Diagnostic device for internal combustion engine

Abstract

To improve accuracy of diagnosing misfiring abnormality.SOLUTION: An electronic control unit 20 diagnoses whether there is a misfiring abnormality of an internal combustion engine 10 that performs a specific cylinder fuel-cut in which combustion in a partial cylinder 11 is stopped while the combustion in remaining cylinders 11 is continued, on the basis of a frequency of misfiring of the engine. Further, while a misfiring is being diagnosed, the electronic control unit 20 performs normality recovery diagnostic processing to diagnose that the misfiring abnormality has been eliminated in a case where a count value of a misfiring frequency returns to a pre-specified normal recovery determination value or less. The normality recovery diagnostic processing is such that the diagnosis of the misfiring being eliminated is not performed while the specific cylinder fuel-cut is performed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a diagnostic device for an internal combustion engine. [Background technology]

[0002] In an internal combustion engine mounted on a vehicle, etc., an increase in the frequency of misfires, i.e., a misfire abnormality, may occur due to an abnormality in the fuel system, ignition system, etc. Patent Document 1 describes a diagnostic device that detects the occurrence of misfires based on the rotation fluctuation of the internal combustion engine caused by the misfire, and determines that a misfire abnormality has occurred when the frequency of the detected misfires is equal to or higher than a certain level. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-271701 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, even if a misfire abnormality occurs, the abnormality may be temporary and subsequently disappear naturally. Therefore, in the above-mentioned diagnostic device, if the frequency of misfires becomes low after a misfire abnormality is determined, the diagnostic device may determine that the misfire abnormality has disappeared and that the engine has returned to normal.

[0005] Meanwhile, in internal combustion engines, specific cylinder fuel cuts may be implemented, in which combustion is stopped in some cylinders while combustion continues in the remaining cylinders. In the target cylinders for combustion stop in such specific cylinder fuel cuts, no combustion occurs in the first place, so misfires do not occur. Therefore, if a misfire abnormality occurs in a target cylinder for combustion stop, misfires that should occur will not occur during the specific cylinder fuel cut. Therefore, even if the misfire abnormality continues potentially during the specific cylinder fuel cut, the frequency of misfires may decrease, and it may be erroneously determined that the misfire abnormality has been resolved. [Means for solving the problem]

[0006] The diagnostic device for an internal combustion engine that solves the above problem is an internal combustion engine that performs a specific cylinder fuel cut in which combustion is stopped in some cylinders and combustion continues in the remaining cylinders. The misfire frequency is the number of misfires that occur during a given number of combustions. The diagnostic device is configured to execute a normal return diagnostic process for diagnosing the misfire abnormality as resolved when the misfire frequency measurement value falls below a predetermined normal return determination value when the misfire abnormality is diagnosed as being present. By stopping the measurement of misfire frequency for diagnosis in the normal return diagnosis process while a specific cylinder fuel cut is being performed, During specific cylinder fuel cut Normal recovery diagnostic process The system is configured not to diagnose that the misfire abnormality has been eliminated.

[0007] In the above-mentioned internal combustion engine diagnostic device, when fuel cut is being performed on a specific cylinder, which may conceal a potential misfire, the normal return diagnosis process is not performed. Therefore, it is difficult to erroneously diagnose a misfire abnormality as having been resolved when in fact the misfire abnormality has not been resolved. Therefore, the above-mentioned internal combustion engine diagnostic device has the effect of increasing the accuracy of misfire abnormality diagnosis.

[0009] Another diagnostic device for an internal combustion engine that solves the above problem is a diagnostic device for an internal combustion engine that performs a specific cylinder fuel cut in which combustion is stopped in some cylinders and combustion continues in the remaining cylinders. The misfire frequency is the number of misfires that occur during a given number of combustions. The diagnostic device is configured to perform a normal return diagnostic process for diagnosing that the misfire has been eliminated if the measured value of the misfire frequency falls below a predetermined normal return judgment value when the misfire has been diagnosed as occurring, and a storage process for storing the operating state of the internal combustion engine when the misfire has been diagnosed as occurring. When the operating state of the internal combustion engine stored by the storage process does not match the current operating state of the internal combustion engine, the measurement of the misfire frequency for diagnosis in the normal return diagnosis process is stopped. If the operating state of the internal combustion engine stored by the storage process does not match the current operating state of the internal combustion engine, Normal recovery diagnostic process The misfire abnormality is not diagnosed as having been eliminated. The operating conditions of the internal combustion engine stored in the storage process include whether or not a fuel cut has been performed for a specific cylinder.

