JP5263123B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress erroneous diagnosis of a clogging abnormality of a filter. <P>SOLUTION: An exhaust passage 14 of an internal combustion engine 10 is provided with a filter 22 collecting PM and an exhaust throttle valve 18 arranged in this order from upstream of the exhaust passage 14. A pressure sensor 33 detecting exhaust pressure Pex is disposed upstream of the filter 22 of the exhaust passage 14. An electronic control device 40 controls open/close of the exhaust throttle valve 18, and diagnoses the clogging abnormality of the filter 22 based on the exhaust pressure Pex detected by the pressure sensor 33. Based on an engine operating condition, a determination value Pexth, which is exhaust pressure upstream of the exhaust throttle valve 18 of the exhaust passage 14, larger than pressure of the fully opened valve 18, and smaller than pressure of the fully closed valve 18, is set. The abnormality diagnosis is prohibited when it is determined that the exhaust pressure Pex is larger than the determination value Pexth, before execution of abnormality diagnosis of the filter 22. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention provides a filter that is provided in an exhaust passage of an internal combustion engine and collects particulate matter in exhaust gas, and an exhaust gas that is provided on the downstream side of the filter in the exhaust passage and has a variable cross-sectional area of the exhaust passage. The present invention relates to an exhaust emission control device for an internal combustion engine that includes a throttle valve and pressure detection means for detecting the pressure of exhaust gas upstream of a filter in an exhaust passage, and diagnoses clogging abnormality based on the detection result of the pressure detection means.

  As this type of exhaust gas purification device for an internal combustion engine, for example, there is one described in Patent Document 1. In a conventional general exhaust purification device including the one described in Patent Document 1, a filter that collects particulate matter (Particulate Matter, hereinafter referred to as “PM”) in exhaust in order from the upstream side in the exhaust passage, and An exhaust throttle valve is provided that makes the cross-sectional area of the exhaust passage variable. Further, a pressure sensor for detecting the pressure of the exhaust is provided on the upstream side of the filter in the exhaust passage.

  In such an exhaust purification device, there is a possibility that an abnormality such that the exhaust throttle valve does not open while the exhaust throttle valve is closed may occur, so the presence or absence of such an abnormality is diagnosed through the following closed adhesion abnormality diagnosis. . That is, when the valve is closed by outputting a valve closing command to the exhaust throttle valve, the pressure of the exhaust on the upstream side of the valve becomes high accordingly. On the other hand, when the valve is opened by outputting a valve opening command to the exhaust throttle valve, the pressure of the exhaust on the upstream side of the valve is lowered accordingly. Therefore, in a state where a valve closing command is output to the exhaust throttle valve, a valve opening command is output, and after a predetermined period has elapsed, the pressure of the exhaust detected by the pressure sensor is equal to or higher than the predetermined pressure. In some cases, it is diagnosed that the exhaust throttle valve is closed abnormally.

  Further, in the exhaust purification device, when the amount of PM trapped in the filter (hereinafter referred to as “PM deposition amount”) increases, the pressure of exhaust on the upstream side of the filter increases, and accordingly, the internal combustion engine There arises a problem that the amount of fuel consumption deteriorates. Therefore, when the predetermined execution condition is satisfied and the exhaust pressure detected by the pressure sensor is larger than the allowable value, it is determined that the PM accumulation amount may exceed the allowable amount. The filter is regenerated by removing it by combustion.

Conventionally, the execution condition of the filter clogging abnormality diagnosis is established when, for example, all of the following conditions (A) to (C) are satisfied.
(A) The engine operation state is a steady operation state.

(B) The exhaust throttle valve closing control is not executed.
(C) As a result of the exhaust sticker closing abnormality diagnosis, no abnormality is diagnosed.

JP 2008-12519 A

  By the way, in the exhaust gas purification device of the conventional internal combustion engine, after the exhaust throttle valve becomes closed and stuck abnormally, before the exhaust throttle valve closed stuck and abnormal diagnosis is completed, the execution condition of the filter clogging abnormality diagnosis is If it is established and the diagnosis is made, there arises a problem that an erroneous diagnosis that a filter clogging abnormality has occurred is made. That is, for example, as shown in FIG. 10, it is assumed that a valve closing command is output to the exhaust throttle valve at timing t1, and this is fixed in a state where the exhaust throttle valve is actually fully closed. In this case, the exhaust throttle valve remains fully closed even if a valve closing command is output at the subsequent timing t2. At this time, a predetermined time is required until the abnormality diagnosis of the exhaust throttle valve is completed at the subsequent timing t3 and it is determined that the closed stuck abnormality is detected. However, in the conventional control device for an internal combustion engine, the conditions (A) to (C), which are the execution conditions of the filter clogging abnormality diagnosis, are satisfied immediately after the timing t2, that is, before the timing t3. Accordingly, the filter clogging abnormality diagnosis is executed. Therefore, the exhaust pressure Pex detected by the pressure sensor is equal to or more than the allowable value Pfth due to the exhaust throttle valve being closed and stuck abnormally even though no filter clogging abnormality actually occurs. As a result, it is erroneously diagnosed that a filter clogging abnormality has occurred.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can prevent erroneous diagnosis of filter clogging abnormality.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
(1) The invention according to claim 1 is a filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust, and the exhaust passage provided in the exhaust passage on the downstream side of the filter. An exhaust throttle valve having a variable flow passage cross-sectional area, an open / close control means for controlling the opening / closing of the exhaust throttle valve, a pressure detection means for detecting the pressure of exhaust gas upstream of the filter in the exhaust passage, An abnormality diagnosis means for diagnosing clogging abnormality of the filter based on the pressure of the exhaust gas detected by the pressure detection means, and the exhaust pressure upstream of the exhaust throttle valve in the exhaust passage. A judgment value setting means for setting a judgment value that is larger than the pressure when the valve is fully open and smaller than the pressure when the valve is fully closed based on the engine operating state; Prohibition of prohibiting the abnormality diagnosis when it is determined that the exhaust pressure detected by the pressure detection means is larger than the judgment value set by the judgment value setting means prior to the abnormality diagnosis of the filter. The gist is to provide the means.

