JP3767483B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus (an exhaust gas after-treatment system) for an internal combustion engine, and more particularly to its regeneration technology.
[0002]
[Prior art]
As a conventional exhaust gas purification device for an internal combustion engine, there is a device described in Japanese Patent Laid-Open No. 9-53442.
In this device, a PM trap for trapping PM is arranged in the exhaust passage for the purification treatment of NOx (nitrogen oxide) discharged from the diesel engine and PM (Particulate Matter) which is exhaust particulate, and further downstream side thereof. In addition, when the air-fuel ratio of the inflowing exhaust gas is lean, NOx is trapped. When the air-fuel ratio of the inflowing exhaust gas becomes rich and the O2 (oxygen) concentration in the exhaust gas decreases, HC (hydrocarbon which is a reducing component in the exhaust gas) ), A NOx trap catalyst for reducing and purifying NOx trapped by CO (carbon monoxide) is disposed.
[0003]
And periodically, NOx trapped from the NOx trap catalyst is released to recover the NOx trap capability (NOx trap catalyst regeneration operation), and PM trapped in the PM trap is burned and removed to reduce pressure loss. The operation (PM trap regeneration operation) is performed.
The conventional regeneration operation of the NOx trap catalyst is performed for a short time at intervals of several tens of seconds to several minutes, in addition to normal fuel injection of a diesel engine, fuel injection is performed in the exhaust stroke, and the exhaust air / fuel ratio is made higher than the stoichiometric air / fuel ratio. This is achieved by exhausting the unburned components of the fuel to the exhaust passage on the rich side (about 13). That is, the exhaust air-fuel ratio is made rich, the O2 concentration in the exhaust gas is rapidly reduced, and the HC and CO components are increased to regenerate the NOx trap catalyst.
[0004]
The regeneration operation of the PM trap is performed for several minutes at intervals of several tens of minutes to several hours, in the same manner as the regeneration of the NOx trap catalyst, in addition to normal fuel injection, fuel injection is performed in the exhaust stroke, but the exhaust temperature is raised. This is to promote regeneration of the PM trap, and the exhaust air-fuel ratio is maintained at a lean value of about 20.
When the NOx trap catalyst regeneration operation timing comes during the PM trap regeneration operation, the exhaust air-fuel ratio enrichment for regeneration of the NOx trap catalyst is performed during the PM trap regeneration operation. .
[0005]
[Problems to be solved by the invention]
However, in such a conventional exhaust gas purification apparatus for an internal combustion engine, the regeneration operation of the NOx trap catalyst in which the exhaust air-fuel ratio is enriched in a short time at relatively short time intervals, and the regeneration operation of the NOx trap catalyst It is necessary to carry out two types of regeneration operations, ie, a regeneration operation of the PM trap in which the exhaust gas temperature rise is performed while maintaining a lean state for a long time at longer time intervals.
[0006]
These regeneration operations are independent of each other, and the energy (fuel consumption) consumed for regeneration of the NOx trap catalyst cannot be used for regeneration of the PM trap during regeneration of the NOx trap catalyst. The energy consumed (fuel consumption) cannot be used for regeneration of the NOx trap catalyst during regeneration of the PM trap. For this reason, there was a problem that energy efficiency was bad and fuel consumption was greatly deteriorated.
[0007]
In view of such conventional problems, the present invention uses NOx trap catalysts and PM traps to prevent NOx and PM from being released into the atmosphere and to independently regenerate the NOx trap catalysts and PM traps. An object of the present invention is to realize an exhaust emission control device for an internal combustion engine that can be performed by a single operation without shortening the total regeneration time and does not involve a great sacrifice in fuel consumption.
[0008]
[Means for Solving the Problems]
For this reason, in the present invention, a NOx trap catalyst is disposed in the exhaust passage, and a PM trap is disposed downstream thereof. Then, regeneration of the NOx trap catalyst is performed using an air / fuel ratio control device capable of controlling the air / fuel ratio of the exhaust gas flowing into the NOx trap catalyst and an air supply device capable of supplying air to the upstream exhaust passage of the PM trap. At the same time, the air-fuel ratio of the exhaust flowing into the NOx trap catalyst is made rich, and air is supplied to the upstream exhaust passage of the PM trap to make the air-fuel ratio of the exhaust flowing into the PM trap lean.
[0009]
【The invention's effect】
According to the present invention, two types of regeneration operations, namely regeneration of the NOx trap catalyst and regeneration of the PM trap, can be performed simultaneously without performing them individually. For this reason, since the energy consumed for regeneration is greatly reduced, it is possible to minimize the influence on fuel consumption deterioration.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
First, the first embodiment of the present invention will be described. Prior to this, the background art will be described at the embodiment level.
A three-way catalyst is widely used as a catalyst in order to purify exhaust gas in which an oxidizing component and a reducing component are contained almost equally as in a conventional automobile gasoline engine. This is a catalyst mainly composed of activated alumina carrying various components including noble metal components such as Pt (platinum), Pd (palladium), Rh (rhodium) and Ce (ceria) components. Harmful components HC, CO and NOx can be purified with high efficiency.
[0011]
On the other hand, in recent years, so-called lean burn engines that operate even at an air-fuel ratio higher than the stoichiometric air-fuel ratio have attracted attention from the viewpoint of improving fuel efficiency and reducing CO2 (carbon dioxide) emissions. The exhaust during lean combustion of this type of engine has a high oxygen content compared to the exhaust of a conventional engine that operates near the stoichiometric air-fuel ratio, and the above three-way catalyst has insufficient purification of NOx. Become. Therefore, a new catalyst that can efficiently remove NOx in exhaust during lean combustion in a lean burn engine has been desired.
[0012]
As one of them, it has been proposed to use a NOx trap catalyst that traps NOx when the air-fuel ratio of the inflowing exhaust gas is lean and reduces and purifies NOx when the air-fuel ratio of the inflowing exhaust gas becomes rich.
On the other hand, even if NOx can be removed by a NOx trap catalyst, PM cannot be removed. Therefore, in an internal combustion engine that releases PM, for example, a diesel engine, it is necessary to provide a PM trap that traps PM in exhaust gas.
[0013]
Against this background, as disclosed in Japanese Patent Laid-Open No. 9-53442, a PM trap (DPF; Diesel Particulate Filter) is disposed in the exhaust passage, and further, a NOx trap catalyst (NOx absorption catalyst) is disposed downstream thereof. The NOx trap catalyst regeneration operation and the PM trap regeneration operation are periodically performed separately.
