JP3562069B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more specifically, has a NOx adsorption catalyst that adsorbs NOx in an engine exhaust passage, and converts NOx adsorbed by the NOx adsorption catalyst into a combustion state at a stoichiometric air-fuel ratio or lower. The present invention relates to an air-fuel ratio control technique for appropriately purifying the NOx in a system that purifies the reaction by reacting with HC and CO.
[0002]
[Prior art]
Conventionally, as an internal combustion engine provided with the NOx adsorption catalyst, there has been one disclosed in Japanese Patent Application Laid-Open No. Hei 6-129246.
This device has a NOx adsorbent that absorbs NOx when the air-fuel ratio of the inflow exhaust gas is lean, and releases the absorbed NOx when the air-fuel ratio becomes rich, and shifts from lean operation to operation near the stoichiometric air-fuel ratio. In this case, the air-fuel ratio is temporarily made rich and then brought to near the stoichiometric air-fuel ratio, and the degree of enrichment or the period of enrichment is controlled based on the amount of NOx stored in the NOx adsorbent. It has become.
[0003]
According to such a configuration, it is possible to secure HC sufficient for the amount of NOx released according to the shift from the lean operation to the operation near the stoichiometric air-fuel ratio, and thus it is possible to satisfactorily purify NOx.
[0004]
[Problems to be solved by the invention]
However, in the above-mentioned conventional apparatus, since there is no means for determining whether or not the enrichment degree is appropriate, the NOx reduction effect by the enrichment is not exhibited as required, or the enrichment degree is not increased. However, there is a risk that the exhaust gas will become excessive and deteriorate the exhaust properties and fuel efficiency.
[0005]
For example, if the base air-fuel ratio is originally leaner than the stoichiometric (theoretical air-fuel ratio) due to variations in product characteristics, etc., the actual air-fuel ratio will be leaner than the desired value even after enrichment. As a result, a sufficient supply of HC cannot be performed, and the NOx purification performance is reduced, so that the NOx emission cannot be suppressed to a required level or less. Conversely, when the base air-fuel ratio is on the rich side, the actual air-fuel ratio becomes richer than a desired value due to the enrichment, surplus HC is discharged, and the fuel efficiency deteriorates.
[0006]
Here, the base air-fuel ratioLuckAir-fuel ratio learning control is known as a technique for eliminating the air-fuel ratio.However, the air-fuel ratio learning control generally aims at stabilizing the air-fuel ratio during steady-state operation, and stays at the same operating condition for a relatively long time. During this period, a correction amount corresponding to the error is obtained. For this reason, a measurement error of the intake air amount is likely to occur, such as a typical transition from lean operation to stoichiometric air-fuel ratio operation, that is, a transition from the cruise state to the acceleration state by depressing the accelerator, and When the state of the fuel adhering to the intake port wall surface also changes greatly, the air-fuel ratio learning aimed at stabilizing the air-fuel ratio in a steady state involves changing the base air-fuel ratio when shifting from the lean operation to the stoichiometric air-fuel ratio operation. Correction cannot be performed with high accuracy, and as a result, the desired rich air-fuel mixture cannot be formed by the enrichment control.
[0007]
The present invention has been made in view of the above problems, and enables stable enrichment control optimal for NOx reduction even when there is a variation in the base air-fuel ratio, thereby ensuring NOx emission. It is an object of the present invention to be able to avoid an increase in the amount of HC and a deterioration in fuel efficiency while suppressing the fuel consumption.
[0008]
[Means for Solving the Problems]
Therefore, the air-fuel ratio control device for an internal combustion engine according to the first aspect of the present invention adsorbs NOx in exhaust gas in a leaner air-fuel ratio atmosphere than the stoichiometric air-fuel ratio, as shown in FIG. An NOx adsorbing catalyst for desorbing the adsorbed NOx in the atmosphere is provided in the exhaust passage, and the air-fuel ratio is temporarily set to a target value when the operating region shifts from the operating region burning at the lean air-fuel ratio to the operating region burning near the stoichiometric air-fuel ratio. Enrichment means for enriching the air-fuel ratio and air-fuel ratio feedback control for feedback-controlling the air-fuel ratio of the engine intake air-fuel mixture so as to bring the actual air-fuel ratio close to the target air-fuel ratio in an operating region in which combustion is performed near the stoichiometric air-fuel ratio. Means and a control cycle of the air-fuel ratio feedback control means until the air-fuel ratio enriched by the enrichment means reaches the target air-fuel ratio. And enrichment degree control means for controlling the degree of enrichment by the enrichment means, wherein the enrichment degree control means operates in the operating range in which combustion is performed at the lean air-fuel ratio. NOx adsorption amount calculating means for calculating the amount, engine rotational speed detecting means for detecting the engine rotational speed, and cycle detecting means for detecting the control cycle by the air-fuel ratio feedback control means. And the detected engine speed based onNO x The larger the adsorption amount, the larger the engine rotation speed.The degree of enrichment by the enrichment means is controlled so that the actual feedback control cycle detected by the cycle detection means approaches the target value of the set air-fuel ratio feedback control cycle.
