JP2007077995A - Exhaust emission control device for lean burn internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably eliminate nitrogen oxide stored in a nitrogen oxide storage/reduction catalyst without causing instable combustion of a mixture while utilizing evaporating fuel generated in a fuel tank for a lean burn internal combustion engine. <P>SOLUTION: The exhaust emission control device comprises a gas condition discriminating means for discriminating the condition of evaporating fuel gas to be supplied to an intake system for the lean burn internal combustion engine, and an exhaust gas condition control means for selectively controlling a fuel injection valve or a gas supply means depending on the condition of the evaporating fuel gas at a timing for eliminating and releasing nitrogen oxide stored in the nitrogen oxide storage/reduction catalyst provided in an exhaust system for the lean burn internal combustion engine to keep the air/fuel ratio of exhaust gas flowing in the nitrogen oxide storage/reduction catalyst into a desired condition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for a lean combustion internal combustion engine capable of combusting an air-fuel mixture in an oxygen-excess state, and more particularly to an exhaust emission purification device for a lean combustion internal combustion engine having a nitrogen oxide storage reduction catalyst in an exhaust system.

  In an internal combustion engine such as an automobile, a lean combustion internal combustion engine capable of combusting an air / fuel ratio (oxygen excess state) higher than the stoichiometric air / fuel ratio is being developed in order to reduce fuel consumption. As such a lean combustion internal combustion engine, an intake port formed so that an air-fuel mixture flowing into a combustion chamber generates a longitudinal vortex flow (tumble flow), a swirl flow (swirl flow), and the like, and its injection hole are the intake ports. 2. Description of the Related Art A so-called intake port injection type lean combustion internal combustion engine that includes a fuel injection valve mounted so as to face the engine is known.

  In a lean combustion internal combustion engine of the intake port injection type, fuel is injected from the fuel injection valve from the late stage of the exhaust stroke to the early stage of the intake stroke, and the fuel and fresh air are uniformly mixed in the intake port and flow into the combustion chamber. At that time, the air-fuel mixture forms a tumble flow or a swirl flow. When the air-fuel mixture is ignited by the spark plug, the flame in the vicinity of the spark plug is diffused throughout the combustion chamber by the tumble flow or the swirl flow, and combustion is promoted even in a lean air-fuel mixture. It is.

  By the way, the lean combustion internal combustion engine of the intake port injection type introduces an air-fuel mixture in which the fuel and the fresh air are mixed almost uniformly into the combustion chamber. Therefore, the fuel concentration is reduced by reducing the fuel injection amount. As a result, the fuel concentration in the vicinity of the spark plug becomes lean, and ignition by the spark plug becomes impossible.

  On the other hand, the development of an in-cylinder injection type lean combustion internal combustion engine in which a fuel injection valve is attached so that its injection hole faces the combustion chamber is underway. In a cylinder injection internal combustion engine, fresh air is introduced into a combustion chamber in an intake stroke, and then fuel is injected from the fuel injection valve in a compression stroke, so that a combustible air-fuel mixture is formed only in the vicinity of a spark plug. That is, the combustion chamber is in a so-called stratified state in which the vicinity of the spark plug is a combustible air-fuel mixture layer and the other region is an air layer.

  Thus, according to the lean injection internal combustion engine of the cylinder injection type, the fuel concentration in the entire combustion chamber can be made leaner than the lean combustion internal combustion engine of the intake port injection type, and a combustible mixture is formed in the vicinity of the spark plug. Therefore, it is possible to achieve both reduction in fuel consumption and stable combustion.

On the other hand, when the lean combustion is performed in the lean combustion internal combustion engine as described above, the oxygen concentration in the exhaust becomes high, so that the normal three-way catalyst can sufficiently purify the nitrogen oxide (NOx) in the exhaust. Can not. Therefore, a nitrogen oxide storage reduction catalyst is disposed in the exhaust system of the lean combustion internal combustion engine.

Nitrogen oxide storage reduction catalysts store nitrogen oxides (NOx) in exhaust when the oxygen concentration of the inflowing exhaust is high, that is, in a lean state, and the oxygen concentration in the inflowing exhaust decreases to carbonize. When hydrogen (HC) increases, the stored nitrogen oxides (NOx) react with carbon monoxide (CO), hydrocarbons (HC), etc. in the exhaust gas to reduce them to nitrogen (N ₂ ). Has the property of releasing.

In a lean combustion internal combustion engine equipped with a nitrogen oxide storage reduction catalyst, nitrogen oxide (NOx) contained in exhaust gas during lean combustion is absorbed by the nitrogen oxide storage reduction catalyst, and the nitrogen oxide storage reduction catalyst Before the nitrogen oxide (NOx) absorption amount of saturates, the so-called rich spike that increases the reducing components (carbon monoxide CO, hydrocarbon HC), etc. in the exhaust is performed and absorbed by the nitrogen oxide storage reduction catalyst. The released nitrogen oxide (NOx) needs to be released and purified on the catalyst.

As an apparatus for efficiently releasing and purifying nitrogen oxide (NOx) stored in a nitrogen oxide storage reduction catalyst, an exhaust purification apparatus for an internal combustion engine described in Patent Document 1 is known.

In the lean combustion internal combustion engine of the intake port injection type, the exhaust purification device of the internal combustion engine causes the same amount of fuel to be injected from the fuel injection valve as that in the case of forming an oxygen-rich mixture, and is generated in the fuel tank. By introducing gas containing evaporated fuel into the intake system of the internal combustion engine and the exhaust passage upstream of the nitrogen oxide storage reduction catalyst, the hydrocarbon (HC) in the exhaust flowing into the nitrogen oxide storage reduction catalyst is increased. The nitrogen oxide (NOx) occluded in the nitrogen oxide occlusion reduction type catalyst is to be released and purified.
JP-A-6-173660 JP-A-4-194354 JP-A-6-212961 Japanese Patent Laid-Open No. 6-200794

By the way, the above-described exhaust purification device does not consider the amount and concentration of the evaporated fuel, or the time required for the evaporated fuel to actually reach the nitrogen oxide storage reduction catalyst from the start of supply of the evaporated fuel. Exhaust gas containing a desired amount of reducing component cannot be supplied to the nitrogen oxide storage reduction catalyst, and exhaust gas containing a reducing component cannot be supplied to the nitrogen oxide storage reduction catalyst at a desired time. In this case, the nitrogen oxide (NOx) stored in the nitrogen oxide storage reduction catalyst cannot be sufficiently released and purified, and the nitrogen oxide storage reduction catalyst becomes saturated, and the nitrogen oxide (NOx) May be released into the atmosphere without being purified, and exhaust emissions may deteriorate.

