JP4161720B2 - 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 for an internal combustion engine, and more particularly to an apparatus capable of accurately determining sulfur poisoning of a NOx adsorption catalyst.
[0002]
[Prior art]
As an exhaust gas purification device for an internal combustion engine, a NOx adsorption catalyst that adsorbs NOx discharged during lean operation and performs reduction treatment during rich or stoichiometric operation is known. When this NOx adsorption catalyst is poisoned by the sulfur component contained in the fuel, the NOx adsorption performance deteriorates. In order to maintain a good NOx treatment effect, it is necessary to detoxify the NOx adsorption catalyst. For this reason, the fuel supply amount is controlled so that the exhaust temperature temporarily becomes high.
[0003]
In order to release NOx adsorption catalyst poisoning, it is necessary to know the poisoning state accurately. In addition to the travel distance, rotation speed, temperature, lean operation time, etc. of the internal combustion engine, the state of the air-fuel mixture in the cylinder, the internal There is one that determines the poisoning state in consideration of the exhaust gas recirculation amount (see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-11-107810
[0005]
Problems to be Solved by the Invention
However, the determination of the poisoning state of the NOx adsorption catalyst based on the operating state of the internal combustion engine as described above has a limit because the sulfur component contained in the fuel is variously different including the destination. Therefore, since it is very difficult to directly detect the amount of sulfur poisoning, the poisoning state cannot be accurately determined.
[0006]
If the poisoning state of the NOx adsorption catalyst cannot be accurately determined, the NOx purification performance decreases, or if the poisoning process is performed without correctly grasping the poisoning state, unnecessary poisoning processes are repeated. It may lead to deterioration of fuel consumption.
[0007]
An object of this invention is to determine correctly the poisoning state of a NOx adsorption catalyst.
[0008]
[Means for Solving the Problems]
An exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a NOx adsorption catalyst that adsorbs NOx in exhaust during lean operation at an air-fuel ratio and desorbs and reduces NOx adsorbed during rich operation. Means for detecting the excess air ratio of the upstream and downstream exhausts of the NOx adsorption catalyst, and the excess air ratio of the upstream and downstream exhausts during the rich operation And calculate the average value of each of these average values. Poisoning judging means for judging the poisoning state of the NOx adsorption catalyst from the difference.
[0009]
[Action / Effect]
When the NOx adsorption catalyst is poisoned, the NOx adsorption function is reduced and the NOx reduced during the rich operation is reduced. In this state, most of the rich exhaust gas passes through the catalyst without being used for NOx reduction. In this case, similarly to the upstream side of the catalyst, the excess air ratio of the downstream side exhaust also becomes small (rich). Therefore, it is possible to accurately determine the poisoning state of the catalyst by detecting the excess air ratio (exhaust air / fuel ratio) of the exhaust upstream and downstream of the catalyst during operation and judging the difference between them.
[0010]
Embodiment
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
First, a first embodiment is shown in FIGS.
[0012]
In FIG. 1, 1 is an engine, 9 is an intake passage, and 10 is an exhaust passage. The exhaust passage 10 traps (adsorbs) NOx in exhaust during an air-fuel ratio lean operation and desorbs NOx during a rich operation. A NOx trap catalyst (NOx adsorption catalyst) 16 for reduction is installed.
[0013]
An air flow meter 3 for measuring the intake air amount and an intake throttle valve 15 for adjusting the intake air amount are interposed in the intake passage 9.
[0014]
An injector 5 is installed in the engine 1 for each cylinder, and fuel pressurized by the common rail 6 is injected and supplied to each cylinder.
[0015]
The exhaust passage 10 and the intake passage 9 are connected to each other, and an EGR passage 11 for returning a part of the exhaust gas into the intake air is provided. The EGR passage 11 controls an exhaust gas recirculation amount in accordance with an operating state. 12 is provided.