[0009]
According to such a configuration, the operating region shifts from the operating region in which combustion is performed at the lean air-fuel ratio to the operating region in which combustion is performed near the stoichiometric air-fuel ratio, and when NOx is desorbed from the NOx adsorption catalyst, the air-fuel ratio is actively enriched, The amount of HC required for the NOx reduction process is ensured. Here, when the degree of enrichment is set to be the same between the case where the base air-fuel ratio is on the rich side and the case where the base air-fuel ratio is on the lean side, the air-fuel ratio feedback control cycle from the enrichment to the target air-fuel ratio differs, Excess or deficiency occurs in the degree of enrichment. Therefore,When the target value of the air-fuel ratio feedback control cycle is set to NO x NO based on adsorption amount and engine speed x The larger the adsorption amount, the larger the engine speed, the larger the setting.By controlling the degree of enrichment such that the actual air-fuel ratio feedback control cycle becomes the target value, the degree of enrichment is optimized, NOx emissions are suppressed, and an increase in HC emissions is avoided.
[0011]
Claim 2In the invention described above, the enrichment degree control means learns the enrichment degree controlled based on the feedback control cycle for each of a plurality of operation regions divided by the engine load and the engine rotation speed.
[0012]
According to such a configuration, the degree of enrichment that allows the feedback control cycle to be properly learned is learned for each of a plurality of operating regions that are divided according to the engine load and the engine rotational speed. The emission amount can be suppressed, and the increase in HC amount due to excessive enrichment can be avoided.
Claim3In the invention described in the above, acceleration / deceleration operation detection means for detecting acceleration operation and deceleration operation of the engine is provided, and the enrichment degree control means performs feedback control for each of the acceleration operation and the deceleration operation detected by the acceleration / deceleration operation detection means. It is configured to learn the degree of enrichment controlled based on the cycle.
[0013]
According to this configuration, two values for the acceleration operation and the deceleration operation may be prepared as the learning value of the enrichment degree, and the storage amount of the storage device can be significantly reduced, thereby reducing the load on the storage device. it can.
Claim4In the invention described, the air-fuel ratio feedback control means controls the air-fuel ratio of the engine intake air-fuel mixture by at least proportional / integral control so that the actual air-fuel ratio approaches the target air-fuel ratio. By increasing and correcting the proportional operation amount in the enrichment direction in the air-fuel ratio feedback control means, the air-fuel ratio is temporarily made richer than the target air-fuel ratio, and one control cycle by the air-fuel ratio feedback control means is reduced. At the time of completion, the increase correction of the proportional manipulated variable is stopped.
[0014]
According to this configuration, the air-fuel ratio temporarily enriched by the increase correction of the proportional operation amount gradually returns to the vicinity of the target air-fuel ratio, and the proportional control is performed again in the enrichment direction, that is, one control cycle. At the end, the increase correction of the proportional manipulated variable is stopped, so that the state can be smoothly changed from the enrichment control state to a state near the target air-fuel ratio.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
FIG. 2 is a diagram illustrating a system configuration of the internal combustion engine according to the first embodiment.
In FIG. 2, air flowing through an air cleaner 2 is adjusted by a throttle valve 3 and sucked into an internal combustion engine 1.
[0016]
Fuel injected from a fuel injection valve 4 interposed in an intake port of each cylinder is mixed with the air to form an air-fuel mixture. The air-fuel mixture sucked into the cylinder is generated by spark ignition by a spark plug 5. Ignite and burn.
The combustion exhaust gas is purified by a NOx adsorption catalyst 6 having a NOx adsorbent and a three-way catalyst 7, and then discharged into the atmosphere via a muffler 8.
[0017]
The NOx adsorption catalyst 6 has a function of absorbing NOx when the air-fuel ratio of the inflow exhaust gas is lean, and releasing the absorbed NOx when the air-fuel ratio becomes rich.
Detection signals from various sensors are input to a control unit 9 having a microcomputer for controlling the fuel injection amount by the fuel injection valve 4.
That is, the control unit 9 includes a rotation signal from a crank angle sensor 11 as an engine rotation speed detecting means incorporated in the distributor 10, a water temperature signal from a water temperature sensor 12, an oxygen concentration signal from an oxygen sensor 13, an air flow meter. 14, an opening signal from the throttle sensor 15, and the like.
