JP2004052611A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow the recovery of NOx trapping catalysts 22a, 22b and an exhaust particulate trap 23a while avoiding crack or fusion of the exhaust particulate trap 23a. <P>SOLUTION: Four cylinders are parted into cylinder groups A, B in which oxidation catalysts 21a, 21b and the NOx trapping catalysts 22a, 22b are arranged, respectively, and the exhaust particulate trap 23a is located downstream of a combination area 3c. When the NOx trapping catalysts 22a, 22b are recovered, post injection is executed in one cylinder group to make an exhaust air-fuel ratio rich but an exhaust air-fuel ratio in the other cylinder group remains lean. The air-fuel ratio of exhaust gas flowing into the exhaust particulate trap 23a becomes lean to allow the combustion of exhaust particulates and at the same time recovery. When the temperature of the exhaust particulate trap 23a becomes high on a sudden, all cylinders are put into a rich condition to reduce the amount of oxygen in the exhaust gas and suppress the combustion of the exhaust particulates in the exhaust particulate trap 23a. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine represented by a diesel engine, which is provided with an exhaust particulate trap for trapping exhaust particulates, and more particularly to a technique for preventing cracking and melting during regeneration.
[0002]
[Prior art]
For example, in a diesel engine as an internal combustion engine, treatment of exhaust particulates (so-called PM) in exhaust gas has become a major problem. An exhaust particulate trap is disposed in an exhaust passage to collect exhaust particulates, and the collected exhaust particulates are collected. Various exhaust purifying apparatuses have been studied in which exhaust particulates are regenerated by burning and removing exhaust particulates when the particulates reach a predetermined level.
[0003]
In Japanese Patent Application Laid-Open No. 2001-254616, if it is necessary to regenerate the exhaust particulate trap by burning and removing the exhaust particulate trapped in the exhaust particulate trap, the fuel must be supplied during the expansion stroke or the exhaust stroke after the end of the main injection. Although post-injection is performed from the injection valve to promote the combustion of exhaust particulates, the temperature of the exhaust particulate trap during regeneration is monitored, and the temperature of the exhaust particulate trap is at or above a predetermined value and the temperature change rate is at or above a predetermined value. If there is, the reproduction operation is stopped.
[0004]
Further, in Japanese Patent Application Laid-Open No. 8-319819, the engine is operated at a high rotation speed and a high load, and the exhaust gas temperature is changed from a state exceeding 600 ° C. to an operating state in which rapid combustion of exhaust particulates such as idling occurs. In such a case, an excessive increase in temperature is avoided by increasing the EGR more than usual.
[0005]
[Problems to be solved by the invention]
However, even if the post-injection is stopped and the regeneration operation is stopped when the temperature of the exhaust particulate trap is equal to or higher than the predetermined value and the temperature change rate is equal to or higher than the predetermined value, as in JP-A-2001-254616 described above, Although the temperature of the exhaust gas flowing into the exhaust particulate trap decreases, the exhaust air-fuel ratio increases, and conversely, the oxygen concentration that promotes the combustion of the exhaust particulate increases. Therefore, the reburning of the once-ignited exhaust particles cannot be stopped, and the reburning of the exhaust particles continues. There is a possibility that the temperature will be locally high. Therefore, cracking and melting of the exhaust particulate trap cannot be sufficiently prevented.
[0006]
Further, according to the technique disclosed in Japanese Patent Application Laid-Open No. 8-319819, when the operation state changes to a state where rapid combustion of the exhaust particulates occurs, the EGR is increased from the normal state. At first glance, it seems that increasing the EGR to reduce the oxygen concentration seems to suppress the reburning of the exhaust particulates. However, actually, increasing the EGR increases the exhaust temperature and increases the exhaust gas from the exhaust system. The removal of the EGR gas reduces the flow rate of the exhaust gas flowing into the exhaust particulate trap and reduces the amount of heat taken out of the exhaust particulate trap, and consequently creates a condition in which the temperature of the exhaust particulate trap tends to increase due to the combustion of the exhaust particulate. Therefore, similarly to Japanese Patent Application Laid-Open No. 2001-254616, it is not possible to sufficiently prevent the exhaust particulate trap from cracking or melting.
[0007]
[Means for Solving the Problems]
In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, an oxidation catalyst for oxidizing and purifying an inflowing exhaust component is disposed in an exhaust passage of the internal combustion engine, and an exhaust particle trap for trapping an inflowing exhaust particle further downstream thereof. Is arranged. It should be noted that a NOx trap catalyst may be further disposed between the oxidation catalyst and the exhaust particulate trap, and in this case, the oxidation catalyst can be integrated with the NOx trap catalyst.
[0008]
Further, according to the present invention, there is provided a temperature detecting means for detecting a temperature of the exhaust particulate trap, a combustion speed detecting means for detecting a burning rate of the exhaust particulate trapped in the exhaust particulate trap, and injecting fuel in an expansion stroke or an exhaust stroke. Fuel injection means for enabling the post injection to be performed. And an exhaust air-fuel ratio control unit for enriching the exhaust air-fuel ratio by the post-injection when the temperature of the exhaust particulate trap exceeds a predetermined temperature, and when the burning speed of the exhaust particulate exceeds the predetermined speed. I have.
[0009]
When the exhaust air-fuel ratio becomes rich by the post-injection as described above, the oxygen in the exhaust gas discharged from the internal combustion engine reacts with the unburned HC and CO generated by the post-injection by the oxidation catalyst, and the exhaust particulate trap. The amount of oxygen in the exhaust gas flowing into the exhaust gas (oxygen concentration in the exhaust gas) becomes substantially zero. Therefore, combustion of the exhaust particulates is stopped, and an excessive rise in temperature of the exhaust particulate trap is suppressed.
[0010]
Further, as the exhaust air-fuel ratio control means, in addition to the post-injection, means for reducing the intake air amount to the internal combustion engine and increasing the exhaust gas recirculation amount can be used.
[0011]
【The invention's effect】
According to the present invention, regardless of the presence or absence of the regeneration operation of the exhaust particulate trap, a change in exhaust conditions such that ignition combustion of the exhaust particulate collected in the exhaust particulate trap is started and reburning of the exhaust particulate proceeds rapidly. Even when such a situation occurs, the combustion speed of the exhaust particulates can be reliably suppressed to prevent the exhaust particulate trap temperature from rising rapidly. Therefore, cracking and melting of the exhaust particulate trap can be reliably prevented.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 is a system configuration diagram of an exhaust gas purification apparatus according to a first embodiment of the present invention.
[0014]
In FIG. 1, reference numeral 1 denotes a diesel engine (hereinafter simply referred to as an engine), and reference numeral 3 denotes an exhaust passage of the engine 1.
[0015]
The present embodiment is an example in which the present invention is applied to an engine 1 having four cylinders # 1 to # 4 and a four-cylinder in-line arrangement in which the ignition order is # 1- # 3- # 4- # 2. The four cylinders are divided into a cylinder group A consisting of # 2 cylinders and # 3 cylinders and a cylinder group B consisting of # 1 cylinders and # 4 cylinders so that the ignition order is not continuous. Are connected on the upstream side.
[0016]
The reason why the cylinder group is divided into the cylinder group A composed of # 2 and # 3 cylinders and the cylinder group B composed of # 1 and # 4 cylinders is that the exhaust efficiency is reduced due to interference in the exhaust stroke. This is because a reduction in the air charging efficiency is suppressed. When the layout of the exhaust system is prioritized, the cylinder group A is set to the # 1 and # 2 cylinders, and the cylinder group B is set to the # 3 and # 4 cylinders. It can also be.
[0017]
In addition, for example, when considering the suppression of exhaust interference in a six-cylinder in-line engine whose ignition order is # 1- # 5- # 3- # 6- # 2- # 4, the cylinder groups A are set to # 1 and # 2. , # 3 cylinders, and cylinder group B is # 4, # 5, # 6 cylinders. In the present invention, the “cylinder group” includes one or more cylinders, and does not necessarily include a plurality of cylinders.
[0018]
The upstream portion of the exhaust passage 3 connected to the exhaust port of the engine 1 is divided into two systems, an exhaust passage 3a and an exhaust passage 3b. The exhaust port of the cylinder group A is connected to the exhaust passage 3a, An exhaust port is connected to the exhaust passage 3b. The two passages 3a and 3b merge with each other at a downstream junction 3c. The upstream portions of the passages 3a and 3b are configured as a pair of exhaust pipes each corresponding to the number of cylinders.
[0019]
A first catalyst casing 20a is interposed in the exhaust passage 3a corresponding to the cylinder group A. Inside the first catalyst casing 20a, a first oxidation catalyst 21a for oxidizing and purifying an inflowing exhaust component, and absorbing NOx when the inflowing exhaust gas has a lean exhaust air-fuel ratio, and removing the inflowing exhaust gas. A first NOx trap catalyst 22a that releases NOx when the oxygen concentration is reduced is arranged in order. That is, the oxidation catalyst 21a is located upstream of the NOx trap catalyst 22a. Similarly, a second catalyst casing 20b is interposed in the exhaust passage 3b corresponding to the cylinder group B, in which a second oxidation catalyst 21b and a second NOx trap catalyst 22b are provided. They are arranged in order.
[0020]
In addition, the two passages 3a and 3b join at a junction 3c downstream of the first catalyst casing 20a and the second catalyst casing 20b, but the turbine of the turbocharger is located immediately downstream of the junction 3c. 3d is connected. Then, downstream of the turbine 3d, a casing 23 having an exhaust particulate trap 23a therein is arranged in series.
[0021]
Examples of the above-mentioned oxidation catalysts 21a and 21b include those in which a noble metal such as Pd or Pt is supported on an active alumina base, those in which a noble metal such as Pd or Pt and a zeolite are mixed and supported on an active alumina base, or a noble metal. Zeolite obtained by ion-exchanging (particularly, Pt) or a combination of these materials can be used.
