Diagnostic method for internal combustion engine and diagnostic device for internal combustion engine

Abstract

An internal combustion engine (1) comprises a GPF (4) that is disposed in an exhaust passage (2) and collects particulate matter present in exhaust gas. A first collected amount obtained by calculating the collected amount of the particulate matter in the GPF (4) on the basis of the operation state of the internal combustion engine (1), a second collected amount obtained by calculating the collected amount of the particulate matter in the GPF (4) on the basis of the front-rear differential pressure of the GPF (4), and a determination threshold set on the basis of the first collected amount are used to make a determination to increase the frequency at which fuel cut is prohibited when the second collected amount is greater than the determination threshold. By determining the frequency at which fuel cut is prohibited, it can be determined whether the internal combustion engine (1) is in a state in which carrying out of various functional diagnoses of the internal combustion engine (1) is ensured when running during fuel cut.

Description

Diagnostic method and diagnostic device for internal combustion engine

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

[0002] For example, Patent Document 1 discloses a technology that prohibits fuel cut during deceleration if it is determined that a PM filter (particulate filter) that is placed in the exhaust passage of an internal combustion engine and can capture and remove particulate matter is overheating.

[0003] However, Patent Document 1 does not disclose anything about the frequency at which fuel cut is prohibited during deceleration.

[0004] Therefore, in Patent Document 1, if the frequency of prohibiting fuel cut during deceleration increases, there is a risk that the execution of various functional diagnoses of the internal combustion engine during fuel cut may not be guaranteed.

[0005] JP 2009-74426 A

[0006] The internal combustion engine of the present invention has an exhaust particulate filter arranged in an exhaust passage to capture particulate matter in the exhaust, and uses a first collection amount calculated based on the amount of particulate matter captured by the exhaust particulate filter based on the operating state of the internal combustion engine, a second collection amount calculated based on the amount of particulate matter captured by the exhaust particulate filter based on the differential pressure before and after the exhaust particulate filter, and a judgment threshold set based on the first collection amount, and determines that when the second collection amount becomes larger than the judgment threshold, the frequency with which fuel cut will be prohibited will increase.

[0007] According to the present invention, by determining the frequency at which fuel cut is prohibited, it is possible to determine whether or not various functional diagnoses of the internal combustion engine that are performed during fuel cut are guaranteed.

[0008] The present invention is applicable to an internal combustion engine having a function assurance diagnosis system, a timing chart showing changes in various parameters during the function assurance diagnosis of the internal combustion engine, and a flowchart showing an example of a diagnostic procedure in the function assurance diagnosis of the internal combustion engine.

[0009] An embodiment of the present invention will be described in detail below with reference to the drawings.

[0010] 1 is an explanatory diagram that shows a schematic system configuration of an internal combustion engine 1 to which the present invention is applied. The internal combustion engine 1 is mounted on a vehicle and drives the drive wheels of the vehicle.

[0011] A first catalyst 3, a gasoline particulate filter (GPF) 4 serving as an exhaust particulate filter, and a second catalyst 5 are arranged in series in an exhaust passage 2 of an internal combustion engine 1. In this embodiment, the GPF 4 and the second catalyst 5 are unitized in series and housed in a single casing 6. The internal combustion engine 1 is a gasoline engine that uses gasoline as fuel.

[0012] The first catalyst 3 is, for example, a three-way catalyst that purifies the three components of HC, CO, and NOx in the inflowing exhaust gas when the excess air ratio is approximately 1, i.e., when the exhaust gas air-fuel ratio is approximately the stoichiometric air-fuel ratio.

[0013] The GPF 4 collects PM, which is particulate matter in the exhaust gas.

[0014] The GPF 4 is, for example, a filter with a wall-flow honeycomb structure (so-called plugged type) in which a large number of fine honeycomb-shaped passages are formed in a filter material such as cordierite, and the ends of the passages are alternately blocked. The GPF 4 is located downstream of the first catalyst 3 in the exhaust flow direction. The GPF 4 may also support, for example, the same type of catalyst as a three-way catalyst.