[0018]
The control unit 9 controls the injection amount of the fuel injection valve 4 based on the detection signals from the various sensors, and controls the ignition timing of the ignition plug 5 and the opening of the auxiliary air amount adjustment valve 16.
Here, the engine 1 of the present embodiment is a so-called lean combustion engine that burns at an air-fuel ratio that is significantly leaner than the stoichiometric air-fuel ratio (for example, an air-fuel ratio of about 20 to 22), and according to a routine shown in FIG. It is designed to switch between combustion at a lean air-fuel ratio and combustion near a stoichiometric air-fuel ratio.
[0019]
In the flowchart of FIG. 3, in S301, a signal of an idle switch provided in the throttle sensor 15 is read, and in S302, whether or not the idle switch is ON, that is, whether or not the throttle valve 3 is fully closed. Determine whether or not.
When the idle switch is OFF and the throttle valve 3 is open, it is determined that the throttle valve opening is in the lean combustion condition, and the routine proceeds to S303.
[0020]
In S303, the detection signal from the water temperature sensor 12 is read, and in the next S304, it is determined whether or not the water temperature TW is within a predetermined temperature range (TWL ≦ TW ≦ TWH).
In this embodiment, as shown in FIG. 10, air-fuel ratio feedback control (in FIG. 10, indicated by “λ-con”) for feedback-controlling the air-fuel ratio based on the detection signal of the oxygen sensor 13 is shown. A narrower range within the water temperature range to be executed is defined as a lean combustion condition range.
[0021]
If it is determined in S304 that the water temperature TW is in the lean combustion condition range, the process proceeds to S305, and the engine load TP is detected.
In this embodiment, the basics of the fuel injection valve 4 calculated based on the intake air amount Q detected by the air flow meter 14 and the engine speed NE calculated based on the detection signal from the crank angle sensor 11 are described. The fuel injection amount TP (TP = K × Q / NE: K is a constant) is set to a value representing the engine load.
[0022]
In S306, it is determined whether or not the engine load TP is within a predetermined range (TPL ≦ TP ≦ TPH). If it is within the predetermined range, the process proceeds to S307, and based on the detection signal from the crank angle sensor 11, The engine speed NE is detected.
Then, in S308, it is determined whether or not the engine speed NE is within a predetermined range (NEL ≦ NE ≦ NEH). As shown in FIG. 11, the engine load TP and the engine speed NE each fall within the predetermined range. It is determined whether or not the operation corresponds to the lean combustion region specified in advance as the operation region.
[0023]
If it corresponds to the lean combustion region, the flow proceeds to S309, where the throttle sensor 15 detects the throttle valve opening TVO.
In S310, it is determined whether or not the throttle valve opening TVO is equal to or less than a predetermined opening TVOH, and if it is equal to or smaller than the predetermined opening TVOH, the process proceeds to S311.
In S311, the vehicle speed VSP is detected, and in the next S312, it is determined whether or not the vehicle speed VSP is equal to or higher than a predetermined speed VSPL (see FIG. 12).
[0024]
If the vehicle speed VSP is equal to or higher than the predetermined speed VSPL, the process proceeds to S313, and the rate of change ΔVSP of the vehicle speed VSP is detected.
In S314, it is determined whether or not the change rate ΔVSP is equal to or less than a predetermined value DVH (see FIG. 12). If the vehicle speed VSP is substantially stable, the process proceeds to S315, and 1 is set to the lean operation permission flag FLEAN. .
[0025]
On the other hand, if any one of the above conditions is not satisfied, the process proceeds to S316, and the lean operation permission flag FLEAN is set to 0.
The routine shown in the flowchart of FIG. 4 shows the state of the fuel-air ratio control based on the lean operation permission flag FLEAN.
In the flowchart of FIG. 4, first, in S401, the lean operation permission flag FLEAN is determined.
[0026]
Then, when the lean operation permission flag FLEAN is 1, the process proceeds to S402, and the target fuel-air ratio TDML is obtained with reference to a lean fuel-air ratio map.
On the other hand, when the lean operation permission flag FLEAN is 0, the routine proceeds to S403, where the target fuel-air ratio TDML is obtained with reference to a stoichiometric fuel-air ratio (stoichiometric air-fuel ratio) map.
[0027]
In S404, the lean operation permission flag FLEAN is determined again, and when the lean operation permission flag FLEAN is 1, the routine proceeds to S405, in which the fuel-air ratio correction coefficient DML is calculated.
DML = Max (DML-ΔDML, TDML)
Set as
[0028]
As shown in FIG. 13, the ΔDML is a step change amount of the fuel-air ratio correction coefficient DML that is set as a larger value as the opening degree change rate ΔTVO of the throttle valve is larger, and when the lean operation permission flag FLEAN is 0, When the state changes to 1, the engine is made to gradually lean to the target fuel-air ratio TDML at the change speed based on the ΔDML.
