JP2008115712A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for inhibiting NOx stored in a NOx catalyst in a low temperature condition from being discharged without reduction when a NOx reduction control means is performed before performing of a filter regeneration control means in an exhaust emission control device of an internal combustion engine. <P>SOLUTION: When NOx reduction control (S107) is made before making filter regeneration control (S108), if the temperature of a filter detected by an exhaust temperature sensor is lower than a first predetermined value, filter temperature rising control (S105) is made for raising the temperature of the filter by adding fuel in exhaust gas before making the NOx reduction control. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  So-called filter regeneration control is performed on a particulate filter (hereinafter referred to as a filter) carrying an NOx storage reduction catalyst (hereinafter referred to as a NOx catalyst) disposed in an exhaust passage of the internal combustion engine.

  In the filter regeneration control, the amount of particulate matter such as soot trapped in the filter (hereinafter referred to as PM) increases, the flow resistance of the exhaust gas passing through the filter increases, and the exhaust resistance of the internal combustion engine increases. This is done to prevent a decrease in engine output and fuel consumption. Specifically, the temperature of the filter is raised to a temperature at which PM is ignited and burned by supplying fuel to the exhaust, and the PM collected by the filter is burned to regenerate the filter.

And when performing filter regeneration control, the technique which performs NOx reduction | restoration control before filter regeneration control is disclosed (for example, refer patent document 1).
Japanese Patent No. 2722987

  By the way, the NOx catalyst carried by the filter occludes NOx even at a low temperature. The NOx occluded when the NOx catalyst is in a low temperature state is reduced when the temperature of the filter carrying the NOx catalyst is raised from the low temperature state during NOx reduction control as in the technique of Patent Document 1 above. It will be released without.

  It is an object of the present invention to prevent NOx occluded when the NOx catalyst is in a low temperature state without reduction when the NOx reduction control means is executed before the filter regeneration control means is executed in the exhaust gas purification apparatus for an internal combustion engine. It is in providing the technique which suppresses being discharged | emitted in the.

In the present invention, the following configuration is adopted. That is,
A NOx catalyst and a filter disposed in the exhaust passage;
NOx reduction control means for supplying fuel to the exhaust gas to reduce the air-fuel ratio of the exhaust gas and releasing and reducing NOx stored in the NOx catalyst;
Filter regeneration control means for supplying fuel to exhaust gas to raise the temperature of the filter and removing PM from the filter;
With
In the exhaust gas purification apparatus for an internal combustion engine that executes the NOx reduction control means before executing the filter regeneration control means when executing the filter regeneration control means,
Filter temperature detecting means for detecting the temperature of the filter;
When executing the NOx reduction control means before the execution of the filter regeneration control means, if the temperature of the filter detected by the filter temperature detection means is lower than a predetermined temperature, before executing the NOx reduction control means A temperature raising control means for raising the temperature of the filter by adding fuel into the exhaust;
An exhaust emission control device for an internal combustion engine, comprising:

Conventionally, when executing the filter regeneration control means, the NOx reduction control means is executed before the execution of the filter regeneration control means.

  By the way, the NOx catalyst carried by the filter occludes NOx even at a low temperature of about 200 ° C., for example. NOx occluded when such a NOx catalyst is in a low temperature state becomes nitrite and is occluded in the NOx catalyst with a weak adsorption force. For this reason, when the temperature of the filter carrying the NOx catalyst is raised from the low temperature state when the NOx reduction control means is executed, the NOx reduction control means is released without reduction.

  Therefore, in the present invention, when the NOx reduction control means is executed before the execution of the filter regeneration control means, when the temperature of the filter is lower than a predetermined temperature, fuel is added to the exhaust gas before the execution of the NOx reduction control means. Therefore, the temperature raising control means for raising the temperature of the filter is executed.

  Here, the predetermined temperature is a threshold temperature at which NOx is occluded as nitrite because the NOx catalyst supported by the filter is at a low temperature when the filter is at a lower temperature.

