JP3797224B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus (an exhaust gas after-treatment system) for an internal combustion engine, and more particularly to its regeneration technology.
[0002]
[Prior art]
As a conventional exhaust gas purification device for an internal combustion engine, there is a device described in Japanese Patent Laid-Open No. 9-53442.
In this device, a PM trap for trapping PM is arranged in the exhaust passage for the purification treatment of NOx (nitrogen oxide) discharged from the diesel engine and PM (Particulate Matter) which is exhaust particulate, and further downstream side thereof. In addition, when the air-fuel ratio of the inflowing exhaust gas is lean, NOx is trapped. When the air-fuel ratio of the inflowing exhaust gas becomes rich and the O2 (oxygen) concentration in the exhaust gas decreases, HC (hydrocarbon which is a reducing component in the exhaust gas) ), A NOx trap catalyst for reducing and purifying NOx trapped by CO (carbon monoxide) is disposed.
[0003]
And periodically, NOx trapped from the NOx trap catalyst is released to recover the NOx trap capability (NOx trap catalyst regeneration operation), and PM trapped in the PM trap is burned and removed to reduce pressure loss. The operation (PM trap regeneration operation) is performed.
The conventional regeneration operation of the NOx trap catalyst is performed for a short time at intervals of several tens of seconds to several minutes, in addition to normal fuel injection of a diesel engine, fuel injection is performed in the exhaust stroke, and the exhaust air / fuel ratio is made higher than the stoichiometric air / fuel ratio. This is achieved by exhausting the unburned components of the fuel to the exhaust passage on the rich side (about 13). That is, the exhaust air-fuel ratio is made rich, the O2 concentration in the exhaust gas is rapidly reduced, and the HC and CO components are increased to regenerate the NOx trap catalyst.
[0004]
The regeneration operation of the PM trap is performed for several minutes at intervals of several tens of minutes to several hours, in the same manner as the regeneration of the NOx trap catalyst, in addition to normal fuel injection, fuel injection is performed in the exhaust stroke, but the exhaust temperature is raised. This is to promote regeneration of the PM trap, and the exhaust air-fuel ratio is maintained at a lean value of about 20.
When the NOx trap catalyst regeneration operation timing comes during the PM trap regeneration operation, the exhaust air-fuel ratio enrichment for regeneration of the NOx trap catalyst is performed during the PM trap regeneration operation. .
[0005]
[Problems to be solved by the invention]
However, in such a conventional exhaust gas purification apparatus for an internal combustion engine, the regeneration operation of the NOx trap catalyst in which the exhaust air-fuel ratio is enriched in a short time at relatively short time intervals, and the regeneration operation of the NOx trap catalyst It is necessary to carry out two types of regeneration operations, ie, a regeneration operation of the PM trap in which the exhaust gas temperature rise is performed while maintaining a lean state for a long time at longer time intervals.
[0006]
These regeneration operations are independent of each other, and the energy (fuel consumption) consumed for regeneration of the NOx trap catalyst cannot be used for regeneration of the PM trap during regeneration of the NOx trap catalyst. The energy consumed (fuel consumption) cannot be used for regeneration of the NOx trap catalyst during regeneration of the PM trap. For this reason, there was a problem that energy efficiency was bad and fuel consumption was greatly deteriorated.
[0007]
In view of such conventional problems, the present invention uses NOx trap catalysts and PM traps to prevent NOx and PM from being released into the atmosphere and to independently regenerate the NOx trap catalysts and PM traps. An object of the present invention is to realize an exhaust emission control device for an internal combustion engine that can be performed by a single operation without shortening the total regeneration time and does not involve a great sacrifice in fuel consumption.
[0008]
[Means for Solving the Problems]
Therefore, in the present invention, each cylinder group is divided into a plurality of cylinder groups each having one or a plurality of cylinders, and a NOx trap catalyst is provided for each of these cylinder groups. One PM trap is provided. An air-fuel ratio control apparatus capable of controlling the air-fuel ratio of the exhaust for each of the plurality of cylinder groups is used, and the air-fuel ratio of the exhaust flowing into the PM trap is determined at least at one regeneration time among the plurality of NOx trap catalysts. The air-fuel ratio of the exhaust gas is made rich in only one of the plurality of cylinder groups, and the air-fuel ratio of the other exhaust gas is made lean so as to be lean.
[0009]
【The invention's effect】
According to the present invention, two types of regeneration operations, namely regeneration of the NOx trap catalyst and regeneration of the PM trap, can be performed simultaneously without performing them individually. For this reason, since the energy consumed for regeneration is greatly reduced, it is possible to minimize the influence on fuel consumption deterioration.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
First, the first embodiment of the present invention will be described. Prior to this, the background art will be described at the embodiment level.
A three-way catalyst is widely used as a catalyst in order to purify exhaust gas in which an oxidizing component and a reducing component are contained almost equally as in a conventional automobile gasoline engine. This is a catalyst mainly composed of activated alumina carrying various components including noble metal components such as Pt (platinum), Pd (palladium), Rh (rhodium) and Ce (ceria) components. Harmful components HC, CO and NOx can be purified with high efficiency.
[0011]
On the other hand, in recent years, so-called lean burn engines that operate even at an air-fuel ratio higher than the stoichiometric air-fuel ratio have attracted attention from the viewpoint of improving fuel efficiency and reducing CO2 (carbon dioxide) emissions. The exhaust during lean combustion of this type of engine has a high oxygen content compared to the exhaust of a conventional engine that operates near the stoichiometric air-fuel ratio, and the above three-way catalyst has insufficient purification of NOx. Become. Therefore, a new catalyst that can efficiently remove NOx in exhaust during lean combustion in a lean burn engine has been desired.
[0012]
As one of them, it has been proposed to use a NOx trap catalyst that traps NOx when the air-fuel ratio of the inflowing exhaust gas is lean and reduces and purifies NOx when the air-fuel ratio of the inflowing exhaust gas becomes rich.
On the other hand, even if NOx can be removed by a NOx trap catalyst, PM cannot be removed. Therefore, in an internal combustion engine that releases PM, for example, a diesel engine, it is necessary to provide a PM trap that traps PM in exhaust gas.
[0013]
Against this background, as disclosed in Japanese Patent Laid-Open No. 9-53442, a PM trap (DPF; Diesel Particulate Filter) is disposed in the exhaust passage, and further, a NOx trap catalyst (NOx absorption catalyst) is disposed downstream thereof. The NOx trap catalyst regeneration operation and the PM trap regeneration operation are periodically performed separately.
[0014]
Further, in Japanese Patent No. 2727906 and Japanese Patent No. 2722987, it is determined that the NOx trap catalyst (NOx absorbent) is supported on the wall surface of the wall flow honeycomb type PM trap (DPF) and the regeneration start condition of the NOx trap catalyst is satisfied. When the intake throttle valve is closed, fuel is supplied from the reducing agent supply device into the exhaust gas at the PM trap inlet, and the supplied fuel is combusted by the catalytic action of the NOx trap catalyst to consume oxygen in the exhaust gas. As a result, the exhaust air-fuel ratio is enriched, thereby regenerating the NOx trap catalyst.
