JP3633295B2 - Exhaust gas purification device for lean combustion internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly, to NO in exhaust gas when the air-fuel ratio of exhaust gas flowing in is lean._XNO absorbed when the oxygen concentration in the exhaust gas_XNO release_XThe present invention relates to an exhaust emission control device for a lean internal combustion engine equipped with an occlusion reduction catalyst.
[0002]
[Prior art]
NO in exhaust when exhaust air-fuel ratio is lean_X(Nitrogen oxide) absorbed, NO absorbed when the oxygen concentration in the inflowing exhaust gas decreases_XNO release_XOcclusion reduction catalysts are known.
This kind of NO_XAs an example of an exhaust gas purification apparatus using an occlusion reduction catalyst, for example, there is one described in Japanese Patent Registration No. 2600492. The exhaust purification device of the above-mentioned patent has NO in an exhaust passage of an engine that performs lean air-fuel ratio operation._XAn NOx storage reduction catalyst is installed and NO during the lean air-fuel ratio operation of the engine._XNO in exhaust gas to storage reduction catalyst_XAbsorbs NO_XNO of storage reduction catalyst_XBy performing a rich spike operation in which the engine is operated at an air / fuel ratio below the stoichiometric air / fuel ratio for a short time (ie, rich air / fuel ratio) when the amount of absorption increases, NO_XNO absorbed from the storage reduction catalyst_XAs well as released NO_XReduce and purify. That is, when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio, the oxygen concentration in the exhaust gas rapidly decreases as compared with the exhaust gas having an air-fuel ratio larger than the stoichiometric air-fuel ratio (lean air-fuel ratio), and unburned HC, CO in the exhaust gas. The amount of ingredients increases rapidly. Therefore, when the engine operating air-fuel ratio is switched to the rich air-fuel ratio by the rich spike operation, NO_XThe air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst changes from the lean air-fuel ratio to the rich air-fuel ratio, and NO decreases due to the decrease in the oxygen concentration in the exhaust gas._XNO from the storage reduction catalyst_XIs released. Further, as described above, the rich air-fuel ratio exhaust gas contains a relatively large amount of unburned HC and CO components._XNO released from the storage reduction catalyst_XReacts with unburned HC and CO components in the exhaust and is reduced.
[0003]
[Problems to be solved by the invention]
According to the exhaust purification device described in the above-mentioned Patent Registration No. 2600602, NO generated during engine lean air-fuel ratio operation_XNO_XIt is absorbed by the storage reduction catalyst and NO by rich spike operation_XNO from the storage reduction catalyst_XAre released and reduced and purified at the same time.
[0004]
However, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst decreases (changes in the rich air-fuel ratio direction), even if the air-fuel ratio itself is lean, NO_XNO from the storage reduction catalyst_XIs released and NO remains unpurified_XIt has been found that there are cases in which it flows out downstream of the storage reduction catalyst.
As described above, when the exhaust air-fuel ratio changes within the range of the lean air-fuel ratio, the NO_XSpontaneous release (in the following description, NO due to rich spikes, etc._XNO from storage reduction catalyst_XIn order to distinguish it from the intentional release of NO, NO due to the change in the air-fuel ratio within this lean air-fuel ratio range_XNO from storage reduction catalyst_XThis release is called “spontaneous release”. ) Is not fully understood, but NO_XNO of storage reduction catalyst_XStorage capacity (maximum NO_XIt is considered that the cause is that the amount of occlusion changes with the air-fuel ratio.
[0005]
NO_XNO of storage reduction catalyst_XThe storage capacity is affected by the exhaust air / fuel ratio flowing in, and in a weak lean air / fuel ratio region that is relatively close to the stoichiometric air / fuel ratio (for example, a region from the stoichiometric air fuel ratio to the air / fuel ratio of about 20), NO is stored._XIt has been found that the storage capacity decreases with the air / fuel ratio. 4 is NO_XNO of storage reduction catalyst_XStorage capacity (maximum NO_XIt is a graph explaining the relationship with the inflow exhaust air fuel ratio of (occlusion amount). As shown in FIG._XNO of storage reduction catalyst_XThe storage capacity becomes substantially constant regardless of the air-fuel ratio in the region where the air-fuel ratio is 20 or more, but decreases in the region where the air-fuel ratio is 20 or less as the exhaust air-fuel ratio decreases (approaching the stoichiometric air-fuel ratio). It becomes 0 at the fuel ratio.
[0006]
For this reason, NO_XMaximum NO in the lean air-fuel ratio range where the storage reduction catalyst is 20 or more_XNO until near the amount of occlusion_XNO is occluded due to a decrease in occlusion capacity when the air-fuel ratio enters the weak lean air-fuel ratio region of 20 or less from the occluded state._XCan no longer hold all the amount of NO actually occluded_XThe amount of NO corresponding to the difference between the amount and the maximum storage amount_X(Amount shown by hatching in FIG. 4) is spontaneously released. Moreover, since the amount of HC and CO components in the exhaust gas is extremely small in the weak lean air-fuel ratio region, the released NO_XIs NO_XNO on the NOx storage reduction catalyst_XIt will flow out of the storage reduction catalyst.
[0007]
In general, a lean combustion internal combustion engine is often operated in a lean air-fuel ratio range of 20 or more, but in a vehicle engine, when engine output is required for acceleration, climbing, etc., or when negative pressure is required for braking operation For example, the operating air-fuel ratio may be changed from a lean air-fuel ratio to a rich air-fuel ratio. In such a case, the engine operating air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio via an intermediate weak lean air-fuel ratio in order to avoid a sudden change in output torque due to a sudden air-fuel ratio change. For this reason, it is NO when accelerating or climbing._XWhen the exhaust air-fuel ratio flowing into the storage reduction catalyst changes to the rich side, it passes through the weak lean air-fuel ratio region, and NO_XNO from storage reduction catalyst_XSpontaneous release may occur.
