JP2007002676A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of performing the lean operation and the NOx purge under an optimum environment by adequately setting a control parameter on the NOx storage in a NOx catalyst during the lean operation, or a control parameter on the NOx discharge and reduction from the NOx catalyst during the NOx purge. <P>SOLUTION: The exhaust emission control device sets the control parameter corresponding to the reference bed temperature and the correction value for correcting the control parameter to the optimum control parameter at each bed temperature Tbed in advance, corrects the control parameter of the reference bed temperature by the correction value according to the actual bed temperature Tbed, calculates the optimum control parameter corresponding to the actual bed temperature Tbed (S16, 18), and applies the calculated control parameter to the control of the lean operation and the NOx purge (S14). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more specifically, exhaust gas of an internal combustion engine that stores NOx in exhaust gas in a storage-type NOx catalyst during lean operation, and releases and reduces NOx stored in the NOx catalyst by NOx purge. The present invention relates to a purification device.

In lean burn engines, etc., the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio (stoichio), and combustion is performed in an oxidizing atmosphere. Therefore, conventional three-way catalysts have NOx (nitrogen oxide) in exhaust gas due to their characteristics. There is a problem that it cannot be sufficiently purified. Therefore, this type of internal combustion engine is provided with a storage-type NOx catalyst.
The storage-type NOx catalyst stores NOx in exhaust gas as nitrate X-NO ₃ in an oxidizing atmosphere with a low concentration of reducing components, and this stored NOx is reduced by reducing components such as CO (carbon monoxide) and HC (hydrocarbon). It is configured as a catalyst having a characteristic of reducing to N ₂ (nitrogen) in a reducing atmosphere present in a large amount. With this type of storage-type NOx catalyst, NOx in the exhaust gas is stored during lean operation to prevent discharge into the atmosphere, and the air-fuel ratio is controlled to the rich side at an optimal timing (before the NOx catalyst is saturated). The rich spike is executed to release and purify NOx stored in the NOx catalyst (hereinafter referred to as NOx purge).

Inadequate NOx purge causes unnecessary fuel consumption and shortage of NOx release reduction, and various countermeasures have been proposed to prevent such problems (for example, see Patent Document 1). In the exhaust emission control device disclosed in Patent Document 1, the NOx cumulative amount of the NOx catalyst is calculated from the output of the NOx concentration detection means provided before and after the NOx catalyst and the intake air amount, and is detected by the catalyst temperature detection means. The amount of NOx released per unit time when rich control is executed is calculated from the catalyst temperature index value, and the rich control time (the duration of the rich spike) is calculated from the accumulated amount of NOx and the amount of released NOx, The NOx purge is executed based on the obtained rich control time.
JP-A-2005-2954

  However, although the technique of Patent Document 1 is a theoretically correct method, all values such as the accumulated amount of NOx and the released amount of NOx are estimated by the calculation process, and thus it is very important to obtain a value in accordance with reality. It is difficult to. Therefore, the rich control time obtained from these values also includes an error that cannot be ignored. As a result, NOx release / reduction during NOx purge becomes inappropriate, and unnecessary fuel consumption occurs when the rich control time is excessive. As a result, the fuel consumption is deteriorated, and when the rich control time is too short, the purification performance of the NOx catalyst cannot be maximized due to the shortage of NOx release and reduction.

  The present invention has been made to solve such problems. The object of the present invention is to control parameters related to NOx storage in the NOx catalyst during lean operation or NOx release from the NOx catalyst during NOx purge. Control parameters related to reduction and purification are set to appropriate values in accordance with the actual conditions, thereby performing lean operation and NOx purging in an optimal environment, thus preventing problems such as fuel consumption deterioration due to unnecessary fuel consumption. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can maximize the purification performance of a NOx catalyst.