[0015]
Next, when it is determined that the regeneration of the NOx trap catalyst is finished, the fuel supply from the reducing agent supply device is continued, the intake throttle is released, and a large amount of air is supplied to trap the PM trap. PM is ignited and burned to regenerate the PM trap.
Further, in Japanese Patent No. 2727906, when the regeneration of the PM trap is completed, the intake throttle valve is closed again, fuel is supplied from the reducing agent supply device, and the exhaust gas is heated to a high temperature and rich, so that SOx (sulfur oxidation) is generated from the NOx trap catalyst. To release SOx poisoning.
[0016]
Accordingly, even in Japanese Patent No. 2727906 and Japanese Patent No. 2722987, each of the regeneration operations (NOx trap catalyst regeneration operation, PM trap regeneration operation, SOx poisoning elimination operation) has an independent action, and the NOx trap catalyst regeneration is performed. Since the exhaust is rich inside, the PM trap cannot be regenerated, and during regeneration of the PM trap, the exhaust is lean, so the NOx trap catalyst cannot be regenerated, and naturally the PM trap cannot be regenerated even during the SOx poisoning elimination operation. These simply perform each reproduction operation in turn.
[0017]
As described above, as conventional techniques, the regeneration operation of the NOx trap catalyst and the regeneration operation of the PM trap are separately performed (Japanese Patent Laid-Open No. 9-53442) and the one that is performed in order (Japanese Patent No. 2727906 or (Patent No. 2722987), but when performed separately or sequentially (not simultaneously), there is a disadvantage that not only the total regeneration time is lengthened, but also energy efficiency is poor and fuel consumption is greatly deteriorated. .
[0018]
Therefore, in the present embodiment, the regeneration of the NOx trap catalyst and the PM trap can be performed in one operation without being independent of each other, so that the total regeneration time can be shortened and the fuel efficiency can be improved by improving the energy efficiency. Like that.
FIG. 1 is a configuration diagram of an exhaust gas purification apparatus (exhaust gas purification aftertreatment system) for an internal combustion engine showing a first embodiment of the present invention.
[0019]
In FIG. 1, reference numeral 1 denotes a main body of an internal combustion engine (hereinafter referred to as a diesel engine, hereinafter simply referred to as an engine), 2 is an intake passage, and 3 is an exhaust passage.
The engine 1 of the present embodiment has four cylinders # 1 to # 4 and is an engine of a four-cylinder in-line arrangement in which the ignition order is # 1- # 3- # 4- # 2.
In addition, the engine 1 of the present embodiment has its exhaust system grouped into a cylinder group A consisting of # 2 and # 3 cylinders and a cylinder group B consisting of # 1 and # 4 cylinders.
[0020]
Here, the reason why the cylinder group is divided into the cylinder group A consisting of # 2 and # 3 cylinders and the cylinder group B consisting of # 1 and # 4 cylinders is that the exhaust efficiency decreases due to the interference of the exhaust stroke. This is because cylinders whose firing order is not continuous are combined in consideration of suppressing the reduction of the air filling rate. Therefore, if the layout is important, the cylinder group A may be divided into # 1 and # 2, and the cylinder group B may be divided into # 3 and # 4.
[0021]
In addition, when considering the suppression of exhaust interference in a six-cylinder in-line engine with an ignition order of # 1- # 5- # 3- # 6- # 2- # 4, set the cylinder group A to # 1, # 2, # 3. It is desirable to divide the cylinder group B into # 4, # 5, and # 6.
In FIG. 1, the upstream portion of the exhaust passage 3 connected to the exhaust port (not shown) of the engine 1 is connected to the exhaust pipe 3 a connected to the exhaust port of the cylinder group A and the exhaust port of the cylinder group B. And an exhaust pipe 3b.
[0022]
Downstream of the exhaust pipe 3a, NOx is trapped when the air-fuel ratio of the first oxidation catalyst 21a and the inflowing exhaust gas is lean, and NOx trapped when the air-fuel ratio of the inflowing exhaust gas is rich is reduced and purified. The first casing 20a that interposes the first NOx trap catalyst 22a to be inside, and the second oxidation catalyst 21b and the second NOx trap catalyst 22b to the inside downstream of the exhaust pipe 3b. The second casings 20b interposed between the two are connected to each other.
[0023]
Further, the exhaust outlets of the casing 20a and the casing 20b are connected to an exhaust pipe 3c that merges the exhausts of the respective cylinder groups into one, and the outlet part of the exhaust pipe 3c is connected upstream of the exhaust turbine 3d of the supercharger. Is done. A casing 23 having a DPF (Diesel Particulate Filter) 23a as a PM trap for trapping PM (Particulate Matter) in the exhaust gas is arranged in series downstream thereof. The DPF 23a has an oxidation function by supporting an oxidation catalyst on the surface thereof.
[0024]
As the oxidation catalysts 21a and 21b, for example, a catalyst in which a precious metal such as Pd or Pt is supported based on activated alumina, a zeolite in which a precious metal (particularly Pt) is ion-exchanged, or a combination of these two materials can be used.
Further, as the DPF 23a, a conventionally known wall flow honeycomb type or a structure in which ceramic fibers are wound in several layers around a bottomed cylindrical core member provided with a large number of holes in a cylindrical portion can be used.
[0025]
Exhaust temperature sensors 36a and 36b for detecting exhaust temperatures T1a and T1b are respectively provided at the inlet portions of the NOx trap catalysts 22a and 22b (respective outlet portions of the oxidation catalysts 21a and 21b), and at the inlet portion of the DPF 23a, An exhaust temperature sensor 37 for detecting the exhaust temperature T2 and an oxygen concentration sensor 38 for detecting the oxygen concentration O2 are provided.
An EGR passage 4 is provided for branching off the exhaust passage 3, here the exhaust pipe 3 b and returning a part of the exhaust to the intake pipe 2 c of the intake passage 2, and this EGR passage 4 includes an engine control unit. For example, an EGR valve 5 driven by a stepping motor controlled by 30 is provided.
[0026]
The intake passage 2 is provided with an air cleaner 2a, a turbocharger intake compressor 2b, and an intake throttle valve 6 driven by, for example, a stepper motor controlled by an engine control unit 30 from upstream, and intake air is taken in by a downstream intake pipe 2c. Is distributed to each cylinder of the engine 1.
The fuel supply system includes a diesel fuel (light oil) tank 60, a fuel supply passage 16 for supplying diesel fuel to the fuel injection device 10 of the engine 1, and a fuel tank for return fuel (spill fuel) from the fuel injection device 10. A fuel return passage 19 for returning to 60 is formed.
[0027]
The fuel injection device 10 of the engine 1 is a known common rail type fuel injection device, and includes a supply pump 11, a fuel supply passage 12, a common rail (accumulation chamber) 14, and a fuel injection valve 15 provided for each cylinder. After the fuel pressurized by 11 is temporarily stored in the common rail 14 via the fuel supply passage 12, the high-pressure fuel in the common rail 14 is distributed to the fuel injection valves 15 corresponding to the number of cylinders.