[0022]
Further, as the exhaust particulate trap 23a, a well-known wall flow honeycomb type, a ceramic core wound around a core member having a bottomed cylindrical shape having a large number of holes in a cylindrical portion, and a number of layers of ceramic fibers wound thereon, etc. It is desirable to carry the above-mentioned oxidation catalyst on the surface of the exhaust particle trap 23a in order to promote the reburning of the collected exhaust particles.
[0023]
At the inlets of the NOx trap catalysts 22a and 22b, exhaust temperature sensors 36a and 36b for detecting exhaust temperatures (T1a and T1b) at the inlets (outlets of the oxidation catalysts 21a and 21b) are provided, respectively. ing. An exhaust pressure sensor 38 for detecting the exhaust pressure P1 is provided at the inlet of the exhaust particulate trap 23a, and an exhaust temperature sensor 37 for detecting the exhaust temperature T2 is provided at the outlet.
[0024]
An EGR passage 4 for recirculating a part of the exhaust gas is provided between the intake collector 2c and the exhaust passage 3b of the intake passage 2, and the opening thereof can be continuously and variably controlled by a stepping motor. An EGR valve 5 is interposed. The opening of the EGR valve 5 is controlled by the engine control unit 30.
[0025]
The intake passage 2 includes an air cleaner 2a at an upstream position, and a compressor 2b of a supercharger is disposed downstream thereof. An intake throttle valve 6 driven to be opened and closed by an actuator (for example, a stepping motor type) is disposed upstream of the intake collector 2c. The opening degree of the intake throttle valve 6 is controlled by the engine control unit 30.
[0026]
The EGR and the intake throttle valve 6 correspond to “air amount control means” in claim 3.
[0027]
The fuel supply system of the engine 1 includes a fuel tank 60 for storing light oil as a diesel fuel, a fuel supply passage 16 for supplying fuel to the fuel injection device 10 of the engine 1, and a fuel supply passage 16 from the fuel injection device 10 of the engine 1. And a fuel return passage 19 for returning return fuel (spill fuel) to the fuel tank 60.
[0028]
The fuel injection device 10 of the engine 1 is a well-known common rail type fuel injection device, and generally includes a supply pump 11, a common rail (accumulation chamber) 14, and a fuel injection valve 15 provided for each cylinder. After the fuel pressurized by the supply pump 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 valve 15 of each cylinder.
[0029]
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 via an overflow passage 17 provided with a one-way valve 18. Specifically, a pressure control valve 13 that changes the flow area of the overflow passage 17 is provided, and the pressure control valve 13 changes the flow area of the overflow passage 17 according to a duty signal from the control unit 30. Thereby, the substantial fuel discharge amount from the supply pump 11 to the common rail 14 is adjusted, and the pressure of the common rail 14 is controlled.
[0030]
The fuel injection valve 15 is an electronic injection valve that is opened and closed by an ON-OFF signal from the engine control unit 30. The fuel injection valve 15 injects fuel into the combustion chamber by an ON signal, and stops the injection by an OFF signal. The fuel injection amount increases as the period of the ON signal applied to the fuel injection valve 15 increases, and the fuel injection amount increases as the fuel pressure of the common rail 14 increases. The injection period of the fuel injection valve 15, that is, the period of the ON signal, and the fuel pressure of the common rail 14 are controlled by the engine control unit 30.
[0031]
The engine control unit 30 receives a signal from a water temperature sensor 31 (water temperature Tw), a signal from a crank angle sensor 32 for detecting a crank angle (a crank angle signal serving as a basis for the engine speed Ne), and a signal from a crank angle sensor 33 for determining a cylinder. (Cylinder discrimination signal Cyl), a signal of a pressure sensor 34 for detecting the pressure of the common rail 14 (common rail pressure PCR), and a signal of an accelerator opening sensor 35 for detecting the depression amount of an accelerator pedal corresponding to the load (the accelerator opening (load) ) L) are input. Further, the signals (T1a, T1b) of the exhaust temperature sensors 36a, 36b at the inlets of the NOx trap catalysts 22a, 22b, the signal (T2) of the exhaust temperature sensor 37 at the outlet of the exhaust particulate trap 23a, the exhaust particulate trap 23a The signal (P1) of the exhaust pressure sensor 38 for detecting the exhaust pressure at the inlet of the air conditioner is also input.
[0032]
Next, the content of the control of the exhaust gas purification device executed by the engine control unit 30 will be described based on the flowcharts of FIGS.
[0033]
FIG. 3 is a basic control routine for controlling the entire diesel engine 1.
[0034]
In this engine basic control routine, at step 100, the water temperature Tw, the engine speed Ne, the cylinder discrimination signal Cyl, the common rail pressure PCR, the accelerator opening (load) L, the outlet of the first oxidation catalyst 21a (the first NOx) The exhaust temperature T1a at the inlet of the trap catalyst 22a), the exhaust temperature T1b at the outlet of the second oxidation catalyst 21b (the inlet of the second NOx trap catalyst 22b), the exhaust pressure P1 at the inlet of the exhaust particulate trap 23a, and The exhaust temperature T2 at the outlet is read, and the process proceeds to step 200.
[0035]
In step 200, common rail fuel injection control (main rail pressure control and main injection control for engine output control) is performed. In the present invention, the common rail fuel injection control itself is not a main part, and therefore will be briefly described.
[0036]
In the common rail fuel injection control, a predetermined map stored in the ROM of the control unit 30 is searched using the engine speed Ne and the main fuel injection amount (preset in correspondence with the load L) Qmain as parameters. Then, the target reference pressure PCR0 of the common rail 14 is obtained, and the feedback control of the pressure control valve 13 is executed so as to obtain the target reference pressure PCR0.
[0037]
Then, a predetermined map stored in the ROM of the control unit 30 is searched using the main fuel injection amount Qmain and the common rail pressure PCR as parameters so as to obtain the main fuel injection amount Qmain, and the main injection start timing Mstart And the main injection period Mperiod (msec) are obtained, and the main injection is performed based on the crank angle signal (Ne) of the crank angle sensor 32 for detecting the crank angle and the cylinder determination signal (Cyl) of the crank angle sensor 33 for determining the cylinder. During the period from the start timing Mstart to Mperiod, the fuel injection valve 15 of the cylinder to be main-injected is driven to open.
[0038]
If the required main fuel injection amount Qmain is the same, the higher the common rail pressure PCR, the shorter the main injection period Mperiod. If the common rail pressure PCR is the same, the larger the required main fuel injection amount Qmain, the longer the main injection period Mperiod. Becomes longer.
[0039]
Further, for example, when the cooling water temperature is low, the ignition start timing is relatively delayed, so that the main injection start timing Mstart is advanced and the combustion start is corrected so as not to increase the emissions of HC, CO and exhaust particulates (especially SOF). Controls such as keeping the timing constant are also performed.
[0040]
Then, the routine proceeds to step 300, where the protection judgment of the exhaust particulate trap 23a is performed. In other words, in a situation where the ignition and combustion of the exhaust particulates trapped in the exhaust particulate trap 23a are started and the reburning of the exhaust particulates proceeds rapidly, unless the combustion speed of the exhaust particulates is suppressed, the exhaust particulate trap 23a It is determined whether or not it is necessary to protect the exhaust particulate trap 23a because the temperature of the exhaust particulate trap 23a may be broken or melted due to a rapid rise in temperature. In the flowchart, "DPF" means "exhaust particulate trap", and "PM" means "exhaust particulate". As will be described later, if protection is required, the DPF protection flag is set to 1.
[0041]
Then, the process proceeds to a step 400, wherein it is determined whether or not the DPF protection flag is 1 and the protection of the exhaust particulate trap 23a is necessary.
[0042]
If Yes in step 400 and the situation requires protection of the exhaust particulate trap 23a, the process proceeds to step 2000, where the protection control of the exhaust particulate trap 23a is continued or started, and the process returns.
[0043]
If No in step 400 and the situation does not require the protection of the exhaust particulate trap 23a, the process proceeds to step 500, where the after-treatment system (the NOx trap catalysts 22a and 22b requiring regeneration and the exhaust particulate trap 23a are combined, It is determined whether the reproduction flag indicating the reproduction control of the post-processing system is 1 or not, that is, whether or not the reproduction of the post-processing system is necessary.
[0044]
If Yes in step 500, indicating that the post-processing system needs to be reproduced, the process proceeds to step 1000, where the reproduction control of the post-processing system is continued or started, and the process returns.
[0045]
However, even if the regeneration control of the post-processing system is being performed, the regeneration of the post-processing system is interrupted if it is determined in step 400 that the protection of the exhaust particulate trap 23a is necessary.
[0046]
If No in step 500 and the regeneration of the post-processing system is not necessary, the engine exhaust basic control is performed in step 600, the PM trap limit of the exhaust particulate trap 23a is determined in step 700, and the NOx trap is determined in step 800. The regeneration of the catalyst (the first NOx trap catalyst 22a and the second NOx trap catalyst 22b) is determined, and the process returns.
[0047]
FIG. 4 is a subroutine relating to the determination of protection of the exhaust particulate trap 23a performed in step 300 of FIG.
[0048]
In the DPF protection determination routine shown in FIG. 4, in step 310, the exhaust gas temperature T2 at the outlet of the exhaust particulate trap 23a (this is representative of the temperature of the exhaust particulate trap 23a) is changed to the level of the exhaust particulate trapped by the exhaust particulate trap 23a. It is determined whether the temperature exceeds a first predetermined temperature at which combustion is actively performed (for example, 500 ° C. in an exhaust particulate trap with an oxidation catalyst). In the case of the exhaust particulate trap with an oxidation catalyst, the combustion of the exhaust particulates starts at about 400 ° C. or higher. However, at such a temperature, the combustion is not active and there is no possibility of cracking or melting.
