JP2007285156A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of favorably performing the air-fuel ratio degradation control by suppressing degradation of the fuel economy in the air-fuel ratio degradation control in an exhaust emission control device of an internal combustion engine. <P>SOLUTION: In the exhaust emission control device of the internal combustion engine for regenerating the performance of a NOx catalyst by performing the rich spike control for degrading the air-fuel ratio of an exhaust gas by feeding a fuel to the exhaust gas of the internal combustion engine, the wall temperature of an exhaust gas passage is estimated, and the execution permission is determined for permitting the execution of the rich spike control when the estimated wall temperature exceeds the predetermined value, and prohibiting the execution of the rich spike control when the estimated wall temperature is lower than the predetermined value. The estimated wall temperature is corrected for determining acceptance/rejection of the next rich spike control based on the gradient of the change in the air-fuel ratio when the air-fuel ratio is degraded in the rich spike control under execution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that regenerates the performance of an exhaust gas purification catalyst by performing air-fuel ratio lowering control for reducing the air-fuel ratio of the exhaust gas by supplying fuel to the exhaust gas of the internal combustion engine.

  An NOx storage reduction catalyst (hereinafter referred to as “NOx catalyst”) is disposed in an exhaust passage of an internal combustion engine such as a diesel engine, and nitrogen oxides (hereinafter referred to as “NOx”) are removed to purify the exhaust gas. Technology is known.

  When the NOx catalyst is provided in the exhaust passage, NOx or sulfur oxide (hereinafter referred to as “SOx”) stored in the NOx catalyst is released and reduced in order to regenerate the NOx storage capacity of the NOx catalyst. Need to be removed. For this purpose, for example, a fuel as a reducing agent is supplied from a reducing agent addition valve attached to an exhaust passage upstream of the NOx catalyst, and the air-fuel ratio of the exhaust flowing into the NOx catalyst is made the stoichiometric air-fuel ratio or rich (below the stoichiometric air-fuel ratio). It is decreasing.

And when the wall temperature of an exhaust passage is low, the technique which stops reducing the air fuel ratio of exhaust_gas | exhaustion to a theoretical air fuel ratio or rich is proposed (for example, refer patent document 1).
JP 2004-339974 A JP 2002-38925 A

  An object of the present invention is to provide a technique for suppressing the deterioration of fuel efficiency in air-fuel ratio lowering control and executing air-fuel ratio lowering control more suitably in an exhaust gas purification apparatus for an internal combustion engine.

In the present invention, the following configuration is adopted. That is,
In an exhaust gas purification apparatus for an internal combustion engine that regenerates the performance of an exhaust gas purification catalyst by performing air-fuel ratio lowering control that lowers the air-fuel ratio of the exhaust gas by supplying fuel to the exhaust gas of the internal combustion engine,
The wall temperature of a specific part in the exhaust passage of the internal combustion engine is estimated. When the estimated wall temperature is equal to or higher than a predetermined temperature, execution of air-fuel ratio reduction control is permitted. When the estimated wall temperature is lower than the predetermined temperature, the air-fuel ratio is Execution permission determination means for prohibiting execution of the decrease control;
Based on the gradient of the air-fuel ratio change at the time of air-fuel ratio decrease during the air-fuel ratio decrease control being executed, the estimated wall temperature correction or the predetermined temperature Correction changing means for changing, and
An exhaust emission control device for an internal combustion engine, comprising:

  Here, the predetermined temperature is a temperature calculated in advance, and if the estimated wall temperature is lower than that, the performance of the exhaust purification catalyst cannot be regenerated even if the air-fuel ratio lowering control is executed, This is a threshold temperature at which the supplied fuel is considered to be wasted.

According to this, whether or not the next air-fuel ratio lowering control is possible is adjusted by learning based on the gradient of the air-fuel ratio change at the time of air-fuel ratio lowering in the previously executed air-fuel ratio lowering control, and the next air-fuel ratio lowering control is performed. Execution can be performed more suitably. In other words, the air-fuel ratio lowering control is suppressed from being executed in a situation where the air-fuel ratio lowering control is wasted, and the air-fuel ratio lowering control is executed in a situation where the air-fuel ratio lowering control can be suitably executed. Promoted. For this reason, the deterioration of the fuel consumption in the air-fuel ratio lowering control can be suppressed more suitably, and the air-fuel ratio lowering control can be more suitably executed.