  In addition, when the above-described exhaust purification device is applied to an in-cylinder injection lean-burn internal combustion engine, particularly when evaporated fuel is supplied during stratified combustion, the combustion chamber cannot be stratified and combustion is not performed. There is a risk that the fuel concentration in the vicinity of the spark plug becomes higher than necessary, and there is a risk that the ignition plug cannot be ignited and misfire occurs.

The present invention has been made in view of the above-described problems. In a lean combustion internal combustion engine, nitrogen oxide storage is achieved by using evaporated fuel generated in a fuel tank without destabilizing the combustion state. It is an object of the present invention to provide a technique for reliably purifying nitrogen oxide (NOx) occluded in a reduction type catalyst and preventing deterioration of exhaust emission and efficient processing of evaporated fuel.

The present invention employs the following means in order to solve the above problems. That is, an exhaust emission control device for a lean combustion internal combustion engine according to the present invention includes a lean combustion internal combustion engine capable of combusting an air-fuel mixture in an oxygen-excess state, and an evaporated fuel gas containing evaporated fuel generated in a fuel tank. When the exhaust is in an oxygen-excess state, nitrogen oxide in the exhaust is occluded and the oxygen concentration in the exhaust decreases. Is a lean combustion internal combustion engine exhaust gas purification device comprising a nitrogen oxide storage reduction catalyst that purifies the stored nitrogen oxides,
Gas state determining means for determining the state of the evaporated fuel gas supplied to the intake system of the lean combustion internal combustion engine;
According to the state of the evaporated fuel gas determined by the gas state determination means at a time when the nitrogen oxide stored in the nitrogen oxide storage reduction catalyst is to be purified, the fuel injection valve of the lean combustion internal combustion engine and the And an exhaust state control unit that selectively controls the gas supply unit to bring the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage reduction catalyst into a desired state.

  According to the exhaust purification device configured as described above, when performing so-called rich spike control for purifying the nitrogen oxides stored in the nitrogen oxide storage reduction catalyst, the gas state determination means determines the state of the evaporated fuel gas. Determine.

  Examples of the state of the evaporated fuel gas include the fuel concentration in the evaporated fuel gas, the flow rate of the evaporated fuel gas, the flow rate of the evaporated fuel gas (the time required for the evaporated fuel gas to reach the nitrogen oxide storage reduction catalyst), etc. Can be illustrated.

  The exhaust state control means is configured to provide the lean combustion internal combustion engine according to the state of the evaporated fuel gas determined by the gas state determination means at a time when the nitrogen oxide stored in the nitrogen oxide storage reduction catalyst is to be purified. Since the fuel injection valve of the engine and the gas supply means are selectively controlled, the exhaust gas flowing into the nitrogen oxide storage reduction type catalyst is desired without causing unstable combustion of the air-fuel mixture in the lean combustion internal combustion engine. Thus, the nitrogen oxides stored in the nitrogen oxide storage reduction catalyst are reliably purified.

  The gas state determining means includes evaporated fuel concentration determining means for determining the fuel concentration in the evaporated fuel gas supplied to the intake system of the lean combustion internal combustion engine by the gas supply means, and the lean combustion internal combustion engine by the gas supply means. The gas supply amount determining means for determining the amount of the evaporated fuel gas supplied to the intake system of the engine, or the evaporated fuel from the time when the gas supply means starts supplying the evaporated fuel gas to the intake system of the lean combustion internal combustion engine You may make it comprise the gas arrival time discrimination | determination means etc. which discriminate | determine the time required until gas reaches the nitrogen oxide storage reduction catalyst.

  The exhaust state control means includes a fuel injection time of the fuel injection valve, a fuel injection timing of the fuel injection valve, a supply amount of the evaporated fuel gas by the gas supply means, and an amount of the evaporated fuel gas by the gas supply means. The supply time may be selectively controlled.

  Further, when the lean combustion internal combustion engine is an in-cylinder injection type lean combustion internal combustion engine having a fuel injection valve that directly injects fuel into the cylinder, the exhaust state control means is configured so that the fuel injection timing of the fuel injection valve is When purifying the nitrogen oxide stored in the nitrogen oxide storage reduction catalyst when it is set during the compression stroke of the cylinder, the fuel injection timing of the fuel injection valve is changed during the intake stroke of each cylinder, that is, You may make it switch from stratified combustion control to homogeneous combustion control.

  In the exhaust emission control device for a lean combustion internal combustion engine according to the present invention, when so-called rich spike control is performed to purify nitrogen oxides stored in the nitrogen oxide storage reduction catalyst, fuel injection is performed according to the state of the evaporated fuel gas. Since the valve and the gas supply means are controlled, the exhaust gas flowing into the nitrogen oxide storage reduction catalyst can be set to a desired air-fuel ratio without destabilizing the combustion of the air-fuel mixture in the lean combustion internal combustion engine. .

  As a result, using the evaporated fuel generated in the fuel tank, the nitrogen oxide stored in the NOx storage reduction catalyst is reliably purified, preventing exhaust emission deterioration and efficient processing of the evaporated fuel. It becomes possible to do.

  Embodiments of an exhaust emission control device for a lean combustion internal combustion engine according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an internal combustion engine to which an exhaust emission control device according to the present invention is applied and an intake / exhaust system thereof. The internal combustion engine shown in FIG. 1 includes a plurality of cylinders and fuel directly in each cylinder. This is a four-cycle in-cylinder injection internal combustion engine 1 that includes a fuel injection valve that injects fuel.

  The internal combustion engine 1 includes a cylinder block 1b in which a plurality of cylinders 2 are formed, and a cylinder head 1a fixed to an upper portion of the cylinder block 1b. Each cylinder 2 of the cylinder block 1b is loaded with a piston 3 so as to be slidable in the axial direction. The piston 3 is connected to a crankshaft 4 serving as an engine output shaft. A combustion chamber 5 surrounded by the top surface of the piston 3 and the cylinder head 1a is formed above the piston 3.

  An ignition plug 6 is attached to the cylinder head 1 a so as to face the combustion chamber 5, and an igniter 6 a for applying a drive current to the ignition plug 6 is attached to the ignition plug 6. Further, the cylinder head 1 a is formed with the opening ends of the two intake ports 7 and the two exhaust ports 8 facing the combustion chamber 5, and the fuel injection valve 9 so that the injection hole faces the combustion chamber 5. Is attached.

  Subsequently, an intake valve 70 and an exhaust valve 80 for opening and closing the open ends of the intake and exhaust ports 7 and 8 are supported by the cylinder head 1a so as to freely advance and retract, and the intake and exhaust valves 70 and 80 are driven to open and close. The intake side camshaft 11 and the exhaust side camshaft 12 are rotatably supported.

  The intake side camshaft 11 and the exhaust side camshaft 12 are connected to the crankshaft 4 via a timing belt (not shown), and the rotational force of the crankshaft 4 is connected to the intake side camshaft 11 and the crankshaft 4 via the timing belt. It is transmitted to the exhaust side camshaft 12.

