JP2002115536A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of estimating the amount of sulphur oxides absorbed by a NOx purifier more precisely for executing deterioration regeneration treatment at the optimum timing. SOLUTION: This device discriminated lean, stoichiometric or rich driving by comparing a target air-fuel ratio coefficient KCMD with a lean discrimination threshold value KBSDESL and a rich discrimination threshold value KBSDESH (S34, S38). During stoichiometric or rich driving, an adsorption map or a desorption map is detected based on engine speed NE and intake pipe internal absolute pressure PBA to calculate an additional value SABS or a subtraction value SDES corresponding to adsorption amount or desorption amount per hour (S43, S47). A count value CSABS corresponding to SOx absorption amount is calculated by integrating the additional value SABS and the subtraction value SDES (S61, S62).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine having a nitrogen oxide (NOx) purifying apparatus in an exhaust system, and in particular, performs a regeneration process when the NOx purifying apparatus is deteriorated due to sulfur poisoning. About things.

[0002]

2. Description of the Related Art A NOx purifying device is provided in an exhaust system of an internal combustion engine to absorb NOx during a lean operation in which the air-fuel ratio is set to a side leaner than the stoichiometric air-fuel ratio, and to appropriately enrich the air-fuel ratio. 2. Description of the Related Art An exhaust gas purifying apparatus configured to reduce and release NOx absorbed by a NOx purifying apparatus is conventionally known. In addition, the NOx purification device absorbs sulfur oxides contained in fuel, that is, the sulfur poisoning reduces the NOx absorption capability. Therefore, the NOx purification device has an ability to absorb sulfur oxides upstream of the NOx purification device. There is known an exhaust gas purification apparatus provided with an SOx catalyst having the following (for example, Japanese Patent Application Laid-Open No. H11-247650).

In the apparatus disclosed in this publication, the amount of sulfur oxides absorbed in the SOx catalyst is estimated, and when the estimated amount of sulfur oxides reaches a set value, a regeneration process for removing the sulfur oxides is executed. For this purpose, a counter for estimating the amount of absorbed sulfur oxides is provided, and an addition value per unit time of the counter is set according to the engine speed and the intake pipe internal pressure, and the counter is incremented to obtain SOx.
The amount of sulfur oxides absorbed by the catalyst is estimated.

[0004]

If the SOx catalyst is not provided in the exhaust system, the sulfur oxides are absorbed by the NOx purifying device. Therefore, it is necessary to enrich the air-fuel ratio while the temperature of the NOx purifying device is high. Therefore, it is necessary to perform a regeneration treatment for releasing sulfur oxides. In such a case, it is necessary to first estimate the amount of sulfur oxides absorbed in the NOx purification device. However, if the method disclosed in the above publication is applied as it is, there are the following problems.

That is, even when the lean operation of setting the air-fuel ratio of the air-fuel mixture supplied to the engine to the lean side of the stoichiometric air-fuel ratio is frequently used, the stoichiometric operation of setting the air-fuel ratio to the stoichiometric air-fuel ratio or the rich side of the stoichiometric air-fuel ratio is performed. There is also a period during which the rich operation is set. During such a stoichiometric operation or a rich operation, when the temperature of the NOx purification device rises, the sulfur oxides absorbed by the NOx purification device are released. However, in the conventional apparatus disclosed in the above publication, such emission of sulfur oxides during normal stoichiometric operation or rich operation is not taken into consideration, and therefore, the estimation of the amount of sulfur oxides absorbed in the NOx purification device is not performed. There is a problem in that the timing becomes inaccurate and the execution time of the reproduction process is shifted from the optimum time.

The present invention has been made in view of this point, and more accurately estimates the amount of sulfur oxides absorbed by the NOx purifying device, and performs the regeneration process of the sulfur-poisoned NOx purifying device at an optimum time. An object of the present invention is to provide an exhaust gas purification device that can be executed.

[0007]

According to a first aspect of the present invention, there is provided an exhaust system of a fuel engine.
NOx purification means for absorbing NOx in exhaust gas in an exhaust lean state, sulfur oxide amount estimation means for estimating the amount of sulfur oxide absorbed by the NOx purification means, and sulfur oxide amount estimated by the sulfur oxide amount estimation means When reaches a set value, in an exhaust gas purification apparatus for an internal combustion engine comprising: a sulfur oxide removing means for performing a process of removing the sulfur oxide;
The sulfur oxide amount estimating means estimates a change amount of the sulfur oxide amount per unit time according to an air-fuel ratio of an air-fuel mixture supplied to the engine and an operation state of the engine, and integrates the estimated change amount. Thus, the amount of the sulfur oxide is estimated.

According to this structure, the amount of change in the amount of sulfur oxides absorbed by the NOx purifying means per unit time (that is, the amount of absorption or the amount of absorption) depends on the air-fuel ratio of the air-fuel mixture supplied to the engine and the operating state of the engine. The amount of release is estimated, and by integrating the estimated amount of change, the amount of sulfur oxides absorbed by the NOx purifying means is estimated. Therefore, the amount of sulfur oxides is estimated more accurately than in the past. It is possible,
The regeneration process of the sulfur-poisoned NOx purifying means can be executed at an optimal time.

