JP4170935B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  Conventionally, as seen in Patent Document 1, as an exhaust purification device applied to an internal combustion engine such as a vehicle-mounted diesel engine, a PM filter that collects particulates mainly composed of soot contained in the exhaust is used as an exhaust system. What is provided is known.

In an internal combustion engine provided with such an exhaust purification device, for example, in order to avoid clogging of the PM filter with fine particles based on the fact that the amount of accumulated fine particles on the PM filter estimated from the engine operating state or the like is greater than an allowable value. PM regeneration control is performed. In this PM regeneration control, fuel is added to the exhaust gas upstream of the PM filter, and the temperature of the catalyst is raised by the heat generated by the oxidation reaction of the unburned fuel component on the catalyst of the PM filter and the particulate matter of the PM filter Is to burn. When it is determined that the particulates deposited on the PM filter have been burned, the estimated amount of particulates deposited on the PM filter is set to “0” and PM regeneration control is completed.
JP-A-5-44434

  By the way, the PM regeneration control may be interrupted due to an engine stop during the execution of the control. In this case, if the amount of accumulated particulates at the time of interruption is less than the allowable value, the PM regeneration control will not be resumed even if the PM regeneration control can be executed later by restarting the engine. However, if the PM regeneration control is not completed several times due to the interruption of the PM regeneration control, the following problems may occur in relation to the estimated amount of accumulated particulate matter.

  There is a possibility that an error occurs in the estimated accumulation amount of the fine particles with respect to the actual accumulation amount. However, regarding such an error, the estimated fine particles are accumulated at the time of completion of the PM regeneration control in which the fine particles accumulated on the PM filter are completely combusted. This is solved by setting the deposition amount to “0”. However, if execution / interruption of PM regeneration control continues several times, the accumulation of fine particles on the PM filter in normal engine operation without setting the estimated accumulation amount of fine particles to “0”, The combustion of the fine particles in the PM regeneration control until the interruption is repeated. In addition, while the amount of deposited fine particles is increasing or decreasing in this way, the estimated amount of deposition may be greatly deviated from the actual amount of deposition.

  For example, when the estimated accumulation amount of fine particles is significantly smaller than the actual accumulation amount, control is performed to make the exhaust air-fuel ratio rich based on the estimated accumulation amount of fine particles. If executed, the catalyst bed temperature of the PM filter may be excessively increased. This is because when the unburned fuel component is supplied to the PM filter based on the same control and the particulates deposited on the PM filter are burned due to the oxidation reaction of the unburned components, more particulates are deposited than expected. This is because the amount of heat generated when the fine particles are burned increases.

  The present invention has been made in view of such a situation, and the object thereof is between the estimated deposition amount of fine particles around the catalyst and the actual deposition amount due to the suspension of PM regeneration control. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can suppress an increase in error.

In the following, means for achieving the above object and its effects are described.
In order to achieve the above object, according to the first aspect of the present invention, the accumulation amount of fine particles collected around the exhaust system catalyst is estimated, and the estimated accumulation amount of fine particles is above an allowable value. Then, PM regeneration control for supplying unburned fuel components to the catalyst to raise the temperature of the catalyst and combusting the collected fine particles is performed, and when the control is completed, the estimated accumulation amount of fine particles is set to “0”. In the exhaust gas purification apparatus for an internal combustion engine set to ”, at the end of the PM regeneration control, in order to make it possible to burn fine particles remaining at the exhaust upstream end of the exhaust system catalyst, It is assumed that burn-up control is performed in which intensive intermittent fuel addition and stop of the fuel addition are repeated a predetermined number of times.
Fine particles are likely to accumulate around the upstream end of the exhaust of the catalyst. However, in burn-up control performed at the end of PM regeneration control, unburned fuel components and oxygen per unit time are added to the catalyst through concentrated intermittent fuel addition. The supply amount can be increased to a value at which fine particles remaining around the exhaust upstream end of the catalyst can be burned without being burned by normal PM regeneration control. Therefore, by repeating this intensive intermittent fuel addition and stoppage of the fuel addition a predetermined number of times, the fine particles around the exhaust upstream end of the catalyst can be burned, and the actual fine particles around the catalyst after the PM regeneration control is completed. Can be reliably set to “0”. For this reason, when the estimated amount of particulate deposition around the catalyst is set to “0” upon completion of PM regeneration control, particulates remain around the catalyst, and the estimated deposition amount becomes the actual deposition amount. It is possible to avoid the situation of not responding.
According to a second aspect of the present invention, in the first aspect of the invention, when the PM regeneration control is interrupted, the internal combustion engine is in operation later and the deactivation of the catalyst is eliminated. In this case, the PM regeneration control is resumed even if the amount of fine particles deposited around the catalyst is less than the allowable value.