[0014]
Further, in Japanese Patent No. 2727906 and Japanese Patent No. 2722987, it is determined that the NOx trap catalyst (NOx absorbent) is supported on the wall surface of the wall flow honeycomb type PM trap (DPF) and the regeneration start condition of the NOx trap catalyst is satisfied. When the intake throttle valve is closed, fuel is supplied from the reducing agent supply device into the exhaust gas at the PM trap inlet, and the supplied fuel is combusted by the catalytic action of the NOx trap catalyst to consume oxygen in the exhaust gas. As a result, the exhaust air-fuel ratio is enriched, thereby regenerating the NOx trap catalyst.
[0015]
Next, when it is determined that the regeneration of the NOx trap catalyst is finished, the fuel supply from the reducing agent supply device is continued, the intake throttle is released, and a large amount of air is supplied to trap the PM trap. PM is ignited and burned to regenerate the PM trap.
Further, in Japanese Patent No. 2727906, when the regeneration of the PM trap is completed, the intake throttle valve is closed again, fuel is supplied from the reducing agent supply device, and the exhaust gas is heated to a high temperature and rich, so that SOx (sulfur oxidation) is generated from the NOx trap catalyst. To release SOx poisoning.
[0016]
Accordingly, even in Japanese Patent No. 2727906 and Japanese Patent No. 2722987, each of the regeneration operations (NOx trap catalyst regeneration operation, PM trap regeneration operation, SOx poisoning elimination operation) has an independent action, and the NOx trap catalyst regeneration is performed. Since the exhaust is rich inside, the PM trap cannot be regenerated, and during regeneration of the PM trap, the exhaust is lean, so the NOx trap catalyst cannot be regenerated, and naturally the PM trap cannot be regenerated even during the SOx poisoning elimination operation. These simply perform each reproduction operation in turn.
[0017]
As described above, as conventional techniques, the regeneration operation of the NOx trap catalyst and the regeneration operation of the PM trap are separately performed (Japanese Patent Laid-Open No. 9-53442) and the one that is performed in order (Japanese Patent No. 2727906 or (Patent No. 2722987), but when performed separately or sequentially (not simultaneously), there is a disadvantage that not only the total regeneration time is lengthened, but also energy efficiency is poor and fuel consumption is greatly deteriorated. .
[0018]
Further, in Japanese Patent No. 2727906 and Japanese Patent No. 2722987, since the fuel is supplied from the reducing agent supply device, in practice, when the exhaust gas temperature flowing into the PM trap decreases due to a change in the engine operating condition during regeneration (for example, In idling, the catalytic reaction does not occur and the supplied fuel may be discharged without being burned.
[0019]
Therefore, in the present embodiment, the regeneration of the NOx trap catalyst and the PM trap can be performed in one operation without being independent of each other, so that the total regeneration time can be shortened and the fuel efficiency can be improved by improving the energy efficiency. Like that.
FIG. 1 is a configuration diagram of an exhaust gas purification apparatus (exhaust gas purification aftertreatment system) for an internal combustion engine showing a first embodiment of the present invention.
[0020]
In FIG. 1, reference numeral 1 denotes a main body of an internal combustion engine (hereinafter referred to as a diesel engine, hereinafter simply referred to as an engine), 2 is an intake passage, and 3 is an exhaust passage.
The exhaust passage 3 traps NOx downstream of the exhaust gas turbine 3a of the supercharger when the air-fuel ratio of the inflowing exhaust gas is lean and when the air-fuel ratio of the inflowing exhaust gas is rich. A casing 20 is disposed that internally includes a NOx trap catalyst 20b that reduces and purifies trapped NOx. Further downstream, a casing 21 having a DPF (Diesel Particulate Filter) 21a as a PM trap for trapping PM (Particulate Matter) in the exhaust is disposed in series. The DPF 21a has an oxidation function by supporting an oxidation catalyst on the surface thereof.
[0021]
As the oxidation catalyst 20a, for example, a catalyst in which a precious metal such as Pd or Pt is supported based on activated alumina, a zeolite in which a precious metal (particularly Pt) is ion-exchanged, or a combination of these materials can be used.
Further, as the DPF 21a, a conventionally known wall flow honeycomb type or a structure in which ceramic fibers are wound in several layers around a bottomed cylindrical core member provided with a large number of holes in a cylindrical portion can be used.
[0022]
An exhaust temperature sensor 36 for detecting the exhaust temperature T1 is provided at the inlet of the NOx trap catalyst 20b (the outlet of the oxidation catalyst 20a), and an exhaust temperature sensor 37 for detecting the exhaust temperature T2 is provided at the inlet of the DPF 21a. An oxygen concentration sensor 38 for detecting the oxygen concentration O2 is provided.
In order to supply air to the downstream DPF 21a at the outlet of the NOx trap catalyst 20b, the air introduction passage 8 connected to the pressure chamber portion downstream of the intake compressor 2b of the supercharger in the intake passage 2 serving as an air supply source. The opening 8a faces. The air introduction passage 8 is provided with, for example, a stepping motor driven on-off valve 9 controlled by the engine control unit 30. The on-off valve 9 opens and closes the air introduction passage 8 and has a variable passage area. The air supply amount can be controlled.
[0023]
An EGR passage 4 is provided from the upstream side of the exhaust turbine 3a of the supercharger in the exhaust passage 3 in order to recirculate a part of the exhaust to the intake pipe 2c of the intake passage 2, and this EGR passage 4 has an engine control. For example, an EGR valve 5 driven by a stepping motor and controlled by the unit 30 is provided.
The intake passage 2 is provided with an intake throttle valve 7 that is opened and closed by an air cleaner 2a, a supercharger intake compressor 2b, and an engine control unit 30 via an actuator (for example, a stepping motor) 6 from the upstream side. Intake air is distributed to each cylinder of the engine 1 by the intake pipe 2c.
[0024]
The fuel supply system includes a diesel fuel (light oil) tank 60, a fuel supply passage 16 for supplying diesel fuel to the fuel injection device 10 of the engine 1, and a fuel tank for return fuel (spill fuel) from the fuel injection device 10. A fuel return passage 19 for returning to 60 is formed.