[0016]
A controller 8 controls the fuel injection timing, the injection pressure, the injection amount, the exhaust gas recirculation amount, and the like according to the operating state. For this reason, the crank angle sensor 4 for detecting the crank angle (engine speed), the accelerator opening sensor 13 for detecting the opening degree of the accelerator pedal, and the cooling water temperature sensor for detecting the engine cooling water temperature as signals representative of the driving state. 2. A fuel temperature sensor 14 for detecting the fuel temperature and a signal from the air flow meter 3 are input to the controller 8.
[0017]
The controller 8 performs a lean operation such as when the engine is partially loaded, and NOx discharged at this time is adsorbed by the NOx trap catalyst 16, and when the adsorbed amount reaches a predetermined value, the air-fuel ratio is temporarily increased. Rich spike is performed to desorb and reduce adsorbed NOx.
[0018]
Further, the controller 8 determines the poisoning state due to the sulfur content contained in the fuel of the NOx trap catalyst 16, and when the poisoning amount exceeds a predetermined value, the rich operation is temporarily performed and the poisoning release is executed.
[0019]
For this reason, in the present invention, air-fuel ratio sensors (A / F sensors) 17a and 17b are provided upstream and downstream of the NOx trap catalyst 16, and when the rich spike is performed, these are detected upstream and downstream of the catalyst. Based on the air-fuel ratio (excess air ratio λ), the poisoning state of the NOx trap catalyst 16 is determined.
[0020]
When the NOx trap catalyst 16 is poisoned, the NOx adsorption function is reduced, and the NOx reduced during the rich spike is reduced. Therefore, most of the rich exhaust gas discharged by the rich spike is used for NOx reduction. Instead, the catalyst passes through the catalyst as it is, and in this case, the air-fuel ratio on the downstream side becomes rich as well as the upstream side of the catalyst. Therefore, the poisoning state of the catalyst can be determined from the difference in the air-fuel ratio (excess air ratio) between the exhaust gas upstream and downstream of the catalyst during the rich spike.
[0021]
The determination of the poisoning state of the NOx trap catalyst 16 executed by the controller 8 will be described with reference to the flowcharts of FIGS.
[0022]
FIG. 4 shows the main routine for the poisoning determination, which shows the contents of the control operation in time series. On the other hand, the flowcharts of FIGS. It is executed periodically.
[0023]
First, in FIG. 4, in step S101, it is determined whether or not a rich spike has occurred. If rich spike is in progress, the process proceeds to step S102, and if not, the flow ends. The rich spike is executed when the amount of NOx trapped in the NOx trap catalyst 16 reaches a predetermined value, but functions in the same way when a rich operation is performed during engine acceleration or the like.
[0024]
In step S102, the engine speed Ne, the fuel injection amount Qf, the target excess air ratio during the rich spike, the NOx trap amount NOxtrap at the NOx trap catalyst 16 at the rich spike time, and #DEF which is the catalyst poisoning judgment value Is read.
[0025]
The excess air ratio is the ratio of the control air-fuel ratio to the stoichiometric air-fuel ratio, and is 1 when the stoichiometric air-fuel ratio is reached. The lean air-fuel ratio is a value larger than 1, and the rich air-fuel ratio is smaller than 1. The NOx trap amount is calculated based on the lean operation integration time and the like, as will be described in detail later with reference to FIG. The poisoning determination value #DEF will be described later with reference to FIGS.
[0026]
In step S103, the average excess air ratio on the upstream side of the NOx trap catalyst 16 during the rich spike and the average excess air ratio on the downstream side, Aveλf and Aveλr, are calculated. However, this calculation will be described in detail later with reference to FIG.
[0027]
In step S104, if the difference Defλ between the average air excess ratios Aveλf and Aveλr obtained in step S103 is less than the determination value #DEF, the process proceeds to step S105. If not, the flow ends.