[0049]
If the determination in step 310 is No, the process proceeds to step 360 to set the DPF protection flag to 0, and returns to the basic control routine via steps 370 and 380 described later.
[0050]
If the determination in step 310 is Yes, the process proceeds to step 320, where the rate of increase in the exhaust gas temperature T2 at the outlet of the exhaust particulate trap 23a (dT2 / dTime: the rate of increase in the exhaust gas temperature T2 at the outlet of the exhaust particulate trap 23a per unit time) ) Exceeds a predetermined value (for example, a rise of 50 ° C. or more in one second up to the present time).
[0051]
If the determination in step 320 is No, the process proceeds to step 360 to set the DPF protection flag to 0, and returns to the basic control routine via steps 370 and 380 described later.
[0052]
If the determination in step 320 is Yes, the process proceeds to step 330 to determine whether or not the post-processing system regeneration flag is 1, that is, whether or not the regeneration control of the post-processing system is started or continued. Is determined.
[0053]
If the determination in step 330 is No, step 340 is skipped and the process proceeds to step 350. If Yes in step 330, that is, if the reproduction control of the post-processing system is being performed, the reproduction control of the post-processing system is temporarily suspended as described in the basic control routine. Then, the counting of various index values for the regeneration control of the post-processing system (regeneration index values of the exhaust particulate trap 23a and the NOx trap catalysts 22a and 22b, the exhaust air-fuel ratio enrichment time, etc.) is temporarily stopped, and the routine proceeds to step 350.
[0054]
Then, in step 350, the DPF protection flag is set to 1 and the process returns to the basic control routine.
[0055]
In step 370, it is determined whether or not the post-processing system reproduction flag is 1. If the flag is 1, the reproduction control of the post-processing system is being performed. The counting of the index value of the reproduction control of the system is restarted.
[0056]
FIG. 5 is a subroutine relating to the engine exhaust basic control performed in step 600 of FIG. 3 described above. In order to obtain a predetermined engine exhaust emission performance, a predetermined EGR control corresponding to the operating region of the engine is performed. Do.
[0057]
In step 610, it is determined whether or not the engine is in an operation range in which EGR is to be performed, based on the engine speed Ne and the main fuel injection amount Qmain. In other words, the operating frequency is high and the excess air ratio is relatively large, so that the exhaust gas is in a normal operating region where other exhaust components and fuel efficiency do not deteriorate even if NOx is reduced by performing EGR. It is determined whether or not the area is where an increase in the amount of exhaust particulate emissions or a decrease in output occurs.
[0058]
Then, if it is in the EGR region in step 610, the process proceeds to step 620, and if it is not in the EGR region, the process proceeds to step 650.
[0059]
In step 650, EGR is stopped or stopped. That is, the EGR valve 5 is closed, and the intake throttle valve 7 is kept open.
[0060]
In step 620, target EGR data for executing EGR (that is, drive signals of the EGR valve 5 and the intake throttle valve 7) is stored in the ROM of the control unit 30 using the engine speed Ne and the main fuel injection amount Qmain as parameters. A predetermined map stored in advance is searched for and obtained. Then, in step 630, the target EGR data obtained in step 620 is corrected based on the water temperature Tw. For example, when the cooling water temperature is low, the EGR is corrected to decrease, and the routine proceeds to step 640.
[0061]
That is, the lower the water temperature, the lower the temperature of the engine combustion chamber, so that the ignition start timing is relatively delayed. Therefore, in order not to increase the emissions of HC, CO, and exhaust particulates (especially, SOF), it is desirable to reduce the EGR and maintain the combustion start timing constant.
[0062]
In step 640, the EGR valve 5 and the intake throttle valve 7 are driven and controlled based on the respective drive signal values after the water temperature correction to perform EGR.
[0063]
FIG. 6 is a subroutine relating to the PM trap limit of the exhaust particulate trap 23a performed in step 700 of FIG. Here, the determination of the limit of the exhaust particulates in the exhaust particulate trap 23a and the necessity of the regeneration are performed.
[0064]
That is, if the exhaust particulate trap 23a cannot be completely regenerated during normal operation, the exhaust particulate trap amount in the exhaust particulate trap 23a gradually increases. It becomes a situation where deterioration of the engine power performance due to the rise cannot be tolerated. Further, when the combustion conditions of the exhaust particulates are met, the amount of heat generated by the reburning of the exhaust particulates becomes excessive, and the exhaust particulate trap 23a is easily burned. Therefore, the exhaust particulate trap limit is set to a level that can prevent such a problem beforehand, and it is determined whether or not the exhaust particulate trap limit has been reached, and the regeneration of the exhaust particulate trap 23a is preferentially performed. It is trying to make it. As will be described later, in this embodiment, the exhaust particulate trap 23a is basically regenerated at the same time as the regeneration of the NOx trap catalysts 22a and 22b, so that the frequency of reaching the exhaust particulate trap limit is relatively low. .
[0065]
In the subroutine of FIG. 6, in step 710, the exhaust particulate trap limit pressure previously obtained by an experiment or the like corresponding to the engine speed Ne and the load L is calculated from predetermined map data stored in the ROM of the control unit 30 in advance. The search proceeds to step 720.
[0066]
In step 720, it is determined whether or not the actual measured value P1 of the exhaust pressure by the exhaust pressure sensor 38 is equal to or higher than the exhaust particulate trap limit pressure in step 710. If No, the process returns to the basic control routine.
[0067]
In step 720, when Yes, that is, when the actual measured value P1 of the exhaust pressure exceeds the exhaust particulate trap limit pressure and the forced regeneration of the exhaust particulate trap 23a is required, the process proceeds to step 730, where the post-processing system regeneration flag is set. To 1. This flag becomes a reproduction start signal of the post-processing system.
[0068]
Then, in step 740, the DPF regeneration flag is set to 1. This DPF regeneration flag serves as a regeneration start signal for the exhaust particulate trap 23a.
[0069]
Then, the process proceeds to step 750, where the counting of the index value (for example, the total time of the regeneration) of the end of the exhaust particulate trap regeneration is started, and the process returns.
[0070]
FIG. 7 is a subroutine relating to the determination of the necessity of regeneration of the NOx trap catalysts 22a and 22b performed in step 800 of FIG.
[0071]
In step 810, the NOx absorption amount (NOx absorption amount per unit time) of the NOx trap catalysts 22a and 22b is stored in the ROM of the control unit 30 using the engine speed Ne and the load L (or the main fuel injection amount Qmain) as parameters. A predetermined map data stored in advance is searched for and obtained.
[0072]
After obtaining the basic NOx absorption amount per unit time in step 810, the process proceeds to step 820, where a correction is made based on the water temperature Tw. Specifically, when the cooling water temperature is low, the NOx absorption amount is reduced and corrected, and the routine proceeds to step 830. This is because the lower the water temperature, the lower the temperature of the engine combustion chamber. Even if the combustion start timing is kept constant, the lower the engine combustion chamber temperature, the longer the combustion period and the lower the combustion temperature. , NOx emissions tend to decrease. Therefore, the NOx absorption amount also decreases.
[0073]
In step 830, the corrected NOx absorption amount per unit time is sequentially integrated at predetermined time intervals synchronized with the unit time, and the process proceeds to step 840.
[0074]
In step 840, it is determined whether or not the integrated NOx absorption amount exceeds a predetermined absorption limit amount set for the NOx trap catalysts 22a and 22b, that is, whether or not regeneration (release and reduction of NOx) is necessary. I do. If the determination in step 840 is No and reproduction is not necessary, the process returns.
[0075]
On the other hand, when the determination in step 840 is Yes, that is, when it is determined that the NOx trap catalysts 22a and 22b need to be regenerated, the post-processing system regeneration flag is set to 1 in step 850. That is, it is a reproduction start signal of the post-processing system.
[0076]
Then, in step 860, the NOx regeneration flag is set to 1. That is, the signal is used as a start signal of the NOx regeneration of the NOx trap catalysts 22a and 22b.
[0077]
Further, the process proceeds to step 870, where the counting of the index value of the end of NOx regeneration (for example, the total time of regeneration) is started, and the process returns.
[0078]
FIG. 8 is a subroutine relating to the regeneration control of the post-processing system (NOx trap catalysts 22a, 22b and exhaust particulate trap 23a) performed in step 1000 of FIG.
[0079]
In step 1010, it is determined whether or not the DPF regeneration flag is 1, that is, whether or not the priority regeneration of the exhaust particulate trap 23a is necessary. If No, that is, if there is no need for priority reproduction, the process proceeds to step 1020. If Yes, that is, if the preferential regeneration of the exhaust particulate trap 23a is necessary, the process proceeds to step 1100 to perform forced regeneration control of the exhaust particulate trap 23a.
[0080]
In step 1020, it is determined whether or not the NOx regeneration flag for the NOx trap catalysts 22a and 22b is 1, that is, whether or not the regeneration of the NOx trap catalysts 22a and 22b is necessary. Here, if No, that is, there is no need to regenerate NOx, the process returns. If Yes, that is, if the regeneration of the NOx trap catalysts 22a and 22b is necessary, the process proceeds to step 1200 to perform NOx trap catalyst regeneration control.
[0081]
FIG. 9 is a subroutine relating to the forced regeneration control of the exhaust particulate trap 23a performed in the above step 1100 (FIG. 8). In this subroutine, it is necessary to forcibly regenerate the exhaust particulate trap 23a. The purpose is to urgently regenerate the exhaust particulate trap 23a in a case (for example, when the amount of exhaust particulates increases due to continuous operation in a place with a low air density such as a highland). For this forced regeneration, the temperature of the exhaust particulate trap 23a is raised to at least about 400 ° C., which is the ignition temperature of the exhaust particulate, assuming that the exhaust particulate trap 23a carries an oxidation catalyst, and is maintained for several minutes. I have to.