The fuel injection device 10 of the engine 1 is a known common rail type fuel injection device, and includes a supply pump 11, a fuel supply passage 12, a common rail (accumulation chamber) 14, and a fuel injection valve 15 provided for each cylinder. After the fuel pressurized by 11 is temporarily stored in the common rail 14 via the fuel supply passage 12, the high-pressure fuel in the common rail 14 is distributed to the fuel injection valves 15 corresponding to the number of cylinders.
[0025]
Further, in order to control the pressure of the common rail 14, a part of the fuel discharged from the supply pump 11 is returned to the fuel supply passage 16 through an overflow passage 17 provided with a one-way valve 18 in the middle. A pressure control valve 13 capable of changing the flow passage area of the overflow passage 17 is provided. The pressure control valve 13 changes the flow passage area of the overflow passage 17 in accordance with a duty signal from the engine control unit 30. Thus, the pressure of the common rail 14 is controlled by adjusting the fuel discharge amount to the common rail 14.
[0026]
The fuel injection valve 15 is an electromagnetically driven injection valve that opens and closes a fuel supply passage to the engine combustion chamber by an ON-OFF signal from the engine control unit 30, and injects fuel into the combustion chamber by an ON signal. Injection is stopped by an OFF signal. Here, the longer the ON signal to the fuel injection valve 15, the greater the fuel injection amount. However, as will be described later, the fuel injection amount also changes depending on the fuel pressure of the common rail 14.
[0027]
The engine control unit 30 detects the signal (Tw) of the water temperature sensor 31, the signal of the crank angle sensor 32 (which can detect the engine speed Ne), the signal (Cyl) of the cylinder discrimination sensor 33, and the common rail pressure. Pressure sensor 34 signal (PCR), accelerator opening sensor 35 signal (L), exhaust temperature sensor 36 signal (T1) for detecting the exhaust temperature at the inlet of NOx trap catalyst 20b (the outlet of oxidation catalyst 20a) The signal (T2) of the exhaust temperature sensor 37 for detecting the exhaust temperature at the inlet of the DPF 21a and the signal (O2) of the oxygen concentration sensor 38 are input.
[0028]
In this embodiment, the post-injection common rail fuel injection device 10 that injects a small amount of fuel after the main injection can control the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst 20b. Configure. The air introduction passage 8 and the on-off valve 9 constitute an air supply device that can supply air to the upstream exhaust passage of the DPF 21a. Further, the engine control unit 30 constitutes a regeneration timing determination unit and a regeneration control unit.
[0029]
Next, control of the exhaust purification device (exhaust purification post-processing system) by the control unit 30 in the first embodiment will be described with reference to the flowcharts of FIGS.
FIG. 2 is a main routine related to engine output control performed by the control unit 30.
[0030]
In the engine output control routine of FIG. 2, in step 100 (denoted as S100 in the figure, the same applies hereinafter), the engine cooling water temperature Tw, the engine speed Ne, the cylinder discrimination signal Cyl, the common rail pressure PCR, the accelerator opening L, and the NOx trap. The exhaust temperature T1 at the inlet portion of the catalyst 20b (the outlet portion of the oxidation catalyst 20a), the exhaust temperature T2 at the inlet portion of the DPF 21a, and the oxygen concentration O2 are read.
[0031]
In step 200, common rail pressure control is performed according to a subroutine shown in FIG. 3 described later. In the next step 300, main injection control for engine output control is performed according to a subroutine shown in FIG. 4 described later, and the process proceeds to step 400.
In step 400, it is determined whether the flag indicating that the aftertreatment system (in particular, the NOx trap catalyst 20b and the DPF 21a) is being regenerated is 1, and whether the aftertreatment system is being regenerated.
[0032]
If the determination in step 400 is NO and the post-processing system is not being regenerated, the process proceeds to step 500 where engine combustion control is performed according to the subroutine of FIG. 5 described later, and in the next step 600, the subroutine of FIG. Accordingly, the NOx trap amount of the NOx trap catalyst 20b is integrated, and based on this, it is determined whether or not the NOx trap catalyst 20b needs to be regenerated, and the process returns.
[0033]
If the determination in step 400 is YES and the regeneration of the post-processing system is in progress, the process proceeds to step 700, and the regeneration control of the post-processing system is started or continued according to the subroutine of FIG. .
FIG. 3 is a subroutine related to common rail pressure control performed in step 200 of the main routine of FIG.
[0034]
In the common rail pressure control routine of FIG. 3, in step 201 and step 202, the engine speed Ne and the main fuel injection amount (preliminarily set corresponding to the accelerator opening L and the like and representing the load) Qmain are used as parameters. A predetermined map stored in advance in the ROM in the control unit 30 is searched, and the target reference pressure PCR0 of the common rail 14 and the reference duty ratio (reference control signal of the pressure control valve 13 for obtaining the target reference pressure PCR0). ) Determine Duty0 and go to Step 203.
[0035]
In step 203, the absolute value | PCR0−PCR | of the difference between the target reference pressure PCR0 and the actual common rail pressure PCR is obtained and compared with an allowable pressure difference ΔPCR0 preset for the target reference pressure PCR0.
If | PCR0−PCR | is within the allowable range, the process proceeds to step 204 where the same duty ratio is maintained by setting the reference duty ratio Duty0 as the valve opening duty ratio (control signal) Duty. A duty signal is generated from the valve opening duty ratio Duty to drive the pressure control valve 13.
[0036]
On the other hand, if | PCR0-PCR | is not within the allowable range, the process proceeds from step 203 to step 205, where a ROM table preset corresponding to PCR0-PCR (= ΔP) is searched, and the duty is A ratio correction coefficient KD duty is obtained. Here, for example, when ΔP is negative (PCR is larger than PCR0), KDuty is smaller than 1, and conversely when ΔP is positive (PCR is smaller than PCR0), KDuty is smaller than 1. Is also a large value. Specifically, the table data of the duty ratio correction coefficient KDuty is set in accordance with the characteristics of the pressure control valve 13.
[0037]
In step 206, the value obtained by correcting the reference duty ratio Duty0 with the correction coefficient KDuty (Duty0 × KDuty) is set as the valve opening duty ratio (correction control signal) Duty, and then the operation in step 207 is executed.
FIG. 4 is a subroutine related to main injection control performed in step 300 of the main routine of FIG.
[0038]
In the main injection control routine of FIG. 4, in step 301, a predetermined map stored in advance in the ROM in the control unit 30 is searched using the main fuel injection amount Qmain and the common rail pressure PCR as parameters, and the main injection period is determined. Mperiod is obtained and the process proceeds to step 302.