[0010] In the above diagnostic device, the operating state of the internal combustion engine when a misfire abnormality is diagnosed is stored. If the operating state differs from the stored operating state, diagnosis using the normal return diagnostic process is not performed. The operating state of the internal combustion engine stored in the storage process includes whether or not fuel cut has been performed for a specific cylinder. This makes it difficult to erroneously diagnose a misfire abnormality that has not actually been resolved as having been resolved. Therefore, the above diagnostic device for an internal combustion engine has the effect of improving the accuracy of diagnosing a misfire abnormality.

[0011] There are cases where the cylinder in which combustion is stopped is switched each time a specific cylinder fuel cut is performed. In such cases, it is desirable to include the cylinder number of the cylinder in which combustion is stopped by the specific cylinder fuel cut in the operating state of the internal combustion engine stored in the storage process. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating a schematic configuration of a first embodiment of a diagnosis device for an internal combustion engine. [Diagram 2] 3 is a flowchart of a misfire abnormality diagnosis routine executed by the diagnosis device of the embodiment. [Diagram 3] 4 is a flowchart of a normal return diagnosis routine executed by the diagnosis device of the embodiment. [Figure 4] 5 is a flowchart of a misfire abnormality diagnosis routine executed by a second embodiment of a diagnosis device for an internal combustion engine. [Diagram 5] 4 is a flowchart of a normal return diagnosis routine executed by the diagnosis device of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (First embodiment) A first embodiment of a diagnostic device for an internal combustion engine will be described in detail below with reference to Figs. <Diagnostic device configuration> First, the configuration of the diagnostic device of this embodiment will be described with reference to FIG.

[0015] As shown in Fig. 1, an internal combustion engine 10 to which the diagnosis device of this embodiment is applied has a plurality of cylinders 11. In the internal combustion engine 10, an injector 12 that injects fuel to be burned in the cylinder 11 and an ignition device 13 that ignites the fuel introduced into the cylinder 11 are provided for each cylinder 11. In addition, 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 assigned an individual cylinder number.

[0016] The internal combustion engine 10 is controlled by an electronic control unit 20. The electronic control unit 20 includes an arithmetic processing device 21 that executes processing for controlling the internal combustion engine 10, and a storage device 22 that stores programs and data for control. The electronic control unit 20 is connected to various sensors for grasping the operating state of the internal combustion engine 10. These sensors include an air flow meter 23, a crank angle sensor 24, and a water temperature sensor 25. The air flow meter 23 is a sensor that detects the amount of intake air of the internal combustion engine 10. The crank angle sensor 24 is a sensor that detects the rotation phase of the crankshaft, which is the output shaft of the internal combustion engine 10. The water temperature sensor 25 is a sensor that detects the cooling water temperature of the internal combustion engine 10. The electronic control unit 20 controls the internal combustion engine 10 based on the detection results of the sensors. The control of the internal combustion engine 10 is performed through control of the fuel injection amount and fuel injection amount of the injector 12, control of the ignition timing of the ignition device 13, control of the opening degree of the throttle valve 14, and the like. Furthermore, a warning light 26 is connected to the electronic control unit 20 to notify the driver of the occurrence of a misfire abnormality.

[0017] <Specific cylinder fuel cut> The electronic control unit 20 performs a specific cylinder fuel cut as part of the control of the internal combustion engine 10. The specific cylinder fuel cut is a control for stopping combustion in some of the multiple cylinders 11 of the internal combustion engine 10 and continuing combustion in the remaining cylinders 11. When performing the specific cylinder fuel cut, the electronic control unit 20 stops fuel injection from the injector 12 and ignition from the ignition device 13 in the cylinder 11 for which combustion is to be stopped. Note that in order to burn unburned fuel remaining in the cylinder 11, ignition from the ignition device 13 may continue even in the cylinder 11 for which combustion is to be stopped.

[0018] When fuel cut is performed on a specific cylinder, fresh air is discharged directly into the exhaust passage from the cylinder 11 where combustion has stopped. Therefore, it is possible to make the exhaust gas leaner without performing lean combustion in the remaining cylinders 11 where combustion continues.

