JP4692436B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to a technique for regenerating an exhaust purification device provided in an exhaust system of an internal combustion engine.

As a technique for raising the temperature of an exhaust purification device provided in an exhaust system of an internal combustion engine, a plurality of control items such as pilot injection, post injection, low temperature combustion based on EGR control, and fuel addition to the exhaust system by a reducing agent addition valve are included. A technique used in combination is known (see, for example, Patent Document 1).
JP 2003-120392 A

  By the way, in the above-described prior art, when the exhaust purification device does not raise the temperature as intended, it is difficult to specify the factor, and therefore the exhaust purification device may not be heated appropriately.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to exhaust an internal combustion engine in which a specific physical quantity of an exhaust purification device provided in an exhaust system of the internal combustion engine can be changed by a plurality of means. In the purification system, the present invention is to provide a technique capable of suitably changing the physical quantity described above.

  The present invention employs the following means in order to solve the above-described problems. That is, the present invention is an exhaust purification device disposed in an exhaust passage of an internal combustion engine, a first changing means operable to change a specific physical quantity of the exhaust purification device, and a method different from the first changing means. In the exhaust gas purification system for an internal combustion engine provided with second changing means for changing the physical quantity by means of, and detecting means for detecting the physical quantity, the detection value of the detecting means is greater than or equal to a predetermined amount when the first changing means is operated. If no change is indicated, a control means for operating the second changing means is provided.

  According to this configuration, the physical quantity of the exhaust emission control device can be changed by the second changing means if the detection value of the detecting means does not change more than a predetermined amount when the first changing means is activated.

  At that time, if the detection value of the detection means shows a change of a predetermined amount or more by the operation of the second change means, the control means can specify the failure of the first change means. In this case, the control means can continue the physical quantity changing process using the second changing means.

  In addition, when the detection value of the detection unit does not change more than a predetermined amount due to the operation of the second change unit, the control unit can specify the failure of the exhaust purification device and / or the detection unit.

  As an exhaust emission control device according to the present invention, a particulate filter provided with an oxidation catalyst can be exemplified. The particulate filter requires a PM regeneration process for oxidizing and removing the PM collected by the particulate filter.

Since the PM collected in the particulate filter is oxidized when exposed to a high temperature and lean atmosphere of approximately 500 ° C or higher, the temperature in the particulate filter or the particulate filter itself is raised during the PM regeneration process. (Hereinafter simply referred to as “heating the particulate filter”).

  As a method for raising the temperature of the particulate filter, unburned fuel and reducing agent are supplied to an oxidation catalyst provided in the particulate filter, and the temperature of the particulate filter is raised by the oxidation reaction heat of the unburned fuel and reducing agent. A method can be illustrated.

  As a method of supplying unburned fuel and a reducing agent to the oxidation catalyst provided in the particulate filter, a method of adding a reducing agent into the exhaust from a reducing agent addition valve provided in an exhaust passage upstream of the oxidation catalyst, A method of performing post injection from a fuel injection valve capable of direct fuel injection into a cylinder of an internal combustion engine can be exemplified.

  Therefore, when the exhaust purification apparatus according to the present invention includes an oxidation catalyst and a particulate filter, the temperature that is one of the physical quantities of the exhaust purification apparatus is changed by the reducing agent addition valve or the fuel injection valve.

  Therefore, in the exhaust gas purification system for an internal combustion engine according to the present invention, the specific physical quantity of the exhaust gas purification device is the temperature of the particulate filter, the first changing means is a reducing agent addition valve, and the second changing means is a fuel injection valve. can do. Moreover, as a detection means, the temperature sensor which detects the temperature of a particulate filter can be used.

  In such a configuration, when the detected value of the temperature sensor does not change (increase) by more than a predetermined amount due to the addition of the reducing agent by the reducing agent addition valve, the control means starts the temperature increase process by the reducing agent addition valve and starts the fuel injection valve It is possible to switch to a temperature raising process by post injection.

  By the way, as a factor that the detected value of the temperature sensor does not change more than a predetermined amount even when the reducing agent addition valve adds the reducing agent, the reducing agent addition valve failure, the temperature sensor failure, or the oxidation catalyst failure Can be considered.

  When the reducing agent addition valve is out of order, the detected value of the temperature sensor shows a change of a predetermined amount or more when the temperature raising process is performed by the post injection of the fuel injection valve.