Here, the main injection period Mperiod is set in units of msec. As shown in FIG. 9, if the main fuel injection amount Qmain is the same, the higher the common rail pressure PCR, the shorter the main injection period Mperiod and the same common rail pressure PCR. The main injection period Mperiod becomes longer as the main fuel injection amount Qmain increases.
[0039]
In step 302, a predetermined map stored in advance in the ROM in the control unit 30 is searched using the engine speed Ne and the main fuel injection amount Qmain as parameters to obtain the main injection start timing Mstart. move on.
In step 303, the main injection start timing Mstart is corrected based on the engine coolant temperature Tw, and the routine proceeds to step 304.
[0040]
Specifically, the main injection start timing Mstart is advanced when the water temperature Tw is low. The lower the water temperature Tw, the lower the temperature of the engine combustion chamber, so the ignition start time will be relatively delayed. Therefore, in order not to increase emissions of HC, CO and PM (especially SOF: Soluble Organic Fraction), This is because it is desirable to keep the combustion start timing constant by correcting the advance of the injection start timing Mstart.
[0041]
In step 304, the fuel injection valve 15 of the cylinder to be main-injected is signaled to the crank angle sensor 32 and the cylinder discrimination sensor 33 for a period of Mperiod from the main injection start timing Mstart so that the main fuel injection amount Qmain is supplied. Based on this, the valve is opened.
FIG. 5 is a subroutine related to engine combustion control performed in step 500 of the main routine of FIG. 2, and performs control to perform EGR or stop corresponding to the operation region shown in FIG.
[0042]
In the engine combustion control routine of FIG. 5, in step 501, the operating region is determined. That is, it is determined whether or not the engine is in the EGR region based on the engine speed Ne and the main fuel injection amount (load) Qmain. Here, the EGR region is the normal operation region of the region A1 in FIG. 10, and therefore, here, is the normal operation region of the region A1 in FIG. 10 or other operation regions (regions A2, A3). Determine whether.
[0043]
If it is the EGR area in the determination in step 501, the process proceeds to step 502.
In step 502, the target EGR data (drive signals for the EGR valve 5 and the intake throttle valve 7) for executing the EGR are used as parameters, the engine speed Ne and the main fuel injection amount Qmain as parameters, and the ROM in the control unit 30. A predetermined map stored in advance is searched for and obtained, and the process proceeds to step 503.
[0044]
In step 503, EGR is corrected based on the engine coolant temperature Tw, and the process proceeds to step 504.
Specifically, for example, the EGR is corrected to decrease when the water temperature Tw is low. The lower the water temperature Tw, the lower the temperature of the engine combustion chamber, so the ignition start time will be relatively delayed. Therefore, in order not to increase the emissions of HC, CO, and PM (especially SOF), the EGR is corrected to decrease. This is because it is desirable to keep the combustion start time constant.
[0045]
In step 504, EGR is performed by controlling the driving of the EGR valve 5 and the intake throttle valve 7 based on the corrected driving signals.
On the other hand, if it is determined in step 501 that the region is not the EGR region, the process proceeds to step 505.
In step 505, the operation of the EGR valve 5 and the intake throttle valve 7 is stopped in order to stop or hold the EGR.
[0046]
FIG. 6 is a subroutine related to the NOx trap amount integration of the NOx trap catalyst 20b and the regeneration necessity determination performed at step 600 of the main routine of FIG. This routine corresponds to a regeneration time determination means.
In the NOx trap amount integration / determination routine of FIG. 6, in step 601, the NOx trap amount (NOx trap amount per unit time) of the NOx trap catalyst 20b is determined by calculating the engine speed Ne and the main fuel injection amount (load) Qmain. As a parameter, a predetermined map stored in advance in the ROM in the control unit 30 is searched and obtained, and the process proceeds to step 602.
[0047]
In step 602, the NOx trap amount is corrected based on the engine coolant temperature Tw, and the process proceeds to step 603.
Specifically, for example, when the water temperature Tw is low, the NOx trap amount is corrected to decrease. The lower the water temperature Tw is, the lower the temperature of the engine combustion chamber is. Therefore, the ignition start timing is relatively delayed. Therefore, in Step 303 of FIG. 4 and Step 503 of FIG. 5, as described above, HC, CO, PM In order not to increase the discharge amount (especially SOF), the main injection start timing Mstart is advanced and the EGR is decreased, so that the combustion start timing is kept constant. However, even if the combustion start timing is kept constant, the lower the temperature of the engine combustion chamber, the longer the combustion period and the lower the combustion temperature, and the NOx emission tends to decrease. When the NOx emission amount decreases, the NOx trap amount also tends to decrease. For this reason, it is desirable to set a correction coefficient for decreasing the NOx trap amount as the water temperature Tw is lower with the water temperature Tw as a parameter, and to reduce the NOx trap amount. The correction coefficient for the NOx trap amount is obtained in advance by experiments.
[0048]
In step 603, the NOx trap amount is integrated at a predetermined time interval synchronized with the NOx trap amount per unit time, and the process proceeds to step 604.
In step 604, it is determined whether or not the accumulated NOx trap amount exceeds a predetermined trap limit amount set in the NOx trap catalyst 20b, and regeneration (NOx release / reduction) of the NOx trap catalyst 20b is necessary.
[0049]
If the determination in step 604 is NO and regeneration is not necessary, a return is returned.
If the determination in step 604 is YES and the NOx trap amount exceeds the trap limit amount and it is determined that regeneration of the NOx trap catalyst 20b is necessary, the process proceeds to step 605.
[0050]
In step 605, in order to start reproduction control, the reproduction flag is set to 1 (a flag is set as a reproduction start signal).
Then, the process proceeds to step 606, where an index value for end of reproduction, for example, counting of time is started, and a return is made. The regeneration end index value is not limited to the time example, and may be obtained by integrating the multiplier of the exhaust temperature T1 at the inlet of the NOx trap catalyst 20b (the outlet of the oxidation catalyst 20a) and the time. Thus, the accuracy of the regeneration time calculation is improved.
[0051]
FIG. 7 is a subroutine relating to regeneration control of the post-processing system (NOx trap catalyst 20b and DPF 21a) performed in step 700 of the main routine of FIG. This routine corresponds to the reproduction control means.
In the post-processing system regeneration control routine of FIG. 7, in step 701, it is determined from the passage of time that is an index value whether or not a predetermined regeneration operation of the post-processing system has been completed.