[0028]
Further, in order to control the pressure of the common rail 14, a part of the fuel discharged from the supply pump 11 is returned to the fuel supply passage 16 through an overflow passage 17 provided with a one-way valve 18 in the middle. A pressure control valve 13 capable of changing the flow passage area of the overflow passage 17 is provided. The pressure control valve 13 changes the flow passage area of the overflow passage 17 in accordance with a duty signal from the engine control unit 30. Thus, the pressure of the common rail 14 is controlled by adjusting the fuel discharge amount to the common rail 14.
[0029]
The fuel injection valve 15 is an electromagnetically driven injection valve that opens and closes a fuel supply passage to the engine combustion chamber by an ON-OFF signal from the engine control unit 30, and injects fuel into the combustion chamber by an ON signal. Injection is stopped by an OFF signal. Here, the longer the ON signal to the fuel injection valve 15, the greater the fuel injection amount. However, as will be described later, the fuel injection amount also changes depending on the fuel pressure of the common rail 14.
[0030]
The engine control unit 30 detects the signal (Tw) of the water temperature sensor 31, the signal of the crank angle sensor 32 (which can detect the engine speed Ne), the signal (Cyl) of the cylinder discrimination sensor 33, and the common rail pressure. An exhaust temperature sensor that detects a signal (PCR) of the pressure sensor 34, a signal (L) of the accelerator opening sensor 35, and an exhaust temperature of each inlet portion of each of the NOx trap catalysts 22a and 22b (each outlet portion of the oxidation catalysts 21a and 21b). The signals 36a and 36b (T1a and T1b), the exhaust temperature sensor 37 signal (T2) for detecting the exhaust temperature at the inlet of the DPF 23a, and the oxygen concentration sensor 38 signal (O2) are input.
[0031]
In this embodiment, the common rail type fuel injection device 10 capable of post injection that injects a small amount of fuel after main injection can control the air-fuel ratio of the exhaust for each of the plurality of cylinder groups A and B. Configure the control device. Further, the engine control unit 30 constitutes a regeneration timing determination unit and a regeneration control unit.
Next, control of the exhaust purification device (exhaust purification post-processing system) by the control unit 30 in the first embodiment will be described with reference to the flowcharts of FIGS.
[0032]
FIG. 2 is a main routine related to engine output control performed by the control unit 30.
In the engine output control routine of FIG. 2, in step 100 (denoted as S100 in the figure, the same applies hereinafter), the engine cooling water temperature Tw, the engine speed Ne, the cylinder discrimination signal Cyl, the common rail pressure PCR, the accelerator opening L, and the NOx trap. The exhaust temperature T1a at the inlet of the catalyst 22a (the outlet of the oxidation catalyst 21a), the exhaust temperature T1b at the inlet of the NOx trap catalyst 22b (the outlet of the oxidation catalyst 21b), the exhaust temperature T2 and the oxygen concentration O2 at the inlet of the DPF 23a And go to step 200.
[0033]
In step 200, common rail pressure control is performed according to a subroutine shown in FIG. 3 described later. In the next step 300, main injection control for engine output control is performed according to a subroutine shown in FIG. 4 described later, and the process proceeds to step 400.
In step 400, it is determined whether or not the post-processing system (in particular, the NOx trap catalysts 22a and 22b and the DPF 23a) is being regenerated is 1, and the post-processing system is being regenerated.
[0034]
If the determination in step 400 is NO and the post-processing system is not being regenerated, the process proceeds to step 500 where engine combustion control is performed according to the subroutine of FIG. 5 described later, and in the next step 600, the subroutine of FIG. Accordingly, the NOx trap amounts of the NOx trap catalysts (22a and 22b) are integrated, and based on this, it is determined whether or not the regeneration of the NOx trap catalysts (22a and 22b) is necessary, and the process returns.
[0035]
If the determination in step 400 is YES and the regeneration of the post-processing system is in progress, the process proceeds to step 700, and the regeneration control of the post-processing system is started or continued according to the subroutine of FIG. .
FIG. 3 is a subroutine related to common rail pressure control performed in step 200 of the main routine of FIG.
[0036]
In the common rail pressure control routine of FIG. 3, in step 201 and step 202, the engine speed Ne and the main fuel injection amount (preliminarily set corresponding to the accelerator opening L and the like and representing the load) Qmain are used as parameters. A predetermined map stored in advance in the ROM in the control unit 30 is searched, and the target reference pressure PCR0 of the common rail 14 and the reference duty ratio (reference control signal of the pressure control valve 13 for obtaining the target reference pressure PCR0). ) Determine Duty0 and go to Step 203.
[0037]
In step 203, the absolute value | PCR0−PCR | of the difference between the target reference pressure PCR0 and the actual common rail pressure PCR is obtained and compared with an allowable pressure difference ΔPCR0 preset for the target reference pressure PCR0.
If | PCR0−PCR | is within the allowable range, the process proceeds to step 204 where the same duty ratio is maintained by setting the reference duty ratio Duty0 as the valve opening duty ratio (control signal) Duty. A duty signal is generated from the valve opening duty ratio Duty to drive the pressure control valve 13.
[0038]
On the other hand, if | PCR0-PCR | is not within the allowable range, the process proceeds from step 203 to step 205, where a ROM table preset corresponding to PCR0-PCR (= ΔP) is searched, and the duty is A ratio correction coefficient KD duty is obtained. Here, for example, when ΔP is negative (PCR is larger than PCR0), KDuty is smaller than 1, and conversely when ΔP is positive (PCR is smaller than PCR0), KDuty is smaller than 1. Is also a large value. Specifically, the table data of the duty ratio correction coefficient KDuty is set in accordance with the characteristics of the pressure control valve 13.
[0039]
In step 206, the value obtained by correcting the reference duty ratio Duty0 with the correction coefficient KDuty (Duty0 × KDuty) is set as the valve opening duty ratio (correction control signal) Duty, and then the operation in step 207 is executed.
FIG. 4 is a subroutine related to main injection control performed in step 300 of the main routine of FIG.
[0040]
In the main injection control routine of FIG. 4, in step 301, a predetermined map stored in advance in the ROM in the control unit 30 is searched using the main fuel injection amount Qmain and the common rail pressure PCR as parameters, and the main injection period is determined. Mperiod is obtained and the process proceeds to step 302.
Here, the main injection period Mperiod is set in units of msec. As shown in FIG. 9, if the main fuel injection amount Qmain is the same, the higher the common rail pressure PCR, the shorter the main injection period Mperiod and the same common rail pressure PCR. The main injection period Mperiod becomes longer as the main fuel injection amount Qmain increases.
[0041]
In step 302, a predetermined map stored in advance in the ROM in the control unit 30 is searched using the engine speed Ne and the main fuel injection amount Qmain as parameters to obtain the main injection start timing Mstart. move on.
