Filter abnormality detection system

Abstract

To provide a filter abnormality determination system which can determine an abnormality of a filter while inhibiting influence on a combustion state of an internal combustion engine.SOLUTION: A filter abnormality determination system includes: an internal combustion engine having multiple cylinders; an exhaust passage connected to the internal combustion engine; a filter provided at the exhaust passage; a sensor which is provided at the exhaust passage, faces the filter, and outputs a detection value according to an oxygen concentration in exhaust air; and a determination device. The determination device includes: a control unit which executes imbalance control in which an air-fuel ratio of one of the cylinders is controlled to be a value different from air-fuel ratios of the other cylinders; and a determination unit which determines whether or not an abnormality occurs in the filter based on the detection value of the sensor which corresponds to the air-fuel ratio of the exhaust air of the one cylinder when the imbalance control is executed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a filter abnormality determination system. [Background technology]

[0002] There is known a technique for determining whether a filter is abnormal based on the delay between when the air-fuel ratio of an internal combustion engine is changed and when the air-fuel ratio sensor detects this change (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-075458 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned fluctuations in the air-fuel ratio may change the combustion state of the internal combustion engine, which may affect fuel economy, power performance, exhaust emissions, and the like.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a filter abnormality determination system that can determine filter abnormality while minimizing the effect on the combustion state of an internal combustion engine. [Means for solving the problem]

[0006] The object is to provide an internal combustion engine including an internal combustion engine having a plurality of cylinders, an exhaust passage connected to the internal combustion engine, a filter provided in the exhaust passage, a sensor provided in the exhaust passage facing the filter and outputting a detection value corresponding to an oxygen concentration in exhaust, and a determination device, wherein the determination device includes: a control unit that executes imbalance control that controls the air-fuel ratio of one of the plurality of cylinders to a value different from the air-fuel ratios of the remaining cylinders of the plurality of cylinders, and a determination unit that determines whether or not the filter is abnormal based on the detection value of the sensor that corresponds to the air-fuel ratio of the exhaust of the one cylinder during execution of the imbalance control. the imbalance control controls the air-fuel ratio of the one cylinder to a rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, the determination unit determines whether the filter is abnormal by comparing a detection value of the sensor that corresponds to the air-fuel ratio of the exhaust of the one cylinder with a determination value, the exhaust passage has a curved portion that is located upstream of the filter and extends in a curved manner facing the filter, the sensor is provided on the curved portion, the curved portion is curved at a predetermined curvature and includes an inner wall portion and an outer wall portion that face each other in a radial direction of the curvature, the sensor is provided on the inner wall portion side, the determination value is a minimum value of the air-fuel ratio of the exhaust of the one cylinder measured by the sensor when the filter is abnormal during execution of the imbalance control, and the determination unit determines that the filter is abnormal if the detection value is equal to or greater than the determination value, and determines that the filter is normal if the detection value is less than the determination value. This can be achieved by a filter abnormality determination system.