  According to this configuration, when the abnormality diagnosis of the filter is performed, it is determined prior to this whether or not the exhaust pressure upstream of the exhaust throttle valve in the exhaust passage is larger than the above-described determination value. That is, it is determined whether or not the exhaust throttle valve is closed. Then, if it is determined that the exhaust throttle valve is closed, a filter clogging abnormality diagnosis is performed, and even if the exhaust pressure detected by the pressure detection means in the abnormality diagnosis exceeds the allowable value, It is impossible to distinguish whether this is due to filter clogging abnormality or exhaust throttle valve being closed, and filter clogging abnormality cannot be accurately diagnosed. Is prohibited. Accordingly, it is possible to suppress erroneous diagnosis of filter clogging abnormality.

  (2) The invention according to claim 2 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the determination value setting means increases the determination value as the flow rate of the exhaust gas flowing through the exhaust passage increases. The gist is to set it large.

  If the other conditions are the same, the pressure of the exhaust gas upstream of the exhaust throttle valve in the exhaust passage increases as the flow rate of the exhaust gas flowing through the exhaust passage increases. According to the above configuration, since the determination value is set according to the flow rate of the exhaust gas flowing through the exhaust passage through the determination value setting means, the determination value is set to an appropriate value in accordance with the exhaust pressure. Will be able to.

  (3) The invention according to claim 3 is the exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the determination value setting means determines the determination as the flow rate of the intake air flowing through the intake passage of the internal combustion engine increases. The gist is to set a large value.

  The flow rate of the exhaust gas flowing through the exhaust passage increases as the flow rate of the intake air flowing through the intake passage increases. According to the above configuration, the determination value is set according to the flow rate of the intake air flowing through the intake passage, that is, according to the flow rate of the exhaust gas, through the determination value setting means. The appropriate value can be set in a simple manner.

  (4) The invention according to claim 4 is the exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the determination value setting means sets the determination value larger as the fuel injection amount of the internal combustion engine is larger. That is the gist.

  The flow rate of the exhaust gas flowing through the exhaust passage increases as the fuel injection amount increases. According to the above configuration, since the determination value is set according to the fuel injection amount, that is, according to the flow rate of exhaust gas, through the determination value setting means, the determination value is set to an appropriate value according to the exhaust pressure. It becomes possible to set in a simple manner.

  (5) The invention according to claim 5 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 2 to 4, wherein the determination value setting means is configured to control exhaust gas flowing through the exhaust passage. The gist is to set the determination value larger as the temperature is higher.

  If the other conditions are the same, the pressure of the exhaust gas upstream of the exhaust throttle valve in the exhaust passage increases as the temperature of the exhaust gas flowing through the exhaust passage increases. For this reason, in the configuration in which the determination value is set based only on the flow rate of the intake air flowing through the intake passage, when the exhaust temperature greatly deviates from the reference temperature, the determination value is appropriately set according to the exhaust pressure. It may not be possible to set the correct value. In this regard, according to the above configuration, since the determination value is set according to the temperature of the exhaust gas flowing through the exhaust passage through the determination value setting means, even if the temperature of the exhaust gas greatly deviates from the reference temperature, The determination value can be set to an appropriate value in accordance with the exhaust pressure.

  (6) The invention according to claim 6 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the particulate matter deposited on the filter based on an engine operating state is provided. The gist includes an accumulation amount estimation unit that estimates the amount, and the determination value setting unit sets the determination value larger as the accumulation amount estimated by the accumulation amount estimation unit increases.

  The exhaust pressure on the upstream side of the exhaust throttle valve in the exhaust passage becomes higher as the amount of accumulated particulate matter on the filter increases as long as the other conditions are the same. According to the above configuration, since the determination value is set according to the amount of the particulate matter deposited on the filter through the determination value setting means, even if the accumulation amount of the particulate matter greatly deviates from the reference amount, The determination value can be set to an appropriate value in accordance with the exhaust pressure.

  (7) The invention according to claim 7 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the prohibiting means is an exhaust gas detected by the pressure detecting means. The gist of the invention is that the abnormality diagnosis of the filter by the abnormality diagnosing means is prohibited until a predetermined period elapses after the pressure becomes equal to or less than the determination value.

  As the exhaust throttle valve opens, even if the exhaust pressure upstream of the exhaust throttle valve in the exhaust passage falls below the above judgment value, depending on the engine operating condition at that time, The pressure may be temporarily higher than the determination value. In such a case, as soon as the exhaust pressure detected by the pressure detection means reaches the above judgment value, the filter clogging abnormality diagnosis is performed by the abnormality diagnosis means, and the filter clogging abnormality is erroneously diagnosed. There is a risk. In this regard, according to the above configuration, the abnormality diagnosis of the filter by the abnormality diagnosis unit is prohibited until the predetermined period elapses after the exhaust pressure detected by the pressure detection unit becomes equal to or less than the determination value. As the exhaust throttle valve opens, the exhaust pressure upstream of the exhaust throttle valve in the exhaust passage becomes equal to or lower than the above judgment value, and immediately thereafter, the exhaust pressure temporarily exceeds the judgment value. Even if it becomes larger, it is possible to suppress erroneous diagnosis of filter clogging abnormality.