[0019] Such specific cylinder fuel cut is performed for the following purpose, for example. A filter that captures particulate matter (PM) in the exhaust gas may be installed in the exhaust passage of the internal combustion engine 10. Such a filter becomes clogged as PM accumulates. The PM accumulated in the filter can be burned and purified by making the exhaust gas lean and supplying oxygen to the filter. However, if lean combustion is performed in each cylinder 11 to make the exhaust gas lean, the amount of NOx emissions from the internal combustion engine 10 increases. In contrast, when specific cylinder fuel cut is performed, fresh air is discharged as it is from the cylinder 11 where combustion has stopped. Therefore, if specific cylinder fuel cut is performed, the exhaust gas can be made lean without performing lean combustion in the remaining cylinders 11 that continue to burn. In this way, specific cylinder fuel cut can be performed to remove PM accumulated in the filter while suppressing deterioration of emissions.

[0020] <Misfire abnormality diagnosis processing> In the internal combustion engine 10, a misfire abnormality, in which misfires occur frequently, may occur due to an abnormality in the injector 12, the ignition device 13, etc. The electronic control unit 20 performs a misfire abnormality diagnosis process to diagnose the presence or absence of a misfire abnormality in parallel with the control of the internal combustion engine 10. In this embodiment, the electronic control unit 20 corresponds to a diagnostic device. The electronic control unit 20 performs a misfire abnormality diagnosis individually for each of a plurality of misfire determination regions defined by the rotation speed, load, and warm-up state of the internal combustion engine 10.

[0021] 2 shows a flowchart of a misfire abnormality diagnosis routine executed by the electronic control unit 20 for misfire abnormality diagnosis processing. The electronic control unit 20 repeatedly executes this routine at every predetermined control period while the internal combustion engine 10 is in operation.

[0022] When this routine starts, the electronic control unit 20 first measures the misfire frequency in step S100. Here, the number of misfires that occur during a preset number of combustions is defined as the misfire frequency.

[0023] The electronic control unit 20 measures the misfire frequency in the following manner. The internal combustion engine 10 maintains rotation with the torque generated by combustion in each cylinder 11. When a misfire occurs, torque generation is temporarily interrupted, causing rotation fluctuations in the internal combustion engine 10. The electronic control unit 20 performs a misfire determination for each combustion in the internal combustion engine 10, based on the detection signal from the crank angle sensor 24, to check whether rotation fluctuations caused by misfire have occurred. The electronic control unit 20 then determines the number of misfire determinations per predetermined number of combustions as a measurement value of the misfire frequency.

[0024] After measuring the misfire frequency, the electronic control unit 20 determines in the next step S110 whether the misfire frequency is equal to or greater than a preset misfire excess judgment value. If the misfire frequency is equal to or greater than the misfire excess judgment value (YES), the electronic control unit 20 proceeds to step S120. On the other hand, if the misfire frequency is less than the misfire excess judgment value (NO), the electronic control unit 20 ends the processing of this routine for the current control cycle.

[0025] If the process proceeds to step S120, the electronic control unit 20 increments the value of the misfire excess number N in step S120. The misfire excess number N represents the number of times in the current trip that the misfire frequency has exceeded the misfire excess judgment value. More specifically, the misfire excess number N is set individually for each misfire judgment region. Then, in step S120, the electronic control unit 20 increments the value of the misfire excess number N for the misfire judgment region that corresponds to the current operating state of the internal combustion engine 10. Note that the electronic control unit 20 resets the value of the misfire excess number N for each misfire judgment region to "0" at the end of the trip.

[0026] Next, in step S130, the electronic control unit 20 determines whether the value of the excessive misfire count N incremented in step S120 is equal to or greater than a preset misfire abnormality judgment value. If the excessive misfire count N is equal to or greater than the misfire abnormality judgment value (YES), the electronic control unit 20 proceeds to step S140. On the other hand, if the excessive misfire count N is less than the misfire abnormality judgment value (NO), the electronic control unit 20 ends the processing of this routine for the current control cycle.

[0027] If the process proceeds to step S140, the electronic control unit 20 sets a misfire abnormality flag in step S140. The misfire abnormality flag is a flag that indicates whether or not a misfire abnormality has occurred. That is, the electronic control unit 20 sets the misfire abnormality flag when it diagnoses a misfire abnormality. The state of the misfire abnormality flag is maintained even after the trip ends, and is carried over to the next trip.