  According to this configuration, the NOx occluded when the NOx catalyst is in a low temperature state is changed from a nitrite having a weak adsorption force to a nitrate having a strong adsorption force by executing the temperature raising control means. For this reason, after the execution of the temperature raising control means, the NOx occluded in the NOx catalyst is nitrate with a strong adsorption force, so even when the temperature of the filter carrying the NOx catalyst is raised when the NOx reduction control means is executed, NOx is not released without reduction. Then, by executing the actual NOx reduction control means, NOx that has become a strong adsorbing power nitrate stored in the NOx catalyst is released and reduced.

  Therefore, when executing the filter regeneration control means, it is possible to prevent the stored NOx from being released from the NOx catalyst without being reduced when the NOx catalyst is in a low temperature state.

  The temperature increase rate of the filter by the temperature increase control means may be a rate at which NOx occluded as nitrite in the low temperature NOx catalyst is converted into nitrate without being released from the NOx catalyst.

  According to this configuration, NOx occluded when the NOx catalyst is in a low temperature state can be changed from nitrite having a weak adsorption force to nitrate having a strong adsorption force without being released from the NOx catalyst.

  The temperature increase rate of the filter by the temperature increase control means may be slower than the temperature increase rate of the filter by the NOx reduction control means.

  According to this configuration, NOx stored as nitrite in the low-temperature NOx catalyst can be converted into nitrate without being released from the NOx catalyst.

  The temperature raising control means may shorten the execution time of the temperature raising control means as the deterioration state of the filter progresses.

  As the filter deteriorates, the amount of NOx that can be stored in the NOx catalyst at a low temperature is reduced. According to this configuration, when the deterioration state of the filter advances and the amount of NOx occluded in the NOx catalyst decreases, the execution time of the temperature raising control means is shortened, and the NOx occluded in the NOx catalyst is weakly adsorbed nitrite. The time to change from strong to strong nitrate can be shortened. For this reason, the total execution time for executing the filter regeneration control means from the temperature increase control means through the NOx reduction control means can be shortened.

  According to the present invention, in the exhaust gas purification apparatus for an internal combustion engine, when the NOx reduction control means is executed before the execution of the filter regeneration control means, the stored NOx is not accompanied by reduction when the NOx catalyst is in a low temperature state. It is possible to suppress the release.

  Specific examples of the present invention will be described below.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and its exhaust system.

  An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders, and includes a fuel injection valve that directly injects fuel into a combustion chamber of each cylinder.

  An exhaust passage 2 extends from the internal combustion engine 1. In the middle of the exhaust passage 2, a filter 3 carrying an NOx storage reduction catalyst is disposed in order to purify the exhaust discharged from the cylinder of the internal combustion engine 1.

Here, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is lean (greater than the theoretical air-fuel ratio), the NOx catalyst stores NOx in the exhaust gas so as not to be released into the atmosphere, and the exhaust gas flowing into the NOx catalyst When the air-fuel ratio of the engine is the stoichiometric air-fuel ratio or rich, the stored NOx is released. When the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio or rich, if reducing components such as hydrocarbon (HC) and carbon monoxide (CO) are present in the exhaust gas, the nitrogen released from the NOx catalyst The oxide (NOx) is reduced to N ₂ and removed. The NOx catalyst may be arranged in series on the upstream side of the filter 3 in addition to the one supported on the filter 3 as in this embodiment.

  Further, the filter 3 has a wall portion of a wall flow type and formed in a monolith structure, and removes PM from the exhaust gas by capturing the PM when the exhaust gas passes through the minute holes in the wall portion. is there.

  An exhaust temperature sensor 4 for detecting the temperature of the exhaust gas flowing through the exhaust passage 2 is disposed in the exhaust passage 2 immediately downstream of the filter 3, and the temperature of the filter 3 is detected based on an output signal of the exhaust temperature sensor 4. Is done. The exhaust temperature sensor 4 corresponds to the filter temperature detecting means of the present invention.

  On the other hand, a fuel addition nozzle 5 for supplying fuel as a reducing agent into the exhaust gas flowing in the exhaust passage 2 is attached to the exhaust passage 2 upstream of the filter 3.

  The internal combustion engine 1 having the above configuration is provided with an ECU 6 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 6 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. The fuel addition nozzle 5 is electrically connected to the ECU 6 so that the ECU 6 can control the fuel supply and the fuel supply stop of the fuel addition nozzle 5. Further, the exhaust temperature sensor 4 is electrically connected to the ECU 6, and the detection value of the exhaust temperature sensor 4 is output to the ECU 6.