1 is a schematic configuration diagram showing a schematic configuration of an internal combustion engine in an exhaust gas purification apparatus for an internal combustion engine according to the present invention. The flowchart which shows the process sequence of the filter clogging abnormality diagnosis process in the embodiment. 7 is a flowchart showing a processing procedure for setting a high level determination flag in the embodiment. The map which prescribed | regulated the relationship between the temperature of exhaust_gas | exhaustion, and a correction coefficient about the high level determination flag setting process in the embodiment. The map which prescribed | regulated the relationship between the corrected intake air amount and a determination value about the high level determination flag setting process in the embodiment. (A)-(f) The timing chart which shows the effect | action about the filter clogging abnormality diagnosis in the embodiment. (A)-(f) The timing chart which shows the effect | action about the filter clogging abnormality diagnosis in the embodiment. (A)-(f) The timing chart which shows the effect | action about the filter clogging abnormality diagnosis in the embodiment. (A)-(f) The timing chart which shows the effect | action about the filter clogging abnormality diagnosis in the embodiment. The timing chart which shows the effect | action about the filter clogging abnormality diagnosis in a prior art.

  1 to 9, an embodiment in which an exhaust gas purification device for an internal combustion engine according to the present invention is embodied as an exhaust gas purification device for an on-vehicle four-cylinder diesel engine (hereinafter, “internal combustion engine”) will be described. explain.

FIG. 1 shows a schematic configuration of an internal combustion engine 10 of the present embodiment. In the drawing, the cross-sectional structure of one cylinder 11 of the four cylinders constituting the engine 10 is schematically shown.
As shown in the figure, the internal combustion engine 10 discharges exhaust generated by combustion in the combustion chamber 12 formed in the cylinder 11, an intake passage 13 for supplying intake air to the combustion chamber 12, and combustion in the combustion chamber 12. An exhaust passage 14 is provided.

  The intake passage 13 is provided with a throttle valve 15 for metering the intake air supplied to the combustion chamber 12 and an actuator 17 for driving the throttle valve 15 to open and close. When intake air is supplied to the combustion chamber 12 through the intake passage 13, fuel is injected and supplied from the fuel injection valve 16 to the combustion chamber 12, so that the intake air and the fuel are mixed together. It is ignited and burned by being compressed.

  The exhaust passage 14 is provided with an oxidation catalyst 21 that oxidizes and purifies hydrocarbons (HC) and carbon monoxide (CO) in the exhaust. Further, a filter 22 that collects particulate matter (hereinafter referred to as “PM”) in the exhaust gas is provided downstream of the oxidation catalyst 21 in the exhaust passage 14. The filter 22 is made of a porous material. In the present embodiment, the oxidation catalyst 21 and the filter 22 are configured separately, but they can also be configured integrally by supporting the oxidation catalyst on the filter.

  Further, on the downstream side of the filter 22 in the exhaust passage 14, an exhaust throttle valve 18 that makes the flow passage cross-sectional area of the exhaust passage 14 variable, and the exhaust throttle valve 18 for opening and closing between fully open and fully closed are provided. An actuator 19 is provided.

  Various controls of the internal combustion engine 10 are performed by the electronic control unit 40. The electronic control unit includes a CPU that executes various arithmetic processes related to engine control, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores CPU calculation results, and the like. The input / output port for inputting / outputting signals is provided. Engine control such as fuel injection control from the fuel injection valve 16 (hereinafter referred to as fuel injection control), opening control of the throttle valve 15 (hereinafter referred to as throttle opening control), and opening / closing control of the exhaust throttle valve 18 by the electronic control unit 40 Various controls including are performed.

The following various sensors 31 to 38 are connected to the input port of the electronic control unit 40.
(31) An intake air amount sensor 31 that is provided upstream of the throttle valve 15 in the intake passage 13 and detects the intake air amount GA.
(32) A temperature sensor 32 provided between the oxidation catalyst 21 and the filter 22 in the exhaust passage 14 to detect the exhaust gas temperature ThC.
(33) A pressure sensor 33 provided between the oxidation catalyst 21 and the filter 22 in the exhaust passage 14 to detect the exhaust pressure (absolute pressure) Pex.
(34) An engine speed sensor 34 that detects an engine speed that is the speed of the engine output shaft.
(35) An accelerator opening sensor 35 that detects an accelerator opening that is an amount of depression of the accelerator pedal.
(36) A throttle opening sensor 36 that is provided in the vicinity of the throttle valve 15 and detects a throttle opening TA that is the opening of the throttle valve 15.
(37) An air-fuel ratio sensor 37 provided between the filter 22 and the exhaust throttle valve 18 in the exhaust passage 14 to detect the air-fuel ratio A / F of the exhaust.
(38) An upstream exhaust temperature sensor 38 that is provided upstream of the oxidation catalyst 21 in the exhaust passage 14 and detects the temperature of the exhaust.
In addition, drive circuits such as the throttle valve 15, the fuel injection valve 16, and the exhaust throttle valve 18 are connected to the output port of the electronic control unit 40.