When the internal combustion engine is in operation after the PM regeneration control is interrupted and the deactivation of the catalyst has been eliminated, the PM regeneration control is performed even if the estimated amount of deposited fine particles around the catalyst is less than the allowable value. The process is resumed until the control is completed, so that the fine particles around the catalyst can be combusted. When the particulate regeneration is completed and PM regeneration control is completed, the estimated particulate deposition amount is set to “0”, and the error between the estimated particulate deposition amount and the actual deposition amount is eliminated. The Accordingly, it is possible to suppress repeated execution / interruption of the control without completing the PM control, and an error between the estimated amount of deposited fine particles and the actual amount of accumulation during the repetition is large. It can be suppressed.

According to a third aspect of the invention, in the second aspect of the invention, when the PM regeneration control is resumed, the execution time of the PM regeneration control is shorter as the amount of accumulated particulates around the catalyst is estimated to be smaller. It was supposed to be set.

  When the PM regeneration control is interrupted, the combustion of the particulates that have accumulated around the catalyst has progressed to some extent. The smaller the amount of particulates accumulated at that time, the shorter the execution time of the control after restarting the PM regeneration control. Can also burn the fine particles. According to the above configuration, when the suspended PM regeneration control is resumed, the smaller the estimated accumulation amount of fine particles around the catalyst, the shorter the execution time of the PM regeneration control is set. The shortening and suppression of the deterioration of fuel consumption based on the fact that the control is continued unnecessarily for a long time can be achieved.

Hereinafter, an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS.
FIG. 1 shows the configuration of an internal combustion engine 10 to which the exhaust purification system of this embodiment is applied. The internal combustion engine 10 is a diesel engine including a common rail fuel injection device and a turbocharger 11, and mainly includes an intake passage 12, a combustion chamber 13, and an exhaust passage 14.

  In an intake passage 12 constituting the intake system of the internal combustion engine 10, an air flow meter 16, a compressor 17 of the turbocharger 11, an intercooler 18, And an intake throttle valve 19 is provided. The intake passage 12 is branched at an intake manifold 20 provided on the downstream side of the intake throttle valve 19 and connected to the combustion chamber 13 of each cylinder of the internal combustion engine 10 via an intake port 21.

  On the other hand, in the exhaust passage 14 constituting the exhaust system of the internal combustion engine 10, the exhaust port 22 connected to the combustion chamber 13 of each cylinder is connected to the exhaust turbine 24 of the turbocharger 11 via the exhaust manifold 23. Yes. In addition, a NOx catalytic converter 25, a PM filter 26, and an oxidation catalytic converter 27 are disposed downstream from the exhaust turbine 24 in the exhaust passage 14 in order from the upstream side.

  The NOx catalytic converter 25 carries an NOx storage reduction catalyst. The NOx catalyst stores NOx in the exhaust when the oxygen concentration of the exhaust is high, and releases the stored NOx when the oxygen concentration of the exhaust is low. Further, the NOx catalyst reduces and purifies the released NOx if there is sufficient unburned fuel component as a reducing agent at the time of releasing the NOx.

  The PM filter 26 is made of a porous material and collects fine particles (PM) mainly composed of soot in the exhaust gas. Similarly to the NOx catalytic converter 25, the PM filter 26 also carries an NOx storage reduction catalyst so that NOx in the exhaust gas can be purified. Further, the collected PM is burned (oxidized) and removed by a reaction triggered by the NOx catalyst.