[0007] The object is to provide an internal combustion engine having a plurality of cylinders, an exhaust passage connected to the internal combustion engine, a filter provided in the exhaust passage, a sensor provided in the exhaust passage facing the filter and outputting a detection value corresponding to an oxygen concentration in exhaust, and a determination device, wherein the determination device comprises a control unit that executes imbalance control to control the air-fuel ratio of one of the plurality of cylinders to a value different from the air-fuel ratios of the remaining cylinders of the plurality of cylinders, and a determination unit that determines whether or not the filter is abnormal based on the detection value of the sensor corresponding to the air-fuel ratio of the exhaust of the one cylinder during execution of the imbalance control, wherein the imbalance control controls the air-fuel ratio of the one cylinder to a rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and the determination unit determines whether or not the filter is abnormal based on the detection value of the sensor corresponding to the air-fuel ratio of the exhaust of the one cylinder This can also be achieved by a filter abnormality determination system in which a determination is made as to whether the filter is abnormal by comparing the detection value of the sensor with a determination value, the exhaust passage having a curved portion located upstream of the filter and extending in a curved manner opposite the filter, the sensor being provided on the curved portion, the curved portion being curved at a predetermined curvature and including an inner wall portion and an outer wall portion facing each other in the direction of the radius of curvature, the sensor being provided on the outer wall portion side, the determination value being the maximum value of the air-fuel ratio of the exhaust from the one cylinder measured by the sensor when the filter is abnormal during execution of the imbalance control, and the determination unit determining that the filter is abnormal if the detection value is equal to or less than the determination value, and determining that the filter is normal if the detection value is greater than the determination value. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a filter abnormality determination system that can determine a filter abnormality while suppressing the influence on the combustion state of an internal combustion engine. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a filter abnormality determination system according to this embodiment. [Figure 2] FIG. 2A is an enlarged view of the air-fuel ratio sensor and its surroundings, and FIG. 2B is an explanatory diagram of the difference in the air-fuel ratio detected by the air-fuel ratio sensor when the GPF is normal and when it is abnormal during execution of imbalance control. [Figure 3] FIG. 3 is a flowchart showing an example of abnormality determination control executed by the ECU. [Figure 4] 4A and 4B are explanatory diagrams of a first modified example. [Figure 5] FIG. 5A is an explanatory diagram of a second modified example, FIG. 5B is an explanatory diagram of a third modified example, and FIG. 5C is an explanatory diagram of a fourth modified example. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Outline of filter abnormality detection system] FIG. 1 is a schematic diagram of a filter abnormality determination system 1 according to the present embodiment. The filter abnormality determination system 1 includes an engine 10, an exhaust manifold 20, an exhaust passage 30, a three-way catalyst 40, a GPF (Gasoline Particulate Filter) 50, air-fuel ratio sensors 60 and 70, and an ECU (Electronic Control Unit) 100. The engine 10 is an example of an internal combustion engine, and is a spark-ignition gasoline engine, but may also be a compression-ignition diesel engine. The engine 10 is a four-stroke engine in which one combustion cycle is made up of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 10 has four cylinders #1 to #4, but is not limited to this as long as it has multiple cylinders. The exhaust strokes of the cylinders #1 to #4 are executed in the order of #1, #3, #4, and #2, i.e., exhaust occurs at different timings. Each of the cylinders #1 to #4 is provided with an in-cylinder injection valve 11 to 14 that injects fuel into the cylinder, but is not limited to this. For example, port injection valves that inject fuel into the intake ports of the cylinders #1 to #4 may be provided in addition to or instead of the in-cylinder injection valves 11 to 14. An intake pipe is connected to the engine 10 via an intake manifold.

[0014] Exhaust manifold 20 is connected to engine 10, and exhaust gas discharged from each of cylinders #1 to #4 passes through it. In detail, exhaust manifold 20 includes branch pipe sections 21 to 24 connected to cylinders #1 to #4, respectively, and collecting pipe section 25 where these are gathered and connected downstream. The exhaust passage 30 is connected to the downstream end of the collecting pipe portion 25 of the exhaust manifold 20. Exhaust gases discharged at different times from each of the cylinders #1 to #4 flow through the exhaust passage 30 via the exhaust manifold 20. In the exhaust passage 30, an air-fuel ratio sensor 60, a three-way catalyst 40, an air-fuel ratio sensor 70, and a GPF 50 are arranged in this order from upstream to downstream.

[0015] The air-fuel ratio sensor 60 detects the air-fuel ratio of the exhaust gas discharged from the engine 10 and flowing into the three-way catalyst 40. The air-fuel ratio sensor 70 detects the air-fuel ratio of the exhaust gas discharged from the three-way catalyst 40 and flowing into the GPF 50. The air-fuel ratios detected by the air-fuel ratio sensors 60 and 70 are values that correlate with the oxygen concentration in the exhaust gas. Therefore, the air-fuel ratio sensor 70 is an example of a sensor that outputs a detection value corresponding to the oxygen concentration in the exhaust gas. The air-fuel ratio sensor 70 is provided in a position facing the GPF 50.

[0016] The three-way catalyst 40 contains a catalytic metal such as platinum (Pt), palladium (Pd), or rhodium (Rh), has oxygen storage capacity, and purifies NOx, HC, and CO. The GPF 50 is a porous ceramic structure that captures exhaust particulates (hereinafter referred to as PM (Particulate Matter)) in the exhaust gas. The GPF 50 is an example of a filter. If the engine 10 is a diesel engine, for example, a DPF (Diesel Particulate Filter) is provided instead of the GPF 50.