In step 303, the main injection start timing Mstart is corrected based on the engine coolant temperature Tw, and the routine proceeds to step 304.
[0042]
Specifically, the main injection start timing Mstart is advanced when the water temperature Tw is low. The lower the water temperature Tw, the lower the temperature of the engine combustion chamber, so the ignition start time will be relatively delayed. Therefore, in order not to increase emissions of HC, CO and PM (especially SOF: Soluble Organic Fraction), This is because it is desirable to keep the combustion start timing constant by correcting the advance of the injection start timing Mstart.
[0043]
In step 304, the fuel injection valve 15 of the cylinder to be main-injected is signaled to the crank angle sensor 32 and the cylinder discrimination sensor 33 for a period of Mperiod from the main injection start timing Mstart so that the main fuel injection amount Qmain is supplied. Based on this, the valve is opened.
FIG. 5 is a subroutine related to engine combustion control performed in step 500 of the main routine of FIG. 2, and performs control to perform EGR or stop corresponding to the operation region shown in FIG.
[0044]
In the engine combustion control routine of FIG. 5, in step 501, the operating region is determined. That is, it is determined whether or not the engine is in the EGR region based on the engine speed Ne and the main fuel injection amount (load) Qmain. Here, the EGR region is the normal operation region of the region A1 in FIG. 10, and therefore, here, is the normal operation region of the region A1 in FIG. 10 or other operation regions (regions A2, A3). Determine whether.
[0045]
If it is the EGR area in the determination in step 501, the process proceeds to step 502.
In step 502, the target EGR data (drive signals for the EGR valve 5 and the intake throttle valve 6) for executing the EGR are stored in the ROM in 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, and the process proceeds to step 503.
[0046]
In step 503, EGR is corrected based on the engine coolant temperature Tw, and the process proceeds to step 504.
Specifically, for example, the EGR is corrected to decrease when the water temperature Tw is low. The lower the water temperature Tw, the lower the temperature of the engine combustion chamber, so the ignition start time will be relatively delayed. Therefore, in order not to increase the emissions of HC, CO, and PM (especially SOF), the EGR is corrected to decrease. This is because it is desirable to keep the combustion start time constant.
[0047]
In step 504, EGR is performed by controlling the drive of the EGR valve 5 and the intake throttle valve 6 based on the corrected drive signals.
On the other hand, if it is determined in step 501 that the region is not the EGR region, the process proceeds to step 505.
In step 505, the operation of the EGR valve 5 and the intake throttle valve 6 is stopped to stop or hold the EGR.
[0048]
FIG. 6 is a subroutine relating to the NOx trap amount integration of the NOx trap catalyst (22a and 22b) and the determination as to whether regeneration is required, which is performed in step 600 of the main routine of FIG. This routine corresponds to a regeneration time determination means.
In the NOx trap amount integration / determination routine of FIG. 6, in step 601, the NOx trap amount (NOx trap amount per unit time) of the NOx trap catalyst (22a and 22b) is set to the engine speed Ne and the main fuel injection amount (load). ) Using Qmain as a parameter, a predetermined map stored in advance in the ROM in the control unit 30 is searched for and obtained, and the process proceeds to step 602.
[0049]
In step 602, the NOx trap amount is corrected based on the engine coolant temperature Tw, and the process proceeds to step 603.
Specifically, for example, when the water temperature Tw is low, the NOx trap amount is corrected to decrease. The lower the water temperature Tw is, the lower the temperature of the engine combustion chamber is. Therefore, the ignition start timing is relatively delayed. Therefore, in Step 303 of FIG. 4 and Step 503 of FIG. 5, as described above, HC, CO, PM In order not to increase the discharge amount (especially SOF), the main injection start timing Mstart is advanced and the EGR is decreased, so that the combustion start timing is kept constant. However, even if the combustion start timing is kept constant, the lower the temperature of the engine combustion chamber, the longer the combustion period and the lower the combustion temperature, and the NOx emission tends to decrease. When the NOx emission amount decreases, the NOx trap amount also tends to decrease. For this reason, it is desirable to set a correction coefficient for decreasing the NOx trap amount as the water temperature Tw is lower with the water temperature Tw as a parameter, and to reduce the NOx trap amount. The correction coefficient for the NOx trap amount is obtained in advance by experiments.
[0050]
In step 603, the NOx trap amount is integrated at a predetermined time interval synchronized with the NOx trap amount per unit time, and the process proceeds to step 604.
In step 604, the accumulated NOx trap amount exceeds the predetermined trap limit amount set in the NOx trap catalyst (22a and 22b), and regeneration (NOx release / reduction) of the NOx trap catalyst (22a and 22b) is necessary. It is determined whether or not.
[0051]
If the determination in step 604 is NO and regeneration is not necessary, a return is returned.
If the determination in step 604 is YES and the NOx trap amount exceeds the trap limit amount and it is determined that regeneration of the NOx trap catalyst (22a and 22b) is necessary, the process proceeds to step 605.
[0052]
In step 605, in order to start reproduction control, the reproduction flag is set to 1 (a flag is set as a reproduction start signal).
Then, the process proceeds to step 606, where an index value for end of reproduction, for example, counting of time is started, and a return is made. Although details will be described later, in the present embodiment, when the regeneration of each of the first NOx trap catalyst 22a and the second NOx trap catalyst 22b is completed, the regeneration of the post-processing system is completed.
[0053]
The index value for the end of regeneration is not only an example of time, but also the exhaust temperature T1a of the inlet part of the NOx trap catalyst 22a (the outlet part of the oxidation catalyst 21a) and the inlet part of the NOx trap catalyst 22b (the outlet part of the oxidation catalyst 21b). Multipliers of the exhaust temperature T1b and time may be integrated. In this way, the accuracy of the regeneration timing calculation is improved.
FIG. 7 is a subroutine related to regeneration control of the post-processing system (NOx trap catalysts 22a and 22b and DPF 23a) performed in step 700 of the main routine of FIG. This routine corresponds to the reproduction control means.
[0054]
In the post-processing system regeneration control routine of FIG. 7, in step 701, it is determined from the passage of time that is an index value whether or not a predetermined regeneration operation of the post-processing system has been completed.
If the determination in step 701 is NO and regeneration is not complete, the routine proceeds to step 702, where the post-injection data for enriching the exhaust air-fuel ratio, that is, the post-injection amount Qpost, the post-injection period Pperiod, the post-injection The injection start timing Pstart is obtained by searching from a predetermined map stored in the ROM in the control unit 30 using the engine speed Ne and the main fuel injection amount (load) Qmain as parameters of the operating state. move on.
[0055]
The post injection amount Qpost, the post injection period Pperiod, and the post injection start timing Pstart promote the oxidation reaction of the oxidation catalyst 21a (or 21b), and the NOx trap catalyst 22a (or 22b) regenerates (releases NOx / The exhaust air / fuel ratio flowing into the NOx trap catalyst 22a (or 22b) is enriched to increase the exhaust temperature, and the temperature and exhaust composition required to regenerate the DPF 23a as will be described later. As obtained, it is obtained and set in advance by experiments.