The oxidation catalyst converter 27 carries an oxidation catalyst. This oxidation catalyst oxidizes and purifies hydrocarbons (HC) and carbon monoxide (CO) in the exhaust.
In addition, on the upstream side and the downstream side of the PM filter 26 in the exhaust passage 14, an inlet gas temperature sensor 28 that detects the inlet gas temperature that is the temperature of the exhaust gas flowing into the PM filter 26, and the exhaust gas after passing through the PM filter 26. An outgas temperature sensor 29 for detecting an outgas temperature, which is a temperature, is provided. The exhaust passage 14 is provided with a differential pressure sensor 30 for detecting a differential pressure between the exhaust upstream side of the PM filter 26 and the exhaust downstream side thereof. Further, two oxygen sensors 31 and 32 for detecting the oxygen concentration in the exhaust gas are arranged on the exhaust gas upstream side of the NOx catalytic converter 25 in the exhaust passage 14 and between the PM filter 26 and the oxidation catalytic converter 27, respectively. It is installed.

  Further, the internal combustion engine 10 is provided with an exhaust gas recirculation (hereinafter referred to as EGR) device that recirculates a part of the exhaust gas to the air in the intake passage 12. The EGR device includes an EGR passage 33 that allows the exhaust passage 14 and the intake passage 12 to communicate with each other. The most upstream portion of the EGR passage 33 is connected to the exhaust upstream side of the exhaust turbine 24 in the exhaust passage 14. The EGR passage 33 is provided with an EGR catalyst 34 for reforming the recirculated exhaust, an EGR cooler 35 for cooling the exhaust, and an EGR valve 36 for adjusting the flow rate of the exhaust from the upstream side. The most downstream portion of the EGR passage 33 is connected to the downstream side of the intake throttle valve 19 in the intake passage 12.

  On the other hand, an injector 40 for injecting fuel to be used for combustion in the combustion chamber 13 is disposed in the combustion chamber 13 of each cylinder of the internal combustion engine 10. The injector 40 of each cylinder is connected to a common rail 42 via a high pressure fuel supply pipe 41. High pressure fuel is supplied to the common rail 42 through a fuel pump 43. The pressure of the high-pressure fuel in the common rail 42 is detected by a rail pressure sensor 44 attached to the common rail 42. Further, low pressure fuel is supplied from the fuel pump 43 to the addition valve 46 through the low pressure fuel supply pipe 45.

  Various controls of the internal combustion engine 10 are performed by the electronic control unit 50. The electronic control unit 50 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 arithmetic results, and signals between the outside The input / output port for inputting / outputting is provided.

  In addition to the sensors described above, the input port of the electronic control unit 50 includes an NE sensor 51 that detects the engine speed, an accelerator sensor 52 that detects the accelerator operation amount, and a throttle valve sensor that detects the opening of the intake throttle valve 19. 53 etc. are connected. The output port of the electronic control unit 50 is connected to drive circuits such as the intake throttle valve 19, the EGR valve 36, the injector 40, the fuel pump 43, and the addition valve 46.

  The electronic control unit 50 outputs a command signal to the drive circuit of each device connected to the output port according to the engine operating state grasped from the detection signal input from each sensor. Thus, the opening control of the intake throttle valve 19, EGR control based on the opening control of the EGR valve 36, control of the fuel injection amount, fuel injection timing, and fuel injection pressure from the injector 40, Various controls such as fuel addition control are performed by the electronic control unit 50.

  In the present embodiment configured as described above, PM trapped in the NOx catalytic converter 25 and the PM filter 26 is burned in order to prevent clogging due to PM in the NOx catalytic converter 25 and the PM filter 26. PM regeneration control for purification is performed. In such PM control, an unburned fuel component is supplied to the NOx catalyst of the NOx catalytic converter 25 and the PM filter 26, so that the catalyst is generated by heat generated by oxidation of the unburned fuel component in the exhaust or on the catalyst, for example, 600. While raising the temperature to about ˜700 ° C., PM around the catalyst is combusted.

