JP3574203B2 - Exhaust gas purification method for internal combustion engine - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an exhaust gas purification method for an internal combustion engine.
[0002]
[Prior art]
NO when the air-fuel ratio of the inflowing exhaust gas is lean_xIs absorbed, and if the air-fuel ratio of the inflowing exhaust gas is made stoichiometric or rich, the absorbed NO_xReleases NO_xThe absorbent is disposed in the exhaust passage of the engine, and the air-fuel ratio of the air-fuel mixture supplied to the engine is normally set to a lean air-fuel ratio._xNO_xAbsorbed by absorbent, NO_xNO absorbed by the absorbent_xAn internal combustion engine has been proposed by the present applicant to make the mixture supplied to the engine rich when the gas is discharged (see PCT International Publication WO 93/07363).
[0003]
[Problems to be solved by the invention]
However, in a stratified combustion internal combustion engine in which the mixture formed in the combustion chamber is stratified to form an ignitable mixture in a limited area of a part of the combustion chamber, such a stratification action is performed. NO when_xNO from absorbent_xIf the supply fuel is simply increased in order to switch the average air-fuel ratio in the combustion chamber from lean to rich in order to discharge the fuel, the mixture formed in a limited area in a part of the combustion chamber becomes rich, resulting in an ignition plug. Therefore, there is a problem that a misfire occurs because the mixture cannot be ignited satisfactorily.
[0004]
Also, as in the above-described internal combustion engine, NO_xNO from absorbent_xIf the air-fuel mixture supplied to the engine is simply made rich in order to release the gas, the output torque of the engine will increase sharply, causing a problem that a shock will occur.
[0005]
[Means for Solving the Problems]
According to the present invention, in order to solve the above-described problems, when the air-fuel ratio of the inflowing exhaust gas is lean, NO_x And when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich, the NO absorbed_x Releases NO_x In the exhaust gas purification method for an internal combustion engine in which an absorbent is disposed in an engine exhaust passage, when the air-fuel ratio of the inflowing exhaust gas is lean, NO_x And when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich, the NO absorbed_x Releases NO_x In the exhaust gas purifying method for an internal combustion engine in which an absorbent is disposed in an engine exhaust passage, when an air-fuel mixture is burned in a lean air-fuel mixture with an average air-fuel ratio in the combustion chamber being in a lean state,At the end of the compression stroke, injects fuel into the cavity formed on the top surface of the piston to form a combustible mixture in the cavityNO generated at this time_x NO_x Absorbed by the absorbent, NO in the lean mixture combustion operation state_x NO from absorbent_x ReleaseWhen the average air-fuel ratio in the combustion chamber is to be made stoichiometric or rich in order to make the combustion chamber perform the fuel supply, fuel is additionally supplied to the combustion chamber at the end of the compression stroke as well as during the intake stroke, and the non-combustible mixture formed by the additionally supplied fuel With the air, the combustion chambers other than inside the cavity are filled, and at this time, when the average air-fuel ratio is made lean and when the stoichiometric air-fuel ratio or rich, the amount of fuel forming the combustible mixture in the cavity becomes substantially the same, and The amount of fuel injected at the end of the compression stroke is reduced by a smaller amount than the amount of additional fuel during the intake stroke so that part of the fuel additionally supplied during the intake stroke forms an incombustible air-fuel mixture.NO when in the lean mixture combustion operation state_x NO from absorbent_x When to releaseWhile preventing the engine output torque from changingThe average air-fuel ratio in the combustion chamber is reduced from lean to the stoichiometric air-fuel ratio or rich and compared to the amount of decrease in the average air-fuel ratio at this time.In the cavityIt is formedFlammableThe air-fuel ratio fluctuation amount of the air-fuel mixture is reduced.
[0028]
[Action]
In the first invention, NO_x NO from absorbent_x Even if the average air-fuel ratio in the combustion chamber is reduced from lean to stoichiometric or rich to releasecavityFormed inFlammableThe air-fuel ratio of the mixture does not change much. Therefore, this mixture does not become rich, and thus misfire does not occur.At this time, since the engine output torque hardly changes, no shock occurs.
[0044]
【Example】
1 to 18 show a first embodiment in which the present invention is applied to a direct injection internal combustion engine. First, referring to FIG. 1 to FIG. A typical operation will be described.
1 to 5, reference numeral 1 denotes an engine main body, 2 denotes a cylinder block, 3 denotes a piston reciprocating in the cylinder block 2, 4 denotes a cylinder head fixed on the cylinder block 2, and 5 denotes a piston 3. A combustion chamber formed between the cylinder heads 4, 6a is a first intake valve, 6b is a second intake valve, 7a is a first intake port, 7b is a second intake port, 8 is a pair of exhaust valves, and 9 is a pair of exhaust valves. Each of the exhaust ports is shown. As shown in FIG. 3, the first intake port 7a comprises a helical intake port, and the second intake port 7b comprises a straight port extending substantially straight. Further, as shown in FIG. 3, an ignition plug 10 is disposed at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve is provided at a peripheral portion of the inner wall surface of the thin cylinder head 4 between the first intake valve 6a and the second intake valve 6b. 11 are arranged. On the other hand, a cavity 3a is formed on the top surface of the piston 3 as shown in FIGS. The cavity 3a has a generally circular contoured shallow plate 12 extending from below the fuel injection valve 11 to below the spark plug 10, and a hemispherical deep plate formed in the center of the shallow plate 12. 13 A substantially spherical concave portion 14 is formed at a connection portion between the shallow plate portion 12 and the deep plate portion 13 below the ignition plug 10.
[0045]
As shown in FIGS. 1 to 3, the first intake port 7a and the second intake port 7b of each cylinder are respectively connected via a first intake passage 15a and a second intake passage 15b formed in each intake branch pipe 15. An intake control valve 17 is connected to the inside of the surge tank 16 and disposed in each second intake passage 15b. These intake control valves 17 are connected via a common shaft 18 to an actuator 19 composed of, for example, a step motor. The step motor 19 is controlled based on an output signal of the electronic control unit 30. The surge tank 16 is connected to an air cleaner 21 via an intake duct 20, and a throttle valve 23 driven by, for example, a step motor 22 is arranged in the intake duct 20. The step motor 22 is also controlled based on the output signal of the electronic control unit 30.
[0046]
On the other hand, the exhaust port 9 of each cylinder is connected to an exhaust manifold 24, and this exhaust manifold 24 is_xIt is connected to a casing 27 containing an absorbent 26. The exhaust manifold 24 and the surge tank 16 are connected to each other via a recirculated exhaust gas (hereinafter, referred to as EGR gas) passage 28. In the EGR gas passage 28, an EGR valve 29 for controlling an EGR gas amount is disposed. The EGR valve 29 is controlled based on an output signal of the electronic control unit 30. When the EGR valve 29 is closed, only air is supplied into the combustion chamber 5 through the intake ports 7a and 7b. When the EGR valve 29 is opened, air and EGR gas flow through the intake ports 7a and 7b. The fuel is supplied into the combustion chamber 5 via the fuel cell.
[0047]
The electronic control unit 30 is composed of a digital computer, and a RAM (random access memory) 32, a ROM (read only memory) 33, a CPU (microprocessor) 34, an input port 35, and a RAM (random access memory) 32 interconnected via a bidirectional bus 31. An output port 36 is provided. A load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the AD converter 37. The top dead center sensor 42 generates an output pulse when the first cylinder reaches the intake top dead center, for example, and the output pulse is input to the input port 35. The crank angle sensor 43 generates an output pulse every time the crankshaft rotates 30 degrees, for example, and the output pulse is input to the input port 35. The CPU 34 calculates the current crank angle from the output pulse of the top dead center sensor 42 and the output pulse of the crank angle sensor 43, and calculates the engine speed from the output pulse of the crank angle sensor 43. On the other hand, the output port 36 is connected to each of the fuel injection valves 11 and each of the step motors 19 and 22 via a corresponding drive circuit 38.
[0048]
In the embodiment shown in FIGS. 1 to 5, the fuel injection valve 11 is constituted by a swirl valve which injects the fuel while giving a swirl force, and the fuel is injected from the fuel injection valve 11 as shown by F in FIGS. It is injected in a conical shape. FIG. 6 shows the amount of fuel injected from the fuel injection valve 11 and the fuel injection timing. FIG. 7 shows the same amount of fuel injection as FIG. 6, but also the opening of the throttle valve 23 and the opening of the EGR valve 29. And the average air-fuel ratio A / F in the combustion chamber 5. In FIGS. 6 and 7, L indicates the amount of depression of the accelerator pedal 40. As can be seen from FIG. 6, the depression amount L of the accelerator pedal 40 is L₁When the engine is under low load operation, the injection amount Q is at the end of the compression stroke.₂Only the fuel injection is performed. On the other hand, when the depression amount L of the accelerator pedal 40 is L₁And L₂During the engine middle load operation during the intake stroke during the intake stroke₁Fuel injection is performed only at the end of the compression stroke.₂Only fuel is injected. That is, during the engine middle load operation, the fuel injection is performed in two stages: the intake stroke and the end of the compression stroke. Further, the depression amount L of the arcel pedal 40 is L₂During high engine load operation, the injection amount Q during the intake stroke₁Only fuel is injected. In FIG. 6, θS1 and θE1 represent the fuel injection Q performed during the intake stroke.₁.Theta.S2 and .theta.E2 represent the fuel injection Q performed at the end of the compression stroke.₂Respectively indicate the injection start timing and the injection completion timing.
[0049]
On the other hand, as shown in FIG.₂When the engine is operating at a low and medium load, the opening of the throttle valve 23 is considerably small. At this time, the opening of the throttle valve 23 decreases as the depression amount L of the accelerator pedal 40 decreases. On the other hand, when the depression amount L of the₂When it becomes larger, the opening degree of the throttle valve 23 increases rapidly and is fully opened. Also, when the amount of depression L of the accelerator pedal 40 is L₂When the engine is operating at a low and medium load, the opening degree of the EGR valve 29 is considerably large, and the depression amount L of the accelerator pedal 40 is L₂When it becomes larger, the opening degree of the EGR valve 29 rapidly decreases and becomes fully open. The average air-fuel ratio in the combustion chamber 5 is in the high load operation region (L> L₂) At some point L₀At the time of switching from lean to rich. That is, the depression amount L of the accelerator pedal 40 is L₀In a smaller range, the average air-fuel ratio A / F becomes lean. At this time, the average air-fuel ratio A / F becomes leaner as the depression amount L of the accelerator pedal 40 decreases. On the other hand, when the depression amount L of the accelerator pedal 40 is L₀When it is larger than the above, the average air-fuel ratio A / F becomes rich.
[0050]
FIG. 8 shows the relationship between the opening degree of the intake control valve 17 and the depression amount L of the accelerator pedal 40. As shown in FIG. 8, the depression amount L of the accelerator pedal 40 is L₁When the engine is under low load operation, the intake control valve 17 is maintained in the fully closed state, and the depression amount L of the accelerator pedal 40 is L₁When it becomes larger, the intake control valve 17 is opened as the depression amount L of the accelerator pedal 40 becomes larger. When the intake control valve 17 is fully closed, the intake air flows into the combustion chamber 5 while swirling through the helical first intake port 7a. A strong swirling flow is generated as shown by. On the other hand, when the intake control valve 17 opens, the intake air also flows into the combustion chamber 5 from the second intake port 7b.
[0051]
Next, the combustion method will be described with reference to FIGS. FIG. 9 shows a combustion method at the time of low load operation of the engine, and FIG. 10 shows a combustion method at the time of medium load operation of the engine.
As shown in FIG. 6, the depression amount L of the accelerator pedal 40 is L₁When the engine load operation is smaller, fuel is injected at the end of the compression stroke. At this time, the injected fuel F collides with the peripheral wall surface of the deep dish portion 13 as shown in FIGS. 9 (A) and 9 (B). Injection amount Q at this time₂6 increases as the depression amount L of the accelerator pedal 40 increases, as shown in FIG. The fuel that has collided with the peripheral wall surface of the deep dish portion 13 is diffused while being vaporized by the swirling flow S, and as a result, as shown in FIG. 9C, in the concave portion 14 and the deep dish portion 13, that is, in the cavity 3a. A combustible mixture G is formed. At this time, the inside of the combustion chamber 5 other than the concave portion 14 and the deep dish portion 13 is filled with air and EGR gas. Next, the mixture G is ignited by the spark plug 10.
[0052]
On the other hand, in FIG. 6, the depression amount L of the accelerator pedal 40 is L₁And L₂During the engine middle load operation during the intake stroke, the first fuel injection Q₁Is performed, and then at the end of the compression stroke, the second fuel injection Q₂Is performed. That is, first, as shown in FIG. 10A, fuel injection F is performed toward the inside of the cavity 3a at the beginning of the intake stroke, and a lean mixture is formed in the entire combustion chamber 5 by the injected fuel. Next, as shown in FIG. 10B, fuel injection F is performed toward the inside of the cavity 3a at the end of the compression stroke, and as shown in FIG. A combustible air-fuel mixture G serving as a kind of fire is formed in the air-fuel mixture. The combustible air-fuel mixture G is ignited by the ignition plug 10, and the ignition flame causes the entire lean air-fuel mixture in the combustion chamber 5 to burn. In this case, since the fuel injected at the end of the compression stroke is sufficient to produce a spark, as shown in FIG. 6, the fuel injection amount Q at the end of the compression stroke at the engine middle load operation regardless of the depression amount L of the accelerator pedal 40₂Is kept constant. On the other hand, the fuel injection amount Q at the beginning of the intake stroke₁Increases as the depression amount L of the accelerator pedal 40 increases.
[0053]
In FIG. 6, the depression amount L of the accelerator pedal 40 is L₂During a higher engine load operation, fuel is injected only once at the beginning of the intake stroke, thereby forming a homogeneous mixture in the combustion chamber 15. At this time, the fuel injection amount at the beginning of the intake stroke increases as the depression amount L of the accelerator pedal 40 increases as shown in FIG.
The above is the basic combustion method of the direct injection internal combustion engine shown in FIG. Next, a method of purifying exhaust gas suitable for the in-cylinder injection internal combustion engine will be described.