[0056]
In step 703, it is determined from the passage of time that is an index value whether regeneration of the first NOx trap catalyst 22a into which the exhaust gas from the cylinder group A flows is completed. Specifically, it is determined whether or not half of the total regeneration time set to continuously regenerate the two NOx trap catalysts 21a and 22b has elapsed.
If the regeneration of the first NOx trap catalyst 22a is not completed in the determination in step 703, the process proceeds to step 704.
[0057]
In step 704, the fuel injection valve 15 of the cylinder group A (# 2, # 3) to be post-injected for the period of Pperiod from the post injection start timing Pstart is supplied to the crank angle sensor 32 so that the post injection amount Qpost is supplied. The valve is driven to open based on the signal from the cylinder discrimination sensor 33.
Then, the process proceeds to step 705, where post-injection (Qpost) feedback control based on the signal (T1a) of the exhaust temperature sensor 36a at the inlet of the first NOx trap catalyst 22a (outlet of the oxidation catalyst 21a), that is, the above-described predetermined value. If the temperature is such that the catalytic reaction of the first NOx trap catalyst 22a is not accelerated even after the post-injection is performed, the post-injection increase correction is performed to ensure basic exhaust conditions necessary for regeneration of the post-processing system.
[0058]
If the regeneration of the first NOx trap catalyst 22a has been completed in step 703, the process proceeds to step 706.
In step 706, whether or not the regeneration of the second NOx trap catalyst 22b into which the exhaust gas from the cylinder group B flows is completed is determined from the passage of time as an index value. Specifically, it is determined whether or not the total regeneration time set to continuously regenerate the two NOx trap catalysts 21a and 22b has elapsed.
[0059]
If it is determined in step 706 that the regeneration of the second NOx trap catalyst 22b has not ended, the process proceeds to step 707.
In step 707, the fuel injection valve 15 of the cylinder group B (# 1, # 4) to be post-injected for the period of Pperiod from the post-injection start timing Pstart is supplied to the crank angle sensor 32 so that the post-injection amount Qpost is supplied. The valve is driven to open based on the signal from the cylinder discrimination sensor 33.
[0060]
Then, the routine proceeds to step 708, where post-injection (Qpost) feedback control based on the signal (T1b) of the exhaust temperature sensor 36b at the inlet portion of the second NOx trap catalyst 22b (outlet portion of the oxidation catalyst 21b), that is, the above-described predetermined control. If the temperature is such that the catalytic reaction of the second NOx trap catalyst 22b is not promoted even after the post-injection is performed, the post-injection increase correction is performed to ensure basic exhaust conditions necessary for regeneration of the post-processing system.
[0061]
Here, in the post-injection, the NOx trap catalyst 22a (or 22b) is first regenerated, so that the amount of fuel that can enrich the exhaust air-fuel ratio of the cylinder group A (or B) (for example, the air-fuel ratio of 13 or less) is increased. In addition to injection, injection is performed in the expansion stroke or exhaust stroke of each cylinder, and not fuel injection for obtaining output.
Therefore, part of the post-injected fuel burns in the cylinder to raise the exhaust temperature, and the rest flows into the oxidation catalyst 21a (or 21b) in an unburned state (HC, CO). Here, in order to promote the oxidation reaction of the oxidation catalyst 21a (or 21b), the temperature of the exhaust gas flowing into the oxidation catalyst 21a (or 21b) is set to, for example, 250 ° C. or more, which is the activation temperature of the oxidation catalyst 21a (or 21b). And
[0062]
That is, since all of the post-injected fuel does not burn in the cylinder, oxygen (O2) and unburned fuel components (HC, CO) that have not been consumed in the cylinder are the lowest in the oxidation catalyst 21a (or 21b). However, it flows in while maintaining the exhaust temperature of 250 ° C.
Then, a part of the unburned fuel that has flowed in and O2 react with each other in the oxidation catalyst 21a (or 21b), so that O2 is consumed and the temperature further rises. Here, considering that the downstream DPF 23a is regenerated, the temperature of the exhaust gas flowing into the NOx trap catalyst 22a (or 22b) is set to 500 ° C. or more, for example.
[0063]
Then, the same as when the engine was burned in a richer state than the theoretical mixing ratio (for example, an air-fuel ratio of 13 or less), it contains almost no O2 and contains a lot of unburned components as a reducing agent, and high-temperature exhaust gas. As a result of flowing into the NOx trap catalyst 22a (or 22b), the NOx trap catalyst 22a (or 22b) is regenerated, and the temperature further rises due to the catalytic reaction in the NOx trap catalyst 22a (or 22b).
[0064]
As described above, when the NOx trap catalyst 22a (or 22b) is regenerated, when the exhaust air-fuel ratio enrichment control is performed in the cylinder group A, the enrichment control is not performed in the cylinder group B. Conversely, when the exhaust air-fuel ratio enrichment control is performed in the cylinder group B, the enrichment control is not performed in the cylinder group A.
Therefore, in the exhaust pipe 3c immediately downstream of the NOx trap catalysts 22a and 22b, the rich exhaust gas and the normal lean exhaust gas merge, but the exhaust of the diesel engine is at least about λ≈1.5. The excess air ratio is large. For this reason, even if the exhaust air-fuel ratio of one cylinder group is enriched to 13 (λ≈0.9), for example, the average exhaust air-fuel ratio after merging is at least about 18 (λ≈1.2). It contains O2 at a considerable concentration (4-5%).
[0065]
As a result, exhaust gas that has been heated to a high temperature by the catalytic reaction by the oxidation catalyst 21a (or 21b) and the NOx trap catalyst 22a (or 22b) and contains a large amount of O2 flows into the DPF 23a. The PM that is burned burns and the DPF 23a is also regenerated.
Here, SOF such as hydrocarbons in the PM component can be removed at a relatively low temperature (oxidation treatment at about 200 ° C. or higher), whereas carbon is used for dry soot in the PM component. Since it is a main component and carbon is a stable substance, it cannot normally be incinerated unless it is at a relatively high temperature of about 600 ° C or higher. However, an oxidation catalyst is supported on the surface of the DPF 23a to promote the oxidation reaction by O2. By doing so, even if the PM component collected in the DPF 23a is almost carbon, combustion can be started at about 450 ° C. or higher. Therefore, the temperature of the exhaust gas flowing into the catalyst-carrying DPF 23a is set to about 450 ° C. or higher.
[0066]
The time required to regenerate the NOx trap catalyst by enriching the exhaust air-fuel ratio varies depending on the capacity of the catalyst and the regeneration interval (NOx trap amount), but in recent engines, the time ratio is approximately 1-2%. is necessary. The time required to regenerate the DPF also varies depending on the capacity of the DPF and the regeneration interval (PM deposition amount). However, in recent engines, the operation frequency at a temperature of 450 ° C. or higher is about 2 to 4% with a catalyst-supported DPF. Is necessary.