  Therefore, if the detected value of the temperature sensor shows a change of a predetermined amount or more when the temperature raising process by the reducing agent addition valve is switched to the temperature raising process by the post injection of the fuel injection valve, the control means is configured so that the reducing agent addition valve It can be determined that a failure has occurred, and the temperature raising process can be continued using the post injection of the fuel injection valve.

  On the other hand, when the temperature sensor or the oxidation catalyst is out of order, the detected value of the temperature sensor does not change more than a predetermined amount when the temperature raising process is performed by the post injection of the fuel injection valve.

  Therefore, if the detected value of the temperature sensor does not show a change of a predetermined amount or more when the temperature increasing process by the reducing agent addition valve is switched to the temperature increasing process by the post injection of the fuel injection valve, the control means It can be determined that the catalyst has failed.

  When the temperature sensor is out of order, it is possible to increase the temperature of the particulate filter if unburned fuel or a reducing agent is supplied to the oxidation catalyst. However, when unburned fuel is supplied to the oxidation catalyst by post-injection of the fuel injection valve, the fuel post-injected from the fuel injection valve tends to adhere to the cylinder bore wall surface and induce dilution of the lubricating oil, etc. It is preferable to continue the temperature raising process by adding a reducing agent to the addition valve.

  When the oxidation catalyst is out of order, it is difficult to increase the temperature of the particulate filter even if an unburned fuel component or a reducing agent is supplied to the oxidation catalyst. Therefore, the temperature of the exhaust discharged from the internal combustion engine may be raised by advancing the timing of post injection. In this case, since the temperature of the particulate filter is raised by the heat of the exhaust, the temperature raising process can be continued.

  If it cannot be determined which of the temperature sensor and the oxidation catalyst has failed, it is preferable to continue the temperature raising process by advancing the timing of post injection. In this case, the temperature raising process is continued while suppressing dilution of the lubricating oil and the like.

  Next, a NOx catalyst can be illustrated as an exhaust emission control device according to the present invention. The NOx catalyst here is a catalyst that reduces and purifies NOx in exhaust gas and / or NOx stored in the NOx catalyst when exposed to a reducing atmosphere.

  As a method for making the NOx catalyst a reducing atmosphere, a method of supplying a reducing agent into the exhaust gas upstream of the NOx catalyst is suitable. As a method of supplying the reducing agent into the exhaust gas upstream of the NOx catalyst, a method of performing post injection from the fuel injection valve, or a reducing agent into the exhaust gas from the reducing agent addition valve provided in the exhaust passage upstream of the NOx catalyst. The method of adding can be illustrated.

  When the reducing agent is supplied by the above-described method, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is lowered and the inside of the NOx catalyst becomes a reducing atmosphere.

  Therefore, when the exhaust purification apparatus according to the present invention is a NOx catalyst, the air-fuel ratio, which is one of the physical quantities of the exhaust purification apparatus, is changed by the reducing agent addition valve or the fuel injection valve.

  Therefore, in the exhaust gas purification system for an internal combustion engine according to the present invention, the specific physical quantity of the exhaust gas purification device is the air-fuel ratio of the exhaust gas flowing into the NOx catalyst, the first changing means is a reducing agent addition valve, and the second changing means is It can be a fuel injection valve. As the detection means, an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas flowing into the NOx catalyst can be used.

  According to such a configuration, when the detected value of the air-fuel ratio sensor does not change more than a predetermined amount due to the addition of the reducing agent by the reducing agent addition valve, the reducing agent addition valve performs the post injection of the fuel injection valve from the reducing agent supply process. It is possible to switch to the reducing agent supply process.

  By the way, as a factor that the detected value of the air-fuel ratio sensor does not change more than a predetermined amount even when the reducing agent addition valve adds the reducing agent, a failure of the reducing agent addition valve or an air-fuel ratio sensor can be considered.

  When the reducing agent addition valve is out of order, the detected value of the air-fuel ratio sensor changes more than a predetermined amount when the reducing agent supply process is performed by the post injection of the fuel injection valve.