[0054]
First, referring to FIG. 11, FIG. 11 schematically shows the relationship between the concentration of typical components in the exhaust gas discharged from the combustion chamber 5 and the average air-fuel ratio A / F in the combustion chamber 5. I have. As can be seen from FIG. 11, the concentration of unburned HC and CO in the exhaust gas discharged from the combustion chamber 5 increases as the average air-fuel ratio A / F in the combustion chamber 5 becomes rich, and is discharged from the combustion chamber 5. Oxygen O in exhaust gas₂Increases as the average air-fuel ratio A / F in the combustion chamber 5 becomes leaner.
[0055]
On the other hand, the NO stored in the casing 27 shown in FIG._xThe absorbent 26 uses, for example, alumina as a carrier. On the carrier, for example, potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, barium Ba, an alkaline earth such as calcium Ca, lanthanum La, and yttrium Y are used. At least one selected from such rare earths and a noble metal such as platinum Pt are supported. Engine intake passage, combustion chamber 5 and NO_xThe ratio of the total amount of air supplied to the exhaust passage upstream of the absorbent 26 to the total amount of fuel (hydrocarbon) is set to NO._xThis NO, which is called the air-fuel ratio of the exhaust gas flowing into the absorbent 26,_xThe absorbent 26 is NO when the air-fuel ratio of the inflowing exhaust gas is lean._xNO when the oxygen concentration in the inflowing exhaust gas decreases_xReleases NO_xPerforms the absorption and release action. Note that NO_xWhen no fuel (hydrocarbon) or air is supplied into the exhaust passage upstream of the absorbent 26, the air-fuel ratio of the inflowing exhaust gas matches the average air-fuel ratio A / F in the combustion chamber 5, and therefore NO in this case._xThe absorbent 26 is NO when the average air-fuel ratio A / F in the combustion chamber 5 is lean._xIs absorbed, and when the oxygen concentration in the gas in the combustion chamber 5 decreases, the absorbed NO_xWill be released.
[0056]
NO above_xIf the absorbent 26 is arranged in the engine exhaust passage, this NO_xAbsorbent 26 is actually NO_xHowever, there is a part where the detailed mechanism of the absorption / release action is not clear. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking platinum Pt and barium Ba supported on a carrier as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
[0057]
That is, when the average air-fuel ratio A / F in the combustion chamber 5 is lean, and therefore, when the inflowing exhaust gas is lean, the oxygen concentration in the inflowing exhaust gas increases. At this time, as shown in FIG. These oxygen O₂Is O₂ ⁻Or O^2-On the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas becomes O 2 on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). NO generated next₂Is absorbed in the absorbent while being oxidized on the platinum Pt and combined with barium oxide BaO, as shown in FIG.₃ ⁻Diffuses into the absorbent in the form of NO in this way_xIs NO_xIt is absorbed in the absorbent 26.
[0058]
NO on the surface of platinum Pt as long as the oxygen concentration in the inflowing exhaust gas is high₂Is generated, and the NO_xNO unless absorption capacity is saturated₂Is absorbed in the absorbent and nitrate ion NO₃ ⁻Is generated. On the other hand, the oxygen concentration in the inflowing exhaust gas decreases and NO₂The reaction proceeds in the reverse direction (NO₃ ⁻→ NO₂) And thus the nitrate ions NO in the absorbent₃ ⁻Is NO₂Released from the absorbent in the form of That is, when the oxygen concentration in the inflowing exhaust gas decreases, NO_xNO from absorbent 26_xWill be released. As can be seen from FIG. 11, when the lean degree of the inflowing exhaust gas decreases, the oxygen concentration in the inflowing exhaust gas decreases, and therefore, when the leanness of the inflowing exhaust gas decreases, the air-fuel ratio of the inflowing exhaust gas becomes lean. NO_xNO from absorbent 26_xWill be released.
[0059]
On the other hand, at this time, when the average air-fuel ratio A / F in the combustion chamber 3 is made rich and the air-fuel ratio of the inflowing exhaust gas becomes rich, a large amount of unburned HC and CO is discharged from the engine as shown in FIG. These unburned HC and CO are oxygen O on platinum Pt.₂ ⁻Or O^2-And oxidize. Further, when the air-fuel ratio of the inflowing exhaust gas becomes rich, the oxygen concentration in the inflowing exhaust gas extremely decreases.₂Is released and this NO₂Is reduced by reacting with unburned HC and CO as shown in FIG. Thus, NO on the surface of platinum Pt₂When no longer exists, NO is changed from one absorbent to the next₂Is released. Therefore, if the air-fuel ratio of the inflowing exhaust gas is made rich, NO_xNO from absorbent 26_xWill be released.
[0060]
That is, when the air-fuel ratio of the inflowing exhaust gas is made rich, first, the unburned HC and CO₂ ⁻Or O^2-And immediately oxidized, then O on platinum Pt₂ ⁻Or O^2-If unburned HC and CO still remain even after the fuel is consumed, NO released from the absorbent by the unburned HC and CO_xAnd NO emitted from the engine_xIs reduced. Therefore, if the air-fuel ratio of the inflowing exhaust gas is made rich, NO_xNO absorbed by the absorbent 26_xIs released, and the released NO_xNO in the atmosphere to be reduced_xCan be prevented from being discharged. NO_xSince the absorbent 26 has the function of a reduction catalyst, even if the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio, NO_xNO released from absorbent 26_xIs reduced. However, when the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio, NO_xNO from absorbent 26_xIs released only slowly_xTotal NO absorbed in absorbent 26_xIt takes a slightly longer time to release.
[0061]
As described above, when the average air-fuel ratio A / F in the combustion chamber 5 is lean, NO_xIs NO_xIt is absorbed by the absorbent 26. However, NO_xNO of absorbent 26_xAbsorption capacity is limited, NO_xNO of absorbent 26_xNO if absorption capacity is saturated_xAbsorbent 26 is no longer NO_xCan not be absorbed. Therefore NO_xNO of absorbent 26_xNO before absorption capacity is saturated_xNO from absorbent 26_xMust be released, which requires NO_xHow much NO in the absorbent 26_xNeeds to be estimated. So next, this NO_xA method for estimating the amount of absorption will be described.
[0062]
When the average air-fuel ratio A / F in the combustion chamber 5 is lean, the NO discharged from the engine per unit time increases as the engine load increases._xNO per unit time due to increased amount_xNO absorbed by the absorbent 26_xAs the amount increases and the engine speed increases, the NO discharged from the engine per unit time_xNO per unit time due to increased amount_xNO absorbed by the absorbent 26_xIncrease. Therefore, NO per unit time_xNO absorbed by the absorbent 26_xThe quantity is a function of engine load and engine speed. In this case, the engine load can be represented by the depression amount L of the accelerator pedal 40, so that_xNO absorbed by the absorbent 26_xThe amount is a function of the depression amount L of the accelerator pedal 40 and the engine speed N. Therefore, in the embodiment shown in FIG._xNO absorbed by the absorbent 26_xThe amount A is obtained by an experiment in advance as a function of the depression amount L of the accelerator pedal 40 and the engine speed N._xThe quantity A is stored in advance in the ROM 33 as a function of L and N in the form of a map shown in FIG.
[0063]
On the other hand, if the average air-fuel ratio A / F in the combustion chamber 5 becomes stoichiometric or rich, NO_xNO from absorbent 26_xIs released, but NO at this time_xThe amount of emission is mainly affected by the amount of exhaust gas and the average air-fuel ratio. That is, as the exhaust gas amount increases, the NO._xNO released from absorbent 26_xAs the amount increases and the average air-fuel ratio becomes rich,_xNO released from absorbent 26_xThe amount increases. In this case, the exhaust gas amount, that is, the intake air amount, is a function of the depression amount L of the accelerator pedal 40 and the engine speed N, and the average air-fuel ratio A / F is also a function of the depression amount L of the accelerator pedal 40 and the function of the engine speed N. Become. Therefore, NO per unit time_xNO released from absorbent 26_xThe amount D is a function of the depression amount L of the accelerator pedal 40 and the engine speed N._xThe quantity D is stored in the ROM 33 in advance as a function of L and N in the form of a map shown in FIG.
[0064]
As described above, when the average air-fuel ratio A / F in the combustion chamber 5 is lean, NO per unit time_xWhen the absorption amount is represented by A and the average air-fuel ratio A / F in the combustion chamber 5 is the stoichiometric air-fuel ratio or rich, the NO per unit time_xNO since the release amount is represented by D_xNO estimated to be absorbed by the absorbent 26_xThe quantity ΣNOX can be calculated using the following equation.
[0065]
ΣNOX = ΣNOX + AD
FIG. 13 shows this NO_xThe relationship between the amount ΣNOX and the average air-fuel ratio A / F in the combustion chamber 5 is shown. As can be seen from FIG.₀Is lower than the average air-fuel ratio A / F in the combustion chamber 5 is lean._xIs NO_xAs shown in FIG. 13, NO is absorbed by the absorbent 26._xThe amount ΣNOX increases. On the other hand, as shown in FIG.₀If the pressure becomes higher than this, the average air-fuel ratio A / F in the combustion chamber 5 becomes rich._xNO from absorbent 26_xIs released. Therefore, as shown by X in FIG.₀NO when the average air-fuel ratio A / F becomes rich_xThe quantity ΣNOX decreases.
[0066]
On the other hand, the average air-fuel ratio A / F is continuously made lean and NO_xWhen the amount ΣNOX exceeds the allowable value MAX, the average air-fuel ratio A / F in the combustion chamber 5 is forcibly made rich as shown by Y in FIG. NO if the average air-fuel ratio A / F is made rich_xNO from the absorbent 26 rapidly_xIs released, and thus NO as shown in FIG._xThe quantity ΣNOX decreases rapidly. Then NO_xWhen the amount ΣNOX decreases to the lower limit value MIN, the average air-fuel ratio A / F is returned from rich to lean.
[0067]
By the way, as shown in FIG. 9, for example, an air-fuel mixture formed in the combustion chamber 5 is stratified to form an ignitable air-fuel mixture in a partly limited area in the combustion chamber 5, that is, in the cavity 3a. When such a stratification action is performed, NO_xNO from absorbent 26_xWhen the injection amount in the compression stroke is simply increased in order to switch the average air-fuel ratio in the combustion chamber 5 from lean to rich in order to discharge the gas, the air-fuel ratio is formed in a limited area in the combustion chamber 5, that is, in the cavity 3a. The mixture becomes too rich. As a result, there arises a problem that the air-fuel mixture in the cavity 3a cannot be properly ignited by the ignition plug 10 and is misfired.
[0068]
In general, when the average air-fuel ratio A / F in the combustion chamber 5 is switched from lean to rich, a shock occurs because the engine output torque sharply increases. Of course, such shocks must be prevented from occurring in order to cause discomfort to the driver. Therefore, in the embodiment according to the present invention, the combustible air-fuel mixture formed in the cavity 3a is prevented from becoming excessively rich, and the average air-fuel ratio A / F is switched from lean to rich so that the above-mentioned shock does not occur. Next, this will be described with reference to FIGS. 15 and 16.
[0069]
In FIG. 15, broken lines indicate the fuel injection amount Q, the opening of the throttle valve 23, and the average air-fuel ratio A / F in the combustion chamber 5 during the normal operation shown in FIG. First, the engine load L is L₁NO at low engine low load operation_xNO from absorbent 26_xA case in which the average air-fuel ratio A / F is switched from lean to rich in order to discharge the fuel will be described. At the time of engine low load operation, the engine load L is set to a predetermined lower limit load L._minHereinafter, even if ΔNOX> MAX (FIG. 13), the switching operation of the average air-fuel ratio A / F from lean to rich is not performed, and the engine load L is reduced to the lower limit load L._minAt this time, if ΣNOX> MAX, the average air-fuel ratio A / F is switched from lean to rich. That is, when the engine load L is L_min<L <L₁If ΣNOX> MAX at this time, NO as shown in FIG._xThe release flag is set, and the average air-fuel ratio A / F in the combustion chamber 5 is switched from lean to rich. Referring to FIG. 15, at this time, the average air-fuel ratio A / F is switched from lean indicated by a broken line to rich indicated by a solid line.
[0070]
At this time, the switching operation of the average air-fuel ratio A / F from lean to rich is performed as shown in FIGS.₂In addition to the intake stroke injection Q₁And the compression stroke injection amount Q as shown in FIG.₂Is reduced as compared with the normal operation indicated by the broken line, and the compression stroke injection amount Q₂And intake stroke injection quantity Q₁Is increased as compared with the injection amount during normal operation indicated by the broken line. Therefore, in this case, the intake stroke injection amount Q₁Is divided into an injection amount portion Qa and an injection amount portion Qb by a broken line, and the compression stroke injection amount Q₂And the injection amount Qa are equal to the injection amount Q in the normal operation indicated by the broken line, and the injection amount Qb is an increase in the supplied fuel.
[0071]
By the way, in this case, the compression stroke injection Q₂Is formed in the cavity 3a by the fuel of the injection amount Qa and the fuel of the injection amount portion Qa, and the air-fuel ratio of the air-fuel mixture formed in the cavity 3a if the fuel of the injection amount portion Qb is dispersed in a region other than the cavity 3a. Is the same as during normal operation. That is, even if the total injection amount is increased, the air-fuel mixture formed in the cavity 3a does not become excessively rich, and thus the air-fuel mixture formed in the cavity 3a without misfire is generated by the ignition plug 10. It will be ignited well.
[0072]
On the other hand, in this case, the compression stroke injection Q₂If the fuel in the injection portion Qa is burned and the fuel in the injection amount portion Qb is not burned, the amount of fuel to be burned becomes the same as the fuel amount during normal operation indicated by the broken line. The output torque does not change, and the fuel in the injection amount portion Qb is used merely for switching the average air-fuel ratio A / F from lean to rich. Therefore, in the embodiment according to the present invention, the compression stroke injection Q₂To form a combustible air-fuel mixture to be burned by the fuel of the injection amount portion Qa and the fuel of the injection amount portion Qb, which is an increase of the supplied fuel, thereby preventing the occurrence of misfire. The average air-fuel ratio A / F is switched from lean to rich while preventing the output torque of the engine from changing._xNO from absorbent 26_xIs to be released.