  The unburned fuel component is supplied to the catalyst in the PM regeneration control by sub-injection (after-injection) performed in the exhaust stroke or the expansion stroke after the fuel supplied from the injector 40 for combustion in the combustion chamber 13 is injected. Alternatively, the fuel is added to the exhaust from the addition valve 46. In addition, the amount of unburned fuel components supplied to the catalyst in PM regeneration control is kept to a minimum value that can increase the required catalyst bed temperature in order to suppress excessive fuel consumption associated with the execution of the control as much as possible. It is done.

Incidentally, in the present embodiment, the PM regeneration control is performed when all of the following conditions are satisfied.
・ When PM regeneration is requested. The PM regeneration request here is made when the occurrence of clogging of the PM filter 26 is confirmed based on the fact that the PM accumulation amount in the PM filter 26 or the like estimated from the engine operating state exceeds an allowable value. .
The detected value (input gas temperature thci) of the input gas temperature sensor 28 is equal to or higher than the lower limit temperature A (for example, 150 ° C.) of the PM regeneration control. Further, the catalyst bed temperature of the NOx catalyst estimated from the history of the engine operation state is equal to or higher than the lower limit temperature B of the PM regeneration control. These lower limit temperatures A and B are respectively set to an exhaust temperature and a lower limit value of the catalyst bed temperature that can cause an oxidation reaction sufficient to raise the catalyst bed temperature with the supply of unburned fuel components. .
-The detection value of the inlet gas temperature sensor 28 is less than the upper limit C of the temperature range in which excessive temperature rise of the catalyst due to heat generation accompanying PM regeneration control can be avoided.
The detection value of the outgas temperature sensor 29 is less than the upper limit value D of the temperature range that can avoid the excessive temperature rise of the catalyst due to the heat generation accompanying the PM regeneration control.
・ Addition of fuel to the exhaust is permitted. In other words, the engine is in an operating state in which exhaust fuel addition can be allowed. In the internal combustion engine 10, addition of exhaust fuel is permitted if the cylinder determination is not completed and the accelerator opening is not limited, while the engine is not stalling.

Here, details of the control content of the PM regeneration control will be described with reference to FIGS.
FIG. 2 is a graph showing how the combustion rate of unburned fuel (HC) and PM adhering to the catalyst surface changes as the catalyst temperature rises in the NOx catalytic converter 25 and the PM filter 26. is there. As can be seen from the figure, the unburned fuel adhering to the catalyst burns at a relatively low catalyst bed temperature (around 300 ° C.), and the PM adhering to the catalyst has a catalyst bed temperature of 600 to 700 ° C. as described above. Combustion occurs when the temperature is raised to such a temperature. Therefore, in PM regeneration control, when the catalyst bed temperature is suddenly raised to a temperature close to 700 ° C., a large amount of unburned fuel and PM adhering to the catalyst burns, and the catalyst receives heat at that time and the catalyst bed temperature is excessively exceeded. There is a risk of rising.

  For this reason, in the PM regeneration control, the catalyst bed temperature is set to 300, 600, 630, for example, as shown in FIG. 3B in order to burn the unburned fuel (HC) and PM adhering to the catalyst surface stepwise. The temperature is raised stepwise in the order of 650 ° C. to suppress the excessive increase in the catalyst bed temperature as described above. Specifically, first, the minimum necessary unburned fuel component is supplied to the catalyst in order to raise the catalyst bed temperature to 300 ° C. By such an increase in the catalyst bed temperature toward 300 ° C., the unburned fuel adhering to the catalyst is combusted. When the catalyst bed temperature reaches 300 ° C., the catalyst bed temperature is raised to 600 ° C. and maintained for the holding time t2, and then the catalyst bed temperature is raised to 630 ° C. and the state is held for holding time t3. The catalyst bed temperature is increased to 650 ° C.

