JP3680245B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection control device for an internal combustion engine that controls a combustion air-fuel ratio of the internal combustion engine in accordance with a required engine load.
[0002]
[Prior art]
In-cylinder fuel injection valve that directly injects fuel into each cylinder of the engine, and controls the engine operating air-fuel ratio to a lean air-fuel ratio and a rich air-fuel ratio as needed, and engine combustion mode to lean air-fuel ratio stratification Internal combustion engines that switch between combustion and homogeneous mixture combustion are known.
[0003]
In such an in-cylinder injection type internal combustion engine, for example, during light and medium load operation of the engine, fuel is injected from the in-cylinder fuel injection valve during the compression stroke of each cylinder, and the combustible mixture is stratified in the vicinity of the spark plug. This makes it possible to operate the engine with a very lean air-fuel ratio as a whole. Also, in these engines, during high-load operation, fuel injection is performed during the intake stroke of each cylinder, and homogeneous combustion is performed to form a homogeneous combustible air-fuel ratio mixture in the entire combustion chamber, thereby increasing engine output. Yes. That is, in these in-cylinder fuel injection engines, the operation mode of the engine is switched between the stratified combustion mode with the lean air-fuel ratio and the homogeneous mixture combustion mode in accordance with the engine load condition.
[0004]
On the other hand, NO in the exhaust of lean air-fuel ratio_XNO to purify_XAn exhaust emission control device provided with an occlusion reduction catalyst is known. NO_XThe NOx in the exhaust is reduced when the air-fuel ratio of the inflowing exhaust is lean._XNO is absorbed when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or a rich air-fuel ratio lower than that._XIt has the property of releasing and reducing and purifying. NO like this_XIn an exhaust purification system using an occlusion reduction catalyst, after continuing operation at a lean air-fuel ratio, the engine is operated at a rich air-fuel ratio regardless of the load required for the engine._XNO absorbed from the storage reduction catalyst_XNeeds to be released and reduced and purified.
[0005]
An example of this type of in-cylinder fuel injection internal combustion engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-332071.
The engine of the publication is NO in the exhaust passage._XIt is equipped with an occlusion reduction catalyst and is operated in a wide air-fuel ratio range depending on the engine operating condition, from extremely lean air-fuel ratio stratified combustion to rich air-fuel ratio homogeneous mixture combustion. In addition, the engine disclosed in the publication discloses NO during the lean air-fuel ratio operation._XNO absorbed by the storage reduction catalyst_XIn order to release and reduce purification, when the lean air-fuel ratio operation continues for a certain period of time, the engine operation mode is changed to a rich air-fuel ratio homogeneous mixture combustion mode for a predetermined time regardless of the load required for the engine (engine operation state) Rich spike operation to switch to.
[0006]
By the way, the engine of the publication is provided with an electronically controlled throttle valve that operates independently of the driver's accelerator pedal operation, and the throttle valve opening degree is maintained at an almost nearly fully opened position in the stratified combustion mode of the engine. . For this reason, in the stratified combustion mode of the publication, the engine controls the amount of control (for example, ignition timing, fuel injection amount, fuel injection timing, throttle valve opening, etc.) for controlling the engine operating state. Degree) and the engine speed are set based on a predetermined relationship to control the operating state of the engine. Also, during a rich spike, when the operation mode is suddenly switched from the lean air-fuel ratio stratified combustion mode to the rich air-fuel ratio homogeneous mixture combustion mode, a sudden change in the engine output torque occurs due to the difference in the combustion mode and the change in the air-fuel ratio There is. For this reason, in order to prevent torque fluctuations in the engine disclosed in the publication, the accelerator opening and the engine speed are determined during the rich spike operation in the same manner as in the stratified combustion mode, including after the transition to the rich air-fuel ratio homogeneous combustion mode. The control amount is set based on the above, and the control amount is gradually changed from the value in the stratified combustion mode to the value in the rich air-fuel ratio homogeneous mixture combustion mode.
[0007]
[Problems to be solved by the invention]
However, in the engine disclosed in Japanese Patent Laid-Open No. 7-332071, a problem may occur because the engine control amount, particularly the fuel injection amount, is set based on the accelerator opening and the engine speed during the rich spike operation. .
That is, in this publication, the control amount of the engine including the fuel injection amount, the throttle valve opening, etc. at the time of the rich spike operation is determined from a numerical map prepared in advance based on the accelerator opening and the engine speed. In addition, as a numerical map used for determining the control amount, a lean air-fuel ratio stratified combustion mode map, a rich air-fuel ratio homogeneous mixture combustion mode map, and an operation mode map at an intermediate air-fuel ratio are prepared, When the air-fuel ratio is switched, the control amount is changed with time by switching the map to be used in sequence, so that the lean air-fuel ratio stratified combustion mode is shifted to the rich air-fuel ratio homogeneous mixture combustion mode.