[0073]
That is, the intake stroke injection Q₁Is performed, the injected fuel is dispersed throughout the combustion chamber 5, but the intake stroke injection amount Q₁Is an amount capable of forming a lean mixture in which the flame cannot propagate. However, even with such a lean mixture, the compression stroke injection Q₂If it mixes into the combustible mixture G (see FIG. 9C) formed by the above, it is burned. In this case, the compression stroke injection Q₂The flammable mixture G formed by the above formula occupies almost the entirety of the cavity 3a, so that the combustion of the injection amount portion Qa occupies almost the entirety of the cavity 3a.₁Is determined, the amount of fuel to be burned is the same as during normal operation. Therefore, even if the average air-fuel ratio A / F is switched from lean to rich, no misfire occurs and the output torque of the engine does not change. become.
[0074]
Next, this will be described using concrete numerical values (not actual numerical values). For example, the average air-fuel ratio during normal operation is lean, the air amount is 17 (g), and the fuel amount is 17 (g). 1 (g). When the average air-fuel ratio A / F is switched from lean to rich, 55% of the combustible mixture in the cavity 3a is subjected to the compression stroke injection Q₂, And the remaining 45% is taken as the intake stroke injection Q₁, The compression stroke injection amount Q₂Becomes 0.55 (g), and the intake stroke injection amount Q₁Is 0.45 (g). On the other hand, if the volume of the cavity 3a is 65% of the total volume of the combustion chamber 5, the total intake stroke injection amount (Qa + Qb) is 0.45 (g) /0.65≒0.7 (g). Therefore, the intake stroke injection Q₁The air-fuel ratio of the lean mixture formed by the formula (17) is 17 (g) /0.7 (g) ≒ 24.3, which is an incombustible mixture. On the other hand, the average air-fuel ratio A / F in the combustion chamber 5 is 17 (g) / [0.55 (g) +0.7 (g)] = 13.6, which is rich. Also, at this time, the fuel contained in the combustible mixture formed in the cavity 3a is 1 (g), which is the same as in the normal operation.
[0075]
Thus, the intake stroke injection amount Q₁And compression stroke injection amount Q₂Is appropriately set, the average air-fuel ratio A / F can be switched from lean to rich without changing the air-fuel ratio of the air-fuel mixture formed in the cavity 3a and without changing the amount of combusted fuel. The intake stroke injection amount Q shown in FIG.₁(Qa + Qb) and compression stroke injection amount Q₂Is stored in the ROM 33 in advance in the form of a function of the depression amount L of the accelerator pedal 40 and the engine speed N.
[0076]
Next, when the engine load L is L₁L greater than₀NO when lower than_xNO from absorbent 26_xA case in which the average air-fuel ratio A / F is switched from lean to rich in order to discharge the fuel will be described. At this time, the throttle valve 23 is closed by a predetermined opening as shown by the solid line in FIG. When the throttle valve 23 is closed, the amount of air supplied into the combustion chamber 5 decreases, so that the average air-fuel ratio A / F in the combustion chamber 5 decreases. At this time, the throttle valve 23 is closed so that the average air-fuel ratio A / F becomes a predetermined rich air-fuel ratio indicated by a solid line in FIG. 15, and the closing amount of the throttle 23 is determined by the depression amount L of the accelerator pedal 40. And in the form of a function of the engine speed N in the ROM 33 in advance.
[0077]
When the throttle valve 23 is closed, the pumping loss increases, so that the output torque of the engine decreases. Therefore, in the embodiment according to the present invention, the intake stroke injection amount Q is set so that the output torque of the engine does not decrease at this time.₁Is increased by Qc (only the portion above the broken line in FIG. 15). Note that this intake stroke injection Q₁Is stored in the ROM 33 in advance in the form of a function of the depression amount L of the accelerator pedal 40 and the engine speed N. At this time, the compression stroke injection amount Q₂Is the optimal fuel quantity for forming a spark, so the compression stroke injection quantity Q₂Stroke injection quantity Q without increasing₁To increase the amount.
[0078]
Next, a fuel injection control routine will be described with reference to FIGS. This routine is executed by interruption every predetermined time.
Referring to FIGS. 17 and 18, first, in step 100, NO_xNO estimated to be absorbed by the absorbent 26_xIt is determined whether the amount ΣNOX is larger than the allowable value MAX. When ΣNOX ≦ MAX, the routine proceeds to step 101, where NO_xIt is determined whether the release flag is set. Normally NO_xSince the release flag has been reset, the routine proceeds to step 102. In step 102, based on the depression amount L of the accelerator pedal 40 and the engine speed N, the intake stroke injection amount Q is obtained from the relationship shown in FIG.₁And compression stroke injection amount Q₂Next, at step 103, the injection timing is calculated from the relationship shown in FIG. 6 stored in the ROM 33 in advance based on the depression amount L of the accelerator pedal 40 and the engine speed N. Next, at step 104, the accelerator pedal 40 is calculated. The opening degree of the throttle valve 23 is calculated from the relationship shown in FIG. 7 stored in the ROM 33 in advance based on the depression amount L and the engine speed N of the engine.
[0079]
Next, at step 105, the opening degree of the EGR valve 29 is calculated from the relationship shown in FIG. 7 previously stored in the ROM 33 based on the depression amount L of the accelerator pedal 40 and the engine speed N, and then at step 106 The degree of opening of the intake control valve 17 is calculated from the relationship shown in FIG. Next, at step 107, the depression amount L of the accelerator pedal 40 becomes L₀It is determined whether it is lower than (FIG. 7). L <L₀In the case of, the routine proceeds to step 108, where NO is determined from the map shown in FIG._xThe release amount A is calculated. Next, at step 109, NO_xThe release amount D is set to zero, and then the routine proceeds to step 112. On the other hand, in step 107, L ≧ L₀When it is determined that the answer is NO, the routine proceeds to step 110, where NO is determined from the map shown in FIG._xThe release amount D is calculated. Next, at step 111, NO_xThe absorption amount A is set to zero, and then the routine proceeds to step 112.
[0080]
NO at step 112_xNO estimated to be absorbed by the absorbent 26_xThe quantity ΣNOX (= ΣNOX + AD) is calculated. Next, at step 113, it is determined whether or not ΣNOX has become negative. When ΣNOX <0, the routine proceeds to step 114, where ΣNOX is made zero. Next, at step 115, it is determined whether or not ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 116, where NO is determined._xThe release flag is reset.
[0081]
On the other hand, in step 100 ΣNOX>When it is determined that the maximum has been reached, the process proceeds to step 117 and NO_x  The release flag is set. NO_x  When the release flag is set, the routine proceeds from step 101 to step 118, where the engine load L is reduced to the lower limit load L_min  Is determined. L <L_min  If so, the process proceeds to step 102. Therefore, at this time, even if ΔNOX> MAX, the average air-fuel ratio A / F in the combustion chamber 5 is maintained lean.
[0082]
On the other hand, L ≧ L_minIn step 119, the routine proceeds to step 119, and based on the depression amount L of the accelerator pedal 40 and the engine speed N, the intake stroke injection amount Q is obtained from the relationship shown in FIG.₁And compression stroke injection amount Q₂Then, at step 120, the injection timing is calculated from the relationship stored in the ROM 33 in advance based on the depression amount L of the accelerator pedal 40 and the engine speed N. Next, at step 121, the depression amount L of the accelerator pedal 40 is calculated. The opening of the throttle valve 23 is calculated from the relationship shown in FIG. 15 stored in advance in the ROM 33 based on the engine speed N.
[0083]
Next, at step 122, the opening degree of the EGR valve 29 is calculated from the relationship previously stored in the ROM 33 based on the depression amount L of the accelerator pedal 40 and the engine speed N. Next, at step 123, the depression amount L of the accelerator pedal 40 is calculated. The opening of the intake control valve 17 is calculated from the relationship shown in FIG. At this time, the average air-fuel ratio in the combustion chamber 5 is made rich and NO_xNO from absorbent 26_xIs released.
[0084]
As described above, the depression amount L of the accelerator pedal 40 is L₁During low engine low load operation, fuel is injected only at the end of the compression stroke. At this time, an air-fuel mixture is formed only in the cavity 3a, and a region other than the cavity 3a is substantially filled with air and EGR gas, so that a stratified state having a very high degree of stratification is obtained.
On the other hand, when the depression amount L of the accelerator pedal 40 is L₁And L₂During the engine middle load operation, a lean mixture is formed entirely in the combustion chamber 5 by the intake stroke injection, and a richer mixture than the lean mixture is formed in the cavity 3a by the compression stroke injection. Therefore, at this time, a weak stratification state is obtained in which the degree of stratification is lower than that in the strong stratification state at the time of engine low load operation.
[0085]
Also, when the amount of depression L of the accelerator pedal 40 is L₂When the engine is running at a higher engine load, only the intake stroke injection is performed, so that a uniform mixture is formed in the combustion chamber 5 at this time.
By the way, in the embodiments described so far, at the time of engine low load operation, that is, in the case of strong stratification, NO_xNO from absorbent 26_xThe average air-fuel ratio A / F is switched from lean to rich without causing misfire and maintaining a strong stratified state so that the output torque does not fluctuate.
[0086]
In contrast, in the embodiment described below, NO_xNO from absorbent 26_xWhen it is necessary to release the fuel, the average air-fuel ratio A / F is theoretically changed by switching from the strong stratified state to the weak stratified state or the homogeneous mixture state, and increasing the intake stroke injection amount in the weak stratified state or the homogeneous mixture state. NO with air / fuel ratio or rich_xNO from absorbent 26_xIs to be released. If the average air-fuel ratio A / F is increased to the stoichiometric air-fuel ratio or rich by increasing the intake stroke injection amount in this way, the air-fuel ratio of the air-fuel mixture formed in the cavity 3a does not change much as compared with the time of strong stratification. Thus, the occurrence of misfire can be prevented.
[0087]
In the embodiment described below, NO_xNO from absorbent 26_xWhen the average air-fuel ratio A / F is set to the stoichiometric air-fuel ratio or rich so as to release the fuel, all the injected fuel is burned in the combustion chamber 5, and therefore NO_xNO from absorbent 26_xWhen the average air-fuel ratio A / F is set to the stoichiometric air-fuel ratio or rich so as to discharge the engine, the output torque of the engine increases. This increase in the output torque is suppressed by reducing the amount of intake air supplied into the combustion chamber 5, and if the output torque still increases, the output torque is prevented from increasing by, for example, retarding the ignition timing. Is done.
[0088]
Next, a basic routine for controlling fuel injection will be described first with reference to FIGS.
FIG. 19 is NO_xThis shows a routine for controlling the release flag, and this routine is executed by interruption every predetermined time. Referring to FIG. 19, first, in step 120, NO_xIt is determined whether the amount ΣNOX has exceeded the allowable value MAX shown in FIG.と き に は When NOX> MAX, proceed to step 121 and NO_xThe release flag is set.
[0089]
FIG. 20 shows a routine for performing the injection control, and this routine is executed, for example, by interruption every predetermined time.
Referring to FIG. 20, first, in step 130, NO_xIt is determined whether the release flag is set. NO_xIf the release flag has not been set, the routine proceeds to step 131, where the intake stroke injection amount Q is stored based on the depression amount L of the accelerator pedal 40 and the engine speed N from the relationship shown in FIG.₁And compression stroke injection amount Q₂Is calculated. Next, at step 132, the injection timing is calculated from the relationship shown in FIG. 6 stored in the ROM 33 in advance based on the depression amount L of the accelerator pedal 40 and the engine speed N. Next, at step 133, the injection amount L of the accelerator pedal 40 is calculated. The opening degree of the throttle valve 23 is calculated from the relationship shown in FIG. 7 stored in the ROM 33 in advance based on the engine speed N and the engine speed N. Next, at step 134, the throttle valve 23 is depressed based on the depression amount L of the accelerator pedal 40 and the engine speed N. Then, the opening degree of the EGR valve 29 is calculated from the relation stored in the ROM 33 in advance, and then in step 135, the intake air is calculated from the relation shown in FIG. The opening of the control valve 17 is calculated.
[0090]
Next, at step 136, the depression amount L of the accelerator pedal 40 becomes L₀It is determined whether it is lower than (FIG. 7). L <L₀In the case of, the routine proceeds to step 137, where NO from the map shown in FIG._xThe release amount A is calculated. Next, at step 138, NO_xThe release amount D is set to zero, and then the routine proceeds to step 141. On the other hand, in step 136, L ≧ L₀If it is determined that the answer is NO, the routine proceeds to step 139, where NO is determined from the map shown in FIG._xThe release amount D is calculated. Next, at step 140, NO_xThe absorption amount A is set to zero, and then the routine proceeds to step 141. NO at step 141_xNO estimated to be absorbed by the absorbent 26_xThe quantity ΣNOX (= ΣNOX + AD) is calculated. Next, at step 142, it is determined whether or not ΣNOX has become negative. When ΣNOX <0, the routine proceeds to step 143, where ΣNOX is made zero.
[0091]
On the other hand, in step 130, NO_x  If it is determined that the release flag has been set, the routine proceeds to step 144, where the depression amount L of the accelerator pedal 40 is₁  It is determined whether or not it is smaller than. L <L₁  In step 146, the process proceeds to step 146, where a rich process I for making the average air-fuel ratio A / F rich is performed. On the other hand, L ≧ L₁  In step 145, the routine proceeds to step 145, where the depression amount L of the accelerator pedal 40 is L₂  It is determined whether or not it is smaller than. L <L₂  In step 147, the routine proceeds to step 147, where a rich process II for enriching the average air-fuel ratio A / F is performed, and L ≧ L₂  In step 148, the routine proceeds to step 148, where a rich process III for making the average air-fuel ratio A / F rich is performed.