[0067]
In normal operation (operation in which DPF forced regeneration operation is not performed), the operation frequency at a temperature of 450 ° C. or higher is only about 1 to 2%, and a frequency shortage of about 3% at maximum occurs. For this reason, a forced temperature increase operation (regeneration operation in a lean state) is required. This point has also been confirmed in the applicant's research.
As described in JP-A-9-53442, if the regeneration of the NOx trap catalyst (reduction reaction) by the enrichment and the regeneration of the DPF (oxidation reaction) in a lean state are performed separately, the deterioration of fuel consumption will inevitably occur. growing.
[0068]
In other words, if both regeneration operations can be performed at the same time, the regeneration frequency can be halved, and the efficiency of using the energy used for regeneration can be increased, so fuel consumption deterioration can be minimized. .
After securing the basic exhaust conditions necessary for regeneration of the aftertreatment system in step 705 or step 708, the process proceeds to step 709.
[0069]
In step 709, post-injection (Qpost) refeedback control is performed based on the signal (T2) of the exhaust temperature sensor 37 at the inlet of the DPF 23a and the signal (O2) of the oxygen concentration sensor 38, so that the DPF 23a The exhaust conditions (temperature and O2 concentration) suitable for regeneration are maintained, and a return is obtained.
Here, assuming that the PM trapped in the DPF 23a is almost carbon, the exhaust condition suitable for regenerating the DPF 23a by the oxidation reaction with O2 requires a temperature of about 450 ° C. or higher as described above. is there. As the O2 concentration, at least about 4% is necessary.
[0070]
This exhaust condition (particularly temperature) is set in advance so as to be obtained by post-injection up to step 705 (or step 708) and catalytic reaction by the oxidation catalyst 21a (or 21b) and the NOx trap catalyst 22a (or 22b). .
In the post-injection amount Qpost correction control performed in step 709, feedback increase / decrease correction control is performed to maintain the above-mentioned temperature condition (about 450 ° C. or higher with catalyst-supported DPF) to ensure the minimum required O2 concentration (for example, 4%). .
[0071]
If it is determined in step 706 that the regeneration of the second NOx trap catalyst 22b has been completed, the process returns.
Accordingly, the determination in step 701 is inevitably YES, and it is determined that the predetermined reproduction operation has been completed. In this case, the process proceeds to step 710, and the regeneration control of the post-processing system is initialized. That is, the post-injection is stopped, the regeneration flag, the NOx trap amount integrated value, and the regeneration time count are reset to 0, respectively, and the process returns.
[0072]
According to the present embodiment, the NOx trap catalysts 22a and 22b are provided for each of a plurality of cylinder groups, and a single DPF 23a is commonly provided on the downstream side of these, and the exhaust air flowing into the DPF 23a at the regeneration time is exhausted. The NOx trap catalysts 22a and 22b are regenerated and the DPF 23a is regenerated by making the air-fuel ratio of the exhaust gas rich in only one of the plurality of cylinder groups and making the air-fuel ratio of the other exhaust gas lean so that the fuel ratio becomes lean. Since the two types of regeneration operations can be performed simultaneously without performing each individually, the energy consumed for regeneration can be greatly reduced, and the influence on fuel consumption deterioration can be minimized.
[0073]
Further, according to this embodiment, when the air-fuel ratio of the exhaust gas is made rich in only one of the plurality of cylinder groups and the air-fuel ratio of the other exhaust gas is made lean, the exhaust of the cylinder group in which the air-fuel ratio of the exhaust gas is made rich. The exhaust temperature at the inlet of the DPF 23a is controlled to a temperature at which the DPF 23a can be regenerated (a temperature at which PM can be combusted), so that the regeneration of the DPF 23a can be ensured.
[0074]
In addition, according to the present embodiment, the oxidation catalyst 21a includes the oxidation catalysts 21a and 21b that correspond to the plurality of NOx trap catalysts 22a and 22b and that are disposed in the upstream exhaust passage and oxidize the inflowing exhaust components. , 21b can be used, that is, to enrich the exhaust air-fuel ratio, when HC and CO discharged from the engine are increased in an unburned state, they are burned by a catalytic reaction with O2, and further Because the temperature rises, when controlling the exhaust temperature of the cylinder group that has made the exhaust air-fuel ratio rich, this exhaust temperature can be kept low, thereby reducing the energy consumption spent on regeneration and deteriorating fuel consumption The impact on can be minimized. The same as when the engine is burned in a state richer than the theoretical mixing ratio, the exhaust gas at a high temperature contains NO 2 and contains a large amount of unburned components as a reducing agent. As a result, the regeneration of the NOx trap catalyst 22a (or 22b) is also promoted.
[0075]
Further, according to the present embodiment, the temperature at which the DPF 23a can be regenerated (the temperature at which PM can be combusted) can be lowered to about 450 ° C. by supporting the catalyst on the DPF 23a to have an oxidation function. When controlling the exhaust temperature of the cylinder group in which the exhaust air-fuel ratio is made rich, this exhaust temperature can be kept low (particularly in combination with the one having an oxidation catalyst upstream of the NOx trap catalyst). This can reduce the energy consumption spent for regeneration, thereby minimizing the effect on fuel consumption deterioration, and more reliable regeneration of the DPF 23a. .
[0076]
Further, according to the present embodiment, in order to enrich the air-fuel ratio of only one of the plurality of cylinder groups and make the air-fuel ratio of the other exhaust gas lean, post-injection is performed in the enriched cylinder group. Therefore, if a fuel injection device capable of post-injection (a common rail fuel injection device) is provided, it can be carried out, and there is no need to provide a special device.
Further, according to the present embodiment, at least one of the post-injection injection amount, the injection period, and the injection start timing is set according to the operating state (engine load, engine speed), so that the exhaust suitable for the operating state is set. It is possible to enrich the air-fuel ratio.
[0077]
Next, a second embodiment of the present invention will be described.
Diesel engines in recent years have adopted technologies such as electronically controlled EGR and fuel injection control technology, supercharger mounting, or common rail fuel injection systems, and have made significant progress in purifying exhaust and improving fuel efficiency. Therefore, the exhaust gas temperature characteristic tends to decrease as the combustion efficiency improves.
[0078]
For this reason, in a recent diesel engine, the engine operating region is divided into regions A1 to A3 as shown in FIG.
[Area A1]
It is a normal operation region where the operation frequency is high, and most regions are operated at a low exhaust temperature of 250 ° C. or less. Further, in recent diesel engines, NOx is reduced by EGR in this region.
[0079]
[Area A2]
It is an area where emphasis is placed on improving the output characteristics without discharging smoke. In recent diesel engines, a turbocharger is installed, and the air filling rate is increased by adopting 4-valve technology etc. It has been. Moreover, EGR is small and it stops at a high load. Of course, the exhaust gas temperature is higher than that in the region A1.
[0080]
[Area A3]
This is an area where emphasis is placed on increasing torque in order to improve start acceleration performance, and the maximum allowable fuel is supplied to the engine in a range below the level where smoke is not visible. In general, the air filling efficiency is relatively low at a low rotation, and the efficiency of the supercharger is also relatively low. As in the region A2, the EGR is stopped at a high load, and the exhaust temperature is relatively high.