[0008]
For this reason, for example, when the engine shifts from lean air-fuel ratio operation to rich air-fuel ratio homogeneous mixture combustion mode, the throttle valve opening and the fuel injection amount are determined from the numerical map for the rich air-fuel ratio homogeneous mixture combustion mode and the accelerator opening. The value is immediately changed to a value determined based on the engine speed. However, in actual operation, the throttle valve opening changes relatively rapidly and reaches the set value in a short time. However, since the amount of air actually drawn into the engine is delayed with respect to the change in the throttle valve opening, the throttle valve Immediately after the opening change, the engine intake air amount may not be a value corresponding to the throttle valve opening. For example, when the operation is switched from the lean air-fuel ratio operation to the rich air-fuel ratio homogeneous mixture combustion mode, the throttle valve opening is a value determined from the rich air-fuel ratio homogeneous mixture combustion mode map based on the accelerator opening and the engine speed. Similarly, the fuel injection amount is increased based on the map to achieve a predetermined rich air-fuel ratio. However, immediately after switching, the actual engine intake air amount may not be sufficiently reduced to a value corresponding to the throttle valve opening after the change. Immediately after switching, the predetermined rich air-fuel ratio is maintained at the fuel injection amount determined from the map. In some cases, the actual combustion air-fuel ratio of the engine temporarily becomes a lean air-fuel ratio near the stoichiometric air-fuel ratio. NO_XIn the lean air-fuel ratio region, the NOx storage reduction catalyst becomes more NO as the exhaust air-fuel ratio approaches the stoichiometric air-fuel ratio._XAs a result, the engine air-fuel ratio is temporarily operated at a lean air-fuel ratio in the vicinity of the theoretical air-fuel ratio immediately after shifting to the rich air-fuel ratio homogeneous mixture combustion mode during the rich spike operation. NO absorbed_XMay be released without being purified.
[0009]
For this reason, in the engine of the above publication, unpurified NO is obtained every time the rich spike operation is performed._XIs released into the atmosphere, and the exhaust properties deteriorate.
Further, in the engine of the above publication, the engine operation mode is switched between the stratified combustion mode and the homogeneous mixture combustion mode during the rich spike operation, but the rich spike operation (for example, lean air-fuel ratio) without switching the engine operation mode is performed. The fuel injection amount is determined based on the accelerator opening and the engine speed when the engine combustion air-fuel ratio changes to the rich air-fuel ratio even when the engine is operated in the homogeneous mixture combustion mode during operation. Similarly, problems such as deterioration of exhaust properties due to a delay in the change of the engine intake air amount occur.
[0010]
Also, rich spike operation of the engine is NO_XNO from the storage reduction catalyst_XThis is also executed when it is necessary to secure the brake operating negative pressure, which will be described later, in addition to the time when the pressure should be released._XThe lean air-fuel ratio exhaust near the stoichiometric air-fuel ratio flows into the storage reduction catalyst and unpurified NO_XMay be released into the atmosphere.
In view of the above-described problems, the present invention shifts the actual engine combustion air-fuel ratio to the rich air-fuel ratio in a short time during the rich spike operation, so that NO._XIt is an object of the present invention to provide a fuel injection control device for an internal combustion engine that can prevent deterioration of exhaust properties even when an occlusion reduction catalyst is used.
[0011]
[Means for Solving the Problems]
  According to the first aspect of the present invention, there is provided a fuel injection control device for an internal combustion engine that controls an engine combustion air-fuel ratio in accordance with a required engine load, wherein the fuel injection of the engine is made into an engine intake air amount and an engine speed. And a second fuel injection control means for setting the fuel injection of the engine based on the required engine load and the engine speed, and the engine is operated at a lean air-fuel ratio. A rich spike operation for operating the engine at a rich air-fuel ratio at the request of the engine auxiliary machine regardless of the required engine load, and when the air-fuel ratio is switched in the rich spike operation,While operating with a lean air-fuel ratioThe engine fuel injection is controlled by the second fuel injection control means, and the engineTheOperation with rich air-fuel ratioDoIn the meantime, a fuel injection control device for an internal combustion engine is provided which controls fuel injection of the engine by the first fuel injection control means.
[0012]
  That is, according to the first aspect of the present invention, when the rich spike operation is performed, the engineWhile operating with a lean air-fuel ratioAs in the prior art, engine fuel injection is controlled based on the required engine load (for example, accelerator opening) and the engine speed, but when the combustion air-fuel ratio of the engine is switched to the rich air-fuel ratio, the engine fuel injection is performed as intake air. It is controlled based on the amount and the engine speed. For this reason, after shifting to the rich air-fuel ratio operation, the engine fuel injection amount is also set according to the actual intake air amount. Therefore, even if the actual engine intake air amount does not correspond to the throttle valve opening immediately after shifting to the rich air-fuel ratio homogeneous mixture combustion mode, the fuel injection amount is based on the actual intake air amount. The air-fuel ratio is set to a value that makes the predetermined rich air-fuel ratio, and the predetermined rich air-fuel ratio can be obtained immediately after switching the engine combustion air-fuel ratio to the rich air-fuel ratio.
[0013]
  According to the second aspect of the present invention, the stratified charge combustion mode includes the in-cylinder fuel injection valve that directly injects fuel into the cylinder, and injects fuel during the compression stroke of each cylinder to perform lean air-fuel ratio stratified combustion, and A fuel injection control device for an internal combustion engine that operates by switching between a homogeneous mixture combustion mode in which fuel is injected during each intake stroke of each cylinder to perform homogeneous mixture combustion. And a first fuel injection control means for controlling the engine based on the engine speed, and a second fuel injection control means for setting the fuel injection of the engine based on the required engine load and the engine speed. The operation is switched between the stratified charge combustion mode and the homogeneous mixture combustion mode according to the load, and the engine is operated in the rich air / fuel ratio homogeneous mixture combustion mode at the request of the engine auxiliary equipment regardless of the required engine load. Rich Spa Perform click operation, it is in said rich spike operation performed when the engine is operated at a lean air-fuel ratio stratified charge combustion mode, engineWhile operating with lean air-fuel ratioControls engine fuel injection by the second fuel injection control means,TheOperates in rich air-fuel ratio homogeneous combustion modeDoIn the meantime, a fuel injection control device for an internal combustion engine is provided which controls fuel injection of the engine by the first fuel injection control means.