[0092]
That is, the rich process I is performed during the low engine load operation, that is, when the engine_xNO from absorbent 26_xThe rich process II is performed during the engine middle load operation, that is, in the weakly stratified state._xNO from absorbent 26_xThe rich process III is performed when the engine is under a high load operation, that is, when the mixture is in a uniform state._xNO from absorbent 26_xFIG. 7 shows a rich process for releasing. Then, these rich processes I, II, and III will be described in order.
[0093]
FIG. 21 shows a time chart of one embodiment of the rich processing I. NO as shown in FIG._xIn the engine low-load operation state before the release flag is set, that is, in the strong stratification operation state, the intake stroke injection is not performed, only the compression stroke injection is performed, and the average air-fuel ratio A / F in the combustion chamber 5 becomes It is lean. At this time, the throttle valve 23 and the EGR valve 29 are opened.
[0094]
Then NO_xNO from absorbent 26_xNO to release_xWhen the release flag is set, the EGR valve 29 is fully closed. At this time, the opening degree of the throttle valve 23 is also determined so that the average air-fuel ratio A / F in the combustion chamber 5 does not become extremely lean. It is closed until. When the throttle valve 23 is closed to the set opening, the compression stroke injection amount is slightly increased so that the output torque of the engine does not decrease.
[0095]
Then NO_xT after the release flag is set₁After a lapse of time, the compression stroke injection is stopped, and the intake stroke injection is started. That is, the state is switched from the strong stratification state to the uniform mixture state. At this time, the injection amount does not change, and therefore, the average air-fuel ratio A / F in the combustion chamber 5 does not change. At this time, the fuel injection amount is small, and when such a small amount of fuel is burned in a homogeneous mixture state, the risk of misfiring increases if a large amount of EGR gas is supplied. Therefore, in this embodiment, as shown in FIG. 21, the EGR valve 29 is fully closed before shifting to the homogeneous mixture combustion. In this case, the EGR valve 29 does not always need to be fully closed, and it may be sufficient to reduce the opening of the EGR valve 29 to some extent.
[0096]
Then NO_xT after the release flag is set₂After a lapse of time, the intake stroke injection amount is increased to make the average air-fuel ratio A / F in the combustion chamber 5 rich, and the throttle valve 23 is further closed to a set opening determined by the operation state of the engine. At this time, the throttle valve 23 is closed to reduce the amount of intake air supplied into the combustion chamber 5, to make the average air-fuel ratio A / F rich with as little fuel as possible, and to reduce the average air-fuel ratio A / F. This is to prevent the output torque of the engine from increasing as much as possible when enrichment is made. At this time, if the increase in the output torque of the engine increases and a shock occurs, it is necessary to take measures such as enriching the average air-fuel ratio A / F and simultaneously delaying the ignition timing.
[0097]
NO if the average air-fuel ratio A / F is made rich_xNO from absorbent 26_xThe release action is started. Then NO_xNO from absorbent 26_xWhen the release action of is completed, the state returns to the strong stratification state again in the reverse order. That is, NO_xIs completed, the intake stroke injection amount is reduced and the throttle valve 23 is opened. Then NO_xT after the release action of₁After a lapse of time, the intake stroke injection is stopped, and the compression stroke injection is started._xT after the release action of₂After a lapse of time, the throttle valve 23 and the EGR valve 29 are opened and NO_xThe release flag is reset.
[0098]
FIG. 22 shows NO shown in FIG._x7 shows a routine of a rich process I for executing release control. Referring to FIG. 22, first, in step 150, NO_xIt is determined whether or not the release completion flag indicating that the release has been completed is set. Immediately after the start of the rich process I, since the release completion flag is not set, the process proceeds to step 151, where a pre-process until the average air-fuel ratio A / F is made rich is performed. In the embodiment shown in FIG._xWhen the release flag is set, that is, when the rich process I is started, the process of closing the throttle valve 23 and the EGR valve 29, and after the rich process I is started, t₁After the lapse of time, a process for switching from the compression stroke injection to the intake stroke injection, and t after the rich process I is started.₂The process comprises closing the throttle valve 23 after a lapse of time.
[0099]
Next, at step 152, it is determined whether or not this preprocessing has been completed. When the pre-processing is completed, the routine proceeds to step 153, where rich processing for making the average air-fuel ratio A / F rich is performed. In this embodiment, the rich process is performed by increasing the intake stroke injection amount. Next, at step 154, NO_x  NO during release action_x  The release amount D 'is calculated. This NO_x  The release amount D 'is stored in advance in the ROM 33 in the form of a map as shown in FIG. 23 as a function of the depression amount L of the accelerator pedal 40 and the engine speed N. Next, at step 155, NO_x  Quantity ΣNOX to NO_x  The release amount D 'is subtracted, and then, in step 156, NO_x  It is determined whether or not the amount ＸNOX has become smaller than the lower limit value MIN..と き に は NO when NOX <MIN_x  It is determined that the release operation has been completed, and the routine proceeds to step 157, where the release completion flag is set. Next, the routine proceeds to step 158. Once the release completion flag is set, the process jumps from step 150 to step 158.
[0100]
NO at step 158_xThe post-treatment is performed from the completion of the release operation of the carbon dioxide to the return to the strong stratified state. In the embodiment shown in FIG._xA process of reducing the intake stroke injection amount and opening the throttle valve 23 when the release operation of_xAfter the release action of₁Processing for switching from the intake stroke injection to the compression stroke injection after a lapse of time;_xAfter the release action is completed₂The processing comprises opening the throttle valve 23 and the EGR valve 29 after a lapse of time. In step 159, it is determined whether or not this post-processing has been completed._xThe release flag and the release completion flag are reset.
[0101]
FIG. 24 shows another embodiment of the rich processing I performed in the strong stratification state. In this embodiment, NO_xWhen the release flag is set, the throttle valve 23 is slightly closed, and the EGR valve 29 is closed by about half. Then NO_xT after the release flag is set₁After a lapse of time, the compression stroke injection amount is decreased, and the intake stroke injection is started. That is, at this time, two injections of the intake stroke injection and the compression stroke injection are performed, and therefore, a weak stratification state is obtained. Then NO_xT after the release flag is set₂After a lapse of time, the compression stroke injection is stopped, and only the intake stroke injection is performed. At this time, the throttle valve 23 is slightly closed again.
[0102]
Then NO_xT after the release flag is set₃After a lapse of time, the EGR valve 29 is fully closed and the throttle valve 23 is further closed slightly. Further, at this time, the intake stroke injection amount is increased, and the average air-fuel ratio A / F is made rich._xNO from absorbent 26_xThe release action is started.
On the other hand, NO_xUpon completion of the release action, the composition returns to a strong stratified state in the reverse order. That is, NO_xIs completed, the intake stroke injection amount is reduced, and the throttle valve 23 and the EGR valve 29 are opened. Then NO_xT after the release action of₁After a lapse of time, the intake stroke injection amount is reduced, the compression stroke injection is started, and the stratified state is established. At this time, the throttle valve 23 is further opened. Then NO_xT after the release action of₂After a lapse of time, the intake stroke injection is stopped, a strong stratification state is established, and then NO_xT after the release action of₃After a lapse of time, the throttle valve 23 and the EGR valve 29 are further opened and NO_xThe release flag is reset.
[0103]
In this embodiment, NO_xWhen the release action of NO is started, the state is changed from a strong stratified state to a homogeneous stratified state through a weak stratified state, and NO_xIs completed, the mixture is changed from a homogeneous mixture state to a weak stratification state to a strong stratification state. As described above, the mode of combustion gradually changes by interposing the weak stratification state when switching between the strong stratification state and the homogeneous mixture state, thereby preventing misfire from occurring at the time of switching. .
[0104]
FIG. 25 shows the NO shown in FIG._x7 shows a routine of a rich process I for executing release control. Referring to FIG. 25, first, at step 170, it is determined whether or not the release completion flag is set. If the release completion flag has not been set, the process proceeds to step 171. If the release completion flag has been set, the process jumps to step 178. NO in step 171_xPreprocessing is performed from when the release flag is set to when the average air-fuel ratio A / F is made rich. Next, at step 172, it is determined whether or not the pre-processing is completed. When the pre-processing is completed, the routine proceeds to step 173, where the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount.
[0105]
Next, at step 174, NO from FIG._xThe release amount D 'is calculated, and then at step 175, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 176, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. If ΣNOX <MIN, the routine proceeds to step 177, where the release completion flag is set._xThe post-treatment is performed from the completion of the release to the return to the strong stratified state. Next, at step 179, it is determined whether or not the post-processing has been completed. When the post-processing has been completed, the routine proceeds to step 180, where NO_xThe release flag and the release completion flag are reset.
[0106]
26 and 27 show still another routine in the rich processing I. As described above, in order to smoothly transition from the strong stratified state to the homogeneous mixture state without causing misfire, it is preferable to interpose a weak stratified state between them. However, if the fuel injection amount is small and the stratified state is set, the lean mixture spread throughout the combustion chamber 5 becomes extremely lean, and there is a danger that these lean mixtures cannot be burned. Therefore, in this embodiment, when the fuel injection amount is small, the transition from the strong stratified state to the homogeneous mixture state is directly made from the strong stratified state to the homogeneous mixture state without passing through the weak stratified state. In FIG. 26, steps 191, 192, and 193 in a frame indicated by X indicate pre-processing, and steps 200, 201, and 202 indicated by Y indicate post-processing.
[0107]
That is, referring to FIGS. 26 and 27, first, at step 190, it is determined whether or not the release completion flag is set. If the release completion flag has not been set, the process proceeds to step 191 of preprocessing X, and if the release completion flag has been set, the process jumps to step 200 of postprocessing Y. In step 191, the fuel injection amount Q is set to a predetermined set value Q.₀It is determined whether the value is larger than. Q> Q₀In the case of, the routine proceeds to step 192, where the pre-processing shown in FIG. 24, that is, the pre-processing for shifting from the strong stratification state to the uniform mixture state via the weak stratification state is performed. On the other hand, Q ≦ Q₀In the case of, the routine proceeds to step 193, where the pretreatment shown in FIG. 21, that is, the pretreatment for directly shifting from the strong stratified state to the homogeneous mixture state without passing through the weak stratified state is performed.
[0108]
Next, at step 194, it is determined whether or not the pre-processing has been completed. When the pre-processing has been completed, the routine proceeds to step 195, where the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. Next, at step 196, NO from FIG._xThe release amount D 'is calculated, and then at step 197, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 198, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 199, where the release completion flag is set, and then proceeds to step 200.
[0109]
In step 200, the fuel injection amount Q is set to a predetermined set value Q.₀It is determined whether the value is larger than. Q> Q₀In the case of, the routine proceeds to step 201, where the post-processing shown in FIG. 24, that is, the post-processing for shifting from the homogeneous mixture state to the strong stratification state via the weak stratification state is performed. On the other hand, Q ≦ Q₀In step 202, the process proceeds to step 202 to perform the post-processing shown in FIG. 21, that is, the post-processing for directly shifting from the homogeneous mixture state to the strong stratification state without passing through the weak stratification state. Next, at step 203, it is determined whether or not the post-processing has been completed._xThe release flag and the release completion flag are reset.
[0110]
FIG. 28 shows another embodiment of the rich processing I performed in the strong stratification state. In this embodiment, NO_xWhen the release flag is set, the throttle valve 23 is slightly closed, and the EGR valve 29 is fully closed. Then NO_xT after the release flag is set₁After a lapse of time, the compression stroke injection amount is decreased, and the intake stroke injection is started. That is, at this time, two injections of the intake stroke injection and the compression stroke injection are performed, and therefore, a weak stratification state is obtained. At this time, the throttle valve 23 is slightly closed. Then NO_xT after the release flag is set₂After a lapse of time, the compression stroke injection is stopped, and only the intake stroke injection is performed. At this time, the throttle valve 23 is slightly closed again.
[0111]
Then NO_xT after the release flag is set₃After a lapse of time, the throttle valve 23 is further closed slightly, and the intake stroke injection amount is increased, so that the average air-fuel ratio A / F is made rich._xNO from absorbent 26_xThe release action is started.
On the other hand, NO_xIs completed, the intake stroke injection amount is reduced. Then NO_xT after the release action of₄After a lapse of time, the injection of the intake stroke is stopped and a stratified state is established. At this time, the throttle valve 23 is opened. Then NO_xT after the release action of₅After a lapse of time, the throttle valve 23 and the EGR valve 29 are opened and NO_xThe release flag is reset.
[0112]
In this embodiment, NO_xWhen the release action of NO is started, the state is changed from a strong stratified state to a homogeneous stratified state through a weak stratified state, and NO_xIs completed, the mixture is directly changed from the homogeneous mixture state to the strong stratified state without passing through the weak stratified state. Also in this embodiment, in the pre-processing when shifting from the strong stratified state to the homogeneous mixture state, it is determined whether or not the vehicle is going through the weak stratified state according to the fuel injection amount.
[0113]
FIG. 29 and FIG._x7 shows a routine of a rich process I for executing release control. Note that the frame indicated by X represents preprocessing. Referring to FIGS. 29 and 30, first, at step 210, it is determined whether or not the release completion flag is set. If the release completion flag has not been set, the process proceeds to step 211 of the preprocessing X. If the release completion flag has been set, the process jumps to step 220. In step 211, the fuel injection amount Q is set to a predetermined set value Q.₀It is determined whether the value is larger than. Q> Q₀In the case of, the routine proceeds to step 212, where the pre-processing shown in FIG. 24, that is, the pre-processing for shifting from the strong stratification state to the homogeneous mixture state through the weak stratification state, is performed. On the other hand, Q ≦ Q₀In step 213, the routine proceeds to step 213, where the pre-processing shown in FIG. 21, that is, the pre-processing for directly shifting from the strong stratification state to the homogeneous mixture state without passing through the weak stratification state, is performed.
[0114]
Next, at step 214, it is determined whether or not the pre-processing has been completed. When the pre-processing has been completed, the routine proceeds to step 215, where the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. Next, at step 216, NO from FIG._xThe release amount D 'is calculated, and then in step 217, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 218, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 219, where the release completion flag is set._xThe post-treatment is performed from the completion of the release to the return to the strong stratified state. Next, at step 221, it is determined whether or not the post-processing is completed. When the post-processing is completed, the process proceeds to step 222 and NO_xThe release flag and the release completion flag are reset.