  The ECU 6 performs four types of control on the filter 3 such as normal operation control for purifying exhaust, filter regeneration control, S poison recovery control, and NOx reduction control.

Here, in the filter regeneration control, fuel is continuously and repeatedly added from the fuel addition nozzle 5, the temperature of the filter 3 is raised to, for example, 600 to 700 ° C., and PM accumulated in the filter 3 is burned and discharged. In this control, PM is removed from the filter 3. Here, this filter regeneration control corresponds to the filter regeneration control means of the present invention.

  In the S poison recovery control, the fuel is continuously and repeatedly added from the fuel addition nozzle 5 to raise the temperature of the filter 3 to, for example, 600 to 700 ° C. and to make the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or rich. In this control, SOx is released from the supported NOx catalyst.

  In the NOx reduction control, fuel is intermittently added from the fuel addition nozzle 5 at a relatively long time, the air-fuel ratio of the exhaust is made the stoichiometric air-fuel ratio or rich, and NOx is released and reduced from the NOx catalyst carried on the filter 3. Control. Note that the NOx reduction control is repeatedly executed within a relatively short time. Here, this NOx reduction control corresponds to the NOx reduction control means of the present invention.

  Here, when executing the filter regeneration control, as shown in FIG. 2, when the temperature of the filter is raised, the catalyst bed temperature of the NOx catalyst also rises, and NOx is not reduced from the NOx catalyst at that time. Will be released. For this reason, when the filter regeneration control is executed, the NOx reduction control is executed before the filter regeneration control is executed in order to release and reduce the NOx of the NOx catalyst first.

  By the way, as shown in FIG. 3, the NOx catalyst carried on the filter 3 can occlude NOx even in a low temperature state of about 200 ° C., for example (circled in the figure). NOx occluded when such a NOx catalyst is in a low temperature state becomes nitrite and is occluded in the NOx catalyst with a weak adsorption force. For this reason, when the temperature of the filter carrying the NOx catalyst is raised from the low temperature state when the NOx reduction control is executed, the NOx reduction control is released without reduction.

  Therefore, in this embodiment, when the NOx reduction control is executed before the filter regeneration control is executed, if the temperature of the filter 3 is lower than the first predetermined value, the fuel is discharged into the exhaust gas before the NOx reduction control means is executed. The filter temperature increase control for gradually increasing the temperature of the filter 3 by addition was performed.

  Here, the first predetermined value is a threshold temperature at which the NOx catalyst is occluded as nitrite having a low adsorption power because the NOx catalyst supported by the filter 3 is at a low temperature when the filter 3 is at a lower temperature. It is.

  In this way, by executing the filter temperature raising control, the NOx occluded when the NOx catalyst is in a low temperature state changes from weakly adsorbing nitrite to strong adsorbing nitrate. For this reason, after the execution of the filter temperature raising control, the NOx occluded in the NOx catalyst is a nitrate having a strong adsorption power, so even if the temperature of the filter 3 carrying the NOx catalyst is raised when the NOx reduction control is executed, NOx is not released without reduction. Then, by executing the actual NOx reduction control, the NOx that has become nitrate with strong adsorptive power stored in the NOx catalyst is released and reduced.

  Therefore, when executing the filter regeneration control, it is possible to suppress the stored NOx from being released from the NOx catalyst without being reduced when the NOx catalyst is in a low temperature state.

  Here, the temperature increase rate of the filter 3 by the filter temperature increase control is a rate at which NOx occluded as nitrite in the low-temperature NOx catalyst is converted into nitrate without being released from the NOx catalyst. For this reason, the temperature increase rate of the filter 3 by the filter temperature increase control is slower than the temperature increase rate of the filter 3 by the NOx reduction control.

  Thereby, NOx occluded when the NOx catalyst is in a low temperature state can be changed from nitrite having a weak adsorption force to nitrate having a strong adsorption force without being released from the NOx catalyst.

  Here, a control routine for performing the filter regeneration control of the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 6 and is a routine that is periodically executed.