[0028] Next, 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 region corresponding to the current operating state of the internal combustion engine 10. Then, in step S160, the electronic control unit 20 turns on the warning light 26, and then ends the processing of this routine in the current control cycle.

[0029] As described above, the misfire abnormality flag is set for each misfire determination region. Therefore, the misfire determination region for which the misfire abnormality flag is set is clear by checking which misfire determination region the flag belongs to. Therefore, in practice, the electronic control unit 20 performs the processes of steps S140 and S150 by setting the misfire abnormality flag for the misfire determination region that corresponds to the current operating state of the internal combustion engine 10.

[0030] <Normal recovery diagnosis process> The above-mentioned misfire abnormality is temporary and may disappear naturally over time. Next, a normal recovery diagnosis process for diagnosing a recovery from such a misfire abnormality will be described.

[0031] 3 shows a flowchart of a normal return diagnosis routine executed by the electronic control unit 20 for the normal return diagnosis process. The electronic control unit 20 repeatedly executes this routine at every predetermined control period while the internal combustion engine 10 is in operation. Note that "F / C" in FIG. 3 and the following figures stands for fuel cut.

[0032] When this routine starts, the electronic control unit 20 first determines whether or not the misfire abnormality flag is set in step S200. If the misfire abnormality flag is set (YES), the electronic control unit 20 proceeds to step S210, and if the misfire abnormality flag is not set (NO), the electronic control unit 20 ends the processing of this routine for the current control cycle.

[0033] When the process proceeds to step S210, the electronic control unit 20 determines in step S210 whether the current operating state of the internal combustion engine 10 is the same as when the misfire abnormality flag was set. More specifically, in step S210, the electronic control unit 20 determines whether the operating state stored in step S150 of FIG. 2 matches the current operating state. In step S150 of FIG. 2, the misfire determination region in which the misfire abnormality flag is set is stored. Therefore, in step S210, it is determined whether the misfire determination region corresponding to the current operating state of the internal combustion engine 10 is the same as the misfire determination region in which the misfire abnormality flag is set. Then, if the operating state belongs to the same misfire determination region as when the misfire abnormality flag was set (YES), the electronic control unit 20 proceeds to step S220. If the operating state does not belong to the same misfire determination region as when the misfire abnormality flag was set (NO), the electronic control unit 20 ends the process of this routine in the current control cycle. As described above, the misfire abnormality flag is set for each misfire determination region individually. Therefore, by checking the state of the misfire abnormality flag for the misfire determination region corresponding to the current operating state of the internal combustion engine 10, the determinations in steps S200 and S210 can be performed simultaneously.

[0034] When the process proceeds to step S220, the electronic control unit 20 determines whether or not a specific cylinder fuel cut is being performed in step S220. If a specific cylinder fuel cut is being performed (YES), the electronic control unit 20 ends the process of this routine in the current control cycle. On the other hand, if a specific cylinder fuel cut is not being performed (NO), the electronic control unit 20 proceeds to step S230.

[0035] If the process proceeds to step S230, the electronic control unit 20 measures the misfire frequency in step S230, similar to step S100 in FIG. 2. Next, in step S240, the electronic control unit 20 determines whether the measured misfire frequency is equal to or less than a preset normal return judgment value. The normal return judgment value is set to a positive value equal to or less than the above-mentioned misfire excess judgment value. If the misfire frequency is equal to or less than the normal return judgment value (YES), the electronic control unit 20 proceeds to step S250. On the other hand, if the misfire frequency exceeds the normal return judgment value (NO), the electronic control unit 20 ends the process of this routine for the current control cycle.

[0036] When the process proceeds to step S250, the electronic control unit 20 clears the misfire abnormality flag for the misfire judgment region corresponding to the current operating state of the internal combustion engine 10 in step S250. In other words, it is determined that the misfire abnormality has been eliminated. Then, the electronic control unit 20 ends the process of this routine for the current control cycle. Note that the electronic control unit 20 turns off the warning light 26 when the misfire abnormality flags for all misfire judgment regions have been cleared.