  Therefore, if the detected value of the air-fuel ratio sensor shows a change of a predetermined amount or more when the reducing agent supply processing by the reducing agent addition valve is switched to the reducing agent supply processing by the post injection of the fuel injection valve, the control means It can be determined that the addition valve has failed, and the reducing agent supply process can be continued using the post injection of the fuel injection valve.

  On the other hand, when the air-fuel ratio sensor is out of order, the detected value of the air-fuel ratio sensor does not change more than a predetermined amount when the reducing agent supply process is performed by the post injection of the fuel injection valve.

Therefore, if the detected value of the air-fuel ratio sensor does not show a change of a predetermined amount or more when the reducing agent supply process by the reducing agent addition valve is switched to the reducing agent supply process by the post injection of the fuel injection valve, the control means It can be determined that the fuel ratio sensor has failed.

  When the air-fuel ratio sensor is out of order, it is possible to reduce and purify NOx if a reducing agent is supplied to the NOx catalyst. However, when reducing agent (unburned fuel) is supplied to the NOx catalyst by post injection of the fuel injection valve, the fuel post-injected from the fuel injection valve is likely to adhere to the cylinder bore wall surface and induce dilution of the lubricating oil, etc. Therefore, it is preferable to continue the reducing agent supply process by adding the reducing agent to the reducing agent addition valve.

  According to the present invention, in the exhaust gas purification system for an internal combustion engine capable of changing a specific physical quantity of the exhaust purification device using a plurality of means, the above-described physical quantity can be suitably changed.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purification system for an internal combustion engine.

  In FIG. 1, an internal combustion engine 1 is a compression ignition type internal combustion engine (diesel engine) operated using light oil as fuel. The internal combustion engine 1 has a plurality of cylinders 2, and each cylinder 2 is provided with a fuel injection valve 3 that injects fuel directly into the cylinder 2.

  Each cylinder 2 of the internal combustion engine 1 communicates with the intake passage 4. In the middle of the intake passage 4, a compressor housing 50, an intercooler 6, an intake throttle valve 7 and the like of the turbocharger 5 are arranged. The intake air supercharged by the compressor housing 50 is cooled by the intercooler 6 and then introduced into each cylinder 2. The intake air introduced into each cylinder 2 is ignited and burned in the cylinder 2 together with the fuel injected from the fuel injection valve 3.

  The gas burned in each cylinder 2 (burned gas) is discharged to the exhaust passage 8. The exhaust discharged into the exhaust passage 8 is released into the atmosphere via the turbine housing 51 and the exhaust purification device 9 disposed in the middle of the exhaust passage 8.

  The exhaust purification device 9 is a particulate filter on which a catalyst having oxidation ability is supported. Instead of supporting the catalyst having oxidation ability on the particulate filter, the oxidation catalyst may be arranged immediately upstream of the particulate filter. Hereinafter, the exhaust purification device 9 is referred to as a particulate filter 9.

  A reducing agent addition valve 10 is attached to the exhaust passage 8 upstream of the turbine housing 51. The reducing agent addition valve 10 is a device that adds a reducing agent into the exhaust gas flowing through the exhaust passage 8. Note that the fuel of the internal combustion engine 1 can be used as the reducing agent added from the reducing agent addition valve 10.

  The internal combustion engine 1 is also provided with an ECU 11 as control means according to the present invention. The ECU 11 is electrically connected to various sensors such as an air flow meter 12, a differential pressure sensor 13, an exhaust temperature sensor 14, and an accelerator position sensor 15.

The air flow meter 12 is a sensor that measures the amount of intake air flowing through the intake passage 4. The differential pressure sensor 13 is a sensor that measures the difference between the exhaust pressure upstream of the particulate filter 9 and the exhaust pressure downstream of the particulate filter 9 (differential pressure before and after the filter). The exhaust temperature sensor 14 is a sensor that measures the temperature of the exhaust gas flowing out from the particulate filter 9. The accelerator position sensor 15 is a sensor that measures an operation amount (accelerator opening) of an accelerator pedal (not shown).

  The ECU 11 controls the fuel injection valve 3, the intake throttle valve 7, the reducing agent addition valve 10 and the like based on the measured values of the various sensors described above. For example, the ECU 11 performs PM regeneration processing for the particulate filter 9.