  When the absolute value of the gradient of the air-fuel ratio change is smaller than a first predetermined value, the correction changing unit lowers the estimated wall temperature for the next determination of whether or not the air-fuel ratio decrease control is performed by the execution permission determining unit. It is good to correct to the side.

  Here, the first predetermined value is a value calculated in advance, and is a threshold value for correcting the estimated wall temperature to the low temperature side when the absolute value of the gradient of the air-fuel ratio change is smaller than that.

  According to this, the estimated wall temperature is corrected to the low temperature side in the next determination of whether or not the air-fuel ratio decrease control is performed by the execution permission determination means, and the actual wall temperature is higher than the wall temperature when the air-fuel ratio decrease control being performed is permitted. If the temperature does not become higher, the next air-fuel ratio lowering control is not permitted. Therefore, when the actual wall temperature is low and the fuel adheres to the exhaust passage, it is difficult to reach the exhaust purification catalyst and it is difficult to regenerate the performance of the exhaust purification catalyst. Execution of the fuel ratio reduction control is suppressed. Therefore, the deterioration of the fuel consumption in the air-fuel ratio reduction control can be suppressed.

  When the absolute value of the gradient of the air-fuel ratio change is smaller than a first predetermined value, the correction changing means sets the predetermined temperature to a higher temperature side for the next determination of whether or not the air-fuel ratio lowering control is performed by the execution permission determining means. It is good to change to.

  Here, the first predetermined value is a value calculated in advance, and is a threshold value for changing the predetermined temperature to the high temperature side when the absolute value of the gradient of the air-fuel ratio change is smaller than that.

  According to this, the predetermined temperature in the next determination of whether or not the air-fuel ratio lowering control is performed by the execution permission determining means is changed to the high temperature side, and the actual wall temperature is higher than the wall temperature when the air-fuel ratio lowering control being performed is permitted. If the temperature does not become higher, the next air-fuel ratio lowering control is not permitted. Therefore, when the actual wall temperature is low and the fuel adheres to the exhaust passage, it is difficult to reach the exhaust purification catalyst and it is difficult to regenerate the performance of the exhaust purification catalyst. Execution of the fuel ratio reduction control is suppressed. Therefore, the deterioration of the fuel consumption in the air-fuel ratio reduction control can be suppressed.

  When the absolute value of the gradient of the air-fuel ratio change is greater than a second predetermined value, the correction change unit increases the estimated wall temperature for the next determination of whether or not the air-fuel ratio decrease control is performed by the execution permission determination unit. It is good to correct to the side.

  Here, the second predetermined value is a value calculated in advance, and is a threshold value for correcting the estimated wall temperature to the high temperature side when the absolute value of the gradient of the air-fuel ratio change is larger than that.

  According to this, the estimated wall temperature in the next determination of whether or not the air-fuel ratio lowering control is performed by the execution permission determining means is corrected to the high temperature side, and the actual wall temperature is higher than the wall temperature when the air-fuel ratio lowering control being performed is permitted. Even if the temperature is lower, the next air-fuel ratio lowering control is permitted. Therefore, the air-fuel ratio lowering control is performed in a situation where the air-fuel ratio lowering control can be suitably executed, such as when the actual wall temperature is high and the fuel easily reaches the exhaust purification catalyst and the performance of the exhaust purification catalyst can be regenerated. It is promoted to be executed. Therefore, the air-fuel ratio reduction control can be executed more suitably.

  When the absolute value of the gradient of the air-fuel ratio change is greater than a second predetermined value, the correction changing means sets the predetermined temperature to a low temperature side for the next determination of whether or not the air-fuel ratio decrease control is performed by the execution permission determining means. It is good to change to.

  Here, the second predetermined value is a value calculated in advance, and is a threshold value for changing the predetermined temperature to the low temperature side when the absolute value of the gradient of the air-fuel ratio change is larger than that.

  According to this, the predetermined temperature in the next determination of whether or not the air-fuel ratio decrease control by the execution permission determination means is changed to the low temperature side, and the actual wall temperature is higher than the wall temperature when the air-fuel ratio decrease control being performed is permitted. Even if the temperature is lower, the next air-fuel ratio lowering control is permitted. Therefore, the air-fuel ratio lowering control is performed in a situation where the air-fuel ratio lowering control can be suitably executed, such as when the actual wall temperature is high and the fuel easily reaches the exhaust purification catalyst and the performance of the exhaust purification catalyst can be regenerated. It is promoted to be executed. Therefore, the air-fuel ratio reduction control can be executed more suitably.