[0008]
Further, when the engine operating air-fuel ratio passes through the weak lean air-fuel ratio region, the NO from the engine_XEmissions are also known to increase. FIG. 5 shows the engine operating air-fuel ratio (combustion air-fuel ratio in the engine combustion chamber) and NO in the engine exhaust._XIt is a figure explaining the relationship with a density | concentration. As shown in Fig. 5 curve A, NO in the engine exhaust_XIn the vicinity of the stoichiometric air-fuel ratio, the amount increases as the operating air-fuel ratio rises, reaches a maximum in the region of 20 to 23 at the air-fuel ratio, and thereafter shows a tendency to decrease as the air-fuel ratio increases. NO_XIn an engine having an exhaust purification catalyst, such as a three-way catalyst, in the exhaust passage upstream of the storage reduction catalyst, the NO in the exhaust is exhausted at an air fuel ratio richer than the stoichiometric air fuel ratio._XIn this case, the NO on the downstream side of the exhaust purification catalyst is reduced._XNO in the exhaust gas flowing into the storage reduction catalyst_XAs indicated by curve B in FIG. 5, the concentration becomes substantially zero at an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio, and rapidly increases near the stoichiometric air-fuel ratio to coincide with curve A. Therefore, when the engine is operated in a weak lean air-fuel ratio region (region from the stoichiometric air-fuel ratio to about 20 air-fuel ratio), NO_XNO in the exhaust gas flowing into the storage reduction catalyst_XIs the engine's largest NO_XIncreases to near discharge. On the other hand, as described above, in the weak lean air-fuel ratio region, NO_XNO of storage reduction catalyst_XSince the storage capacity declines, NO is temporarily assumed in this region._XNO of storage reduction catalyst_XThe amount of occlusion is relatively small, NO_XNO from storage reduction catalyst_XEven when there is no spontaneous release of engine, the engine NO._XNOx in the exhaust when the emission increases_XCan not absorb the entire amount of NO in the exhaust_XIs unpurified NO_XIt may flow out of the storage reduction catalyst.
[0009]
In view of the above problems, the present invention provides an engine in which the operating air-fuel ratio changes in the region from the lean air-fuel ratio to the rich air-fuel ratio._XWhen the storage reduction catalyst is applied, NO changes due to changes in engine operating conditions._XUnpurified NO from the storage reduction catalyst_XAn object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can prevent the release of exhaust gas.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, the exhaust of the lean combustion internal combustion engine that changes the operating air-fuel ratio within the air-fuel ratio range from the air-fuel ratio leaner than the stoichiometric air-fuel ratio to the air-fuel ratio richer than the stoichiometric air-fuel ratio as necessary. A purification device, which is disposed in an engine exhaust passage and is NO in exhaust when the air-fuel ratio of inflowing exhaust is lean_XNO absorbed when the oxygen concentration in the exhaust gas_XNO release_XNOx resulting from changes in operating conditions of the storage reduction catalyst and engine_XNO from storage reduction catalyst_XA predicting means for predicting the spontaneous release of NO in advance, and NO_XThe NO from the storage reduction catalyst_XWhen spontaneous release of NO is predicted, NO_XThe air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is adjusted to a rich air-fuel ratio, and before the spontaneous release occurs, NO_XNO absorbed from the storage reduction catalyst_XNO is released and reduced and purified_XNO to perform the discharge operation_XRelease control means, NO_XA release control means, andThe internal combustion engine changes the engine operating state by controlling a throttle valve disposed in the engine intake passage, accelerator means operated by a driver, and controlling the throttle valve opening according to the operation of the accelerator means by the driver. Throttle control means for causing the prediction means to perform the NO based on the operation of the accelerator means. _X Predicting the spontaneous release of NO in advance, the NO _X The release control means is the NO _X NO is released during the period from when the accelerator is operated by the driver until the throttle valve opening is changed by the throttle control means. _X An exhaust emission control device for a lean combustion internal combustion engine that performs a discharge operation is provided.
[0011]
That is, in the invention of claim 1, the NO caused by the change in the engine operating state by the prediction means_XNO from storage reduction catalyst_XIf it is predicted in advance that spontaneous release of NO will occur, NO_XRelease control means is NO_XNO before spontaneous release of_XBy adjusting the exhaust air-fuel ratio flowing into the storage reduction catalyst to a rich air-fuel ratio, NO in advance._XNO from the storage reduction catalyst_XTo reduce and purify. Therefore, after that, the engine operation state is NO_XNO when the spontaneous release of_XThe NOx storage reduction catalyst_XThe amount of occlusion is extremely small. Therefore, even if spontaneous release occurs, NO_XNO of storage reduction catalyst_XThe amount of occlusion remains in a state with sufficient margin._XNO from the storage reduction catalyst_XIs not released. For this reason, unpurified NO_XIs NO_XOutflow from the storage reduction catalyst is prevented.
[0012]
The “change in engine operating state” in the present invention means, for example, that the air-fuel ratio of exhaust at the engine outlet changes, and NO even if the exhaust air-fuel ratio at the engine outlet does not change._XThis includes both cases where the exhaust air-fuel ratio flowing into the storage reduction catalyst changes.
[0013]
Furthermore, in the present inventionThe engine is provided with throttle control means for controlling the throttle valve based on the operation of the accelerator means. For example, the engine is configured like an electronically controlled throttle valve. The predicting means determines that the driving state requested by the driver from the driver's accelerator means operation is NO._XIn the case where it causes spontaneous release of NO in a short time_XExpect spontaneous release to occur. NO_XThe release control means performs NO in a short time from the accelerator operation by the prediction means._XIf it is predicted that spontaneous release will occur, after the accelerator operation, the throttle control means changes the throttle valve opening and before the engine operating state changes, NO_XRelease operation, NO_XNO of storage reduction catalyst_XReduce occlusion. For this reason, the operating state of the engine actually changes and NO_XWhen it becomes a state where spontaneous release of NO occurs, NO_XNO of storage reduction catalyst_XThe amount of occlusion remains in a state with sufficient margin._XNO from the storage reduction catalyst_XIs not released. As a result, unpurified NO_XIs NO_XOutflow from the storage reduction catalyst is prevented.
[0014]
According to the second aspect of the present invention, the exhaust of the lean combustion internal combustion engine that changes the operating air-fuel ratio within an air-fuel ratio range from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio as necessary. A purification device, which is disposed in an engine exhaust passage, and has NO in exhaust when the air-fuel ratio of the inflowing exhaust is lean _X NO absorbed when the oxygen concentration in the exhaust gas _X NO release _X NOx resulting from changes in operating conditions of the storage reduction catalyst and engine _X NO from storage reduction catalyst _X A predicting means for predicting the spontaneous release of NO in advance, and NO _X The NO from the storage reduction catalyst _X When spontaneous release of NO is predicted, NO _X The air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is adjusted to a rich air-fuel ratio, and before the spontaneous release occurs, NO _X NO absorbed from the storage reduction catalyst _X NO is released and reduced and purified _X NO to perform the discharge operation _X A release control means; andThe internal combustion engine changes the engine operating state by controlling a throttle valve disposed in the engine intake passage, an accelerator means operated by a driver, and controlling the throttle valve opening according to the operation of the accelerator means by the driver. Throttle control means for causing the NOx based on the operation of the accelerator means._XPredicting the spontaneous release of NO in advance, the NO_XThe release control means is the NO_XWhen the spontaneous release of NO is predicted_XAn exhaust emission control device for a lean combustion internal combustion engine is provided that prohibits change of the throttle valve opening by the throttle control means until the release operation is completed.