[0029]
On the other hand, when the lean operation permission flag FLEAN is 0, the routine proceeds to S406, where the fuel-air ratio correction coefficient DML is
DML = Min (DML + ΔDML, TDML)
Set as
That is, when switching from the lean combustion state to the stoichiometric (stoichiometric air-fuel ratio), the air-fuel ratio is gradually enriched to the target fuel-air ratio TDML at the change speed based on ΔDML (see FIG. 13).
[0030]
In S407, it is determined whether or not the fuel-air ratio correction coefficient DML is 1.0. When the fuel-air ratio correction coefficient DML is 1.0 and the combustion at the stoichiometric air-fuel ratio is to be performed, This routine ends.
On the other hand, if it is determined in step S407 that the fuel-air ratio correction coefficient DML is not 1.0, the air-fuel ratio feedback control for bringing the actual air-fuel ratio closer to the stoichiometric air-fuel ratio is not performed. Clamp the coefficient ALPHA to 1.0.
[0031]
The routine shown in the flowchart of FIG. 5 is for calculating the NOx adsorption amount in the NOx adsorption catalyst 6. The function shown in the flowchart of FIG. 5 corresponds to the NOx adsorption amount calculating means.
In S501, it is determined whether or not the engine is in a lean combustion state based on whether or not the fuel-air ratio correction coefficient DML is less than 1.0.
[0032]
When the fuel-air ratio correction coefficient DML is less than 1.0 and lean combustion is being performed, NOx is adsorbed on the NOx adsorption catalyst 6, so the process proceeds to S502, and the NOx adsorption speed DABSR is calculated by the following equation. Estimate based on
DABSR = DABSR0 # × TP / TP0 × Q / Q0 × (ABSFC # -ABSTC) / ABSFC #
Here, DABSR0 # is the reference adsorption speed, TP0 is the reference load, Q0 is the reference air amount, ABSFC # is the maximum adsorption amount, ABSTC is the current adsorption amount, and the larger the load TP, the more the intake air amount Q The configuration is such that the larger the adsorption speed DABSR, the larger the adsorption speed DABSR is estimated, and the larger the adsorption amount ABSTC, the lower the adsorption speed DABSR is estimated.
[0033]
In the next step S503, the current NOx adsorption amount ABSTC is estimated according to the following equation using the adsorption speed DABSR.
ABSTC = ABSTC (old) + DABSR
On the other hand, when it is determined in S501 that the fuel-air ratio correction coefficient DML is not less than 1.0, the stoichiometric air-fuel ratio is being burned, and NOx adsorbed by the NOx adsorbing catalyst 6 is released. In S504, the NOx desorption rate DPRGR is estimated according to the following equation.
[0034]
DPRGR = DPRGR0 # × TP / TP0 × Q / Q0 × ABSTC / ABSFC #
Here, the DPRGR0 # is a reference desorption speed.
In S505, the NOx adsorption amount ABSTC at the present time is estimated using the desorption speed DPRGR according to the following equation.
[0035]
ABSTC = ABSTC (old) -DPRGR
The routine shown in the flowchart of FIG. 6 indicates the air-fuel ratio feedback control, and is executed every one revolution of the engine. The functions shown in the flowchart of FIG. 6 correspond to the air-fuel ratio feedback control means, the enrichment means, and the enrichment degree control means.
[0036]
In S601, it is determined whether or not the engine is in a lean combustion state based on whether or not the fuel-air ratio correction coefficient DML is less than 1.0.
If it is during the lean combustion, the enrichment execution flag FRSFT is set to 1 in S610, the air-fuel ratio feedback correction coefficient ALPHA is clamped to 1.0 in S611, and this routine is terminated.
[0037]
On the other hand, when the fuel-air ratio correction coefficient DML is 1.0 and the stoichiometric air-fuel ratio is being burned, the routine proceeds to S602, where it is determined whether or not a predetermined clamp condition is satisfied. However, if the predetermined clamp condition is satisfied, the routine proceeds to S611, where the air-fuel ratio feedback correction coefficient ALPHA is clamped to 1.0, and this routine ends.
[0038]
If the clamp condition is not satisfied, the process proceeds to S603, and it is determined whether or not 1 is set in the enrichment execution flag FRSFT.
When the enrichment execution flag FRSFT is 0, the process proceeds to S612, and the integral i, the proportional PR, and the PL (see FIG. 14) used for the proportional integral control of the air-fuel ratio feedback correction coefficient ALPHA are respectively referred to with reference to a map. Ask.