According to a second aspect of the present invention, in the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect, the sulfur oxide amount estimating means determines whether the air-fuel ratio is set near the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. Is it set leaner than fuel ratio?
Alternatively, the change amount is estimated according to whether the air-fuel ratio is set to a rich side from the stoichiometric air-fuel ratio and the engine operating state.

The amount of sulfur oxide absorbed by the NOx purifying means increases when the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio, and when the air-fuel ratio is set near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio. When it is, it increases or decreases depending on the engine operation state. Therefore, the air-fuel ratio is set near the stoichiometric air-fuel ratio, is set leaner than the stoichiometric air-fuel ratio, or is set richer than the stoichiometric air-fuel ratio, and according to the engine operating state,
By estimating the amount of change in the amount of sulfur oxide, it is possible to accurately estimate the amount of change in the amount of sulfur oxide per unit time, that is, the amount of absorption or release.

Further, the sulfur oxide amount estimating means includes: first estimating means for estimating the amount of change in accordance with the engine operating state when the air-fuel ratio is set near the stoichiometric air-fuel ratio; A second estimating means for estimating the change amount according to the engine operating state when the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio; It is desirable to have a third estimating means for estimating the change amount according to the engine operating state.

[0012] The first estimating means may include a first negative change (SDESS) in an engine operating state in which the temperature of the nitrogen oxide purifying device is equal to or higher than a first predetermined temperature (700 ° C).
T), and outputs a first positive change amount (SABSST) in an engine operating state in which the temperature of the nitrogen oxide purifying device is lower than the first predetermined temperature. The second positive change amount (S
ABSL), and the third estimating means outputs a second negative value in an engine operating state in which the temperature of the nitrogen oxide purifying device is equal to or higher than a second predetermined temperature (600 ° C.) lower than the first predetermined temperature. And outputting a third positive change amount (SABSR) in an engine operating state in which the temperature of the nitrogen oxide purification device is lower than the second predetermined temperature (600 ° C.). desirable.

The first estimating means may be configured to increase the absolute value of the first negative change amount as the rotational speed of the engine and / or the intake pressure of the engine increases. Calculating the first positive change amount such that the higher the rotational speed of the engine and / or the intake pressure of the engine becomes, the smaller the first positive change amount becomes; The second estimating means calculates the second positive change amount such that the second positive change amount increases as the rotation speed of the engine and / or the intake pressure of the engine increases. The third estimating means calculates the second negative change amount so that the absolute value of the second negative change amount increases as the rotational speed of the engine and / or the intake pressure of the engine increases. Calculated, and the rotational speed of the engine and / or the intake pressure of the engine increase. More, the third as a positive variation is reduced, it is desirable to calculate the positive variation of the third.

The sulfur oxide removing means sets the air-fuel ratio of the air-fuel mixture supplied to the engine to a value close to the stoichiometric air-fuel ratio for a predetermined period of time when performing the processing for removing the sulfur oxide. Thereafter, it is desirable to set the air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio.

The sulfur oxide removing means, when executing the process for removing the sulfur oxide, retards the ignition timing of the engine from a normal set value, stops the exhaust gas recirculation, and controls the engine to recirculate. It is desirable to control the intake air amount of the engine so that the output torque does not change.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an internal combustion engine (hereinafter referred to as “engine”) including an exhaust gas purification apparatus according to one embodiment of the present invention.
FIG. 1 is a diagram showing the overall configuration of a control device, for example, a throttle valve 3 is disposed in the middle of an intake pipe 2 of a four-cylinder engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3 and outputs an electric signal corresponding to the opening of the throttle valve 3 to output an electronic control unit for engine control (hereinafter referred to as “ECU”).
5

An auxiliary air passage 17 that bypasses the throttle valve 3 is connected to the intake pipe 2.
7, an auxiliary air control valve 18 for controlling the amount of auxiliary air.
Is provided. The auxiliary air control valve 18 is connected to the ECU 5, and the ECU 5 controls the valve opening amount.

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). The ECU 5 is electrically connected to the ECU 5 and controls a valve opening time of the fuel injection valve 6 based on a signal from the ECU 5.

On the other hand, an intake pipe absolute pressure (PBA) sensor 8 is provided immediately downstream of the throttle valve 3, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is supplied to the ECU 5. . Further, an intake air temperature (TA) sensor 9 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies the electric signal to the ECU 5.