[0081]
In the first embodiment (the post-processing system regeneration control routine in FIG. 7), the post-processing system is regenerated by post injection regardless of the operation region.
However, as described above, the region A1 is a normal operation region with a low load, and even if EGR is performed, the excess air ratio is relatively large (λ = about 3 to 5). In order to enrich the exhaust air-fuel ratio by performing post-injection in such a low-load operating region, it is necessary to post-inject fuel that is twice to four times the amount of main injection fuel, and for a short time (time Even if the ratio is about 1 to 2%), the fuel consumption deterioration rate increases.
[0082]
For this reason, in this region A1, post-injection is preferably performed in combination with EGR enhancement (reduction of the intake throttle valve opening, increase of the EGR valve opening) in order to assist the enrichment of the exhaust air-fuel ratio. The NOx release / reduction reaction is improved by the exhaust gas temperature increase due to the reduction in the intake air amount due to the throttle and the gas amount passing through the catalyst (SV ratio decrease).
[0083]
It should be noted that, when the EGR is strengthened, it is desirable that the EGR is naturally performed in a range where compression ignition is established (EGR strengthening that does not cause misfire). If this level of EGR strengthening is performed, the region A1 has a large excess air ratio. Since dry soot containing carbon as a main component does not increase and gas components that can be treated with a catalyst such as HC and CO increase, it is convenient for post-treatment.
[0084]
Regions A2 and A3 are regions with a relatively high load, and the excess air ratio is relatively small (approximately λ = 1.5 to 3). Therefore, the post-injection amount required to enrich the exhaust air-fuel ratio by performing post-injection can be dealt with by injecting fuel in an amount about 0.5 to at most twice the amount of main injection fuel. The fuel consumption deterioration rate can be relatively small.
[0085]
In addition, since the excess air ratio is relatively small, dry soot (smoke) containing carbon as a main component increases drastically when EGR is performed. become. Therefore, it is preferable to enrich the exhaust air-fuel ratio by post injection in the regions A2 and A3.
Therefore, in the second embodiment of the present invention, the regeneration control (air-fuel ratio enrichment) method is changed according to the operating state (region A1, regions A2, A3).
[0086]
The system configuration of the second embodiment is the same as that of the first embodiment (FIG. 1), but in the second embodiment, a common rail fuel injection device capable of post injection that injects a small amount of fuel after main injection. In addition to 10, the intake throttle valve 6 and the EGR valve 5 constitute an air-fuel ratio control apparatus capable of controlling the air-fuel ratio of the exhaust for each of the plurality of cylinder groups A and B.
The control flow of the second embodiment includes the flow of FIGS. 2 to 6 (common to the first embodiment) and the flow of FIG. 8 executed in place of the flow of FIG.
[0087]
FIG. 8 is a subroutine relating to regeneration control of the post-processing system in the second embodiment, and is executed in step 700 of the main routine of FIG. 2 instead of the subroutine of FIG. Therefore, this routine corresponds to the reproduction control means in the second embodiment. In FIG. 8, the functional parts similar to those in FIG. 7 will be described briefly.
[0088]
In the post-processing system regeneration control routine of FIG. 8, in step 711, it is determined whether or not a predetermined regeneration operation of the post-processing system has ended, from the passage of time as an index value.
If the determination in step 711 is NO and the reproduction has not ended, the process proceeds to step 712.
[0089]
In step 712, the operation region is determined. That is, based on the engine speed Ne and the main fuel injection amount (load) Qmain, is the normal operation region of the region A1 as shown in FIG. 10 or the other operation regions (regions A2, A3)? Determine. And if it is the normal operation area | region of area | region A1, it will progress to step 713.
In step 713, EGR reinforcement data (driving signals for the intake throttle valve 6 and the EGR valve 5) for assisting the enrichment of the exhaust air-fuel ratio is operated, and the engine speed Ne and the main fuel injection amount (load) Qmain are operated. As a state parameter, a predetermined map stored in advance in the ROM in the control unit 30 is searched for and obtained. In step 714, the intake throttle valve 6 and the EGR valve 5 are driven and controlled based on the respective drive signals, the EGR is strengthened to assist the enrichment of the exhaust air / fuel ratio, and the flow proceeds to step 715.
[0090]
In step 715, post injection data (post injection amount Qpost1, post injection period Pperiod1, post injection start timing Pstart1) for regenerating the NOx trap catalyst 22a (or 22b) in the region A1 is obtained.
When the determination in step 712 is not the normal operation region (in the case of regions A2 and A3), the process proceeds to step 716, and post injection data (post) for regenerating the NOx trap catalyst 22a (or 22b) in regions A2 and A3. The injection amount Qpost2, the post injection period Pperiod2, and the post injection start timing Pstart2) are obtained.
[0091]
After retrieving post-injection data for regeneration of the NOx trap catalyst 22a (or 22b) in step 715 or step 716, the process proceeds to step 717, where the first NOx trap catalyst 22a into which the exhaust gas of the cylinder group A flows. It is determined from the lapse of time as an index value whether or not the reproduction of has been completed.
If the regeneration of the first NOx trap catalyst 22a has not ended in the determination at step 717, the routine proceeds to step 718, where the post injection start timing Pstart1 (or so that the post injection amount Qpost1 (or Qpost2) is supplied. The fuel injection valve 15 of the cylinder group A (# 2, # 3) to be post-injected is driven to open based on the signals of the crank angle sensor 32 and the cylinder discrimination sensor 33 for a period of Pperiod1 (or Pperiod2) from Pstart2). .
[0092]
In step 719, feedback control of post injection (Qpost1 or Qpost2) based on the signal (T1a) of the exhaust temperature sensor 36a at the inlet of the first NOx trap catalyst 22a (outlet of the oxidation catalyst 21a), that is, the above-mentioned. If the temperature is such that the catalytic reaction of the first NOx trap catalyst 22a is not promoted even if the predetermined post-injection is performed, the post-injection increase correction is performed to ensure basic exhaust conditions necessary for regeneration of the post-processing system.
[0093]
If the regeneration of the first NOx trap catalyst 22a has been completed as determined in step 717, the process proceeds to step 720 to determine whether the regeneration of the second NOx trap catalyst 22b into which the exhaust gas from the cylinder group B flows has been completed. Judgment is made from the lapse of time as an index value.
If the regeneration of the second NOx trap catalyst 22b is not completed in the determination in step 720, the process proceeds to step 721, and the post injection start timing Pstart1 (or so that the post injection amount Qpost1 (or Qpost2) is supplied. From Pstart2) to Pperiod1 (or Pperiod2), the fuel injection valves 15 of the cylinder group B (# 1, # 4) to be post-injected are driven to open based on signals from the crank angle sensor 32 and the cylinder discrimination sensor 33. .