[0028]
As will be described in detail later, if the NOx trap catalyst 16 is poisoned by sulfur, the NOx trap function is lowered, and even if a rich spike for NOx desorption and reduction treatment is performed, the HC in the exhaust gas is exhausted. , CO passes through the catalyst as it is without contributing to the reduction of NOx, and in this state, the difference between the exhaust air-fuel ratio upstream of the catalyst and the exhaust air-fuel ratio downstream is reduced. If the NOx trap catalyst 16 is functioning normally, HC and CO contained in the exhaust during rich spike are used for NOx desorption and reduction, and the air-fuel ratio downstream of the catalyst is not rich and Become. For this reason, the difference in the air-fuel ratio between the upstream side and the downstream side becomes large. Therefore, the sulfur poisoning state of the NOx trap catalyst 16 can be known by comparing the difference Defλ of the average excess air ratio between the upstream side and the downstream side of the catalyst with the determination value #DEF.
[0029]
For example, as shown in the table of FIG. 11, the determination value #DEF is larger as the excess air ratio is smaller, and the excess air ratio becomes larger (the air-fuel ratio is the stoichiometric air-fuel ratio). It is set to be smaller as it gets closer to ().
[0030]
Alternatively, as shown in the table of FIG. 12, the characteristic is set such that the determination value #DEF increases as the rich spike time increases. Further, as shown in the table of FIG. 13, the determination value #DEF is larger as the NOx trap amount is smaller, and is set to a characteristic that decreases as the trap amount increases.
[0031]
Thus, when the difference Defλ between the average excess air ratios of the exhaust upstream and downstream of the catalyst is smaller than the determination value #DEF, it is assumed that the NOx trap catalyst 16 is in a poisoned state. First, in step S105, the NOx trap catalyst 16 Perform a rich or lean poison removal operation.
[0032]
This will be described in detail later with reference to FIG. 7. As for poisoning of the NOx trap catalyst, there are poisoning due to sulfur and poisoning due to rich or lean operation. Although it is necessary to perform the poisoning release operation at a higher temperature than usual, the removal of the poisoning by the rich and lean operation can be performed at a relatively low temperature side compared to the time of releasing the sulfur poisoning. Therefore, the release operation is performed for a predetermined time with the air-fuel ratio as the theoretical air-fuel ratio. By canceling such rich and lean poisoning in advance, only the poisoning due to sulfur can be accurately determined in the poisoning determination of the NOx trap catalyst 16 performed thereafter.
[0033]
Next, in step S106, the process waits for the next rich spike to be performed. If the rich spike is executed again, the process proceeds to step S107.
[0034]
In step S107, similarly to step S103, the average excess air ratios Aveλf and Aveλr of the exhaust upstream and downstream of the NOx trap catalyst 16 are calculated again.
[0035]
Then, in step S108, in the same manner as in step S104, it is determined whether or not the difference Defλ of the average excess air ratio is less than a predetermined value #DEF. If it is smaller, the process proceeds to step S109, where it is determined that the poisoning state is caused by sulfur, and if not, the flow ends.
[0036]
Next, the routine for calculating the average excess air ratio will be described with reference to FIG.
[0037]
In step S201, the engine speed Ne and the fuel injection amount Qf are read. In step S202, a rich spike timing determination (flag) Frich for NOx reduction processing of the NOx trap catalyst 16, which will be described in detail later with reference to FIG. 6, is calculated.
[0038]
In Step S203, it is determined whether or not the calculated rich spike determination flag Frich is True. If True, the process proceeds to Step S204. If False, the process proceeds to Step S205.
[0039]
In step S204, it is determined whether or not a predetermined delay time #DELAY or more has elapsed after shifting to the rich spike. If it has elapsed, the process proceeds to step S206, and if not, the process proceeds to step S208.
[0040]
This delay time #DELAY corresponds to the time from when the rich spike is entered until the exhaust gas reaches the NOx trap catalyst 16, and is calculated from a table as shown in FIG. 14 according to the exhaust flow rate Qexh at that time. .
[0041]
The delay time #DELAY is longer as the exhaust flow rate Qexh is smaller, and becomes shorter as it becomes larger. The exhaust flow rate Qexh is based on the engine speed Ne, the fuel injection amount Qf (mg / st), and the intake air amount Qac (mg / st).