[0015]
That is,Claim 2In this invention, the engine is provided with throttle control means for controlling the throttle valve based on the operation of the accelerator means, and has a configuration such as an electronically controlled throttle valve. The predicting means determines that the driving state requested by the driver from the driver's accelerator means operation is NO._XIn the case where it causes spontaneous release of NO in a short time_XExpect spontaneous release to occur. NO_XThe release control means makes NO in a short time by the prediction means._XIf spontaneous release is predicted, NO immediately after the accelerator operation_XRelease operation and NO_XNO of storage reduction catalyst_XWhile reducing the amount of occlusion, NO_XThe throttle valve opening change by the throttle control means is prohibited until the release operation is completed. For this reason, when the throttle control means changes the throttle valve opening and the engine operating state actually becomes a state where spontaneous release occurs, the NO_XNO of storage reduction catalyst_XThe amount of occlusion remains in a state with sufficient margin._XNO from the storage reduction catalyst_XIs not released. For this reason, unpurified NO_XIs NO_XOutflow from the storage reduction catalyst is prevented.
[0016]
Claim 3According to the invention described in the item (2), the predicting means is the NO when the acceleration of the engine is predicted._XJudgment of spontaneous release ofClaim 1 or 2An exhaust emission control device for a lean combustion internal combustion engine as described in 1) is provided.
That is,Claim 3In the invention of the present invention, the predicting means is NO in a short time when the acceleration of the engine is predicted._XIs determined to occur spontaneously. During engine acceleration, the engine operating air-fuel ratio is changed from the lean air-fuel ratio to the rich air-fuel ratio, and the air-fuel ratio decreases. For this reason, NO_XSpontaneous release is likely to occur due to a decrease in the storage capacity of the storage reduction catalyst. Therefore, NO based on engine acceleration_XBy predicting the spontaneous release of NO_XThe discharge operation can be performed.
[0017]
Claim 4According to the invention described in the above, the NO_XThe release control means operates the engine at a rich air-fuel ratio, thereby_XAdjust the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst to a rich air-fuel ratioClaim 1 or 2An exhaust emission control device for a lean combustion internal combustion engine as described in 1) is provided.
That is,Claim 4In the invention of NO_XThe releasing operation is performed by setting the engine operating air-fuel ratio to a rich air-fuel ratio. NO_XNO from storage reduction catalyst_XNO and reduction and purification are completed in a short time._XDuring the discharge operation, the engine operating air-fuel ratio is changed to the rich air-fuel ratio for a short time.
[0018]
Claim 5According to the invention described in the above, the NO_XThe release control means supplies the engine with fuel that does not contribute to the combustion in the engine combustion chamber, thereby reducing NO._XAdjust the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst to a rich air-fuel ratioClaim 1 or 2An exhaust emission control device for a lean combustion internal combustion engine as described in 1) is provided.
That is,Claim 5In the invention of NO_XThe discharge operation is performed by supplying the engine with fuel that does not contribute to combustion. For example, when secondary fuel injection is performed in which fuel in the combustion chamber is directly injected during the expansion or exhaust stroke of the cylinder from an in-cylinder fuel injection valve that injects fuel directly into the cylinder, or exhaust port fuel injection into the exhaust port of the engine When exhaust port fuel injection is performed by providing a valve, the injected fuel is vaporized without being burned in the combustion chamber, and is mixed into the exhaust as unburned fuel (unburned hydrocarbon). For this reason,The present inventionThen, by supplying fuel that does not contribute to combustion to the engine, the exhaust air-fuel ratio is adjusted to a rich air-fuel ratio independently of the engine operating air-fuel ratio (combustion air-fuel ratio in the combustion chamber), and torque fluctuations are prevented.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to an automobile internal combustion engine.
In FIG. 1, reference numeral 1 denotes an automobile internal combustion engine. In the present embodiment, the engine 1 is a four-cylinder gasoline engine having four cylinders # 1 to # 4, and the fuel injection valves 111 to 114 for injecting fuel directly into the cylinders are provided for the # 1 to # 4 cylinders. Is provided. As will be described later, the internal combustion engine 1 of the present embodiment is a lean burn engine that can be operated at an air fuel ratio higher (lean) than the stoichiometric air fuel ratio.
[0020]
Further, in the present embodiment, the cylinders # 1 to # 4 are grouped into two cylinder groups including two cylinders whose ignition timings are not continuous with each other. (For example, in the embodiment of FIG. 1, the cylinder firing order is 1-3-4-2, and the cylinders # 1 and # 4 and the cylinders # 2 and # 3 each constitute a cylinder group. In addition, the exhaust port of each cylinder is connected to an exhaust manifold for each cylinder group, and is connected to an exhaust passage for each cylinder group. In FIG. 1, reference numeral 21a denotes an exhaust manifold for connecting the exhaust ports of the cylinder group consisting of # 1 and # 4 cylinders to the individual exhaust passage 2a, and 21b denotes the exhaust port of the cylinder group consisting of # 2 and # 4 cylinders to the individual exhaust passage 2b. Is an exhaust manifold connected to In the present embodiment, start catalysts (hereinafter referred to as “SC”) 5a and 5b made of a three-way catalyst are arranged on the individual exhaust passages 2a and 2b, respectively. Further, the individual exhaust passages 2a and 2b merge with the common exhaust passage 2 on the downstream side of the SC.
[0021]
On the common exhaust passage 2, NO, which will be described later, is provided._XAn occlusion reduction catalyst 7 is arranged. In FIG. 1, 29a and 29b indicate air-fuel ratio sensors disposed upstream of the start catalyst 5a and 5b of the individual exhaust passages 2a and 2b, and 31 indicates the NO in the exhaust passage 2._XAn air-fuel ratio sensor disposed at the outlet of the storage reduction catalyst 7. The air-fuel ratio sensors 29a, 29b, and 31 are so-called linear air-fuel ratio sensors that output a voltage signal corresponding to the exhaust air-fuel ratio in a wide air-fuel ratio range.
[0022]
In FIG. 1, the intake ports of cylinders # 1 to # 4 of one engine are connected to a surge tank 10 a via intake manifolds 11 to 14, and the surge tank is connected to a common intake passage 10. Yes. Further, in the present embodiment, a throttle valve 15 is provided on the intake passage 10. The throttle valve 15 of the present embodiment is a so-called electronically controlled throttle valve, which is driven by an actuator 15a of an appropriate type such as a stepper motor and has an opening corresponding to a control signal from an ECU 30 described later.