[0039]
Then, the process proceeds to S609, where the proportional integral control of the air-fuel ratio feedback correction coefficient ALPHA is performed based on the rich / lean actual air-fuel ratio with respect to the stoichiometric air-fuel ratio detected by the oxygen sensor 13.
On the other hand, when it is determined in S603 that the enrichment execution flag FRSFT is 1, the process proceeds to S604, and the enrichment degree LRPL is set according to the NOx adsorption amount ABSTC. Here, the larger the amount of NOx adsorbed, the larger the amount of HC required for reduction when the NOx is adsorbed, and therefore, the larger the amount of NOx adsorbed, the larger the enrichment degree LRPL is set.
[0040]
In the next step S605, the enrichment degree learning correction coefficient LRPLHS is referred from the map according to the engine load TP and the rotational speed NE. The learning setting of the enrichment degree learning correction coefficient LRPLHS will be described later, but is learned based on the air-fuel ratio feedback control cycle from the enrichment of the air-fuel ratio by the enrichment control to the stoichiometric air-fuel ratio. (See FIG. 15).
[0041]
In S606, the proportional component PL (see FIG. 15) used for increasing the air-fuel ratio feedback correction coefficient ALPHA by the proportional control is set as follows:
PL = LRPL × LRPLHS
And the PR used for the decrease proportional control is set to 0.
Further, a predetermined value LRI # is set as an integral i used for the integral control of the correction coefficient ALPHA.
[0042]
As described above, by increasing the proportional component PL (proportional operation amount) used for setting the correction coefficient ALPHA by the proportional control, the air-fuel ratio is temporarily enriched at the time of switching from lean to stoichiometric. In S607, it is determined whether or not the enrichment has been performed for one cycle of the feedback. When the enrichment is performed for one cycle, the process proceeds to S608, where the enrichment execution flag FRSFT is set to 0, and thereafter, the normal feedback control is performed. Is done.
[0043]
The routine shown in the flowchart of FIG. 7 shows the state of learning of the enrichment degree learning correction coefficient LRPLHS. After the enrichment control based on the flowchart of FIG. 6, that is, the enrichment execution flag FRSFT is changed from 1 to 1 It is to be executed every time it is switched to 0. The function shown in the flowchart of FIG. 7 also corresponds to the enrichment degree control means.
[0044]
In S701, the number of engine revolutions CO2INV between the peaks of ALPHA during the enrichment control (see FIG. 15) is calculated. This step S701 is a function corresponding to the period detecting means.
In S702, operating conditions such as the engine load TP and the rotational speed NE are detected.
In S703, a threshold value SO2INV of the number of engine revolutions CO2INVA at the time of switching from lean to stoichiometric is obtained from the map based on the NOx adsorption amount ABSTC and the engine speed NE.
[0045]
In S704, it is determined whether or not the number of engine revolutions CO2INV calculated in S701 is equal to or greater than a value obtained by adding a predetermined value HYSINV # to the threshold value SO2INV. When the actual number of engine revolutions CO2INV greatly exceeds the threshold value SO2INV, the process proceeds to S705, and the enrichment degree learning correction coefficient LRPLHS is referred to from the corresponding area of the map.
[0046]
Then, in S706, the correction coefficient LRPLHS is reduced and corrected by a predetermined value DPL #. In the next S707, the map data is rewritten to the correction coefficient LRPLHS after the reduction correction.
That is, when the number of engine revolutions CO2INV greatly exceeds the target, the air-fuel ratio feedback control cycle is long because the base air-fuel ratio is rich (indicated by the dashed line in FIG. 15), and the degree of enrichment is smaller than a predetermined degree of enrichment. Also means that the actual degree of enrichment is large, and it is estimated that the amount of HC emission is excessive. Therefore, in order to suppress the amount of HC emission and prevent deterioration of fuel efficiency, the correction coefficient LRPLHS is reduced to reduce Avoiding
[0047]
On the other hand, when it is determined in S704 that the actual engine rotation number CO2INV is less than the value obtained by adding the predetermined value HYSINV # to the threshold value SO2INV, the process proceeds to S708, and the actual engine rotation number CO2INV is reduced from the threshold value SO2INV by the predetermined value. It is determined whether the difference is equal to or less than the value obtained by subtracting HYSINV #.
If the actual number of engine revolutions CO2INV is equal to or less than the value obtained by subtracting the predetermined value HYSINV # from the threshold value SO2INV, the process proceeds to S709, where the current correction coefficient LRPLHS is read from the map, and at S710, the read correction coefficient is read. LRPLHS is increased by a predetermined value DPL #, and in S711, the map data is updated based on the corrected correction coefficient LRPLHS.