Qexh = (Qf + Qac) × Ne / 60/2 × CYLNUMBER
Can be calculated as However, CYLNUMBER is the number of engine cylinders.
[0042]
On the other hand, in step S205, if #DELAY or more has elapsed after the end of the rich spike, the process proceeds to step S208, and if not, the process proceeds to step S206.
[0043]
In step S206, the count value counted during the rich spike is calculated as RICHTIME = RICHTIME (n−1) +1.
[0044]
In step S207, the integrated values of the upstream and downstream excess air ratios of the NOx trap catalyst 16 are converted into the excess air ratio λ after the outputs of the upstream and downstream air-fuel ratio sensors 17a and 17b are converted into the following. Calculate by integration.
[0045]
That is,
Upstream integrated value Sλf = λf (n) + Sλf (n−1)
Downstream integrated value Sλr = λr (n) + Sλr (n−1)
Calculate as
[0046]
In addition, the integration of the excess air ratio of the upstream and downstream starts when the transition to the rich spike and the delay time elapses, and ends when the rich spike ends and the delay time elapses. That is, the NOx trap catalyst 16 is executed for a time corresponding to a section where the excess air ratio is actually changing due to a rich spike.
[0047]
On the other hand, in step S208, the average excess air ratio upstream and downstream of the catalyst is calculated as follows from the integrated value of the excess air ratio during the rich spike and the count value of the rich spike time calculated as described above. To do.
[0048]
That is,
Upstream average excess air ratio Aveλf = Sλf / RICHTIME
Downstream average excess air ratio Aveλr = Sλr / RICHTIME
Calculate as
[0049]
The calculation of rich spike time determination will be described with reference to the flowchart of FIG.
[0050]
In step S301, the engine speed Ne, the fuel injection amount Qf, the previous rich spike counter value Count (n-1), and the previous rich determination Frich (n-1) are read.
[0051]
In step S302, it is determined whether or not the previous rich determination flag Frich (n-1) is True. If True, the process proceeds to step S303 as a rich spike, and if false, the process proceeds to step S307.
[0052]
In step S303, the rich counter threshold value SCount is set to a preset value SCOUNTL.
[0053]
In step S304, since rich spike is being performed, the rich counter value is subtracted. Here, a preset subtraction amount #DCOUNT is subtracted every 100 msec from Count (n−1).
[0054]
In step S305, it is determined whether or not the calculated rich counter value Count is smaller than a preset threshold value SCount. If it is smaller, the rich spike is terminated, and the process proceeds to step S306, where the rich counter value Count is counted. The determination flag Frich is set to Frich = False, and the flow ends.
[0055]
In contrast, when the rich spike is not being performed, the rich counter value SCount is set to a preset threshold value #SCOUNTH in step S307. In step S308, for example, as shown in FIG. 15, a counter increment determined from the engine speed Ne and the fuel injection amount Qf is calculated, and this is set as ICount.
[0056]
In step S309, since the rich spike is not being performed, the rich counter increment ICount calculated in step S308 is added to the rich counter value every 100 msec.
[0057]
Then, in step S310, the rich counter value Count is compared with the counter threshold value #SCOUNTH set in step S307, and when the count becomes larger than the threshold value, it is determined that the rich spike time has been reached. Then, the rich determination flag Frich = True is set and the flow ends.
[0058]
On the other hand, if the rich counter value is smaller than the threshold value in step S310, the process proceeds to step S306 and the rich determination flag is set to Frich = False.
[0059]
Next, the rich and lean poisoning release operation will be described with reference to the flowchart of FIG.
[0060]
In step S401, the target excess air ratio tLambda at the time of releasing rich and lean poisoning is set to tLambda = 1. This corresponds to the theoretical air fuel ratio.
[0061]
In step S402, a target value of the intake throttle valve opening at the time of releasing the poisoning is calculated. This will be described in detail later (see FIG. 8).