[0023]
An electronic control unit (ECU) of the engine 1 is indicated by 30 in FIG. In this embodiment, the ECU 30 is a microcomputer having a known configuration including a RAM, a ROM, and a CPU, and performs basic control such as ignition timing control and fuel injection control of the engine 1. In the present embodiment, the ECU 30 performs the basic control described above, and changes the fuel injection mode of the in-cylinder injection valves 111 to 114 in accordance with the engine operating state to change the operating air-fuel ratio of the engine, as will be described later. In addition to controlling etc., NO_XNO is expected when spontaneous release is expected_XRelease operation, NO_XUnpurified NO downstream of the storage reduction catalyst_XIs prevented from leaking.
[0024]
The input port of the ECU 30 includes a signal indicating the exhaust air / fuel ratio at the inlets of the start catalyst 5a and 5b from the air / fuel ratio sensors 29a and 29b, and the NO / NO from the air / fuel ratio sensor 31._XIn addition to a signal representing the exhaust air / fuel ratio at the outlet of the storage reduction catalyst 7 and a signal corresponding to the intake pressure of the engine from an intake pressure sensor 33 provided in an unillustrated engine intake manifold, an engine crankshaft ( A signal corresponding to the engine speed is input from a speed sensor 35 arranged in the vicinity. Furthermore, in the present embodiment, a signal representing the accelerator pedal depression amount (accelerator opening) of the driver is input to an input port of the ECU 30 from an accelerator opening sensor 37 disposed in the vicinity of an accelerator pedal (not shown) of the engine 1. Has been. The output port of the ECU 30 is connected to the fuel injection valves 111 to 114 of each cylinder through a fuel injection circuit (not shown) in order to control the fuel injection amount and fuel injection timing to each cylinder. The opening of the throttle valve 15 is controlled by being connected to the actuator 15b of the valve 15 via a drive circuit (not shown).
[0025]
In the present embodiment, the ECU 30 operates the engine 1 in the following five combustion modes according to the operating state of the engine.
(1) Lean air-fuel ratio stratified combustion (injection once in the compression stroke)
(2) Lean air-fuel ratio homogeneous mixture / stratified combustion (intake stroke / compression stroke twice injection)
(3) Lean air-fuel ratio homogeneous mixture combustion (intake stroke one injection)
(4) Theoretical air-fuel ratio homogeneous mixture combustion (intake stroke one injection)
(5) Rich air-fuel ratio homogeneous mixture combustion (intake stroke one injection)
That is, in the light load operation region of the engine 1, the lean air-fuel ratio stratified combustion (1) is performed. In this state, in-cylinder fuel injection is performed only once in the latter half of the compression stroke of each cylinder, and the injected fuel forms a combustible mixture layer near the cylinder spark plug. Further, the fuel injection amount in this operation state is extremely small, and the air-fuel ratio as a whole in the cylinder is about 25 to 30.
[0026]
Further, when the load increases from the state (1) to the low load operation region, (2) the lean air-fuel ratio homogeneous mixture / stratified combustion is performed. As the engine load increases, the amount of fuel injected into the cylinder increases. However, in the stratified combustion of (1), the fuel injection is performed in the latter half of the compression stroke, so the injection time is limited and the amount of fuel that can be stratified Has its limits. Therefore, in this load region, a target amount of fuel is supplied to the cylinders by injecting in advance into the first half of the intake stroke an amount of fuel that is insufficient only by fuel injection in the latter half of the compression stroke. The fuel injected into the cylinder in the first half of the intake stroke generates a very lean homogeneous mixture by the time of ignition. In the latter half of the compression stroke, further fuel is injected into this extremely lean homogeneous mixture to generate a combustible mixture layer that can be ignited in the vicinity of the spark plug. At the time of ignition, the combustible air-fuel mixture layer starts to burn, and the flame propagates to the surrounding lean air-fuel mixture layer, so that stable combustion is performed. In this state, the amount of fuel supplied by the injection in the intake stroke and the compression stroke is increased from (1), but the overall air-fuel ratio becomes slightly low (for example, about 20 to 30 in the air-fuel ratio).
[0027]
When the engine load further increases, the engine 1 performs the lean air-fuel ratio homogeneous mixture combustion of (3) above. In this state, fuel injection is executed only once in the first half of the intake stroke, and the fuel injection amount is further increased from the above (2). In this state, the homogeneous air-fuel mixture generated in the cylinder has a lean air-fuel ratio that is relatively close to the stoichiometric air-fuel ratio (for example, about 15 to 25 as the air-fuel ratio).
[0028]
When the engine load further increases and the engine high load operation region is reached, the fuel is further increased from the state (3), and the stoichiometric air-fuel ratio homogeneous mixture operation (4) is performed. In this state, a homogeneous air-fuel mixture having a stoichiometric air-fuel ratio is generated in the cylinder, and the engine output increases. When the engine load is further increased and the engine is fully loaded, the fuel injection amount is further increased from the state (4), and the rich air-fuel ratio homogeneous mixture operation (5) is performed. In this state, the air-fuel ratio of the homogeneous mixture generated in the cylinder becomes rich (for example, about 12 to 14 as the air-fuel ratio).
[0029]
In the present embodiment, the optimum operation mode (above (1) to (5)) is set in advance based on experiments or the like according to the accelerator opening (the amount by which the driver depresses the accelerator pedal) and the engine speed. , Stored in the ROM of the ECU 30 as a map using the accelerator opening and the engine speed. During the engine 1 operation, the ECU 30 determines which one of the above operation modes (1) to (5) should be selected based on the accelerator opening detected by the accelerator opening sensor 37 and the engine speed. The fuel injection amount, the fuel injection timing, the number of times, and the throttle valve opening are determined according to the mode.
[0030]
Further, when mode (4) (theoretical air-fuel ratio homogeneous mixture combustion) is selected, the ECU 30 further calculates the fuel injection amount calculated as described above from the air-fuel ratio sensor so that the engine exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio. Air-fuel ratio control for feedback correction is performed based on the outputs of 29a and 29b.
That is, when the mode (1) to (3) (lean air-fuel ratio combustion) is selected, the ECU 30 determines the accelerator based on the map prepared in advance for each mode (1) to (3). The fuel injection amount is determined from the opening degree and the engine speed. When the modes (4) and (5) (theoretical air-fuel ratio or rich air-fuel ratio homogeneous mixture combustion) are selected, the ECU 30 is prepared in advance for each of the modes (4) and (5). Based on the map, the fuel injection amount is set based on the intake pressure detected by the intake pressure sensor 33 and the engine speed.
[0031]
Further, the throttle valve 15 opening is controlled according to the accelerator opening in a region close to full opening in the modes (1) to (3). In this region, the throttle valve opening decreases as the accelerator opening decreases.However, since the throttle valve opening changes, the intake pressure remains substantially constant even when the throttle valve opening changes. Absent.