  In order to achieve the above object, the invention of claim 1 is provided in an exhaust passage of an internal combustion engine, and stores NOx in exhaust gas when the exhaust air / fuel ratio of the internal combustion engine is lean, and the exhaust air / fuel ratio is the stoichiometric air / fuel ratio or rich. At this time, the storage NOx catalyst for releasing and reducing the stored NOx, the catalyst temperature detecting means for detecting the temperature of the NOx catalyst, and the NOx purge for the NOx release and reduction are executed every predetermined lean operation time. In addition to controlling the internal combustion engine, the catalyst temperature detected by the catalyst temperature detecting means is set based on the control parameter related to lean operation or NOx purge set in advance corresponding to the reference temperature and the correction value set for each catalyst temperature. And a control means for correcting the control parameter corresponding to the reference temperature with the corresponding correction value and applying the corrected control parameter to the control of the internal combustion engine. That.

  Therefore, the optimum control parameter for lean operation or NOx purge is set in advance corresponding to the reference temperature, and the correction value for correcting this control parameter to the optimum control parameter at each catalyst temperature is set. When the lean operation or NOx purge is executed, the control parameter corresponding to the reference temperature is corrected by the correction value corresponding to the catalyst temperature detected by the catalyst temperature detecting means, and the optimal control parameter corresponding to the catalyst temperature is calculated. The internal combustion engine is controlled based on the control parameter.

  Since the control parameter and each correction value corresponding to the reference temperature can be set in advance by, for example, the bench operation of the internal combustion engine or the purification characteristics of the NOx catalyst, the control temperature and the correction value have high reliability and the reliability is high. Because the control parameters at each catalyst temperature are obtained by correction processing based on the control parameters of the above, optimal control parameters in accordance with the reality with few errors can be obtained, and the NOx catalyst during lean operation can be obtained regardless of the catalyst temperature. Thus, NOx release and reduction during NOx occlusion and NOx purge can always be performed in an optimum environment. This is because the characteristics of the NOx purge performed with each control parameter are easily affected by the catalyst temperature.

According to a second aspect of the present invention, in the first aspect, the reference temperature is set as a temperature at which the NOx catalyst exhibits good purification performance, and the control means sets the control parameter set corresponding to the reference temperature to the catalyst temperature. Correction is performed with a corresponding correction value.
Therefore, since the temperature at which the NOx catalyst exhibits good purification performance is set as the reference temperature, the reliability of the control parameter corresponding to the reference temperature is further improved, and consequently each catalyst calculated based on the control parameter The reliability of the control parameter at the temperature is also improved, and more appropriate lean operation and NOx purge control can be realized.

According to a third aspect of the present invention, in the first aspect, the lean operation time is preset as a control parameter corresponding to the reference temperature, and the control means corrects the lean operation time with a correction value corresponding to the catalyst temperature. is there.
Therefore, when the lean operation is executed, the lean operation time corresponding to the reference temperature is corrected by the correction value corresponding to the catalyst temperature, and NOx occlusion to the NOx catalyst is performed based on the optimum lean operation time according to the reality with few errors. It runs under an optimal environment.

According to a fourth aspect of the present invention, in the first aspect, the NOx purge target air-fuel ratio is set in advance as a control parameter corresponding to the reference temperature, and the control means corrects the NOx purge target air-fuel ratio in accordance with the catalyst temperature. Is to be corrected.
Therefore, at the time of execution of NOx purge, the target air-fuel ratio of NOx purge corresponding to the reference temperature is corrected by the correction value according to the catalyst temperature, and NOx based on the optimum target air-fuel ratio of NOx purge according to the reality with few errors. The NOx emission reduction of the catalyst is performed under an optimal environment.

According to a fifth aspect of the present invention, in the first aspect, the duration of the NOx purge is previously set as a control parameter corresponding to the reference temperature, and the control means corrects the duration of the NOx purge with a correction value corresponding to the catalyst temperature. To do.
Therefore, when the NOx purge is executed, the duration of the NOx purge corresponding to the reference temperature is corrected by the correction value corresponding to the catalyst temperature, and the NOx catalyst is adjusted based on the optimum duration of the NOx purge according to the reality with few errors. NOx emission reduction is performed in an optimal environment.