  The electronic control unit 40 outputs a command signal to the drive circuit of each device connected to the output port according to the engine operating state grasped by the detection signals input from the various sensors. Thus, various controls such as fuel injection control, throttle opening control, and exhaust throttle valve opening / closing control are performed.

  In such an exhaust purification device of the internal combustion engine 10, there is a possibility that an abnormality such as the exhaust throttle valve 18 being closed and not being opened may occur. I am trying to diagnose. That is, when the valve 18 is closed by outputting a valve closing command to the exhaust throttle valve 18, the pressure of the exhaust gas upstream of the valve 18 becomes high accordingly. On the other hand, when the valve 18 is opened by outputting a valve opening command to the exhaust throttle valve 18, the pressure of the exhaust on the upstream side of the valve 18 is lowered accordingly. For these reasons, the valve opening command is output in a state in which the valve closing command is output to the exhaust throttle valve 18, and the magnitude relationship between the exhaust pressure Pex and the judgment value Pexth is compared after a lapse of a predetermined period thereafter. As a result, when the exhaust pressure Pex is equal to or higher than the determination value Pexth, it is diagnosed that the exhaust throttle valve 18 is abnormally closed and stuck.

  Further, in the exhaust purification device of the internal combustion engine 10, when the PM accumulation amount (hereinafter, “PM accumulation amount”) collected by the filter 22 increases, the exhaust pressure upstream of the filter 22 increases. Accordingly, there arises a problem that the fuel consumption of the internal combustion engine 10 is deteriorated. Therefore, when the predetermined execution condition is satisfied and the exhaust pressure Pex is larger than the allowable value Pfth, the PM accumulation amount may exceed the allowable amount, and the PM accumulated on the filter 22 is burned and purified. Filter regeneration control is performed. Such filter regeneration control is performed by raising the temperature of exhaust gas and the pressure of exhaust gas by operating the exhaust throttle valve 18 and supplying unburned fuel components to the oxidation catalyst carried on the filter 22. As a result, the catalyst is activated by the heat generated by the oxidation of the unburned fuel component in the exhaust or on the catalyst, and the PM around the catalyst is combusted. The unburned fuel component is supplied to the catalyst in the filter regeneration control after the fuel injection from the fuel injection valve 16 that contributes to the driving of the internal combustion engine 10, for example, post injection that is fuel injection in the exhaust stroke, etc. Is done by.

Conventionally, as an execution condition for such a filter 22 clogging abnormality diagnosis, for example, the following conditions (A) to (C) are all satisfied.
(A) The engine operation state is a steady operation state.

(B) The valve closing control of the exhaust throttle valve 18 is not executed.
(C) As a result of diagnosing the closed stuck abnormality of the exhaust throttle valve 18, it is diagnosed that there is no abnormality.
Incidentally, when the engine operation state is a steady operation state, the exhaust pressure P1 when the exhaust throttle valve 18 is fully closed is such that the exhaust throttle valve 18 is fully open and the PM accumulation amount of the filter 22 is greater than the allowable amount. Is larger than the pressure P2 of the exhaust gas at the time of (P1 >> P2). Therefore, the allowable value Pfth in the diagnosis of the clogging abnormality of the filter 22 is set as a value smaller than the determination value Pexth in the diagnosis of the closed stuck abnormality of the exhaust throttle valve 18 (Pfth <Pexth).

  By the way, in such a conventional exhaust purification device of the internal combustion engine 10, as described above, after the exhaust throttle valve 18 becomes closed and stuck abnormally, before the closed stuck abnormality diagnosis of the exhaust throttle valve 18 is completed, When the conditions for executing the abnormality diagnosis for clogging of the filter 22 are satisfied and the diagnosis is performed, there arises a problem that an erroneous diagnosis that the clogging abnormality of the filter 22 has occurred is made.

  Therefore, in this embodiment, prior to performing the abnormality diagnosis of the filter 22, when it is determined that the exhaust pressure Pex detected by the pressure sensor 33 is larger than the determination value Pexth, the abnormality diagnosis is prohibited. ing. Further, the determination value Pexth is set based on the engine operating state at that time. As a result, erroneous diagnosis of clogging abnormality of the filter 22 is suppressed.

Next, the clogging abnormality diagnosis process for the filter 22 according to the present embodiment will be described in detail with reference to FIGS.
FIG. 2 is a flowchart showing the processing procedure of the filter 22 clogging abnormality diagnosis process. The series of processes shown in the figure is repeatedly executed at predetermined intervals during engine operation.

  As shown in the figure, in this series of processes, first, the engine operating state grasped based on the detection results from the various sensors 31 to 38 is read (step S1). Then, a high level determination flag setting process is performed (step S2).

Here, the high level determination flag setting process will be described with reference to FIG.
FIG. 3 is a flowchart showing a processing procedure for setting a high level determination flag. The series of processes shown in the figure is executed when the process proceeds to step S2 in the flowchart shown in FIG.

  As shown in the figure, in this series of processes, first, a determination value Pexth is set based on the intake air amount GA and the exhaust gas temperature ThC (step S21). Specifically, the determination value Pexth is set with reference to the maps shown in FIGS. Here, the determination value Pexth is the pressure of the exhaust gas upstream of the exhaust throttle valve 18 in the exhaust passage 14, and is larger than the pressure when the valve 18 is fully open, and than the pressure when the valve 18 is fully closed. Set as a small value. Accordingly, the determination value Pexth is set to a larger value as the engine operation state is such that the exhaust pressure becomes higher. In the present embodiment, if the other states are the same, paying attention to the fact that as the intake air amount GA increases, the flow rate of the exhaust gas increases and the pressure of the exhaust gas increases. The determination value Pexth is set. Further, if the intake air amount GA is the same, the exhaust gas pressure becomes higher as the exhaust gas temperature ThC becomes higher, and the intake air amount GA is corrected based on the exhaust air temperature ThC and based on the corrected intake air amount GAC. The determination value Pexth is set.