[0017] The ECU 100 is an electronic control unit including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and a backup RAM. The ECU 100 is electrically connected to air-fuel ratio sensors 60 and 70, and receives measurement values from these sensors. The ECU 100 controls the amount of fuel injected from the direct injection valves 11 to 14 based on the detection results of the air-fuel ratio sensors 60 and 70.

[0018] The ECU 100 executes determination control to determine whether or not there is an abnormality in the GPF 50, based on the detection value of the air-fuel ratio sensor 70 during execution of imbalance control, which will be described later. The ECU 100 is an example of a determination device, and functionally realizes a control unit and a determination unit, which will be described in detail later.

[0019] Imbalance control is a control that changes the air-fuel ratio of one of cylinders #1 to #4 to a value different from the air-fuel ratios of the remaining cylinders. For example, in this embodiment, imbalance control is achieved by controlling the air-fuel ratios of cylinders #2 to #4 to the stoichiometric air-fuel ratio while controlling the air-fuel ratio of cylinder #1 to a rich air-fuel ratio lower than the stoichiometric air-fuel ratio. Specifically, imbalance control is achieved by increasing the fuel injection amount of the direct injection valve 11 of cylinder #1 by a predetermined amount from a state in which the air-fuel ratios of cylinders #1 to #4 are all controlled to the stoichiometric air-fuel ratio. During imbalance control, the air-fuel ratios of the exhaust gas from cylinders #2 to #4 are approximately the stoichiometric air-fuel ratio, while the air-fuel ratio of the exhaust gas from cylinder #1 is a rich air-fuel ratio. In other words, the air-fuel ratio of the exhaust gas from cylinder #1 is lower than the air-fuel ratios of the exhaust gas from cylinders #2 to #4.

[0020] The air-fuel ratio sensor 70 and its surroundings will be described in detail. FIG. 2A is an enlarged view of the air-fuel ratio sensor 70 and its surroundings. Between the three-way catalyst 40 and the GPF 50 in the exhaust passage 30, a straight portion 32, a curved portion 34, and a straight portion 36 are formed, in this order from upstream to downstream. The straight portions 32 and 36 each extend linearly. The curved portion 34 extends while being curved at a predetermined curvature. The air-fuel ratio sensor 70 is provided at the downstream end of the curved portion 34. The curved portion 34, which is curved at a predetermined curvature, includes an inner wall portion 341 and an outer wall portion 342 that face each other in the direction of the radius of curvature. The outer wall portion 342 has a larger radius of curvature than the inner wall portion 341. The air-fuel ratio sensor 70 is provided on the inner wall portion 341 side, and the tip of the air-fuel ratio sensor 70 is provided so as to be located near the center of the passage cross section of the exhaust passage 30.

[0021] [Filter Abnormality] Next, an abnormality in the GPF 50 will be described. In FIG. 2A, arrows indicate the difference in the way exhaust gas flows when the GPF 50 is normal and abnormal during imbalance control. FIG. 2B is an explanatory diagram of the difference in the air-fuel ratio detected by the air-fuel ratio sensor 70 when the GPF 50 is normal and abnormal during imbalance control. In FIGS. 2A and 2B, the normal case is indicated by a solid line, and the abnormal case is indicated by a dotted line. Here, an abnormality in the GPF 50 refers to, for example, when a portion of the GPF 50 is missing or melted. In this case, the pressure loss of the exhaust gas is smaller than when it is normal.

[0022] As shown in FIG. 2A, under normal conditions, exhaust gas flows near the center of the passage cross section of the curved portion 34. In contrast, under abnormal conditions, the pressure loss of the exhaust gas is smaller than under normal conditions, so the exhaust gas flows unevenly toward the outer wall portion 342. As a result, under abnormal conditions, the flow rate of exhaust gas impinging on the air-fuel ratio sensor 70 is lower than under normal conditions. For this reason, as shown in FIG. 2B, under abnormal conditions, the fluctuation range of the air-fuel ratio detected by the air-fuel ratio sensor 70 is narrower than under normal conditions. Therefore, during execution of imbalance control, the detected air-fuel ratio of the exhaust gas from cylinder #1 by the air-fuel ratio sensor 70 indicates a larger value under abnormal conditions than under normal conditions. In other words, under abnormal conditions, the degree of richness is lower than under normal conditions. In this way, it is possible to determine whether the GPF 50 is normal or abnormal based on the detected air-fuel ratio of the exhaust gas from cylinder #1 by the air-fuel ratio sensor 70.