[0062]
In step S403, the EGR valve opening target value is similarly calculated (see FIG. 9).
[0063]
The calculation of the target value of the intake throttle valve opening will be described with reference to FIG.
[0064]
In step S501, the engine speed Ne, the fuel injection amount Qf, and the target excess air ratio tLambda are read.
[0065]
In step S502, the target intake air amount tQac is calculated from the fuel injection amount Qf and the target excess air ratio tLambda.
[0066]
That is,
tQac = tLambda × 14.6 × Qf
However, 14.6 is the theoretical air-fuel ratio
Calculate as
[0067]
In step S503, a target working gas ratio tQh0 is obtained from the target intake air amount tQac calculated in step S502, the engine exhaust amount VCE # per cylinder, and the air density ROU #.
[0068]
That is,
tQh0 = tQac / (VCE # × ROU #)
Calculate as
[0069]
In step S504, based on the target working gas ratio tQh0 calculated in this way, for example, a target throttle valve coefficient tADNV is calculated from a table as shown in FIG. The coefficient tADNV is set to a characteristic that increases rapidly in a region where the target working gas ratio is large.
[0070]
In step S505, the target opening area tAtvob of the intake throttle valve is calculated from tADDNV, the engine speed Ne, and the total engine displacement VOL #.
[0071]
That is,
tAtvob = tADNV × Ne × VOL #
Calculate as
[0072]
In step S506, the intake throttle valve opening TVO is calculated from the target opening area of the intake throttle valve calculated in step S505, for example, using a table as shown in FIG. 17, and the flow is terminated. Note that the intake throttle valve opening increases in proportion to the target opening area.
[0073]
The routine for calculating the target opening value of the EGR valve will be described with reference to FIG.
[0074]
In step S601, the engine speed Ne, the fuel injection amount Qf, and the target intake air amount tQac are read.
[0075]
In step S602, for example, a target EGR rate MEGR is calculated from the map as shown in FIG. 18 based on the engine speed Ne and the fuel injection amount Qf.
[0076]
The EGR rate MEGR is set so as to be large in a region where the engine speed and the fuel injection amount are small and small in a region where the engine speed and the injection amount are large.
[0077]
In step S603, the target EGR amount MQEC is calculated from the target intake air amount tQac and the target EGR rate MEGR.
MQEC = tQac × MEGR / 100
Calculate as
[0078]
In step S604, the EGR valve opening degree is calculated based on, for example, a table as shown in FIG. 19, and the flow ends.
[0079]
Next, the NOx trap amount estimation calculation for the NOx trap catalyst will be described with reference to the flowchart of FIG.
[0080]
In step S701, the engine speed Ne, the fuel injection amount Qf, the intake air amount Qac, and the engine coolant temperature Tw are read.
[0081]
In step S702, for example, the NOx amount per unit output time of the engine, that is, NOxgkw 20 ms is calculated from a table as shown in FIG. 20 based on the intake air amount Qac. The unit of this NOx amount is g / kW / 20 ms (in the case of 20 msec. Job). Note that the NOx amount increases approximately in proportion to the intake air amount.
[0082]
In step S703, the NOx amount NOxg20ms per unit time is calculated based on the product of the NOxgkw20ms calculated in this way and the engine output Pe at that time.
NOxg20ms = NOxgkw20ms x Pe
Calculate as The engine output Pe can be calculated as Pe = Ne × Qf.
[0083]
In step S704, the correction coefficient kNOxeoe based on the NOx emission amount per unit time is calculated based on, for example, a table as shown in FIG.
[0084]
This kNOxeoe is set to approximately 1 when the amount of NOx emission per unit time is small, and is set to a characteristic that decreases toward 0 as it increases.
[0085]
However, this correction coefficient is set to a characteristic that becomes smaller as the engine exhaust flow rate becomes larger, for example, using a table as shown in FIG. 22, or, as shown in FIG. 23, the engine speed Ne and fuel injection. From the map set by Qf, the correction coefficient can be set to be smaller as both the engine speed and the fuel injection amount are larger.