[0082]
More specifically, in recent engines, the time required to regenerate the NOx trap catalyst by enriching the exhaust air-fuel ratio needs to be approximately 1 to 2% in terms of the operation frequency (a few seconds per operation). Within). The time required to regenerate the exhaust particulate trap 23a is sufficient if the frequency of operation at a temperature of 400 ° C. or higher is about 2 to 4%, for example, in the case of the catalyst-loaded exhaust particulate trap 23a. It is not necessary to perform a forced temperature increase operation (regeneration operation in a lean state) only for the regeneration of the exhaust particulate trap 23a.
[0083]
However, in a normal operation, the operation frequency at a temperature of 400 ° C. or more is only about 1 to 2%, and a frequency shortage of about 3% at maximum occurs. Therefore, a forced temperature increase operation is required only for the regeneration of the exhaust particulate trap 23a.
[0084]
On the other hand, in the present invention, when the regeneration of the NOx trap catalysts 22a and 22b is carried out, the temperature of the exhaust particulate trap 23a is simultaneously raised to 400 ° C. or more under lean conditions, and the time required for the regeneration of the exhaust particulate trap 23a is increased. I'm trying to get In other words, the regeneration of the NOx trap catalysts 22a and 22b and the regeneration of the exhaust particulate trap 23a in a lean state are not basically performed separately. I am trying to stop it.
[0085]
In the subroutine of FIG. 9, in step 1110, after the regeneration is started, it is determined from the exhaust particulate trap regeneration index value whether the predetermined regeneration of the exhaust particulate trap 23a is completed.
[0086]
As the index value of the end of the exhaust particulate trap regeneration, for example, the total time of the regeneration can be used as described above, but not only the time elapsed since the start of the regeneration, but also the exhaust gas temperature at the outlet of the exhaust particulate trap 23a. Integrating a multiplier of T2 and time, or alternately enriching cylinder group A and cylinder group B at predetermined time intervals to count the total number (or time) of enrichment, or a combination thereof , Etc., and it is desirable to select an optimal method according to the characteristics of the system and the like.
[0087]
If Yes in step 1110, that is, if it is determined that the regeneration of the exhaust particulate trap 23a has been completed, the process proceeds to step 1130 to initialize the exhaust particulate trap regeneration control. That is, post-injection to be described later is stopped, and the post-processing system regeneration flag, the exhaust particulate trap regeneration flag, and the NOx trap catalyst regeneration flag are set to 0. Then, the NOx absorption amount integrated value, the exhaust particulate trap regeneration index value, and the NOx trap catalyst regeneration index value are each reset to 0, and the routine returns.
[0088]
Although the exhaust particulate trap 23a is regenerated, the reason for setting the NOx trap catalyst regeneration flag to 0 and resetting the NOx absorption amount integrated value to 0 is that the exhaust particulate trap 23a is regenerated as described above. For this purpose, it is necessary to increase the temperature of the exhaust particulate trap to at least about 400 ° C., which is the ignition temperature of the exhaust particulate, and maintain the trap for several minutes, assuming that the exhaust particulate trap carries an oxidation catalyst. On the other hand, the enrichment time required for regeneration of the NOx trap catalysts 22a and 22b is a short time of several seconds.
[0089]
Then, in the present embodiment, in the first rich air-fuel ratio adjustment performed by the cylinder group A and the cylinder group B for forced regeneration of the exhaust particulate trap 23a, the temperature target of the exhaust particulate trap 23a is set to 500 ° C. (first predetermined value). The target of the inlet temperature of the NOx trap catalysts 22a and 22b corresponding to the cylinder group to be enriched (necessarily set to a temperature higher than the inlet temperature of the exhaust particulate trap 23a) is set to 600 ° C. , Set to and maintain for several minutes. Therefore, regeneration of the NOx trap catalysts 22a and 22b can be realized at the same time.
[0090]
If No in step 1110, that is, if the regeneration of the exhaust particulate trap 23a has not been completed, the process proceeds to step 1111 to set the target EGR data necessary to assist the first rich air-fuel ratio for regeneration of the exhaust particulate trap 23a. That is, the drive signal Eduty1 of the EGR valve 5 and the drive signal Tduty1 of the intake throttle valve 6 are stored in advance in the ROM of the control unit 30 using the engine speed Ne and the load L (or the main fuel injection amount Qmain) as parameters. A predetermined map is searched and found. Then, the process proceeds to a step 1112, wherein the EGR valve 5 and the intake throttle valve 6 are drive-controlled based on the respective drive signals, and the EGR for assisting the first rich air-fuel ratio is performed. Then, the process proceeds to step 1113.
[0091]
Here, in the first rich air-fuel ratio for regenerating the exhaust particulate trap 23a, the oxidation reaction amount between the unburned fuel component and oxygen in the oxidation catalysts 21a and 21b disposed upstream of the NOx trap catalysts 22a and 22b is determined. Thus, the temperature is promoted by increasing the air-fuel ratio to a second rich air-fuel ratio for NOx regeneration, which will be described later.
[0092]
In order to increase the amount of oxidation reaction, increasing only the unburned fuel component has little effect, and it is necessary to increase the amount of oxygen in the exhaust gas flowing into the oxidation catalyst. 5, it is necessary to reduce the EGR control as compared with the case of the second rich air-fuel ratio to be described later. For this, an optimum value is obtained in advance by an experiment or the like.
[0093]
In step 1113, first rich air-fuel ratio post-injection data corresponding to the aforementioned first rich air-fuel ratio EGR is obtained. That is, the post-injection amount Qpost1, the post-injection period Pperiod1, and the post-injection timing Pstart1 necessary for the first rich air-fuel ratio conversion are set in the ROM of the control unit 30 by using the engine speed Ne and the load L (or the main fuel injection amount Qmain) as parameters. From a predetermined map stored in the storage device. The first rich air-fuel ratio post-injection data is also set in advance by obtaining an optimum value through experiments or the like.
[0094]
This post-injection is performed separately from the main injection in the expansion stroke and the exhaust stroke of each cylinder, and is not a fuel injection for obtaining an output. Therefore, a part of the post-injected fuel burns in the cylinder to increase the exhaust gas temperature, thereby promoting the oxidation reaction of the oxidation catalysts 21a and 21b, and the rest in an unburned state (HC, CO). , 21b. That is, since all of the post-injected fuel does not burn in the cylinder, the oxidation catalysts 21a and 21b have oxygen (O) not consumed in the cylinder. ₂ ) And unburned fuel components (HC, CO) flow in.
[0095]
Then, a part of the unburned fuel reacts with the oxygen in the oxidation catalysts 21a and 21b, thereby consuming the oxygen and further increasing the temperature. Then, in the same manner as when the engine is burned in a rich state (for example, an air-fuel ratio of 13 or less), exhaust gas containing almost no oxygen and containing many unburned components as a reducing agent flows into the NOx trap catalysts 22a and 22b.
[0096]
After searching for the first rich air-fuel ratio-enhanced post-injection data in step 1113, the process proceeds to step 1114, and it is determined from the index value (for example, elapsed time) whether the enrichment of the cylinder group A has been completed.
[0097]
If it is determined in step 1114 that the enrichment of the cylinder group A has not been completed, the process proceeds to step 1115, and the fuel of the cylinder group A (# 2, # 3 cylinder) to be post-injected according to the first rich air-fuel ratio post-injection data. The injection valve 15 is driven to open based on signals from a crank angle sensor 32 for detecting a crank angle and a crank angle sensor 33 for detecting a cylinder. That is, post injection is performed for the cylinder group A.
[0098]
Then, the process proceeds to step 1116, where feedback control of post-injection (for example, increase / decrease of Qpost1 or advance / retardation of Pstart1) is performed based on the signal (T1a) of the exhaust temperature sensor 36a. That is, in order to simultaneously realize the regeneration of the NOx trap catalyst 22a and the regeneration of the exhaust particulate trap 23a, the post-injection is corrected so as to obtain necessary exhaust conditions without excess and deficiency, and the basics necessary for regeneration of the post-processing system are obtained. Ensure exhaust conditions.
[0099]
If it is determined in step 1114 that the enrichment of the cylinder group A has been completed, the process proceeds to step 1118, and it is determined whether the enrichment of the cylinder group B has been completed from an index value (e.g., elapsed time). If the enrichment of the cylinder group B has been completed in step 1118, the process returns.
[0100]
If the enrichment of the cylinder group B has not been completed, the process proceeds to step 1119, and the fuel injection valves of the cylinder group B (# 1, # 4 cylinders) to be post-injected according to the first rich air-fuel ratio post-injection data. 15 is driven to open based on signals from a crank angle sensor 32 for detecting a crank angle and a crank angle sensor 33 for detecting a cylinder. That is, post injection is performed for the cylinder group B.
[0101]
Then, the process proceeds to step 1120, where feedback control of post-injection (for example, increase / decrease of Qpost2 or advance / retardation of Pstart2) is performed based on the signal (T1a) of the exhaust temperature sensor 36b, as in step 1116.
[0102]
After securing the basic exhaust conditions necessary for the regeneration of the post-processing system in step 1116 or 1120, the process proceeds to step 1117, where the exhaust particulates are detected based on the signal (T2) of the exhaust temperature sensor 37 at the outlet of the exhaust particulate trap 23a. Refeedback control of the post injection is performed so that the target temperature of the trap 23a of 500 ° C. (same as the first predetermined temperature) is obtained, and the process returns.
[0103]
Here, as a result of the determination in steps 1114 and 1118, when the first rich air-fuel ratio control is being performed in the cylinder group A, the first rich air-fuel ratio control is not performed in the cylinder group B. Conversely, when the first rich air-fuel ratio control is performed in the cylinder group B, the first rich air-fuel ratio control is not performed in the cylinder group A.