  The holding time t2 for maintaining the catalyst bed temperature at 600 ° C. is shortened as shown in FIG. 4 as the PM deposition amount c at the time of switching the catalyst bed temperature from 300 ° C. to 600 ° C. (timing Tc) is smaller. . In addition, the holding time t3 for maintaining the catalyst bed temperature at 630 ° C. is shortened as shown in FIG. 5 as the PM deposition amount b at the time of switching the catalyst bed temperature from 600 ° C. to 630 ° C. (timing Tb) decreases. . The reason for making the holding times t2 and t3 variable in accordance with the PM accumulation amounts c and b is to keep the execution time of the PM regeneration control to the minimum necessary for burning PM and to use the fuel used in the control. This is to suppress the deterioration of the fuel consumption of the minute as much as possible.

  As described above, in the PM regeneration control, the PM deposited around the catalyst is combusted as the catalyst bed temperature is raised stepwise, and the PM deposition amount decreases as shown in FIG. . However, even if PM regeneration control is performed as described above, PM that cannot be combusted by itself remains at the exhaust upstream end of the NOx catalytic converter 25 and the exhaust upstream end of the PM filter 26. Thus, PM remains in the exhaust upstream end of the NOx catalytic converter 25 and the exhaust upstream end of the PM filter 26 where PM is likely to accumulate, and supply of unburned fuel components to the catalyst in PM regeneration control. Then, it is considered that the supply amount of the unburned fuel component per unit time is not sufficient to burn all the PM. In particular, in the NOx catalytic converter 25 located upstream of the PM filter 26, a large amount of PM that cannot be combusted by PM regeneration control remains at the exhaust upstream end.

  Therefore, at the end of the PM regeneration control, that is, when the PM accumulation amount decreases to a determination value a (eg, 0.3 g) that is very close to “0”, PM that cannot be combusted only by the PM regeneration control described above is burned. Burn-up control is performed. Hereinafter, the outline of the burn-up control will be described with reference to the time chart of FIG. In FIG. 6, (a) shows the fuel addition mode of the addition valve 46, and (b) shows the transition of the exhaust air-fuel ratio.

  As can be seen from the figure, in the burn-up control, intensive intermittent fuel addition from the addition valve 46 and stop of the fuel addition are repeated. In such intensive intermittent fuel addition, the amount of unburned fuel components and oxygen supplied to the catalyst of the NOx catalytic converter 25 and the PM filter 26 per unit time is burned with the PM that cannot be burned only by PM regeneration control. Can be raised to a possible value. Therefore, the PM is combusted by the concentrated intermittent fuel addition.

  If intensive intermittent fuel addition is performed as described above, it is inevitable that the catalyst bed temperature will rise significantly. Therefore, in order to suppress an excessive increase in the catalyst bed temperature, the fuel addition is periodically stopped. I am doing so. As a result, intensive intermittent fuel addition and stop of the fuel addition are repeated, and the exhaust air-fuel ratio is reversed between rich and lean as shown in FIG. 6B. In the burn-up control, the number of repetitions of intensive intermittent fuel addition and stop of the fuel addition is set to the number of times (three times in the present embodiment) that PM remaining in the NOx catalytic converter 25 and the PM filter 26 can be burned. It is terminated based on what has been reached.

  The PM regeneration control is completed based on the end of the burn-up control. When the PM regeneration control is thus completed, the amount of PM deposited around the catalyst estimated from the engine operating state becomes “0”. In other words, when the PM regeneration control is completed, the PM accumulation amount is set to “0”.

  By the way, the PM regeneration control described above may be interrupted during the execution of the control. For example, when the operation of the internal combustion engine 10 is stopped, the control is interrupted even if PM regeneration control is being executed. Also, PM regeneration control is interrupted when a catalyst deactivation phenomenon occurs in which the catalyst bed temperature decreases due to a decrease in exhaust temperature during PM regeneration control, even though unburned fuel components are supplied. Is done.