[0086]
In step S705, considering that the NOx trap amount of the NOx trap catalyst 16 varies depending on the support temperature of the catalyst, a correction coefficient kNOxtbed based on the catalyst support temperature Tbed is calculated based on, for example, a table as shown in FIG. To do. This correction coefficient is set to 0 when the catalyst carrier temperature is low and close to 1 as the catalyst carrier temperature increases.
[0087]
However, as shown in FIG. 25, the catalyst carrier temperature Tbed has a correlation with the engine coolant temperature Tw. Therefore, the catalyst carrier temperature Tbed may be set based on the relationship with the coolant temperature Tw by a table as shown in FIG. it can. In this case, the correction coefficient kNOxeoe is set to a characteristic that approaches 1 as the coolant temperature Tw increases.
[0088]
In step S706, taking into account that the amount of NOx trapped by the NOx trap catalyst 16 varies based on the relationship with the amount of NOx trapped so far, the trap as shown in FIG. A correction coefficient kNOxtrap according to the quantity is calculated.
[0089]
This correction coefficient kNOxtrap is set to 1 when the NOx trap amount NOxtrap is zero, and is set to a characteristic that decreases toward 0 as the NOx trap amount increases.
[0090]
In step S707, the final correction coefficient kNOx is calculated as a product of the correction coefficients calculated so far.
[0091]
That is,
kNOx = kNOxeoe × kNOxtbed × kNOxtrap
Calculate as
[0092]
In step S708, the NOx trap amount NOxtrap is calculated by multiplying the total NOx trap amount NOxtrap (n-1) calculated up to the previous time by the product of the NOx amount NOxg 20 ms per unit time, which is the current calculated value, and the correction coefficient kNOx. Add to find.
[0093]
That is,
NOxtrap = NOxtrap (n−1) + NOxg 20 ms × kNOx
And this flow is finished.
[0094]
Next, the overall operation will be described with reference to FIGS.
[0095]
As the lean operation continues, NOx in the exhaust gas is trapped in the NOx trap catalyst 16, and the amount gradually increases. When the controller 8 estimates that the NOx trap amount has reached a predetermined value, it performs a rich spike that temporarily increases the air-fuel ratio, thereby performing separation reduction of the NOx adsorbed and held by the NOx trap catalyst 16. .
[0096]
The rich spike is determined according to the amount of NOx trapped in the NOx trap catalyst 16, and the air-fuel ratio and rich spike time at the time of the rich spike are determined, and the trapped NOx is caused by HC and CO in the exhaust, It leaves the catalyst and is reduced.
[0097]
FIGS. 2 and 3 show the exhaust air-fuel ratio upstream and downstream of the NOx trap catalyst 16 at this time, that is, the state of the excess air ratio.
[0098]
In FIG. 2, while the NOx trap catalyst 16 is not poisoned by sulfur and is functioning normally, the NOx trapped during the rich spike is released and reduced. Even if the exhaust air-fuel ratio is rich, the downstream air-fuel ratio is stoichiometric, that is, the excess air ratio λ is maintained at λ = 1. That is, since HC and CO contained in the rich exhaust are used for the NOx reduction action in the catalyst, the downstream air-fuel ratio is maintained at stoichiometry.
[0099]
However, if the NOx trap catalyst 16 is poisoned by sulfur and its function is reduced, the amount of trapped NOx is reduced, and the amount of NOx that is reduced even after a rich spike is reduced. It passes through the catalyst and is discharged downstream. For this reason, the exhaust air-fuel ratio becomes a rich state on the downstream side of the catalyst as well as on the upstream side.
[0100]
FIG. 3 shows a case where the rich spike time is longer than that in FIG. Even when the NOx trap catalyst 16 is normal, if the rich spike time becomes long and continues even if the total amount of NOx trapped in the catalyst is reduced, the air-fuel ratio downstream of the catalyst is the same rich air-fuel ratio as upstream after reduction. It becomes.