[0015] The second catalyst 5 is, for example, a three-way catalyst, and is located downstream of the GPF 4 in the exhaust gas flow direction.

[0016] A muffler 7 is disposed downstream of the second catalyst 5 .

[0017] The internal combustion engine 1 is controlled by a control unit 11. The control unit 11 is a well-known digital computer equipped with a CPU, a ROM, a RAM, and an input / output interface.

[0018] The control unit 11 receives signals from various sensors, such as an oxygen sensor 12 that detects the air-fuel ratio on the outlet side (downstream side) of the first catalyst 3, an air flow meter 13 that detects the amount of intake air of the internal combustion engine 1, an outside air temperature sensor 14 that detects the outside air temperature, an accelerator opening sensor 15 that detects the amount of depression of an accelerator pedal (not shown), a crank angle sensor 16 that detects the crank angle of a crankshaft (not shown) of the internal combustion engine 1, a differential pressure sensor 17 that detects the differential pressure before and after the GPF 4, and a vehicle speed sensor 18 that detects the speed of the vehicle.

[0019] The oxygen sensor 12 is a sensor that detects only rich or lean air-fuel ratios by changing its output voltage ON / OFF (rich, lean) within a narrow range near the stoichiometric air-fuel ratio. The differential pressure sensor 17 is capable of detecting the pressure difference (differential pressure ΔP) between the exhaust pressure in the exhaust passage 2 upstream of the GPF 4 and the exhaust pressure in the exhaust passage 2 downstream of the GPF 4. In addition, the control unit 11 is capable of calculating the engine speed of the internal combustion engine 1, which is the rotation speed of the crankshaft, based on the detection signal of the crank angle sensor 16.

[0020] The control unit 11 corresponds to a control unit, and when predetermined fuel cut permission conditions are met while the internal combustion engine 1 is operating, it implements a fuel cut to stop the supply of fuel to the internal combustion engine 1. The fuel cut permission conditions are met, for example, when, after warm-up of the internal combustion engine 1 is complete, the engine speed is equal to or higher than a predetermined fuel cut rotation speed, and the accelerator opening is equal to or lower than a predetermined opening (for example, the accelerator is off), or the required torque (required output) of the internal combustion engine 1 is equal to or lower than a predetermined value. The fuel cut is implemented by stopping fuel injection from a fuel injection valve (not shown) of the internal combustion engine 1.

[0021] The control unit 11 is also capable of calculating the amount (accumulation amount) of exhaust particulate matter trapped in the GPF 4 using two different methods.

[0022] That is, the control unit 11 is capable of calculating the first trapped amount based on the operating history (operating state) of the internal combustion engine 1 and the second trapped amount based on the differential pressure across the GPF 4 .

[0023] The first collection amount is calculated by accumulating the amount of exhaust particulate matter deposited in the GPF 4 (collection amount) per unit time, which is determined by the operating conditions of the internal combustion engine 1. The load and engine speed of the internal combustion engine 1 are used as the operating conditions of the internal combustion engine 1. The first collection amount can be calculated, for example, by preparing a map in advance, which is obtained by experiments or the like, showing the relationship between these parameters and the amount of exhaust particulate matter deposited in the GPF 4 (collection amount) per unit time. In this embodiment, the first collection amount is constantly calculated.

[0024] The second collection amount can be expressed, for example, by a function having parameters of a differential pressure ΔP, which is the differential pressure between the upstream and downstream sides of the GPF 4, and the exhaust gas flow rate Q flowing (passing) through the GPF 4. When the exhaust gas flow rate Q is constant, the differential pressure ΔP increases as the amount of exhaust particulate matter trapped in the GPF 4 increases. Therefore, the second collection amount can be calculated by preparing a map that predefines the relationship between the exhaust gas flow rate Q and the differential pressure ΔP for the collection amounts of a plurality of different exhaust particulate matter. In this embodiment, the second collection amount is calculated at predetermined time intervals.