According to a sixth aspect of the present invention, in the first aspect, the injection pattern for executing the NOx purge is set in advance as the control parameter corresponding to the reference temperature, and the control means sets the NOx purge injection pattern in accordance with the catalyst temperature. Correction is performed using the correction value.
Therefore, when the NOx purge is executed, the NOx purge injection pattern corresponding to the reference temperature is corrected by the correction value corresponding to the catalyst temperature, and the NOx catalyst is determined based on the optimum NOx purge injection pattern in accordance with the reality with few errors. NOx emission reduction is performed in an optimal environment.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the first to third aspects of the invention, the control parameter relating to NOx occlusion in the NOx catalyst during lean operation, or NOx release from the NOx catalyst during NOx purge. Control parameters related to reduction are set appropriately, so that lean operation and NOx purge are executed in an optimal environment, thus preventing problems such as fuel consumption deterioration due to unnecessary fuel consumption, and purification performance of NOx catalyst Can be maximized.

  According to the exhaust gas purification apparatus for an internal combustion engine of the second aspect of the invention, in addition to the first aspect, the reliability is improved by setting the control parameter corresponding to the reference temperature at which the NOx catalyst exhibits good purification performance. Therefore, more appropriate lean operation and NOx purge control can be realized.

Hereinafter, an embodiment of an exhaust gas purification apparatus for an internal combustion engine embodying the present invention will be described.
FIG. 1 is an overall configuration diagram showing an exhaust purification device for an internal combustion engine according to the present embodiment. The exhaust purification device according to the present embodiment is configured for an in-cylinder injection type in-line four-cylinder gasoline internal combustion engine 1. The internal combustion engine 1 employs a DOHC 4-valve type valve operating mechanism, and an intake camshaft 3 and an exhaust camshaft 4 provided on the cylinder head 2 are rotationally driven by a crankshaft (not shown). , 4 open and close the intake valve 5 and the exhaust valve 6 at a predetermined timing.

  An electromagnetic fuel injection valve 8 is attached to the cylinder head 2 for each cylinder together with an ignition plug 7, and high-pressure fuel supplied from a fuel pump (not shown) directly enters the combustion chamber 9 according to the opening and closing of the fuel injection valve 8. Be injected. An intake port 10 is formed in the cylinder head 2 so as to pass between the camshafts 3 and 4 in a substantially upright direction. As the intake valve 5 is opened, intake air flows from the air cleaner 11 to the throttle valve 12 and the surge tank 13. Then, it is introduced into the combustion chamber 9 through the intake manifold 14 and the intake port 10. The exhaust gas after combustion is discharged from the combustion chamber 9 to the exhaust port 15 as the exhaust valve 6 is opened, and further discharged to the atmosphere through the exhaust passage 16 and the underfloor catalyst 17.

The underfloor catalyst 17 includes an upstream storage-type NOx catalyst 18 and a downstream three-way catalyst 19. The NOx catalyst 18 is made of, for example, a noble metal such as platinum (Pt), palladium (Pd), or rhodium (Rh), an alkali metal such as barium (Ba), potassium (K), or sodium (Na), or an alkaline earth metal. NOx in the exhaust gas is stored as nitrate X-NO ₃ when the exhaust air-fuel ratio is lean, and NOx stored when the exhaust air-fuel ratio is rich is released to release nitrogen (N ₂ ) etc. have the function of reducing and purifying. The three-way catalyst 19 includes a noble metal such as platinum, palladium, and rhodium, and has a function of purifying harmful substances in the exhaust gas when the exhaust air-fuel ratio is near the stoichiometric air-fuel ratio or during NOx purge.