On the other hand, in modes {circle around (4)} and {circle around (5)}, the throttle valve opening is controlled to an opening substantially equal to the accelerator opening. That is, when the accelerator opening (accelerator pedal depression amount) is 0, the throttle opening is also 0, and when the accelerator opening is 100% (when the accelerator pedal is fully depressed), the throttle opening is also 100% (fully open). Set to
[0032]
As described above, in the engine 1 of the present embodiment, the fuel injection amount is increased as the engine load increases, and the operation mode is changed and the throttle opening is changed according to the fuel injection amount.
Next, the start catalyst 5a, 5b and NO of this embodiment_XThe storage reduction catalyst will be described.
[0033]
The start catalyst (SC) 5a, 5b uses a carrier such as cordierite formed in a honeycomb shape, and a thin coating of alumina is formed on the surface of the carrier, and platinum Pt, palladium Pd, rhodium Rh, etc. are formed on the alumina layer. It is comprised as a three-way catalyst which supported the noble metal catalyst component. The three-way catalyst is near HC, CO, NO near the stoichiometric air-fuel ratio._XThese three components are purified with high efficiency. The three way catalyst is NO when the air-fuel ratio of the inflowing exhaust gas becomes higher than the stoichiometric air-fuel ratio._XBecause the reduction capacity of the engine 1 is reduced, the NO in the exhaust when the engine 1 is operated with a lean air-fuel ratio is reduced._XCannot be sufficiently purified.
[0034]
NO of this embodiment_XThe occlusion reduction catalyst 7 uses, for example, alumina as a carrier, and on this carrier, for example, an alkali metal such as potassium K, sodium Na 2, lithium Li 2, cesium Cs, an alkaline earth such as barium Ba 2, calcium Ca 2, lanthanum La 2, cerium. It carries at least one component selected from rare earths such as Ce and yttrium Y and a noble metal such as platinum Pt. NO_XThe NOx storage reduction catalyst is used when the air-fuel ratio of the inflowing exhaust gas is lean._X(NO₂, NO) to nitrate ion NO₃ ⁻NO is absorbed when the inflowing exhaust gas becomes rich_XNO release_XPerforms absorption and release action.
[0035]
This absorption / release mechanism will be described below using platinum Pt and barium Ba as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
When the oxygen concentration in the inflowing exhaust gas increases (that is, when the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio), these oxygens become O on the platinum Pt.₂ ⁻Or O^2-NO in the exhaust_XIs O on platinum Pt₂ ⁻Or O^2-To react with NO₂Is generated. In addition, NO in inflow exhaust₂And NO produced by the above₂Is absorbed in the absorbent while being further oxidized on platinum Pt and combined with barium oxide BaO and nitrate ions NO.₃ ⁻Diffuses into the absorbent in the form of For this reason, NO in the exhaust gas in a lean atmosphere_XIs NO_XIt becomes absorbed in the form of nitrate in the absorbent.
[0036]
Further, when the oxygen concentration in the inflowing exhaust gas is greatly reduced (that is, when the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio), NO on the platinum Pt is increased.₂Since the production amount decreases, the reaction proceeds in the reverse direction, and nitrate ion NO in the absorbent₃ ⁻Is NO₂From the absorbent in the form of In this case, reducing components such as CO, HC, CO₂If there are components such as NO on the platinum Pt,₂Is reduced.
[0037]
In the present embodiment, the engine 1 capable of lean air-fuel ratio operation is used, and when the engine 1 is operated at the lean air-fuel ratio, NO_XThe storage reduction catalyst is NO in the exhaust gas flowing in._XTo absorb. Further, when the engine 1 is operated at a rich air-fuel ratio, NO_XThe NOx storage reduction catalyst 7 has absorbed NO._XRelease, reduce and purify. In this embodiment, NO during lean air-fuel ratio operation._XNO absorbed by the storage reduction catalyst 7_XWhen the amount increases, a rich spike operation is performed in which the engine air-fuel ratio is switched from a lean air-fuel ratio to a rich air-fuel ratio for a short time._XNO from storage reduction catalyst_XRelease and reduction purification (NO_XThe regeneration of the storage reduction catalyst is performed.
[0038]
In this embodiment, the ECU 30 is NO_XNO by increasing or decreasing the value of counter CNOX_XNO absorbed and stored by the storage reduction catalyst 7_XEstimate the amount. NO_XNO absorbed by the storage reduction catalyst 7 per unit time_XAmount of NO_XNO in exhaust flowing into the storage reduction catalyst per unit time_XQuantity, ie NO generated per unit time in engine 1_XIt is proportional to the amount. On the other hand, NO generated per unit time in the engine_XIs determined by the amount of fuel supplied to the engine, air-fuel ratio, exhaust flow rate, etc., so if the engine operating conditions are determined, NO_XNO absorbed by the storage reduction catalyst_XYou can know the amount. In the present embodiment, the engine operation conditions (accelerator opening, engine speed, intake air amount, intake air pressure, air fuel ratio, fuel supply amount, etc.) are changed in advance, and the NO generated by the engine per unit time._XMeasure the amount, NO_XNO absorbed by the storage reduction catalyst 7 per unit time_XThe amount is stored in the ROM of the ECU 30 in the form of a numerical map using, for example, the engine load (fuel injection amount) and the engine speed. The ECU 30 uses this map to determine NO per unit time from the engine load (fuel injection amount) and the engine speed at regular intervals (every unit time)._XNO absorbed by the storage reduction catalyst_XCalculate the amount, NO_XThe value of the counter CNOX is set to this NO_XIncrease the amount absorbed. This makes NO_XThe value of the counter CNOX is always NO_XNO absorbed by the storage reduction catalyst 7_XTo represent the amount of. The ECU 30 performs the above NO during the lean air-fuel ratio operation of the engine._XWhen the value of the counter CNOX increases to a predetermined value or more, the engine is operated for a short time (for example, about 0.5 to 1 second) in the above-described mode (4) or (5) (theoretical air-fuel ratio or rich air-fuel ratio homogeneous mixture). Rich spike operation that operates with combustion). As a result, NO_XNO absorbed from the storage reduction catalyst_XIs released and reduced and purified. Note that the time required to keep the exhaust air-fuel ratio rich with a rich spike is NO in detail._XIt is determined by experiments or the like based on the type and capacity of the storage reduction catalyst. Also, execute rich spike and NO_XNO from the storage reduction catalyst_XNO is released and reduced and purified_XThe value of the counter CNOX is reset to 0. Like this, NO_XNO of storage reduction catalyst 7_XBy performing rich spike according to the amount of absorption, NO_XThe storage reduction catalyst 7 is properly regenerated, and NO_XNO absorbed by the storage reduction catalyst_XSaturation is prevented.
