following purpose. Sometimes, filters that capture particulate matter (PM) from exhaust gas are installed in the exhaust passage of the internal combustion engine 10. Such filters can become clogged as PM buildup progresses. PM accumulated in the filter can be purified by combustion by supplying oxygen to the filter through exhaust gas leaning. However, when lean combustion occurs in each cylinder 11 to lean the exhaust gas, the NOx emissions from the internal combustion engine 10 increase. In contrast, when specific cylinder fuel cutoff is implemented, fresh air is discharged directly from the cylinder 11 where combustion has ceased. Therefore, if specific cylinder fuel cutoff is implemented, exhaust gas can be leaned even if lean combustion is not performed in the remaining cylinders 11 where combustion continues. In this way, specific cylinder fuel cutoff can be implemented to remove PM accumulated in the filter while suppressing emissions deterioration.

[0025] <Diagnosis and Management of Fire-Related Anomalies>

[0026] In the internal combustion engine 10, misfires can occur frequently due to malfunctions in the injector 12, ignition device 13, etc. The electronic control unit 20 performs misfire diagnosis processing in parallel with the control of the internal combustion engine 10 to diagnose the presence or absence of misfires. In this embodiment, the electronic control unit 20 corresponds to a diagnostic device. The electronic control unit 20 performs misfire diagnosis individually for each of the multiple misfire determination zones defined based on the engine speed, load, and preheating state of the internal combustion engine 10.

[0027] Figure 2 A flowchart is shown of the misfire anomaly diagnosis routine executed by the electronic control unit 20 for misfire anomaly diagnosis processing. The electronic control unit 20 repeatedly executes this routine at predetermined control cycles during the operation of the internal combustion engine 10.

[0028] When this routine begins, the electronic control unit 20 first performs a misfire frequency measurement in step S100. Here, the number of misfires that occur during a predetermined number of combustion cycles is defined as the misfire frequency.

[0029] The electronic control unit 20 measures the misfire frequency as follows. The internal combustion engine 10 maintains rotation using the torque generated by combustion in each cylinder 11. When a misfire occurs, torque generation is temporarily interrupted, resulting in rotational fluctuations in the internal combustion engine 10. The electronic control unit 20 determines whether a misfire caused by rotational fluctuations has occurred during each combustion cycle of the internal combustion engine 10 based on the detection signal from the crankshaft angle sensor 24. Furthermore, the electronic control unit 20 calculates the number of misfire determinations per predetermined number of combustion cycles as the measured value of the misfire frequency.

[0030] After measuring the fire frequency, the electronic control unit 20 determines in the next step S110 whether the fire frequency exceeds a predetermined fire exceedance threshold. If the fire frequency exceeds the fire exceedance threshold (yes), the electronic control unit 20 proceeds to step S120. On the other hand, if the fire frequency is below the fire exceedance threshold (no), the electronic control unit 20 terminates the processing of this routine for the current control cycle.

[0031] When the process proceeds to step S120, the electronic control unit 20 increments the value of the number of misfires exceeding N in step S120. The number of misfires exceeding N represents the number of times the misfire frequency exceeds the misfire exceeding judgment value during this trip. More specifically, the number of misfires exceeding N is set separately for each misfire judgment zone. Furthermore, in step S120, the electronic control unit 20 increments the value of the number of misfires exceeding N for the misfire judgment zone corresponding to the current operating state of the internal combustion engine 10. At the end of the trip, the electronic control unit 20 resets the value of the number of misfires exceeding N for each misfire judgment zone to "0".

[0032] Next, in step S130, the electronic control unit 20 determines whether the value of the number of fires exceeding the threshold N, which was incremented in step S120, is above or equal to a predetermined fire anomaly determination value. If the number of fires exceeding the threshold N is above (yes), the electronic control unit 20 proceeds to step S140. Conversely, if the number of fires exceeding the threshold N is below (no), the processing of this routine for the current control cycle ends.

[0033] When the process proceeds to step S140, the electronic control unit 20 sets a fire malfunction flag in step S140. The fire malfunction flag is a flag indicating whether a fire malfunction has occurred. That is, the electronic control unit 20 sets the fire malfunction flag when a fire malfunction is diagnosed. The state of the fire malfunction flag is maintained after the process ends and is inherited by the next process.

[0034] Next, in step S150, the electronic control unit 20 stores the current operating state of the internal combustion engine 10. Specifically, the electronic control unit 20 stores the misfire determination zone corresponding to the current operating state of the internal combustion engine 10. Then, in step S160, after illuminating the warning light 26, the electronic control unit 20 ends the processing of this routine for the current control cycle.