The engine water temperature (TW) sensor 10 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5. The ECU 5 is connected to a crank angle position sensor 10 for detecting a rotation angle of a crankshaft (not shown) of the engine 1, and supplies a signal corresponding to the rotation angle of the crankshaft to the ECU 5. The crank angle position sensor 10 outputs a signal pulse (hereinafter referred to as a “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, and a top dead center (TDC) at the start of an intake stroke of each cylinder. TDC that outputs a TDC signal pulse at a crank angle position that is a predetermined crank angle earlier than the above (every 180 degrees of crank angle in a four-cylinder engine)
A CRK sensor that generates one pulse (hereinafter referred to as a “CRK signal pulse”) at a constant crank angle cycle (for example, a 30-degree cycle) shorter than the TDC signal pulse,
The YL signal pulse, the TDC signal pulse, and the CRK signal pulse are supplied to the ECU 5. These signal pulses are used for various timing controls such as fuel injection timing, ignition timing, etc., and detection of an engine speed (engine speed) NE.

The exhaust pipe 12 is provided with N as NOx purifying means.
An Ox purification device 15 is provided. NOx purification device 1
Reference numeral 5 contains a NOx absorbent for absorbing NOx and a catalyst for promoting oxidation and reduction. NOx purification device 15
In the state where the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set leaner than the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is relatively high (hereinafter referred to as “the exhaust lean state”), NO
x, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is relatively low, and HC, CO
In a state with a large amount of components (hereinafter referred to as an “exhaust-rich state”), the absorbed NOx is reduced by HC and CO,
It is configured to be discharged as nitrogen gas, and HC and CO are oxidized and discharged as water vapor and carbon dioxide.

When NOx is absorbed up to the limit of the NOx absorbing capacity of the NOx absorbent, that is, up to the maximum NOx absorption amount, NOx can no longer be absorbed. Therefore, the air-fuel ratio is increased to release and reduce NOx in a timely manner. That is, reduction enrichment is performed. Further, when a sulfur oxide (hereinafter referred to as “SOx”) is absorbed by the NOx absorbent and the absorbed SOx amount reaches a set value, a regeneration process for removing (purging) SOx is executed. In the present embodiment,
NOx adsorbent of the type that adsorbs NOx is used,
The “absorption” of SOx by the NOx absorbent is also called “adsorption”. The “release” of SOx from the NOx absorbent is also referred to as “desorption”.

A proportional type air-fuel ratio sensor 14 (hereinafter referred to as "LAF sensor 14") is mounted at an upstream position of the NOx purifying device 15, and the LAF sensor 14 detects the oxygen concentration (air-fuel ratio) of the exhaust gas. A proportional electric signal is output and supplied to the ECU 5. A spark plug 11 provided for each cylinder of the engine 1 is connected to the ECU 5,
The drive signal of the ignition plug 11, that is, the ignition signal
Supplied from 5.

An exhaust gas recirculation passage 21 is provided between the intake pipe 2 downstream of the throttle valve 3 and the exhaust pipe 12 upstream of the NOx purification device 15. An exhaust gas recirculation valve (hereinafter referred to as “EG
22) is provided. EGR valve 22
Is a solenoid valve having a solenoid, the opening of which is E
It is controlled by CU5. The EGR valve 22 has a lift sensor 23 for detecting the valve opening (valve lift amount) LACT.
The detection signal is supplied to the ECU 5. The exhaust gas recirculation passage 21 and the EGR valve 22 constitute an exhaust gas recirculation mechanism.

In the engine 1, the valve timing of the intake valve and the exhaust valve can be switched between two stages: a high-speed valve timing suitable for a high-speed rotation region of the engine and a low-speed valve timing suitable for a low-speed rotation region. It has a mechanism 30. The switching of the valve timing includes the switching of the valve lift amount. Further, when the low-speed valve timing is selected, one of the two intake valves is stopped to stabilize the air-fuel ratio even when the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio. We have tried to ensure the combustion that we did.

The valve timing switching mechanism 30 switches the valve timing via a hydraulic pressure. An electromagnetic valve and a hydraulic pressure sensor for switching the hydraulic pressure are connected to the ECU 5. The detection signal of the oil pressure sensor is supplied to the ECU 5, and the ECU 5 controls the solenoid valve to control the switching of the valve timing according to the operating state of the engine 1.

The ECU 5 is connected to a vehicle speed sensor 31 for detecting a running speed (vehicle speed) VP of a vehicle driven by the engine 1, and a detection signal is supplied to the ECU 5. The ECU 5 has an input circuit 5a having functions of shaping input signal waveforms from various sensors, correcting a voltage level to a predetermined level, converting an analog signal value to a digital signal value, and the like, and a central processing unit (hereinafter referred to as “CPU”). 5b), storage means 5c for storing various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.

The ECU 5 determines the engine operation state based on various engine parameter signals, and sets EG which is set according to the engine speed NE and the intake pipe absolute pressure PBA.
The valve opening command value LCMD of the R valve 22 and the lift sensor 23
The control signal is supplied to the solenoid of the EGR valve 22 so as to make the deviation from the actual valve opening LACT detected by the control routine to zero.