  The internal combustion engine 1 includes a crank position sensor 13 including a timing rotor 13a attached to an end of the crankshaft 4 and an electromagnetic pickup 13b attached to the cylinder block 1b.

  Furthermore, a water temperature sensor 14 that outputs an electrical signal corresponding to the temperature of the cooling water flowing in the cooling water flow path 1c formed in the cylinder block 1b is attached to the cylinder block 1b.

  Next, one of the two intake ports 7 is formed as a straight port having a straight flow path from an open end formed on the outer wall of the cylinder head 1a to an open end facing the combustion chamber 5. The other intake port 7 is formed as a helical port having a flow path that turns from the opening end of the outer wall of the cylinder head 1 a toward the opening formed in the opening end of the combustion chamber 5.

  Each intake port 7 communicates with an intake branch pipe 16 attached to the cylinder head 1a. At that time, the intake branch pipe 16 communicating with the straight port is provided with a swirl control valve 10 for opening and closing the flow path of the intake branch pipe 16, and this swirl control valve 10 is composed of a step motor or the like, and applies an applied current. Accordingly, an actuator 10a for opening and closing the swirl control valve 10 is attached.

  The intake branch pipe 16 is connected to a surge tank 17, and the surge tank 17 is connected to an air cleaner box 19 via an intake pipe 18. The intake pipe 18 is provided with a throttle valve 20 that opens and closes an intake passage in the intake pipe 18. The throttle valve 20 is driven to open and close by an actuator 21 composed of a step motor or the like. The throttle valve 20 is provided with a throttle position sensor 20a that outputs an electrical signal corresponding to the opening of the throttle valve 20.

  Subsequently, an air flow meter 22 that outputs an electrical signal corresponding to the mass of fresh air (intake air mass) flowing through the intake pipe 18 is attached to the intake pipe 18 upstream of the throttle valve 20.

  A vacuum sensor 17 a that outputs an electrical signal corresponding to the pressure in the surge tank 17 is attached to the surge tank 17, and a purge passage 30 is connected to the surge tank 17. The purge passage 30 is connected to a charcoal canister 31. In the middle of the purge passage 30, a duty-controlled electromagnetic valve 34 is attached to adjust the flow rate in the purge passage 30.

  Subsequently, an evaporated fuel passage 32 and an air introduction passage 35 are connected to the charcoal canister 31. The evaporative fuel passage 32 is connected to a fuel tank 33, and the air introduction passage 35 has an open end in the atmosphere.

  Here, the evaporated fuel generated in the fuel tank 33 is introduced into the charcoal canister 31 through the evaporated fuel passage 32 and is adsorbed by the activated carbon built in the charcoal canister 31. When the solenoid valve 34 is opened and the purge passage 30 becomes conductive, the intake pipe negative pressure generated in the surge tank 17 is introduced into the charcoal canister 31 through the purge passage 30.

  In this case, the atmosphere is introduced into the charcoal canister 31 through the atmosphere introduction passage 35, and the atmosphere is purged together with the evaporated fuel adsorbed by the activated carbon (hereinafter, the atmosphere including the evaporated fuel is referred to as evaporated fuel gas). A so-called purge of evaporated fuel gas is realized which is sucked into the passage 30 and then introduced into the surge tank 17. Thus, the purge passage 30, the electromagnetic valve 34, and the charcoal canister 31 realize the gas supply means according to the present invention.

  The evaporated fuel gas purged to the surge tank 17 is mixed with fresh air introduced into the surge tank 17 through the air cleaner 19 and the intake pipe 18 when the intake valve 70 of the internal combustion engine 1 is opened. The fuel is sucked into each cylinder 2 and burned together with the fuel injected from the fuel injection valve 9.

  On the other hand, the exhaust port 8 communicates with an exhaust branch pipe 25 attached to the cylinder head 1 a, and the exhaust branch pipe 25 is connected to an exhaust pipe 27 via a first catalyst 26. Next, the exhaust pipe 27 is connected to a muffler (not shown) downstream.

  A first air-fuel ratio sensor 29 a that outputs an electric signal corresponding to the air-fuel ratio of the exhaust gas flowing in the exhaust branch pipe 25 is attached to the exhaust branch pipe 25 upstream of the first catalyst 26.

  A second catalyst 28 is provided in the middle of the exhaust pipe 27, and the exhaust pipe 27 downstream of the second catalyst 28 corresponds to the air-fuel ratio in the exhaust gas flowing out from the second catalyst 28. A second air-fuel ratio sensor 29b for outputting the electrical signal is attached.

  Here, the first catalyst 26 is a three-way catalyst having a capacity smaller than that of the second catalyst 28. The second catalyst 28 uses, for example, alumina as a carrier, and potassium K, sodium on the carrier. Supports at least one selected from alkali metals such as Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. A nitrogen oxide storage reduction catalyst (hereinafter referred to as NOx storage catalyst 28).

Air (oxygen O ₂ ) and fuel (hydrocarbon HC) in the exhaust gas flowing into the NOx storage catalyst 28
The exhaust air / fuel ratio is defined as the exhaust air / fuel ratio upstream of the NOx storage catalyst 28.
If no fuel or air is supplied into the combustion chamber 7, it corresponds to the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 5.

In the NOx storage catalyst 28, the exhaust air-fuel ratio (air-fuel ratio of the air-fuel mixture) is in an oxygen excess state.
During the so-called lean state, nitrogen oxide NOx in the exhaust is absorbed and exhausted (in the mixture)
In a state where the concentration of oxygen is lowered and the concentration of hydrocarbon (HC) is high, that is, in a so-called rich state, the absorbed nitrogen oxides NOx are released.

Specifically, in the case of a NOx storage catalyst in which platinum Pt and barium Ba are supported on a carrier, when the exhaust air-fuel ratio becomes lean, oxygen O ₂ in the exhaust is in the form of O ²⁻ or O ²⁻ . It adheres on the surface of platinum Pt. On the other hand, the nitrogen oxides NOx in the exhaust are O on the surface of platinum Pt.
It reacts with ^2- or O ^2- and becomes NO ₂ (2NO + O ₂ → 2NO ₂ ). NO ₂ of NO ₂ and the exhaust thus produced while being oxidized on the platinum Pt, and binds with barium oxide BaO, nitrate ions NO ₃ ^- become.

Subsequently, when the oxygen concentration in the exhaust gas flowing into the NOx storage catalyst decreases, the NOx storage catalyst decreases the amount of NO ₂ generated, and the reaction proceeds in the reverse direction (NO ₃ → NO ₂ ), and absorption. The nitrate ions NO ₃ ⁻ that have been released are released in the form of NO ₂ . The NO ₂ released in this manner reacts with the reducing components (HC, CO, O ₂ ) in the exhaust gas on the NOx storage catalyst 28 to react with nitrogen N
Reduced to ₂ .