[0101]
If the NOx trap catalyst 16 is poisoned with sulfur, the amount of trapped NOx is reduced. In this case, the downstream air-fuel ratio immediately becomes rich.
[0102]
Therefore, in the controller 8, when the difference between the upstream and downstream air-fuel ratios of the NOx trap catalyst 16 during the rich spike, that is, the difference in excess air ratio between the upstream and downstream is smaller than a predetermined value, the catalyst is functioning normally. Judge that there is no.
[0103]
However, as shown in FIG. 3, the air-fuel ratio characteristics on the downstream side also vary depending on the rich spike time and the air-fuel ratio at that time, so the average of the excess air ratio on the upstream and downstream sides during the rich spike is averaged. By taking a value and comparing the average excess air ratio with the poisoning judgment value, the judgment of the poisoning state of the NOx trap catalyst 16 is performed accurately.
[0104]
In addition to sulfur poisoning, the NOx trap catalyst 16 is poisoned by being exposed to a rich or lean exhaust gas atmosphere for a long time. Either poisoning will cause a decrease in NOx purification efficiency, but in order to remove poisoning when sulfur poisoning is performed, a poisoning removal operation in which the temperature of the catalyst is 600 ° C. or higher is required. However, it is possible to cancel the rich or lean poisoning by maintaining the temperature at about 400 ° C., for example.
[0105]
Therefore, in the present invention, when the poisoning determination of the NOx trap catalyst 16 is performed, first, it is assumed that the poisoning is rich or lean. The poisoning release operation is performed to reach about 400 ° C. If rich and lean poisoning is present, the rich and lean poisoning is released from the catalyst during this period. Thereby, the poisoning determination of the NOx trap catalyst 16 can correctly determine the poisoning state which is based on only the sulfur poisoning without rich and lean poisoning.
[0106]
In addition, if the poisoning determination by sulfur is performed directly without releasing the rich or lean poisoning, and the poisoning removal operation is performed based on the result, all of them become the high temperature sulfur poisoning removal operation, and the fuel consumption is reduced. Even worse.
[0107]
Here, the effects of this embodiment are listed as follows.
[0108]
An exhaust sensor 17a17b for detecting the excess air ratio between the upstream and downstream exhausts of the NOx trap catalyst 16 is provided, and the NOx trap catalyst 16 is poisoned from the difference in the excess air ratio between the upstream and downstream exhausts during a rich spike. Since the determination is made, the poisoning state of the catalyst can be accurately determined.
[0109]
Further, since the poisoning determination of the NOx trap catalyst 16 is determined based on the average values of the excess air ratios of the exhaust on the upstream side and the downstream side of the catalyst, the determination accuracy is improved and accurate determination can be performed.
[0110]
Further, by setting the poisoning determination value according to the air-fuel ratio at the time of rich spike and the rich spike time, the influence of the excess air ratio that fluctuates due to these is eliminated, and accurate determination is possible.
[0111]
Furthermore, by setting the poisoning determination value according to the NOx trap amount at the time of shifting to the rich spike, the same highly accurate poisoning determination can be performed.
[0112]
The calculation of the average value of the excess air ratio starts after a predetermined delay time has elapsed since the transition to the rich spike, and the average value is calculated when the predetermined delay time has elapsed since the end of the rich operation. By ending, the delay from when the rich spike is performed until the exhaust reaches the NOx trap catalyst 16 can be taken into account, and the calculation accuracy of the average value of the excess air ratio is increased.
[0113]
In addition, after the NOx trap catalyst 16 is determined to be poisoned, the rich or lean poisoning is canceled by operating for a predetermined time at the stoichiometric air-fuel ratio, and then the poisoning determination is performed again. Therefore, it is possible to reduce the wasteful sulfur poisoning release operation and improve the fuel consumption.
[0114]
The present invention is not limited to the above-described embodiments, and it is obvious that various modifications and improvements that can be made by those skilled in the art are included within the scope of the technical idea described in the claims.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a first embodiment of the present invention.