  The first predetermined value or the second predetermined value may be changed based on the intake air amount every time the air-fuel ratio lowering control is executed.

  According to this, even in a situation where the fuel transportation delay changes depending on the intake air amount and affects the slope value of the air-fuel ratio change, the first predetermined value or the second predetermined value is taken into consideration. A value can be defined.

In an exhaust gas purification apparatus for an internal combustion engine that regenerates the performance of an exhaust gas purification catalyst by performing air-fuel ratio lowering control that lowers the air-fuel ratio of the exhaust gas by supplying fuel to the exhaust gas of the internal combustion engine,
A supply amount calculating means for estimating a wall temperature of a specific part in the exhaust passage of the internal combustion engine and calculating a fuel supply amount in the air-fuel ratio reduction control based on the estimated wall temperature;
The supply amount calculation means corrects the estimated wall temperature based on the slope of the air-fuel ratio change at the time of air-fuel ratio decrease in the air-fuel ratio decrease control that is being executed, so that the fuel for the next air-fuel ratio decrease control is corrected. An exhaust emission control device for an internal combustion engine, characterized in that a supply amount is changed.

  According to this, the estimated wall temperature is corrected by learning based on the gradient of the air-fuel ratio change at the time of air-fuel ratio decrease in the air-fuel ratio decrease control that is being executed in advance, and the next air-fuel ratio decrease calculated based on the estimated wall temperature The amount of fuel supplied for control becomes a more suitable amount. For this reason, the deterioration of the fuel consumption in the air-fuel ratio reduction control can be suppressed, and the air-fuel ratio reduction control can be executed more suitably.

In an exhaust gas purification apparatus for an internal combustion engine that regenerates the performance of an exhaust gas purification catalyst by performing air-fuel ratio lowering control that lowers the air-fuel ratio of the exhaust gas by supplying fuel to the exhaust gas of the internal combustion engine,
A control stopping means for stopping the air-fuel ratio lowering control being executed when the absolute value of the slope of the air-fuel ratio change at the time of air-fuel ratio lowering is smaller than the third predetermined value in the air-fuel ratio lowering control being executed; An exhaust gas purification apparatus for an internal combustion engine characterized by the above.

  Here, the third predetermined value is a value calculated in advance, and is a threshold value at which the air-fuel ratio reduction control being executed is stopped when the absolute value of the gradient of the air-fuel ratio change is smaller than that.

  According to this, it is determined whether or not the air-fuel ratio reduction control being executed is to be stopped. If the air-fuel ratio lowering control is being executed despite the situation where the air-fuel ratio lowering control is wasted, the air-fuel ratio lowering control being executed is stopped. For this reason, the deterioration of the fuel consumption in the air-fuel ratio reduction control can be suppressed, and the air-fuel ratio reduction control can be executed more suitably.

  According to the present invention, in the exhaust gas purification apparatus for an internal combustion engine, it is possible to suppress the deterioration of fuel consumption in the air-fuel ratio lowering control, and more appropriately execute the air-fuel ratio lowering control.

  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 an exhaust gas purification apparatus according to Embodiment 1 of the present invention is applied and its intake / 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 intake passage 2 extends from the internal combustion engine 1. An air flow meter 3 for detecting the amount of intake air taken into the internal combustion engine 1 is provided in the intake passage 2.

  On the other hand, an exhaust passage 4 extends from the internal combustion engine 1. The exhaust passage 4 is connected to a muffler (not shown) downstream. An occlusion reduction type NOx catalyst (hereinafter referred to as NOx catalyst) 5 for purifying the exhaust discharged from the cylinder of the internal combustion engine 1 is disposed in the middle of the exhaust passage 4.

  A fuel addition valve 6 is attached to the exhaust passage 4 upstream of the NOx catalyst 5 to supply fuel as a reducing agent into the exhaust gas flowing through the exhaust passage 4.

  An air-fuel ratio sensor 7 for detecting the air-fuel ratio of the exhaust is provided in the exhaust passage 4 downstream of the fuel addition valve 6 and immediately upstream of the NOx catalyst 5.

The internal combustion engine 1 having the above configuration is provided with an electronic control unit (ECU) 8 for controlling the internal combustion engine 1. The ECU 8 includes a CPU, a ROM,
A control computer including a RAM, a backup RAM, and the like.