[0014]
  That is, in the invention of claim 2, when the rich spike operation is performed, the engineWhile operating with lean air-fuel ratioAs in the prior art, engine fuel injection is controlled based on the required engine load (for example, accelerator opening) and the engine speed, but when the engine operation is switched to the rich air-fuel ratio homogeneous mixture combustion mode, the engine fuel is injected. The injection is controlled based on the intake air amount and the engine speed. For this reason, after the shift to the rich air-fuel ratio homogeneous mixture combustion mode, the engine fuel injection amount is also set according to the actual intake air amount. Therefore, even if the actual engine intake air amount does not correspond to the throttle valve opening immediately after shifting to the rich air-fuel ratio homogeneous mixture combustion mode, the fuel injection amount is based on the actual intake air amount. The air-fuel ratio is set to a value that makes the predetermined rich air-fuel ratio, and the predetermined rich air-fuel ratio can be obtained immediately after switching to the rich air-fuel ratio homogeneous combustion mode.
[0015]
According to a third aspect of the present invention, the engine auxiliary device is disposed in the engine exhaust passage, and the NO in the exhaust is exhausted when the inflowing exhaust air-fuel ratio is lean._XAbsorbed when the exhaust air-fuel ratio that flows in becomes rich._XNO is released and reduced and purified._XIt is an occlusion reduction catalyst, and the rich spike operation is NO_XNO absorbed from the storage reduction catalyst_XA fuel injection control device for an internal combustion engine according to claim 1 or 2 executed when reducing and purifying the fuel.
[0016]
That is, in the invention of claim 3, NO is determined._XNO absorbed from the storage reduction catalyst_XEven when a rich spike operation is performed to release the engine, the actual engine combustion air-fuel ratio becomes the predetermined rich air-fuel ratio immediately after switching to the rich air-fuel ratio homogeneous mixture combustion mode. Fuel ratio exhaust is NO_XUnpurified NO, no longer flowing into the storage reduction catalyst_XIs prevented from being released into the atmosphere.
[0017]
According to the fourth aspect of the present invention, an air-fuel ratio sensor that is disposed in the engine exhaust passage and detects the air-fuel ratio of the exhaust is further provided, and the engine combustion air-fuel ratio is determined based on the air-fuel ratio sensor output during the rich spike operation. The fuel injection control device for an internal combustion engine according to claim 1 or 2, wherein the fuel injection control device is controlled to a predetermined air-fuel ratio.
That is, according to the fourth aspect of the invention, the engine combustion air-fuel ratio is controlled based on the actual exhaust air-fuel ratio (engine combustion air-fuel ratio) detected by the exhaust air-fuel ratio sensor during the rich spike operation. The accuracy of air-fuel ratio control is improved.
[0018]
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 when the present invention is applied to an automobile internal combustion engine.
In FIG. 1, reference numeral 1 denotes an automobile internal combustion engine. In this embodiment, the engine 1 is a four-cylinder gasoline engine having four cylinders # 1 to # 4, and each cylinder is provided with in-cylinder fuel injection valves 111 to 114 for directly injecting fuel into the cylinder. ing. As will be described later, the internal combustion engine 1 of the present embodiment is an engine that can be operated in a wide range of air-fuel ratios from a lean air-fuel ratio higher than the stoichiometric air-fuel ratio to an air-fuel ratio lower than the stoichiometric air-fuel ratio (rich). Yes.
[0019]
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 this embodiment, start catalysts (hereinafter referred to as “SC”) 5a and 5b made of a known 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.
[0020]
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._XIt is an air-fuel ratio sensor arranged on the downstream side 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.
[0021]
In FIG. 1, reference numeral 10 b denotes an intake manifold that connects an intake port of each cylinder of the engine to the intake passage 10, and reference numeral 10 a denotes a surge tank provided in the intake passage 10.
In the present embodiment, the SC2b upstream side of the individual exhaust passages 2b of the # 2 and # 3 cylinders and the surge tank 10a of the engine intake passage 10 are connected by an EGR passage 43. Further, an EGR valve 41 is provided on the EGR passage 43. The EGR valve 41 is a flow rate control valve that controls an exhaust flow rate that flows back from the exhaust passage 2b to the intake passage 10 through the EGR passage. The EGR valve 41 includes an actuator 41a of an appropriate type such as a stepper motor or a negative pressure actuator that operates according to a control signal from the ECU 30, which will be described later, and takes an opening degree according to the control signal from the ECU 30.
[0022]
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.
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, NO_XNO from the storage reduction catalyst 7_XA rich spike operation for switching the operating air-fuel ratio to the rich air-fuel ratio is performed during the lean air-fuel ratio operation of the engine in order to ensure the release operation and brake negative pressure.
[0023]
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 pipe pressure of the engine from an intake pressure sensor 35 provided in an unillustrated engine intake manifold, the engine crankshaft A pulse signal is input at every engine crankshaft rotation angle from a rotation speed sensor 33 arranged in the vicinity (not shown). 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 ECU 30 AD-converts the intake pressure sensor 35 output and the accelerator opening sensor 37 output at predetermined intervals and stores them in a predetermined area of the RAM of the ECU 30 as the intake pipe pressure PM and the accelerator opening ACCP. The engine speed NE is calculated from the interval of the pulse signals from and stored in a predetermined area of the RAM. 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).