  The catalyst deactivation phenomenon is caused by the catalyst becoming inactive due to a decrease in exhaust temperature during PM regeneration control, and the oxidation reaction of the unburned fuel component is temporarily delayed. This is caused by a vicious cycle in which the degree of activity of the catalyst is further reduced because the surface area of the catalyst that remains with unburned fuel remaining and exposed to the exhaust gas is reduced. Then, when the unburned fuel component is supplied to the catalyst in the PM regeneration control in a state where the deactivation phenomenon of the catalyst has occurred, the unburned fuel component is released to the outside air in a state of incomplete combustion. As a result, exhaust emissions such as a large amount of smoke may be deteriorated. For this reason, PM regeneration control is interrupted when a catalyst deactivation phenomenon occurs.

  However, if the PM regeneration control is not completed several times due to the interruption of the PM regeneration control as described above, the deviation of the estimated PM deposition amount from the actual deposition amount becomes large, which becomes a problem. . Here, the reason why the deviation of the estimated PM deposition amount from the actual deposition amount becomes larger due to repeated execution / interruption of PM regeneration control will be described with reference to FIGS.

  Since the PM accumulation amount used in the PM regeneration control is a value estimated based on the engine operating state, an error may occur with respect to the actual accumulation amount. For example, as shown in FIG. 7A, the estimated PM deposition amount (solid line L1) may deviate from the actual deposition amount (broken line L2) as illustrated. Normally, such an error is eliminated by setting the estimated PM accumulation amount to “0” at the completion of PM regeneration control in which PM accumulated around the catalyst is completely combusted. That is, as shown in FIG. 7B, when the PM regeneration control started at the time point (timing T1) when the estimated amount of PM deposition exceeds the allowable value (timing T2) is completed (timing T2), it accumulates around the catalyst. As a result, the estimated PM accumulation amount is set to “0”. As a result, the estimated PM accumulation amount and the actual accumulation amount coincide with each other, and the error between them is eliminated.

  If the PM regeneration control can be completed as described above, the error between the estimated PM accumulation amount and the actual accumulation amount is eliminated, but the PM regeneration control is interrupted before the PM regeneration control is completed. In some cases, the error remains unresolved. For example, as shown in FIG. 8 (a), if the control is interrupted at the timing T3 during PM regeneration control due to engine stoppage or catalyst deactivation, the PM accumulation amount is allowed at the time of the interruption. If it falls below, even if the engine operation is started later or the catalyst is activated and the PM regeneration control can be executed, the control is not resumed. In this case, since the PM regeneration control is not completed, the above error is not eliminated by setting the PM accumulation amount to “0”. Then, when the PM accumulation amount becomes equal to or greater than the allowable value again, PM regeneration control is executed again (timing T4).

  When the execution / interruption of such PM regeneration control continues several times as shown in FIG. 8B (T4 to T7 in the figure), there is no chance to set the PM accumulation amount to “0”. The PM accumulation around the catalyst in the engine operation and the combustion of the PM in the PM regeneration control until the interruption are repeated. As a result, the estimated PM deposition amount increases or decreases as shown in FIG. 8A, and the PM deposition amount may greatly deviate from the actual deposition amount while increasing or decreasing as shown in FIG. is there. When the PM deposition amount is significantly smaller than the actual deposition amount, for example, the actual deposition amount is indicated by a broken line L3 with respect to the PM deposition amount in the state indicated by the solid line L1 in FIG. In the state shown, the following situation occurs at the end of the PM regeneration control.

  That is, the burn-up control started based on the estimated PM accumulation amount (L1) being reduced to the determination value a (0.3 g) is actually much larger than the determination value a around the catalyst ( The process starts with PM accumulated in “X” in the figure. When unburned fuel components are supplied to the catalyst by the same control, PM burns with the oxidation reaction of the unburned fuel components, but the amount of accumulated PM is from an assumed value (0.3 g). Therefore, the amount of heat generated during PM combustion also increases, and the catalyst bed temperatures of the NOx catalytic converter 25 and the PM filter 26 may excessively rise.