  The PM regeneration process is a process of oxidizing and removing PM collected in the particulate filter 9 by raising the temperature, which is one of the physical quantities of the particulate filter 9, to a temperature range where PM can be oxidized. . This PM regeneration process is executed on condition that the amount of PM collected by the particulate filter 9 (PM collection amount) is a certain amount or more.

  The above-mentioned fixed amount is, for example, an amount determined so that the back pressure acting on the internal combustion engine 1 falls within an allowable range. Further, as a method of acquiring the PM trapped amount of the particulate filter 9, a method of converting the measured value of the differential pressure sensor 13 into the PM trapped amount, or exhausting from the internal combustion engine 1 using the engine load and the engine speed as parameters. A method of calculating the amount of collected PM by determining the amount of PM to be obtained and integrating the amount of PM can be exemplified.

  ECU11 discriminate | determines whether PM collection amount is more than fixed amount. When the amount of collected PM is equal to or greater than a certain amount, the ECU 11 executes a PM regeneration process. Specifically, the ECU 11 performs a temperature raising process for raising the temperature of the particulate filter 9 to a temperature range where PM oxidation is possible.

  As a method of executing the temperature raising process, a method of supplying unburned fuel to the particulate filter 9 can be exemplified. When unburned fuel is supplied to the particulate filter 9, the unburned fuel is oxidized by the catalyst carried on the particulate filter 9, and the temperature of the particulate filter 9 is raised by the oxidation reaction heat at that time.

  Means for supplying unburned fuel to the particulate filter 9 include means for adding fuel into the exhaust gas from the reducing agent addition valve 10 (first changing means), and fuel injection valve 3 in the cylinder 2 in the latter half of the expansion stroke. Examples of means for performing post injection (second changing means) can be given.

  If the fuel injection valve 3 performs post injection in the cylinder 2 in the latter half of the expansion stroke, the post-injected fuel may adhere to the cylinder bore wall surface and induce dilution of the lubricating oil. For this reason, when supplying unburned fuel to the particulate filter 9, it is preferable to use the reducing agent addition valve 10 as much as possible.

  In the temperature raising process as described above, the ECU 11 feedback-controls the supply amount of unburned fuel so that the temperature of the particulate filter 9 does not deviate from the temperature range where PM oxidation is possible.

  Specifically, when the temperature of the particulate filter 9 is lower than the temperature range where PM oxidation is possible, the ECU 11 controls the reducing agent addition valve 10 to increase the amount of unburned fuel supplied, and the temperature of the particulate filter 9 Is higher than the temperature range in which PM oxidation is possible, the reducing agent addition valve 10 is controlled to reduce the supply amount of unburned fuel.

At this time, since the temperature of the particulate filter 9 correlates with the temperature of the exhaust gas flowing out from the particulate filter 9, the ECU 11 causes the reducing agent addition valve so that the measured value of the exhaust temperature sensor 14 converges to a temperature range where PM oxidation is possible. 10 may be feedback controlled.

  By the way, when the oxidation catalyst of the reducing agent addition valve 10, the exhaust temperature sensor 14, or the particulate filter 9 fails, the measured value of the exhaust temperature sensor 14 changes by an amount (predetermined amount) corresponding to the supply amount of unburned fuel. Not shown.

  If the failure location is not specified in such a case, the actual temperature of the particulate filter 9 cannot be converged to a temperature range where PM oxidation is possible, and various problems may occur.

  Therefore, in the PM regeneration process of the present embodiment, the ECU 11 specifies the factor when the measured value of the exhaust temperature sensor 14 does not show a change in the amount (predetermined amount) commensurate with the supply amount of unburned fuel. The PM regeneration process was continued as much as possible.

  Hereinafter, the PM regeneration process in the present embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing a PM regeneration processing routine in the present embodiment. This PM regeneration processing routine is a routine stored in the ROM of the ECU 11 in advance, and is executed by the ECU 11 every predetermined period.

  In the PM regeneration processing routine, the ECU 11 first determines in step S101 whether a PM regeneration condition is satisfied. Examples of the PM regeneration condition include a condition that the PM collection amount is a certain amount or more, the oxidation catalyst of the particulate filter 9 is activated, and the like.

  If a negative determination is made in S101, the ECU 11 once terminates execution of this routine. On the other hand, if an affirmative determination is made in S101, the ECU 11 proceeds to S102, and reads a measured value Tex1 of the exhaust temperature sensor 14 (hereinafter referred to as “first measured value Tex1”).