[0035] As described above, a misfire anomaly flag is set separately for each misfire detection zone. Therefore, it is clear which misfire detection zone the flag belongs to simply by observing which zone it belongs to. Thus, in practice, the electronic control unit 20 performs steps S140 and S150 by setting misfire anomaly flags for the misfire detection zones corresponding to the current operating state of the internal combustion engine 10.

[0036] <Normal Recovery Diagnosis and Treatment>

[0037] Sometimes, the fire anomalies described above are only temporary and will naturally disappear over time. Next, the diagnostic procedures for normal recovery from a fire anomaly will be explained.

[0038] Figure 3 A flowchart is shown of the normal recovery diagnostic routine executed by the electronic control unit 20 for normal recovery diagnostic processing. The electronic control unit 20 repeatedly executes this routine at predetermined control cycles during the operation of the internal combustion engine 10. Figure 3 In subsequent diagrams, "F / C" indicates fuel cut.

[0039] When this routine begins, the electronic control unit 20 first determines in step S200 whether a fire alarm flag has been set. Then, if the fire alarm flag has been set (yes), the electronic control unit 20 proceeds to step S210; otherwise, it terminates the processing of this routine for the current control cycle.

[0040] When the process proceeds to step S210, the electronic control unit 20 determines whether the current operating state of the internal combustion engine 10 is the same as when the misfire alarm was set. More specifically, in step S210, the electronic control unit 20 determines whether the current operating state of the internal combustion engine 10 is the same as when the misfire alarm was set. Figure 2Is the operating state stored in step S150 consistent with the current operating state? Figure 2 In step S150, the misfire determination areas for which misfire anomaly flags are set are stored. Therefore, in step S210, it is determined whether the misfire determination area corresponding to the current operating state of the internal combustion engine 10 is the same as the misfire determination area when the misfire anomaly flag was set. Furthermore, if the operating state belongs to the same misfire determination area as when the misfire anomaly flag was set (yes), the electronic control unit 20 proceeds to step S220. Otherwise, if the operating state does not belong to the same misfire determination area as when the misfire anomaly flag was set (no), the electronic control unit 20 terminates the processing of this routine for the current control cycle. As described above, a misfire anomaly flag is set separately for each misfire determination area. Therefore, by simply confirming the state of the misfire anomaly flag in the misfire determination area corresponding to the current operating state of the internal combustion engine 10, the determinations in steps S200 and S210 can be performed simultaneously.

[0041] If the process proceeds to step S220, the electronic control unit 20 determines in step S220 whether a specific cylinder fuel cutoff is being implemented. If a specific cylinder fuel cutoff is being implemented (yes), the electronic control unit 20 terminates the processing of this routine for the current control cycle. On the other hand, if a specific cylinder fuel cutoff is not being implemented (no), the electronic control unit 20 proceeds to step S230.

[0042] If the process has entered step S230, the electronic control unit 20, in step S230, communicates with... Figure 2 Step S100 similarly performs the measurement of the fire frequency. Next, in step S240, the electronic control unit 20 determines whether the measured fire frequency is below a predetermined normal recovery determination value. The normal recovery determination value is set to a positive value indicating that the fire frequency exceeds the determination value. If the fire frequency is below the normal recovery determination value (yes), the electronic control unit 20 proceeds to step S250. On the other hand, if the fire frequency exceeds the normal recovery determination value (no), the processing of this routine in the current control cycle ends.

[0043] When the process proceeds to step S250, the electronic control unit 20 clears the misfire abnormality flag for the misfire determination zone corresponding to the current operating state of the internal combustion engine 10. That is, it diagnoses that the misfire abnormality has been eliminated. Then, the electronic control unit 20 ends the processing of this routine for the current control cycle. With the misfire abnormality flags for all misfire determination zones cleared, the electronic control unit 20 turns off the warning light 26.

[0044] <Effects of the first implementation method>

[0045] The function and effects of this implementation method are explained.

[0046] The electronic control unit 20 counts the number of times the measured fire frequency exceeds the fire alarm threshold after the start of the trip as the number of fire alarms exceeding the threshold, designated as N. Then, if the number of fire alarms exceeding the threshold N is above the fire alarm alarm threshold, the electronic control unit 20 diagnoses a fire alarm alarm as having occurred. That is, the electronic control unit 20 diagnoses a fire alarm alarm if the measured fire frequency indicates a high fire frequency. Furthermore, if the measured fire frequency falls below the normal recovery threshold after the fire alarm alarm is diagnosed, the electronic control unit 20 diagnoses that the fire alarm alarm has been eliminated.