  The air flow meter 3 and the air-fuel ratio sensor 7 are electrically connected to the ECU 8, and output signals from the air flow meter 3 and the air-fuel ratio sensor 7 are input to the ECU 8. Further, the fuel addition valve 6 is electrically connected to the ECU 8 so that the ECU 8 can adjust the fuel supply / stop and the fuel supply amount at the fuel addition valve 6.

  Here, the NOx catalyst 5 disposed in the internal combustion engine 1 occludes NOx in the exhaust and does not release it into the atmosphere when the air-fuel ratio of the exhaust flowing into the NOx catalyst 5 is lean (stoichiometric air-fuel ratio or higher). Thus, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 5 is the stoichiometric air-fuel ratio or rich, the stored NOx is released and reduced to be removed. Further, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 5 is lean, the NOx catalyst 5 also stores SOx in the exhaust gas.

  For this reason, when the internal combustion engine 1 is operated in lean combustion, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 becomes lean and the oxygen concentration of the exhaust becomes high, so that NOx or SOx contained in the exhaust becomes NOx. Although the catalyst 5 is occluded, if the lean combustion operation of the internal combustion engine 1 is continued for a long time, the NOx occlusion capacity of the NOx catalyst 5 is saturated, and NOx in the exhaust is not occluded in the NOx catalyst 5. It will be released into the atmosphere.

  In particular, in a diesel engine such as the internal combustion engine 1, the lean air-fuel mixture is combusted in most of the operation region, and the air-fuel ratio of the exhaust gas becomes lean accordingly, so that the NOx occlusion capability of the NOx catalyst 5 is easily saturated. .

Therefore, when the internal combustion engine 1 is lean-burned, before the NOx occlusion capacity of the NOx catalyst 5 is saturated, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is lowered and the fuel concentration is increased, so that the NOx catalyst 5 It is necessary to release and reduce NOx or SOx occluded.

  Therefore, the ECU 8 spikes the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 5 such as NOx reduction processing or SOx poisoning recovery processing in a relatively short cycle (in a short time) according to the application program stored in the ROM. Rich spike control is executed to make it rich. Here, the rich spike control corresponds to the air-fuel ratio lowering control of the present invention. However, the air-fuel ratio lowering control of the present invention is not limited to the rich spike control, and is a control for reducing the air-fuel ratio of the exhaust by supplying fuel to the exhaust gas. If it is.

  In the NOx reduction treatment, fuel is spiked into the exhaust gas from the fuel addition valve 6 to enrich the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 5, and the NOx occluded in the NOx catalyst 5 is released and released. This is a reduction process.

  In the SOx poisoning recovery process, fuel is spiked into the exhaust gas from the fuel addition valve 6 to oxidize the added fuel in the NOx catalyst 5, and the catalyst temperature is changed from 600 ° C. to 800 ° C. by the heat accompanying the oxidation reaction. The temperature of the exhaust gas flowing into the NOx catalyst 5 is made rich, and the SOx occluded in the NOx catalyst 5 is released and reduced.

  Here, it is desired to suppress the deterioration of fuel consumption in the rich spike control and to execute the rich spike control more suitably.

  By the way, when the above-described rich spike control is performed in a state where the wall temperature of the exhaust passage 4 is low, the fuel added to the exhaust from the fuel addition valve 6 adheres to the exhaust passage 4 and hardly reaches the NOx catalyst 5 directly. Become. Then, it may be difficult to release and reduce NOx or SOx stored in the NOx catalyst 5. If the rich spike control is performed in such a situation, the fuel added in the control may be wasted, resulting in deterioration of fuel consumption. Here, the wall temperature of the exhaust passage 4 cannot be directly measured, but can be estimated based on the engine operating state. Therefore, whether or not the rich spike control can be performed can be determined according to the estimated wall temperature of the exhaust passage 4. On the other hand, the present inventors can correct the estimated wall temperature of the exhaust passage 4 based on the gradient of the air-fuel ratio change when the air-fuel ratio is lowered in the rich spike control, and determine whether or not the rich spike control can be executed by performing the correction. Found that accuracy could be improved.