[0115]
FIG. 31 and FIG. 32 show still another embodiment of the rich processing I performed in the strong stratification state. In this embodiment, NO_xNO from absorbent 26_xIs to be injected into the combustion chamber 5 during the expansion stroke or the exhaust stroke. FIG. 31 shows a case where the additional fuel is supplied to the expansion stroke or the compression stroke in this manner. In this case, the additional fuel is supplied from the fuel injection valve 11 in the zone Z of FIG. During the expansion stroke and the exhaust stroke, the temperature of the burned gas in the combustion chamber 5 is considerably high, so that when additional fuel is injected into the burned gas, hydrocarbons are broken down into small molecules and some hydrocarbons are converted into radicals. And thus the fuel is activated to NO_xWill have a strong reactivity to Therefore NO_xNO from the absorbent 26_xIs released and the released NO_xWill be reduced well. Note that NO_xIt is preferable to inject additional fuel when the temperature of the burned gas is high in order to increase the reactivity with respect to the fuel pressure. Therefore, the additional fuel injection is preferably performed in the expansion stroke as shown in FIG.
[0116]
It should be noted that the additional fuel does not contribute to the generation of output even if burned, and therefore the output torque of the engine does not fluctuate by supplying the additional fuel.
As shown in FIG. 32, in this embodiment, NO_xWhen the release flag is set, the throttle valve 23 is closed, and the EGR valve 29 is fully closed. Then NO_xT after the release flag is set₁After a lapse of time, the compression stroke injection amount is maintained as it is, and additional fuel is injected during the expansion stroke and NO_xNO from absorbent 26_xThe release action of is started. At this time, the intake stroke injection is not performed.
[0117]
On the other hand, NO_xUpon completion of the release action, the composition returns to a strong stratified state in the reverse order. That is, NO_xIs completed, additional fuel injection in the expansion stroke is stopped, and then NO_xT after the release action of₁After a lapse of time, the throttle valve 23 and the EGR valve 29 are opened and NO_xThe release flag is reset.
[0118]
FIG. 33 shows NO shown in FIG._x  7 shows a routine of a rich process I for executing release control. Referring to FIG. 33, first, at step 230, it is determined whether or not the release completion flag is set. If the release completion flag is not set, the process proceeds to step 231. If the release completion flag is set, the process proceeds to step 231.8Jump to NO in step 231_x  Preprocessing is performed from when the release flag is set to when additional fuel is supplied. Next, at step 232, it is determined whether or not the pre-processing has been completed. When the pre-processing has been completed, the routine proceeds to step 233, where additional fuel is supplied.
[0119]
Next, at step 234, NO from FIG._xThe release amount D 'is calculated, and then at step 236, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 236, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. If ΣNOX <MIN, the routine proceeds to step 237, where the release completion flag is set._xThe post-treatment is performed from the completion of the release to the return to the strong stratified state. Next, at step 239, it is determined whether or not the post-processing has been completed._xThe release flag and release completion are reset.
[0120]
FIG. 34 shows a time chart of one embodiment of the rich process II. NO as shown in FIG._xDuring engine middle load operation before the release flag is set, two injections of an intake stroke injection and a compression stroke injection are performed. That is, at this time, the vehicle is in a weakly stratified state, and the average air-fuel ratio A / F in the combustion chamber 5 is lean. NO_xWhen the release flag is set, the average air-fuel ratio A / F in the combustion chamber 5 is made rich by increasing the intake stroke injection amount while maintaining the weak stratified state, and NO_xNO from absorbent 26_xRelease effect. NO_xIs completed, the intake stroke injection amount is reduced.
[0121]
FIG. 35 shows NO shown in FIG._x9 shows a routine of a rich process II for executing release control. Referring to FIG. 35, first, at step 250, the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. Next, at step 251, NO from FIG._xThe release amount D 'is calculated, and then at step 252, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 253, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. If ΣNOX <MIN, the routine proceeds to step 254, where the intake stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 255, NO_xThe release flag is reset.
[0122]
FIG. 36 shows another embodiment of the rich process II performed in the weakly stratified state. In this embodiment, NO_xWhen the release flag is set, the compression stroke injection is stopped, and the intake stroke injection amount is increased. That is, NO_xWhen the release flag is set, the state is switched from the weak stratification state to the homogeneous mixture state, and the average air-fuel ratio A / F in the combustion chamber 5 is made rich, and NO_xNO from absorbent 26_xThe release action of is started. NO_xIs completed, the state of the homogeneous mixture is returned to the weakly stratified state.
[0123]
FIG. 37 shows the NO shown in FIG._x9 shows a routine of a rich process II for executing release control. Referring to FIG. 37, first, at step 260, the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. Next, at step 261, NO from FIG._xThe release amount D 'is calculated, and then at step 262, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 263, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. If ΣNOX <MIN, the routine proceeds to step 264, where the intake stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 265, NO_xThe release flag is reset.
[0124]
FIG. 38 shows still another embodiment of the rich processing II performed in the weakly stratified state. In this embodiment, NO_xNO from absorbent 26_xIs selected in accordance with the fuel injection amount Q when the fuel is to be released in the weakly stratified state or in the homogeneous mixture state. In the routine shown in FIG. 38, the frame indicated by Z indicates a rich process.
[0125]
Referring to FIG. 38, first, at step 270, the fuel injection amount Q is set to a predetermined set value Q._iIt is determined whether the value is larger than. When Q> Qi, the routine proceeds to step 271, where the enrichment is performed by the uniform mixture state. That is, NO_xWhen the discharge flag is set, the compression stroke injection is stopped as shown in FIG. 36, and the intake stroke injection amount is increased. On the other hand, when Q ≦ Qi, the routine proceeds to step 272, where the enrichment is performed in the weakly stratified state. That is, NO_xWhen the discharge flag is set, the intake stroke injection amount is increased while performing the compression stroke injection as shown in FIG.
[0126]
Next, at step 273, NO from FIG._xThe release amount D 'is calculated, and then at step 274, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 275, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. If ΣNOX <MIN, the routine proceeds to step 276, where the intake stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 277, NO_xThe release flag is reset.
[0127]
FIG. 39 shows a time chart of one embodiment of the rich processing III. NO as shown in FIG._xDuring high engine load operation before the release flag is set, only the intake stroke injection is performed, and uniform mixture combustion is performed._xWhen the release flag is set, the intake stroke injection amount is increased, and the average air-fuel ratio A / F is made rich.
[0128]
FIG. 40 shows NO shown in FIG._x3 shows a routine of a rich process III for executing release control. Referring to FIG. 40, first, at step 280, the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. Next, at step 281, NO from FIG._xThe release amount D 'is calculated, and then at step 282, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 283, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 284, where the intake stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 285, NO_xThe release flag is reset.
[0129]
41 to 48 show still another embodiment. In this embodiment, as shown in FIG. 41, a fuel injection valve 50 for injecting fuel toward the second intake port 7b downstream of the intake control valve 17, that is, a so-called port injection valve 50 is provided. Fuel to be supplied into the combustion chamber 5 is supplied from the port injection valve 50. That is, in this embodiment, during normal operation, L> L as shown in FIG.₁If the engine is at low load operation, the compression stroke injection Q₂Only performed, L₁≤L≤L₂If the engine is operating at medium load, the compression stroke injection Q₂Injection Q from the port injection valve 50 in addition to₁Is performed, and L> L₂If the engine is operating at high load, the port injection Q₁Only done.
[0130]
Therefore, also in this embodiment, similarly to the above-described embodiments, the engine is in a strong stratified state at the time of engine low load operation, andDuring ~At the time of load operation, the engine is in a weak stratified state, and at the time of engine high load operation, it is in a uniform mixture state. In this embodiment, the fuel injection control uses the injection control routine shown in FIG. 20, and the rich process I, the rich process II, and the rich process III shown in FIG. 20 will be sequentially described below.
[0131]
FIG. 43 shows a rich process I performed in the strong stratification state. As shown in FIG. 43, NO at the time of engine low load operation_xWhen the discharge flag is not set, only the compression stroke injection is performed. Then NO_xWhen the release flag is set, the compression stroke injection is stopped, and the intake stroke injection is performed from the fuel injection valve 11 into the combustion chamber 5. At this time, port injection from the port injection valve 50 is not performed. Accordingly, at this time, a homogeneous mixture having a rich average air-fuel ratio A / F is formed in the combustion chamber 5 by the intake stroke injection from the fuel injection valve 11, whereby NO_xNO from absorbent 26_xRelease effect.
[0132]
At the time of engine low load operation, port injection is not performed._xWhen the port injection is started in order to perform the discharge operation, the injected fuel adheres to the inner wall surface of the second intake port 7b immediately after the start of the injection, so that the average air-fuel ratio A / F does not immediately become rich. That is, NO_xResponse delay in the release action of Therefore, when port injection is not performed, NO_xNO from absorbent 26_xIs to be released, the average air-fuel ratio A / F is made rich by increasing the amount of fuel injected from the fuel injection valve 11. On the other hand, when port injection is being performed, a response delay does not occur even if the port injection amount is increased._xNO from absorbent 26_xIs released, the average air-fuel ratio A / F is made rich by increasing the port injection amount.
[0133]
FIG. 44 shows the NO shown in FIG._x7 shows a routine of a rich process I for executing release control. Referring to FIG. 44, first, at step 290, the average air-fuel ratio A / F is made rich by starting the intake stroke injection. Next, at step 291, NO from FIG._xThe release amount D 'is calculated, and then at step 292, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 293, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 294, where the intake stroke injection is stopped, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 295, NO_xThe release flag is reset.
[0134]
FIG. 45 shows a rich process II performed in a weakly stratified state. As shown in FIG. 45, NO during engine middle load operation_xBefore the release flag is set, port injection is performed in addition to compression stroke injection. NO_xWhen the release flag is set, the compression stroke injection is continuously performed, and the average air-fuel ratio A / F is made rich by increasing the port injection amount, and NO_xNO from absorbent 26_xRelease effect.
[0135]
FIG. 46 shows the NO shown in FIG._x9 shows a routine of a rich process II for executing release control. Referring to FIG. 46, first, at step 300, the average air-fuel ratio A / F is made rich by increasing the port injection amount. Next, at step 301, NO from FIG._xThe release amount D 'is calculated, and then at step 302_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 303, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 304, where the port injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 305, NO_xThe release flag is reset.
[0136]
FIG. 47 shows a rich process III performed in a uniform gas mixture state. As shown in FIG. 47, NO during engine high load operation_xBefore the release flag is set, only the port injection is performed, and therefore, at this time, the uniform fuel mixture is being performed. NO_xWhen the release flag is set, the port injection amount is increased and the average air-fuel ratio A / F is made rich.
[0137]
FIG. 48 shows the NO shown in FIG._x3 shows a routine of a rich process III for executing release control. Referring to FIG. 48, first, at step 310, the average air-fuel ratio A / F is made rich by increasing the port injection amount. Next, at step 311, NO from FIG._xThe release amount D 'is calculated, and then in step 312, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 313, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 314, where the port injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 315, NO_xThe release flag is reset.
[0138]
FIGS. 49 to 56 show still another embodiment in which port injection is performed. As shown in FIG. 49, also in this embodiment, the compression stroke Q₂Only done. On the other hand, in this embodiment, L₁<L <L_mIf so, the intake stroke injection Q by the fuel injection valve 11₁And compression stroke injection Q₂Is performed, and L_m<L <L₂If so, the injection Q by the fuel injection valve 11₁, Q₂In addition, port injection from the port injection valve 50 is also performed. In addition, fuel is injected from both the fuel injection valve 11 and the port injection valve 50 during high engine load operation.
[0139]
FIG. 50 shows the rich process I performed during low engine load operation. NO as shown in FIG._xWhen the release flag is set, the strong stratification state is continued as it is, and additional fuel is injected during the expansion stroke._xNO from absorbent 26_xIs released.
FIG. 51 shows NO shown in FIG._x7 shows a routine of a rich process I for executing release control. Referring to FIG. 51, first, at step 320, the average air-fuel ratio A / F is made rich by injecting additional fuel during the expansion stroke. Next, at step 321, NO from FIG._xThe release amount D 'is calculated, and then at step 322, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 323, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. If ΣNOX <MIN, the routine proceeds to step 324, where additional fuel injection is stopped, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 325, NO_xThe release flag is reset.
[0140]
FIG. 52 shows L in FIG.₁<L <L_mAt the time of engine middle load operation. In this case, NO_xWhen the release flag is not set, the fuel is injected from the fuel injection valve 11 to make a weak stratified state, and NO_xWhen the release flag is set, additional fuel is injected during the expansion stroke to_xNO from absorbent 26_xIs released. On the other hand, FIG._m<L <L₂At the time of engine middle load operation. In this case, NO_xWhen the release flag is not set, the fuel is in a weak stratified state by the fuel injected from the fuel injection valve 11 and the port injection valve 50, and NO_xWhen the release flag is set, the port injection amount is increased.
[0141]
FIG. 54 shows NO shown in FIGS. 52 and 53._x7 shows a routine of a rich process II for selectively executing release control. In FIG. 54, a frame indicated by Z indicates a rich process. Referring to FIG. 54, first, at step 330, the depression amount L of the accelerator pedal 40 is set to the set value L._mIt is determined whether it is greater than (FIG. 49). L> L_mIn the case of, the process proceeds to step 331, and the enrichment is performed by increasing the port injection amount as shown in FIG. On the other hand, L ≦ L_mIn the case of, the process proceeds to step 332, and as shown in FIG. 52, the enrichment is performed by injecting additional fuel during the expansion stroke.
[0142]
Next, at step 333, NO from FIG._xThe release amount D 'is calculated, and then at step 334, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 335, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 336, where the enrichment of the air-fuel ratio is stopped, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 337, NO_xThe release flag is reset.
[0143]
FIG. 55 shows a rich process III at the time of engine high load operation. NO as shown in FIG._xBefore the release flag is set, fuel is injected from both the fuel injection valve 11 and the port injection valve 50 to burn a uniform mixture, and NO_xWhen the release flag is set, the average air-fuel ratio A / F is made rich by increasing the port injection amount.