[0047] On the other hand, the electronic control unit 20 performs fuel cut-off for specific cylinders during operation of the internal combustion engine 10. During fuel cut-off for specific cylinders, combustion in a portion of cylinders 11 is stopped. In the following description, the cylinders 11 that stop combustion during such fuel cut-off will be referred to as F / C cylinders.

[0048] In specific cylinder fuel cutoff, cylinder 11, where a misfire anomaly occurs, sometimes becomes an F / C cylinder. In such cases, even if a misfire anomaly is potentially and persistent in an F / C cylinder, it is not considered a misfire due to the cessation of combustion. Therefore, when cylinder 11, where the misfire anomaly occurs, is an F / C cylinder, the misfire that should have occurred no longer manifests. Consequently, the misfire frequency measured during the specific cylinder fuel cutoff period may be lower than the original value. Therefore, if the measured misfire frequency during the specific cylinder fuel cutoff period is used in normal recovery diagnostic procedures, it is possible to misdiagnose that the misfire anomaly has been eliminated, even if it has not actually been eliminated.

[0049] In contrast, the normal recovery diagnostic process performed by the electronic control unit 20 is configured such that, during the period when fuel cutoff is performed on a specific cylinder that may conceal a potential misfire, the measurement of the misfire frequency and the determination of whether the misfire anomaly based on the measured value has been eliminated are not performed. That is, the normal recovery diagnostic process is configured such that, during the period when fuel cutoff is performed on a specific cylinder, a diagnosis of whether the misfire anomaly has been eliminated is not performed. Therefore, in this embodiment, the diagnosis of whether the misfire anomaly has been eliminated in the normal recovery diagnostic process is not performed during the period when fuel cutoff is performed on a specific cylinder.

[0050] The diagnostic device according to the above embodiment can achieve the following effects.

[0051] (1) The normal recovery diagnostic process is configured such that no diagnosis of misfire abnormality elimination is performed during the period when fuel cut-off is performed on a specific cylinder. Therefore, even if the cylinder 11 where the misfire abnormality occurred is an F / C cylinder, it will not be misdiagnosed as having eliminated the misfire abnormality during the normal recovery diagnostic process. Therefore, the diagnostic device of this embodiment has the effect of improving the diagnostic accuracy of misfire abnormalities.

[0052] (2) During the period of specific cylinder fuel cut-off, the measurement of misfire frequency used for diagnosis in normal recovery diagnostic procedures was stopped. Therefore, unnecessary misfire frequency measurement that is not used for diagnosis of misfire anomaly elimination can be omitted.

[0053] (3) Diagnose misfire anomalies and their recovery individually for each of the multiple misfire determination zones defined based on the engine speed, load, and preheating status of the internal combustion engine 10. Misfire anomalies sometimes occur only under specific operating conditions of the internal combustion engine 10. Therefore, by diagnosing each misfire determination zone individually, the occurrence and elimination of misfire anomalies can be accurately diagnosed.

[0054] (Second Implementation)

[0055] Next, refer to Figure 4 and Figure 5 A second embodiment of the diagnostic device for an internal combustion engine will be described in detail. In this embodiment, the same reference numerals are used for components common to the above embodiments, and detailed descriptions thereof are omitted. The difference between the diagnostic device of the first embodiment and this embodiment lies in the inclusion of a portion of the misfire anomaly diagnostic processing and the normal recovery diagnostic processing.

[0056] <Diagnosis and Management of Fire-Related Anomalies>

[0057] Figure 4 A flowchart is shown of the fire malfunction diagnostic routine executed by the electronic control unit 20 in the diagnostic apparatus of this embodiment. Figure 4 In the routine, Figure 3 The process of step S150 is replaced by the process of step S150A described below.