The CPU 5b determines various engine operating states based on the various engine parameter signals described above, and according to the determined engine operating states,
Based on the following equation (1), a fuel injection time TOUT of the fuel injection valve 6 that operates to open in synchronization with the TDC signal pulse is calculated. TOUT = TIM × KCMD × KLAF × K1 + K2 (1)

Here, TIM is a basic fuel amount, specifically, a basic fuel injection time of the fuel injection valve 6, and T is set according to the engine speed NE and the intake pipe absolute pressure PBA.
It is determined by searching the I map. The TI map is set such that the air-fuel ratio of the air-fuel mixture supplied to the engine substantially becomes the stoichiometric air-fuel ratio in the operating state corresponding to the engine speed NE and the intake pipe absolute pressure PBA. That is,
The basic fuel amount TIM has a value substantially proportional to the intake air amount (mass flow rate) per unit time of the engine.

KCMD is a target air-fuel ratio coefficient, which is set according to engine operating parameters such as the engine speed NE, the throttle valve opening θTH, and the engine coolant temperature TW.
The target air-fuel ratio coefficient KCMD is proportional to the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F / A.
Therefore, it is also called a target equivalent ratio. In addition, the target air-fuel ratio coefficient KCMD is determined by enrichment or SO
enrichment for x removal (hereinafter “SOx removal enrichment”
Is set to a value greater than 1.0.

KLAF performs PID (proportional, integral, differential) control so that the detected equivalence ratio KACT calculated from the detected value of the LAF sensor 14 matches the target equivalence ratio KCMD when the conditions for executing the feedback control are satisfied. Is an air-fuel ratio correction coefficient calculated by

K1 and K2 are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration characteristics can be optimized according to the engine operating condition. Is determined to be a predetermined value. The CPU 5b performs a drive signal for opening the fuel injection valve 6, an ignition signal for driving the ignition plug 11, a drive signal for the auxiliary air amount control valve 18, and an EGR valve 22 based on the fuel injection time TOUT obtained as described above. Is output via the output circuit 5d.

FIG. 2 is a flowchart of a process for performing regeneration control when the amount of SOx adsorbed on the NOx absorbent of the NOx purifying device 15 (hereinafter referred to as “SOx adsorption amount”) reaches a set value. This processing is executed by the CPU 5b in synchronization with the generation of the TDC signal pulse.

In step S10, the SOx saturation determination process shown in FIG. 3 is executed. In this process, the SOx adsorption amount is calculated according to the set air-fuel ratio (target air-fuel ratio coefficient KCMD) and the operating state of the engine 1, the SOx absorption amount reaches the set value, and the engine 1 executes the regeneration process. The regeneration mode flag FSRC is in an operation state suitable for
MODE is set to "1".

In the following step S11, it is determined whether or not the reproduction mode flag FSRCMODE is "1".
When SRCMODE = 0 and the SOx adsorption amount has not reached the set value, normal fuel supply control, ignition timing control, auxiliary air amount control, and exhaust gas recirculation control are executed (step S12).

When the regeneration mode flag FSRCMODE is set to "1" in the process of step S10, the process proceeds from step S11 to S13, where the temperature increase mode control for promoting the temperature increase of the NOx purification device 15 is executed. In this heating mode control, the fuel supply control is performed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio, the ignition timing is controlled so that the ignition timing is retarded from the optimal ignition timing, and the fuel supply control and the ignition timing control are further performed. Correspondingly, the control of the auxiliary air amount is performed so that the output torque of the engine 1 becomes substantially the same as that in the normal control, and the control of closing the EGR valve 22 and stopping the exhaust gas recirculation is performed (step S13). By such a temperature increase mode control, the temperature increase of the NOx purification device 15 can be promoted while suppressing the fluctuation of the output torque of the engine.

FIG. 9 shows a target air-fuel ratio coefficient KCMD setting process corresponding to the temperature raising mode control in step S13. In this process, as described later, control for maintaining the target air-fuel ratio coefficient KCMD at “1.0” is performed for a predetermined time T.
At the time when the MTCAT is executed, a temperature rise completion flag FTCATOK indicating that the temperature rise has been completed is set to "1".

In step S14, a temperature raising completion flag FT
It is determined whether CATOK is "1" or not, and FTCAT
As long as OK = 0, this process is immediately terminated. FTC
When ATOK = 1, SOx removal (purge) mode processing is executed (step S15). In this process, the fuel supply control that makes the air-fuel ratio richer than the stoichiometric air-fuel ratio is performed, the ignition timing control that retards the ignition timing from the optimal ignition timing is performed, and further, such fuel supply control and ignition timing control are performed. Correspondingly, the auxiliary air amount control is performed so that the output torque of the engine 1 becomes substantially the same as that during the normal control, and the stop of the exhaust gas recirculation is continued. By executing such an SOx removal mode process, the SOx absorbed by the NOx purification device 15 is reduced and released together with the exhaust gas while suppressing the fluctuation of the output torque of the engine.
The NOx absorption capacity of the purification device 15 can be restored.