Various sensors such as the crank position sensor 13, the water temperature sensor 14, the vacuum sensor 17a, the throttle position sensor 20a, the air flow meter 22, the first and second air-fuel ratio sensors 29a and 29b are electrically wired. Via an engine control electronic control unit (ECU) 36, and output signals of various sensors are input to the ECU 36.

  The ECU 36 is connected to the igniter 6a, the fuel injection valve 9, the actuator 10a, the actuator 21, the electromagnetic valve 34, and the like through electric wiring.

The ECU 36 determines the operating state of the internal combustion engine 1, the evaporated fuel storage state of the charcoal canister 31, the nitrogen oxide NOx storage amount of the NOx storage catalyst 28, and the like using the output signals from the various sensors as parameters. Various controls of the igniter 6a, the fuel injection valve 9, the actuator 10a, the actuator 21, the electromagnetic valve 34, and the like are performed according to the determination result.

  Here, as shown in FIG. 2, the ECU 36 includes a CPU 38, a ROM 39, a RAM 40, a backup RAM 41, an input port 42, and an output port 43 that are connected to each other by a bidirectional bus 37, and the input port 42. An A / D converter (A / D) 44 connected to the.

  The input port 42 receives signals from the crank position sensor 13 and the throttle position sensor 20a and transmits these signals to the CPU 38 or the RAM 40. Further, the input port 42 inputs signals from the water temperature sensor 14, the vacuum sensor 17a, the air flow meter 22, and the first and second air-fuel ratio sensors 29a and 29b via the A / D converter 44, and these signals. Is transmitted to the CPU 38 or the RAM 40.

  The output port 43 outputs a control signal from the CPU 38 to the igniter 6a, the fuel injection valve 9, the actuator 10a, the actuator 21, the electromagnetic valve 34, and the like.

  The ROM 39 stores a fuel injection amount control routine for determining the fuel injection amount, a fuel injection timing control routine for determining the fuel injection timing, an ignition timing control routine for determining the ignition timing, or the NOx storage catalyst 28. An application program such as a nitrogen oxide purification control routine for purifying and simultaneously purifying the stored nitrogen oxide NOx and various control maps are stored.

The control map is, for example, a fuel injection amount control map showing the relationship between the operating state of the internal combustion engine 1 and the fuel injection amount, a fuel injection timing control map showing the relationship between the operating state of the internal combustion engine 1 and the fuel injection timing, and the internal combustion engine An ignition timing control map showing the relationship between the operating state of the engine 1 and the ignition timing, the time required for the evaporated fuel gas to reach the NOx storage catalyst 28 from the start of the purge of the evaporated fuel gas (purge gas arrival time), and the engine speed Purge gas arrival time control map showing the relationship between the fuel injection amount and the fuel injection timing showing the relationship between the fuel injection amount to be increased at the time when the nitrogen oxide NOx stored in the NOx storage catalyst 28 should be purified and the correction amount of the fuel injection timing A correction map or the like.

Subsequently, the RAM 40 stores output signals from the sensors, calculation results of the CPU 38, and the like. The calculation results include, for example, the engine speed calculated from the output signal of the crank position sensor 13, the amount of evaporated fuel (purge vapor amount QV) per unit time that can be purged from the charcoal canister 31 to the surge tank 17, and the nitrogen oxide NOx. The fuel injection amount (fuel injection increase QF) to be increased when releasing and purifying the fuel. The output signal from each sensor, the calculation result of the CPU 38, and the like are rewritten to the latest data every time the crank position sensor 13 outputs a signal.

  The backup RAM 41 is a non-volatile memory that retains data even after the internal combustion engine 1 is stopped. Next, the CPU 38 operates in accordance with the application program stored in the ROM 39, determines the operating state of the internal combustion engine 1 from the output signals of the sensors, and determines the fuel injection amount and fuel injection from the operating state and each control map. Timing, ignition timing, fuel injection increase amount, fuel injection timing correction amount, etc. are calculated. Then, the CPU 38 controls the igniter 6a, the fuel injection valve 9, the actuator 10a, the actuator 21 and the like based on the calculation result.

  For example, the CPU 38 determines the operating state of the internal combustion engine 1 from the output signals of various sensors. If it is determined that the engine operating state is in the low load operating region, the CPU 38 controls the actuator 10a to reduce the opening of the swirl control valve 10 and drive the actuator 21 in order to realize stratified combustion. Then, the throttle valve 20 is controlled to an opening at which the intake air flow rate becomes substantially the same as when fully opened, and further, a drive current is applied to the fuel injection valve 9 during the compression stroke of each cylinder 2 to perform the compression stroke injection. In this case, in the combustion chamber 5 of each cylinder 2, a combustible air-fuel mixture layer is formed only in the vicinity of the spark plug 6, and an air layer is formed in other regions, thereby realizing stratified combustion.

When the CPU 38 determines that the engine operating state is in the medium load operating region, the CPU 38 controls the actuator 10a to reduce the opening of the swirl control valve 10 in order to achieve homogeneous combustion by the lean air-fuel mixture, During the intake stroke of each cylinder 2, a drive current is applied to the fuel injection valve 9 to perform intake stroke injection. In this case, a lean air-fuel mixture in which air and fuel are homogeneously mixed is formed over substantially the entire area in the combustion chamber 5 of each cylinder 2, and homogeneous combustion is realized.

  If the CPU 38 determines that the engine operating state is in the high load region, the CPU 38 controls the actuator 10a to fully open the swirl control valve 10 in order to achieve homogeneous combustion by the air-fuel mixture near the stoichiometric air-fuel ratio, The actuator 21 is controlled so that the throttle valve 20 has an opening corresponding to the depression amount of an accelerator pedal (not shown), and a drive current is applied to the fuel injection valve 9 during the intake stroke of each cylinder 2 to perform intake stroke injection. In this case, a stoichiometric air-fuel ratio mixture in which air and fuel are homogeneously mixed is formed over substantially the entire area in the combustion chamber 5 of each cylinder 2 to achieve homogeneous combustion.

  Further, when the CPU 38 shifts from the stratified combustion control to the homogeneous combustion control, or when it shifts from the homogeneous combustion control to the stratified combustion control, the CPU 38 at the time of the compression stroke and the intake stroke of each cylinder 2 is prevented. A drive current is applied to the fuel injection valve 9 in two steps. In this case, in the combustion chamber 5 of each cylinder 2, a combustible air-fuel mixture layer is formed in the vicinity of the spark plug 6, and a lean air-fuel mixture layer is formed in other regions, so-called weak stratified combustion is realized. .

  Next, the CPU 38 includes a rich spike execution counter that counts a value corresponding to the amount of nitrogen oxides NOx stored in the NOx storage catalyst 28. The rich spike execution counter is a counter that is incremented according to the load of the internal combustion engine 1, the engine speed, the fuel injection amount, and the like, and includes a register or the like. The rich spike execution counter is reset at the end of execution of rich spike control.