[0024]
Further, the ECU 30 is connected to the actuator 41a of the EGR valve 41 via a drive circuit (not shown) and controls the opening degree of the EGR valve 41 so that a part of the exhaust gas in the exhaust passage 2b is returned to the intake passage 10 according to the engine operating state. Perform EGR operation.
In the present embodiment, during normal operation of the engine 1 (when a rich spike operation described later is not performed), the ECU 30 operates the engine 1 in one of the following five modes according to operating conditions.
[0025]
(1) Lean air-fuel ratio stratified combustion (injection once in the compression stroke)
(2) Lean air-fuel ratio weak stratified combustion (intake stroke / injection stroke twice)
(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 in the mode (1) is performed. The engine 1 includes two intake valves, an intake valve having a swirl port for generating a swirl (swirl flow) of intake air in the cylinder, and an intake valve having a normal straight port, and an intake passage communicating with the straight port The amount of intake air flowing into the cylinder from the swirl port can be controlled by adjusting the opening degree of a swirl control valve (SCV) (not shown) provided in the cylinder. When stratified combustion is performed, the SCV opening is fully closed, the amount of intake air from the swirl port is increased, and a strong swirl is generated in the cylinder. 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 in the vicinity of 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 or more.
[0026]
Further, when the load increases from the state of the mode (1) to enter the low load operation region, the lean air-fuel ratio weak stratified combustion in the mode (2) is performed. As the engine load increases, the amount of fuel injected into the cylinder increases. In this load region, in addition to fuel injection in the latter half of the compression stroke, fuel is injected into the cylinder in the first half of the intake stroke in advance. I am trying to supply. 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 mode (1), but the overall air-fuel ratio is slightly low (for example, about 20 to 30 in the air-fuel ratio).
[0027]
When the engine load further increases, the engine 1 performs lean air-fuel ratio homogeneous mixture combustion in the mode (3). In this state, the SCV is fully opened, and most of the intake air flows into the cylinder from the straight port. In this state, the fuel injection is executed only once in the first half of the intake stroke, and the fuel injection amount is further increased from that in the mode (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 of mode (3), and the stoichiometric air-fuel ratio homogeneous mixture operation of mode (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. Further, when the engine load further increases and the engine is fully loaded, the fuel injection amount is further increased from the state of mode (4), and the rich air-fuel ratio homogeneous mixture operation of mode (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 operation of the engine 1, the ECU 30 determines which one of the operation modes (1) to (5) should be selected based on the accelerator opening detected by the accelerator opening sensor 37 and the engine speed, Control amounts for controlling the engine operating state, such as fuel injection amount, fuel injection timing and frequency, ignition timing, throttle valve opening, EGR amount (EGR valve opening), are determined according to each 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.
More specifically, when the mode (1) to (3) (lean air-fuel ratio combustion) is selected, the ECU 30 is based on a map prepared in advance for each of the modes (1) to (3). Control amounts such as the fuel injection amount, fuel injection timing, throttle opening, EGR amount, and ignition timing are determined from the accelerator opening and the engine speed. The accelerator opening represents the engine load required by the driver. Accordingly, in modes {circle around (1)} to {circle around (3)}, the value of each control amount such as the fuel injection amount is set based on the required engine load and the engine speed.
[0031]
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 control amount such as the fuel injection amount is set based on the throttle valve opening, the engine speed, and the intake pipe pressure detected by the intake pressure sensor 35. Generally, the engine intake air amount is expressed as a function of the engine speed and the intake pipe negative pressure. Further, the engine intake air amount and the engine speed are used as parameters representing the engine load state. For this reason, in the modes (4) and (5), each control amount such as the fuel injection amount is set to a desired idle speed by further considering the engine speed in addition to the engine intake air amount determined from the engine speed and the intake pipe negative pressure. It is set to a value necessary for obtaining the fuel ratio. That is, in the present embodiment, in the homogeneous mixture combustion operation in modes (4) and (5), the value of each control amount such as the fuel injection amount is set based on the engine intake air amount and the engine speed.
[0032]
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, when the accelerator opening decreases, the throttle valve opening also decreases.However, since this is a region corresponding to the throttle valve fully open, the intake pipe pressure becomes substantially constant even if the throttle valve opening changes, and the intake throttle is almost constant. Does not occur.
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 (the amount of depression of the accelerator pedal) is 0, the throttle opening is also 0 (fully closed), and when the accelerator opening is 100% (when the accelerator pedal is fully depressed), the throttle opening Is also set to 100 percent (fully open).
[0033]
The opening degree of the EGR valve 41 is set so that a relatively large amount of EGR gas is recirculated in the mode (1), and is controlled so that the EGR gas amount decreases as the mode changes from (2) to (3). . In modes (4) and (5), EGR is almost stopped.
Next, NO of this embodiment_XThe storage reduction catalyst 7 will be described.
NO of this embodiment_XThe occlusion reduction catalyst 7 uses, for example, alumina as a carrier, and an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earth such as barium Ba and calcium Ca, lanthanum La, cerium, and the like. 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 NO_Three ^-NO is absorbed when the inflowing exhaust gas becomes rich_XNO release_XPerforms absorption and release action.