FIG. 3 is a flowchart of the SOx saturation determination process executed in step S10 of FIG. In step S20, the SOx adsorption amount estimation processing shown in FIGS. 4 and 5 is executed. In this processing, SO 2 is set according to the set air-fuel ratio (target air-fuel ratio coefficient KCMD) and the operating state of the engine 1.
An x adsorption amount estimation value is calculated. More specifically, SOx
The SOx adsorption amount estimated value is calculated by incrementing or decrementing the value of the adsorption amount counter CSABS. The value of the counter CSABS is stored in the backup memory that retains the stored contents even when the ignition switch is turned off.

In step S21, it is determined whether or not the value of the SOx adsorption amount counter CSABS is equal to or larger than the set value CSRMAC1, and if CSABS <CSRMAC1, the present process is immediately terminated. When CSABS ≧ CSRMAC1, the process proceeds from step S21 to step S22, and it is determined whether the engine operating state and the vehicle speed VP satisfy predetermined conditions. That is, the engine speed NE is set to the predetermined upper and lower limit values NESRMH, NESRML (for example, 3000 rpm).
m, 1500 rpm), the absolute pressure PBA in the intake pipe is determined by predetermined upper and lower limits PBSRMH, PBSRM.
L (for example, 81.3 kPa, 61.3 kPa), and determines whether the intake air temperature TA is a predetermined upper / lower limit value TASRM.
H, TASRML (for example, 100 ° C., 0 ° C.) to determine whether the engine coolant temperature TW is a predetermined upper / lower limit TWSR
MH, TWSRML (for example, 100 ° C., 80 ° C.), whether the vehicle speed VP is a predetermined upper / lower limit value VSRMH,
It is determined whether it is within the range of VSRML (for example, 120 km / h, 60 km / h). If all the answers to these determinations are affirmative (YES), the reproduction mode flag FSRCMODE is set to "1" (step S23), while if any of the answers is negative (NO),
The reproduction mode flag FSRCMODE is set to "0" (step S24).

FIGS. 4 and 5 are flowcharts of the SOx adsorption amount estimation processing executed in step S20 of FIG. In step S30, it is determined whether or not the engine is in a start mode, that is, whether or not cranking is being performed. If not, it is determined whether or not a fuel cut flag FFC indicating "1" indicating that the fuel supply cutoff operation is being performed is "1". Is determined (step S31). Then, when the engine is in the start mode or during the fuel supply cutoff operation, the present process is immediately terminated.

If the fuel supply cutoff operation is not being performed, it is further determined whether or not an idle flag FIDLE indicating "1" indicating that the engine is being idle is "1" (step S32), and FIDLE = 1. During idle operation, the added value SABS is changed to the added value SABS for idle.
It is set to IDL (step S33). And SOx
The suction amount counter CSABS is incremented by the added value SABS (step S61), and the process ends.

If FIDLE = 0 and the engine is not idling, it is determined whether the target air-fuel ratio coefficient KCMD is smaller than a lean determination threshold KBSDDESL (for example, 0.9) (step S34), and KCMD <KBSDESL. During lean operation, the engine speed NE
The lean area adsorption map shown in FIG. 6A is searched according to the intake pipe internal absolute pressure PBA and the lean operation addition value SA.
The BSL is calculated (Step S36). The lean region adsorption map is set for a region in which the lean operation is performed, which is indicated by hatching in the figure, and is added as the engine speed NE increases and the intake pipe absolute pressure PBA increases. The value SABSL is set to increase.

Next, the addition value SABS is set to this lean operation addition value SABSL (step S37), and the routine proceeds to step S61. On the other hand, in step S34, the KCM
If D ≧ KBSDESL, it is further determined whether the target air-fuel ratio coefficient KCMD is larger than a rich determination threshold KBSDESH (for example, 1.1) (step S3).
8). When KCMD ≦ KBSDESH and the stoichiometric operation in which the air-fuel ratio is set to the stoichiometric air-fuel ratio is performed, the stoichiometric boundary table shown in FIG. 7A is searched according to the engine speed NE to calculate the stoichiometric boundary pressure PBSTG. (Step S39). This stoichiometric boundary table is N
The setting is made such that a set of the engine speed NE and the intake pipe absolute pressure PBA at which the temperature of the Ox purification device 15 becomes approximately 700 ° C. is obtained. When the intake pipe absolute pressure PBA is higher than the line LST defined by this table, N
The temperature of the Ox purification device 15 becomes higher than 700 ° C.
The SOx adsorbed by the Ox absorbent is desorbed. Conversely, when the intake pipe absolute pressure PBA is lower than the line LST, N
The temperature of the Ox purification device 15 becomes lower than 700 ° C.
SOx is adsorbed on the Ox absorbent. Therefore, in the processing of steps S40 to S48, the added value SABS of the SOx adsorption amount counter CSABS is calculated in the operating state where SOx is adsorbed, while the added value SABS of the SOx adsorption amount counter CSABS is calculated in the operating state where SOx is desorbed. Subtraction value SDE
Calculate S.