[0052]
If the determination in step 701 is NO and regeneration is not complete, the routine proceeds to step 702, where the post-injection data for enriching the exhaust air-fuel ratio, that is, the post-injection amount Qpost, the post-injection period Pperiod, the post-injection The injection start timing Pstart is obtained by searching from a predetermined map stored in the ROM in the control unit 30 using the engine speed Ne and the main fuel injection amount (load) Qmain as parameters of the operating state. move on.
[0053]
The post injection amount Qpost, the post injection period Pperiod, and the post injection start timing Pstart promote the oxidation reaction of the oxidation catalyst 20a, and the NOx trap so that the NOx trap catalyst 20b can be regenerated (release and reduce NOx). Even if the exhaust air-fuel ratio flowing into the catalyst 20b is enriched to raise the exhaust gas temperature and air for regenerating the DPF 21a is supplied as will be described later, the temperature and the exhaust composition required to regenerate the DPF 21a Is obtained and set in advance by experiments.
[0054]
In step 703, the fuel injection valve 15 of the cylinder to be post-injected during the period of Pperiod from the post-injection start timing Pstart is determined based on the signals from the crank angle sensor 32 and the cylinder discrimination sensor 33 so that the post-injection amount Qpost is supplied. To open the valve.
In step 704, feedback control of post injection (Qpost) based on the signal (T1) of the exhaust temperature sensor 36 at the inlet portion of the NOx trap catalyst 20b (outlet portion of the oxidation catalyst 20a), that is, the predetermined post injection described above. If the temperature is such that the catalytic reaction of the NOx trap catalyst 20b is not promoted even after the operation is performed, the post-injection increase correction is performed to ensure basic exhaust conditions necessary for regeneration of the aftertreatment system.
[0055]
Here, in the post-injection, the NOx trap catalyst 20b is regenerated, so that an amount of fuel that can enrich the exhaust air-fuel ratio (for example, the air-fuel ratio of 13 or less) can be increased in the expansion stroke or exhaust stroke of each cylinder separately from the main injection. It is an injection, not a fuel injection for obtaining output.
Therefore, a part of the post-injected fuel burns in the cylinder to raise the exhaust temperature, and the rest flows into the oxidation catalyst 20a in an unburned state (HC, CO). Here, in order to promote the oxidation reaction of the oxidation catalyst 20a, the temperature of the exhaust gas flowing into the oxidation catalyst 20a is set to, for example, 250 ° C. or more, which is the activation temperature of the oxidation catalyst 20a.
[0056]
That is, since all of the post-injected fuel does not burn in the cylinder, oxygen (O 2) and unburned fuel components (HC, CO) that are not consumed in the cylinder are at least 250 ° C. in the oxidation catalyst 20a. It will flow in while maintaining the exhaust temperature.
Then, a part of the unburned fuel that has flowed in reacts with O2 in the oxidation catalyst 20a, so that O2 is consumed and the temperature further rises. Here, considering that the downstream DPF 21a is regenerated, the temperature of the exhaust gas flowing into the NOx trap catalyst 20b is set to 500 ° C. or more, for example.
[0057]
Then, the same as when the engine was burned in a richer state than the theoretical mixing ratio (for example, an air-fuel ratio of 13 or less), it contains almost no O2 and contains a lot of unburned components as a reducing agent, and high-temperature exhaust gas. As a result of flowing into the NOx trap catalyst 20b, the NOx trap catalyst 20b is regenerated, and the temperature further increases due to the catalytic reaction in the NOx trap catalyst 20b.
[0058]
After the basic exhaust conditions necessary for regeneration of the aftertreatment system are secured in step 704, the process proceeds to step 705.
In step 705, data relating to the air supply for regeneration of the DPF 21a (lean exhaust air-fuel ratio flowing into the DPF 21a), that is, the air amount Qair supplied to the DPF 21a, the engine speed Ne and the main fuel injection amount (load). Using Qmain as a parameter of the operating state, a search is made from a predetermined map stored in the ROM in the control unit 30 to obtain it, and the process proceeds to step 706.
[0059]
In step 706, the on-off valve 9 is driven to open so that the air amount Qair is supplied.
As a result, exhaust gas that has been heated to a high temperature by the catalytic reaction of the oxidation catalyst 20a and the NOx trap catalyst 20b and that contains a large amount of O2 due to the air supply flows into the DPF 21a, so that the PM collected and deposited in the DPF 21a burns. Thus, the DPF 21a is also regenerated.
[0060]
Here, SOF such as hydrocarbons in the PM component can be removed at a relatively low temperature (oxidation treatment at about 200 ° C. or higher), whereas carbon is used for dry soot in the PM component. Since it is a main component and carbon is a stable substance, it cannot normally be incinerated unless it is at a relatively high temperature of about 600 ° C or higher. However, an oxidation catalyst is supported on the surface of the DPF 21a to promote the oxidation reaction by O2. By doing so, even if the PM component collected in the DPF 21a is almost carbon, combustion can be started at about 450 ° C. or higher. Therefore, the temperature of the exhaust gas flowing into the catalyst-supported DPF 21a is set to about 450 ° C. or higher.
[0061]
The time required to regenerate the NOx trap catalyst by enriching the exhaust air-fuel ratio varies depending on the capacity of the catalyst and the regeneration interval (NOx trap amount), but in recent engines, the time ratio is approximately 1-2%. is necessary. The time required to regenerate the DPF also varies depending on the capacity of the DPF and the regeneration interval (PM deposition amount). However, in recent engines, the operation frequency at a temperature of 450 ° C. or higher is about 2 to 4% with a catalyst-supported DPF. Is necessary.
[0062]
In normal operation (operation in which DPF forced regeneration operation is not performed), the operation frequency at a temperature of 450 ° C. or higher is only about 1 to 2%, and a frequency shortage of about 3% at maximum occurs. For this reason, a forced temperature increase operation (regeneration operation in a lean state) is required. This point has also been confirmed in the applicant's research.
As described in JP-A-9-53442, if the regeneration of the NOx trap catalyst (reduction reaction) by the enrichment and the regeneration of the DPF (oxidation reaction) in a lean state are performed separately, the deterioration of fuel consumption will inevitably occur. growing.
[0063]
In other words, if both regeneration operations can be performed at the same time, the regeneration frequency can be halved, and the efficiency of using the energy used for regeneration can be increased, so fuel consumption deterioration can be minimized. .
After the air supply in step 706, the process proceeds to step 707.