[0037] <Effects of the First Embodiment> The operation and effects of this embodiment will be described. The electronic control unit 20 counts the number of times the misfire frequency measurement value becomes equal to or greater than the misfire excess judgment value after the start of a trip as the misfire excess number N. The electronic control unit 20 then diagnoses that a misfire abnormality has occurred when the misfire excess number N is equal to or greater than the misfire abnormality judgment value. That is, the electronic control unit 20 diagnoses a misfire abnormality when it determines that the misfire frequency is high based on the misfire frequency measurement results. Furthermore, after diagnosing a misfire abnormality, the electronic control unit 20 diagnoses that the misfire abnormality has been resolved when the misfire frequency measurement value becomes equal to or less than the normal return judgment value.

[0038] Meanwhile, the electronic control unit 20 performs specific cylinder fuel cut during operation of the internal combustion engine 10. In specific cylinder fuel cut, combustion is stopped in some of the cylinders 11. In the following description, the cylinders 11 in which combustion is stopped in such specific cylinder fuel cut are referred to as F / C cylinders.

[0039] In the specific cylinder fuel cut, the cylinder 11 in which a misfire abnormality occurs may become the F / C cylinder. In such a case, the F / C cylinder is not subject to misfire determination because combustion has been stopped, even if the misfire abnormality actually continues to exist. Therefore, if the cylinder 11 in which a misfire abnormality occurred is the F / C cylinder, the misfire that should have occurred will not be apparent. Therefore, the misfire frequency measured during the specific cylinder fuel cut may be a value smaller than the actual value. Therefore, if the measurement value of the misfire frequency during the specific cylinder fuel cut is used in the normal return diagnosis process, there is a risk of erroneously diagnosing that the misfire abnormality has been resolved, even if it has not actually been resolved.

[0040] In contrast, the normal return diagnosis process executed by the electronic control unit 20 is configured not to measure the misfire frequency or to determine whether the misfire abnormality has been eliminated based on the measurement value while fuel cut for a specific cylinder is being performed. In other words, the normal return diagnosis process is configured not to diagnose that the misfire abnormality has been eliminated while fuel cut for a specific cylinder is being performed. Therefore, in this embodiment, the normal return diagnosis process does not diagnose that the misfire abnormality has been eliminated while fuel cut for a specific cylinder is being performed.

[0041] According to the above-described diagnostic device of this embodiment, the following effects can be obtained. (1) In this embodiment, the normal return diagnosis process is configured not to diagnose that the misfire abnormality has been resolved while fuel cut is being performed on a specific cylinder. Therefore, even if the cylinder 11 in which the misfire abnormality occurred is an F / C cylinder, the normal return diagnosis process will not erroneously diagnose that the misfire abnormality has been resolved. Therefore, the diagnosis device of this embodiment has the effect of improving the accuracy of diagnosing the misfire abnormality.

[0042] (2) In this embodiment, the measurement of the misfire frequency for diagnosis in the normal return diagnosis process is stopped while the fuel cut for the specific cylinder is being performed. Therefore, it is possible to omit unnecessary measurement of the misfire frequency that is not used for diagnosis of the elimination of the misfire abnormality.

[0043] (3) In this embodiment, the diagnosis of misfire abnormality and normal recovery is performed separately for each of a plurality of misfire determination ranges defined by the rotation speed, load, and warm-up state of the internal combustion engine 10. Misfire abnormality may occur only in a specific operating state of the internal combustion engine 10. Therefore, by performing a diagnosis separately for each misfire determination range, it is possible to accurately diagnose the occurrence and elimination of misfire abnormality.

[0044] Second embodiment Next, a second embodiment of the internal combustion engine diagnostic device will be described in detail with reference to Fig. 4 and Fig. 5. In this embodiment, the same components as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The difference between the first embodiment and the diagnostic device of this embodiment is a part of the misfire abnormality diagnostic process and the normal return diagnostic process.

[0045] <Misfire abnormality diagnosis processing> 4 shows a flowchart of a misfire abnormality diagnosis routine executed by the electronic control unit 20 in the diagnosis device of this embodiment. In the routine of FIG. 4, the process of step S150 in FIG. 3 is replaced with the process of step S150A described below.

[0046] In this embodiment, the electronic control unit 20 also diagnoses a misfire abnormality when the misfire excess number N is equal to or greater than the misfire abnormality judgment value (S130: YES) and sets a misfire abnormality flag (S140). After that, in the first embodiment, in step S150 of FIG. 3, the misfire judgment region in which the misfire abnormality flag was set is stored as the operating state of the internal combustion engine 10 at that time. In contrast, in the case of this embodiment, in step S150A, the electronic control unit 20 stores, in addition to the misfire judgment region, whether or not a specific cylinder fuel cut has been performed and the cylinder number of the F / C cylinder as the operating state of the internal combustion engine 10 when the misfire abnormality flag was set. At this time, instead of the cylinder number itself, identification information of the cylinder 11 that can identify the cylinder number of the F / C cylinder may be stored. In this embodiment, the process of step S150A corresponds to a storage process for storing the operating state of the internal combustion engine 10 when the misfire abnormality is diagnosed.