[0048]
That is, when the actual number of engine revolutions CO2INV is much lower than the threshold value, the air-fuel ratio feedback control cycle is short because the base air-fuel ratio is lean (shown by a broken line in FIG. 15), and the predetermined richness degree Also means that the actual enrichment degree was small, and it is presumed that the HC amount required for NOx purification is insufficient. Therefore, the enrichment degree was increased to increase the HC amount and NOx In order to further suppress the emission amount, the correction coefficient LRPLHS is increased and corrected.
[0049]
On the other hand, when the actual number of engine revolutions CO2INV is within the range of the threshold value SO2INV ± HYSINV #, it is determined that the current rich shift amount is appropriate, and this routine ends without updating the map data.
Next, a second embodiment will be described with reference to FIGS.
The differences between the second embodiment and the first embodiment are the air-fuel ratio feedback control routine and the learning routine for the enrichment degree learning correction coefficient shown in FIGS. 8 and 9. The hardware configuration of FIGS. 2 to 5 described in the first embodiment, the lean / stoichiometric air-fuel ratio switching control routine, the NOx adsorption amount calculation routine, the fuel-air ratio control routine, and the like are the same as those of the first embodiment. Yes, and the description is omitted here.
[0050]
The routine shown in the flowchart of FIG. 8 shows the air-fuel ratio feedback control of the second embodiment, and is executed every one revolution of the engine.
In S801, it is determined whether or not the fuel is in the lean combustion state based on whether or not the fuel-air ratio correction coefficient DML is less than 1.0. When the fuel is in the lean combustion, 1 is set to the enrichment execution flag FRSFT in S812. In step S813, the air-fuel ratio feedback correction coefficient ALPHA is clamped to 1.0, and the routine ends.
[0051]
On the other hand, when the fuel-air ratio correction coefficient DML is 1.0 and the stoichiometric air-fuel ratio is being burned, the routine proceeds to S802, where it is determined whether or not a predetermined clamp condition is satisfied. However, if the predetermined clamp condition is satisfied, the routine proceeds to S813, where the air-fuel ratio feedback correction coefficient ALPHA is clamped to 1.0, and this routine is terminated.
[0052]
If the clamp condition is not satisfied, the process proceeds to S803, and it is determined whether or not the enrichment execution flag FRSFT is set to 1. If the enrichment execution flag FRSFT is 0, the process proceeds to S814. The integral i and the proportional PR and PL used for the proportional integral control of the air-fuel ratio feedback correction coefficient ALPHA are obtained by referring to the maps.
[0053]
Then, the process proceeds to S811, and the proportional integral control of the air-fuel ratio feedback correction coefficient ALPHA is performed based on the rich / lean actual air-fuel ratio with respect to the stoichiometric air-fuel ratio detected by the oxygen sensor 13.
On the other hand, when it is determined in S803 that the enrichment execution flag FRSFT is 1, the flow proceeds to S804, and the enrichment degree LRPL is set according to the NOx adsorption amount ABSTC as in the first embodiment.
[0054]
In the next step S805, it is determined whether the vehicle is accelerating or decelerating based on whether an idle switch as acceleration / deceleration operation state detection means is ON. When the idle switch is not ON, it is determined that the vehicle is accelerating, and the process proceeds to S806, where the enrichment degree learning correction coefficient LRHSAC during acceleration is selected as the enrichment degree learning correction coefficient LRPLHS. On the other hand, when the idle switch is ON, it is determined that the vehicle is decelerating, and the process proceeds to S807, where the enrichment degree learning correction coefficient LRHSDC is selected as the enrichment degree learning correction coefficient LRPLHS.
[0055]
In S808, the proportional component PL used for the increase setting by the proportional control of the air-fuel ratio feedback correction coefficient ALPHA, the PR used for the decrease proportional control, and the integral component i used for the integral control of the correction coefficient ALPHA are compared with those in the first embodiment. Set in the same way.
In S809, it is determined whether or not the enrichment operation in S808 has been performed only for one cycle of feedback. When enrichment is performed for one cycle, the process proceeds to S810, where the enrichment execution flag FRSFT is set to 0, and thereafter. The normal feedback control is performed.
[0056]
The routine shown in the flow chart of FIG. 9 shows how the enrichment degree learning correction coefficient LRHSAC during acceleration and the enrichment degree learning correction coefficient LRHSDC during deceleration are learned, and the enrichment control based on the flow chart of FIG. Later, that is, each time the enrichment execution flag FRSFT is switched from 1 to 0, it is executed every time.
[0057]
In S901, the number of engine revolutions CO2INV between the peaks of the ALPHA during the enrichment control is calculated.
In S902, operating conditions such as the engine load TP and the rotational speed NE are detected.