In step 707, feedback control of air supply (Qair) based on the signal (T2) of the exhaust temperature sensor 37 at the inlet of the DPF 21a and the signal (O2) of the oxygen concentration sensor 38, that is, the predetermined air supply described above is performed. Then, Qair is corrected so as to maintain the exhaust conditions (temperature and O2 concentration) suitable for regenerating the DPF 21a, the exhaust conditions suitable for regenerating the DPF 23a are maintained, and a return is made.
[0064]
Here, assuming that the PM trapped in the DPF 21a is almost carbon, the exhaust condition suitable for regenerating the DPF 21a by the oxidation reaction with O2 requires a temperature of about 450 ° C. or higher as described above. is there. As the O2 concentration, at least about 4% is necessary.
This exhaust condition (especially temperature) is set in advance so as to be obtained by post injection in steps 703 and 704, catalytic reaction by the oxidation catalyst 20a and NOx trap catalyst 20b, and air supply for leaning in step 706. .
[0065]
The correction control of the air amount Qair performed in step 707 performs feedback increase / decrease correction control that maintains the temperature condition (about 450 ° C. or higher for the catalyst-supported DPF) and secures the minimum required O 2 concentration (for example, 4%).
If the determination in step 701 is YES and it is determined that the predetermined playback operation has ended, the process proceeds to step 708. In step 708, the regeneration control of the post-processing system is initialized. That is, the post injection is stopped, the air supply is stopped, the regeneration flag, the NOx trap amount integrated value, and the regeneration time count are reset to 0, respectively, and a return is made.
[0066]
According to the present embodiment, the NOx trap catalyst 20b is disposed in the exhaust passage 3, the DPF 21a is disposed downstream thereof, and the air-fuel ratio of the exhaust flowing into the NOx trap catalyst 20b is made rich at the regeneration timing. By supplying air to the upstream exhaust passage of the DPF 21a and making the air-fuel ratio of the exhaust flowing into the DPF 21a lean, the two types of regeneration operations of regeneration of the NOx trap catalyst 20b and regeneration of the DPF 21a are not performed individually. The energy consumed for regeneration can be greatly reduced and the impact on fuel consumption deterioration can be minimized.
[0067]
Further, according to the present embodiment, when the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst 20b is made rich, the exhaust gas temperature is controlled so that the exhaust gas temperature at the inlet of the DPF 21a can be regenerated (PM) The combustible temperature) can ensure the regeneration of the DPF 21a.
Further, according to the present embodiment, since the oxidation catalyst 20a is provided in the upstream exhaust passage of the NOx trap catalyst 21b and oxidizes the inflowing exhaust component, the oxidation heat of the oxidation catalyst 20a can be used. In order to enrich the exhaust air-fuel ratio, when the HC and CO exhausted from the engine are increased, the temperature of the exhaust gas is controlled because combustion occurs due to the catalytic reaction with O2 and the temperature further increases. In this case, the exhaust temperature can be kept low, thereby reducing the energy consumption for regeneration and minimizing the influence on the deterioration of fuel consumption. And, the high temperature exhaust gas flows into the NOx trap catalyst 20b with almost no O2 and much unburned component as a reducing agent, which is the same as when the engine is burned in a richer state than the theoretical mixing ratio. As a result, regeneration of the NOx trap catalyst 20b is also promoted.
[0068]
Further, according to the present embodiment, the temperature at which the DPF 21a can be regenerated (the temperature at which PM can be combusted) can be lowered to about 450 ° C. by supporting the catalyst on the DPF 21a to have an oxidation function. When controlling the exhaust temperature, this exhaust temperature can be kept low (especially when combined with an oxidation catalyst upstream of the NOx trap catalyst, it can be lowered to about 250 ° C.). As a result, the energy consumption spent for regeneration can be reduced, the influence on the deterioration of fuel consumption can be minimized, and the regeneration of the DPF 21a can be made more reliable.
[0069]
Further, according to the present embodiment, the post-injection is performed in order to make the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst 20b rich, so that the fuel injection device capable of post-injection (common rail fuel injection device) ), And there is no need to provide a special device.
Further, according to the present embodiment, at least one of the post-injection injection amount, the injection period, the injection start timing, and the air supply air amount is set according to the operating state (engine load, engine speed). Therefore, it is possible to enrich and lean the exhaust air / fuel ratio suitable for the operating state.
[0070]
In addition, according to the present embodiment, the air introduction passage 8 for supplying air to the upstream exhaust passage of the DPF 21a communicates with the intake passage 2 downstream of the intake compressor 2b of the supercharger. Using the supercharging pressure, it is possible to reliably supply air to the exhaust passage, which can be carried out without providing an electric air pump or the like for supplying air.
[0071]
Next, a second embodiment of the present invention will be described.
Diesel engines in recent years have adopted technologies such as electronically controlled EGR and fuel injection control technology, supercharger mounting, or common rail fuel injection systems, and have made significant progress in purifying exhaust and improving fuel efficiency. Therefore, the exhaust gas temperature characteristic tends to decrease as the combustion efficiency improves.
[0072]
For this reason, in a recent diesel engine, the engine operating region is divided into regions A1 to A3 as shown in FIG.
[Area A1]
It is a normal operation region where the operation frequency is high, and most regions are operated at a low exhaust temperature of 250 ° C. or less. Further, in recent diesel engines, NOx is reduced by EGR in this region.
[0073]
[Area A2]
It is an area where emphasis is placed on improving the output characteristics without discharging smoke. In recent diesel engines, a turbocharger is installed, and the air filling rate is increased by adopting 4-valve technology etc. It has been. Moreover, EGR is small and it stops at a high load. Of course, the exhaust gas temperature is higher than that in the region A1.
[0074]
[Area A3]
This is an area where emphasis is placed on increasing torque in order to improve start acceleration performance, and the maximum allowable fuel is supplied to the engine in a range below the level where smoke is not visible. In general, the air filling efficiency is relatively low at a low rotation, and the efficiency of the supercharger is also relatively low. As in the region A2, the EGR is stopped at a high load, and the exhaust temperature is relatively high.
[0075]
In the first embodiment (the post-processing system regeneration control routine in FIG. 7), the enrichment of the exhaust air-fuel ratio for the regeneration of the post-processing system is performed by post-injection regardless of the operation region.