  Further, a value A of a rich spike execution counter when the NOx storage amount of the NOx storage catalyst 28 reaches a saturated state is obtained in advance through experiments or the like, and a value A obtained by subtracting a predetermined amount as a margin from the counter value. Is set as the upper limit value of the rich spike execution counter.

  When the value of the rich spike execution counter reaches the upper limit value A, the CPU 38 executes a rich spike to bring the air-fuel ratio of the exhaust into a desired state. Specifically, the CPU 38 realizes a rich spike by purging the evaporated fuel gas and correcting the increase in the fuel injection amount.

By the way, since it takes time for the evaporated fuel gas to reach the NOx storage catalyst 28 after the purge of the evaporated fuel gas is started, when the counter value of the rich spike execution counter reaches a predetermined value A, When the purge control and the fuel injection amount increase control are started, the interval between the time when the fuel injected from the fuel injection valve 9 reaches the NOx storage catalyst 28 and the time when the purged evaporated fuel gas reaches the NOx storage catalyst 28. Shift to the desired amount of reducing component (HC
, CO) cannot be supplied to the NOx storage catalyst 28 at a desired time.

  Therefore, in the present embodiment, the CPU 38 evaporates the fuel when the value of the rich spike execution counter reaches the value (A−ΔA) obtained by subtracting the value ΔA corresponding to the purge gas arrival time Δt from the upper limit value A. Gas purge is started, and when the value of the rich spike execution counter reaches the upper limit value A, the fuel injection amount increase control is performed. In this case, the increased amount of injected fuel and the evaporated fuel gas flow into the NOx storage catalyst 28 substantially simultaneously.

  The purge gas arrival time Δt decreases as the intake air flow rate of the internal combustion engine 1 increases, and the intake air flow rate increases as the engine rotational speed increases. N is calculated, and a purge gas arrival time Δt corresponding to the engine speed N is calculated from a purge gas arrival time control map as shown in FIG. ΔA is a value obtained in advance through experiments or the like, and is determined using, for example, engine speed, purge gas arrival time, and the like as parameters.

  Further, the increased fuel amount (rich spike fuel amount QRS) necessary for releasing and purifying the nitrogen oxide NOx stored in the NOx storage catalyst 28 is compensated by purging the evaporated fuel gas and increasing the fuel injection. At that time, the purge of the evaporated fuel gas is mainly performed, and the fuel amount which is insufficient by the purge of the evaporated fuel gas is supplemented by the fuel injection increase.

In this case, the fuel injection amount to be increased includes the state of the evaporated fuel gas to be purged, the amount of fuel that can be supplied from the charcoal canister 31 to the surge tank 17 (the amount of evaporated fuel (purge vapor amount) QV / solenoid valve 34 per unit time). Therefore, it is necessary to determine the amount of increase in the fuel injection amount after specifying the vapor amount QV.

  The purge vapor amount QV is a value obtained by multiplying the fuel concentration CP in the vaporized fuel gas to be purged by the vaporized fuel gas flow rate (purge gas flow rate QP) per unit time. The purge gas flow rate QP changes in accordance with the pressure difference ΔP between the intake pipe negative pressure generated in the surge tank 17 and the atmospheric pressure, but the in-cylinder injection type internal combustion engine 1 as exemplified in the present embodiment. When the lean combustion control (stratified combustion control) is being executed in step 1, the throttle valve 20 is controlled so as to have substantially the same intake flow rate as in the fully open state except during an extremely low load. Becomes substantially constant. As a result, the differential pressure ΔP also becomes constant, and the purge gas flow rate QP becomes constant.

  As a method of specifying the fuel concentration CP, when performing normal purge control, the output signal value of the first air-fuel ratio sensor 29a immediately before the purge is performed and the output signal value of the first air-fuel ratio sensor 29a at the time of purge are A method of calculating the fuel concentration of the evaporated fuel gas from the difference between the two and using the calculated fuel concentration as a learning value, or a method of directly detecting with a HC sensor or the like attached to the purge passage 30 or the charcoal canister 31 is exemplified. it can.

Then, the CPU 38 multiplies the calculated fuel concentration CP and the purge gas flow rate QP to calculate the purge vapor amount QV, and then multiplies the purge vapor amount QV and the solenoid valve maximum valve opening time Tmax to generate a surge from the charcoal canister 31. The amount of fuel that can be supplied to the tank 17 (purge fuel amount QV · Tmax) is calculated. Subsequently, the CPU 38 calculates the calculated purge fuel amount QV ·
Tmax is compared with the rich spike fuel amount QRS. When the purge fuel amount QV · Tmax is larger than the rich spike fuel amount QRS, the CPU 38 divides the rich spike fuel amount QRS by the purge vapor amount QV to calculate the valve opening time T of the solenoid valve 34 and fuel injection. Increase QF is set to zero.

In this case, the CPU 38 realizes a rich spike by controlling the electromagnetic valve 34 according to the valve opening time T. On the other hand, when the purge fuel amount QV · Tmax is equal to or less than the rich spike fuel amount QRS, the CPU 38 sets the valve opening time of the electromagnetic valve 34 to the electromagnetic valve maximum valve opening time Tmax and from the rich spike fuel amount QRS. A value (QRS−QV · Tmax) obtained by subtracting the purge fuel amount QV · Tmax is set as the fuel injection increase amount QF.

In this case, the total amount of fuel to be injected from the fuel injection valve 9 (total fuel injection amount Qtotal) is a value (Q + QF) obtained by adding the fuel injection amount Q calculated from the fuel injection amount control map and the fuel injection increase amount QF. Therefore, in order to realize the total fuel injection amount Qtotal, it is necessary to start the fuel injection at a time earlier than the fuel injection timing IT calculated from the fuel injection timing control map and extend the fuel injection time.

At that time, the CPU 38 calculates the fuel injection timing correction advance amount ΔIT corresponding to the fuel injection increase amount QF from the fuel injection timing correction map as shown in FIG. 4, and the fuel injection timing IT and the fuel injection timing are calculated. The fuel injection timing I when the rich spike is executed by adding the corrected advance amount ΔIT
Ttotal is calculated. Then, the CPU 38 realizes a rich spike by controlling the fuel injection valve 9 according to the fuel injection timing ITtotal.

  When realizing the rich spike by the control as described above, especially when executing the rich spike during lean operation such as stratified combustion, the air-fuel ratio in the combustion chamber is suddenly made rich by purging the evaporated fuel gas and increasing the fuel injection. Since there is a possibility that a rich misfire may occur, the CPU 38 changes the total fuel amount, which is the sum of the fuel amount in the purged evaporated fuel gas and the injected fuel amount, to a change rate that does not induce a rich misfire. As described above, the fuel amount change speed due to the purge of the evaporated fuel gas and the fuel amount change speed due to the fuel injection increase are adjusted.