[0039]
However, in an engine operated in a wide air-fuel ratio range as in this embodiment, for example, when acceleration is performed from a lean air-fuel ratio (mode (1), (2)) of 20 or more, the engine load As a result, the operating air-fuel ratio is switched from the lean air-fuel ratio to the weak lean air-fuel ratio or the rich air-fuel ratio. As described above, when the engine operating air-fuel ratio is switched from the lean air-fuel ratio (mode (1), (2)) to the weak lean air-fuel ratio (mode (3)) during acceleration,_XNO of storage reduction catalyst_XNO occlusion decreases_XOccurs spontaneously. In addition, when the air-fuel ratio is switched from the lean air-fuel ratio (mode (1), (2)) to the rich air-fuel ratio (mode (3) or (4)) at the time of sudden acceleration or the like, due to a sudden change in the air-fuel ratio. In order to avoid sudden torque changes, the engine spends several revolutions to change from mode (1) (lean air-fuel ratio stratified combustion (injection once in the compression stroke)) to mode (2) (lean air-fuel ratio homogeneous mixture / stratified combustion ( (5) (Rich air-fuel ratio homogeneous mixture combustion (intake stroke) after operation mode of intake stroke / compression stroke twice injection) and mode (3) (lean air-fuel ratio homogeneous mixture combustion (intake stroke once injection)) Therefore, when the engine accelerates, the engine operating air-fuel ratio always changes to the rich direction._XIt passes through a weak lean air-fuel ratio region (20 or less in air-fuel ratio) in which the storage capacity of the storage reduction catalyst decreases. In this area, NO_XNO stored in the storage reduction catalyst_XOf which, the amount of NO that exceeds the maximum storage amount_XIs NO_XAlthough it is spontaneously released from the storage reduction catalyst, it is released because the exhaust air-fuel ratio is lean._XIs not reduced and remains unpurified NO_XIn some cases, it flows out downstream of the storage reduction catalyst. Further, as described with reference to FIG. 5, NO exhausted from the engine in the weak lean air-fuel ratio region._XSince the amount also increases, when the engine operating air-fuel ratio is changed from the lean air-fuel ratio to the weak lean air-fuel ratio, NO_XNO released from the storage reduction catalyst_XAs well as NO emissions from institutions_XNO unpurified_XThere is a risk of flowing out downstream of the storage reduction catalyst.
[0040]
Therefore, in the embodiment described below, when the air-fuel ratio passes through the weak lean air-fuel ratio region due to engine acceleration or the like, or the operating air-fuel ratio may change in the rich direction within the weak lean air-fuel ratio region, When the engine operating air-fuel ratio actually enters the weak lean air-fuel ratio region, NO_XNO from storage reduction catalyst_XBefore spontaneous release of NO occurs_XAdjust the exhaust air-fuel ratio flowing into the storage reduction catalyst to a rich air-fuel ratio and force NO_XNO from the storage reduction catalyst_XIs released to reduce and purify. Thus, NO in advance_XNO absorbed from the storage reduction catalyst_XNO is released when the engine operating air-fuel ratio is actually in the weak lean air-fuel ratio region._XNO that should be released spontaneously to the storage reduction catalyst_XIs not occluded. For this reason, even during the passage of the weak lean air-fuel ratio region, NO_XNO from storage reduction catalyst_XDoes not occur spontaneously. NO_XIn the state where the occlusion amount is reduced to almost zero, even in the weak lean air-fuel ratio region, NO_XThere is a sufficient margin in the storage capacity of the storage reduction catalyst. Therefore, a relatively large amount of NO from the engine in the weak lean air-fuel ratio region._XEven if NO is discharged, NO discharged_XThe total amount of NO_XUnpurified NO, now absorbed by the storage reduction catalyst_XIs NO_XA situation of flowing out downstream of the storage reduction catalyst is prevented.
[0041]
The above NO_XNO to prevent spontaneous release_XAn embodiment of the release control operation will be described.
(1) First embodiment
In the present embodiment, the ECU 30 determines that the driver is requesting acceleration based on the rate of increase in the accelerator opening. When the driver requests acceleration, acceleration is executed in a short time and the air-fuel ratio changes in the rich direction. However, actually, in the electronically controlled throttle valve as in this embodiment, the throttle valve opening does not change immediately due to the change in the accelerator opening, but the throttle valve opening actually starts changing from the change in the accelerator opening. Slight delay time T_dOccurs.
[0042]
That is, when the accelerator opening changes, the ECU 30 calculates a target throttle valve opening according to the accelerator opening, and outputs a control signal to the actuator 15 b of the throttle valve 15 to drive the throttle valve 15. For this reason, the time required for calculating the throttle opening and the time from the input of the control signal to the start of the operation of the actuator 15b from the change of the accelerator opening to the actual operation of the throttle valve, and further the throttle It takes time such as time required for the torque of the actuator 15b to increase until the reaction force due to friction or the like of each part of the valve mechanism is overcome, and the sum of these times is the delay time T._dIt becomes. Usually T_dIs a time from several tens of milliseconds to about 200 milliseconds. In the present embodiment, the delay time T after the accelerator opening starts changing._dUntil a period of time elapses, a predetermined amount of fuel is simultaneously injected into all the cylinders. This fuel injection is an asynchronous fuel injection performed independently of the stroke of each cylinder. Further, the fuel injection amount in the asynchronous fuel injection is set so that the exhaust air-fuel ratio from each cylinder is richer than the stoichiometric air-fuel ratio. Thereby, in some cylinders of the engine, fuel by asynchronous fuel injection is supplied during the intake or compression stroke of the cylinder. In this case, the combustion air-fuel ratio in the combustion chamber becomes the rich air-fuel ratio, and the exhaust with the rich air-fuel ratio is discharged from the cylinder. In other cylinders, fuel is supplied by asynchronous fuel injection during the expansion or exhaust stroke of the cylinder. In this case, since asynchronous fuel injection becomes secondary fuel injection, the injected fuel is discharged to the exhaust passage without contributing to combustion, and the combustion air-fuel ratio in the combustion chamber is not affected by the asynchronous fuel injection. For this reason, NO_XA rich air-fuel ratio exhaust gas containing a large amount of unburned hydrocarbons will reach the storage reduction catalyst, and in a short time NO_XNO from the storage reduction catalyst_XIs released and reduced and purified. Therefore, the delay time T_dWhen the throttle valve opening actually starts changing after_XAlmost all of the NO from the storage reduction catalyst_XHas been released and NO due to changes in throttle opening_XNO even when the exhaust air-fuel ratio flowing into the storage reduction catalyst is in the weak lean air-fuel ratio region_XDoes not occur spontaneously. NO_XThe NOx discharged from the engine in the weak lean air-fuel ratio region because the NOx storage reduction catalyst is in a state of almost zero storage._XIs NO_XIt is absorbed by the storage reduction catalyst and does not flow downstream.