[0144]
FIG. 56 shows NO shown in FIG._x3 shows a routine of a rich process III for executing release control. Referring to FIG. 56, first, at step 340, the average air-fuel ratio A / F is made rich by increasing the port injection amount. Next, at step 341, NO from FIG._xThe release amount D 'is calculated, and then at step 342, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 343, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 344, where the port injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 345, NO_xThe release flag is reset.
[0145]
57 to 63 show another embodiment. In this embodiment, an automatic transmission 60 is attached to the engine body 1, and the automatic transmission 60 detects a vehicle speed sensor 61 for detecting a vehicle speed and detects that the automatic transmission 60 is in a neutral position. A neutral position sensor 62 is mounted. FIG. 58 shows a torque converter 63 of the automatic transmission 60, in which a lock-up mechanism 64 is provided. That is, the torque converter 63 is connected to the engine crankshaft and rotates with the crankshaft, the pump cover 65, the pump impeller 66 supported by the pump cover 65, and the turbine runner 68 attached to the input shaft 67 of the automatic transmission 60. And a stator 69, and the rotational motion of the crankshaft is transmitted to the input shaft 67 via the pump cover 65, the pump impeller 66 and the turbine runner 68.
[0146]
On the other hand, the lock-up mechanism 64 includes a lock-up clutch plate 69 that is mounted movably in the axial direction with respect to the input shaft 67 and that rotates together with the input shaft 67. Normally, that is, at the time of lock-up off, pressurized oil is supplied into the room 70 between the lock-up clutch plate 69 and the pump cover 65 via the oil passage in the input shaft 67, and then the pressurized oil flowing out of this room 70 Is fed into a room 71 around the pump impeller 66 and the turbine runner 68 and then discharged through an oil passage in the input shaft 67. At this time, there is almost no pressure difference between the chambers 70 and 71 on both sides of the lock-up clutch plate 69, so that the lock-up clutch 64 is separated from the pump cover 65 as shown in FIG. The rotational force of the shaft is transmitted to the input shaft 67 via the pump cover 65, the pump impeller 66, and the turbine runner 68.
[0147]
On the other hand, when the lock-up is to be turned on, pressurized oil is supplied into the room 71 through the oil passage in the input shaft 67, and the oil in the room 70 is discharged through the oil passage in the input shaft 67. At this time, the pressure in the room 71 becomes higher than the pressure in the room 70, and thus the lock-up clutch 69 is pressed against the pump cover 65 as shown in FIG. Are connected directly to rotate at the same speed. The oil supply control to the chambers 70 and 71, that is, the ON / OFF control of the lock-up mechanism 64, is controlled by a control valve provided in the automatic transmission 60. The control valve is controlled based on an output signal of the electronic control unit 30. Controlled.
[0148]
In this embodiment as well, the fuel injection control is performed according to the routine shown in FIG. 20, so that the engine is in a strong stratified state at the time of engine low load operation. By the way, when the output torque of the engine fluctuates, the lower the engine load, the larger the rate of fluctuation of the output torque. Therefore, when the output torque of the engine fluctuates, a shock is particularly likely to occur during low engine load operation. Become. Therefore NO_xNO from absorbent 26_xIf the output torque of the engine fluctuates when the average air-fuel ratio A / F is made rich to release the engine, the fluctuation of the engine output torque is most likely to appear as a shock at the time of engine low load operation.
[0149]
By the way, as shown in FIG. 58 (A), if the engine output torque fluctuates when the lock-up clutch 69 is turned on and in the direct connection state, this fluctuation is directly transmitted to the automatic transmission 60, and a large shock occurs. I do. On the other hand, if the engine output torque fluctuates while the lock-up clutch 69 is off as shown in FIG. 58 (B), almost no shock No longer occurs. Therefore, from the viewpoint of the occurrence of a shock, when the lock-up clutch 69 is off, the engine output torque may fluctuate.IHowever, it is preferable that the output torque of the engine does not fluctuate when the lock-up clutch 69 is on.
[0150]
Therefore, in this embodiment, NO_xNO from absorbent 26_xWhen the lock-up clutch 69 is off when the average air-fuel ratio A / F is made rich so as to release the air-fuel ratio from the strong stratified state to the uniform air-fuel mixture state as shown in FIG. / F is made rich, and if the lock-up clutch 69 is on, the average air-fuel ratio A / F is made rich by injecting additional fuel during the expansion stroke as shown in FIG. The control method shown in FIG. 59 is the same as the control method shown in FIG. 24 already described, and the control method shown in FIG. 60 is the same as the control method shown in FIG. 32 already described. A description of the control method shown in FIG. 60 will be omitted.
[0151]
FIG. 61 shows NO_xThis figure shows a control routine of the release flag, and this routine is executed by interruption every predetermined time.
Referring to FIG. 61, first, at step 350, NO_xNO estimated to be absorbed by the absorbent 26_xIt is determined whether the amount ΣNOX has become larger than the allowable value MAX. If ＸNOX> MAX, proceed to step 351 and NO_xThe release flag is set. Next, at step 352, the depression amount L of the accelerator pedal 40 becomes L₁Is determined, that is, whether the engine is operating at a low load. L <L₁In step 353, it is determined whether the lock-up clutch 69 is on. When the lock-up clutch 69 is on, the routine proceeds to step 354, where the flag X is set. When the lock-up clutch 69 is off, the routine proceeds to step 355, where the flag X is reset.
[0152]
62 and 63 show the rich processing I. In FIGS. 62 and 63, the inside of the frame indicated by X indicates the pre-processing, and the inside of the frame indicated by Y indicates the post-processing.
Referring to FIGS. 62 and 63, first, at step 360, it is determined whether or not the release completion flag is set. If the release completion flag has not been set, the process proceeds to step 361 of pre-processing X. If the release completion flag has been set, the process proceeds to step 361 of post-processing Y.370Jump to At step 361, it is determined whether or not the flag X is set. When the flag X is set, the routine proceeds to step 362, where the pre-processing shown in FIG. 60, that is, the pre-processing for shifting to the expansion stroke injection, is performed. On the other hand, when the flag X has not been set, the routine proceeds to step 363, where the pre-processing shown in FIG. 59, that is, the pre-processing for shifting from a strong stratified state to a homogeneous stratified state through a weak stratified state is performed.
[0153]
Next, at step 364, it is determined whether or not the pre-processing is completed. When the pre-processing is completed, the routine proceeds to step 365, at which the average air-fuel ratio A / F is increased by performing the expansion stroke injection or performing the intake stroke injection. It is said to be rich. Next, at step 366, NO from FIG._xThe release amount D 'is calculated, and then at step 367, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 368, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 369, where the release completion flag is set, and then proceeds to step 370.
[0154]
At step 370, it is determined whether or not the flag X is set. When the flag X is set, the routine proceeds to step 371, where the post-processing shown in FIG. 60, that is, the post-processing for shifting to the strong stratification state after the completion of the expansion stroke injection, is performed. On the other hand, when the flag X is not set, the routine proceeds to step 372, where the post-processing shown in FIG. 59, that is, the post-processing of shifting from the homogeneous mixture state to the weak stratification state through the weak stratification state is performed. Next, at step 373, it is determined whether or not the post-processing has been completed. When the post-processing has been completed, the process proceeds to step 374 to determine NO._xThe release flag and the release completion flag are reset.
[0155]
FIGS. 64 to 66 show still another embodiment. In this embodiment as well, the fuel injection control is performed according to the routine shown in FIG. 20, so that the engine is in a strong stratified state at the time of engine low load operation. As described above, when the output torque of the engine fluctuates, the lower the engine load, the larger the output torque fluctuation rate. Therefore NO_xNO from absorbent 26_xIf the output torque of the engine fluctuates when the average air-fuel ratio A / F is made rich in order to discharge the engine, the fluctuation of the engine output torque is most likely to appear as a shock during the engine idling operation.
[0156]
By the way, even if a shock occurs during the engine idling operation, almost no shock occurs when the automatic transmission 60 (FIG. 57) is in the neutral position. Therefore, in this embodiment, NO is set during engine idling operation._xNO from absorbent 26_xIn the case where the average air-fuel ratio A / F is made rich to release the fuel, if the starting transmission 60 is in the neutral position, the state is shifted from the strong stratified state to the uniform mixture state as shown in FIG. F is made rich, and if the automatic transmission 60 is not in the neutral position, the average air-fuel ratio A / F is made rich by injecting additional fuel during the expansion stroke as shown in FIG.
[0157]
FIG. 64 shows NO_xThis figure shows a control routine of the release flag, and this routine is executed by interruption every predetermined time.
Referring to FIG. 64, first, at step 380, NO_xNO estimated to be absorbed by the absorbent 26_xIt is determined whether the amount ΣNOX has become larger than the allowable value MAX. If ΣNOX> MAX, proceed to step 381 and NO_xThe release flag is set. Next, at step 382, the depression amount L of the accelerator pedal 40 becomes L₁Is determined, that is, whether the engine is operating at a low load. L <L₁In the case of, the routine proceeds to step 383, where it is determined whether or not the engine is in the engine and ring operation. When the engine is not idling, the routine proceeds to step 586, where the flag X is reset. On the other hand, when the engine is idling, the process proceeds to step 384.
[0158]
At step 384, it is determined whether or not the automatic transmission 60 is at the neutral position based on the output signal of the neutral position sensor 62 (FIG. 57). When the automatic transmission 60 is not at the neutral position, the routine proceeds to step 385, where the flag X is set. When the automatic transmission 60 is at the neutral position, the routine proceeds to step 386 to reset the flag X.
[0159]
65 and 66 show the rich processing I. The routine shown in FIGS. 65 and 66 is the same as the routine shown in FIGS. 62 and 63.
That is, referring to FIG. 65 and FIG.390It is determined whether or not the release completion flag is set in. If the release completion flag has not been set, the process proceeds to step 391 of pre-processing X, and if the release completion flag has been set, the process jumps to step 400 of post-processing Y. In step 391, it is determined whether the flag X is set. When the flag X is set, the routine proceeds to step 392, where the preprocessing shown in FIG. 60, that is, the preprocessing for shifting to the expansion stroke injection, is performed. On the other hand, when the flag X is not set, the routine proceeds to step 393, where the pre-processing shown in FIG. 59, that is, the pre-processing for shifting from the strong stratified state to the homogeneously-mixed state through the weak stratified state is performed.
[0160]
Then step394Then, it is determined whether or not the pre-processing has been completed. When the pre-processing has been completed, the routine proceeds to step 395, where the average air-fuel ratio A / F is made rich by performing the expansion stroke injection or performing the intake stroke injection. You. Next, in step 396, NO from FIG._x  The release amount D 'is calculated, and then in step 397, NO_x  Quantity ΣNOX to NO_x  The release amount D 'is subtracted. Next, at step 398, NO_x  It is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 399, where the release completion flag is set, and then proceeds to step 400.
[0161]
In step 400, it is determined whether the flag X is set. When the flag X is set, the routine proceeds to step 401, where the post-processing shown in FIG. 60, that is, the post-processing for shifting to the strong stratification state after the completion of the expansion stroke injection, is performed. On the other hand, when the flag X is not set, the routine proceeds to step 402, where the post-processing shown in FIG. 59, that is, the post-processing of shifting from the homogeneous mixture state to the weak stratification state via the weak stratification state is performed. Next, at step 403, it is determined whether or not the post-processing has been completed._xThe release flag and the release completion flag are reset.
[0162]
FIG. 67 shows the same NO as in FIG._x3 shows a time chart of release control. In FIG. 67, Y₁As shown by, in the embodiment described so far, ΣNO_xNO when> MAX_xNO from absorbent 26_xThe average air-fuel ratio A / F is made to be rich in order to discharge the air. In this case, in any engine operating state, ΣNO_xIt is not known whether> MAX, and it is not known in what engine operating state the average air-fuel ratio A / F is made rich.
[0163]
By the way, the fuel injection amount is large at the time of engine high load operation, and therefore, in order to make the average air-fuel ratio A / F rich at this time, a large amount of fuel to be increased is required. On the other hand, during low engine load operation, the average air-fuel ratio A / F can be made rich only by increasing a small amount of fuel because the fuel injection amount is small. Therefore NO_xNO from absorbent 26_xThe amount of fuel to be increased for discharge is smaller when the engine load is lower. Thus, in order to improve the fuel consumption, NO is required during engine low load operation._xNO from absorbent 26_xIt would be preferable to have a release action.
[0164]
Therefore, in the embodiment described below, NO as shown in FIG._xAn intermediate determination value MID which is an intermediate value between the allowable value MAX and the lower limit value MIN is set for the amount ΣNOX, and NO_xIn the case where the engine low load operation is performed when the amount ΣNOX does not reach the allowable value MAX but exceeds the intermediate determination value MID, in FIG.₂NO as shown by_xNO from absorbent 26_xThe release action is performed. By doing so, NO during engine low load operation_xNO from absorbent 26_xThe opportunity for the release action to be increased increases, and thus the fuel consumption can be reduced.
[0165]
FIG. 68 shows an embodiment in which the intermediate judgment value MID is used. In this embodiment, a routine shown in FIG. 20 is used for controlling the fuel injection.
Referring to FIG. 68, first, in step 410, NO_xIt is determined whether the amount ΣNOX has exceeded the allowable value MAX. ΣIf NOX> MAX, proceed to step 413 and NO_xThe release flag is set. Therefore, at this time, the average air-fuel ratio A / F is made rich by the routine shown in FIG._xNO from absorbent 26_xA release action takes place. On the other hand, when it is determined in step 410 that ΣNOX ≦ MAX, the process proceeds to step 411 and NO_xIt is determined whether the amount ΣNOX is greater than the intermediate determination value MID. At this time, if ΣNOX> MID, the process proceeds to step 412.
[0166]
In step 412, it is determined whether or not the vehicle is stopped based on the output signal of the vehicle speed sensor 61 (FIG. 57). At this time, if the vehicle is stopped, the process proceeds to step 413 and NO_xThe release flag is set, and the average air-fuel ratio A / F is made rich by the routine shown in FIG. When the vehicle is stopped, idling operation is normally performed, and at this time, NO_xNO from absorbent 26_xSince the release operation is performed, the fuel consumption can be reduced.