[0034]
In the present embodiment, an engine 1 capable of lean air-fuel ratio operation is used, and when the engine 1 is operated at a 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._XNO released by using HC and CO components in rich air-fuel ratio exhaust gas_XReduce 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.
[0035]
Next, the rich spike operation of the engine 1 of the present embodiment will be described.
In this embodiment, the ECU 30 is NO_XNO by increasing or decreasing the counter value_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 operating conditions (accelerator opening degree, engine speed, intake air amount, intake pipe pressure, air-fuel ratio, fuel supply amount, EGR 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_XSet this counter to NO_XIncrease the amount absorbed. This makes NO_XThe counter value 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 increases to a predetermined value or more, a rich spike operation is performed in which the engine is operated in the mode (5) (rich air-fuel ratio homogeneous mixture combustion) for a short time. As a result, NO_XNO absorbed from the storage reduction catalyst_XIs released and reduced and purified. When the engine is operated at a rich air-fuel ratio, the amount of HC and CO in the exhaust increases, and NO_XNO from the storage reduction catalyst_XIs released and reduced by HC and CO in the exhaust. Here, NO per unit time_XNO released from the storage reduction catalyst and reduced by HC and CO in the exhaust_XIs determined by the air-fuel ratio of the exhaust gas (HC and CO amount in the exhaust gas) and the exhaust gas flow rate. In this embodiment, the engine is operated at a rich air-fuel ratio by changing the engine operating conditions (accelerator opening, engine speed, intake air amount, intake pipe pressure, air-fuel ratio, fuel supply amount, EGR amount, etc.) in advance._XNO released from the storage reduction catalyst 7 per unit time and reduced and purified_XMeasure the amount, NO during engine rich air-fuel ratio operation_XNO released from 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) during the rich air-fuel ratio operation of the engine._XNO released from the storage reduction catalyst_XCalculate the amount, NO_XSet this counter to NO_XDecrease by the amount absorbed. And during rich spike operation, this NO_XWhen the counter value reaches zero, the rich spike operation is terminated.
[0036]
  That is, in this embodiment, the lean air-fuel ratio operation of the engine 1 continues and NO_XNO stored in the storage reduction catalyst 7_XWhen the amount increases to a predetermined amount, a rich spike operation is performed in which the engine is operated at a rich air-fuel ratio regardless of the engine load required from the engine operating state. Rich spike operation is NO_XNO stored in the NOx storage reduction catalyst_XMay be done separately from quantity. That is, in the engine of this embodiment, the mode(1)From(3)In this lean air-fuel ratio operation, the throttle valve 15 has an opening close to full open, so the negative pressure in the intake pipe is low (the absolute pressure is high). On the other hand, when using a booster that uses negative pressure for vehicle braking, it is necessary to always maintain a negative pressure for operating the booster. Since the pressure is low, negative pressure cannot be introduced into the booster from the intake passage downstream of the throttle valve. Therefore, in the present embodiment, the booster is provided with a negative pressure tank, and the booster is operated using the negative pressure stored in the negative pressure tank during the lean air-fuel ratio operation. Further, when the pressure in the negative pressure tank increases (negative pressure decreases) due to the operation of the booster, a rich spike operation similar to the above is performed. When the rich spike operation is performed in the load region where the lean air-fuel ratio operation is performed, the opening degree of the throttle valve 15 decreases and a large negative pressure is generated downstream of the throttle valve 15. In this embodiment, even when the negative pressure of a negative pressure tank or the like that supplies negative pressure to the booster decreases, the rich spike operation is performed regardless of the required load of the engine.
  Mode during normal operation(1)When the engine load increases due to acceleration, etc., from lean air-fuel ratio stratified combustion operation, it takes some time to change the engine operation mode.(1)From(2),(3),(4)Through the mode(5)Is switched to the rich air-fuel ratio mode. During rich spike operation, it is necessary to switch the air-fuel ratio to rich as soon as possible.(1)Direct mode from lean air-fuel ratio stratified combustion operation(5)When switching to a rich air-fuel ratio homogeneous mixture combustion of the engine, both the combustion mode change (stratified combustion to homogeneous mixture combustion) and the air-fuel ratio change (lean air-fuel ratio to rich air-fuel ratio) occur simultaneously, so the engine output torque Will fluctuate greatly. Therefore, normally, lean air-fuel ratio stratified combustion operation (mode(1)Rich air-fuel ratio homogeneous mixture combustion operation (mode)(5)Mode)(2),(3)Thus, the engine is operated for about several engine revolutions, and the air-fuel ratio and the operation mode are gradually switched. Also, as described above, the mode during normal operation(5)In (rich air-fuel ratio homogeneous mixture combustion), the control amount such as the fuel injection amount of the engine is set based on the engine intake air amount and the engine speed (engine intake pipe negative pressure and engine speed). Rich spike operation mode(5)Because the operation time is short, the mode during rich spike operation(5)In operation, the mode(1)From(3)In the same manner as above, the control is simplified by setting based on the required engine load and the engine speed (accelerator opening and engine speed). In other words, the conventional mode for rich spike operation(5)(richA separate numerical map is prepared for (air-fuel ratio homogeneous mixture air-fuel ratio combustion) and mode during rich spike(3)From mode(5)When the switch to is made, each control amount including the fuel injection amount is determined based on the required engine load and the engine speed (accelerator opening and engine speed).