First, in step S40, it is determined whether or not the intake pipe absolute pressure PBA is lower than the stoichiometric boundary pressure PBSTG. If PBA <PBSTG, a down count timer tDES referred to in step S46 described later.
The TLHD is set to a predetermined delay time TDESTHD (for example, 3
Second) and start (step S41).
Next, it is determined whether or not the value of a down-count timer tDESTHLD started in step S45 described later is “0” (step S42), and tDESTHLD>
While it is 0, the process proceeds to step S47, where tDESTHLD
When = 0, the process proceeds to step S43, and FIG.
Then, the stoichiometric region adsorption map shown in (1) is searched to calculate the stoichiometric operation addition value SABSST. The stoichiometric region adsorption map is shown in FIG.
The region where Ox is adsorbed by the NOx absorbent is set, and the added value SABSST increases as the engine speed NE increases and the intake pipe absolute pressure PBA increases.
Is set to decrease. The region surrounded by the broken line in FIG. 6 is the lean operation region shown in FIG.

Next, the added value SABS is set to the added value SABSST for stoichiometric operation (step S4).
4), and proceed to step S61. Step S40
If PBA ≧ PBSTG, the down count timer tDESTHLD is set to a predetermined delay time TDESTHLD.
(For example, 3 seconds) and start (step S45). Next, it is determined whether or not the value of the down count timer tDESTLHD started at step S41 is "0" (step S46), and tDESTLHD is determined.
If> 0, the process proceeds to step S43, where tDESTLH
When D = 0, the process proceeds to step S47, and according to the engine speed NE and the absolute pressure PBA in the intake pipe, as shown in FIG.
The stoichiometric region departure map shown in FIG. 3B is searched to calculate a stoichiometric operation subtraction value SDESST. The stoichiometric region desorption map is set for a region in which SOx is desorbed from the NOx absorbent, which is indicated by hatching in the lower right of the figure, and as the engine speed NE increases,
Also, as the intake pipe absolute pressure PBA increases, the subtraction value SD
The ESST is set to increase.

Next, the subtraction value SDES is set to the stoichiometric operation subtraction value SDESST (step S4).
8) The process proceeds to step S62, and the SOx adsorption amount counter C
The value of SABS is decremented by the subtraction value SDES,
This processing ends. Steps S41, S42, S45, and S46 are provided to delay switching of the control until the engine operation state is stabilized when the engine operation state changes from the adsorption region to the desorption region or vice versa. .

In step S38, KCMD> KBSDE
If the engine is in the rich operation in which the air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio during SH, the rich boundary table shown in FIG. 7B is searched according to the engine speed NE, and the rich boundary pressure PBRICHG is determined. It is calculated (FIG. 5, step S51). This rich boundary table is set such that a set of the engine speed NE and the intake pipe absolute pressure PBA at which the temperature of the NOx purification device 15 becomes approximately 600 ° C. is obtained. When the intake pipe absolute pressure PBA is higher than the line LR defined in this table, the NOx purification device 1
5 is higher than 600 ° C., and SOx is desorbed from the NOx absorbent. Conversely, when the absolute pressure PBA in the intake pipe is lower than the line LR, the temperature of the NOx purifier 15 is lower than 600 ° C. SOx is adsorbed on the NOx absorbent. Therefore, in the processing of the following steps S52 to S60, the added value SABS of the SOx adsorption amount counter CSABS is calculated in the operating state where SOx is adsorbed, while the added value SABS of the SOx adsorption amount counter CSABS is calculated in the operating state where SOx is desorbed. Calculate the subtraction value SDES.

First, in step S52, it is determined whether or not the intake pipe absolute pressure PBA is lower than the rich boundary pressure PBRICHG. If PBA <PBRICHG, a down count timer t which will be referred to in step S58 described later is determined.
DESRRLHD is set to a predetermined delay time TDESRLHD (for example, 3 seconds) and started (step S5).
3). Next, it is determined whether or not the value of the down count timer tDESRHD started in step S57 described later is “0” (step S54), and tDESRH is determined.
While LD> 0, the process proceeds to step S59, where tDESR
When HLD = 0, the process proceeds to step S55, and in accordance with the engine speed NE and the absolute pressure PBA in the intake pipe, as shown in FIG.
The rich area adsorption map shown in (c) is searched to calculate the rich operation addition value SABSR. The rich area adsorption map is shown in FIG.
x is set in a region where the NOx adsorbent is adsorbed, and is set so that the added value SABSR decreases as the engine speed NE increases and the intake pipe absolute pressure PBA increases. The region surrounded by the broken line in FIG. 6 is the lean operation region shown in FIG.