However, as described above, the region A1 is a normal operation region with a low load, and even if EGR is performed, the excess air ratio is relatively large (λ = about 3 to 5). In order to enrich the exhaust air-fuel ratio by performing post-injection in such a low-load operating region, it is necessary to post-inject fuel that is twice to four times the amount of main injection fuel, and for a short time (time Even if the ratio is about 1 to 2%), the fuel consumption deterioration rate increases.
[0076]
For this reason, in this region A1, post-injection is preferably performed in combination with EGR enhancement (reduction of the intake throttle valve opening, increase of the EGR valve opening) in order to assist the enrichment of the exhaust air-fuel ratio. The NOx release / reduction reaction is improved by the exhaust gas temperature increase due to the reduction in the intake air amount due to the throttle and the gas amount passing through the catalyst (SV ratio decrease).
[0077]
It should be noted that, when the EGR is strengthened, it is desirable that the EGR is naturally performed in a range where compression ignition is established (EGR strengthening that does not cause misfire). If this level of EGR strengthening is performed, the region A1 has a large excess air ratio. Since dry soot containing carbon as a main component does not increase and gas components that can be treated with a catalyst such as HC and CO increase, it is convenient for post-treatment.
[0078]
Regions A2 and A3 are regions with a relatively high load, and the excess air ratio is relatively small (approximately λ = 1.5 to 3). Therefore, the post-injection amount required to enrich the exhaust air-fuel ratio by performing post-injection can be dealt with by injecting fuel in an amount about 0.5 to at most twice the amount of main injection fuel. The fuel consumption deterioration rate can be relatively small.
[0079]
In addition, since the excess air ratio is relatively small, dry soot (smoke) containing carbon as a main component increases drastically when EGR is performed. become. Therefore, it is preferable to enrich the exhaust air-fuel ratio by post injection in the regions A2 and A3.
Therefore, in the second embodiment of the present invention, the regeneration control (air-fuel ratio enrichment) method is changed according to the operating state (region A1, regions A2, A3).
[0080]
The system configuration of the second embodiment is the same as that of the first embodiment (FIG. 1). However, in the second embodiment, the intake throttle valve 7 and the EGR valve 5 flow into the NOx trap catalyst 20b in addition to the post-injection common rail fuel injection device 10 that injects a small amount of fuel after the main injection. An air-fuel ratio control device capable of controlling the air-fuel ratio of exhaust gas is configured.
[0081]
The control flow of the second embodiment includes the flow of FIGS. 2 to 6 (common to the first embodiment) and the flow of FIG. 8 executed in place of the flow of FIG.
FIG. 8 is a subroutine relating to regeneration control of the post-processing system in the second embodiment, and is executed in step 700 of the main routine of FIG. 2 instead of the subroutine of FIG. In FIG. 8, the functional parts similar to those in FIG. 7 will be described briefly.
[0082]
In the post-processing system regeneration control routine of FIG. 8, in step 711, it is determined whether or not a predetermined regeneration operation of the post-processing system has ended, from the passage of time as an index value.
If the determination in step 711 is NO and the reproduction has not ended, the process proceeds to step 712.
[0083]
In step 712, the operation region is determined. That is, based on the engine speed Ne and the main fuel injection amount (load) Qmain, is the normal operation region of the region A1 as shown in FIG. 10 or the other operation regions (regions A2, A3)? Determine. And if it is the normal operation area | region of area | region A1, it will progress to step 713.
In step 713, EGR reinforcement data (driving signals for the intake throttle valve 7 and the EGR valve 5) for assisting the enrichment of the exhaust air-fuel ratio is operated, and the engine speed Ne and the main fuel injection amount (load) Qmain are operated. As a state parameter, a predetermined map stored in advance in the ROM in the control unit 30 is searched for and obtained. Then, the process proceeds to step 714, where the intake throttle valve 7 and the EGR valve 5 are driven and controlled based on the respective drive signals, the EGR is strengthened to assist the enrichment of the exhaust air / fuel ratio, and the process proceeds to step 715.
[0084]
In step 715, post injection data (post injection amount Qpost1, post injection period Pperiod1, post injection start timing Pstart1) for regenerating the NOx trap catalyst 20b (enriching the exhaust air / fuel ratio) in the region A1 is stored in a predetermined map. Search from and ask. Then, the process proceeds to step 716, and the fuel injection valve 15 of the cylinder to be post-injected is opened for a period of Pperiod1 from the post-injection start timing Pstart1 so that the post-injection amount Qpost1 is supplied.
[0085]
In step 717, feedback control of post injection (Qpost1) is performed based on the signal (T1) of the exhaust temperature sensor 36 at the inlet of the NOx trap catalyst 20b (outlet of the oxidation catalyst 20a).
After the basic exhaust condition necessary for regeneration of the aftertreatment system is secured in step 717, the process proceeds to step 718.
[0086]
In step 718, data relating to air supply for regenerating the DPF 21a in the region A1 (lean the exhaust air / fuel ratio flowing into the DPF 21a), that is, the air amount Qair1 supplied to the DPF 21a is searched from a predetermined map. In step 719, the on-off valve 9 is driven to open so that the air amount Qair1 is supplied.
[0087]
In step 720, feedback control of air supply (Qair1) is performed on the basis of the signal (T2) of the exhaust temperature sensor 37 at the inlet of the DPF 21a and the signal (O2) of the oxygen concentration sensor 38, and the DPF 21a in the region A1. The exhaust condition suitable for performing the regeneration is ensured, and a return is made.
If it is determined in step 712 that the vehicle is not in the normal operation region (in the case of regions A2 and A3), EGR reinforcement is not performed and the process proceeds to step 721.
[0088]
In step 721, post injection data (post injection amount Qpost2, post injection period Pperiod2, post injection start timing Pstart2) for regenerating the NOx trap catalyst 20b in the regions A2 and A3 (enriching the exhaust air-fuel ratio) Search from the map. In step 722, the fuel injection valve 15 of the cylinder to be post-injected is opened for a period of Pperiod2 from the post injection start timing Pstart2 so that the post injection amount Qpost2 is supplied.
[0089]
In step 723, feedback control of post injection (Qpost2) is performed based on the signal (T1) of the exhaust temperature sensor 36 at the inlet of the NOx trap catalyst 20b (outlet of the oxidation catalyst 20a).
After the basic exhaust condition necessary for regeneration of the aftertreatment system is secured in step 723, the process proceeds to step 724.