[0043]
FIG. 2 shows the above NO._XIt is a flowchart explaining discharge | release control operation. This operation is performed by a routine executed by the ECU 30 at regular intervals.
When the operation of FIG. 2 starts, it is determined in step 201 whether or not the change ΔACCP in the accelerator opening from the previous routine execution is greater than a predetermined value α. If ΔACCP ≦ α, the accelerator pedal depression amount does not increase greatly, and it is considered that acceleration is not currently requested by the driver. Therefore, this operation sets the value of the time counter CT described later in step 215. Exit immediately after setting to 0. On the other hand, if ΔACCP> α, it means that the driver has depressed the accelerator pedal at a certain speed or higher, and it is determined that the driver is requesting acceleration. For this reason, NO_XSince there is a possibility that the discharge operation needs to be performed, the process proceeds to step 203, and the current NO_XNO stored in the storage reduction catalyst_XNO representing quantity_XIt is determined whether or not the value of the counter CNOX exceeds a predetermined value β. β is practically NO_XNO of storage reduction catalyst_XIt is a value of CNOX that can be considered that the occlusion amount is almost zero. NO if CNOX ≦ β_XSince it is not necessary to perform the discharge operation, this operation is immediately terminated after executing Step 215.
[0044]
If CNOX> β in step 203, then in step 205, the current NO._XIt is determined based on the value of the execution permission flag XAREA whether the conditions under which the discharge operation can be performed are satisfied. For example, when the engine is idling, the engine speed may fluctuate significantly when asynchronous injection is performed. The ECU 30 sets a value of the execution permission flag XAREA to 0 by a routine that is separately executed, for example, when the engine is in an idling operation._XProhibit execution of release operation. Therefore, if XAREA ≠ 1 in step 205, the operation is terminated immediately after execution of step 215. On the other hand, if XAREA = 1 in step 205, that is, the current NO._XIf it is possible to execute the discharge operation, NO in steps 207 to 213_XA release operation is performed.
[0045]
That is, in step 207, the value of the time counter CT is set to the predetermined value CT._dIt is determined whether it is smaller than CT <CT_dIf NO, NO at step 209_XThe fuel injection amount for the release operation is calculated, and immediately, asynchronous injection of the amount of fuel calculated for all the cylinders in step 211 is executed. Then, after the asynchronous injection is executed, the value of the time counter CT is increased by 1 in step 213, and this operation ends.
[0046]
Since the time counter CT is always reset to 0 in step 215 when ΔACCP ≦ α in step 201, the value of CT in step 213 represents the number of operation executions after ΔACCP> α in step 201. It becomes. Further, since this operation is executed at regular time intervals, the value of the counter CT corresponds to the elapsed time after the acceleration request is made (after ΔACCP> α). Therefore, in the present embodiment, the predetermined value CT is obtained after an acceleration request is made._dAsynchronous injection is executed every time the operation is executed until the time elapses. CT_dIs the delay time T until the throttle valve opening starts to change._dIs set to a value corresponding to. That is, by performing the operation of FIG. 2, NO is detected after the driver's acceleration request is detected until the throttle valve opening starts to change in response to the acceleration request._XThe release operation will be performed, and the engine operating state will change due to the change in the throttle opening._XNO until the spontaneous release of_XNO stored in the storage reduction catalyst_XAlmost the entire amount is released and reduced and purified. For this reason, according to this embodiment, NO changes due to changes in the engine operating state._XUnpurified NO downstream of the storage reduction catalyst_XIs prevented from leaking.
[0047]
(2) Second embodiment
Next, a second embodiment of the present invention will be described. In the first embodiment, NO is detected during the delay time from when the driver requests acceleration until the throttle valve opening starts to change._XIn the present embodiment, when a driver's acceleration request is detected, first, NO is performed._XThe difference from the first embodiment is that the release operation is executed and the change of the throttle valve opening is permitted after the release operation is completed. As a result, NO_XSince the engine operating state does not change until after the discharge operation has been executed, it is ensured that the NO changes when the operating state changes._XNO of storage reduction catalyst_XIt becomes possible to make the occlusion amount substantially zero.
[0048]
FIG. 3 shows the above NO._XIt is a flowchart explaining discharge | release control operation. This operation is performed by a routine executed by the ECU 30 at regular intervals.
When the operation of FIG. 3 starts, it is determined in step 301 whether or not there is a driver's acceleration request, and in step 303 the current NO._XNO of storage reduction catalyst_XWhether or not the occlusion amount is equal to or greater than the predetermined value β, step 305 is_XIt is determined whether or not the discharge operation can be executed. Steps 301 to 305 are the same operations as steps 201 to 205 in FIG.
[0049]
If at least one of the conditions in steps 301 to 305 is not satisfied, the value of a flag XINJ, which will be described later, is reset to 0 in step 315, and this operation executes a throttle valve opening control operation in step 317 End after. In step 317, the ECU 30 calculates the target opening of the throttle valve 15 from a predetermined relationship based on the accelerator opening, and drives the actuator 15b to control the throttle valve 15 opening to the target opening.
[0050]
If all the conditions in steps 301 to 305 are satisfied, it is determined in step 307 whether or not the value of the flag XINJ is set to 1, and if XINJ = 1, step 317 is executed.
If XINJ ≠ 1 at step 307, then NO at step 309._XThe fuel injection amount for the release operation is calculated, and immediately after that, asynchronous fuel injection for all cylinders is executed in step 311. Steps 309 and 311 are the same operations as steps 209 and 211 in FIG. When asynchronous injection is completed as described above, in step 313, the value of the flag XINJ described above is set to 1, and the current operation ends.
[0051]
In this embodiment, when the acceleration request is not detected (when ΔACCP ≦ α in step 301), the value of the flag XINJ is always reset to 0 in step 315. Therefore, when an acceleration request (ΔACCP> α in step 301) is first detected, asynchronous fuel injection in steps 309 and 311 is executed in step 307 because XINJ = 0, and this asynchronous fuel injection is executed. Until this is done, the throttle valve opening control in step 317 is not executed. In addition, when asynchronous fuel injection is executed once after the acceleration request is detected, the value of the flag XINJ is set to 1 in step 313. Therefore, step 317 is executed immediately after step 307 from the next operation. The throttle valve opening degree control is executed.
[0052]
That is, in this embodiment, when there is a driver's acceleration request, first, asynchronous fuel injection is executed once for all cylinders (steps 309 to 313) and NO._XRelease operation, NO_XThe throttle opening control operation is started only after the releasing operation is completed (step 313). This ensures that when the engine operating state changes, NO_XBecause the discharge operation is complete, NO_XUnpurified NO downstream of the storage reduction catalyst_XIs reliably prevented from flowing out.