Next, the addition value SABS is set to the addition value SABSR for rich operation (step S56), and the routine proceeds to step S61. In step S52, PBA
If ≥PBRICHG, the downcount timer tDESRHLD is set to a predetermined delay time TDESRHLD (for example, 3 seconds) and started (step S5).
7). Next, it is determined whether or not the value of the down count timer tDESRLHD started in step S53 is "0" (step S58), and tDESRLHD> 0.
, The process proceeds to step S55, where tDESRLHD =
When the value becomes 0, the process proceeds to step S59, where the rich region departure map shown in FIG. 6C is searched according to the engine speed NE and the intake pipe absolute pressure PBA, and the subtraction value SDESR for rich operation is calculated. The rich region departure map is shown in the same figure with hatching downward and to the right.
x is set for the area desorbed from the absorbent,
The subtraction value SDESR is set to increase as the engine speed NE increases and the intake pipe absolute pressure PBA increases.

Next, the subtraction value SDES is set to the subtraction value SDESR for the rich operation (step S60), and the routine proceeds to step S62, where the SOx adsorption amount counter CSABS is set.
Is decremented by the subtraction value SDES, and this processing ends. As described above, according to the processing of FIGS.
The value of the x adsorbing amount counter CSABS is calculated by adding an additional value SABS corresponding to the SOx adsorbing amount per unit time and the SO
The value is incremented or decremented by the subtraction value SDES corresponding to the x desorption amount. That is, the estimated value of the amount of SOx absorbed by the NOx absorbent is calculated by integrating the added value SABS and the subtracted value SDES set according to the air-fuel ratio and the engine operating state. As a result, S adsorbed on the NOx absorbent of the NOx purification device 15
The Ox amount can be accurately estimated, and the SOx removal processing can be executed at an optimal time.

FIG. 8 is a flowchart of a process for calculating the target air-fuel ratio coefficient KCMD.
Is executed in synchronization with the generation of the TDC signal pulse. In step S101, the reproduction mode flag FSRC
It is determined whether or not MODE is “1”, and FSRCMO
When DE = 0, the normal control, that is, the setting of the target air-fuel ratio coefficient KCMD according to the engine operating state is performed (step S103). The target air-fuel ratio coefficient KCMD is basically based on the engine speed NE and the absolute pressure PB in the intake pipe.
A is calculated according to A, and is changed to a value corresponding to the operating state in a low temperature state of the engine coolant temperature TW or a predetermined high load operating state. Next, the counters NFISMD1, NFISMD2, and NF referred to in the processing of FIG.
Predetermined values N1, N2, and N3 are set in ISRMD3 (step S104), and the process ends. F
When SRCMODE = 1 and the regeneration process of the NOx purification device 15 is executed, the NOxCAT regeneration KCMD calculation process shown in FIG. 9 is executed (step S102).

In step S70 of FIG. 9, the counter NF
It is determined whether or not the value of ISRMD1 is “0”. Initially,
Since NFISRMD1> 0, this counter NFI
The value of SRMD1 is decremented by "1" (step S71), and the down count timer tmTCA
T is the execution time TMTCAT (for example, 60
Second) and start (step S72). Further, a temperature raising completion flag FTCATOK indicating that the temperature raising mode is completed is set to “0” (step S).
73), the down-count timer tmSPRG is set to the execution time TMSPRG (for example, 30 seconds) in the SOx removal mode and started (step S74), and this processing ends.

When the value of the counter NFISRMD1 becomes "0", the process proceeds from step S70 to step S75, and it is determined whether or not the temperature raising completion flag FTCATOK is "1". Initially, FTCATOK = 0, so the target air-fuel ratio coefficient KCMD is set to a value for the temperature increase mode, that is, “1.0” corresponding to the stoichiometric air-fuel ratio (step S7).
6) It is determined whether or not the value of the timer tmTCAT is “0” (step S77). If tmTCAT> 0, the process proceeds to step S74. If tmTCAT = 0, the temperature rise completion flag FTCATOK is set to “1” (step S78). Temperature rise completion flag FTCATOK
Is set to "1", the process immediately proceeds from step S75 to step S80.

In the following step S80, the counter NFI
It is determined whether or not the value of SRMD2 is "0". Since NFISMD2> 0 at first, this counter NF
The value of ISRMD2 is decremented by "1" (step S79), and the process proceeds to step S74. NFISR
When MD2 = 0, steps S80 to S8
The engine speed NE and the intake pipe absolute pressure PB
A KCMDSPRG map is searched according to A, and a rich set value KCMDSPRG for the SOx removal mode is calculated. The KCMDSPRG map is set such that the richer set value KCMDSPRG increases as the engine speed NE increases and the intake pipe absolute pressure PBA increases. Note that the enrichment set value KCMDSPRG for SOx removal may be a fixed value (for example, a value corresponding to A / F 12.5).

In the following step S82, the target air-fuel ratio coefficient KCMD is set to the enrichment set value KCMDSPRG,
It is determined whether or not the value of the timer tmSPRG is “0” (step S83). This process is immediately terminated while tmSPRG> 0, and when tmSPRG = 0, it is determined whether or not the value of the counter NFISRMD3 is "0" (step S84). Since NFISRMD3> 0 at first, the value of the counter NFISRMD3 is decremented by "1" (step S85), and this processing ends. When NFISRMD3 = 0, the reproduction mode flag FSRCMODE is returned to “0” (step S86), and the value of the SOx adsorption amount counter CSABS is set to “0”.
(Step S87), and the process ends.