[0167]
FIG. 69 shows another embodiment using the intermediate judgment value MID. In this embodiment, the routine shown in FIG. 20 is used for controlling the fuel injection.
Referring to FIG. 69, first in step 420, NO_xIt is determined whether the amount ΣNOX has exceeded the allowable value MAX. ΣIf NOX> MAX, proceed to step 424 and NO_xThe release flag is set. Therefore, at this time, the average air-fuel ratio A / F is made rich by the routine shown in FIG._xNO from absorbent 26_xA release action takes place. On the other hand, when it is determined in step 420 that ΣNOX ≦ MAX, the process proceeds to step 421 and NO_xIt is determined whether the amount ΣNOX is greater than the intermediate determination value MID. At this time, if ΣNOX> MID, the process proceeds to step 422.
[0168]
In step 422, it is determined whether or not the vehicle is stopped based on the output signal of the vehicle speed sensor 61 (FIG. 57). At this time, if the vehicle is stopped, the routine proceeds to step 423, where it is determined whether or not the automatic transmission 60 is at the neutral position based on the output signal of the neutral position sensor 62 (FIG. 57). At this time, if the automatic transmission 60 is at the neutral position, the process proceeds to step 423 and NO_xThe release flag is set, and the average air-fuel ratio A / F is made rich by the routine shown in FIG. When the vehicle is stopped, idling operation is normally performed, and at this time, NO_xNO from absorbent 26_xSince the release operation is performed, the fuel consumption can be reduced. Further, in this embodiment, when the automatic transmission 60 is in the neutral position, the average air-fuel ratio A / F is made rich, so that generation of a shock can be prevented.
[0169]
FIG. 70 shows still another embodiment using the intermediate judgment value MID. In this embodiment, the routine shown in FIG. 20 is used for controlling the fuel injection.
Referring to FIG. 70, first, in step 430, NO_x  It is determined whether the amount ΣNOX has exceeded the allowable value MAX.と Step 4 if NOX> MAX3Go to 4 and NO_x  The release flag is set. Therefore, at this time, the average air-fuel ratio A / F is made rich by the routine shown in FIG._x  NO from absorbent 26_x  A release action takes place. On the other hand, when it is determined in step 430 that ΣNOX ≦ MAX, the process proceeds to step 431 and NO_x  It is determined whether the amount ΣNOX is greater than the intermediate determination value MID. At this time, if ΣNOX> MID, the process proceeds to step 432.
[0170]
In step 432, it is determined from the output signal of the load sensor 41 and the engine speed whether or not deceleration operation is being performed. At this time, if the vehicle is decelerating, the routine proceeds to step 433, where it is determined whether or not the lock-up clutch 69 (FIG. 58) is off. Step 4 when the lock-up clutch 69 is off3Go to 4 and NO_x  The release flag is set, and the average air-fuel ratio A / F is made rich by the routine shown in FIG. When the vehicle decelerates, the fuel injection amount is small._x  NO from absorbent 26_x  Since the release operation is performed, the fuel consumption can be reduced. In this embodiment, when the lock-up clutch 69 is off, the average air-fuel ratio A / F is made rich, so that the occurrence of a shock can be prevented.
[0171]
FIG. 71 shows still another embodiment using the intermediate judgment value MID. In this embodiment, the routine shown in FIG. 20 is used for controlling the fuel injection.
Referring to FIG. 71, first, at step 440, NO_xIt is determined whether the amount ΣNOX has exceeded the allowable value MAX. ΣIf NOX> MAX, proceed to step 445 and NO_xThe release flag is set. Therefore, at this time, the average air-fuel ratio A / F is made rich by the routine shown in FIG._xNO from absorbent 26_xA release action takes place. On the other hand, if it is determined in step 440 that ΣNOX ≦ MAX, the routine proceeds to step 441, where NO_xIt is determined whether the amount ΣNOX is greater than the intermediate determination value MID. At this time, if ΣNOX> MID, the process proceeds to step 442.
[0172]
In step 442, it is determined from the output signal of the load sensor 41 and the engine speed whether or not deceleration operation is being performed. At this time, if the vehicle is decelerating, the routine proceeds to step 443, where it is determined whether or not the lock-up clutch 69 (FIG. 58) is off. When the lock-up clutch 69 is off, the routine proceeds to step 444, where the engine speed NE is set to a predetermined set speed NE.₀  Is determined. At this time, NE <NE₀  If so, step 445Proceed to NO_x  The release flag is set, and the average air-fuel ratio A / F is made rich by the routine shown in FIG. When the vehicle decelerates, the fuel injection amount is small, and NE <NE₀  In the case of, the fuel injection amount is further reduced. Thus, in this embodiment, when the fuel injection amount is extremely small, NO_x  NO from absorbent 26_x  Since the release operation is performed, the fuel consumption can be reduced. In this embodiment, when the lock-up clutch 69 is off, the average air-fuel ratio A / F is made rich, so that the occurrence of a shock can be prevented.
[0173]
FIG. 72 shows still another embodiment using the intermediate judgment value MID. In this embodiment, the routine shown in FIG. 20 is used for controlling the fuel injection.
Referring to FIG. 72, first, at step 450, NO_xIt is determined whether the amount ΣNOX has exceeded the allowable value MAX. ΣIf NOX> MAX, go to step 453 and NO_xThe release flag is set. Therefore, at this time, the average air-fuel ratio A / F is made rich by the routine shown in FIG._xNO from absorbent 26_xA release action takes place. On the other hand, if it is determined in step 450 that ΣNOX ≦ MAX, the routine proceeds to step 451, where NO_xIt is determined whether the amount ΣNOX is greater than the intermediate determination value MID. At this time, if ΣNOX> MID, the process proceeds to step 452.
[0174]
At step 452, it is determined from the output signal of the load sensor 41 and the engine speed whether or not the deceleration operation is being performed, the fuel injection is stopped, and the lock-up clutch 69 is turned on so that the engine braking operation is performed. Is done. If the fuel injection has been stopped and the lock-up clutch 69 is on during the deceleration operation, the routine proceeds to step 453, where NO_xThe release flag is set, and the average air-fuel ratio A / F is made rich by the routine shown in FIG. When the vehicle is decelerated, the amount of intake air is small. Therefore, at this time, the average air-fuel ratio A / F can be made rich only by injecting a small amount of fuel. As described above, in this embodiment, only a small amount of fuel is injected and NO_xNO from absorbent 26_xSince the release operation is performed, the fuel consumption can be reduced.
[0175]
73 to 77 show still another embodiment using the intermediate judgment value MID. In this embodiment, when ΣNOX> MID, the MID flag is set. As shown in FIG. 73, when the MID flag is set, the operating state of the engine should be changed from the weak stratified state to the medium load operation to the strong stratified state. When the operation is changed to the low load operation, the weak stratification state is continued for a while, and during this period, the intake stroke injection amount is increased to make the average air-fuel ratio A / F rich. Then NO_xNO from absorbent 26_xIs completed, the average air-fuel ratio A / F is switched from rich to lean and the weak stratified state is shifted to the strong stratified state.
[0176]
That is, in this embodiment, when the operation state in which the weak stratification state is set to the operation state in which the strong stratification state is to be changed when the MID flag is set, the transition from the weak stratification state to the strong stratification state is delayed. NO_xNO from absorbent 26_xRelease effect. As described above, also in this embodiment, when the engine load is reduced, the average air-fuel ratio A / F is made rich, so that the fuel consumption can be reduced. When the average air-fuel ratio A / F is made rich after the engine load becomes low and the vehicle is shifted from the weak stratification state to the strong stratification state, the engine is returned from the strong stratification state to the weak stratification state again. The average air-fuel ratio A / F is made rich. Therefore, since the stratification state is frequently changed, combustion becomes unstable, and there is a risk that torque fluctuations may occur. Therefore, in this embodiment, when the engine load is reduced, NO_xRelease action, and this NO_xThe stratification state is changed after the release operation of is completed.
[0177]
On the other hand, in this embodiment, as shown in FIG. 74, even when the MID flag is set during the low engine load operation, the average air-fuel ratio A / F is not enriched at this time, and the engine load is reduced after the MID flag is set. The average air-fuel ratio A / F is made rich immediately in the weak stratification state when the operation shifts from the low-load operation to the medium-load operation. In this case as well, frequent switching of the stratification state is prevented, and when the engine load is relatively low, NO_xRelease effect.
[0178]
FIG. 75 shows a routine for controlling the flag, and this routine is executed by interruption every predetermined time.
Referring to FIG. 75, first, at step 460, NO_xIt is determined whether the amount ΣNOX has become larger than the allowable value MAX. If ΣNOX ≦ MAX, the routine jumps to step 462, and if ΣNOX> MAX, the routine proceeds to step 461 and NO_xAfter the release flag is set, the process proceeds to step 462. NO at step 462_xIt is determined whether the amount ΣNOX has become larger than the intermediate set value MID. If と き に は NOX> MID, the routine proceeds to step 463, where the MID flag is set.
[0179]
FIGS. 76 and 77 show a fuel injection control routine, which is executed, for example, by interruption every predetermined time.
Referring to FIGS. 76 and 77, first, at step 470, NO_xIt is determined whether the release flag is set. NO_xIf the release flag has not been set, the routine proceeds to step 471, where it is determined whether the execution flag has been set. This execution flag is set when the MID flag is set and when the engine load changes from a medium-high load to a low load, or when the engine load changes from a low load to a medium-high load. If the execution flag has not been set, the routine proceeds to step 472, where it is determined whether the MID flag has been set. If the MID flag has not been set, the process proceeds to step 475.
[0180]
In step 475, based on the depression amount L of the accelerator pedal 40 and the engine speed N, the intake stroke injection amount Q is determined from the relationship shown in FIG.₁And compression stroke injection amount Q₂Is calculated. Next, at step 476, the injection timing is calculated from the relationship shown in FIG. 6 stored in the ROM 33 in advance based on the depression amount L of the accelerator pedal 40 and the engine speed N. Next, at step 477, the injection amount L of the accelerator pedal 40 is calculated. The opening degree of the throttle valve 23 is calculated from the relationship shown in FIG. 7 stored in the ROM 33 in advance based on the engine speed N and the engine speed N. Next, at step 478, the opening degree of the accelerator pedal 40 and the engine speed N are calculated. The degree of opening of the EGR valve 29 is calculated from the relationship stored in the ROM 33 in advance, and then in step 479, the intake air is calculated from the relationship shown in FIG. The opening of the control valve 17 is calculated.
[0181]
Next, at step 480, the depression amount L of the accelerator pedal 40 becomes L₀It is determined whether it is lower than (FIG. 7). L <L₀In the case of, the routine proceeds to step 481, where NO from the map shown in FIG._xThe release amount A is calculated. Next, at step 482, NO_xThe release amount D is set to zero, and then the routine proceeds to step 485. On the other hand, at step 480, L ≧ L₀If it is determined that the answer is NO, the flow advances to step 483 to determine NO from the map shown in FIG._xThe release amount D is calculated. Next, at step 484, NO_xThe absorption amount A is set to zero, and then the process proceeds to step 485. NO at step 485_xNO estimated to be absorbed by the absorbent 26_xThe quantity ΣNOX (= ΣNOX + AD) is calculated. Next, at step 486, it is determined whether or not ΣNOX has become negative. When ΣNOX <0, the routine proceeds to step 487, where ΣNOX is made zero.
[0182]
On the other hand, when it is determined in step 472 that the MID flag has been set, the process proceeds to step 473 where the depression amount L of the accelerator pedal 40 is set to L₁It is determined whether or not the following conditions have been met, that is, whether or not the engine load has changed from a medium to high load to a low load. L <L₁If not, the process proceeds to step 474, where the depression amount L of the accelerator pedal 40 becomes L₁It is determined whether or not the above has occurred, that is, whether or not the engine load has changed from a low load to a medium to high load. L> L₁If not, the process proceeds to step 475.
[0183]
On the other hand, after the MID flag is set, in step 473, the depression amount L of the accelerator pedal 40 becomes L₁When it is determined that the load has become the following, that is, when the engine load has changed from the medium-high load to the low load, the routine proceeds to step 488, where the execution flag is set, and then the routine proceeds to step 489. Once the execution flag is set, the process jumps from 471 to step 489. In step 489, a weak stratification state is performed in which the intake stroke injection and the compression stroke injection are performed. As shown in FIG. 73, in this weak stratification state, the average air-fuel ratio A / F is made rich by increasing the intake stroke injection amount. Is done.
[0184]
Next, at step 490, NO from FIG._xThe release amount D 'is calculated, and then at step 491, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 492, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 493, where the MID flag and the execution flag are reset. When these flags are reset, the state is shifted to the normal strong stratification state.
[0185]
On the other hand, after the MID flag is set, in step 474, the depression amount L of the accelerator pedal 40 becomes L₁When this is the case, that is, when it is determined that the engine load has changed from a low load to a medium-high load, the routine proceeds to step 488, where the execution flag is set, and then the routine proceeds to step 489. In step 489, if the engine is in the middle load operation, as shown in FIG. 74, the intake stroke injection and the compression stroke injection are performed in a weakly stratified state, and in this weakly stratified state, the intake stroke injection amount is increased. The average air-fuel ratio A / F is made rich. On the other hand, at this time, in the case of high load operation, the average air-fuel ratio A / F is made rich in the uniform mixture state.
[0186]
Next, the routine proceeds to steps 492 via steps 489, 490 and 491, and if ΣNOX <MIN, the routine proceeds to step 493 where the MID flag and the execution flag are reset. When these flags are reset, the state is returned to a normal weak stratified state or a homogeneous mixture state.