[0058] In this embodiment, the electronic control unit 20 also diagnoses a fire anomaly and sets a fire anomaly flag (S140) when the number of fires exceeds N and the fire anomaly determination value is higher than (S130: Yes). Then, in the first embodiment, in Figure 3In step S150, the misfire determination area where the misfire abnormality flag is set is stored as the operating state of the internal combustion engine 10 at this time. In contrast, in this embodiment, in step S150A, the electronic control unit 20, in addition to the misfire determination area, also stores whether a specific cylinder fuel cutoff and the cylinder number of the F / C cylinder are implemented as the operating state of the internal combustion engine 10 when the misfire abnormality flag is set. In this case, the electronic control unit 20 may also store the cylinder identification information of the cylinder 11 that can determine the cylinder number of the F / C cylinder, instead of the cylinder number itself. In this embodiment, the processing in step S150A corresponds to the storage processing of the operating state of the internal combustion engine 10 when a misfire abnormality is diagnosed.

[0059] <Normal Recovery Diagnosis and Treatment>

[0060] Figure 5 A flowchart illustrating the normal recovery diagnostic routine executed by the electronic control unit 20 in the diagnostic device of this embodiment is shown. Figure 5 In the routine, Figure 4 The processing of steps S210 and S220 is replaced by the processing of step S210A described below.

[0061] In this example, the electronic control unit 20 first determines in step S200 whether a misfire alarm has been set. If a misfire alarm has been set, the electronic control unit 20 proceeds to step S210A. In step S210A, the electronic control unit 20 determines whether the current operating state of the internal combustion engine 10 is consistent with the previous state. Figure 4 The operating state is the same as when the fire alarm flag stored in step S150A was set. Furthermore, if the operating state is the same (yes), the electronic control unit 20 proceeds to step S240; if the operating state is different (no), the processing of this routine in the current control cycle ends.

[0062] <Effects of the second implementation method>

[0063] In the diagnostic apparatus of the first embodiment, the determination of whether the misfire abnormality in the normal recovery diagnostic process has been eliminated is not performed during the period of specific cylinder fuel cut-off. In this embodiment, the determination of whether the misfire abnormality in the normal recovery diagnostic process has been eliminated is performed even during the period of specific cylinder fuel cut-off in the following case: That is, when specific cylinder fuel cut-off is performed during misfire abnormality diagnosis, and the cylinder number of the current F / C cylinder is the same as the cylinder number of the F / C cylinder stored during misfire abnormality diagnosis. In this case, the misfire abnormality diagnosis is performed with combustion of cylinder 11, which is the same as the current F / C cylinder, stopped. That is, in this case, the misfire abnormality diagnosed in the misfire abnormality diagnostic routine is not caused by the current F / C cylinder.

[0064] The diagnostic device according to this embodiment can achieve the following effects.

[0065] (1) The operating state of the internal combustion engine 10 is stored when a misfire anomaly is diagnosed, including whether a specific cylinder fuel cutoff and the cylinder number of the F / C cylinder have been implemented. Furthermore, the normal recovery diagnostic process is configured such that if the stored operating state of the internal combustion engine 10 is inconsistent with the current operating state of the internal combustion engine 10, a misfire anomaly clearance diagnosis is not performed. Therefore, if the cylinder 11 where the misfire anomaly occurred is the current F / C cylinder, and the misfire that should have occurred due to the specific cylinder fuel cutoff is concealed, the misfire anomaly is not diagnosed as clearance. Therefore, the diagnostic device of this embodiment has the effect of improving the diagnostic accuracy of misfire anomalies.

[0066] (2) When a specific cylinder fuel cut-off is performed during the diagnosis of a misfire anomaly, and the current F / C cylinder has the same cylinder number as the F / C cylinder stored during the misfire anomaly diagnosis, the diagnosis of whether the misfire anomaly has been eliminated during the normal recovery diagnostic process is performed even during the period when the specific cylinder fuel cut-off is performed. Therefore, compared with the case of the first embodiment, there are more opportunities to perform the diagnosis of whether the misfire anomaly has been eliminated.

[0067] (3) Stop measuring the fire frequency without conducting a diagnosis during normal recovery diagnostic procedures. Therefore, unnecessary fire frequency measurements that are not used for diagnosing fire anomalies can be omitted.

[0068] (4) Diagnose misfire anomalies and their recovery individually for each of the multiple misfire determination zones defined based on the engine speed, load, and preheating status of the internal combustion engine 10. Misfire anomalies sometimes occur only under specific operating conditions of the internal combustion engine 10. Therefore, by diagnosing each misfire determination zone individually, the occurrence and elimination of misfire anomalies can be accurately diagnosed.

[0069] (Other implementation methods)

[0070] The above-described embodiments can be implemented by modification as follows. This embodiment and the following modifications can be combined with each other within the scope of technical inconsistency.