  Therefore, in the present embodiment, the estimated wall temperature is corrected in the next rich spike control execution permission determination based on the slope of the air-fuel ratio change when the air-fuel ratio decreases during the rich spike control being executed. . Further, by correcting the estimated wall temperature, the amount of fuel added to the fuel addition valve 6 in the next rich spike control is changed. Further, when the absolute value of the gradient of the air-fuel ratio change when the air-fuel ratio is reduced in the rich spike control being executed is smaller than a predetermined threshold, the rich spike control being executed is stopped.

  Here, a control routine for performing the above-described various controls in the rich spike control of the present embodiment will be described based on the flowchart shown in FIG. Note that this routine is stored in advance in the ECU 8, and is periodically executed when the rich spike control is executed.

When an execution request for rich spike control is instructed and processing of this routine is started, the ECU 8 first determines whether or not rich spike control can be executed in S101. The ECU 8 that executes this step corresponds to execution permission determination means of the present invention. Specifically, the ECU 8 permits the execution of rich spike control when the estimated wall temperature obtained by estimating the wall temperature of a specific part in the exhaust passage 4 of the internal combustion engine 1 exceeds a predetermined temperature, and the estimated wall temperature is predetermined. If the temperature is lower than this, execution of rich spike control is prohibited. Here, the predetermined temperature is a temperature calculated in advance, and if the estimated wall temperature is lower than that, NOx or SOx stored in the NOx catalyst 5 can be released and reduced even if the rich spike control is executed. This is a temperature that is considered difficult and wastes the fuel supplied to the exhaust.

  Here, the estimated wall temperature which estimated the wall temperature of the specific site | part in the exhaust passage 4 is demonstrated. The estimated wall temperature is estimated based on the engine operating state, specifically, the fuel injection amount in the cylinder of the internal combustion engine 1 and the engine speed. The reason estimated in this way is that the exhaust temperature rises and the wall temperature of the exhaust passage 4 becomes higher as the fuel injection amount increases. When the engine speed increases, the exhaust flow rate increases and the exhaust gas is discharged from the exhaust. This is because the amount of heat transferred to the wall surface of the passage 4 increases and the wall temperature of the exhaust passage 4 becomes high. The fuel injection amount in the cylinder of the internal combustion engine 1 is calculated based on the accelerator opening, the engine speed, and the like.

  Further, if the correction value is learned when the previous routine is executed, the estimated wall temperature is calculated by reading the correction value from the ECU 8 and reflecting the correction value. For example, if the correction value is “−5 ° C.”, the estimated wall temperature is corrected to the −5 ° C. low temperature side, and if the correction value is “5 ° C.”, the estimated wall temperature is corrected to the 5 ° C. high temperature side. The correction value learning will be described later.

  If the estimated wall temperature is equal to or higher than the predetermined temperature and the execution of the rich spike control can be permitted, the ECU 8 proceeds to S102. If the estimated wall temperature is lower than the predetermined temperature and the execution of the rich spike control cannot be permitted, the process of this routine is temporarily terminated.

  In S102, the ECU 8 calculates the fuel addition amount α to be supplied from the fuel addition valve 6 in the exhaust passage 4 during the entire period of the rich spike control to be performed. The ECU 8 that executes this step corresponds to the supply amount calculating means of the present invention. The amount of fuel added α is the amount of intake air detected by the air flow meter 3, the target air-fuel ratio that lowers the air-fuel ratio of the exhaust by rich spike control to be performed, the estimated wall temperature used in S101, the fuel in the cylinder of the internal combustion engine 1 Calculated based on the injection amount.

  In S102, since the estimated wall temperature is taken into consideration in the calculation of the fuel addition amount α, the correction value of the estimated wall temperature learned when the previous routine is executed is reflected as in S101. Will be. Therefore, the fuel addition amount α in the rich spike control to be performed in the future becomes a more suitable amount by executing the previous routine and correcting the estimated wall temperature. For this reason, the deterioration of the fuel consumption in rich spike control can be suppressed. Next, the process proceeds to S103.

  In S103, the ECU 8 starts executing the rich spike control, and starts adding the fuel of the addition amount α calculated in S102 from the fuel addition valve 6 into the exhaust gas in a spike manner. Next, the process proceeds to S104.