[0053]
In the first and second embodiments, NO is used._XAsynchronous fuel injection is performed during the release operation so that the combustion air-fuel ratio of some cylinders is made richer than the theoretical air-fuel ratio, and fuel that does not contribute to combustion is supplied to other cylinders. For this reason, compared with the case where the combustion air-fuel ratios of all the cylinders are made richer than the stoichiometric air-fuel ratio, the increase in the output torque of the engine as a whole is reduced and the occurrence of torque shock is prevented.
[0054]
Further, in an engine provided with an exhaust port fuel injection valve, exhaust port fuel injection may be executed instead of the asynchronous fuel injection shown in FIGS. In this case, since the fuel injected into the exhaust port does not contribute to combustion, the engine combustion air-fuel ratio is not affected in all cylinders, and fluctuations in output torque are completely prevented.
Further, NO in step 209 in FIG. 2 and step 309 in FIG._XThe fuel injection amount for the discharge operation is NO_XAlthough it may be a constant value so that the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst becomes a sufficiently rich air-fuel ratio, it may be calculated according to the engine operating state.
[0055]
For example, if the engine operating air-fuel ratio is relatively low, NO_XEven if the fuel injection amount for the release operation is relatively small, the exhaust air-fuel ratio can be made sufficiently rich. For this reason, NO_XThe fuel injection amount for the release operation may be set according to the engine operating air-fuel ratio.
NO_XA large amount of NO in the storage reduction catalyst_XNO is stored, NO_XNO released by the discharge operation_XA large amount of HC (hydrocarbon) is required to purify the water. For this reason, NO_XThe fuel injection amount for the discharge operation is NO_XNO of storage reduction catalyst_XStorage amount (NO_XIt may be set according to the value of the counter CNOX.
[0056]
【The invention's effect】
According to the invention described in each claim, the engine in which the operating air-fuel ratio changes in the region from the stoichiometric air-fuel ratio to the lean air-fuel ratio is NO._XWhen the storage reduction catalyst is applied, NO changes due to changes in engine operating conditions._XUnpurified NO from the storage reduction catalyst_XThis has the common effect of preventing the release of.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to an automobile internal combustion engine.
FIG. 2 shows NO of the present invention._XIt is a flowchart explaining one Embodiment of discharge | release control operation.
FIG. 3 shows NO of the present invention._XIt is a flowchart explaining another embodiment of discharge | release control operation.
FIG. 4 NO_XNO of storage reduction catalyst_XIt is a figure explaining the change tendency by the air fuel ratio of storage capacity.
FIG. 5: NO of internal combustion engine_XIt is a figure explaining the change tendency by the operating air fuel ratio of discharge | emission amount.
[Explanation of symbols]
1. Internal combustion engine
2 ... Exhaust passage
7 ... NO_XOcclusion reduction catalyst
15 ... Throttle valve
29a, 29b, 31 ... air-fuel ratio sensor
30 ... Electronic control unit (ECU)
37 ... Accelerator opening sensor

Claims (5)

An exhaust emission control device for a lean combustion internal combustion engine that changes the operating air-fuel ratio in an air-fuel ratio range from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio as required,
Disposed in the engine exhaust passage, and _the NO _X storage reduction catalyst air-fuel ratio of the exhaust gas flowing into the oxygen concentration in the exhaust gas to absorb flowing the NO _X in the exhaust gas when the lean releasing NO _X absorbed to decrease ,
A predicting means for predicting in advance that spontaneous release of NO _X from the NO _X storage reduction catalyst due to a change in engine operating state occurs;
When the spontaneous emission of the NO _X from _the NO _X storage reduction catalyst has been predicted by the predicting means to adjust the air-fuel ratio of the exhaust gas flowing to the NO _X occluding and reducing catalyst to a rich air-fuel ratio, before the spontaneous emission occurs and NO _X emission control means for NO _X release operation to release NO _X absorbed from _the NO _X storage reduction catalyst reduces and purifies the,
In addition,
The internal combustion engine changes the engine operating state by controlling the throttle valve opening according to the throttle valve disposed in the engine intake passage, the accelerator means operated by the driver, and the operation of the accelerator means by the driver. Throttle control means for causing
The predicting means predicts in advance that spontaneous release of the NO _x will occur based on the operation of the accelerator means ,
When the the NO _X release controlling means predicted spontaneous emission of the NO _X, after the operation of the accelerator means by the driver, the until the throttle valve opening is changed by said throttle control means NO _X An exhaust emission control device for a lean combustion internal combustion engine that performs a discharge operation. An exhaust emission control device for a lean combustion internal combustion engine that changes the operating air-fuel ratio in an air-fuel ratio range from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio as required,
NO in the exhaust when the air-fuel ratio of the exhaust flowing into the engine exhaust passage is lean _X NO absorbed when the oxygen concentration in the exhaust gas _X NO release _X An occlusion reduction catalyst;
NO resulting from changes in engine operating conditions _X NO from storage reduction catalyst _X A predictive means for predicting in advance that spontaneous release of
NO by the prediction means _X The NO from the storage reduction catalyst _X When spontaneous release of NO is predicted, NO _X The air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is adjusted to a rich air-fuel ratio, and before the spontaneous release occurs, NO _X NO absorbed from the storage reduction catalyst _X NO is released and reduced and purified _X NO to perform the discharge operation _X Release control means;
In addition,
The internal combustion engine changes the engine operating state by controlling the throttle valve opening according to the throttle valve disposed in the engine intake passage, the accelerator means operated by the driver, and the operation of the accelerator means by the driver. Throttle control means for causing
The prediction means is based on the operation of the accelerator means and the NO _X Predicting the spontaneous release of
NO _X The release control means is the NO _X When the spontaneous release of NO is predicted _X An exhaust emission control device for a lean combustion internal combustion engine, which prohibits a change of the throttle valve opening by the throttle control means until a release operation is completed. The exhaust emission control device of a lean burn internal combustion engine according to claim 1 or 2, wherein the prediction means determines that the spontaneous release of the NO _x occurs when the acceleration of the engine is predicted . NO _X The release control means operates the engine at a rich air-fuel ratio, thereby _X The exhaust gas purification apparatus for a lean combustion internal combustion engine according to claim 1 or 2, wherein the air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst is adjusted to a rich air-fuel ratio. The NO _x release control means adjusts the air- fuel ratio of the exhaust gas flowing into the NO _x storage reduction catalyst to a rich air- fuel ratio by supplying the engine with fuel that does not contribute to combustion in the engine combustion chamber. 2. An exhaust emission control device for a lean burn internal combustion engine .

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