[0023] [Abnormality detection control] FIG. 3 is a flowchart showing an example of abnormality determination control executed by ECU 100. This control is repeatedly executed at predetermined intervals while the ignition is on. ECU 100 determines whether a predetermined determination condition is met (step S1). This determination condition is a condition indicating that the operating state of engine 10 is not in a transient state. For example, the determination condition is that the rate of change of engine speed or accelerator opening degree falls within a predetermined range, and that warm-up control, regeneration control of GPF 50, or fuel cut control is stopped. If step S1 is No, this control ends. If step S1 is Yes, ECU 100 executes imbalance control (step S2).

[0024] Next, the ECU 100 determines whether the air-fuel ratio of the exhaust gas from cylinder #1 detected by the air-fuel ratio sensor 70 is equal to or greater than a determination value (step S3). The determination value indicates the minimum value of the air-fuel ratio of the exhaust gas from cylinder #1 detected by the air-fuel ratio sensor 70 when the GPF 50 is abnormal during execution of imbalance control. The determination value is set in advance based on experimental results and simulation results. Whether the air-fuel ratio detected by the air-fuel ratio sensor 70 is the air-fuel ratio of the exhaust gas from cylinder #1 or the air-fuel ratio of the exhaust gas from the other cylinders can be determined based on the engine speed and the combustion timing of each of cylinders #1 to #4. The determination value may be a fixed value or may be a variable value that varies depending on the intake air amount and engine speed.

[0025] If the answer is Yes in step S3, the ECU 100 determines that the GPF 50 is abnormal (step S4). If the GPF 50 is determined to be abnormal, the ECU 100 may, for example, turn on a Malfunction Indicator Light (MIL) to notify the driver that an abnormality has occurred in the GPF 50. If the answer is No in step S3, the ECU 100 determines that the GPF 50 is normal (step S5).

[0026] As described above, the imbalance control executed to determine whether the GPF 50 has an abnormality is performed by changing only the air-fuel ratio of cylinder #1. Therefore, compared to when the imbalance control is executed by changing the air-fuel ratio of all cylinders, it is possible to determine whether the GPF 50 has an abnormality while minimizing the impact on the combustion state of the engine 10. As a result, it is possible to ensure the frequency with which the abnormality determination control is executed.

[0027] 2A, by providing the air-fuel ratio sensor 70 in the curved portion 34, the flow rate of the exhaust gas impinging on the air-fuel ratio sensor 70 changes significantly between when the GPF 50 is normal and when it is abnormal. This allows for accurate determination of whether the GPF 50 is abnormal.

[0028] In the above embodiment, the imbalance control is performed by controlling the air-fuel ratio of cylinder #1 to a rich air-fuel ratio lower than the stoichiometric air-fuel ratio. However, this is not limited to this, and the imbalance control may be performed by controlling the air-fuel ratio of cylinder #1 to a lean air-fuel ratio higher than the stoichiometric air-fuel ratio. Specifically, this imbalance control can be achieved by reducing the fuel injection amount of the direct injection valve 11 of cylinder #1 by a predetermined amount from a state in which the air-fuel ratios of cylinders #1 to #4 are all controlled to the stoichiometric air-fuel ratio. In this case, the air-fuel ratio of cylinder #1 detected by the air-fuel ratio sensor 70 is smaller in an abnormal state than in a normal state. That is, the degree of leanness in an abnormal state is lower than in a normal state. Therefore, it is sufficient to determine that the GPF 50 is abnormal when the air-fuel ratio of cylinder #1 detected by the air-fuel ratio sensor 70 is equal to or lower than a predetermined determination value. Note that, from the viewpoint of preventing deterioration of fuel economy, it is preferable to achieve the imbalance control by controlling the air-fuel ratio of cylinder #1 to a lean air-fuel ratio. Furthermore, from the viewpoint of preventing misfires in the engine 10, it is preferable to achieve imbalance control by controlling the air-fuel ratio of cylinder #1 to a rich air-fuel ratio.