In the vehicle compartment, an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storing control programs and control maps, a central processing unit (CPU), an ECU (engine control unit) equipped with a timer counter, etc. ) 21 is installed, and comprehensive control of the internal combustion engine 1 is performed. On the input side of the ECU 21, a rotational speed sensor 22 that detects the rotational speed Ne of the internal combustion engine 1, a throttle sensor 23 that detects the throttle opening θth, and an exhaust gas that is provided upstream of the NOx catalyst 18 and flows into the NOx catalyst 18. Are connected to various sensors such as a temperature sensor 24 (catalyst temperature detecting means) for detecting the temperature (hereinafter referred to as inlet temperature Tin) and an O ₂ sensor 25 provided in the exhaust passage 16. Various devices such as an igniter 26 for driving the spark plug 7 and a fuel injection valve 8 are connected.

The ECU 21 determines the ignition timing, the fuel injection amount, and the like based on the detection information from each sensor, and operates the internal combustion engine 1 by drivingly controlling the igniter 23 and the fuel injection valve 8 based on the determined control amount.
Regarding the fuel injection control, the intake stroke injection mode in which the injection timing is set to the intake stroke and the compression stroke injection mode in which the injection timing is set to the compression stroke are switched according to the operation region of the internal combustion engine 1, specifically, Based on the throttle opening θth and the engine speed Ne, a target average effective pressure Pe that correlates with the engine load is obtained, and fuel injection to be executed according to a map set in advance from the target average effective pressure Pe and the engine speed Ne. In addition to determining the mode, the fuel injection control is executed by determining the fuel injection amount based on the target air-fuel ratio obtained from the target average effective pressure Pe and the engine speed Ne in the determined fuel injection mode.

The compression stroke injection mode is executed in a relatively low rotation and low load region, and an air-fuel mixture near the stoichiometric air-fuel ratio is secured around the spark plug 7 by using the reverse tumble flow generated by the intake air flowing in from the intake port 10. in terms of the extremely lean air-fuel ratio as a whole (e.g., about 40) performs a stratified combustion to ignite, whereas the intake stroke injection mode is executed at a relatively high speed and high load region, the output of the O ₂ sensor 25 Based on the stoichiometric F / B control that feeds back the exhaust air-fuel ratio to the stoichiometric air-fuel ratio, or O / L control that controls the air-fuel ratio on the rich side in an open loop, the fuel spray injected in the intake stroke is changed to the intake air. Uniform combustion is performed by thoroughly mixing and burning.

  During the lean operation in the compression stroke injection mode, the NOx amount contained in the exhaust gas is occluded in the NOx catalyst 18 to prevent discharge into the atmosphere, while the NOx occlusion amount of the NOx catalyst 18 is close to the saturation amount. When it reaches, the NOx purge for controlling the exhaust air-fuel ratio to the rich side and releasing and reducing NOx stored in the NOx catalyst 18 is executed. In the present embodiment, the control parameters related to the lean operation and the NOx purge are corrected according to the bed temperature Tbed (catalyst temperature) of the NOx catalyst 18, and the control will be described below.

First, prior to the description of the actual processing of the ECU 21, the NOx and HC purification characteristics of the NOx catalyst 18 and the control parameters of the ECU 21 set on the premise of the purification characteristics will be described.
FIG. 2 is a diagram showing the NOx purification characteristics with respect to the bed temperature Tbed of the NOx catalyst. The NOx purification performance and the NOx purification ratio have characteristics that gradually decrease in the high temperature region and the low temperature region with a specific bed temperature Tbed as a peak. In the example, a peak exists around 500 ° C. FIG. 3 is also a graph showing the HC purification characteristics with respect to the bed temperature Tbed of the NOx catalyst 18, and the HC purification performance and the THC purification ratio have characteristics that gradually decrease as the bed temperature Tbed decreases.