[0037]
However, in this case, the fuel injection amount and the throttle valve opening immediately change to values determined from a numerical map prepared in advance based on the required engine load and the engine speed. The amount of air that is changed changes later than the change in the throttle valve opening, so that there is a slight time delay until the value corresponds to the throttle valve opening after the change. Therefore, when the mode is switched to the mode (5), the actual engine intake air amount does not decrease immediately even if the throttle valve opening decreases immediately. On the other hand, since the fuel injection amount is changed to a value corresponding to the throttle valve opening immediately after switching to the mode (5), the actual engine intake air amount becomes larger than the fuel injection amount immediately after the switching. There arises a problem that the air-fuel ratio deviates from the target value (rich air-fuel ratio) to the lean side.
[0038]
For this reason, immediately after the engine air-fuel ratio is switched to the rich air-fuel ratio (mode (5)) during the rich spike operation, the engine air-fuel ratio is operated in a lean air-fuel ratio region (for example, 20 or less in the air-fuel ratio) near the stoichiometric air-fuel ratio. NO_XUnpurified NO due to reduced storage capacity of storage reduction catalyst_XWas released into the atmosphere.
In the present embodiment, this problem is solved by setting the fuel injection amount based on the engine intake air amount and the engine speed in the rich air-fuel ratio homogeneous mixture combustion mode during the rich spike operation. That is, in this embodiment, when the engine operation mode is switched to the rich air-fuel ratio homogeneous mixture combustion mode of mode (5) during the rich spike operation, the fuel injection amount is detected by the intake pipe pressure and the engine speed detected by the intake pressure sensor. Is set to a value that obtains a predetermined rich air-fuel ratio (for example, 12 to 14 as the air-fuel ratio) based on the actual engine intake air amount determined from the engine rotational speed. Therefore, immediately after the engine operation mode is switched to the rich air-fuel ratio homogeneous mixture combustion mode, the fuel injection amount is set to a value that provides a predetermined rich air-fuel ratio with respect to the actual engine intake air amount. A stable rich air-fuel ratio can be obtained immediately after switching.
[0039]
FIG. 2 is a timing diagram showing changes in the throttle valve opening TA, the intake pipe pressure PM, the fuel injection amount QINJ, and the engine combustion air-fuel ratio A / F during the rich spike operation of the present embodiment. As shown in FIG. 2, when the rich spike operation is started from the mode (1) (lean air-fuel ratio stratified combustion), the operation mode is switched to the mode (5) through the modes (2) and (3). . At this time, when the throttle valve opening TA is switched to the mode (2) and the mode (3), the accelerator opening and the engine speed (required engine load) are based on the numerical maps for the respective operation modes during the rich spike operation. And the engine speed). In this case, as shown in FIG. 2, even if the throttle valve opening TA changes, the intake air amount (intake pipe pressure PM) does not immediately become a value corresponding to the changed throttle valve opening but changes relatively slowly. Thus, the air amount in the steady state of mode (5) is reached.
[0040]
Also in this embodiment, the fuel injection amount QINJ is set based on the accelerator opening and the engine speed in the modes (1) to (3), so that the operation mode is ▲ as shown in FIG. Each time it is switched between 2 ▼ and 3), it changes in a step-like manner similar to the throttle valve opening TA. However, in this embodiment, when the operating state is switched from mode (3) to mode (5), the fuel injection amount QINJ is set according to the engine intake air amount and the engine speed (intake pipe negative pressure and engine speed). Therefore, immediately after the mode (5) is switched, it temporarily increases to a value corresponding to the actual intake air amount, and then decreases as the intake air amount (PM) decreases. Therefore, the engine combustion air-fuel ratio A / F immediately changes to a predetermined rich air-fuel ratio (about 12 to 14) when the operation mode is switched from mode (3) to mode (5).
[0041]
On the other hand, the dotted line in FIG. 2 shows the fuel immediately after the start of the mode (5) when the fuel injection amount is set based on the required engine load and the engine speed during operation in the mode (5) at the time of rich spike as in the prior art. Changes in the injection amount QINJ and the engine air-fuel ratio A / F are shown. In this case, as shown by a dotted line in FIG. 2, when the mode (3) is switched to (5), the fuel injection amount QINJ changes in a step shape in accordance with the change in the throttle valve opening TA, and the mode (5) It is maintained at a constant value during the operation of ▼. However, since the engine intake air amount actually changes with a delay with respect to the change in the throttle valve opening TA as described above, the intake air amount is not sufficiently reduced immediately after the start of the operation in the mode (5). For this reason, the intake air amount becomes excessive with respect to the fuel injection amount, and the engine air-fuel ratio A / F is sufficient rich air-fuel ratio until the intake air amount is sufficiently reduced to a value corresponding to the throttle valve opening. do not become. Therefore, the time during which the engine air-fuel ratio stays in the lean air-fuel ratio region near the stoichiometric air-fuel ratio becomes longer, and NO_XUnpurified NO from the storage reduction catalyst_XWill be released.
[0042]
FIG. 3 is a flowchart showing the calculation operation of the fuel injection amount QINJ described above. This operation is performed as a routine executed by the ECU 30 at regular intervals.
In FIG. 3, in step 301, the current engine operation mode (modes (1) to (5)) is read. In step 303, the current operation mode read in step 301 is mode (4) (stoichiometric air-fuel ratio homogeneous mixture combustion) during normal operation (operation other than when the rich spike operation is performed) or mode (5) ( In step 305, the current mode is the mode (5) (rich air-fuel ratio homogeneous mixture) during the rich spike operation. It is determined whether or not it is (combustion).