  FIG. 4 is a map that defines the relationship between the exhaust gas temperature ThC and the correction coefficient K. FIG. 5 is a map that defines the relationship between the corrected intake air amount GAC, which is a value obtained by multiplying the intake air amount GA by the correction coefficient K, and the determination value Pexth.

  As shown in FIG. 4, the correction coefficient K is set to increase as the exhaust gas temperature ThC increases. Further, as shown in FIG. 5, the determination value Pexth is set to increase as the corrected intake air amount GAC increases. Therefore, in the present embodiment, the determination value Pexth is set to a larger value as the intake air amount GA is larger or as the exhaust gas temperature is higher.

  When the determination value Pexth is thus set in step S21, it is next determined whether or not the exhaust pressure Pex at that time is equal to or higher than the determination value Pexth (step S22). As a result, when the exhaust pressure Pex is equal to or higher than the determination value Pexth (step S22: “YES”), it is determined that the exhaust throttle valve 18 is closed, and then the high level determination flag F is set to “ON”. (Step S23), this series of processes is terminated.

  On the other hand, when the exhaust pressure Pex is not equal to or higher than the determination value Pexth in step S22 (step S22: “NO”), it is determined that the exhaust throttle valve 18 is not closed, and then the high level determination flag F is set to “OFF”. "(Step S24), and this series of processing ends.

  When the high level determination flag F is set in this way, next, as shown in FIG. 2, it is determined whether or not the engine operating state at that time is a steady operating state (step S3). In this embodiment, for example, the change amount per unit time of the intake air amount GA is less than a predetermined amount, the change amount per unit time of the engine rotation speed is less than a predetermined amount, and the fuel injection amount per unit time When all the conditions such that the change amount of the engine is less than the predetermined amount are satisfied, it is determined that the engine operation state is the steady operation state. When the engine operating state is not a steady operating state, for example, when the amount of change in the intake air amount GA per unit time is large, the exhaust pressure greatly fluctuates accordingly, and the clogging abnormality of the filter 22 is accurately diagnosed. Can not do it. Therefore, in step S3, it is determined whether or not this is the case.

  Here, when the engine operation state is a steady operation state (step S3: “YES”), it is next determined whether or not a valve closing command is output to the exhaust throttle valve 18 (step S3). S4). When a valve closing command is output to the exhaust throttle valve 18, the exhaust pressure Pex becomes equal to or higher than the allowable value Pfth regardless of the degree of clogging of the filter 22, and the clogging abnormality of the filter 22 is accurately diagnosed. I can't. Therefore, in step S4, it is determined whether or not this is the state.

  Here, when the valve closing command to the exhaust throttle valve 18 is not output (step S4: “YES”), it is next determined whether or not the high level determination flag F is “OFF” ( Step S5). When the high level determination flag F is “ON”, it can be said that the exhaust throttle valve 18 is closed, and a clogging abnormality diagnosis of the filter 22 is temporarily performed, and the exhaust pressure detected by the pressure sensor 33 in the abnormality diagnosis. Even if Pex exceeds the allowable value Pfth, it cannot be distinguished whether this is due to an abnormal clogging of the filter 22 or due to the exhaust throttle valve 18 being closed. Abnormalities cannot be diagnosed with high accuracy. Therefore, in step S5, it is determined whether or not this is the state.

  When the high level determination flag F is “OFF” (step S5: “YES”), it is determined that the condition for executing the clogging abnormality diagnosis of the filter 22 is satisfied, and then the exhaust pressure Pex at that time is It is determined whether it is larger than the allowable value Pfth (step S6). As a result, if the exhaust pressure Pex is larger than the allowable value Pfth (step S6: “YES”), then it is determined that the PM accumulation amount exceeds the allowable amount, and then the filter 22 is diagnosed as having a clogging abnormality. (Step S7), and this series of processes is temporarily terminated.

On the other hand, when the exhaust pressure Pex is equal to or smaller than the allowable value Pfth (step S6: “NO”), the series of processes is temporarily terminated, assuming that the PM accumulation amount is equal to or smaller than the allowable amount.
When the engine operation state is not a steady operation state (step S3: “NO”) or when a valve closing command to the exhaust throttle valve 18 is output (step S4: “NO”), a high level determination flag If F is “ON” (step S5: “NO”), the series of processing is temporarily terminated, assuming that the execution condition for the clogging abnormality diagnosis of the filter 22 is not satisfied.

Next, the operation of the filter clogging abnormality diagnosis in this embodiment will be described with reference to FIGS.
FIG. 6 is a timing chart in the case where the PM accumulation amount of the filter 22 is equal to or less than the allowable amount, and the closed adhering abnormality of the exhaust throttle valve 18 does not occur.

FIG. 7 is a timing chart in the case where the PM accumulation amount of the filter 22 is equal to or less than the allowable amount, and the exhaust throttle valve 18 is closed abnormally.
In the timing charts shown in FIGS. 6 and 7, it is assumed that the engine operation state is a steady operation state (see FIGS. 6A and 7A).