  In the present embodiment, on the premise of such characteristics of the NOx catalyst 18, a bed temperature Tbed at which the NOx catalyst 18 exhibits good purification performance with respect to NOx and HC is set in advance as a reference bed temperature. Specifically, the bed temperature Tbed corresponding to the peak of the NOx purification performance and the NOx purification ratio is 500 ° C., but the NOx purification performance and the THC purification ratio are considerably reduced at 500 ° C. The reference bed temperature is set to 550 ° C. slightly higher than the peak of the NOx purification ratio.

  The reference bed temperature does not necessarily need to be set in a temperature range where the NOx catalyst 18 exhibits good purification performance with respect to both NOx and HC, but is set with priority given to the purification performance of either NOx or HC. The reference bed temperature may be arbitrarily set as long as the bed temperature Tbed of the NOx catalyst 18 can be changed according to the operating state of the internal combustion engine 1 without being limited to a temperature range in which the purification performance is good. Is possible.

And assuming this reference bed temperature, the optimum value of the control parameter relating to the lean operation (NOx occlusion) such as the lean operation time is set, the target air-fuel ratio of the NOx purge, the injection pattern for executing the NOx purge, When the theoretical air-fuel ratio is set as the NOx purge duration and the target air-fuel ratio, optimal values of control parameters related to NOx purge (NOx release reduction) such as the presence or absence of air-fuel ratio feedback based on the output of the O ₂ sensor 25 are set. Has been. Here, since the optimum value of each control parameter is influenced by the target average effective pressure Pe and the engine speed Ne of the internal combustion engine 1, each optimum value for each operation region defined by the engine speed Ne and the target average effective pressure Pe is set. Control parameters are set.

  For example, the lean operation time (that is, the NOx purge interval) is a control parameter that is set mainly according to the NOx performance of the NOx catalyst 18 so that the lean operation time ends immediately before the NOx catalyst 18 is saturated. Is set. Further, the target air-fuel ratio and injection pattern of the NOx purge are control parameters that are mainly set according to the HC performance of the NOx catalyst 18, and the target air-fuel ratio is an HC with no excess or deficiency corresponding to the HC performance of the NOx catalyst 18. And CO are set to be supplied as a reducing agent, and the injection pattern is set as the optimal fuel injection to achieve the target air-fuel ratio, specifically, expansion after intake stroke injection to supply HC and CO In the injection pattern for executing the stroke injection, the injection amount of the expansion stroke injection, the injection timing, the number of injections, etc. are set to optimum values. The duration of the NOx purge is a control parameter set mainly according to the lean operation time (in other words, the NOx occlusion amount of the NOx catalyst 18), and the timing at which the stored NOx is released and reduced is completed. Is set to end the NOx purge.

Here, these control parameters are values derived from a bench test of the internal combustion engine 1. For example, with respect to the lean operation time, the NOx catalyst 18 is operated by causing the internal combustion engine 1 to perform a lean operation for each operation region (Pe, Ne). NOx is occluded and the NOx catalyst 18 is set based on the time required until the NOx catalyst 18 reaches saturation and allows NOx to pass through.
Then, after each control parameter is set as an optimum value for the reference bed temperature in this way, a correction value for deriving an optimum control parameter corresponding to the actual bed temperature Tbed from each control parameter corresponding to the reference bed temperature. Is set corresponding to each bed temperature Tbed for each control parameter.

  In the present embodiment, the correction value of each control parameter corresponding to the reference bed temperature is regarded as 1.0, and the correction value is calculated based on the relative performance index of the NOx catalyst 18 exhibited at each bed temperature Tbed. It is set as a map. For example, in the lean operation time set according to the NOx performance of the NOx catalyst 18 as described above, the NOx performance becomes 1.1 times at 500 ° C. according to the characteristics of FIG. 2 compared to the reference bed temperature of 550 ° C. Assuming that it becomes 0.7 times at 600 ° C., 1.1 is set as a correction value for the bed temperature Tbed 500 ° C. and 0.7 is set as a correction value for the bed temperature Tbed 6000 ° C. Is multiplied by the lean operation time of the reference bed temperature to calculate the optimum lean operation time at the corresponding bed temperature Tbed.