  In order to avoid such a problem, in this embodiment, when the PM regeneration control can be executed after the interruption, the PM regeneration is performed regardless of whether or not the PM accumulation amount is less than the allowable value. Control is resumed, and PM regeneration restart processing for completing the control is executed. FIG. 9 shows an example of the transition of the PM accumulation amount and the execution mode of the PM regeneration control when the PM regeneration restart process is performed.

  In the figure, if the regeneration control is interrupted and the control can be executed at the timing T8, the PM regeneration control is resumed even if the PM accumulation amount is less than the allowable value, and the control is performed at the timing T9. It will be completed. By completing the PM regeneration control in this way, the PM accumulated around the catalyst is combusted and the PM accumulation amount is set to “0”, so the error between the PM accumulation amount and the actual accumulation amount is eliminated. The Therefore, it is possible to avoid the occurrence of the above-described problem due to the error not being eliminated.

  Next, the execution procedure of the PM regeneration control restart process will be described in detail with reference to the flowchart of FIG. 10 showing the restart process routine. This restart processing routine is executed through the electronic control unit 50 by, for example, a time interruption every predetermined time.

  In this routine, it is first determined from the history of the engine operation state whether or not the previous PM regeneration control is interrupted (S101). If the determination is affirmative, it is determined whether or not the PM regeneration control can be executed at present, for example, whether or not the engine is in operation and the deactivation of the catalyst has been resolved (S102). Note that whether or not the deactivation of the catalyst has been resolved is, for example, whether or not the catalyst bed temperature is a value at which unburned fuel adhering to the catalyst can be burned (for example, 300 ° C.) Judgment is made based on whether or not the catalyst bed temperature after being continued for a period of time can reach the above value.

  If an affirmative determination is made in step S102, PM regeneration control is executed regardless of the PM accumulation amount at that time (S103), and the control is continued until the control is completed. After the PM regeneration control is resumed based on the process in step S103, the PM regeneration control is completed because the same control is resumed based on the processes in steps S101 to S103 even if the control is interrupted again. Continue until you do.

  Even in the PM regeneration control restarted after the interruption, the catalyst bed temperature is gradually raised, and the PM deposition amounts c and b are about the retention times t3 and t4 at the catalyst bed temperature 600 ° C. and 630 ° C. at that time. The shorter it is, the shorter it is. Also in the restarted PM regeneration control, burn-up control is performed to burn up PM accumulated around the catalyst at the end thereof.

According to the embodiment described in detail above, the following effects can be obtained.
(1) When the PM regeneration control becomes executable after the PM regeneration control is interrupted, the PM regeneration control is resumed even if the PM accumulation amount at that time is less than the allowable value. Thus, the PM deposited around the catalyst can be burned out. When PM is completely burned and PM regeneration control is completed, the estimated PM accumulation amount is set to “0”, and the error between the PM accumulation amount and the actual accumulation amount is eliminated. Therefore, it is possible to suppress repeated execution / interruption of the control without completing the PM regeneration control, and to prevent an error between the PM accumulation amount and the actual accumulation amount from increasing during the repetition. can do.

  (2) When the PM regeneration control is interrupted, the combustion of the PM accumulated around the catalyst has progressed to some extent, and the smaller the amount of PM accumulated at that time, the shorter the execution time of the control after the PM regeneration control is resumed. Even so, it is possible to completely burn PM deposited around the catalyst. In consideration of this, also in the PM regeneration control after restart, the holding times t2, t3, and t4 are shortened as the PM accumulation amounts c and b are reduced, and thus the execution time of the control is reduced to a small amount of PM accumulation. The length is set accordingly. For this reason, it is possible to reduce the time until the completion of the execution of the control after the restart and to suppress the deterioration of the fuel consumption based on the control being continued for a long time.

  (3) In the PM regeneration control restarted after the interruption, burn-up control is performed at the end of the PM regeneration control, whereby the PM accumulated around the catalyst is completely burned and the actual PM accumulation amount is set to “0”. . For this reason, when the estimated PM accumulation amount is set to “0” when the resumed PM regeneration control is completed, PM remains around the catalyst, and the PM accumulation amount does not correspond to the actual accumulation amount. The situation can be avoided.