[0029] The imbalance control may be achieved by controlling the air-fuel ratios of the cylinders #2 to #4 to lean air-fuel ratios so as to offset the amount of decrease in the air-fuel ratio from the stoichiometric air-fuel ratio that would occur if the air-fuel ratio in the cylinder #1 were controlled to a rich air-fuel ratio. Alternatively, the air-fuel ratios of the cylinders #2 to #4 may be controlled to rich air-fuel ratios so as to offset the amount of increase in the air-fuel ratio from the stoichiometric air-fuel ratio that would occur if the air-fuel ratio in the cylinder #1 were controlled to a lean air-fuel ratio. In either case, fluctuations in the air-fuel ratio of the entire engine 10 can be suppressed, thereby suppressing fluctuations in the output of the engine 10 due to the imbalance control.

[0030] Imbalance control may be achieved, for example, by changing the air-fuel ratio of two or more cylinders. However, changing the air-fuel ratio of all cylinders has a significant impact on the combustion state, so it is preferable not to change the air-fuel ratio of at least one remaining cylinder. Alternatively, when the air-fuel ratios of multiple cylinders are changed to a rich air-fuel ratio, it is preferable to leave the air-fuel ratio of the remaining cylinders unchanged or change it to the lean side. Similarly, when the air-fuel ratios of multiple cylinders are changed to a lean air-fuel ratio, it is preferable to leave the air-fuel ratio of the remaining cylinders unchanged or change it to the rich side.

[0031] [First Modification] Next, several modified examples will be described. In the modified examples, the same components as those in the above-described embodiment are designated by the same reference numerals, and redundant description will be omitted. FIGS. 4A and 4B are explanatory diagrams of a first modified example. FIGS. 4A and 4B correspond to FIGS. 2A and 2B, respectively. In the first modified example, the air-fuel ratio sensor 70 is provided on the outer wall portion 342 side. Unlike the above-described embodiment, the flow rate of exhaust gas impinging on the air-fuel ratio sensor 70 increases during an abnormal state compared to normal operation. Therefore, even when imbalance control similar to that in the above-described embodiment is performed, the detected air-fuel ratio of the exhaust gas from cylinder #1 exhibits a smaller value during an abnormal state than during normal operation, unlike the above-described embodiment. In other words, the richness increases during an abnormal state compared to normal operation. Therefore, in the first modified example, the ECU 100 determines that the GPF 50 is abnormal if the detected air-fuel ratio of the exhaust gas from cylinder #1 measured by the air-fuel ratio sensor 70 is equal to or less than a predetermined determination value. The determination value in this case indicates the maximum value of the air-fuel ratio of the exhaust gas from cylinder #1 measured by the air-fuel ratio sensor 70 when the GPF 50 is abnormal during imbalance control.

[0032] In this way, even in the first modified example, imbalance control is performed by changing only the air-fuel ratio of cylinder #1, so it is possible to determine an abnormality in the GPF 50 while suppressing the effect on the combustion state of the engine 10. Also, in the first modified example, the air-fuel ratio sensor 70 is provided in the curved portion 34. Therefore, the flow rate of exhaust gas impinging on the air-fuel ratio sensor 70 changes significantly between when the GPF 50 is normal and when it is abnormal, and it is possible to accurately determine an abnormality in the GPF 50.

[0033] In the first modified example, the air-fuel ratio of cylinder #1 may also be controlled to be leaner than the stoichiometric air-fuel ratio. In this case, the air-fuel ratio of cylinder #1 detected by the air-fuel ratio sensor 70 is greater in an abnormal state than in a normal state. That is, the air-fuel ratio is leaner in an abnormal state than in a normal state. Therefore, it is sufficient to determine that the GPF 50 is abnormal when the air-fuel ratio of cylinder #1 detected by the air-fuel ratio sensor 70 is equal to or greater than a predetermined determination value.

[0034] In the first modified example and the above embodiment, the air-fuel ratio sensor 70 is provided in the curved portion 34, but it may also be provided in the straight portion 36, which is downstream of the curved portion 34. In this case as well, when the GPF 50 is normal, the exhaust gas flows near the center of the passage cross section of the straight portion 36, whereas when an abnormality occurs, the exhaust gas flows unevenly to one side of the side wall of the straight portion 36. As a result, the flow rate of the exhaust gas impinging on the air-fuel ratio sensor 70 changes significantly between normal and abnormal conditions, making it possible to accurately determine whether the GPF 50 is abnormal.