  Instead of setting the correction value based on the NOx purification characteristic of the NOx catalyst 18 as described above, the correction value may be obtained for each bed temperature Tbed by a bench test in the same manner as the control parameter corresponding to the reference bed temperature. Good. The form of the correction value is not limited to the above. For example, for each control parameter, a correction gain (correction value) is set so as to correspond to a change in the control parameter with respect to a temperature change centered on the reference bed temperature. The optimum control parameter corresponding to the bed temperature Tbed may be calculated by multiplying the deviation between the reference bed temperature and the actual bed temperature Tbed by a correction gain.

FIG. 4 is a flowchart showing a control parameter optimization routine executed by the ECU 21, and the ECU 21 executes the routine at a predetermined control interval.
First, in step S2, it is determined whether or not an execution condition for lean operation is satisfied. That is, it is determined whether or not the current operation region of the internal combustion engine 1 is in the region of the compression stroke injection mode on the map. When the determination is No (No), the routine is terminated. When the determination in step S2 becomes Yes (positive), the ECU 21 proceeds to step S4 and starts the lean operation in the compression stroke injection mode. In the subsequent step S6, the current bed temperature Tbed of the NOx catalyst 18, the engine speed Ne, A target average effective pressure Pe is obtained. The bed temperature Tbed is estimated from the inlet temperature Tin. For example, a temperature difference between the inlet temperature Tin and the bed temperature Tbed is obtained by a test for each operation region of the internal combustion engine 1, and the bed temperature Tbed is determined from the inlet temperature Tin according to a map based on the test result. calculate.

  Thereafter, it is determined whether or not the bed temperature Tbed estimated in step S8 is within a specific range near the reference bed temperature (for example, within a range of 540 to 560 ° C.). When the determination is Yes, the process proceeds to step S10, and the lean operation time corresponding to the reference bed temperature is read from the map based on the engine speed Ne and the target average effective pressure Pe at this time, and the value is set as the lean operation time as it is. To do. Similarly, in the subsequent step S12, the target air-fuel ratio of NOx purge corresponding to the reference bed temperature, the injection pattern, the duration, and the execution status of the air-fuel ratio feedback are read from the map based on the engine speed Ne and the target average effective pressure Pe. Are set as control parameters as they are.

  In the subsequent step S14, the NOx purge is executed. At this time, the NOx purge is performed with the contents reflecting the control parameters set in the processes in the steps S10 and S12. That is, when the lean operation time set in step S10 has elapsed, the lean operation is terminated and NOx purge is started, and the target air-fuel ratio, injection pattern, duration, and air-fuel ratio feedback execution status set in step S12 According to the NOx purge, and then the routine is terminated.

Since the bed temperature Tbed of the NOx catalyst 18 at this time is in the vicinity of the reference bed temperature, the lean operation is performed at the optimum timing immediately before the NOx catalyst 18 is saturated by applying the lean operation time corresponding to the reference bed temperature. The NOx purification performance of the NOx catalyst 18 is utilized to the maximum while the NOx leakage due to the saturation of the NOx catalyst 18 is prevented.
In addition, during the NOx purge, by applying the target air-fuel ratio corresponding to the reference bed temperature, an excessive or insufficient reducing agent corresponding to the HC performance of the NOx catalyst 18 is supplied, and an excessive reducing agent exceeding the HC performance is supplied. The NOx emission and reduction is efficiently performed while preventing the passage of HC and CO due to the supply of NOx, and the optimum air-fuel ratio for realizing the target air-fuel ratio is achieved by applying the NOx purge injection pattern corresponding to the reference bed temperature. The optimal NOx purge is performed while suppressing wasteful fuel consumption and drivability deterioration based on the injection pattern, and the NOx purge reduction is completed by applying the NOx purge duration corresponding to the reference bed temperature. The NOx purge is completed at a proper timing, and fuel consumption due to continued useless NOx purge is suppressed.