[0043]
If the current engine operation mode is the normal operation mode (4) or (5) in step 303, or the current operation mode is the rich spike operation mode (5) in step 305, step 307 is executed. Then, the value of the fuel injection amount QINJ is determined from a numerical map prepared in advance based on the intake pipe pressure PM detected by the intake pressure sensor 35 (FIG. 1) and the engine speed NE. As a result, the fuel injection amount QINJ is set to a value capable of obtaining a predetermined rich air-fuel ratio based on the actual engine speed and the actual engine intake air amount, and the engine air-fuel ratio immediately becomes the predetermined rich air-fuel ratio. Change.
[0044]
On the other hand, if the current engine operation mode is not any of the normal operation mode (4), (5) and the rich spike operation mode (5) in steps 303 and 305, step 309 is executed and the fuel is The injection amount QINJ is set based on the accelerator opening ACCP detected by the accelerator opening sensor 37 and the engine speed. As a result, in the modes (1) to (3), the fuel injection amount QINJ is always set to a value according to the required engine load and the engine speed.
[0045]
In the present embodiment, as described above, the engine air-fuel ratio changes to the predetermined rich air-fuel ratio as soon as the operation of the mode (5) is performed during the rich spike operation._XUnpurified NO from the storage reduction catalyst_XIs prevented from being released. For example, NO_XThe degradation of the storage reduction catalyst is NO_XNO when the exhaust air-fuel ratio flowing into the storage reduction catalyst changes from lean to rich_XThe determination can be made based on the time required for the exhaust air-fuel ratio at the storage reduction catalyst outlet to change richly. That is, NO during rich spike operation_XNO absorbed from the storage reduction catalyst_XNO is released when HC and CO components in the exhaust are released_XBecause it is oxidized by NO_XThe exhaust air-fuel ratio at the storage reduction catalyst outlet does not immediately change to the rich air-fuel ratio,_XNO from storage reduction catalyst_XWhile being released, it is maintained near the stoichiometric air-fuel ratio, and NO_XAs soon as the release of the gas is completed, the air-fuel ratio changes to a rich air-fuel ratio. Therefore, when the engine air-fuel ratio is switched from lean to rich during the rich spike operation, NO_XBy measuring the time until the exhaust air-fuel ratio detected by the air-fuel ratio sensor 31 downstream of the storage reduction catalyst 7 changes to the rich air-fuel ratio, NO_XNO absorbed by the storage reduction catalyst_XThe amount can be calculated and the calculated NO_XAbsorption NO of storage reduction catalyst_XNO if the amount drops below a predetermined value_XNO of storage reduction catalyst_XOcclusion capacity declines, ie NO_XIt can be determined that the storage reduction catalyst has deteriorated.
[0046]
However, if the fuel injection amount is set based on the required engine load and the engine speed at the time of rich spike operation as in the prior art, the engine operation mode can be switched to the rich air-fuel ratio homogeneous mixture combustion mode. Immediately, the actual air-fuel ratio does not change to the rich air-fuel ratio, and NO_XVariations occur in the air-fuel ratio of the exhaust flowing into the storage reduction catalyst. For this reason, NO_XWhen the deterioration of the storage reduction catalyst is determined, there is a problem that an error occurs in the determination of the deterioration.
[0047]
On the other hand, in this embodiment, NO immediately after the rich air-fuel ratio homogeneous mixture operation during the rich spike operation._XSince the exhaust air-fuel ratio flowing into the storage reduction catalyst changes to a stable rich air-fuel ratio, it is possible to prevent the deterioration determination error.
In this embodiment, the actual engine intake air amount is obtained based on the intake pipe pressure and the engine speed. However, for example, when the intake passage has an air flow meter, the intake air amount directly detected by the air flow meter. The fuel injection amount during the rich air-fuel ratio homogeneous mixture combustion operation during the rich spike operation may be determined based on the engine speed.
[0048]
In the present embodiment, the fuel injection amount is set based on the engine intake air amount and the engine speed during the rich air-fuel ratio homogeneous mixture combustion during the rich spike operation._XFuel injection set based on the engine intake air amount and the engine speed so that the exhaust air-fuel ratio detected by the air-fuel ratio sensors 29a, 29b in the exhaust passage upstream of the storage reduction catalyst 7 becomes a predetermined rich air-fuel ratio. If the amount is further corrected based on the outputs of the air-fuel ratio sensors 29a and 29b, the air-fuel ratio can be accurately controlled to a predetermined rich air-fuel ratio during the rich spike operation.
[0049]
As described above, in the above embodiment, the fuel injection amount is set based on the engine intake air amount and the engine speed during the rich air-fuel ratio homogeneous mixture combustion during the rich spike operation, so that the lean air-fuel ratio is changed to the rich air-fuel ratio. The time required for the engine air-fuel ratio to change to a predetermined rich air-fuel ratio when switching to is shortened. However, it is possible to shorten the time while setting the fuel injection amount based on the required engine load and the engine speed as in the prior art.