  In step S101, the ECU 6 first determines whether or not the filter regeneration process is required to be executed with reference to the vehicle travel history, the operation history of the internal combustion engine 1, and the like. Specifically, the PM accumulation amount is estimated with reference to the travel distance of the vehicle, the exhaust gas flow rate flowing into the filter 3, and the filter regeneration is performed when the PM accumulation amount has reached the threshold value for starting the filter regeneration processing. Judge that the situation requires the implementation of the process.

  If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  Subsequently, in step S102, the ECU 6 establishes a filter regeneration process start flag to start the filter regeneration process. Thereby, the control regarding the filter regeneration process is started.

  In step S <b> 103, the ECU 6 detects the temperature of the filter 3 based on the detection value of the exhaust temperature sensor 4.

  In step S104, the ECU 6 determines whether or not the temperature of the filter 3 is lower than the first predetermined value. The first predetermined value is, for example, 300 ° C., and when the temperature of the filter 3 is lower than that, the NOx catalyst supported by the filter 3 occludes NOx as nitrite having a low adsorption power because the NOx catalyst supported by the filter 3 is at a low temperature. This is the threshold temperature.

  If an affirmative determination is made in step S104, the process proceeds to step S105, whereas if a negative determination is made, the process proceeds to step S107.

  Subsequently, in step S105, the ECU 6 executes filter temperature increase control. Specifically, the fuel is repeatedly added from the fuel addition nozzle 5, and the temperature of the filter 3 is gradually raised. Here, the temperature increase rate of the filter 3 by the filter temperature increase control is a rate at which NOx occluded as nitrite in the low-temperature NOx catalyst is converted into nitrate without being released from the NOx catalyst. For this reason, the temperature increase rate of the filter 3 by the filter temperature increase control is slower than the temperature increase rate of the filter 3 by the NOx reduction control. Note that the filter temperature increase control in this step corresponds to the temperature increase control means of the present invention.

  In step S106, the ECU 6 determines whether or not the temperature of the filter 3 is higher than a second predetermined value. The second predetermined value is, for example, 450 ° C., and when the filter 3 reaches a temperature higher than that, the threshold value at which it can be determined that the NOx occluded in the NOx catalyst has changed from a nitrite having a weak adsorption power to a nitrate having a strong adsorption power. Temperature.

  If an affirmative determination is made in step S106, the process proceeds to step S107. On the other hand, if a negative determination is made, the process returns to step S105.

Subsequently, in step S107, the ECU 6 executes NOx reduction control. Specifically, fuel is intermittently added from the fuel addition nozzle 5 at a relatively long time, the air-fuel ratio of the exhaust is made the stoichiometric air-fuel ratio or rich, and NOx is released and reduced from the NOx catalyst carried on the filter 3. Let

  In step S108, the ECU 6 executes filter regeneration control. Specifically, the fuel is continuously and repeatedly added from the fuel addition nozzle 5, the temperature of the filter 3 is raised to, for example, 600 to 700 ° C., PM accumulated in the filter 3 is burned and discharged, and the filter 3 To remove PM.

  Then, after the end of this step, the processing of this routine is temporarily ended.

  By executing this routine as described above, when the NOx reduction control is executed before the filter regeneration control is executed, the filter temperature increase control is executed before the NOx reduction control is executed, and the NOx catalyst is in a low temperature state. It is possible to prevent the stored NOx from being released without reduction.

<Example 2>
Next, Example 2 will be described. In this embodiment, the execution time of the filter temperature raising control is shortened according to the deterioration state of the filter 3. Since other configurations are the same as those in the above embodiment, the description thereof is omitted.

  In the present embodiment, in the filter temperature increase control, the execution time of the filter temperature increase control is shortened as the deterioration state of the filter 3 progresses.

  As the deterioration state of the filter 3 progresses, the amount of NOx that can be stored in the low temperature state of the NOx catalyst decreases. According to this configuration, when the deterioration state of the filter 3 progresses and the amount of NOx occluded in the NOx catalyst decreases, the execution time of the filter temperature raising control is shortened and the NOx occluded in the NOx catalyst is weakly absorbed. Time to change from nitrate to nitrate with strong adsorption power can be shortened. For this reason, the total execution time for executing the filter regeneration control from the filter temperature raising control to the NOx reduction control can be shortened.

  Here, a control routine for performing the filter regeneration control of the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 6 and is a routine that is periodically executed.