[0071] In the second embodiment, the cylinder number of the F / C cylinder, along with whether or not a specific cylinder fuel cutoff is performed, is stored as part of the operating state of the internal combustion engine 10 during misfire diagnosis. Sometimes, the same cylinder 11 is always designated as the F / C cylinder for specific cylinder fuel cutoff. In this case, the cylinder number of the F / C cylinder is always the same. Alternatively, sometimes the F / C cylinders are switched sequentially according to a certain rule during specific cylinder fuel cutoff. In these cases, the cylinder number of the F / C cylinder can also be removed from the stored operating state of the internal combustion engine 10.

[0072] • In the above embodiments, the frequency of fires is measured in the fire anomaly diagnosis routine and the normal recovery diagnosis routine, but this measurement can also be performed as a routine different from these routines.

[0073] • In the above embodiments, if the diagnosis in the normal recovery diagnosis is not performed, the measurement of the fire frequency used for that diagnosis is also stopped. If the measurement of the fire frequency is used for purposes other than the diagnosis in the normal recovery diagnosis, the measurement of the fire frequency can continue even if the diagnosis in the normal recovery diagnosis is not performed.

[0074] In the above embodiment, a misfire anomaly is diagnosed when the number of misfires exceeding the threshold is deemed to be above the misfire anomaly threshold. This diagnosis can be based on the misfire frequency of the internal combustion engine 10, or it can be performed using a different method. Furthermore, the misfire determination for each combustion cycle can also be performed using a method different from the above embodiment.

[0075] In the above embodiments, during the misfire anomaly diagnosis process, a misfire determination area is stored when a misfire anomaly is diagnosed. Alternatively, the engine speed, load, and preheating status of the internal combustion engine 10 may be stored instead of the misfire determination area. Additionally, parameters other than those mentioned above that indicate the operating status of the internal combustion engine 10 may also be stored.

[0076] In the above embodiments, each fire detection zone is individually diagnosed for both fire anomaly and normal recovery. Alternatively, these diagnoses can be performed without defining a fire detection zone.

[0077] • The electronic control unit 20 is not limited to having a processing circuit equipped with a CPU and ROM configured to perform software processing. That is, the electronic control unit 20 may be configured as any of the following (a) to (c).

[0078] (a) The electronic control unit 20 includes a processor that performs various processes according to a computer program. The processor includes a CPU and memories such as RAM and ROM. The memories store program code or instructions configured to cause the CPU to perform processes. Memory, i.e., computer-readable media, includes all available media that can be accessed by a general-purpose or special-purpose computer.

[0079] (b) The electronic control unit 20 has dedicated hardware circuitry for performing one or more of the various processes. Examples of dedicated hardware circuitry include application-specific integrated circuits, i.e., ASICs or FPGAs. ASIC stands for "Application Specific Integrated Circuit," and FPGA stands for "Field Programmable Gate Array."

[0080] (c) The electronic control unit 20 has a processor that performs a portion of various processes according to a computer program, and dedicated hardware circuitry that performs the remaining processes in the various processes.

Claims

1. A diagnostic device for an internal combustion engine, The internal combustion mechanism is configured to cut off fuel to specific cylinders, stopping combustion in a portion of the cylinders while allowing combustion to continue in the remaining cylinders. The diagnostic device is configured to perform the following processes: The misfire anomaly diagnosis and processing is based on the misfire frequency of the internal combustion engine to diagnose whether the internal combustion engine has a misfire anomaly; In the normal recovery diagnostic process, if the fire anomaly is diagnosed, the fire anomaly is considered to have been eliminated if the measured value of the fire frequency falls below the predetermined normal recovery judgment value. as well as The storage process stores the operating status of the internal combustion engine when the misfire anomaly is diagnosed. The normal recovery diagnostic process is configured such that if the operating state of the internal combustion engine stored in the storage process is inconsistent with the current operating state of the internal combustion engine, the diagnosis that the misfire abnormality has been eliminated will not be performed. The operating status of the internal combustion engine stored in the storage process includes whether or not the fuel cut-off of the specific cylinder has been implemented.

2. The diagnostic device for an internal combustion engine according to claim 1, The operating status of the internal combustion engine stored in the storage process includes the cylinder number of the cylinder that stopped combustion during the fuel cut-off of the specific cylinder.

3. The diagnostic device for an internal combustion engine according to claim 1, The diagnostic device is configured to stop measuring the misfire frequency used in the normal recovery diagnostic process when the operating state of the internal combustion engine stored in the storage process is inconsistent with the current operating state of the internal combustion engine.

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