On the other hand, in step 470, NO_x  When it is determined that the release flag has been set, the routine proceeds to step 494, where the depression amount L of the accelerator pedal 40 is set to L₁  It is determined whether or not it is smaller than. L <L₁  In step 496, the routine proceeds to step 496, where a rich process I for making the average air-fuel ratio A / F rich is performed. On the other hand, L ≧ L₁  In step 495, the routine proceeds to step 495, where the depression amount L of the accelerator pedal 40 is L₂  It is determined whether or not it is smaller than. L <L₂  In step 497, the routine proceeds to step 497, where a rich process II for making the average air-fuel ratio A / F rich is performed, and L ≧ L₂  In step 498, the routine proceeds to step 498, where a rich process III for making the average air-fuel ratio A / F rich is performed.
[0187]
78 to 81 show still another embodiment. In this embodiment, as shown in FIGS. 78 and 79, an air injection valve 80 is arranged at the center of the inner wall surface of the cylinder head 4 on the side of the ignition plug 10. NO_xNO from absorbent 26_xWhen the average air-fuel ratio A / F is made rich so as to release the air, air is injected from the air injection valve 80 into the combustion chamber 5 around the ignition plug 10 as indicated by J. In the embodiment shown in FIGS. 78 and 79, the air injection from the air injection valve 80 is performed at the end of the compression stroke.
[0188]
When air is injected around the ignition plug 10 in this way, the oxygen concentration in the air-fuel mixture around the ignition plug 10 increases, and thus, even if an over-enriched air-fuel mixture is formed around the ignition plug 10 Also, good ignition can be ensured without misfiring.
FIG. 80 shows NO during low engine load operation when such an air injection valve 80 is used._x4 shows an example of release control. In this example, as shown in FIG._xBefore the release flag is set, only the compression stroke injection is performed, and NO_xEven if the release flag is set, only the compression stroke injection is performed. However, NO_xWhen the release flag is set, the compression injection amount is increased, and the air injection from the air injection valve 80 is performed. At this time, the average air-fuel ratio A / F becomes rich due to the increase in the compression injection amount, but the air injected from the air injection valve 80 forms an air-fuel mixture having an optimum air-fuel ratio around the ignition plug 10.
[0189]
FIG. 81 shows the NO shown in FIG._xThe rich process I for performing the release control is shown. In this embodiment, a routine shown in FIG. 20 is used as a fuel injection control routine. Referring to FIG. 81, first, at step 500, a process of opening the air injection valve 80 at the end of the compression stroke is performed. Next, at step 501, the average air-fuel ratio A / F is made rich by increasing the compression stroke injection amount. Next, at step 502, NO from FIG._xThe release amount D 'is calculated, and then in step 503, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 504, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. When ΣNOX <MIN, the routine proceeds to step 505, where the compression stroke injection amount is reduced, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 506, the air injection valve 80 is kept in the closed state. Next, at step 507, NO_xThe release flag is reset.
[0190]
FIGS. 82 and 83 show the rich process in the case where the intake control valve 17 (FIG. 3) is controlled. In the embodiment shown in FIGS. 1 to 5, the intake control valve 17 is closed at the time of engine low load operation, and at this time, a swirling flow S (FIG. 3) is generated in the combustion chamber 5. The fuel injected during the compression stroke is collected in a predetermined limited area by the swirling flow, and the fuel collected in the limited area is ignited by the spark plug 10.
[0191]
As described above, it may be necessary to generate a swirl flow to create a strong stratified state in which good ignition can be obtained during low-load operation of the engine. There is no particular need to generate it. Therefore, in the embodiment shown in FIG. 82, when making the average air-fuel ratio A / F rich, the intake control valve 17 is opened. That is, as shown in FIG. 82 showing the rich process at the time of engine low load operation, NO_xBefore the discharge flag is set, only the compression stroke injection is performed, and at this time, the intake control valve 17 is closed. NO_xWhen the release flag is set, the compression stroke injection is stopped and the intake stroke injection is started. At this time, the intake control valve 17 is opened. At this time, a uniform air-fuel mixture in which the average air-fuel ratio A / F is rich is formed and NO_xNO from absorbent 26_xA release action takes place.
[0192]
FIG. 83 shows the NO shown in FIG._xThe rich process I for performing the release control is shown. In this embodiment, a routine shown in FIG. 20 is used as a fuel injection control routine. Referring to FIG. 83, first, at step 510, the intake control valve 17 is fully opened. Next, at step 511, the average air-fuel ratio A / F is made rich by stopping the compression stroke injection and starting the intake stroke injection. Next, at step 512, NO from FIG._xThe release amount D 'is calculated, and then at step 513, NO_xQuantity ΣNOX to NO_xThe release amount D 'is subtracted. Next, at step 514, NO_xIt is determined whether the amount ΣNOX has become smaller than the lower limit value MIN. If ΣNOX <MIN, the routine proceeds to step 515, where the intake stroke injection is stopped and the compression stroke injection is started, and the average air-fuel ratio A / F changes from rich to lean. Next, at step 516, the intake control valve 17 is fully closed. Next, at step 517, NO_xThe release flag is reset.
[0193]
FIG. 84 shows an internal combustion engine having no fuel injection valve in the combustion chamber 5 and having the fuel injection valve 11 mounted on the intake branch pipe 15, and the present invention also applies to such an internal combustion engine. Can be applied. In such a so-called port injection type internal combustion engine, the air-fuel mixture is conventionally stratified by various methods, and the present invention is applied to all the internal combustion engines in which the air-fuel mixture is stratified during low engine load operation. can do. For example, in an internal combustion engine that is stratified during engine low load operation, NO_xWhen the average air-fuel ratio is switched from lean to rich for release, the degree of stratification is reduced or the mixture is made uniform.
[0194]
In an internal combustion engine that stratifies by generating a swirling flow in the combustion chamber 5, NO_xWhen the average air-fuel ratio is switched from lean to rich for release, the swirling flow is weakened, or the generation of the swirling flow is stopped to reduce the degree of stratification, or to achieve a uniform mixture.
[0195]
【The invention's effect】
NO in a stratified combustion internal combustion engine_xNO from absorbent_xMisfire can be prevented when the supply fuel is increased in order to release the fuel.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine showing a cross section of an engine body.
FIG. 2 is a plan view schematically showing the entire internal combustion engine shown in FIG.
FIG. 3 is a plan sectional view of a cylinder head.
FIG. 4 is a plan view of a piston top surface.
FIG. 5 is a side sectional view of FIG. 3;
FIG. 6 is a diagram showing a fuel injection amount and a fuel injection timing.
FIG. 7 is a diagram showing a fuel injection amount, a throttle opening, an EGR valve opening, and an average air-fuel ratio in a combustion chamber.
FIG. 8 is a diagram showing an opening degree of an intake control valve.
FIG. 9 is a diagram for explaining a combustion method during low load operation.
FIG. 10 is a diagram for explaining a combustion method during a medium load operation.
FIG. 11 shows CO, HC, and O in exhaust gas.₂FIG.
FIG. 12 NO_xAbsorbent NO_xIt is a figure for demonstrating a suction / release operation.
FIG. 13 NO_xIt is a time chart of release control.
FIG. 14 NO_xAbsorption and NO_xIt is a figure showing a map of an amount of release.
FIG. 15 is a diagram showing a fuel injection amount, a throttle valve opening, and an average air-fuel ratio in a combustion chamber.
FIG. 16 NO_xIt is a time chart which shows discharge control.
FIG. 17 is a flowchart for performing injection control.
FIG. 18 is a flowchart for performing injection control.
FIG. 19_xIt is a flowchart for controlling a release flag.
FIG. 20 is a flowchart for performing injection control.
FIG. 21 is a diagram illustrating NO for performing rich processing I;_xIt is a time chart which shows discharge control.
FIG. 22 is a flowchart for performing a lynching process I;
FIG. 23_xIt is a figure showing a map of an amount of release.
FIG. 24 is a diagram showing another embodiment for performing the rich process I;_xIt is a time chart of release control.
FIG. 25 is a flowchart showing another embodiment for performing the rich process I.
FIG. 26 is a flowchart showing still another embodiment for performing the rich process I.
FIG. 27 is a flowchart showing still another embodiment for performing the rich process I.
FIG. 28 is a diagram showing a still further embodiment for performing the rich process I;_xIt is a time chart of release control.
FIG. 29 is a flowchart showing still another embodiment for performing the rich process I.
FIG. 30 is a flowchart showing still another embodiment for performing a rich process.
FIG. 31 is a diagram showing additional fuel injection.
FIG. 32 is a diagram showing a still further embodiment for performing the rich process I;_xIt is a time chart of release control.
FIG. 33 is a flowchart showing still another embodiment for performing the rich process I.
FIG. 34: NO for performing rich processing II_xIt is a time chart which shows discharge control.
FIG. 35 is a flowchart for performing a rich process II.
FIG. 36: NO showing another embodiment for performing lynching process II_xIt is a time chart of release control.
FIG. 37 is a flowchart showing another embodiment for performing the rich process II.
FIG. 38 is a flowchart showing still another embodiment for performing the rich process II.
FIG. 39 is a diagram showing a still further embodiment for performing rich processing III._xIt is a time chart of release control.
FIG. 40 is a flowchart showing still another embodiment for performing the rich process III.
FIG. 41 is a sectional plan view of a cylinder head showing another embodiment.
FIG. 42 is a diagram showing a fuel injection amount.
FIG. 43: NO for performing rich processing I_xIt is a time chart which shows discharge control.
FIG. 44 is a flowchart for performing a rich process I.
FIG. 45: NO for performing rich processing II_xIt is a time chart which shows discharge control.
FIG. 46 is a flowchart for performing a rich process II.
FIG. 47: NO for performing rich processing III_xIt is a time chart which shows discharge control.
FIG. 48 is a flowchart for performing a rich process III.
FIG. 49 is a diagram showing a fuel injection amount.
FIG. 50: NO for performing rich processing I_xIt is a time chart which shows discharge control.
FIG. 51 is a flowchart for performing a rich process I;
FIG. 52: NO for performing rich processing II_xIt is a time chart which shows discharge control.
FIG. 53 NO for performing rich processing II_xIt is a time chart which shows discharge control.
FIG. 54 is a flowchart for performing a rich process II.
FIG. 55: NO for performing rich processing III_xIt is a time chart which shows discharge control.
FIG. 56 is a flowchart for performing a rich process III.
FIG. 57 is an overall view of an internal combustion engine showing another embodiment.
FIG. 58 is a side view schematically showing the torque converter.
FIG. 59 is NO for performing rich processing I;_xIt is a time chart which shows discharge control.
FIG. 60: NO for performing rich processing I_xIt is a time chart which shows discharge control.
FIG. 61 NO_xIt is a flowchart for controlling a release flag.
FIG. 62 is a flowchart for performing a rich process I;
FIG. 63 is a flowchart for performing a rich process I;
FIG. 64_xIt is a flowchart for controlling a release flag.
FIG. 65 is a flowchart showing still another embodiment for performing the rich process I.
FIG. 66 is a flowchart showing still another embodiment for performing the rich process I.
FIG. 67_xIt is a time chart of release control.
FIG. 68_xIt is a flowchart for controlling a release flag.
FIG. 69_x9 is a flowchart illustrating another embodiment for controlling the release flag.
FIG. 70_x9 is a flowchart illustrating yet another embodiment for controlling a release flag.
FIG. 71_x9 is a flowchart illustrating yet another embodiment for controlling a release flag.
FIG. 72_x9 is a flowchart illustrating yet another embodiment for controlling a release flag.
FIG. 73 shows a still further embodiment for performing the rich process._xIt is a time chart of release control.
FIG. 74: NO showing still another embodiment for performing rich processing_xIt is a time chart of release control.
FIG. 75 is a flowchart for controlling a flag.
FIG. 76 is a flowchart for performing injection control.
FIG. 77 is a flowchart for performing injection control.
FIG. 78 is a side sectional view showing another embodiment of the internal combustion engine.
FIG. 79 is a plan sectional view of the cylinder head shown in FIG. 78;
FIG. 80: NO for performing rich processing I_xIt is a time chart which shows discharge control.
FIG. 81 is a flowchart for performing a rich process I;
FIG. 82 is a diagram showing another embodiment for performing the rich process I;_xIt is a time chart of release control.
FIG. 83 is a flowchart showing still another embodiment for performing the rich process I.
FIG. 84 is an overall view showing another embodiment of the internal combustion engine.
[Explanation of symbols]
10. Spark plug
11 ... Fuel injection valve
16 ... Surge tank
24… Exhaust manifold
26 ... NO_xAbsorbent
28 EGR gas passage

Claims (1)

Air-fuel ratio of the exhaust gas flowing absorbs NO _x when the lean, the _the NO _x absorbent when the air-fuel ratio of the inflowing exhaust gas to release NO _x absorbed to become stoichiometric or rich engine exhaust passage In the exhaust gas purification method for an internal combustion engine, a cavity formed on the top surface of the piston at the end of the compression stroke in a lean air-fuel mixture combustion operation state in which the air-fuel mixture is burned while the average air-fuel ratio in the combustion chamber is lean. the NO _x generated at this time along with by injecting fuel toward the inside to form a combustible mixture in the cavity is taken up in _the NO _x absorbent and makes releasing the NO _x from the NO _x absorbent in the lean mixture combustion operating state Therefore, when the average air-fuel ratio in the combustion chamber is to be set to the stoichiometric air-fuel ratio or rich, additional fuel is supplied to the combustion chamber at the end of the compression stroke and also during the intake stroke. The non-combustible mixture formed by the fuel fills the combustion chambers other than the inside of the cavity, and at this time, when the average air-fuel ratio is made lean and the stoichiometric air-fuel ratio or rich, the combustible mixture in the cavity is made. The amount of fuel to be formed is substantially the same, and the amount of fuel injected at the end of the compression stroke is smaller than the amount of additional fuel during the intake stroke so that part of the fuel additionally supplied during the intake stroke forms the incombustible mixture. Weight loss allowed, whereby the lean mixture the average air-fuel ratio theory from lean air-fuel ratio in the combustion chamber while preventing from changing the engine output torque is when releasing the NO _x from the NO _x absorbent when the combustion operating state, or internal combustion which is adapted to reduce the air-fuel ratio variation amount of the combustible mixture formed in the cavity as compared to the decrease in the average air-fuel ratio at this time along with lowering rich Exhaust gas purifying method of the function.

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