  In S104, the ECU 8 calculates the absolute value N of the slope of the change in the air-fuel ratio when the air-fuel ratio is lowered in the rich spike control accompanying the addition of fuel from the fuel addition valve 6. Specifically, as shown in FIG. 3, the ECU 8 calculates the air-fuel ratio reduction rate per unit time based on the air-fuel ratio of the exhaust detected by the air-fuel ratio sensor 7 from the start of fuel addition, and the air-fuel ratio reduction rate. At a time t1 when the air-fuel ratio has stabilized at a constant value for a predetermined period, the stable air-fuel ratio decrease rate is set as the inclination of the air-fuel ratio change when the air-fuel ratio decreases, and the absolute value N of the inclination is calculated. Next, the process proceeds to S105.

  When calculating the absolute value N of the gradient of the air-fuel ratio change when the air-fuel ratio is lowered in S104, the deviation of the intake air amount detected by the air flow meter 3 or the deviation of the fuel injection amount in the cylinder of the internal combustion engine 1 is calculated. May be within a certain range, or may have already been learned as to the mass production variation at the time of manufacture of the air flow meter 3 or the internal combustion engine 1 as an execution condition.

  In S105, the ECU 8 derives two threshold values A and B that are compared with the absolute value N of the gradient of the air-fuel ratio change calculated in S104. The two threshold values A and B are based on the intake air amount calculated by the air flow meter 3, and the fuel generated by the intake air amount from the map set so that the threshold value becomes smaller (gradient slope) as the intake air amount decreases. Derived in consideration of changes in transport delay. Here, the two threshold values A and B are a small threshold value (threshold value A) and a large threshold value (threshold value B) with respect to the absolute value of the standard gradient of the air-fuel ratio change that allows the rich spike control to continue to the end. And the relationship of threshold A <threshold B is satisfied. The threshold A corresponds to the first and third predetermined values of the present invention, and the threshold B corresponds to the second predetermined value of the present invention. Next, the process proceeds to S106.

  In S106, the ECU 8 compares the absolute value N of the gradient of the air-fuel ratio calculated in S104 with the threshold A, and determines whether the absolute value N of the gradient of the air-fuel ratio change is smaller than the threshold A (absolute value N < Threshold A?).

  If the absolute value N of the gradient of the air-fuel ratio change is smaller than the threshold A (absolute value N <the threshold A is satisfied), the ECU 8 proceeds to S107. If the absolute value N of the gradient of the air-fuel ratio change is not smaller than the threshold A (absolute value N <the threshold A is not satisfied), the process proceeds to S109.

  In S107, the ECU 8 immediately stops the rich spike control being executed. The ECU 8 that executes this step corresponds to control stop means of the present invention. The reason for canceling the rich spike control that is being executed in this way is that if the absolute value N of the gradient of the air-fuel ratio change is smaller than the threshold value A, the rich spike control indicated by the broken line in FIG. Unlike the change, as shown by the solid line in FIG. 4, even if the fuel addition is continued by rich spike control thereafter, the wall temperature of the actual exhaust passage 4 is low and the fuel adheres to the exhaust passage 4. Since it is difficult to reach the NOx catalyst 5 directly, the air-fuel ratio does not decrease to the target air-fuel ratio, and NOx and SOx stored in the NOx catalyst 5 cannot be released and reduced, so that fuel added thereafter is wasted. Because. For this reason, the fuel consumption deterioration in the rich spike control can be suppressed by stopping the rich spike control thereafter. Next, the process proceeds to S108.

  In S108, the ECU 8 learns a correction value “−5 ° C.” to be added to the estimated wall temperature in order to correct the estimated wall temperature used in S101 and S102 in the next main routine to the low temperature side, and stores it in the ECU 8. deep. The reason for learning in this way is the next time the wall temperature of the exhaust passage 4 is low and the fuel adheres to the exhaust passage 4 and hardly reaches the NOx catalyst 5 and the fuel is wasted. This is because the execution of the rich spike control is permitted again in S101 during the execution of this routine, and the next rich spike control is prevented from being executed. For this reason, deterioration of fuel consumption can be suppressed by not performing unnecessary rich spike control. Then, the processing of this routine is temporarily terminated.

  On the other hand, the ECU 8 executes rich spike control to the end in S109. If the absolute value N of the gradient of the air-fuel ratio change is not smaller than the threshold value A, the fuel reaches the NOx catalyst 5 directly, the air-fuel ratio decreases to the target air-fuel ratio, and NOx and SOx stored in the NOx catalyst 5 are released and Since it can be reduced, fuel is added thereafter and rich spike control is performed to the end. Next, the process proceeds to S110.