  As shown in FIG. 6, when a valve closing command is output to the exhaust throttle valve 18 at timing t11 (b), the exhaust throttle valve 18 that has been fully opened until then is fully closed (c). As a result, the exhaust pressure Pex rises from the predetermined value P0 (<Pfth) so far, and reaches the predetermined value P1 (> Pexth) at timing t13 (d). Thereafter, when a valve opening command is output to the exhaust throttle valve 18 at timing t14 (b), the exhaust throttle valve 18 is normally driven and fully opened (c). As a result, the exhaust pressure Pex decreases from the predetermined value P1 so far, and reaches the predetermined value P0 at time t16 (d). Here, the high level determination flag F is switched from “OFF” to “ON” as the exhaust pressure Pex becomes equal to or higher than the determination value Pexth (Pfth <Pexth <P1) at the timing t12. Thereafter, when the exhaust pressure Pex becomes less than the determination value Pexth at timing t15, the engine is switched from “ON” to “OFF”. Further, the condition for executing the abnormality diagnosis of the clogging of the filter 22 is not established from the timing t11 when the valve closing command is output to the exhaust throttle valve 18 to the timing t15 when the exhaust pressure Pex becomes less than the determination value Pexth. That is, it is established after timing t15.

  On the other hand, as shown in FIG. 7, if the closed throttle abnormality occurs in the exhaust throttle valve 18 at the timing between the timing t13 and the timing t14, the exhaust pressure Pex remains at the determination value Pexth even after the timing t15. Since it remains as described above, the high level determination flag F remains “ON” and is not switched (e). For this reason, after the timing t15, the execution condition of the clogging abnormality diagnosis of the filter 22 remains unsatisfied. Therefore, after timing t14, the closed stuck abnormality diagnosis of the exhaust throttle valve 18 that has occurred immediately before has not been completed, the previous diagnosis result is no abnormality, and the engine operating state is a steady operating state. (A) and the fact that the valve closing command to the exhaust throttle valve 18 has not been output, the clogging abnormality diagnosis of the filter 22 is not performed.

FIG. 8 is a timing chart in the case where the PM accumulation amount of the filter 22 is larger than the allowable amount, and the closed adhering abnormality of the exhaust throttle valve 18 does not occur.
FIG. 9 is a timing chart in the case where the PM accumulation amount of the filter 22 is larger than the allowable amount and the exhaust throttle valve 18 is stuck closed abnormally.

In the timing charts shown in FIGS. 8 and 9, it is assumed that the engine operating state is a steady operating state (see FIGS. 8A and 9A).
As shown in FIG. 8, when a valve closing command is output to the exhaust throttle valve 18 at timing t21 (b), the exhaust throttle valve 18 that has been fully opened until then is fully closed (c). Here, since the PM accumulation amount of the filter 22 is larger than the allowable amount, the exhaust pressure Pex increases from the predetermined value P2 (Pfth <P2 <Pexth) so far, and at the timing t23, the predetermined value P1 (> Pexth). (D). Thereafter, when a valve opening command is output to the exhaust throttle valve 18 at timing t24 (b), the exhaust throttle valve 18 is normally driven and fully opened (c). As a result, the exhaust pressure Pex decreases from the predetermined value P1 so far, and reaches the predetermined value P2 at timing t26 (d). Here, the high level determination flag F is switched from “OFF” to “ON” when the exhaust pressure Pex becomes equal to or higher than the determination value Pexth (Pfth <Pexth <P1) at the timing t22. After that, when the exhaust pressure Pex becomes less than the determination value Pexth at timing t25, the engine is switched from “ON” to “OFF”. Further, the condition for executing the abnormality diagnosis of the clogging of the filter 22 is not established from the timing t21 when the valve closing command is output to the exhaust throttle valve 18 to the timing t25 when the exhaust pressure Pex becomes less than the determination value Pexth. That is, it is established after timing t25.

  On the other hand, as shown in FIG. 9, when the closed throttle abnormality occurs in the exhaust throttle valve 18 between the timing t23 and the timing t24, the exhaust pressure Pex is equal to or higher than the determination value Pexth even after the timing t25. Therefore, the high level determination flag F remains “ON” and is not switched (e). Therefore, after timing t25, the condition for executing the abnormality diagnosis for clogging of the filter 22 remains unsatisfied. Accordingly, after timing t24, the closed stuck abnormality diagnosis of the exhaust throttle valve 18 that has occurred immediately before has not been completed, the previous diagnosis result is normal, and the engine operating state is a steady operating state. (A) and the fact that the valve closing command to the exhaust throttle valve 18 has not been output, the clogging abnormality diagnosis of the filter 22 is not performed.