As described above, by the processing of FIG. 9, the target air-fuel ratio coefficient KCMD is set to "1.0" in the temperature raising mode, and the target air-fuel ratio coefficient KCMD is rich in the SOx removal mode after the temperature raising of the NOx purifying device 15 is completed. Is set to the set value KCMDSPRG. As a result, the temperature rise of the NOx purification device 15 is promoted, the absorbed SOx can be reduced and released, and the sulfur-poisoned NOx purification device 15 can be regenerated.

In this embodiment, the ECU 5 constitutes sulfur oxide amount estimating means and sulfur oxide removing means. More specifically, the processes in FIGS. 4 and 5 correspond to a sulfur oxide amount estimating unit, and steps S13 and S15 in FIG. 2 correspond to a sulfur oxide removing unit. Note that the present invention is not limited to the above-described embodiment, and various modifications are possible. For example,
In the above-described embodiment, the amount of SOx absorbed by the NOx purification device 15 is estimated, and the SOx removal processing is performed when the estimated amount of SOx reaches a set value. NO as indicated in the gazette
The present invention may be applied to estimating the amount of SOx absorbed by the SOx purification device arranged upstream of the x purification device.

In the above-described embodiment, the addition value SABS or the subtraction value SDE is determined according to the target air-fuel ratio coefficient KCMD, the engine speed NE and the intake pipe absolute pressure PBA.
S is calculated, but the target air-fuel ratio coefficient KCMD
Is the detected equivalent ratio KA detected by the LAF sensor 14.
It may be replaced with CT.

[0061]

As described above, according to the first aspect of the present invention, the amount of sulfur oxide absorbed per unit time according to the air-fuel ratio of the air-fuel mixture supplied to the engine and the operating state of the engine. And the amount of release are estimated, and by integrating the estimated amount of absorption and release, the amount of sulfur oxides absorbed by the NOx purifying means is estimated. More accurate, NOx
The deterioration regeneration process of the purifying means can be executed at an optimal time.

According to the second aspect of the present invention, the air-fuel ratio is set near the stoichiometric air-fuel ratio, set leaner than the stoichiometric air-fuel ratio, or set richer than the stoichiometric air-fuel ratio. Since the amount of change in the amount of sulfur oxide is estimated according to the operating state and the engine operating state, the amount of change in the amount of sulfur oxide per unit time, that is, the amount of absorption or release can be accurately estimated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine and an exhaust purification device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart of a process for performing control for regenerating a sulfur-poisoned NOx purification device.

FIG. 3 is a flowchart showing a SOx saturation determination process of FIG. 2 in detail.

FIG. 4 is a flowchart showing details of an SOx adsorption amount estimation process in FIG. 3;

FIG. 5 is a flowchart showing details of an SOx adsorption amount estimation process of FIG. 3;

FIG. 6 is a diagram showing a map used in the processing of FIG. 4 or 5;

FIG. 7 is a diagram showing a table used in the processing of FIG. 4 or 5;

FIG. 8 is a flowchart of a process for calculating a target air-fuel ratio coefficient (KCMD).

FIG. 9 is a flowchart of a process for setting a target air-fuel ratio coefficient during execution of a regeneration process of the NOx purification device.

[Explanation of symbols]

Reference Signs List 1 internal combustion engine 5 electronic control unit (sulfur oxide amount estimating means, sulfur oxide removing means) 7 intake pipe absolute pressure sensor 10 crank angle position sensor 12 exhaust pipe 15 NOx purification device (NOx purification means)

Claims (2)

[Claims] 1. A NOx purifying means provided in an exhaust system of an internal combustion engine for absorbing NOx in exhaust gas in an exhaust lean state;
A sulfur oxide amount estimating means for estimating the amount of sulfur oxide absorbed by the NOx purification means; and removing the sulfur oxide when the sulfur oxide amount estimated by the sulfur oxide amount estimating means reaches a set value. An exhaust gas purifying apparatus for an internal combustion engine, comprising: a sulfur oxide removing unit that performs processing; wherein the sulfur oxide amount estimating unit is configured to perform the sulfur oxidation according to an air-fuel ratio of an air-fuel mixture supplied to the engine and an operating state of the engine. An exhaust gas purification apparatus for an internal combustion engine, comprising: estimating a change amount of a physical quantity per unit time; and estimating the sulfur oxide amount by integrating the estimated change amount. 2. The method according to claim 1, wherein the sulfur oxide amount estimating means is configured to set the air-fuel ratio to a value close to the stoichiometric air-fuel ratio, to a value leaner than the stoichiometric air-fuel ratio, or to a value richer than the stoichiometric air-fuel ratio. 2. The method according to claim 1, wherein the control unit estimates the amount of change in accordance with the operating state of the engine.
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1.