  In S110, the ECU 8 compares the absolute value N of the gradient of the air-fuel ratio calculated in S104 with the threshold B, and determines whether or not the absolute value N of the gradient of the air-fuel ratio change is larger than the threshold B (absolute value N> Threshold value B?).

  If the absolute value N of the gradient of the air-fuel ratio change is greater than the threshold value B (absolute value N> the threshold value B is satisfied), the ECU 8 proceeds to S111. Further, when the absolute value N of the gradient of the air-fuel ratio change is not larger than the threshold value B (absolute value N> the threshold value B is not satisfied), the processing of this routine is once ended.

  In S111, the ECU 8 learns a correction value of “5 ° C.” to be added to the estimated wall temperature to correct the estimated wall temperature used in S101 and S102 in the next main routine to the high temperature side, and stores it in the ECU 8. . The reason for learning in this way is that the next time, even if the wall temperature of the exhaust passage 4 is slightly lowered, the fuel reaches the NOx catalyst 5 directly, the air-fuel ratio decreases to the target air-fuel ratio, and the NOx stored in the NOx catalyst 5 is stored. Or SOx can be released and reduced, the execution of the rich spike control is permitted in the next execution of this routine even if the wall temperature of the exhaust passage 4 is lower than this time in S101. This is because the spike control is executed. Then, the processing of this routine is temporarily terminated.

  Here, ECU8 which performs steps, such as S101, S104, S105, S106, S108, S110, S111, is equivalent to the correction change means of this invention.

  Then, in the subsequent rich spike control, the processing of this routine is performed every time the control is performed.

  By executing the routine as described above, in the present embodiment, the estimation at the time of determining whether or not to execute the next rich spike control based on the gradient of the air-fuel ratio change at the time of air-fuel ratio decrease during the rich spike control being executed. Correct the wall temperature. According to this, whether or not the next rich spike control can be executed is adjusted by learning based on the gradient of the air-fuel ratio change when the air-fuel ratio decreases in the rich spike control that is being executed in advance, and the next rich spike control is executed. It becomes possible to perform more suitably. In other words, the rich spike control is suppressed from being executed in a situation where the rich spike control is wasted, and the rich spike control is promoted to be executed in a situation where the rich spike control can be suitably executed. For this reason, the deterioration of the fuel consumption in rich spike control can be suppressed more suitably, and rich spike control can be performed more suitably.

  In this embodiment, the fuel addition amount α of the fuel addition valve 6 in the next rich spike control is changed by correcting the estimated wall temperature. According to this, the estimated wall temperature is corrected by learning based on the gradient of the air-fuel ratio change when the air-fuel ratio is lowered in the rich spike control that is being executed in advance, and in the next rich spike control that is calculated based on the estimated wall temperature. The added amount α of fuel becomes a more suitable amount. For this reason, the deterioration of the fuel consumption in rich spike control can be suppressed, and rich spike control can be performed more suitably.

  Further, in the present embodiment, when the absolute value of the gradient of the air-fuel ratio change when the air-fuel ratio is lowered in the rich spike control being executed is smaller than the threshold A, the rich spike control being executed is stopped. According to this, it is determined whether or not the rich spike control being executed is to be stopped. If the rich spike control is being executed in spite of the situation where the rich spike control is wasted, the running rich spike control is stopped. For this reason, the deterioration of the fuel consumption in rich spike control can be suppressed, and rich spike control can be performed more suitably.

In the above embodiment, S1 in the next control routine of FIG.
The estimated wall temperature used in 01 and S102 was corrected. However, the present invention is not limited to this, and the predetermined wall temperature in S101 may be changed without correcting the estimated wall temperature, as shown in S201 and S202 in the control routine of FIG.

  Specifically, in S201, the ECU 8 learns to change the predetermined temperature used in S101 in the next control routine of FIG. 5 to the “5 ° C.” high temperature side, and stores it in the ECU 8. In S202, the ECU 8 learns to change the predetermined temperature used in S101 in the next control routine to the “−5 ° C.” low temperature side, and stores it in the ECU 8. In the next control routine, in S101, the predetermined temperature learned by the execution of the previous control routine is read from the ECU 8, and it is determined whether or not the rich spike control can be executed. Even if it does in this way, the effect of the present invention can be produced.

  In the above embodiment, the fuel addition valve for supplying fuel to the exhaust gas is provided. However, the present invention can also be applied to fuel supply by performing fuel injection together with exhaust emission (after injection) using a fuel injection valve that injects fuel into a cylinder or an intake port of an internal combustion engine.