In addition, the said embodiment can also be changed as follows, for example.
-The execution time of PM regeneration control does not necessarily need to be variable according to the amount of accumulated PM, and the execution time may be fixed to a time sufficient for burning PM deposited around the catalyst by PM regeneration control. .

  Further, fixing the execution time as described above may not be performed in the PM regeneration control restarted after the interruption, but only in the PM regeneration control that is completed without interruption.

1 is a schematic diagram showing the overall configuration of an internal combustion engine to which an exhaust emission control device of the present embodiment is applied. The graph which shows the change of the combustion rate of unburned fuel (HC) and PM around a catalyst with respect to the change of a catalyst bed temperature. (A) And (b) is a time chart which shows transition of PM deposit amount and catalyst bed temperature in PM regeneration control. The graph which shows the relationship between PM deposition amount c and holding time t2. The graph which shows the relationship between PM deposition amount b and holding time t3. (A) And (b) is a time chart which shows the transition of the fuel addition aspect in burn-up control, and the exhaust air-fuel ratio accompanying the fuel addition. In (a) and (b), PM regeneration control is performed in a state in which the estimated PM accumulation amount and the actual accumulation amount are deviated, and the execution mode of the control when completed and the transition of the accumulation amount are shown. Time chart shown. (A) And (b) is a time chart which shows transition of PM accumulation amount when execution and interruption of PM regeneration control are repeated, and an execution mode of the control. (A) And (b) is a time chart which shows the transition of PM deposition amount at the time of resuming and completing the control by the PM regeneration resuming process after the PM regeneration control is interrupted, and the execution mode of the control. The flowchart which shows the execution procedure of PM reproduction | regeneration restart processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Turbocharger, 12 ... Intake passage, 13 ... Combustion chamber, 14 ... Exhaust passage, 15 ... Air cleaner, 16 ... Air flow meter, 17 ... Compressor, 18 ... Intercooler, 19 ... Intake throttle valve, 20 DESCRIPTION OF SYMBOLS ... Intake manifold, 21 ... Intake port, 22 ... Exhaust port, 23 ... Exhaust manifold, 24 ... Exhaust turbine, 25 ... NOx catalytic converter, 26 ... PM filter, 27 ... Oxidation catalytic converter, 28 ... Incoming gas temperature sensor, 29 ... Outgas temperature sensor, 30 ... Differential pressure sensor, 31 ... Oxygen sensor, 32 ... Oxygen sensor, 33 ... EGR passage, 34 ... EGR catalyst, 35 ... EGR cooler, 36 ... EGR valve, 40 ... Injector, 41 ... High pressure fuel supply Pipe 42. Common rail 43 Fuel pump 44 Rail pressure sensor 45 Low pressure fuel supply pipe 6 ... addition valve, 50 ... electronic control unit, 51 ... NE sensor 52: accelerator sensor, 53 ... throttle valve sensor.

Claims (3)

The amount of particulates collected around the exhaust system catalyst is estimated, and based on the estimated amount of particulates being accumulated above an allowable value, unburned fuel components are supplied to the catalyst. In an exhaust gas purification apparatus for an internal combustion engine that performs PM regeneration control for raising the temperature and burning the collected fine particles, and sets the estimated amount of accumulated fine particles to “0” when the control is completed,
At the end of the PM regeneration control, in order to make it possible to burn fine particles remaining at the exhaust upstream end of the exhaust system catalyst, concentrated intermittent fuel addition to the catalyst upstream and stop of the fuel addition An exhaust emission control device for an internal combustion engine, wherein burn-up control is performed that repeats a predetermined number of times . When the PM regeneration control is interrupted, the accumulated amount of fine particles around the catalyst is less than an allowable value when the internal combustion engine is in operation and the deactivation of the catalyst is eliminated. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the PM regeneration control is resumed even if there is . 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2 , wherein when the PM regeneration control is restarted, the execution time of the PM regeneration control is set to be shorter as the amount of accumulated particulates around the catalyst is estimated to be smaller .

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