  In S103, the ECU 11 operates the reducing agent addition valve 10 to start the temperature raising process (PM regeneration process).

  In S104, the ECU 11 reads the measured value Tex2 of the exhaust temperature sensor 14 (hereinafter referred to as “second measured value Tex2”).

  In S105, the ECU 11 first calculates the temperature increase amount (= Tex2-Tex1) of the particulate filter 9 by subtracting the first measurement value Tex1 from the second measurement value Tex2. Subsequently, the ECU 11 determines whether or not the temperature increase amount (= Tex2−Tex1) is less than a predetermined amount ΔT.

  The predetermined amount ΔT is an amount corresponding to the temperature rise amount of the particulate filter 9 at the normal time, and is determined according to the amount of unburned fuel supplied from the reducing agent addition valve 10 to the particulate filter 9.

  If a negative determination is made in S105 (Tex2-Tex1 ≧ ΔT), the ECU 11 proceeds to S113, and continues the temperature raising process and PM regeneration process by the reducing agent addition valve 10.

On the other hand, when an affirmative determination is made in S105 (Tex2-Tex1 <ΔT), the ECU 11 proceeds to S106. In S <b> 106, the ECU 11 stops the operation of the reducing agent addition valve 10.

  In S107, the ECU 11 starts the post injection of the fuel injection valve 3. That is, the ECU 11 switches from the temperature raising process by the reducing agent addition valve 10 to the temperature raising process by post injection of the fuel injection valve 3 in S106 and S107.

  In S108, the ECU 11 reads the measured value Tex3 of the exhaust temperature sensor 14 (hereinafter referred to as “third measured value Tex3”).

  In S109, the ECU 11 first calculates the temperature increase amount (= Tex3-Tex1) of the particulate filter 9 by subtracting the first measurement value Tex1 from the third measurement value Tex3. Subsequently, the ECU 11 determines whether or not the temperature increase amount (= Tex3−Tex1) is less than a predetermined amount ΔT.

  Since the temperature of the particulate filter 9 may be slightly changed due to the operation of the reducing agent addition valve 10, the second measurement value Tex2 is used instead of the first measurement value Tex1 in S109. It may be. That is, the ECU 11 may determine whether or not the difference (= Tex3−Tex2) between the third measurement value Tex3 and the second measurement value Tex2 is less than the predetermined amount ΔT in S109. .

  If a negative determination is made in S109 (Tex3−Tex1 ≧ ΔT), the ECU 11 proceeds to S112 and determines that the reducing agent addition valve 10 has failed. Next, the ECU 11 proceeds to S113, and continues the temperature raising process and the PM regeneration process by the post injection of the fuel injection valve 3.

  In this case, a failure of the reducing agent addition valve 10 can be detected, and the temperature raising process and the PM regeneration process can be continued.

  On the other hand, when an affirmative determination is made in S109 (Tex3-Tex1 <ΔT), the ECU 11 proceeds to S110. In S110, the ECU 11 determines that the oxidation catalyst of the particulate filter 9 or the exhaust temperature sensor 14 has failed.

  In S111, the ECU 11 stops the post injection by the fuel injection valve 3, and ends the temperature raising process and the PM regeneration process.

  According to the embodiment described above, in the exhaust gas purification system for an internal combustion engine in which the temperature of the particulate filter 9 can be changed by a plurality of means, the failure location can be specified when the failure of the system occurs, The temperature rising process and PM regeneration process of the particulate filter 9 can be continued as much as possible.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIG. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  In the first embodiment described above, an example in which the temperature increase process and the PM regeneration process of the particulate filter 9 are stopped when the oxidation catalyst of the particulate filter 9 or the exhaust temperature sensor 14 fails is described.

On the other hand, in the present embodiment, an example will be described in which the temperature increasing process and the PM regeneration process of the particulate filter 9 are continued even when the oxidation catalyst of the particulate filter 9 or the exhaust temperature sensor 14 fails.

  Hereinafter, the PM regeneration process of the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing a PM regeneration processing routine in the present embodiment. In the PM regeneration processing routine of FIG. 3, the same processes as those in the PM regeneration processing routine of the first embodiment are denoted by the same reference numerals.