[0047] <Normal recovery diagnosis process> 5 shows a flowchart of the normal return diagnosis executed by the electronic control unit 20 in the diagnosis device of this embodiment. In the routine of FIG. 5, the processes of steps S210 and S210 in FIG. 4 are replaced with the process of step S210A described below.

[0048] In this routine, the electronic control unit 20 first determines whether or not the misfire abnormality flag is set in step S200. If the misfire abnormality flag is set, the electronic control unit 20 proceeds to step S210A. In step S210A, the electronic control unit 20 determines whether or not the current operating state of the internal combustion engine 10 is the same as the operating state when the misfire abnormality flag was set, which was stored in step S150A of Fig. 4. If the operating state is the same (YES), the electronic control unit 20 proceeds to step S240, and if not (NO), the electronic control unit 20 ends the processing of this routine for the current control cycle.

[0049] <Effects of the Second Embodiment> In the diagnosis device of the first embodiment, the determination of whether the misfire abnormality in the normal return diagnosis process has been resolved is not performed while fuel cut is being performed on a specific cylinder. In this embodiment, the determination of whether the misfire abnormality in the normal return diagnosis process has been resolved is performed even while fuel cut is being performed on a specific cylinder in the following cases. That is, when fuel cut is being performed on a specific cylinder even when the misfire abnormality is diagnosed, and the cylinder number of the F / C cylinder is the same. In this case, the misfire abnormality is diagnosed in a state where combustion is stopped in the same cylinder 11 as the current F / C cylinder. In other words, in this case, the diagnosed misfire abnormality is not caused by the current F / C cylinder.

[0050] According to the diagnostic device of this embodiment, the following effects can be achieved. (1) In this embodiment, the operating state of the internal combustion engine 10 when diagnosing a misfire abnormality is stored as the presence or absence of a specific cylinder fuel cut and the cylinder number of the F / C cylinder. Then, the normal return diagnosis process is configured so as not to diagnose that the misfire abnormality has been eliminated if the stored operating state of the internal combustion engine 10 does not match the current operating state of the internal combustion engine 10. Therefore, if the cylinder 11 in which the misfire abnormality occurred is the current F / C cylinder and the misfire that should have occurred is concealed by the specific cylinder fuel cut, the misfire abnormality is not diagnosed as having been eliminated. Therefore, the diagnosis device of this embodiment has the effect of improving the accuracy of diagnosing a misfire abnormality.

[0051] (2) If fuel cut is being performed on a specific cylinder when a misfire abnormality is diagnosed and the F / C cylinder is the same, a diagnosis is made as to whether the misfire abnormality has been resolved in the normal return diagnosis process even while fuel cut is being performed on the specific cylinder. This provides more opportunities to diagnose whether the misfire abnormality has been resolved than in the first embodiment.

[0052] (3) When a diagnosis is not performed in the normal return diagnosis process, the measurement of the misfire frequency is stopped. Therefore, it is possible to omit unnecessary measurement of the misfire frequency that is not used in diagnosing the elimination of the misfire abnormality. (4) In this embodiment, the diagnosis of misfire abnormality and normal recovery is performed separately for each of a plurality of misfire determination ranges defined by the rotation speed, load, and warm-up state of the internal combustion engine 10. Misfire abnormality may occur only in a specific operating state of the internal combustion engine 10. Therefore, by performing a diagnosis separately for each misfire determination range, the occurrence and elimination of misfire abnormality can be accurately diagnosed.

[0053] (Other embodiments) The above embodiment can be modified as follows: The present embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.

[0054] In the second embodiment, the cylinder number of the F / C cylinder was stored as the operating state of the internal combustion engine 10 when a misfire abnormality was diagnosed, along with whether or not fuel cut was performed for the specific cylinder. There are cases where the same cylinder 11 is always set as the F / C cylinder and fuel cut for the specific cylinder is performed. In this case, the cylinder number of the F / C cylinder will always be the same. There are also cases where the F / C cylinder is switched sequentially under certain rules during fuel cut for the specific cylinder. In these cases, the cylinder number of the F / C cylinder may be excluded from the operating state of the internal combustion engine 10 that is stored.