According to the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment described above, the following effects can be obtained.
(1) The internal combustion engine 10 includes a filter 22 provided in the exhaust passage 14 for collecting PM in the exhaust, and a flow passage cross-sectional area of the exhaust passage 14 provided on the downstream side of the filter 22 in the exhaust passage 14. A variable exhaust throttle valve 18 is provided. The opening / closing of the exhaust throttle valve 18 is controlled through the electronic control unit 40. Further, a pressure sensor 33 for detecting the exhaust pressure Pex on the upstream side of the filter 22 in the exhaust passage 14 is provided, and an abnormal clogging of the filter 22 is detected based on the exhaust pressure Pex detected by the pressure sensor 33 through the electronic control unit 40. It was supposed to be diagnosed. Then, the electronic control unit 40 determines the judgment value Pexth that is the pressure of the exhaust gas upstream of the exhaust throttle valve 18 in the exhaust passage 14 and that is larger than the pressure when the valve 18 is fully open and smaller than the pressure when it is fully closed. Was set based on the engine operating condition. Further, prior to performing an abnormality diagnosis of the filter 22, when it is determined that the exhaust pressure Pex detected by the pressure sensor 33 is larger than the determination value Pexth, the abnormality diagnosis is prohibited. Thereby, when the abnormality diagnosis of the filter 22 is performed, it is determined whether or not the exhaust pressure Pex on the upstream side of the exhaust throttle valve 18 in the exhaust passage 14 is larger than the determination value Pexth. . That is, it is determined whether or not the exhaust throttle valve 18 is closed. If it is determined that the exhaust throttle valve 18 is closed, the filter 22 is diagnosed as being clogged, and the exhaust pressure Pex detected by the pressure sensor 33 in the abnormality diagnosis is equal to or greater than the allowable value Pfth. Even if this is the case, it cannot be distinguished whether this is due to the clogging abnormality of the filter 22 or due to the exhaust throttle valve 18 being closed, and the clogging abnormality of the filter 22 can be accurately diagnosed. As a result, the abnormality diagnosis of the filter 22 is prohibited. Therefore, it is possible to suppress erroneous diagnosis of clogging abnormality of the filter 22.

  (2) The determination value Pexth is set to be larger through the electronic control unit 40 as the intake air amount GA is larger. The exhaust pressure on the upstream side of the exhaust throttle valve 18 in the exhaust passage 14 becomes higher as the flow rate of the exhaust gas flowing through the exhaust passage 14 increases if the other conditions are the same. Further, the flow rate of the exhaust gas increases as the flow rate of the intake air flowing through the intake passage 13 increases. According to the embodiment, since the determination value Pexth is set according to the intake air amount GA, that is, according to the exhaust gas flow rate, through the electronic control unit 40, the determination value Pexth is appropriately set in accordance with the exhaust pressure. It becomes possible to set a simple value in a simple manner.

  (3) The determination value Pexth is set to be larger as the temperature ThC of the exhaust gas flowing through the exhaust passage 14 is higher through the electronic control unit 40. The exhaust pressure on the upstream side of the exhaust throttle valve 18 in the exhaust passage 14 becomes higher as the temperature of the exhaust gas flowing through the exhaust passage 14 is higher if the other conditions are the same. Therefore, in the configuration in which the determination value Pexth is set based only on the intake air amount GA, when the exhaust gas temperature ThC greatly deviates from the reference temperature, the determination value Pexth is an appropriate value in accordance with the exhaust gas pressure. May not be set. In this regard, according to the above configuration, since the determination value Pexth is set according to the temperature ThC of the exhaust gas flowing through the exhaust passage 14 through the electronic control unit 40, the exhaust temperature ThC greatly deviates from the reference temperature. Even in this case, the determination value Pexth can be set to an appropriate value in accordance with the exhaust pressure.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention is not limited to the configuration exemplified in the above embodiment, and can be implemented as, for example, the following form appropriately modified.

  In the above embodiment, the internal combustion engine 10 that does not include a supercharger is illustrated, but the present invention can be applied to an internal combustion engine that includes a supercharger or an exhaust gas recirculation device instead. . In particular, in an internal combustion engine having an exhaust-driven supercharger, a catalyst may be provided between the turbine and the oxidation catalyst 21 constituting the supercharger.

  In the above embodiment, the high level determination flag F is set to “OFF” as soon as the exhaust pressure Pex becomes equal to or lower than the determination value Pexth. However, even if the exhaust pressure Pex becomes equal to or lower than the above-described determination value Pexth as the exhaust throttle valve 18 is opened, the exhaust pressure Pex immediately increases depending on the engine operating state at that time. It may be temporarily larger than Pexth. In such a case, immediately after the exhaust pressure Pex detected by the pressure sensor 33 reaches the determination value Pexth, when the filter 22 clogging abnormality diagnosis is performed, the filter 22 clogging abnormality is erroneously diagnosed. There is a risk. Accordingly, the abnormality diagnosis of the filter 22 may be prohibited without setting the high level determination flag F to “OFF” until a predetermined period elapses after the exhaust pressure Pex becomes equal to or lower than the determination value Pexth. Thus, as the exhaust throttle valve 18 is opened, the exhaust pressure upstream of the exhaust throttle valve 18 in the exhaust passage 14 becomes equal to or less than the determination value Pexth, and immediately thereafter, the exhaust pressure Pex immediately increases. Even if the determination value Pexth is temporarily larger, it is possible to suppress erroneous diagnosis of clogging abnormality of the filter 22. Incidentally, as the predetermined period here, a value obtained in advance by an experiment or the like can be set.

  In the above embodiment, the determination value Pexth is set based on the intake air amount GA and the exhaust gas temperature ThC. In addition to this, the determination value is based on the PM accumulation amount estimated by a known accumulation amount estimation means. Can also be set. In other words, the exhaust pressure Pex detected by the pressure sensor 33 increases as the PM accumulation amount of the filter 22 increases as long as other conditions are the same. Therefore, as described above, if the determination value Pexth is set larger as the PM accumulation amount is larger, the determination value can be set to an appropriate value in accordance with the exhaust pressure.

  As described in the above embodiment, the determination value Pexth is set to be larger as the temperature ThC of the exhaust gas flowing through the exhaust passage 14 is higher, even if the exhaust temperature ThC greatly deviates from the reference temperature. This is desirable in setting Pexth to an appropriate value in accordance with the exhaust pressure. However, the present invention is not limited to this. For example, if the present invention is applied only when the degree of deviation between the exhaust gas temperature ThC and the reference temperature is small, the determination value Pexth is based on the exhaust gas temperature ThC. Does not have to be set.