  In the PM regeneration processing routine, when it is determined in S110 that the oxidation catalyst of the particulate filter 9 or the exhaust temperature sensor 14 is out of order, the ECU 11 proceeds to S201.

  In S201, the ECU 11 advances the timing of post injection by the fuel injection valve 3. For example, the ECU 11 advances the post injection timing from the latter half of the expansion stroke to the middle of the expansion stroke or the first half.

  When the post injection timing is advanced in this way, the post-injected fuel is exposed to a high temperature and high pressure atmosphere and burned. In this case, the temperature of the exhaust discharged from the internal combustion engine 1 increases. As a result, the particulate filter 9 receives the heat of the exhaust gas and rises in temperature.

  Therefore, according to the exhaust gas purification system of the internal combustion engine of the present embodiment, even if the oxidation catalyst of the particulate filter 9 or the exhaust temperature sensor 14 is out of order, the temperature increasing process and PM regeneration process of the particulate filter 9 are performed. It is possible to continue.

  As described above, when the timing of post injection is advanced, the torque generated by the internal combustion engine 1 may increase considerably. Therefore, the increase in torque may be offset by retarding the timing of main injection by the fuel injection valve 3 or reducing the fuel injection amount of the main injection.

<Example 3>
Next, a third embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  In the first embodiment described above, an example in which a particulate filter is used as the exhaust gas purification apparatus according to the present invention has been described. In this embodiment, an example in which a NOx catalyst is used will be described.

  FIG. 4 is a diagram showing a schematic configuration of an exhaust gas purification system for an internal combustion engine in the present embodiment. In the figure, the same components as those of the first embodiment described above are denoted by the same reference numerals.

  In FIG. 4, a NOx catalyst 90 is disposed in the exhaust passage 8 downstream from the turbine housing 51. The NOx catalyst 90 occludes or absorbs NOx in the exhaust when the oxygen concentration in the exhaust is high (when the air-fuel ratio of the exhaust is lean), and when the oxygen concentration in the exhaust is low and a reducing agent is present (exhaust (When the air-fuel ratio of the gas is rich) is a storage-reduction type NOx catalyst that reduces the stored NOx while releasing it.

  An air-fuel ratio sensor 16 that measures the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 90 is attached to the exhaust passage 8 upstream from the NOx catalyst 90.

In the exhaust gas purification system for an internal combustion engine configured as described above, the ECU 11 performs a NOx regeneration process for the NOx catalyst 90. The NOx regeneration process is performed by reducing the air-fuel ratio (specifically, the air-fuel ratio of the exhaust gas in the NOx catalyst 90), which is one of the physical quantities of the NOx catalyst 90, to the air-fuel ratio at which NOx is released and reduced. In this process, NOx occluded in the catalyst 90 is released and reduced.

  Specifically, the ECU 11 reduces the air-fuel ratio of the exhaust gas in the NOx catalyst 90 to a desired air-fuel ratio by performing rich spike processing that intermittently supplies a reducing agent to the NOx catalyst 90.

  Specific means for intermittently supplying the reducing agent to the NOx catalyst 90 include means for intermittently adding fuel from the reducing agent addition valve 10 into the exhaust (first changing means), and the expansion stroke of each cylinder 2. A means (second changing means) for causing the fuel injection valve 3 to perform post injection in the second half can be exemplified.

  If the fuel injection valve 3 performs post injection in the cylinder 2 in the latter half of the expansion stroke, the post-injected fuel may adhere to the cylinder bore wall surface and induce dilution of the lubricating oil. For this reason, when supplying a reducing agent to the NOx catalyst 90, it is preferable to utilize the reducing agent addition valve 10 as much as possible.

  In the rich spike process as described above, the ECU 11 feedback-controls the amount of reducing agent (fuel) supplied so that the air-fuel ratio of the exhaust gas in the NOx catalyst 90 becomes a desired air-fuel ratio. For example, when the air-fuel ratio of the exhaust gas in the NOx catalyst 90 is leaner than the desired air-fuel ratio, the ECU 11 controls the reductant addition valve 10 to increase the supply amount of the reductant, and the exhaust gas in the NOx catalyst 90 is emptied. When the fuel ratio is richer than the desired air-fuel ratio, the reducing agent addition valve 10 is controlled to reduce the supply amount of the reducing agent.