[0035] In the above embodiment, the flow rate of exhaust gas impinging on the air-fuel ratio sensor 70 decreases in an abnormal state compared to normal states, whereas in the first modified example, the flow rate of exhaust gas impinging on the air-fuel ratio sensor 70 increases in an abnormal state compared to normal states. For this reason, in the first modified example, the air-fuel ratio sensor 70 needs to be installed in a position where the flow rate of exhaust gas increases in an abnormal state, which places more restrictions on the installation location of the air-fuel ratio sensor 70 than in the above embodiment. For this reason, considering the restrictions on the installation location of the air-fuel ratio sensor 70, it is preferable to install the air-fuel ratio sensor 70 as in the above embodiment.

[0036] [Second Modification] 5A is an explanatory diagram of a second modified example. FIG. 5A corresponds to FIG. 2A. Unlike the above embodiment, the second modified example does not include a three-way catalyst 40 or an air-fuel ratio sensor 60. Even with this configuration, it is possible to determine whether or not the GPF 50 is abnormal based on the air-fuel ratio detected by the air-fuel ratio sensor 70 while imbalance control is being executed.

[0037] [Third Modification] 5B is an explanatory diagram of a third modified example. FIG. 5B corresponds to FIG. 2A. Unlike the above-described embodiment, the third modified example does not include a three-way catalyst 40 or an air-fuel ratio sensor 60, but instead includes an air-fuel ratio sensor 80 in the exhaust passage 30 downstream of the GPF 50. Even with this configuration, it is possible to determine whether the GPF 50 is abnormal based on the air-fuel ratio detected by the air-fuel ratio sensor 70 while imbalance control is being executed.

[0038] In a third modified example, an abnormality of the GPF 50 may be determined based on the detected air-fuel ratio of the air-fuel ratio sensor 80 provided downstream of the GPF 50. Since the pressure loss of the exhaust gas is smaller during an abnormal state than during normal operation, the pressure loss of the exhaust gas discharged from the GPF 50 is also smaller. As a result, the flow rate of the exhaust gas impinging on the air-fuel ratio sensor 80 increases during an abnormal state compared to normal operation. Therefore, in the third modified example, the ECU 100 may determine whether the detected air-fuel ratio of the exhaust gas from cylinder #1 measured by the air-fuel ratio sensor 80 is equal to or greater than a reference value, and may determine an abnormality if the detected air-fuel ratio is less than the reference value. Here, the housing of the GPF 50 has a cone portion on the downstream side that narrows in the exhaust flow direction. This cone portion narrows the exhaust gas, increasing its flow velocity. Since the air-fuel ratio sensor 80 is provided at a position where the cone portion increases the flow velocity of the exhaust gas, the flow velocity of the exhaust gas increases downstream of the cone portion during an abnormal state compared to normal operation, and the flow rate of the exhaust gas impinging on the air-fuel ratio sensor 80 increases. As a result, it is possible to accurately determine an abnormality in the GPF 50. For example, the GPF 50 may be installed near the engine 10 in consideration of the temperature rise of the GPF 50 due to exhaust gas. In this case, instead of installing the air-fuel ratio sensor 70 upstream of the GPF 50, an air-fuel ratio sensor 80 may be installed downstream of the GPF 50, and an abnormality determination may be performed based on the air-fuel ratio detected by the air-fuel ratio sensor 80. For example, the air-fuel ratio sensor 80 may be installed in a cone portion downstream of the housing of the GPF 50.

[0039] [Fourth Modification] FIG. 5C is an explanatory diagram of a fourth modified example. FIG. 5C corresponds to FIG. 2A. Unlike the above-described embodiment, the exhaust passage 30a in the fourth modified example extends linearly. The air-fuel ratio sensor 70 is provided in a linear portion of the exhaust passage 30a. Even in this case, exhaust pressure loss is smaller during abnormal conditions than during normal conditions. Because the exhaust passage 30a extends linearly, the exhaust flow pattern does not change significantly between normal and abnormal conditions. However, the exhaust flow velocity is faster during abnormal conditions than during normal conditions. As a result, the flow rate of exhaust impinging on the air-fuel ratio sensor 70 is greater during abnormal conditions than during normal conditions. Therefore, in the fourth modified example, the ECU 100 determines whether the air-fuel ratio of the exhaust gas from cylinder #1 detected by the air-fuel ratio sensor 70 is equal to or greater than a threshold value. If the detected air-fuel ratio is less than the threshold value, the ECU 100 determines an abnormality.