In S903, it is determined whether or not the engine rotation number CO2INV calculated in S901 is equal to or greater than a value obtained by adding a predetermined value HYSINV # to the engine rotation number threshold SO2INV obtained from the map based on the NOx adsorption amount ABSTC and the engine rotation speed NE. Is determined.
[0058]
If the actual number of engine revolutions CO2INV greatly exceeds the threshold value SO2INV, the process proceeds to S904, where it is determined whether or not the idle switch is ON. If not, the process proceeds to S905, where the stored acceleration is stored. The time enrichment degree learning correction coefficient LRHSAC is reduced and corrected by a predetermined value DPL # to update the stored value in the memory. On the other hand, when the idle switch is ON, the process proceeds to S906, in which the stored deceleration enrichment degree learning correction coefficient LRHSDC is corrected to decrease by a predetermined value DPL # to update the stored value of the memory.
[0059]
That is, if the engine rotation number CO2INV is much higher than the target and it is estimated that the amount of HC emission is excessive due to the rich base air-fuel ratio, the amount of HC emission is suppressed and the fuel efficiency is deteriorated. In order to prevent the excessive enrichment, the enrichment degree learning correction coefficient LRHSAC during acceleration is reduced during acceleration, and the enrichment degree learning correction coefficient LRHSDC during deceleration is reduced during deceleration.
[0060]
On the other hand, in S903, when it is determined that the actual engine rotation number CO2INV is less than the value obtained by adding the predetermined value HYSNOX # to the threshold value SO2INV, the process proceeds to S907, and the actual engine rotation number CO2INV is reduced from the threshold value SO2INV by the predetermined value. It is determined whether the difference is equal to or less than the value obtained by subtracting HYSINV #.
If the actual number of engine revolutions CO2INV is equal to or less than the value obtained by subtracting the predetermined value HYSINV # from the threshold value SO2INV, the process proceeds to S908, where it is determined whether or not the idle switch is ON. , And the data is updated by increasing and correcting the enrichment degree learning correction coefficient LRHSAC during acceleration by a predetermined value DPL #. On the other hand, when the idle switch is ON, the processing proceeds to S910, where the enrichment degree learning correction coefficient during deceleration is calculated. The data is updated by increasing and correcting LRHSDC by a predetermined value DPL #.
[0061]
That is, when the actual number of engine revolutions CO2INV is significantly lower than the threshold, it is estimated that the amount of HC required for NOx purification is insufficient due to the lean base air-fuel ratio, In order to increase the amount of enrichment and increase the amount of HC to further suppress NOx emissions, increase correction of the enrichment degree learning correction coefficient LRHSAC during acceleration or the enrichment degree learning correction coefficient LRHSDC during deceleration corresponding to the operating conditions. I do.
[0062]
On the other hand, when the actual engine rotation number CO2INV is within the range of the threshold value SO2INV ± HYSINV #, it is determined that the current rich shift amount is appropriate, and the present routine is terminated without updating the data.
According to the second embodiment, the enrichment degree learning correction coefficient is a binary value during acceleration and during deceleration. This is because, if the rich / lean error of the base air-fuel ratio during steady operation can be substantially eliminated by the air-fuel ratio learning control, the rich / lean error of the base air-fuel ratio mainly occurs during acceleration / deceleration transition. If the air-fuel ratio learning control is used in combination, sufficient effects can be obtained only by providing the two enrichment degree learning correction coefficients for acceleration and deceleration. For this reason, in the second embodiment, since a map for storing the enrichment degree learning correction coefficient according to the driving state is not required, the amount of data to be stored in the storage device is small, and the load on the storage device is reduced. There are advantages that can be done.
[0063]
【The invention's effect】
As described above, according to the first aspect of the invention, when NOx is desorbed from the NOx adsorption catalyst, the air-fuel ratio is temporarily enriched to secure the amount of HC required for the NOx reduction process. In the configuration to aim for,When the target value of the air-fuel ratio feedback control cycle is set to NO x NO based on adsorption amount and engine speed x The larger the adsorption amount, the larger the engine speed, and the larger the target value.Since the degree of enrichment is controlled so that the actual control cycle approaches, even if the base air-fuel ratio is different, the degree of enrichment is appropriately controlled to increase the amount of HC due to excessive enrichment and the amount of NOx due to excessive enrichment. There is an effect that the increase in the number of the pixels can be reliably avoided.
[0064]
Claim 2According to the invention described above, even if the operating conditions change, the appropriate enrichment control can be executed under each operating condition to stably control the NOx emission amount to be low, and the HC amount increases due to excessive enrichment. There is an effect that it is possible to avoid doing.