  In the above embodiment, the exhaust pressure upstream of the exhaust throttle valve 18 in the exhaust passage 14 increases as the flow rate of exhaust flowing through the exhaust passage 14 increases if the other conditions are the same. Considering that the flow rate of the exhaust gas increases as the flow rate of the intake air flowing through the intake passage 13 increases, the determination value Pexth is set based on the intake air amount GA. However, the configuration for estimating the flow rate of the exhaust gas is not limited to this. For example, the flow rate of the exhaust gas may be estimated based on the fuel injection amount Q of the internal combustion engine 10. In this case, the determination value may be set larger as the fuel injection amount Q is larger. Further, in a configuration including means for directly detecting the exhaust flow rate, a determination value may be set based on the exhaust flow rate detected by the means.

  In the above embodiment, the clogging abnormality diagnosis of the filter 22 is executed when the conventional execution conditions (A) to (C) are satisfied and the high level determination flag F is “OFF”. However, the present invention is not limited to this, and the clogging abnormality diagnosis of the filter 22 may be performed only when the high level determination flag F is “OFF”.

  -In the above embodiment, for the closed stuck abnormality diagnosis of the exhaust throttle valve 18, in the conventional diagnosis mode, that is, in the state where the valve closing command is output to the exhaust throttle valve 18, a valve opening command is output, Thereafter, when the exhaust pressure Pex is equal to or higher than the determination value Pexth after a predetermined period has elapsed, a mode is adopted in which it is diagnosed that the closed throttle abnormality of the exhaust throttle valve 18 has occurred. However, based on the technical idea of the present invention, the following closed fixation abnormality diagnosis can be performed. That is, the abnormality diagnosis of the filter is performed when the valve closing command to the exhaust throttle valve 18 is output, and it is determined that the exhaust pressure Pex is larger than the determination value Pexth before performing the abnormality diagnosis of the filter. When this is done, the abnormality diagnosis is prohibited, and the exhaust throttle valve 18 is diagnosed as having a closed stuck abnormality. By performing such a diagnosis, if an abnormal close-fixing abnormality of the exhaust throttle valve 18 has occurred, this can be grasped earlier.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder, 12 ... Combustion chamber, 13 ... Intake passage, 14 ... Exhaust passage, 15 ... Throttle valve, 16 ... Fuel injection valve, 17 ... Actuator, 18 ... Exhaust throttle valve, 19 ... Actuator, 21 ... oxidation catalyst, 22 ... filter, 31 ... air flow meter, 32 ... temperature sensor, 33 ... pressure sensor (pressure detection means), 34 ... engine rotation speed sensor, 35 ... accelerator opening sensor, 36 ... throttle opening sensor, 37 ... Air-fuel ratio sensor, 38 ... Upstream exhaust temperature sensor, 40 ... Electronic control device (opening / closing control means, diagnosis means, judgment value setting means, prohibition means).

Claims (7)

A filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust, and an exhaust throttle valve provided on the downstream side of the filter in the exhaust passage and having a variable cross-sectional area of the exhaust passage An opening / closing control means for controlling the opening / closing of the exhaust throttle valve, a pressure detecting means for detecting the pressure of the exhaust gas upstream of the filter in the exhaust passage, and an exhaust pressure detected by the pressure detecting means. In an exhaust gas purification apparatus for an internal combustion engine, comprising an abnormality diagnosis means for diagnosing a clogging abnormality in the filter,
A judgment value that is set based on the engine operating condition, and a judgment value that is an exhaust pressure upstream of the exhaust throttle valve in the exhaust passage and that is larger than a pressure when the valve is fully open and smaller than a pressure when the valve is fully closed Setting means;
Prior to performing abnormality diagnosis of the filter by the abnormality diagnosis unit, when it is determined that the exhaust pressure detected by the pressure detection unit is larger than the determination value set by the determination value setting unit, An exhaust purification device for an internal combustion engine, comprising: prohibiting means for prohibiting abnormality diagnosis. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The exhaust gas purification apparatus for an internal combustion engine, wherein the determination value setting means sets the determination value larger as the flow rate of exhaust gas flowing through the exhaust passage is larger. The exhaust gas purification apparatus for an internal combustion engine according to claim 2,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the determination value setting means sets the determination value larger as the flow rate of intake air flowing through the intake passage of the internal combustion engine increases. The exhaust gas purification apparatus for an internal combustion engine according to claim 2,
The exhaust gas purification apparatus for an internal combustion engine, wherein the determination value setting means sets the determination value larger as the fuel injection amount of the internal combustion engine is larger. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 2 to 4,
The exhaust gas purification apparatus for an internal combustion engine, wherein the determination value setting means sets the determination value larger as the temperature of the exhaust gas flowing through the exhaust passage is higher. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 5,
A deposition amount estimating means for estimating an amount of the particulate matter deposited on the filter based on an engine operation state;
The exhaust gas purifying apparatus for an internal combustion engine, wherein the determination value setting means sets the determination value to be larger as the accumulation amount estimated by the accumulation amount estimation means is larger. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 6,
The prohibiting means prohibits the abnormality diagnosis of the filter by the abnormality diagnosing means until a predetermined period elapses after the exhaust pressure detected by the pressure detecting means becomes equal to or less than the determination value. An exhaust purification device for an internal combustion engine.

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