[0090]
In step 724, data related to air supply for regenerating the DPF 21a in the regions A1 and A2 (lean the exhaust air-fuel ratio flowing into the DPF 21a), that is, the air amount Qair2 supplied to the DPF 21a is searched from a predetermined map. Ask. In step 725, the on-off valve 9 is driven to open so that the air amount Qair2 is supplied.
[0091]
Then, the process proceeds to step 726, where feedback control of air supply (Qair2) is performed based on the signal (T2) of the exhaust temperature sensor 37 at the inlet of the DPF 21a and the signal (O2) of the oxygen concentration sensor 38, and the regions A2, A3 As a result, exhaust conditions suitable for regeneration of the DPF 21a are ensured and a return is obtained.
If the determination in step 711 is YES and it is determined that the predetermined playback operation has ended, the process proceeds to step 727. In step 727, the regeneration control of the post-processing system is initialized. That is, the post injection is stopped, the EGR reinforcement is stopped, the air supply is stopped, the regeneration flag, the NOx trap amount integrated value, and the regeneration time count are reset to 0, respectively, and the process returns.
[0092]
In particular, according to the present embodiment, in order to make the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst rich, the intake throttle valve opening decreases when the load is low (low load and low rotation), and In addition, at least one of the EGR valve opening increases (EGR strengthening) and post-injection is performed, and at high load (high load high rotation or medium-load medium rotation or more), only post injection is performed. A post-injectable fuel injection device (common rail fuel injection device), an intake throttle valve, and an EGR valve can be used, and there is no need to provide a special device. Since the exhaust air-fuel ratio can be enriched and energy consumption for regeneration can be further saved, the influence on the deterioration of fuel consumption can be further reduced.
[0093]
According to the present embodiment, at least one of the post-injection injection amount, the injection period, the injection start timing, and the air supply air amount is set according to the operating state (engine load, engine speed). In particular, since the EGR strengthening region and the other region are set separately, post injection and air supply suitable for the operating state can be set, and there is no waste and the post-processing system can be regenerated with high efficiency.
[0094]
In the above, the case where the present invention is applied to an engine arranged in series has been described. However, the exhaust emission control device of the present invention is applicable not only to an engine arranged in series but also to a 6-cylinder or 8-cylinder engine arranged in V-shape. it can.
Moreover, although embodiment shows the example of the engine with a supercharger, a naturally aspirated engine may be sufficient. However, in the case of a naturally aspirated engine, it is desirable to provide an electric air pump or the like for air supply because the supercharging pressure of the intake compressor cannot be used when supplying air to the exhaust system.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an aftertreatment system for exhaust gas purification according to a first embodiment of the present invention.
FIG. 2 is a flowchart of an engine output control routine.
FIG. 3 is a flowchart of a common rail pressure control routine.
FIG. 4 is a flowchart of a main injection control routine
FIG. 5 is a flowchart of an engine combustion control routine.
FIG. 6 is a flowchart of a NOx trap amount integration / determination routine.
FIG. 7 is a flowchart of a post-processing system regeneration control routine in the first embodiment.
FIG. 8 is a flowchart of a post-processing system regeneration control routine in the second embodiment.
FIG. 9 is a characteristic diagram of the fuel injection amount according to the common rail pressure and the fuel injection period.
[Fig. 10] Characteristic chart of operation area
[Explanation of symbols]
1 engine
2 Intake passage
3 Exhaust passage
4 EGR passage
5 EGR valve
7 Inlet throttle valve
8 Air introduction passage
9 On-off valve
10 Fuel injector
11 Supply pump
14 Common rail
15 Fuel injection valve
20a oxidation catalyst
20b NOx trap catalyst
21a DPF with oxidation function
30 Control unit

Claims (8)

A NOx trap catalyst that is disposed in the exhaust passage of the engine and traps NOx when the air-fuel ratio of the inflowing exhaust is lean, and reduces and purifies NOx trapped when the air-fuel ratio of the inflowing exhaust is rich;
A PM trap that is disposed in an exhaust passage downstream of the NOx trap catalyst and traps PM in inflowing exhaust gas;
An air-fuel ratio control device capable of controlling the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst;
An air supply device capable of supplying air to the upstream exhaust passage of the PM trap;
Regeneration timing determination means for determining the regeneration timing of the NOx trap catalyst;
At the regeneration timing of the NOx trap catalyst, the air-fuel ratio control device makes the air-fuel ratio of the exhaust flowing into the NOx trap catalyst rich, and the air supply device supplies air to the upstream exhaust passage of the PM trap. Regeneration control means for leaning the air-fuel ratio of the exhaust gas supplied and flowing into the PM trap;
An exhaust emission control device for an internal combustion engine, comprising: The regeneration control means controls the temperature of the exhaust when making the air-fuel ratio of the exhaust flowing into the NOx trap catalyst rich so that the exhaust temperature at the PM trap inlet becomes a temperature at which the PM trap can be regenerated. 2. An exhaust emission control device for an internal combustion engine according to claim 1, wherein: The exhaust purification device for an internal combustion engine according to claim 2, further comprising an oxidation catalyst that is disposed in an upstream exhaust passage of the NOx trap catalyst and that oxidizes inflowing exhaust components. The exhaust purification device for an internal combustion engine according to claim 2 or 3, wherein the PM trap has an oxidation function. The air-fuel ratio control device includes a fuel injection device capable of post injection that injects a small amount of fuel after main injection,
The internal combustion engine according to any one of claims 1 to 4, wherein the regeneration control means performs post-injection in order to make the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst rich. Exhaust purification device. The air-fuel ratio control device includes a post-injection fuel injection device that injects a small amount of fuel after main injection, an intake throttle valve that can control the intake air amount, and an EGR that can control the exhaust gas recirculation amount to the intake passage. With a valve,
In order to enrich the air-fuel ratio of the exhaust gas flowing into the NOx trap catalyst, the regeneration control means reduces the intake throttle valve opening and increases the EGR valve opening when the load is low, depending on the operating state. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein at least one of them is performed, post injection is performed, and only post injection is performed at high load. . 6. The regeneration control means sets at least one of an injection amount of the post injection, an injection period, an injection start timing, and an air amount of the air supply according to an operating state. Or the exhaust gas purification apparatus of the internal combustion engine of Claim 6. 8. The air supply device according to claim 1, wherein an air introduction passage for supplying air to an upstream exhaust passage of the PM trap communicates with an intake passage downstream of the intake compressor. An exhaust emission control device for an internal combustion engine according to claim 1.

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