  The CPU 38 may prohibit the stratified combustion control and perform the homogeneous combustion control for the purpose of stabilizing the combustion in each cylinder 2 when performing the rich spike control by the fuel injection increase.

  As described above, the CPU 38 executes the application program stored in the ROM 39 to realize the gas state determination unit and the exhaust state control unit according to the present invention.

  Hereinafter, the operation and effects according to the present embodiment will be described. The CPU 38 executes a nitrogen oxide purification control routine as shown in FIG. 5 every predetermined time (every time the crank position sensor 13 outputs a signal) during execution of stratified charge combustion control of the internal combustion engine 1. In this nitrogen oxide purification control routine, the CPU 38 first accesses the RAM 40 and reads the engine speed N in S501. Subsequently, the CPU 38 accesses the purge gas arrival time control map in the ROM 39, calculates a purge gas arrival time Δt corresponding to the engine speed N, and calculates a value ΔA corresponding to the purge gas arrival time Δt.

  Next, the CPU 38 proceeds to S502, and subtracts the value ΔA calculated in S501 from the upper limit value A of the rich spike execution counter. Then, the CPU 38 determines whether or not the counter value of the rich spike execution counter is not less than the value (A−ΔA) obtained by the subtraction process.

  When it is determined in S502 that the counter value of the rich spike execution counter is less than the subtraction result (A−ΔA), the CPU 38 once ends the execution of this routine.

On the other hand, if it is determined in S502 that the counter value of the rich spike execution counter is greater than or equal to the subtraction result (A−ΔA), the CPU 38 proceeds to S503, where the counter value of the rich spike execution counter is the upper limit value. It is determined whether or not it is greater than or equal to A, that is, whether or not the NOx storage amount of the NOx storage catalyst 28 is in a saturated state.

  If it is determined in S503 that the counter value of the rich spike execution counter is less than the upper limit value A, the CPU 38 proceeds to S507 and determines whether or not the execution of the rich spike control is in a provisionally permitted state. . The provisionally permitted state of rich spike control execution here refers to a state in which rich spike control by purging of evaporated fuel gas is being executed before execution of rich spike control by increasing fuel injection.

  The RAM 40 has a rich spike control execution temporary permission flag area that is set to “1” when the rich spike control execution by the purge of the evaporated fuel gas is started and reset to “0” when the rich spike control execution by the purge of the evaporated fuel gas is completed. The CPU 38 determines whether “1” is stored in the rich spike control execution temporary permission flag area or “0” is stored, so that the execution of the rich spike control is temporarily performed. You may make it discriminate | determine whether it is in the state of permission.

  If it is determined in S507 that the execution of the rich spike control is not temporarily permitted, the CPU 38 proceeds to S508 and sets “1” in the rich spike control execution temporary permission flag area of the RAM 40.

Next, the CPU 38 proceeds to S509, and the nitrogen oxide N stored in the NOx storage catalyst 28 is obtained.
An increased fuel amount (rich spike fuel amount QRS) required to release and purify Ox is determined. At this time, the CPU 38 determines the rich spike fuel amount QRS on the assumption that the counter value of the rich spike execution counter has reached the upper limit value A.

Then, the CPU 38 proceeds to S510 and multiplies the purge gas flow rate QP per unit time by the fuel concentration CP to calculate the amount of fuel purged per unit time (purge vapor amount QV). Subsequently, the CPU 38 sets the purge valve amount QV to the maximum solenoid valve opening time Tmax.
To calculate the purge fuel amount QV · Tmax, and based on the purge fuel amount QV · Tmax and the rich spike fuel amount QRS calculated in S509, the valve opening time T of the solenoid valve 34 and the fuel injection increase amount are calculated. QF is determined. At that time, the CPU 38 compares the purge fuel amount QV · Tmax with the rich spike fuel amount QRS, and if the purge fuel amount QV · Tmax is larger than the rich spike fuel amount QRS, the rich spike fuel amount QRS is set to the purge vapor amount QV. The electromagnetic valve opening time T is calculated by division, and the fuel injection increase QF is set to zero.

On the other hand, if the purge fuel amount QV · Tmax is equal to or less than the rich spike fuel amount QRS,
The PU 38 sets the solenoid valve opening time T to the solenoid valve maximum opening time Tmax, and a value obtained by subtracting the purge fuel amount QV · Tmax from the rich spike fuel amount QRS (QRS−QV ·
Tmax) is defined as a fuel injection increase amount QF.

  The CPU 38 stores the solenoid valve opening time T and the fuel injection increase QF calculated as described above in a predetermined area of the RAM 40, and then proceeds to S511. In S511, the CPU 38 fully opens the electromagnetic valve 34 in order to execute a rich spike by purging the evaporated fuel gas, and temporarily ends the execution of this routine.

  Thereafter, the CPU 38 executes this routine again, and if it is determined in S502 and S503 that the counter value of the rich spike execution counter is equal to or larger than (A−ΔA) and less than A, the rich spike control is executed in S507. It is determined that the temporary permission state is set, and the execution of this routine is temporarily terminated.

  If this routine is repeatedly executed as described above and it is determined in S503 that the counter value of the rich spike execution counter is equal to or greater than the upper limit value A, the CPU 38 proceeds to S504.

  In S <b> 504, the CPU 38 writes “1” in the rich spike control execution permission flag area set in the RAM 40. In the rich spike control execution permission flag area, “1” is set when the rich spike control execution by the fuel injection increase is started, and is reset to “0” when the rich spike control execution by the fuel injection increase is completed.

  Subsequently, the CPU 38 proceeds to S505, where the fuel injection amount Q determined by the fuel injection amount control routine, the fuel injection timing IT determined by the fuel injection timing control routine, and the fuel injection increase amount QF determined by S510 are described. And the total fuel injection amount Qtotal and the fuel injection timing ITtotal are calculated according to the fuel injection timing correction map.

Then, the CPU 38 proceeds to S506 and switches from the stratified combustion control to the homogeneous combustion control in order to execute the rich spike due to the fuel injection increase, and the fuel injection according to the total fuel injection amount Qtotal and the fuel injection timing ITtotal calculated in S505. The valve 9 is controlled.

According to the embodiment described above, the increase in fuel injection and the evaporated fuel gas are substantially simultaneously with NOx.
Since the rich spike control is performed so as to reach the storage catalyst 28, the evaporated fuel gas is located in the combustion chamber 5 at the same time as the fuel injected in an increased amount. That is, the evaporative fuel gas is introduced into the combustion chamber 5 after the internal combustion engine 1 shifts from the stratified combustion state to the homogeneous combustion state, so that the stratified combustion is not hindered and the combustion of the internal combustion engine 1 is stabilized. Can be made.