[0065]
Claim3According to the invention described above, only two learning values of the degree of enrichment to be stored are required for the acceleration operation and the deceleration operation, and the storage amount of the storage device can be reduced, so that the load on the storage device can be reduced. .
Claim4According to the invention described above, even if the air-fuel ratio is temporarily set to a rich state in order to reduce the released NOx, it is possible to smoothly change the air-fuel ratio to a state near the target air-fuel ratio thereafter.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of the invention according to claim 1;
FIG. 2 is a system configuration diagram of an internal combustion engine.
FIG. 3 is a flowchart showing lean operation control.
FIG. 4 is a flowchart showing fuel-air ratio control.
FIG. 5 is a flowchart showing a calculation for estimating the NOx adsorption amount.
FIG. 6 is a flowchart illustrating air-fuel ratio feedback control according to the first embodiment of the present invention.
FIG. 7 is a flowchart showing learning control of the degree of enrichment according to the first embodiment;
FIG. 8 is a flowchart showing air-fuel ratio feedback control according to a second embodiment of the present invention.
FIG. 9 is a flowchart showing learning control of the degree of enrichment according to the second embodiment;
FIG. 10 is a diagram showing a water temperature range as a lean operation condition.
FIG. 11 is a diagram showing a lean operation region.
FIG. 12 is a diagram showing a vehicle speed and a vehicle speed change rate as lean operating conditions.
FIG. 13 is a time chart showing a state of fuel-air ratio control.
FIG. 14 is a time chart showing a state of air-fuel ratio feedback control.
FIG. 15 is a time chart showing a state of an air-fuel ratio feedback control cycle according to a base air-fuel ratio.
[Explanation of symbols]
1 Internal combustion engine
3 Throttle valve
4 Fuel injection valve
5 Spark plug
6 NOx adsorption catalyst
7 Three-way catalyst
9 Control unit
11 Crank angle sensor
12 Water temperature sensor
13 Oxygen sensor
14 Air flow meter
15 Throttle sensor

Claims (4)

An air-fuel ratio of an internal combustion engine having a NOx adsorption catalyst in an exhaust passage for adsorbing NOx in exhaust gas in an air-fuel ratio atmosphere leaner than the stoichiometric air-fuel ratio and desorbing the adsorbed NOx in an air-fuel ratio atmosphere lower than the stoichiometric air-fuel ratio A control device,
Enrichment means for temporarily enriching the air-fuel ratio from the target air-fuel ratio when shifting from the operation region burning at the lean air-fuel ratio to the operation region burning near the stoichiometric air-fuel ratio,
Air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the engine intake air-fuel mixture so as to bring the actual air-fuel ratio closer to the target air-fuel ratio in an operation region where combustion is performed near the stoichiometric air-fuel ratio;
Rich-enrichment control means for controlling the enrichment degree by the enrichment means based on a control cycle by the air-fuel ratio feedback control means until the air-fuel ratio enriched by the enrichment means reaches the target air-fuel ratio. ,
The enrichment degree control means,
NOx adsorbing amount calculating means for calculating an adsorbed amount of NOx adsorbed on the NOx adsorbing catalyst in an operating region in which combustion is performed at the lean air-fuel ratio, engine rotational speed detecting means for detecting an engine rotational speed, and the air-fuel ratio feedback control. a period detecting means for detecting the control cycle by means, as the larger the engine rotational speed the NO x adsorption amount increases based on the calculated NOx adsorbed amount and the detected engine rotational speed is set higher increases larger empty The engine is configured to control a degree of enrichment by the enrichment means so that an actual feedback control cycle detected by the cycle detection means approaches a target value of a fuel ratio feedback control cycle. Fuel ratio control device. 2. The internal combustion engine according to claim 1, wherein the enrichment degree control unit learns the enrichment degree controlled based on a feedback control cycle for each of a plurality of operating regions divided by an engine load and an engine rotation speed. Engine air-fuel ratio control device. An acceleration / deceleration operation detection means for detecting acceleration operation and deceleration operation of the engine,
2. The internal combustion engine according to claim 1, wherein the rich degree control means learns a rich degree controlled based on a feedback control cycle for each of the acceleration operation and the deceleration operation detected by the acceleration / deceleration operation detection means. Air-fuel ratio control device. The air-fuel ratio feedback control means controls the air-fuel ratio of the engine intake air-fuel mixture by at least proportional / integral control so that the actual air-fuel ratio approaches the target air-fuel ratio,
The enrichment means temporarily increases the air-fuel ratio from the target air-fuel ratio by increasing and correcting the proportional operation amount in the enrichment direction in the air-fuel ratio feedback control means, and the air-fuel ratio feedback control means The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 3, wherein the increase correction of the proportional operation amount is stopped when one control cycle is completed.

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