  Since the air-fuel ratio of the exhaust gas in the NOx catalyst 90 correlates with the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 90, the ECU 11 controls the reducing agent addition valve so that the measured value of the air-fuel ratio sensor 16 becomes a desired air-fuel ratio. 10 is feedback controlled.

  By the way, when the reducing agent addition valve 10 or the air-fuel ratio sensor 16 fails, the measured value of the air-fuel ratio sensor 16 does not change by an amount (predetermined amount) corresponding to the amount of reducing agent supplied.

  In such a case, if the failure location is not specified, the air-fuel ratio in the NOx catalyst 90 cannot be converged to a desired air-fuel ratio, and various problems may occur.

  Therefore, in the NOx regeneration process of the present embodiment, the ECU 11 specifies the factor when the measured value of the air-fuel ratio sensor 16 does not show a change in the amount (predetermined amount) commensurate with the supply amount of the reducing agent, and determines the factor. The regeneration process was continued as much as possible.

  Hereinafter, the NOx regeneration process in the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing the NOx regeneration processing routine in the present embodiment. This NOx regeneration processing routine is a routine stored in advance in the ROM of the ECU 11 and is executed by the ECU 11 at predetermined intervals.

  In the NOx regeneration processing routine, the ECU 11 first determines in S301 whether or not a NOx regeneration condition is satisfied. Examples of the NOx regeneration condition include a condition that the NOx occlusion amount of the NOx catalyst 90 is equal to or greater than a certain amount, or that a certain period has elapsed since the end of the previous execution of the NOx regeneration process.

If a negative determination is made in S301, the ECU 11 once terminates execution of this routine. On the other hand, when a positive determination is made in S301, the ECU 11 proceeds to S302.

  In S302, the ECU 11 reads a measured value A / F1 of the air-fuel ratio sensor 16 (hereinafter referred to as “first measured value A / F1”).

  In S303, the ECU 11 intermittently operates the reducing agent addition valve 10 to perform rich spike processing.

  In S304, the ECU 11 reads the measured value A / F2 of the air-fuel ratio sensor 16 (hereinafter referred to as “second measured value A / F2”).

  In S305, the ECU 11 subtracts the second measurement value A / F2 from the first measurement value A / F1 to calculate an air-fuel ratio decrease amount (= A / F1-A / F2). Next, the ECU 11 determines whether or not the reduction amount (= A / F1-A / F2) is less than a predetermined amount ΔA / F.

  The above-described predetermined amount ΔA / F is an amount corresponding to the amount of decrease in the air-fuel ratio at the normal time, and is determined according to the amount of reducing agent (fuel) supplied from the reducing agent addition valve 10 to the NOx catalyst 90. .

  When a negative determination is made in S305 (A / F1-A / F2 ≧ ΔA / F), the process proceeds to S313, and the rich spike process and the NOx regeneration process by the reducing agent addition valve 10 are continued.

  When an affirmative determination is made in S305 (A / F1-A / F2 <ΔA / F), the process proceeds to S306 and the operation of the reducing agent addition valve 10 is stopped.

  In S307, the ECU 11 starts post injection by the fuel injection valve 3. That is, the ECU 11 switches from the rich spike process by the reducing agent addition valve 10 to the rich spike process by the post injection of the fuel injection valve 3 in S306 and S307.

  In S308, the ECU 11 reads the measurement value A / F3 of the air-fuel ratio sensor 16 (hereinafter referred to as “third measurement value A / F3”).

  In step S309, the ECU 11 first calculates the air-fuel ratio decrease amount (= A / F1-A / F3) by subtracting the third measurement value A / F3 from the first measurement value A / F1. . Next, the ECU 11 determines whether or not the reduction amount (= A / F1-A / F3) is less than a predetermined amount ΔA / F.

  Since the air-fuel ratio of the exhaust gas may be slightly changed due to the operation of the reducing agent addition valve 10, the second measured value A / F2 is used instead of the first measured value A / F1 in S309. You may be made to do. That is, in S309, the ECU 11 determines whether the difference (= A / F2-A / F3) between the third measurement value A / F3 and the second measurement value A / F2 is less than the predetermined amount ΔA / F. You may make it discriminate | determine.