  Further, since the fuel injection increase is performed according to the state of the evaporated fuel gas, the nitrogen oxide NOx stored in the NOx storage catalyst 28 can be released and purified with the minimum required fuel injection increase, and the mixture is excessive. It doesn't become a rich state. As a result, combustion of the air-fuel mixture is stabilized and an increase in fuel consumption due to rich spike control is suppressed.

  Further, since the evaporated fuel adsorbed on the canister is used for the rich spike, the opportunity to purge the evaporated fuel increases, and the canister can be reliably regenerated.

<Other embodiments>
Hereinafter, another embodiment of the exhaust emission control device according to the present invention will be described with reference to FIG. FIG. 6 is a flowchart showing a nitrogen oxide purification control routine according to the present embodiment.

  In the nitrogen oxide purification control routine shown in the above-described embodiment, the rich spike fuel amount QRS, the valve opening time T of the solenoid valve 34, and the fuel injection increase amount QF are determined when the execution of the rich spike control is temporarily permitted. On the other hand, in the nitrogen oxide purification control routine shown in FIG. 6, the rich spike fuel amount QRS, the valve opening time T of the solenoid valve 34, and the fuel injection increase amount QF are determined before the execution of the rich spike control is temporarily permitted. I tried to do it.

  That is, the CPU 38 accesses the RAM 40 and reads the engine speed N in S601. Subsequently, the CPU 38 accesses the purge gas arrival time control map in the ROM 39, calculates a purge gas arrival time Δt corresponding to the engine speed N, and calculates a value ΔA corresponding to the purge gas arrival time Δt.

Subsequently, the CPU 38 proceeds to S602, and determines an increase fuel amount (rich spike fuel amount QRS) necessary for releasing and purifying the nitrogen oxide NOx stored in the NOx storage catalyst 28. At this time, the CPU 38 determines the rich spike fuel amount QRS on the assumption that the counter value of the rich spike execution counter has reached the upper limit value A.

Then, the CPU 38 proceeds to S603, detects the purge gas flow rate QP and the fuel concentration CP per unit time, multiplies these purge gas flow rate QP and the fuel concentration CP, and purges the fuel amount (purge vapor amount) per unit time. QV) is calculated. Next, the CPU 38 multiplies the purge vapor amount QV by the solenoid valve maximum valve opening time Tmax to calculate the purge fuel amount QV · Tmax, and the purge fuel amount QV · Tmax and the rich spike fuel amount QRS calculated in S509. Based on the above, the valve opening time T of the electromagnetic valve 34 and the fuel injection increase QF are determined.

At that time, the CPU 38 compares the purge fuel amount QV · Tmax with the rich spike fuel amount QRS, and if the purge fuel amount QV · Tmax is larger than the rich spike fuel amount QRS, the rich spike fuel amount QRS is set to the purge vapor amount QV. The electromagnetic valve opening time T is calculated by division, and the fuel injection increase QF is set to zero.

On the other hand, if the purge fuel amount QV · Tmax is equal to or less than the rich spike fuel amount QRS,
The PU 38 sets the solenoid valve opening time T to the solenoid valve maximum opening time Tmax, and a value obtained by subtracting the purge fuel amount QV · Tmax from the rich spike fuel amount QRS (QRS−QV ·
Tmax) is defined as a fuel injection increase amount QF.

  Then, the CPU 38 stores the solenoid valve opening time T and the fuel injection increase QF calculated as described above in a predetermined area of the RAM 40. Next, the CPU 38 proceeds to S604, and subtracts the value ΔA calculated in S601 from the upper limit value A of the rich spike execution counter. Then, the CPU 38 determines whether or not the counter value of the rich spike execution counter is not less than the value (A−ΔA) obtained by the subtraction process.

  If it is determined in S604 that the counter value of the rich spike execution counter is less than the subtraction result (A−ΔA), the CPU 38 once ends the execution of this routine.

On the other hand, if it is determined in S604 that the counter value of the rich spike execution counter is equal to or greater than the subtraction result (A−ΔA), the CPU 38 proceeds to S605, where the counter value of the rich spike execution counter is set to the upper limit value. It is determined whether or not it is greater than or equal to A, that is, whether or not the NOx storage amount of the NOx storage catalyst 28 is in a saturated state.

  If it is determined in S605 that the counter value of the rich spike execution counter is less than the upper limit value A, the CPU 38 proceeds to S609, accesses the rich spike control execution temporary permission flag area of the RAM 40, and "1" is set. It is determined whether it is stored or “0” is stored.

  If “0” is stored in the rich spike control execution temporary permission flag area in S609 and it is determined that the execution of the rich spike control is not in the temporary permission state, the CPU 38 proceeds to S610 and executes the rich spike control execution. “1” is set in the temporary permission flag area.

  Subsequently, the CPU 38 proceeds to S611, accesses a predetermined area of the RAM 40, and reads the electromagnetic valve opening time T calculated in S603. Then, the CPU 38 performs control so that the solenoid valve 34 is fully opened for the solenoid valve opening time T in order to execute the rich spike by purging the evaporated fuel gas, and temporarily ends the execution of this routine.

  Thereafter, the CPU 38 executes this routine again, and when it is determined in S604 and S605 that the counter value of the rich spike execution counter is equal to or larger than (A−ΔA) and less than A, the rich spike control is executed in S609. It is determined that the temporary permission state is set, and the execution of this routine is temporarily terminated.

  As described above, when this routine is repeatedly executed and it is determined in S605 that the counter value of the rich spike execution counter is greater than or equal to the upper limit value A, the CPU 38 proceeds to S606.

  In S606, the CPU 38 sets “1” in the rich spike control execution permission flag area of the RAM 40, and proceeds to S607. In S607, the CPU 38 determines the fuel injection amount Q determined by the fuel injection amount control routine, the fuel injection timing IT determined by the fuel injection timing control routine, the fuel injection increase amount QF determined in S603, and the fuel injection. The total fuel injection amount Qtotal and the fuel injection timing ITtotal are calculated according to the timing correction map.

  Then, the CPU 38 proceeds to S608 to switch from stratified combustion control to homogeneous combustion control in order to execute a rich spike by increasing the fuel injection amount, and to inject fuel according to the total fuel injection amount Qtotal and the fuel injection timing ITtotal calculated in S607. The valve 9 is controlled.

According to the embodiment described above, the same effects as those of the above-described embodiment can be obtained. In the two embodiments described above, as an example of a method for selectively controlling the fuel injection valve and the solenoid valve, an example in which the increased amount of injected fuel and the evaporated fuel gas are controlled to flow into the NOx storage catalyst substantially simultaneously. 7 and 8, as shown in FIGS. 7 and 8, the exhaust air / fuel ratio is enriched by purging the evaporated fuel gas in the first half of the rich spike, and the fuel amount that is insufficient only by purging the evaporated fuel gas is injected into the fuel in the latter half. You may make it supplement with the injection increase from a valve. In this case, it is possible to reduce the amount of fuel injection applied to the rich spike, and to reliably regenerate the canister.