[0104]
For this reason, at the junction 3c of the exhaust passage 3, the rich exhaust and the normal lean exhaust merge, but the exhaust of the diesel engine is at least about λ ≒ 1.5, and the excess air ratio is basically large. For this reason, even if one of the cylinder groups is enriched to an exhaust air-fuel ratio of 13 (λ ≒ 0.9), the average exhaust air-fuel ratio after merging becomes at least about 18 (λ ≒ 1.2), so that oxygen is considerably increased. (4-5%). Then, the exhaust gas containing a large amount of the oxygen component heated by the catalytic reaction of the oxidation catalysts 21a and 21b and the NOx trap catalysts 22a and 22b flows into the exhaust particulate trap 23a, so that the exhaust particulate trap 23a is forcibly regenerated.
[0105]
FIG. 10 is a subroutine related to the regeneration control of the NOx trap catalysts 22a and 22b performed in step 1200 of FIG.
[0106]
Basically, the regeneration control of the NOx trap catalysts 22a and 22b has a shorter interval and is frequently performed as compared with the emergency forced regeneration control of the exhaust particulate trap 23a. Accordingly, if the first rich air-fuel ratio control, which is the same as the emergency forced regeneration control of the exhaust particulate trap 23a, is performed, the fuel efficiency will be greatly deteriorated. Therefore, the inlet temperature of the NOx trap catalyst corresponding to the enriched cylinder group becomes NOx. The second rich air-fuel ratio is set to target the lower limit temperature of 500 ° C. at which the trap catalyst can be regenerated, and set the target temperature of the exhaust particulate trap 23a to 400 ° C. (second predetermined temperature) at which the exhaust particulate trap 23a can be regenerated. Control.
[0107]
In the subroutine of FIG. 10, in step 1210, it is determined from the NOx trap catalyst regeneration index value whether regeneration of the NOx trap catalysts 22a and 22b has been completed.
[0108]
If Yes in step 1210, that is, if the regeneration is completed, the process proceeds to step 1211 to initialize the NOx trap catalyst regeneration control. That is, the post injection is stopped, and the post-processing system regeneration flag and the NOx trap catalyst regeneration flag are set to 0. Then, the NOx absorption amount integrated value and the NOx trap catalyst regeneration index value are each reset to 0, and the process returns.
[0109]
It should be noted that the index value of the end of the regeneration of the NOx trap catalyst does not need to be only the lapse of time from the start of the regeneration.
[0110]
If No in step 1210, that is, if the regeneration of the NOx trap catalysts 22a and 22b is not completed, the process proceeds to step 1211 and the target EGR required to assist the second rich air-fuel ratio for the regeneration of the NOx trap catalyst. The data, that is, the drive signal Eduty2 of the EGR valve 5 and the drive signal Tduty2 of the intake throttle valve 6 are stored in advance in the ROM of the control unit 30 using the engine speed Ne and the load L (or the main fuel injection amount Qmain) as parameters. Search for and find a given map. Then, the routine proceeds to step 1212, where the EGR valve 5 and the intake throttle valve 6 are drive-controlled based on the respective drive signals, and EGR for assisting the second rich air-fuel ratio is performed. Then, the process proceeds to step 1213.
[0111]
Here, in the second rich air-fuel ratio conversion for regenerating the NOx trap catalysts 22a and 22b, the oxidation reaction between the unburned fuel component and oxygen in the oxidation catalysts 21a and 21b disposed upstream of the NOx trap catalysts 22a and 22b. The amount is increased more than in the basic exhaust control shown in FIG. 5, but the optimum value is previously determined by experiments or the like so that the degree of increase is smaller than in the first rich air-fuel ratio for forced regeneration of the exhaust particulate trap 23a. Ask.
[0112]
In step 1213, the second rich air-fuel ratio post-injection data corresponding to the aforementioned second rich air-fuel ratio EGR is obtained. In other words, the post-injection amount Qpost2, the post-injection period Pperiod2, and the post-injection timing Pstart2 are determined by using the engine speed Ne and the load L (or the main fuel injection amount Qmain) as parameters in the predetermined map stored in the ROM of the control unit 30. Search from and ask. The second rich air / fuel ratio post-injection data is also set in advance by obtaining an optimum value by an experiment or the like.
[0113]
After searching the second rich air-fuel ratio-enhanced post-injection data in step 1213, the process proceeds to step 1214, where it is determined from the index value (for example, the elapsed time) whether the enrichment of the cylinder group A has been completed.
[0114]
If it is determined in step 1214 that the enrichment of the cylinder group A has not been completed, the process proceeds to step 1215, in which the fuel of the cylinder group A (# 2, # 3 cylinder) to be post-injected according to the second rich air-fuel ratio post-injection data. The injection valve 15 is driven to open based on the signals of the crank angle sensor 32 for detecting the crank angle and the crank angle sensor 33 for determining the cylinder. That is, post injection is performed for the cylinder group A.
[0115]
Then, the process proceeds to step 1216, where feedback control of post-injection (for example, increasing / decreasing Qpost2 or advancing / retarding Pstart2) is performed based on the signal (T1a) of the exhaust temperature sensor 36a.
[0116]
On the other hand, if the enrichment of the cylinder group A has been completed in step 1214, the process proceeds to step 1218, where it is determined whether the enrichment of the cylinder group B has been completed from an index value (for example, elapsed time). If the enrichment of the cylinder group B has been completed in step 1218, the process returns.
[0117]
If the enrichment of the cylinder group B has not been completed, the process proceeds to step 1219, and the fuel injection valves 15 of the cylinder group B (# 1, # 4 cylinders) to be post-injected are set according to the second rich air-fuel ratio post-injection data. The valve is driven to open based on the signals from the crank angle sensor 32 for detecting the crank angle and the crank angle sensor 33 for determining the cylinder. That is, post injection is performed for the cylinder group B.
[0118]
Then, proceeding to step 1220, feedback control of post-injection (for example, Qpost2 increase / decrease, or Pstart2 advance / retard) is performed based on the signal (T1a) of the exhaust temperature sensor 36b, as in step 1216.
[0119]
After securing the basic exhaust conditions necessary for the regeneration of the post-processing system in step 1216 or step 1220, the process proceeds to step 1217, where the exhaust particulates are detected based on the signal (T2) of the exhaust temperature sensor 37 at the outlet of the exhaust particulate trap 23a. Refeedback control of the post-injection is performed so that a lower limit temperature of 400 ° C. (same as the second predetermined temperature) at which the trap 23a can be regenerated is obtained, and the process returns.
[0120]
Next, FIG. 11 shows details of the protection control of the exhaust particulate trap 23a performed in step 2000 of FIG. In this protection control, as described above, in the DPF protection determination routine in FIG. 4, the exhaust temperature T2 at the outlet of the exhaust particulate trap 23a exceeds the first predetermined temperature (500 ° C.), and the rate of increase of the exhaust temperature T2. This is started when (dT2 / dTime) exceeds a predetermined value (for example, a rise of 50 ° C. per second), and the internal temperature of the exhaust particulate trap 23a does not rapidly rise and does not exceed the allowable temperature limit. This is a subroutine relating to control for suppressing the combustion speed of the exhaust particulates and protecting the exhaust particulate traps 23a so that cracks and erosion of the exhaust particulate traps 23a do not occur.
[0121]
In the DPF protection control routine of FIG. 11, in step 2010, target EGR data necessary for assisting the third rich air-fuel ratio for protecting the exhaust particulate trap 23a, that is, the drive signal Eduty3 of the EGR valve 5 and the intake throttle The drive signal Tduty3 of the valve 6 is obtained by searching a predetermined map stored in advance in the ROM of the control unit 30 using the engine speed Ne and the load L (or the main fuel injection amount Qmain) as parameters. Then, the process proceeds to step 2020, where the EGR valve 5 and the intake throttle valve 6 are drive-controlled based on the respective drive signals, and EGR for assisting the third rich air-fuel ratio is performed. Then, the process proceeds to step 2030.
[0122]
Here, in the third rich air-fuel ratio setting for protecting the exhaust particulate trap 23a, in order to suppress the exhaust particulate combustion speed in the exhaust particulate trap 23a, the NOx trap catalysts 22a and 22b are used in regions other than the low rotation and low load. It is necessary to reduce the flow rate of the exhaust gas (the amount of oxygen) flowing into the oxidation catalysts 21a and 21b disposed upstream, thereby reducing the amount of the oxidation reaction between the unburned fuel component and the oxygen. Rather, the intake throttle or EGR is strengthened within a possible range (up to an allowable upper limit in terms of exhaust performance without deteriorating drivability). Also for this, an optimum value is obtained in advance by experiments or the like. Further, in the low-rotation low-load region, control is performed with the same value as the exhaust basic control in FIG. 5 so that the exhaust flow rate is not excessively reduced. Note that, under the first and second rich air-fuel ratios before the third rich air-fuel ratio, the exhaust gas flow rate is large as described above.
[0123]
In step 2030, third rich air / fuel ratio post-injection data corresponding to the third rich air / fuel ratio EGR is obtained. That is, the post-injection amount Qpost3, the post-injection period Pperiod3, and the post-injection timing Pstart3 are determined by using the engine speed Ne and the load L (or the main fuel injection amount Qmain) as parameters in a predetermined map stored in the ROM of the control unit 30. Search from and ask. The third rich air-fuel ratio post-injection data is also set in advance by obtaining an optimum value by an experiment or the like.
[0124]
After searching for the third rich air-fuel ratio post-injection data in step 2030, the process proceeds to step 2040, in which the fuel injection valves 15 of all the cylinders (# 1 to # 4) are set to the crank angle sensor 32 for detecting the crank angle and the cylinder The valve is driven to open based on a signal from the crank angle sensor 33. That is, post-injection is executed for all cylinders.
[0125]
Then, the process proceeds to step 2050, and based on the signal (T1a) of the exhaust temperature sensor 36a, the feedback control of the post injection is performed so that the inlet temperature of the NOx trap catalyst becomes the target temperature, that is, 500 ° C. which is the lower limit temperature at which the NOx trap catalyst can be regenerated. (For example, Qpost3 is increased / decreased, or Pstart3 is advanced / retarded), and the process returns.