[0040] In the fourth modified example, the air-fuel ratio sensor 70 is provided downstream of the three-way catalyst 40. Here, the exhaust gas is constricted by a cone portion downstream of the housing of the three-way catalyst 40, increasing the flow rate. Therefore, in the event of an abnormality, the flow rate of the exhaust gas impinging on the air-fuel ratio sensor 70 is greater than in the normal state, making it possible to accurately determine whether the GPF 50 is abnormal.

[0041] In the above-described embodiment and modified examples, an O2 sensor that detects the oxygen concentration in the exhaust may be used instead of the air-fuel ratio sensor 70. The filter abnormality determination system 1 may be mounted on, for example, an engine vehicle or a hybrid vehicle.

[0042] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0043] 1. Filter abnormality detection system 10 Engine (internal combustion engine) #1 to #4 cylinders 20 Exhaust manifold 30 Exhaust passage 50 GPF (filter) 70 Air-fuel ratio sensor (sensor) 100 ECU (judgment device, control unit, judgment unit)

Claims

1. an internal combustion engine having a plurality of cylinders; an exhaust passage connected to the internal combustion engine; a filter provided in the exhaust passage; a sensor provided in the exhaust passage facing the filter, the sensor outputting a detection value corresponding to the oxygen concentration in the exhaust gas; a determination device, The determination device a control unit that executes imbalance control to control an air-fuel ratio of one of the plurality of cylinders to a value different from the air-fuel ratios of the remaining cylinders of the plurality of cylinders; a determination unit that determines whether or not the filter is abnormal based on a detection value of the sensor corresponding to an air-fuel ratio of exhaust gas from the one cylinder during execution of the imbalance control, the imbalance control controls the air-fuel ratio of the one cylinder to a rich air-fuel ratio that is lower than the stoichiometric air-fuel ratio, the determination unit determines whether the filter is abnormal by comparing a detection value of the sensor corresponding to an air-fuel ratio of the exhaust gas of the one cylinder with a determination value; the exhaust passage has a curved portion that is located upstream of the filter and extends in a curved manner facing the filter, the sensor is provided on the curved portion, the curved portion is curved at a predetermined curvature and includes an inner wall portion and an outer wall portion opposed to each other in a curvature radius direction, The sensor is provided on the inner wall portion side, the determination value is a minimum value of the air-fuel ratio of the exhaust gas from the one cylinder measured by the sensor when the filter is abnormal during execution of the imbalance control, The filter abnormality determination system, wherein the determination unit determines that the filter is abnormal if the detection value is equal to or greater than the determination value, and determines that the filter is normal if the detection value is less than the determination value.

2. An internal combustion engine having a plurality of cylinders; an exhaust passage connected to the internal combustion engine; a filter provided in the exhaust passage; a sensor provided in the exhaust passage facing the filter, the sensor outputting a detection value corresponding to the oxygen concentration in the exhaust gas; a determination device, The determination device a control unit that executes imbalance control to control an air-fuel ratio of one of the plurality of cylinders to a value different from the air-fuel ratios of the remaining cylinders of the plurality of cylinders; a determination unit that determines whether or not the filter is abnormal based on a detection value of the sensor corresponding to an air-fuel ratio of exhaust gas from the one cylinder during execution of the imbalance control, the imbalance control controls the air-fuel ratio of the one cylinder to a rich air-fuel ratio that is lower than the stoichiometric air-fuel ratio, the determination unit determines whether the filter is abnormal by comparing a detection value of the sensor corresponding to an air-fuel ratio of the exhaust gas of the one cylinder with a determination value; the exhaust passage has a curved portion that is located upstream of the filter and extends in a curved manner facing the filter, the sensor is provided on the curved portion, the curved portion is curved at a predetermined curvature and includes an inner wall portion and an outer wall portion opposed to each other in a curvature radius direction, The sensor is provided on the outer wall portion side, the determination value is a maximum value of the air-fuel ratio of the exhaust gas from the one cylinder detected by the sensor when the filter is abnormal during execution of the imbalance control, The filter abnormality determination system, wherein the determination unit determines that the filter is abnormal when the detection value is equal to or less than the determination value, and determines that the filter is normal when the detection value is greater than the determination value.

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