  Further, as shown in FIG. 9, the exhaust air / fuel ratio may be enriched by increasing the fuel injection amount in the first half of the rich spike, and the exhaust air / fuel ratio may be enriched by purging the evaporated fuel gas in the latter half.

  Further, as shown in FIG. 10, after the rich air-fuel ratio is enriched only by increasing the fuel injection amount in the first half of the rich spike, the air-fuel ratio in the combustion chamber is set to an air-fuel ratio (for example, stoichiometric air-fuel ratio) at which combustion is stable Thus, the fuel injection increase and the purge of the evaporated fuel gas may be performed in parallel. In this case, by burning the air-fuel mixture in the vicinity of the stoichiometric air-fuel ratio, the fuel injection amount and the evaporated fuel gas are controlled based on the output signal of the air-fuel ratio sensor so that the air-fuel ratio of the air-fuel mixture (or exhaust gas) becomes the desired air-fuel ratio. It is easy to perform feedback control of the purge, it is possible to prevent a rich misfire or the like due to the purge of the evaporated fuel gas, and it is possible to realize a rich spike without making the combustion unstable.

  The method for selectively controlling the fuel injection valve and the solenoid valve is not limited to the above-described example, and it is preferable to select an optimum method according to the operating state of the internal combustion engine, the state of the evaporated fuel gas, and the like. .

1 is a schematic configuration diagram of an internal combustion engine to which an exhaust emission control device according to the present invention is applied. The figure which shows the internal structure of ECU The figure which shows the specific example of purge gas arrival time control map A figure showing a specific example of a fuel injection timing correction map Flowchart showing a nitrogen oxide purification control routine The flowchart figure which shows the nitrogen oxide purification | cleaning control routine concerning other embodiment. FIG. 6 is a diagram for explaining a rich spike method according to another embodiment (1). FIG. 2 illustrates a rich spike method according to another embodiment. FIG. 3 illustrates a rich spike method according to another embodiment. FIG. 4 illustrates a rich spike method according to another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Combustion chamber 6 ... Spark plug 9 ... Fuel injection valve 16 ... Intake branch pipe 17 ... Surge tank 18 ... Intake pipe 19 ..Air cleaner box 20 ... Throttle valve 20a ... Throttle position sensor 21 ... Actuator 22 ... Air flow meter 25 ... Exhaust branch pipe 26 ... First catalyst 27 ... Exhaust pipe 28 NOx storage catalyst 29a First air-fuel ratio sensor 29b Second air-fuel ratio sensor 30 Purge passage 31 Charcoal canister 32 Evaporative fuel passage 33 Fuel tank 34 Solenoid valve 35 ... Air introduction passage 36 ... ECU

Claims (9)

A lean combustion internal combustion engine capable of combusting an air-fuel mixture in an excess oxygen state, gas supply means for supplying an evaporated fuel gas containing evaporated fuel generated in a fuel tank to an intake system of the lean combustion internal combustion engine, and the lean combustion internal combustion engine A nitrogen oxide storage reduction catalyst that stores nitrogen oxides in the exhaust when the exhaust is in an oxygen excess state, and purifies the stored nitrogen oxides when the oxygen concentration in the exhaust decreases. , An exhaust emission control device for a lean combustion internal combustion engine,
Gas state determining means for determining the state of the evaporated fuel gas supplied to the intake system of the lean combustion internal combustion engine;
According to the state of the evaporated fuel gas determined by the gas state determination means at the time when the nitrogen oxide stored in the nitrogen oxide storage reduction catalyst is to be purified, the fuel injection valve of the lean combustion internal combustion engine and the Exhaust gas purification means for a lean combustion internal combustion engine, characterized by comprising: exhaust state control means for controlling the gas supply means to bring the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage reduction catalyst into a desired state apparatus.   The exhaust state control means controls the fuel injection valve of the lean combustion internal combustion engine and the gas supply means to realize a rich spike so that the air-fuel ratio of the exhaust flowing into the nitrogen oxide storage reduction catalyst is desired. 2. The exhaust emission control device for a lean combustion internal combustion engine according to claim 1, wherein   2. The gas state discriminating means comprises vaporized fuel concentration discriminating means for discriminating a fuel concentration in an evaporated fuel gas supplied to the intake system of the lean burn internal combustion engine by the gas supply means. Or the exhaust gas purification apparatus for a lean combustion internal combustion engine according to 2.   3. The gas state determination means comprises gas supply amount determination means for determining the amount of evaporated fuel gas supplied to the intake system of the lean combustion internal combustion engine by the gas supply means. An exhaust emission control device for a lean burn internal combustion engine.   The gas state determination means is required from the time when the gas supply means starts to supply the evaporated fuel gas to the intake system of the lean combustion internal combustion engine until the time when the evaporated fuel gas reaches the nitrogen oxide storage reduction catalyst. 3. An exhaust emission control device for a lean burn internal combustion engine according to claim 1, further comprising gas arrival time discriminating means for discriminating time.   The exhaust state control means includes a fuel injection time of the fuel injection valve, a fuel injection timing of the fuel injection valve, a supply amount of the evaporated fuel gas by the gas supply means, and a supply of the evaporated fuel gas by the gas supply means 3. An exhaust emission control device for a lean burn internal combustion engine according to claim 1, wherein the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage reduction catalyst is controlled to a desired state by controlling the timing. The lean combustion internal combustion engine is an in-cylinder injection lean combustion internal combustion engine including a fuel injection valve that directly injects fuel into a cylinder.
The exhaust state control means, when purifying the nitrogen oxide stored in the nitrogen oxide storage reduction catalyst when the fuel injection timing of the fuel injection valve is set during the compression stroke of each cylinder, 3. An exhaust emission control device for a lean burn internal combustion engine according to claim 1, wherein the fuel injection timing of the fuel injection valve is changed during the intake stroke of each cylinder. When the exhaust state control means controls both the fuel injection valve of the lean combustion internal combustion engine and the gas supply means to bring the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage reduction catalyst into a desired state. The fuel vapor supplied from the gas supply means is mainly used, and the amount of fuel deficient in the fuel vapor is supplemented by an increase in fuel injection of a fuel injection valve of the lean combustion internal combustion engine. 3. An exhaust emission control device for a lean combustion internal combustion engine according to 1 or 2. The gas supply means supplies the evaporated fuel gas by opening a solenoid valve,
The exhaust state control means is configured such that the amount of fuel that can be supplied by the evaporated fuel gas is equal to or less than the increased amount of fuel that is necessary to bring the air-fuel ratio of the exhaust flowing into the nitrogen oxide storage reduction catalyst into a desired state. The exhaust purification device of a lean burn internal combustion engine according to claim 1 or 2, wherein the opening time of the electromagnetic valve is a maximum time that can be fully opened.

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