[0025] The particulate matter trapped in the GPF 4 is removed by, for example, appropriate combustion using a well-known filter regeneration method. However, if the regeneration process of the GPF 4 is delayed for some reason, the particulate matter trapped in the GPF 4 increases without being burned and removed.

[0026] For example, when the amount of particulate matter trapped in the GPF 4 is equal to or greater than a predetermined amount and the temperature of the GPF 4 is equal to or greater than a predetermined temperature, the control unit 11 prohibits fuel cutoff as a measure to prevent damage due to excessive temperature rise of the GPF 4. This is because if fuel cutoff is performed when the amount of trapped particulate matter is large and the temperature of the GPF 4 is high, and oxygen flows into the GPF 4, the trapped (accumulated) particulate matter may burn all at once, causing significant deterioration of the GPF 4.

[0027] Here, in the internal combustion engine 1, there is a risk that some functional diagnoses, such as a functional diagnosis of the oxygen sensor 12, cannot be performed at the desired timing because fuel cut is prohibited. In other words, if the amount of particulate matter trapped in the GPF 4 increases and fuel cut is prohibited more frequently, there is a risk that the frequency of performing some functional diagnoses of the internal combustion engine 1 will not be guaranteed. The control unit 11 diagnoses whether the oxygen sensor 12 is functioning normally, for example, based on a detection signal of the air-fuel ratio of the oxygen sensor 12, which changes due to fuel cut.

[0028] Therefore, the control unit 11 performs a function assurance diagnosis of the internal combustion engine 1 to determine whether or not the implementation of various function diagnoses of the internal combustion engine 1 that are performed during fuel cut while the vehicle is running is guaranteed, and if the implementation of various function diagnoses of the internal combustion engine 1 that are performed during fuel cut is not guaranteed, it determines that there is a malfunction that prevents the various diagnostic functions from being performed, and notifies the driver of this by turning on a warning light, for example.

[0029] In other words, while the vehicle is running, the control unit 11 performs a functional assurance diagnosis of the internal combustion engine to determine whether the frequency of various functional diagnoses of the internal combustion engine 1 performed during fuel cut is ensured.

[0030] Specifically, the control unit 11 uses the first collection amount, the second collection amount, and a judgment threshold set based on the first collection amount, and determines that when the second collection amount becomes larger than the judgment threshold, the frequency with which the fuel cut will be prohibited will increase, and determines that a malfunction has occurred.

[0031] In more detail, the control unit 11 corresponds to a determination unit, and determines that the frequency of fuel cut prohibition will increase if the second collected amount exceeds the determination threshold value a predetermined number of times in succession at the timing when the second collected amount is calculated (updated). In other words, the control unit 11 determines that the frequency of fuel cut prohibition will increase if the state in which the second collected amount exceeds the determination threshold value continues for a predetermined period of time or more.

[0032] The determination threshold is, for example, a value obtained by adding a predetermined value (constant value) to the first collection amount, and is always a value that is always a constant amount greater than the first collection amount. Note that, in some cases, the first collection amount itself may be used as the determination threshold.

[0033] In addition, when the outside air temperature is below a predetermined outside air temperature threshold, which is a predetermined temperature set in advance, in order to avoid erroneous diagnosis, it is possible not to make a judgment by comparing the calculated second collection amount with the judgment threshold.

[0034] 2 is a timing chart showing changes in various parameters during the performance assurance diagnosis of the internal combustion engine 1. Note that times t1 to t7 are the timings for calculating (updating) the second trapped amount. The performance assurance diagnosis of the internal combustion engine 1 is basically performed at the timings for calculating the second trapped amount.