[0126]
Under the third rich air-fuel ratio, oxygen in the exhaust gas discharged from the engine 1 reacts with HC and CO generated by the post-injection in the oxidation catalysts 21a and 21b, so that the oxygen at the inlet of the exhaust particle trap 23a. The amount of oxygen in the exhaust gas can be made substantially zero, and the combustion of the exhaust particulates can be suppressed. As a result, cracking and melting of the exhaust particulate trap 23a are avoided.
[0127]
The exhaust gas temperature at the inlet of the exhaust particulate trap 23a and the temperature of the exhaust particulate trap 23a also increase due to the heat of oxidation reaction of HC and CO in the oxidation catalysts 21a and 21b. The temperature rise of the particulate trap 23a is reduced by reducing the heat of oxidation reaction itself by reducing the amount of inflowing oxygen by air throttling or EGR, and is particularly small compared to the temperature rise of the exhaust particulate trap 23a due to rapid combustion of exhaust particulates. And so small that they can be ignored.
[0128]
In the low-rotation low-load region, the third rich air-fuel ratio is achieved by post-injection without reducing the exhaust flow rate. However, by not reducing the exhaust flow rate, the engine is operated at a high rotation speed and high load. Thus, when the exhaust particulates self-ignite and then shift to a low-speed low-load region such as idling, a sharp rise in temperature due to a decrease in exhaust gas flow rate is avoided, and cracks and melting damage of the exhaust particulate trap 23a are prevented. You.
[0129]
In the above-described first embodiment, the regeneration of the NOx trap catalysts 22a and 22b and the regeneration of the exhaust particulate trap 23a can be realized at the same time. Therefore, the time and energy consumption for the regeneration are reduced, and the influence on the fuel efficiency deterioration is minimized. Can be limited. Moreover, by utilizing the rich and lean of the two cylinder groups, simultaneous regeneration of both can be realized without providing a special device such as an air pump.
[0130]
By supporting the oxidation catalyst in the exhaust particulate trap 23a, the regeneration temperature of the exhaust particulate trap 23a can be lowered by the catalytic reaction, the energy consumption for regeneration is reduced, and the influence on the fuel efficiency deterioration is minimized. Can be
[0131]
Next, FIG. 2 is a system configuration diagram of an exhaust emission control device according to a second embodiment of the present invention. Hereinafter, portions different from the first embodiment will be mainly described, and the same portions will be denoted by the same reference numerals and the description will be simply given.
[0132]
In this second embodiment, as shown in FIG. 2, the exhaust system is one system, a single catalyst casing 20 is disposed in the exhaust passage 3, and an exhaust particulate trap 23a is provided downstream thereof. A holding casing 21 is provided. Inside the catalyst casing 20, there is a single oxidation catalyst 21 and a single oxidation catalyst 21 that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases NOx when the oxygen concentration of the inflowing exhaust gas decreases. And the NOx trap catalyst 22 are arranged in series.
[0133]
At the inlet of the NOx trap catalyst 22, an exhaust temperature sensor 36 for detecting the exhaust temperature T1 at the inlet of the NOx trap catalyst 22 (the outlet of the oxidation catalyst 21) is provided. An exhaust pressure sensor 38 for detecting the pressure P1 and an exhaust temperature sensor 37 for detecting the exhaust temperature T2 are provided at the outlet.
[0134]
At the outlet of the NOx trap catalyst 22, an air introduction passage 7 for guiding air from a downstream side of a compressor 2b of a supercharger as an air supply source via an on-off valve 8 whose passage area can be variably controlled by, for example, a stepping motor. Are connected. Note that an electric air pump or the like may be used as the air supply source.
[0135]
The engine control unit 30 receives a signal from a water temperature sensor 31 (water temperature Tw), a signal from a crank angle sensor 32 for detecting a crank angle (a crank angle signal serving as a basis for the engine speed Ne), and a signal from a crank angle sensor 33 for determining a cylinder. (Cylinder discrimination signal Cyl), a signal of a pressure sensor 34 for detecting the pressure of the common rail 14 (common rail pressure PCR), and a signal of an accelerator opening sensor 35 for detecting the depression amount of an accelerator pedal corresponding to the load (the accelerator opening (load) ) L) are input. Further, the signal (T1) of the exhaust temperature sensor 36 at the inlet of the NOx trap catalyst 22, the signal (T2) of the exhaust temperature sensor 37 at the outlet of the exhaust particulate trap 23a, and the exhaust pressure at the inlet of the exhaust particulate trap 23a. (P1) of the exhaust pressure sensor 38 for detecting the pressure is input.
[0136]
As in the first embodiment, the post-treatment system for exhaust gas purification of the second embodiment also eliminates the need to separately perform the regeneration of the NOx trap catalyst 22 and the regeneration of the exhaust particulate trap 23a in a lean state. The purpose is to increase the efficiency of use of the energy used for the vehicle and to minimize the deterioration of fuel efficiency.
[0137]
The exhaust gas purifying post-processing system of the second embodiment is also controlled by the engine control unit 30. In the engine basic control routine of FIG. 3, the input signal of the exhaust temperature sensor in step 100 is T1 only (first embodiment). T1a and T1b in the example), the forced regeneration control of the exhaust particulate trap 23a performed in step 1100 of the post-processing system regeneration control routine in FIG. 8, and the regeneration of the NOx trap catalyst performed in step 1200. The control part is different from the first embodiment.
[0138]
This will be described with reference to the flowcharts of FIGS. 12 and 13, but the description of the parts having the same functions as those of the first embodiment will be simplified.
[0139]
FIG. 12 is a subroutine relating to the forced regeneration control of the exhaust particulate trap 23a in step 1100. This subroutine sets the temperature target of the exhaust particulate trap 23a to 500 ° C. or more (same as the first predetermined temperature) as in the first embodiment. ), Set the target of the inlet temperature of the NOx trap catalyst 22 to 600 ° C. and maintain it for several minutes. Therefore, similarly to the first embodiment, regeneration of the NOx trap catalyst 22 can be realized at the same time.
[0140]
In the DPF forced regeneration control routine of FIG. 12, in step 1160, it is determined from the exhaust particulate trap regeneration index value whether the predetermined regeneration of the exhaust particulate trap 23a has been completed.
[0141]
If Yes in step 1160, that is, if the regeneration of the exhaust particulate trap 23a has been completed, the flow advances to step 1172 to initialize the exhaust particulate trap 23a regeneration control. Specifically, the post-injection is stopped, the air supply described later for leaning the exhaust gas flowing into the exhaust particulate trap 23a is stopped, the post-processing system regeneration flag, the DPF regeneration flag, the NOx trap catalyst regeneration flag, 2. Set the predetermined temperature flags (temperature flags) to 0, respectively. Further, the NOx absorption amount integrated value and the exhaust particulate trap regeneration index value are each reset to 0, and the process returns.
[0142]
If No in step 1160, that is, if the regeneration of the exhaust particulate trap 23a is not completed, the process proceeds to step 1161, and the target EGR data necessary to assist the first rich air-fuel ratio for regeneration of the exhaust particulate trap 23a That is, the drive signal Eduty1 of the EGR valve 5 and the drive signal Tduty1 of the intake throttle valve 6 are obtained by searching a predetermined map stored in the ROM of the control unit 30. Then, the process proceeds to a step 1162, where the EGR valve 5 and the intake throttle valve 6 are drive-controlled based on the respective drive signals, and the EGR for assisting the first rich air-fuel ratio is performed. Then, the process proceeds to step 1163.
[0143]
In step 1163, first rich air-fuel ratio post-injection data corresponding to the aforementioned first rich air-fuel ratio EGR is obtained. That is, the post-injection amount Qpost1, the post-injection period Pperiod1, and the post-injection timing Pstart1 are obtained by searching from a predetermined map stored in the ROM of the control unit 30.
[0144]
After searching for the first rich air-fuel ratio post-injection data in step 1163, the process proceeds to step 1164, and the fuel injection valve 15 is set to the crank angle detection crank angle sensor 32 and the cylinder discrimination in accordance with the first rich air-fuel ratio post-injection data. The valve is driven to open based on a signal from the crank angle sensor 33. That is, post-injection is executed for all cylinders.
[0145]
Then, the process proceeds to step 1165 to perform post-injection feedback control (for example, increase / decrease of Qpost1 or advance / retard of Pstart1) based on the signal T1 of the exhaust temperature sensor 36. That is, in order to simultaneously realize the regeneration of the NOx trap catalyst 22 and the regeneration of the exhaust particulate trap 23a, the post-injection is corrected so as to obtain necessary exhaust conditions without excess or deficiency, and the basics necessary for the regeneration of the post-processing system are performed. Ensure exhaust conditions.
[0146]
After securing the basic exhaust conditions necessary for the regeneration of the post-processing system in step 1165, the process proceeds to step 1166 to determine whether or not the temperature flag is 1. This temperature flag is a flag indicating that the temperature T2 of the exhaust particulate trap 23a has reached a lower limit temperature of 400 ° C. (second predetermined temperature) at which the exhaust particulate trap 23a can be regenerated.
[0147]
If Yes in step 1166, that is, if the temperature of the exhaust particulate trap 23a (outlet temperature T2) has reached the lower limit temperature of 400 ° C. at which the exhaust particulate trap 23a can be regenerated, the process proceeds to step 1167.
[0148]
In step 1167, the air supply data necessary to make the exhaust air-fuel ratio lean (for example, the air-fuel ratio is 18 or more), that is, the drive control signal Qair1 of the on-off valve 8, is used to regenerate the exhaust particulate trap 23a. Using Ne and the load L (or the main fuel injection amount Qmain) as parameters, a search is made from a predetermined map previously obtained by experiment and stored in the ROM of the control unit 30 to obtain it.