  On the other hand, if the determination in step S8 is No, assuming that the bed temperature Tbed is not within the specific range near the reference bed temperature, the process proceeds to step S16. In step S16, the lean operation time corresponding to the reference bed temperature is read from the map based on the engine speed Ne and the target average effective pressure Pe, and the correction value of the lean operation time corresponding to the actual bed temperature Tbed is read from the map. Then, the lean operation time corresponding to the reference bed temperature is multiplied by the correction value to calculate the optimum lean operation time corresponding to the actual bed temperature Tbed. Similarly, in step S18, the target air-fuel ratio of NOx purge corresponding to the reference bed temperature, the injection pattern, the duration, and the execution status of air-fuel ratio feedback are read from the map based on the engine speed Ne and the target average effective pressure Pe. At the same time, the correction value of each control parameter corresponding to the actual bed temperature Tbed is read from the map, and each control parameter corresponding to the reference bed temperature is multiplied by the correction value to obtain the optimum control parameter corresponding to the actual bed temperature Tbed. Are respectively calculated (control means).

Thereafter, the ECU 21 proceeds to the above step S14, terminates the lean operation when the lean operation time set in step S16 has elapsed, starts the NOx purge, and sets the target air-fuel ratio, injection pattern, and duration set in step S18. The NOx purge is executed according to the execution status of the air-fuel ratio feedback, and then the routine is terminated.
By the control parameter correction processing in steps S16 and S18, the lean operation and the NOx purge are executed as follows.

  For example, when the bed temperature Tbed is 500 ° C. with respect to the reference bed temperature of 550 ° C., the NOx performance of the NOx catalyst 18 is improved in accordance with the characteristics shown in FIG. While it is extended from the corresponding value of temperature (for example, extended based on the correction value 1.1), the HC performance is reduced according to the characteristics of FIG. 3, so the target is to prevent passage of HC and CO during NOx purge. The air-fuel ratio is corrected to the lean side from the corresponding value of the reference bed temperature, and the NOx purge duration is extended in response to the increase in the NOx occlusion amount accompanying the extension of the lean operation time.

  Further, when the bed temperature Tbed is 600 ° C., the NOx performance of the NOx catalyst 18 is reduced according to the characteristics shown in FIG. 2 and the amount of NOx that can be stored is reduced, so the lean operation time is shorter than the corresponding value of the reference bed temperature (for example, 3), while the HC performance is improved according to the characteristics of FIG. 3, the target air-fuel ratio is set to a richer side than the corresponding value of the reference bed temperature in order to speed up the NOx purge. In addition, the duration of the NOx purge is shortened corresponding to the decrease in the NOx occlusion amount accompanying the shortening of the lean operation time.

  As described above, in this embodiment, the control parameter corresponding to the reference bed temperature is corrected by the correction value corresponding to the bed temperature Tbed and applied to the lean operation and the NOx purge. The NOx and HC purification characteristics shown in FIGS. 2 and 3 are greatly different depending on the specifications of the NOx catalyst 18 and the like, so that optimum control is always performed in all temperature regions on the premise of these NOx and HC purification characteristics. Although it is very difficult to apply the parameters, the control parameter corresponding to the reference bed temperature Tbed and the correction value of each bed temperature Tbed are values obtained by the bench test. Compared to the estimated value based on the calculation process, it has very high reliability, and the control parameter at each bed temperature Tbed is obtained by correction processing based on the control parameter of the reference bed temperature with high reliability. Therefore, it is possible to obtain an optimal control parameter in accordance with the reality with few errors.