[0035] The collection amount shown by a thick solid line in FIG. 2 indicates the first collection amount. The first collection amount is constantly calculated. The collection amount shown by a thick dashed line in FIG. 2 indicates the second collection amount. The second collection amount shown in FIG. 2 is updated each time the second collection amount is calculated, and until the next calculation, a value interpolated using the first collection amount is shown for convenience. Specifically, until the next calculation, the second collection amount shown in FIG. 2 conveniently shows the value obtained by adding the first collection amount at that time to the difference between the most recently calculated second collection amount and the first collection amount when the second collection amount was calculated. The collection amount shown by a thin solid line in FIG. 2 indicates the judgment threshold. As described above, the judgment threshold is a value obtained by adding a predetermined value to the first collection amount.

[0036] 2 is the timing for performing a functional assurance diagnosis of the internal combustion engine 1, but because the outside air temperature is below the outside air temperature threshold, the OK / NG determination execution flag, which serves as a trigger for the functional assurance diagnosis of the internal combustion engine 1, remains OFF. The OK / NG determination execution flag is turned ON if the outside air temperature is equal to or higher than the outside air temperature threshold at the timing for calculating the second trapped amount. When the OK / NG determination execution flag is turned ON, the control unit 11 performs a functional assurance diagnosis of the internal combustion engine 1.

[0037] At time t2 in Figure 2, the outside air temperature exceeds the outside air temperature threshold and the OK / NG determination execution flag is turned ON. When the OK / NG determination execution flag is turned ON, a functional assurance diagnosis of the internal combustion engine 1 is performed and the count value of the execution determination counter is counted up (incremented). When the count value of the execution determination counter reaches a preset execution threshold, it is reset to an initial value (e.g., zero). Note that in Figure 2, since the outside air temperature exceeds the outside air temperature threshold after time t2, the OK / NG determination execution flag is turned ON at the timing when the second collection amount is calculated.

[0038] When the OK / NG judgment execution flag is turned ON, the OK judgment flag and the NG judgment flag are both turned ON. When the OK judgment flag is turned ON, if the updated second trapped amount is equal to or less than the judgment threshold, the diagnostic result of the functional assurance diagnosis of the internal combustion engine 1 is diagnosed as OK, and the count value of the OK judgment counter is counted up (incremented). When the NG judgment flag is turned ON, if the updated second trapped amount is greater than the judgment threshold, the diagnostic result of the functional assurance diagnosis of the internal combustion engine 1 is diagnosed as NG, and the count value of the NG judgment counter is counted up (incremented). In other words, when the OK / NG judgment execution flag is turned ON, the count value of one of the OK judgment counter and the NG judgment counter is counted up.

[0039] At time t2, the updated second collection amount is greater than the judgment threshold, so the count value of the NG judgment counter is counted up (incremented), and the count value of the OK judgment counter is not counted up and remains at the current value.

[0040] At time t3, the updated second collection amount is less than or equal to the judgment threshold, so the count value of the OK judgment counter is counted up (incremented), and the count value of the NG judgment counter is not counted up and remains at the current value.

[0041] Time t4 is the timing when the count value of the enforcement determination counter reaches the enforcement threshold. The count value of the enforcement determination counter is immediately reset to its initial value when it reaches the enforcement threshold. In this embodiment, the count value of the enforcement determination counter is reset to its initial value when the OK / NG determination enforcement flag is turned ON three times in a row. In other words, the enforcement threshold in this embodiment is three times. Note that the value of the enforcement threshold is not limited to three times.

[0042] At time t4, the updated second collection amount is greater than the judgment threshold, so the count value of the NG judgment counter is counted up (incremented), and the count value of the OK judgment counter is not counted up and remains at the current value.

[0043] Furthermore, at time t4, the count value of the OK judgment counter does not reach the OK threshold, so the OK confirmation flag is maintained in the OFF state. Furthermore, at time t4, the count value of the NG judgment counter does not reach the NG threshold, so the NG confirmation flag is maintained in the OFF state. Note that, since the count value of the enforcement judgment counter reaches the enforcement threshold at time t4, the count values ​​of the OK judgment counter and the NG judgment counter are reset to their initial values ​​(e.g., zero) immediately after time t4.