[0055] In the above embodiment, the misfire frequency is measured within the misfire abnormality diagnosis routine and the normal return diagnosis routine. However, the measurement may be performed as part of a routine separate from these routines.

[0056] In the above embodiment, when a normal return diagnosis is not performed, the measurement of the misfire frequency for the normal return diagnosis is also stopped. However, if the measurement of the misfire frequency is also used for purposes other than the normal return diagnosis, the measurement of the misfire frequency may be continued even when a normal return diagnosis is not performed.

[0057] In the above embodiment, the presence or absence of a misfire abnormality is diagnosed by determining that a misfire abnormality exists when the number of times that the misfire frequency is equal to or greater than the misfire excess judgment value is equal to or greater than the misfire abnormality judgment value. However, the presence or absence of a misfire abnormality may be diagnosed in a different manner as long as it is based on the misfire frequency of the internal combustion engine 10. In addition, the misfire judgment for each combustion may also be performed using a method different from that of the above embodiment.

[0058] In the above embodiment, the misfire determination region when a misfire abnormality is diagnosed in the misfire abnormality diagnosis process is stored. Instead of the misfire determination region, the rotation speed, load, and warm-up state of the internal combustion engine 10 may be stored. Also, parameters other than these that indicate the operating state of the internal combustion engine 10 may be stored.

[0059] In the above embodiment, the misfire abnormality diagnosis process and the normal return diagnosis process are performed separately for each misfire determination region. However, these diagnoses may be performed without setting a misfire determination region. [Explanation of symbols]

[0060] 10. Internal combustion engine 11…Cylinder 12...Injector 13...Ignition device 14...Throttle valve 20...Electronic control unit (diagnostic device) 21...Processing device 22…Storage device 23...Air flow meter 24...Crank angle sensor 25...Water temperature sensor 26…warning light

Claims

1. A diagnostic device that is applied to an internal combustion engine that performs a specific cylinder fuel cut in which combustion is stopped in some cylinders and combustion continues in the remaining cylinders, and diagnoses whether or not there is a misfire abnormality in the internal combustion engine based on a misfire frequency, which is the number of misfires that occur during a predetermined number of combustions, a normal return diagnosis process is performed to diagnose that the misfire abnormality has been eliminated when the measured value of the misfire frequency becomes equal to or less than a predetermined normal return determination value when the misfire abnormality has been diagnosed as occurring, Moreover, by stopping the measurement of the misfire frequency for diagnosis in the normal return diagnosis process while the fuel cut for the specific cylinder is being performed, the normal return diagnosis process does not diagnose that the misfire abnormality has been eliminated while the fuel cut for the specific cylinder is being performed. Diagnostic equipment for internal combustion engines.

2. A diagnostic device that is applied to an internal combustion engine that performs a specific cylinder fuel cut in which combustion is stopped in some cylinders and combustion continues in the remaining cylinders, and diagnoses whether or not there is a misfire abnormality in the internal combustion engine based on a misfire frequency, which is the number of misfires that occur during a predetermined number of combustions, a normal return diagnosis process for diagnosing that the misfire abnormality has been eliminated when the measured value of the misfire frequency becomes equal to or less than a predetermined normal return determination value when the misfire abnormality has been diagnosed as occurring; a storage process for storing the operating state of the internal combustion engine when the misfire abnormality is diagnosed; [0023] The present invention is configured to by stopping the measurement of the misfire frequency for diagnosis in the normal return diagnosis process when the operating state of the internal combustion engine stored by the storage process does not match the current operating state of the internal combustion engine, the normal return diagnosis process does not diagnose that the misfire abnormality has been eliminated when the operating state of the internal combustion engine stored by the storage process does not match the current operating state of the internal combustion engine, The operating state of the internal combustion engine stored in the storage process includes whether or not the specific cylinder fuel cut is performed. Diagnostic equipment for internal combustion engines.

3. 3. The diagnostic device for an internal combustion engine according to claim 2, wherein the operating conditions of the internal combustion engine stored in the storage process include a cylinder number of a cylinder in which combustion has been stopped by the specific cylinder fuel cut.

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