[0094]
Then, the process proceeds to step 722, and feedback control of post injection (Qpost1 or Qpost2) based on the signal (T1b) of the exhaust temperature sensor 36b at the inlet of the second NOx trap catalyst 22b (outlet of the oxidation catalyst 21b), that is, the above-mentioned. If the temperature is such that the catalytic reaction of the second NOx trap catalyst 22b is not promoted even if the predetermined post-injection is performed, the post-injection increase correction is performed to ensure basic exhaust conditions necessary for regeneration of the post-processing system.
[0095]
After securing the basic exhaust conditions necessary for regeneration of the aftertreatment system in step 719 or step 722, the process proceeds to step 723, and the signal (T2) of the exhaust temperature sensor 37 at the inlet of the DPF 23a and the signal ( Based on O2), re-feedback control of post injection (Qpost1 or Qpost2) is performed to maintain exhaust conditions (temperature and O2 concentration) suitable for regeneration of the DPF 23a and return.
[0096]
If it is determined in step 720 that the regeneration of the second NOx trap catalyst 22b has been completed, the process returns.
Accordingly, it is inevitably determined as YES in Step 711, and it is determined that the predetermined reproduction operation is finished. In this case, the process proceeds to step 724 to initialize the regeneration control of the post-processing system. That is, the post injection is stopped, the EGR reinforcement is stopped, the regeneration flag, the NOx trap amount integrated value, and the regeneration time count are reset to 0, respectively, and a return is made.
[0097]
In particular, according to the present embodiment, only one of a plurality of cylinder groups has an exhaust air-fuel ratio rich, and other exhaust air-fuel ratios lean. ), At least one of the reduction of the intake throttle valve opening and the increase of the EGR valve opening (EGR strengthening) is performed, and post-injection is performed in the cylinder group to be rich, and a high load (high load high) When the engine is rotating, or more than medium-medium-load rotation), only post-injection is performed in the rich cylinder group. Therefore, a post-injectable fuel injection device (common rail fuel injection device), intake throttle valve, EGR valve It can be implemented if equipped, and it is not necessary to provide a special device. In addition, the exhaust air-fuel ratio can be enriched in a manner suitable for the operating state of the engine, and the energy consumption for regeneration can be further saved. , It is possible to further reduce the impact on fuel economy.
[0098]
Further, according to the present embodiment, at least one of the post-injection injection amount, the injection period, and the injection start timing is set according to the operating state (engine load, engine speed), and in particular, the EGR strengthening region and the others Therefore, the post-injection setting suitable for the operation state can be set, and there is no waste and the post-processing system can be regenerated with high efficiency.
[0099]
In the above, the case where the present invention is applied to an engine arranged in series has been described. However, the exhaust emission control device of the present invention can be applied not only to an engine arranged in series but also to a 6-cylinder or 8-cylinder engine arranged in V shape. In the case of the V type, for example, six cylinders are divided into two cylinder groups each having three cylinders, and the exhaust passages are connected to each other. Therefore, in comparison with a series arrangement in which the exhaust passages need to be divided for grouping. It is easy to apply the present invention.
[0100]
Moreover, although embodiment shows the example of the engine with a supercharger, a naturally aspirated engine may be sufficient.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an aftertreatment system for exhaust gas purification according to a first embodiment of the present invention.
FIG. 2 is a flowchart of an engine output control routine.
FIG. 3 is a flowchart of a common rail pressure control routine.
FIG. 4 is a flowchart of a main injection control routine
FIG. 5 is a flowchart of an engine combustion control routine.
FIG. 6 is a flowchart of a NOx trap amount integration / determination routine.
FIG. 7 is a flowchart of a post-processing system regeneration control routine in the first embodiment.
FIG. 8 is a flowchart of a post-processing system regeneration control routine in the second embodiment.
FIG. 9 is a characteristic diagram of the fuel injection amount according to the common rail pressure and the fuel injection period.
[Fig. 10] Characteristic chart of operation area
[Explanation of symbols]
1 engine
2 Intake passage
3 Exhaust passage
4 EGR passage
5 EGR valve
6 Inlet throttle valve
10 Fuel injector
11 Supply pump
14 Common rail
15 Fuel injection valve
21a, 21b oxidation catalyst
22a, 22b NOx trap catalyst
23a DPF with oxidation function
30 Control unit

Claims (7)

A plurality of cylinder groups each consisting of one or more cylinders;
Each of the cylinder groups is arranged corresponding to the plurality of cylinder groups, and exhaust gas discharged from the corresponding cylinder group flows in. When the air-fuel ratio of the exhaust gas of the corresponding cylinder group is lean, NOx is trapped. A plurality of NOx trap catalysts for reducing and purifying trapped NOx when the air-fuel ratio of exhaust is rich;
A single PM trap that traps the PM in the exhaust that flows in, and traps all the exhaust discharged by the plurality of NOx trap catalysts;
An air-fuel ratio control device capable of controlling the air-fuel ratio of the exhaust for each of the plurality of cylinder groups;
Regeneration timing determination means for determining the regeneration timing of at least one of the plurality of NOx trap catalysts;
When the regeneration time is determined, the air-fuel ratio control device enriches the air-fuel ratio of only one of the plurality of cylinder groups so that the air-fuel ratio of the exhaust flowing into the PM trap becomes lean. And other regeneration control means for leaning the air-fuel ratio of the exhaust,
An exhaust emission control device for an internal combustion engine, comprising: When the regeneration control means makes the air-fuel ratio of the exhaust only one of the plurality of cylinder groups rich and makes the air-fuel ratio of the other exhaust lean, the temperature of the exhaust of the cylinder group that made the exhaust air-fuel ratio rich The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas temperature at the inlet of the PM trap is controlled to a temperature at which the PM trap can be regenerated. The exhaust emission control device for an internal combustion engine according to claim 2, further comprising an oxidation catalyst corresponding to the plurality of NOx trap catalysts and disposed in an upstream exhaust passage thereof for oxidizing an inflowing exhaust component. The exhaust purification device for an internal combustion engine according to claim 2 or 3, wherein the PM trap has an oxidation function. The air-fuel ratio control device includes a fuel injection device capable of post injection that injects a small amount of fuel after main injection,
The regeneration control means performs post-injection in the rich cylinder group in order to enrich the air-fuel ratio of only one of the plurality of cylinder groups and make the air-fuel ratio of the other exhaust gas lean. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4. The air-fuel ratio control device includes a post-injection fuel injection device that injects a small amount of fuel after main injection, an intake throttle valve that can control the intake air amount, and an EGR that can control the exhaust gas recirculation amount to the intake passage. With a valve,
The regeneration control means makes the air-fuel ratio of the exhaust of only one of the plurality of cylinder groups rich, and makes the air-fuel ratio of the other exhausts lean. At least one of reducing the opening degree and increasing the EGR valve opening degree, and post-injecting in the cylinder group to be rich, and only performing post-injection in the cylinder group to be rich at high loads The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, wherein the exhaust gas purification device is an internal combustion engine. The exhaust of the internal combustion engine according to claim 5 or 6, wherein the regeneration control means sets at least one of an injection amount, an injection period, and an injection start timing of the post injection according to an operating state. Purification equipment.

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