  If a negative determination is made in S309 (A / F1-A / F3 ≧ ΔA / F), the ECU 11 proceeds to S312 and determines that the reducing agent addition valve 10 has failed. Subsequently, the ECU 11 proceeds to S313, and continues the rich spike process and the NOx regeneration process by the post injection of the fuel injection valve 3.

  In this case, a failure of the reducing agent addition valve 10 can be detected, and the rich spike process and the NOx regeneration process can be continued.

  If an affirmative determination is made in S309 (A / F1-A / F3 <ΔA / F), the ECU 11 proceeds to S310 and determines that the air-fuel ratio sensor 16 has failed.

  Subsequently, the ECU 11 proceeds to S311 and stops the post injection of the fuel injection valve 3 and operates the reducing agent addition valve 10. That is, the ECU 11 returns from the rich spike processing and NOx regeneration processing by the post injection of the fuel injection valve 3 to the rich spike processing and NOx regeneration processing by the reducing agent addition valve 10.

  In this case, it is possible to detect a failure of the air-fuel ratio sensor 16 and to continue the rich spike process and the NOx regeneration process while suppressing dilution of the lubricating oil and the like.

  According to the embodiment described above, in the exhaust gas purification system for an internal combustion engine in which the air-fuel ratio of the exhaust gas in the NOx catalyst 90 can be changed by a plurality of means, the failure location can be specified when the failure of the system occurs. In addition, the rich spike process and the NOx regeneration process for the NOx catalyst 90 can be continued as much as possible.

It is a figure which shows schematic structure of the exhaust gas purification system of the internal combustion engine in a 1st Example. 6 is a flowchart showing a PM regeneration processing routine in the first embodiment. It is a flowchart which shows PM regeneration process routine in a 2nd Example. It is a figure which shows schematic structure of the exhaust gas purification system of the internal combustion engine in a 3rd Example. It is a flowchart which shows the NOx reproduction | regeneration processing routine in a 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve (2nd change means)
8 ... Exhaust passage 9 ... Particulate filter (exhaust gas purification device)
10... Reducing agent addition valve (first changing means)
11 .... ECU (control means)
13 .... Differential pressure sensor 14 .... Exhaust temperature sensor (detection means)
16 .... Air-fuel ratio sensor (detection means)

Claims (2)

An exhaust purification device that is disposed in an exhaust passage of the internal combustion engine and includes an oxidation catalyst and a particulate filter;
A reducing agent addition valve capable of changing the temperature of the particulate filter by adding a reducing agent into the exhaust gas upstream of the oxidation catalyst;
A fuel injection valve capable of changing the temperature of the particulate filter by performing post injection into the cylinder of the internal combustion engine;
A temperature sensor for detecting the temperature of the particulate filter;
Control means for causing the fuel injection valve to perform post-injection if the detected temperature of the temperature sensor does not show a change of a predetermined amount or more during operation of the reducing agent addition valve;
In an exhaust gas purification system for an internal combustion engine equipped with
The control means, the post injection with the previous SL fuel injection valve is determined that the detected temperature of the temperature sensor when executing the post injection have to show change of a predetermined amount or more, before Symbol oxidation catalyst is faulty An exhaust gas purification system for an internal combustion engine characterized by advancing the timing of the engine. An exhaust purification device that is disposed in an exhaust passage of the internal combustion engine and includes a NOX catalyst;
A reducing agent addition valve capable of changing the air-fuel ratio of the exhaust gas flowing into the NOX catalyst by adding a reducing agent into the exhaust gas upstream of the exhaust gas purification device;
A fuel injection valve capable of changing the air-fuel ratio of the exhaust gas flowing into the NOX catalyst by performing post injection into the cylinder of the internal combustion engine;
An air-fuel ratio sensor for detecting an air-fuel ratio of the exhaust gas flowing into the NOX catalyst;
Control means for causing the fuel injection valve to perform post-injection if the detected value of the air-fuel ratio sensor does not show a change of a predetermined amount or more during operation of the reducing agent addition valve;
In an exhaust gas purification system for an internal combustion engine equipped with
The control means may detect value of the air-fuel ratio sensor when the front Symbol fuel injector executes post injection have to show change of a predetermined amount or more, determines that the previous Kisora ratio sensor is faulty, An exhaust gas purification system for an internal combustion engine, wherein the operation of the reducing agent addition valve is resumed.

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