  The exhaust emission control device according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present invention.

It is a figure which shows schematic structure of the internal combustion engine to which an exhaust gas purification apparatus is applied, and its intake / exhaust system. It is a flowchart which shows the control routine in air fuel ratio fall control. It is a figure which shows the air fuel ratio change at the time of the air fuel ratio fall in air fuel ratio fall control. It is a figure which shows the air fuel ratio change in air fuel ratio fall control. It is a flowchart which shows the control routine in air fuel ratio fall control.

Explanation of symbols

1 Internal combustion engine 2 Intake passage 3 Air flow meter 4 Exhaust passage 5 NOx catalyst 6 Fuel addition valve 7 Air-fuel ratio sensor 8 ECU

Claims (9)

In an exhaust gas purification apparatus for an internal combustion engine that regenerates the performance of an exhaust gas purification catalyst by performing air-fuel ratio lowering control that lowers the air-fuel ratio of the exhaust gas by supplying fuel to the exhaust gas of the internal combustion engine,
The wall temperature of a specific part in the exhaust passage of the internal combustion engine is estimated, and execution of air-fuel ratio reduction control is permitted when the estimated wall temperature exceeds a predetermined temperature, and the air-fuel ratio decreases when the estimated wall temperature is lower than the predetermined temperature. Execution permission determination means for prohibiting execution of control;
Based on the gradient of the air-fuel ratio change at the time of air-fuel ratio decrease during the air-fuel ratio decrease control that is being executed, the estimated wall temperature correction or the predetermined temperature Correction changing means for changing, and
An exhaust emission control device for an internal combustion engine, comprising:   When the absolute value of the gradient of the air-fuel ratio change is smaller than a first predetermined value, the correction changing unit lowers the estimated wall temperature for the next determination of whether or not the air-fuel ratio decrease control is performed by the execution permission determining unit. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the correction is performed to the side.   When the absolute value of the gradient of the air-fuel ratio change is smaller than a first predetermined value, the correction changing means sets the predetermined temperature to a higher temperature side for the next determination of whether or not the air-fuel ratio lowering control is performed by the execution permission determining means. The exhaust emission control device for an internal combustion engine according to claim 1, wherein   When the absolute value of the gradient of the air-fuel ratio change is greater than a second predetermined value, the correction change unit increases the estimated wall temperature for the next determination of whether or not the air-fuel ratio decrease control is performed by the execution permission determination unit. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the correction is performed to the side.   When the absolute value of the gradient of the air-fuel ratio change is greater than a second predetermined value, the correction changing means sets the predetermined temperature to a low temperature side for the next determination of whether or not the air-fuel ratio decrease control is performed by the execution permission determining means. The exhaust emission control device for an internal combustion engine according to claim 1, wherein   4. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the first predetermined value is changed based on an intake air amount every time the air-fuel ratio reduction control is executed.   6. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the second predetermined value is changed based on the intake air amount every time the air-fuel ratio lowering control is executed. In an exhaust gas purification apparatus for an internal combustion engine that regenerates the performance of an exhaust gas purification catalyst by performing air-fuel ratio lowering control that lowers the air-fuel ratio of the exhaust gas by supplying fuel to the exhaust gas of the internal combustion engine,
A supply amount calculating means for estimating a wall temperature of a specific part in the exhaust passage of the internal combustion engine and calculating a fuel supply amount in the air-fuel ratio reduction control based on the estimated wall temperature;
The supply amount calculation means corrects the estimated wall temperature based on the slope of the air-fuel ratio change at the time of air-fuel ratio decrease in the air-fuel ratio decrease control that is being executed, so that the fuel for the next air-fuel ratio decrease control is corrected. An exhaust emission control device for an internal combustion engine, characterized in that the supply amount is changed. In an exhaust gas purification apparatus for an internal combustion engine that regenerates the performance of an exhaust gas purification catalyst by performing air-fuel ratio lowering control that lowers the air-fuel ratio of the exhaust gas by supplying fuel to the exhaust gas of the internal combustion engine,
A control stopping means for stopping the air-fuel ratio lowering control being executed when the absolute value of the slope of the air-fuel ratio change at the time of air-fuel ratio lowering is smaller than the third predetermined value in the air-fuel ratio lowering control being executed; An exhaust gas purification apparatus for an internal combustion engine characterized by the above.

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