[0044] At time t5, the updated second collection amount is greater than the judgment threshold, so the count value of the NG judgment counter is counted up (incremented), and the count value of the OK judgment counter is not counted up and remains at the current value.

[0045] At time t6, the updated second collection amount is greater than the judgment threshold, so the count value of the NG judgment counter is counted up (incremented), and the count value of the OK judgment counter is not counted up and remains at the current value.

[0046] At time t7, the updated second collection amount is greater than the judgment threshold, so the count value of the NG judgment counter is counted up (incremented), while the count value of the OK judgment counter remains the same. Also, at time t7, the count value of the NG judgment counter has reached the NG threshold, so the NG confirmation flag is turned on.

[0047] That is, at time t7, it is determined that the execution of various functional diagnoses of the internal combustion engine 1 that are performed during fuel cut is not guaranteed. The driver is notified, for example, that there is a malfunction that prevents the execution of various diagnostic functions at time t7.

[0048] In addition, the count value of the implementation judgment counter, the count value of the OK judgment counter, and the count value of the NG judgment counter are reset to their initial values ​​immediately after time t7, because the count value of the implementation judgment counter reaches the implementation threshold at time t7.

[0049] As described above, the internal combustion engine 1 can ensure that the frequency of execution of diagnoses that require fuel cut is not lower than expected by determining that the second trapped amount does not become larger than the determination threshold. In other words, the internal combustion engine 1 can determine whether or not execution of various functional diagnoses of the internal combustion engine 1 during fuel cut is guaranteed by determining the frequency at which fuel cut is prohibited.

[0050] Furthermore, in the function assurance diagnosis of the internal combustion engine 1, when the second collected amount is greater than the judgment threshold value for a predetermined number of consecutive times (for example, three times), it is determined that fuel cut-off of the internal combustion engine 1 is frequently prohibited and that the execution of various functional diagnoses of the internal combustion engine 1 is not guaranteed. Therefore, in the function assurance diagnosis of the internal combustion engine 1, it is possible to improve the reliability (accuracy) of the determination result that the execution of various functional diagnoses of the internal combustion engine 1 is not guaranteed.

[0051] Furthermore, in the function assurance diagnosis of the internal combustion engine 1, when the second collected amount is equal to or less than the determination threshold value a predetermined number of times (for example, three times) in succession, it is determined that the frequency with which fuel cut of the internal combustion engine 1 is prohibited is low and that the implementation of various functional diagnoses of the internal combustion engine 1 is guaranteed. Therefore, in the function assurance diagnosis of the internal combustion engine 1, it is possible to improve the reliability (accuracy) of the determination result that the implementation of various functional diagnoses of the internal combustion engine 1 is guaranteed.

[0052] FIG. 3 is a flowchart showing an example of a diagnostic procedure for the function assurance diagnosis of the internal combustion engine 1.

[0053] In step S1, it is determined whether the outside air temperature is equal to or higher than the outside air temperature threshold. If it is determined in step S1 that the outside air temperature is equal to or higher than the outside air temperature threshold, the routine proceeds to step S2. If it is determined in step S1 that the outside air temperature is lower than the outside air temperature threshold, the count values ​​of various determination counters are reset to initial values ​​(e.g., zero), and the current routine ends.

[0054] In step S2, it is determined whether it is time to calculate (update) the second collection amount. If it is determined in step S2 that it is time to calculate (update) the second collection amount, the second collection amount is calculated (updated) and the routine proceeds to step S3. If it is determined in step S2 that it is not time to calculate (update) the second collection amount, the current routine ends without calculating (updating) the second collection amount.

[0055] In step S3, the count value of the execution determination counter is incremented (counted up).

[0056] In step S4, it is determined whether the calculated second collection amount is greater than the determination threshold. If the calculated second collection amount is greater than the determination threshold, the process proceeds to step S5. If the calculated second collection amount is equal to or less than the determination threshold, the process proceeds to step S6.