[0149]
After searching for air supply data for regeneration of the exhaust particulate trap 23a in step 1167, the flow advances to step 1168 to open the on-off valve 8 based on the drive control signal Qair1 so that a required amount of air is supplied. Drive.
[0150]
Proceeding to step 1169, the temperature of the exhaust particulate trap 23a is obtained at the target of 500 ° C. (same as the first predetermined temperature) based on the signal (T2) of the exhaust temperature sensor 37 at the outlet of the exhaust particulate trap 23a. As described above, the feedback control of the supply air amount, that is, the increase / decrease correction of Qair1 is performed, and the exhaust conditions necessary for the regeneration of the exhaust particulate trap 23a are secured, and the return is made.
[0151]
If No in step 1166, that is, the temperature flag is not 1 (indicating that the temperature of the exhaust particulate trap 23a (outlet temperature T2) has not reached 400 ° C., which is the lower limit temperature at which the exhaust particulate trap 23a can be regenerated). In some cases, the process proceeds to step 1170.
[0152]
In step 1170, it is determined whether or not the temperature T2 at the outlet of the exhaust particulate trap 23a is 400 ° C. or higher. If Yes, that is, 400 ° C. or higher, the process proceeds to step 1171 to set the temperature flag to 1 and returns. .
[0153]
If No in step 1170, that is, if the temperature is lower than 400 ° C., the process directly returns.
[0154]
FIG. 13 shows a subroutine relating to the regeneration control of the NOx trap catalyst 22 performed in step 1200 in the second embodiment. In this subroutine, the inlet temperature of the NOx trap catalyst 22 is targeted at the lower limit temperature of 500 ° C. at which the NOx trap catalyst 22 can be regenerated, and the temperature of the exhaust particulate trap 23a is set at 400 ° C. (the lower limit temperature at which the exhaust particulate trap 23a can be regenerated). The second rich air-fuel ratio control is performed with the target set at (2 predetermined temperatures).
[0155]
In the subroutine of FIG. 13, in step 1260, it is determined from the NOx regeneration index value whether the NOx regeneration of the NOx trap catalyst 22 has been completed.
[0156]
If Yes in step 1260, that is, if the NOx regeneration is completed, the process proceeds to step 1270 to initialize the NOx regeneration control. That is, the post injection is stopped, the air supply is stopped, and the post-processing system regeneration flag and the NOx trap catalyst regeneration flag are both set to 0. Then, the NOx absorption amount integrated value and the NOx trap catalyst regeneration index value are each reset to 0, and the process returns.
[0157]
If NO in step 1260, that is, if the NOx regeneration of the NOx trap catalyst 22 has not been completed, the process proceeds to step 1261 and the target EGR data required to assist the second rich air-fuel ratio for NOx regeneration, that is, EGR The drive signal Eduty2 of the valve 5 and the drive signal Tduty2 of the intake throttle valve 6 are obtained by searching a predetermined map stored in the ROM of the control unit 30. Then, the routine proceeds to step 1262, where the EGR valve 5 and the intake throttle valve 6 are drive-controlled based on the respective drive signals, and EGR for assisting the second rich air-fuel ratio is performed. Then, the process proceeds to step 1263.
[0158]
In step 1263, the second rich air-fuel ratio post-injection data corresponding to the above-mentioned second rich air-fuel ratio EGR is obtained. That is, the post-injection amount Qpost2, the post-injection period Pperiod2, and the post-injection timing Pstart2 are searched for and obtained from a predetermined map stored in the ROM of the control unit 30.
[0159]
After the second rich air-fuel ratio post-injection data is retrieved in step 1263, the process proceeds to step 1264, and the fuel injection valve 15 is set to the crank angle detection crank angle sensor 32 and the cylinder discrimination in accordance with the second rich air-fuel ratio post-injection data. The valve is driven to open based on a signal from the crank angle sensor 33. That is, post-injection is executed for all cylinders.
[0160]
Then, the process proceeds to step 1265, where feedback control of post-injection (for example, increasing / decreasing Qpost2 or advancing / retarding Pstart2) is performed based on the signal T1 of the exhaust temperature sensor 36, and regeneration of the NOx trap catalyst 22 and exhaust particulates are performed. The post-injection correction is performed to realize the regeneration of the trap 23a at the same time, and the basic exhaust conditions necessary for the regeneration of the post-processing system are secured.
[0161]
In step 1266, the air supply data necessary to make the exhaust air-fuel ratio lean (for example, an air-fuel ratio of 18 or more), that is, the drive control signal Qair2 of the on-off valve 8, is used to regenerate the exhaust particulate trap 23a. Using Ne and the load L (or the main fuel injection amount Qmain) as parameters, a search is made from a predetermined map previously obtained by experiment and stored in the ROM of the control unit 30 to obtain it.
[0162]
After retrieving data relating to air supply for regeneration of the exhaust particulate trap 23a in step 1266, the flow advances to step 1267 to open the on-off valve 8 based on the drive control signal Qair2 so that a necessary amount of air is supplied. Drive.
[0163]
Proceeding to step 1268, based on the signal (T2) from the exhaust temperature sensor 37 at the outlet of the exhaust particulate trap 23a, the temperature of the exhaust particulate trap 23a is obtained to the target 400 ° C. (same as the second predetermined temperature). Then, feedback control of the supply air amount is performed. That is, Qair1 is increased / decreased so that the exhaust conditions suitable for the regeneration of the exhaust particulate trap 23a are obtained without excess or deficiency, and the exhaust conditions necessary for the regeneration of the exhaust particulate trap 23a are secured, and the process returns.
[0164]
Also in the second embodiment, as in the first embodiment, the regeneration of the NOx trap catalyst 22 and the regeneration of the exhaust particulate trap 23a can be realized at the same time, so that the time and energy consumption for the regeneration are reduced, and the fuel consumption is reduced. The effect on deterioration can be minimized.
[0165]
Next, FIG. 14 is a system configuration diagram of an exhaust emission control device according to a third embodiment of the present invention. Hereinafter, portions different from the first and second embodiments will be mainly described, and the same portions will be denoted by the same reference numerals and the description will be simply given.
[0166]
In the third embodiment, as in the second embodiment, the exhaust system is a single system, a single catalyst casing 20 is disposed in the exhaust passage 3, and an exhaust particulate trap 23a is provided downstream of the single catalyst casing 20. A holding casing 21 is provided. Inside the catalyst casing 20, there is a single oxidation catalyst 21 and a single oxidation catalyst 21 that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases NOx when the oxygen concentration of the inflowing exhaust gas decreases. And the NOx trap catalyst 22 are arranged in series. The third embodiment is a further simplification of the configuration of the second embodiment, and does not include the air introduction passage 7 for air introduction and the on-off valve 8 described above. The other configuration is the same as that of the second embodiment.
[0167]
In the exhaust gas purifying post-processing system of the third embodiment, the exhaust air-fuel ratio of the exhaust gas flowing into the exhaust particulate trap 23a remains rich when the NOx trap catalyst 22 regenerates NOx. The reproduction of 23a is not performed.
[0168]
The exhaust gas purifying post-processing system of the third embodiment is also controlled by the engine control unit 30, but the basic processing is the same as in the first and second embodiments described above. The steps of the forced regeneration control of the exhaust particulate trap 23a performed in step 1100 of the processing system regeneration control routine and the regeneration control of the NOx trap catalyst performed in step 1200 are slightly different from those of the second embodiment.
[0169]
This will be described with reference to the flowcharts of FIGS.
[0170]
FIG. 15 is a subroutine relating to the forced regeneration control of the exhaust particulate trap 23a in step 1100. This subroutine differs from the subroutine of the second embodiment described in FIG. 12 only in part (steps 1180 and 1181). Only the different parts will be described, and the description of the parts that are not particularly changed will be omitted.
[0171]
As described above, in step 1166, it is determined whether or not the temperature flag is 1. This temperature flag is a flag indicating that the temperature T2 of the exhaust particulate trap 23a has reached a lower limit temperature of 400 ° C. (second predetermined temperature) at which the exhaust particulate trap 23a can be regenerated. If Yes in step 1166, that is, if the temperature of the exhaust particulate trap 23a (the outlet temperature T2) has reached the lower limit temperature of 400 ° C. at which the exhaust particulate trap 23a can be regenerated, in this embodiment, step 1180 Proceeding to 1181, the exhaust air-fuel ratio is made lean.
[0172]
In step 1180, target EGR data required to make the exhaust air-fuel ratio lean (for example, an air-fuel ratio of 18 or more) for regeneration of the exhaust particulate trap 23a, that is, the drive signal Duty4 of the EGR valve 5 and the intake throttle valve 6 The drive signal Tduty4 is obtained by searching a predetermined map stored in the ROM of the control unit 30.
[0173]
Then, in step 1181, the EGR valve 5 and the intake throttle valve 6 are drive-controlled based on the respective drive signals to make the exhaust air-fuel ratio lean. Thus, forced regeneration of the exhaust particulate trap 23a is started.
[0174]
FIG. 16 is a subroutine relating to the regeneration control of the NOx trap catalyst 22 performed in step 1200. This subroutine differs from the subroutine of the second embodiment described in FIG. 13 only in part (steps 1280, 1281). Therefore, only the different parts will be described, and the description of the parts that do not particularly change will be omitted.
[0175]
As described above, in step 1260, it is determined from the NOx regeneration index value whether or not the NOx regeneration of the NOx trap catalyst 22 has been completed. If NO in step 1260, that is, if the NOx regeneration of the NOx trap catalyst 22 has not been completed, Goes to step 1280.