FIG. 2 is a time chart showing changes in the excess air ratio between the upstream and downstream of the catalyst during a rich spike.
FIG. 3 is a time chart showing changes in the excess air ratio between the upstream and downstream sides of the catalyst during a rich spike.
FIG. 4 is a flowchart showing a control operation of the present invention.
FIG. 5 is a flowchart showing an operation of calculating an average excess air ratio.
FIG. 6 is a flowchart showing a calculation operation of rich spike timing determination.
FIG. 7 is a flowchart showing a rich / lean poisoning release operation;
FIG. 8 is a flowchart showing a calculation operation of an intake throttle valve opening target value.
FIG. 9 is a flowchart showing an operation of calculating an EGR valve opening target value.
FIG. 10 is a flowchart showing an NOx trap amount estimation calculation operation;
FIG. 11 is a diagram showing a sulfur poisoning determination value in relation to an excess air ratio.
FIG. 12 is a diagram showing a sulfur poisoning determination value in relation to an excess air ratio.
FIG. 13 is a diagram showing a sulfur poisoning determination value in relation to a rich spike time.
FIG. 14 is a diagram showing a delay time in relation to an exhaust flow rate.
FIG. 15 is a diagram showing the increment of the rich counter based on the engine speed and the fuel injection amount.
FIG. 16 is a diagram illustrating characteristics of a correction coefficient for an intake throttle valve opening degree.
FIG. 17 is a view showing the opening characteristic of the intake throttle valve.
FIG. 18 is a diagram showing characteristics of a target EGR rate.
FIG. 19 is a view showing an opening characteristic of an EGR valve.
FIG. 20 is a diagram showing the relationship between the intake air amount and the NOx emission amount.
FIG. 21 is a diagram showing a correction coefficient based on the NOx emission amount.
FIG. 22 is a diagram showing a correction coefficient based on the engine displacement.
FIG. 23 is a diagram showing a correction coefficient based on the engine speed and the fuel injection amount.
FIG. 24 is a diagram showing a correction coefficient based on the catalyst carrier temperature.
FIG. 25 is a graph showing the relationship between catalyst carrier temperature and cooling water temperature.
FIG. 26 is a diagram showing a correction coefficient based on the cooling water temperature.
FIG. 27 is a diagram illustrating a correction coefficient based on the NOx trap amount.
[Explanation of symbols]
1 engine
8 Controller
9 Air intake passage
10 Exhaust passage
16 NOx trap catalyst
17a, 17b Exhaust air / fuel ratio sensor

Claims (5)

In an internal combustion engine equipped with a NOx adsorption catalyst that adsorbs NOx in exhaust during lean operation at an air-fuel ratio and desorbs and reduces NOx adsorbed during rich operation.
Means for detecting the excess air ratio of the upstream and downstream exhaust of the NOx adsorption catalyst;
Poisoning determination means for calculating an average value of the excess air ratios of the upstream side and downstream side exhaust during the rich operation and determining the poisoning state of the NOx adsorption catalyst from the difference between the average values. An exhaust emission control device for an internal combustion engine characterized by the above. The poisoning determination means compares the difference between the average values of the excess air ratios of the upstream and downstream exhausts with the poisoning determination value. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is determined to have been. The poisoning determination means starts calculating the average value of the excess air ratio after a predetermined delay time has elapsed since the shift to the rich operation, and when the predetermined delay time has elapsed since the end of the rich operation The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the calculation of the average value is terminated. 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the predetermined delay time is set longer as the exhaust flow rate is smaller. When the poisoning state of the NOx adsorption catalyst is determined, the poisoning determination means controls the excess air ratio to be the stoichiometric air-fuel ratio for a predetermined time, and after that, during the first rich operation, the NOx adsorption catalyst The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the sulfur poisoning state of the catalyst is determined from a difference in excess air ratio between the upstream side and the downstream side exhaust.

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