  Steps S201 to S204 are the same as steps S101 to S104 in the above embodiment.

  In step S205, the ECU 6 determines the deterioration state of the filter 3. Specifically, the determination is made by accumulating the heat history at which the temperature of the filter 3 becomes 600 ° C. or higher in the ECU 6.

  Next, in step S206, the ECU 6 determines the execution time of the filter temperature increase control. Specifically, a coefficient corresponding to the deterioration state determined in step S205, that is, a coefficient that is 1 in the initial state of the filter 3 becomes 1 or less as the deterioration occurs is set as the basic time of the filter temperature increase control. Calculated by multiplication. For this reason, the execution time of the filter temperature increase control is shortened as the deterioration state of the filter 3 progresses.

  In step S207, the ECU 6 executes filter temperature increase control. The filter temperature raising control is the same as step S105 in the above embodiment.

In step S208, the ECU 6 determines whether or not the execution time of the filter temperature increase control has become the determination time. The determination time is the execution time determined in step S206, and it is determined that the NOx occluded in the NOx catalyst has changed from a nitrite having a weak adsorptive power to a nitrate having a strong adsorbing power after the elapse of this time.

  If an affirmative determination is made in step S208, the process proceeds to step S209, whereas if a negative determination is made, the process returns to step S207.

  Subsequently, in step S209, the ECU 6 executes NOx reduction control. The NOx reduction control is the same as step S107 in the above embodiment.

  In step S210, the ECU 6 executes filter regeneration control. The filter regeneration control is the same as step S108 in the above embodiment.

  Then, after the end of this step, the processing of this routine is temporarily ended.

  By executing this routine as described above, when the NOx reduction control is executed before the filter regeneration control is executed, the filter temperature increase control is executed before the NOx reduction control is executed, and the NOx catalyst is in a low temperature state. It is possible to prevent the stored NOx from being released without reduction.

  In the first and second embodiments, the filter temperature increase control is executed until the temperature of the filter 3 rises to the second predetermined value and when the determination time elapses. It may be executed as a compound condition, or other conditions may be added.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention.

1 is a diagram illustrating an internal combustion engine and an exhaust system thereof according to a first embodiment. It is a figure which shows the NOx discharge | release amount at the time of performing the filter regeneration control which concerns on Example 1. FIG. It is a figure which shows the relationship between the catalyst bed temperature of the NOx catalyst which concerns on Example 1, and NOx occlusion amount. 3 is a flowchart illustrating a control routine for performing filter regeneration control according to the first embodiment. 7 is a flowchart illustrating a control routine for performing filter regeneration control according to a second embodiment.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 3 Filter 4 Exhaust temperature sensor 5 Fuel addition nozzle 6 ECU

Claims (4)

A NOx catalyst and a filter disposed in the exhaust passage;
NOx reduction control means for supplying fuel to the exhaust gas to reduce the air-fuel ratio of the exhaust gas and releasing and reducing NOx stored in the NOx catalyst;
Filter regeneration control means for supplying fuel to exhaust gas to raise the temperature of the filter and removing PM from the filter;
With
In the exhaust gas purification apparatus for an internal combustion engine that executes the NOx reduction control means before executing the filter regeneration control means when executing the filter regeneration control means,
Filter temperature detecting means for detecting the temperature of the filter;
When executing the NOx reduction control means before the execution of the filter regeneration control means, if the temperature of the filter detected by the filter temperature detection means is lower than a predetermined temperature, before executing the NOx reduction control means A temperature raising control means for raising the temperature of the filter by adding fuel into the exhaust;
An exhaust emission control device for an internal combustion engine, comprising:   The temperature increase rate of the filter by the temperature increase control means is a rate at which NOx stored as nitrite in the NOx catalyst in a low temperature state is converted to nitrate without being released from the NOx catalyst. Item 6. An exhaust emission control device for an internal combustion engine according to Item 1.   The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein a temperature rising rate of the filter by the temperature raising control means is slower than a temperature rising speed of the filter by the NOx reduction control means.   The exhaust gas purification of an internal combustion engine according to any one of claims 1 to 3, wherein the temperature rise control means shortens an execution time of the temperature rise control means as the deterioration state of the filter progresses. apparatus.

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