[0176]
In step 1280, the target EGR data necessary for the rich air-fuel ratio for NOx regeneration, that is, the drive signal Eduty5 of the EGR valve 5 and the drive signal Tduty5 of the intake throttle valve 6, are stored in the ROM of the control unit 30 in a predetermined manner. Search and ask for a map. Then, the process proceeds to a step 1281, wherein the EGR valve 5 and the intake throttle valve 6 are drive-controlled based on the respective drive signals, and the exhaust air-fuel ratio is made rich. Here, the target rich air-fuel ratio is set to about 13 (λ = 0.9) required for NOx regeneration. When the excess air ratio decreases, the fuel efficiency deteriorates, and the torque decreases accordingly. Therefore, it is desirable to increase and correct the main fuel injection amount Qmain according to the decrease in the excess air ratio.
[0177]
The case where the present invention is applied to an in-line multi-cylinder engine has been described above. However, the exhaust gas purification apparatus of the present invention is not limited to this, and can also be applied to a V-shaped six-cylinder or eight-cylinder engine. Further, although the above-described embodiment shows an example of a supercharged engine, a naturally aspirated engine may be used.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram showing a first embodiment of the present invention.
FIG. 2 is a system configuration diagram showing a second embodiment of the present invention.
FIG. 3 is a flowchart showing a diesel engine basic control routine.
FIG. 4 is a flowchart illustrating a DPF protection determination routine.
FIG. 5 is a flowchart showing an engine exhaust basic control routine.
FIG. 6 is a flowchart showing an exhaust particulate trap limit determination routine.
FIG. 7 is a flowchart showing a NOx trap catalyst regeneration determination routine.
FIG. 8 is a flowchart showing a post-processing system reproduction control routine.
FIG. 9 is a flowchart showing a DPF forced regeneration control routine.
FIG. 10 is a flowchart showing a NOx trap catalyst regeneration control routine.
FIG. 11 is a flowchart showing a DPF protection control routine.
FIG. 12 is a flowchart illustrating a DPF forced regeneration control routine according to a second embodiment.
FIG. 13 is a flowchart illustrating a NOx trap catalyst regeneration control routine in a second embodiment.
FIG. 14 is a system configuration diagram showing a third embodiment.
FIG. 15 is a flowchart illustrating a DPF forced regeneration control routine according to a third embodiment.
FIG. 16 is a flowchart showing a NOx trap catalyst regeneration control routine in a third embodiment.
[Explanation of symbols]
1. Engine
3. Exhaust passage
5 EGR valve
6 ... intake throttle valve
21, 21a, 21b ... oxidation catalyst
22, 22a, 22b ... NOx trap catalyst
23a: Exhaust particulate trap
30 ... Engine control unit

Claims (13)

An oxidation catalyst disposed in an exhaust passage of the internal combustion engine to oxidize and purify an inflowing exhaust component;
An exhaust particulate trap that is disposed in the exhaust passage downstream of the oxidation catalyst and traps exhaust particulates flowing in;
Temperature detection means for detecting the temperature of the exhaust particulate trap,
Combustion speed detection means for detecting the combustion speed of the exhaust particulates trapped in the exhaust particulate trap,
Fuel injection means for enabling post-injection for injecting fuel in an expansion stroke or an exhaust stroke,
Exhaust air-fuel ratio control means for enriching the exhaust air-fuel ratio by the post-injection when the temperature of the exhaust particulate trap exceeds a predetermined temperature, and the combustion speed of the exhaust particulate exceeds a predetermined speed,
An exhaust gas purifying apparatus for an internal combustion engine, comprising: Regeneration timing determining means for determining a regeneration timing based on the amount of exhaust particulates trapped in the exhaust particulate trap,
Playback control means for performing a predetermined playback operation at the playback time,
The exhaust air-fuel ratio control means, when the temperature of the exhaust particulate trap exceeds a predetermined temperature and the burning speed of the exhaust particulate exceeds a predetermined speed, even during the regeneration operation, the exhaust air The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio is made rich. An air amount control unit that controls an amount of air flowing into a cylinder of the internal combustion engine,
3. The exhaust gas purification system according to claim 1, wherein the exhaust air-fuel ratio control means performs the post-injection and reduces the amount of air flowing into the internal combustion engine to enrich the exhaust air-fuel ratio. apparatus. The exhaust air-fuel ratio control means is configured to control the position of the post-particle when the operating state is low rotation and low load when the temperature of the exhaust particulate trap exceeds a predetermined temperature and the combustion speed of the exhaust particulate exceeds the predetermined speed. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust air-fuel ratio is made rich only by injection. NOx, which is located between the oxidation catalyst and the exhaust particulate trap, traps NOx in the exhaust gas flowing when the exhaust air-fuel ratio is lean, and desorbs and purifies the trapped NOx when the exhaust air-fuel ratio is rich. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 4, further comprising a trap catalyst. The internal combustion engine according to any one of claims 1 to 5, wherein the combustion speed detection means regards the combustion speed of the exhaust particulates as higher as the rate of increase in the temperature of the exhaust particulate trap per unit time is higher. Engine exhaust purification device. The NOx trap catalyst is arranged corresponding to each of a plurality of cylinder groups including one or a plurality of cylinders,
The exhaust particulate trap comprises a single exhaust particulate trap so that all exhaust discharged from the plurality of NOx trap catalysts flows in,
NOx trap catalyst regeneration timing determination means for determining at least one regeneration timing of the plurality of NOx trap catalysts;
When at least one of the plurality of NOx trap catalysts is to be regenerated, the exhaust air-fuel ratio of the cylinder group corresponding to the NOx trap catalyst to be regenerated is such that the exhaust air-fuel ratio flowing into the exhaust particulate trap becomes lean. NOx trap regeneration control means for simultaneously performing the regeneration process of the exhaust particulate trap while performing the regeneration process of the NOx trap catalyst by making the exhaust air-fuel ratio of the other cylinder groups lean, and
Further comprising
The exhaust air-fuel ratio control means may be configured such that when at least one of the plurality of NOx trap catalysts is being regenerated, the temperature of the exhaust particulate trap exceeds a first predetermined temperature and the combustion speed of the exhaust particulate When the speed is exceeded, the exhaust air-fuel ratios of the plurality of cylinder groups are all made rich so that the exhaust air-fuel ratio flowing into the exhaust particulate trap becomes rich, and the NOx trap catalyst is regenerated while performing the regeneration process. The exhaust gas purifying apparatus for an internal combustion engine according to claim 5, wherein a combustion speed of the exhaust particulates is suppressed. The NOx trap regeneration control means, when enriching the exhaust air-fuel ratio of some of the cylinder groups and leaning the exhaust air-fuel ratio of the other cylinder groups, adjusts the exhaust temperature of the cylinder group whose enriched exhaust air-fuel ratio. The exhaust gas purifying apparatus for an internal combustion engine according to claim 7, wherein the temperature of the exhaust particulate trap is controlled to a second predetermined temperature at which the exhaust particulate trap can be regenerated. Air supply means capable of supplying air to an upstream exhaust passage of the exhaust particulate trap,
NOx trap catalyst regeneration timing determination means for determining the regeneration timing of the NOx trap catalyst;
Further comprising
The exhaust air-fuel ratio control means includes:
When it is determined that it is time to regenerate the NOx trap catalyst, the exhaust air-fuel ratio flowing into the NOx trap catalyst by the post injection is made rich, and air is supplied by the air supply means to flow into the exhaust particulate trap. The exhaust air-fuel ratio to be lean, and simultaneously perform the exhaust particle trap regeneration process while performing the NOx trap catalyst regeneration process,
When the temperature of the exhaust particulate trap exceeds a first predetermined temperature and the combustion rate of the exhaust particulate exceeds a predetermined rate, the air supply means may supply air even during regeneration processing of the exhaust particulate trap. 6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5, wherein the supply is stopped to make the exhaust air-fuel ratio flowing into the exhaust particulate trap rich. Exhaust gas trap regeneration timing determination means for determining the regeneration timing of the exhaust particulate trap,
The exhaust air-fuel ratio control means, when it is determined that the exhaust particulate trap is to be regenerated, until the exhaust particulate trap temperature exceeds a second predetermined temperature lower than the first predetermined temperature. The air-fuel ratio is made rich to raise the temperature of the exhaust particulate trap. After the temperature of the exhaust particulate trap exceeds a second predetermined temperature, air is supplied by the air supply means to flow into the exhaust particulate trap. The exhaust air-fuel ratio is made lean and the exhaust particulate trap is regenerated,
When the temperature of the exhaust particulate trap exceeds a first predetermined temperature and the burning rate of the exhaust particulate exceeds a predetermined rate, the air supply means may supply air even during regeneration processing of the exhaust particulate trap. 10. The exhaust gas purifying apparatus for an internal combustion engine according to claim 9, wherein the supply is stopped to make the exhaust air-fuel ratio flowing into the exhaust particulate trap rich. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 5 to 7, wherein the oxidation catalyst is integrally formed with the NOx trap catalyst. An oxidation catalyst disposed in an exhaust passage of the internal combustion engine to oxidize and purify an inflowing exhaust component;
An exhaust particulate trap that is disposed in the exhaust passage downstream of the oxidation catalyst and traps exhaust particulates flowing in;
Temperature detection means for detecting the temperature of the exhaust particulate trap,
Combustion speed detection means for detecting the combustion speed of the exhaust particulates trapped in the exhaust particulate trap,
Exhaust air-fuel ratio control means for enriching the exhaust air-fuel ratio when the temperature of the exhaust particulate trap exceeds a predetermined temperature, and the combustion speed of the exhaust particulate exceeds a predetermined speed,
An exhaust gas purifying apparatus for an internal combustion engine, comprising: The exhaust air-fuel ratio control means enriches the exhaust air-fuel ratio by at least one of post-injection for injecting fuel in an expansion stroke or an exhaust stroke, a reduction in an intake air amount to an internal combustion engine, and an increase in an exhaust gas recirculation amount. The exhaust gas purifying apparatus for an internal combustion engine according to claim 12, wherein:

Images