As a result, NOx occlusion during lean operation and NOx release reduction during NOx purge can always be performed in an optimal environment regardless of the bed temperature Tbed, and this prevents problems such as fuel consumption deterioration due to unnecessary fuel consumption. The purification performance of the NOx catalyst 18 can be maximized.
In addition, since the bed temperature Tbed that provides the best purification performance with respect to NOx and HC is set as the reference bed temperature, the reliability of the control parameter corresponding to the reference bed temperature is further improved. Thus, the reliability of the control parameter at each bed temperature Tbed calculated based on the above can be improved, and more appropriate lean operation and NOx purge control can be realized.

This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above-described embodiment, the exhaust gas purification apparatus for the direct injection gasoline internal combustion engine 1 is embodied. However, the type is not limited to this as long as the internal combustion engine includes the storage type NOx catalyst 18. For example, you may apply to a diesel engine.
In the above embodiment, the bed temperature Tbed estimated from the inlet temperature Tin of the NOx catalyst 18 is used as an index, but the present invention is not limited to this as long as the value correlates with the bed temperature Tbed. For example, instead of the bed temperature Tbed, the inlet temperature Tin is used as an index, and an optimal control parameter corresponding to the actual inlet temperature is calculated by the correction process based on the control parameter set corresponding to the reference inlet temperature. Good.

In the above embodiment, the correction process based on the reference bed temperature is performed on both the control parameter related to the lean operation and the control parameter related to the NOx purge. However, the correction process is performed only on one of them. May be.
Further, the control parameter relating to the NOx purge may be corrected by the engine water temperature or the intake air temperature.

  Further, the control parameters related to NOx purge and lean operation may be corrected by an index indicating the degree of deterioration of the NOx catalyst.

1 is an overall configuration diagram illustrating an exhaust gas purification apparatus for an internal combustion engine according to an embodiment. It is a figure which shows the NOx purification characteristic with respect to the bed temperature of a NOx catalyst. It is a figure which shows the HC purification characteristic with respect to the bed temperature of a NOx catalyst. It is a flowchart which shows the control parameter optimization routine which ECU performs.

Explanation of symbols

1 Internal combustion engine 16 Exhaust passage 18 NOx catalyst 21 ECU (control means)
24 Temperature sensor (catalyst temperature detection means)

Claims (6)

An occlusion-type NOx provided in an exhaust passage of the internal combustion engine that occludes NOx in the exhaust gas when the exhaust air-fuel ratio of the internal combustion engine is lean, and releases and stores the occluded NOx when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or rich A catalyst,
Catalyst temperature detecting means for detecting the temperature of the NOx catalyst;
Controlling the internal combustion engine so as to execute NOx purge for NOx emission reduction every predetermined lean operation time, and control parameters relating to the lean operation or NOx purge set in advance corresponding to a reference temperature; and Based on the correction value set for each catalyst temperature, the control parameter corresponding to the reference temperature is corrected by the correction value corresponding to the catalyst temperature detected by the catalyst temperature detecting means, and the corrected control parameter is set to the internal combustion engine. An exhaust emission control device for an internal combustion engine, comprising: a control unit applied to control of the engine. The reference temperature is set as a temperature at which the NOx catalyst exhibits good purification performance,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control means corrects a control parameter set corresponding to the reference temperature with a correction value corresponding to the catalyst temperature. The lean operation time is previously set as the control parameter corresponding to the reference temperature,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control means corrects the lean operation time with a correction value corresponding to the catalyst temperature. The target air-fuel ratio for the NOx purge is set in advance as the control parameter corresponding to the reference temperature,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control means corrects the target air-fuel ratio of the NOx purge with a correction value corresponding to the catalyst temperature. As the control parameter, the duration of the NOx purge is set in advance corresponding to the reference temperature,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control means corrects the duration of the NOx purge with a correction value corresponding to the catalyst temperature. As the control parameter, an injection pattern for executing the NOx purge corresponding to the reference temperature is set in advance,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control means corrects the injection pattern of the NOx purge with a correction value corresponding to the catalyst temperature.

Images