[0057] In step S5, the count value of the NG determination counter is incremented (counted up).

[0058] In step S6, the count value of the OK determination counter is incremented (counted up).

[0059] In step S7, it is determined whether the count value of the execution determination counter is equal to or greater than the execution threshold value. If it is determined in step S7 that the count value of the execution determination counter is equal to or greater than the execution threshold value, the process proceeds to step S8. If it is determined in step S7 that the count value of the execution determination counter is less than the execution threshold value, the current routine is terminated.

[0060] In step S8, it is determined whether the count value of the NG judgment counter is equal to or greater than the NG threshold. If it is determined in step S8 that the count value of the NG judgment counter is equal to or greater than the NG threshold, the process proceeds to step S9. If it is determined in step S8 that the count value of the NG judgment counter is less than the NG threshold, the process proceeds to step S10.

[0061] In step S9, it is determined that the execution of various functional diagnoses of the internal combustion engine 1 is not guaranteed, resulting in an NG determination.

[0062] In step S10, it is determined whether the count value of the OK judgment counter is equal to or greater than the OK threshold. If it is determined in step S10 that the count value of the OK judgment counter is equal to or greater than the OK threshold, the process proceeds to step S11. If it is determined in step S10 that the count value of the OK judgment counter is less than the OK threshold, the count values ​​of the various judgment counters are reset to their initial values ​​(e.g., zero), and the current routine is terminated.

[0063] In step S11, it is determined that the execution of various functional diagnoses of the internal combustion engine 1 is guaranteed, ie, OK.

[0064] In steps S9 and S11, the count values ​​of the various determination counts are reset to initial values ​​(for example, zero).

[0065] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0066] The above-described embodiments relate to a diagnostic method for an internal combustion engine and a diagnostic device for an internal combustion engine.

Claims

1. A diagnostic method for an internal combustion engine having an exhaust particulate filter arranged in an exhaust passage to capture particulate matter in the exhaust, which prohibits fuel cut-off, which stops fuel injection from a fuel injection valve of the internal combustion engine, when the particulate matter captured on the exhaust particulate filter reaches a predetermined amount or more, the method using: a first collection amount, which is calculated based on the amount of particulate matter captured on the exhaust particulate filter based on the operating state of the internal combustion engine; a second collection amount, which is calculated based on the amount of particulate matter captured on the exhaust particulate filter based on the differential pressure before and after the exhaust particulate filter; and a judgment threshold value set based on the first collection amount, and determining that the frequency of prohibiting fuel cut-off will increase when the second collection amount becomes larger than the judgment threshold value.

2. A diagnostic method for an internal combustion engine as described in claim 1, in which if the second collection amount becomes greater than the judgment threshold at the time the second collection amount is calculated a predetermined number of times in succession, it is determined that the frequency with which the fuel cut will be prohibited will increase.

3. A diagnostic method for an internal combustion engine according to claim 1, wherein when the outside air temperature is equal to or lower than a predetermined temperature, determination based on a comparison of the calculated second trapped amount with the determination threshold value is not performed.

4. A diagnostic device for an internal combustion engine having: an exhaust particulate filter arranged in an exhaust passage for capturing particulate matter in the exhaust; a control unit for prohibiting fuel cut-off, which stops fuel injection from a fuel injection valve of the internal combustion engine, when the amount of particulate matter captured on the exhaust particulate filter reaches a predetermined amount; and a judgment unit for determining, using a first collection amount calculated based on the amount of particulate matter captured on the exhaust particulate filter based on the operating state of the internal combustion engine, a second collection amount calculated based on the amount of particulate matter captured on the exhaust particulate filter based on the differential pressure before and after the exhaust particulate filter, and a judgment threshold value set based on the first collection amount, that if the second collection amount becomes larger than the judgment threshold value, the frequency of prohibiting fuel cut-off will increase.

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