[0050]
As described above, at the time of switching from the lean air-fuel ratio to the rich air-fuel ratio, the cause of the delay in reaching the predetermined rich air-fuel ratio is due to the delay in following the actual change in the intake air amount with respect to the change in the throttle valve opening. For this reason, for example, when the throttle valve opening changes during the rich spike operation (when switching from mode (3) to (5)), the fuel may be increased according to the change speed of the throttle valve opening. In this case, for example, when the change rate (decrease rate) of the throttle valve opening is large, the difference between the actual intake air amount immediately after the change and the intake air amount corresponding to the throttle valve opening becomes large. The fuel may be increased as the change rate of the degree increases.
[0051]
FIG. 4 is a flowchart for explaining the fuel injection amount correction operation in the case of performing fuel increase correction in accordance with the throttle valve opening change speed. This operation is executed by the ECU 30 at regular intervals.
When the operation starts in FIG. 4, the throttle valve opening degree TA, the engine speed NE, and the current engine operation mode (modes (1) to (5)) are read in step 401, and read in step 401 in step 403. It is determined whether or not the current engine operation mode is the mode (5) (rich air-fuel ratio homogeneous mixture combustion mode) during the rich spike operation. If the operation is being performed in the mode (5) in which the rich spike operation is currently performed, the process proceeds to step 405, and the change amount ΔTA of the current throttle valve opening TA from the previous execution time is ΔTA = TA− TA_OLDIs calculated as TA_OLDIs the throttle valve opening read in step 401 when the previous operation was executed. In step 407, the fuel injection amount increase coefficient fdlta is set from a numerical map prepared in advance based on ΔTA and the engine speed NE. In step 419, the fuel injection amount QINJ is determined from the accelerator opening and the engine speed. A value obtained by multiplying the increase coefficient fdlta is newly set as QINJ. As described above, the increase coefficient fdlta is set such that the larger ΔTA is, the larger the positive value and fdlta> 1. If ΔTA is the same, the value of fdlta increases as the engine speed increases.
[0052]
After correcting QINJ as described above, in step 411, the current TA value is used._OLDUpdate the value of and end the operation.
By performing the operation of FIG. 4, the fuel injection amount is increased when the rich air-fuel ratio homogeneous mixture combustion mode is set during the rich spike operation and the throttle valve opening TA is throttled, so that the actual engine intake air amount is sufficient. Even if the air-fuel ratio has not decreased to the actual value, the actual air-fuel ratio of the engine immediately changes to a rich air-fuel ratio._XUnpurified NO from the storage reduction catalyst_XIs prevented from being released.
[0053]
Instead of increasing the fuel in accordance with the throttle valve opening change amount ΔTA as described above, the target air-fuel ratio is set for a predetermined time immediately after the operation mode is switched to the rich air-fuel ratio homogeneous mixture combustion mode during the rich spike operation. Further, it may be set to the rich side. By setting the target air-fuel ratio to be rich for a predetermined time immediately after the rich air-fuel ratio homogeneous mixture combustion mode change, the engine air-fuel ratio becomes a lean air-fuel ratio in the vicinity of the theoretical air-fuel ratio while the intake air amount change is not sufficiently reduced. To prevent_XUnpurified NO from the storage reduction catalyst_XIs prevented from being released.
[0054]
【The invention's effect】
According to the invention described in each claim, it is possible to change the engine air-fuel ratio from the lean air-fuel ratio to the rich air-fuel ratio in a short time during the rich spike operation._XEven when a storage reduction catalyst is used, unpurified NO in the initial stage of rich spike operation_XCan be prevented from being released into the atmosphere.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automotive cylinder injection internal combustion engine.
FIG. 2 is a timing diagram illustrating an example of a rich spike operation according to the present invention.
FIG. 3 is a flowchart for explaining a rich spike operation of FIG. 2;
FIG. 4 is a flowchart for explaining another example of the rich spike operation.
[Explanation of symbols]
1. Internal combustion engine
2 ... Exhaust passage
7 ... NO_XOcclusion reduction catalyst
15 ... Electronically controlled throttle valve
111-114 ... In-cylinder injection valve

Claims (4)

A fuel injection control device for an internal combustion engine that controls an engine combustion air-fuel ratio according to a required engine load,
First fuel injection control means for controlling engine fuel injection based on engine intake air amount and engine speed, and second fuel for setting engine fuel injection based on required engine load and engine speed An injection control means,
When the engine is operated at a lean air-fuel ratio, a rich spike operation is performed to operate the engine at a rich air-fuel ratio at the request of the engine auxiliary machine regardless of the required engine load,
When switching the air-fuel ratio in the rich spike operation, the engine fuel injection is controlled by the second fuel injection control means while the engine is operated at a lean air-fuel ratio, and the first fuel-fuel ratio is controlled while the engine is operated at a rich air-fuel ratio. A fuel injection control device for an internal combustion engine that controls fuel injection of the engine by the fuel injection control means. In-cylinder fuel injection valve that injects fuel directly into the cylinder, stratified combustion mode in which fuel is injected during the compression stroke of each cylinder to perform lean air-fuel ratio stratified combustion, and fuel is injected during the intake stroke of each cylinder A fuel injection control device for an internal combustion engine that operates by switching between a homogeneous mixture combustion mode for performing homogeneous mixture combustion,
First fuel injection control means for controlling engine fuel injection based on engine intake air amount and engine speed, and second fuel for setting engine fuel injection based on required engine load and engine speed An injection control means,
The operation is switched between the stratified combustion mode and the homogeneous mixture combustion mode according to the required engine load, and the engine is operated in the rich air fuel ratio homogeneous mixture combustion mode at the request of the engine auxiliary machine regardless of the requested engine load. Rich spike operation to drive,
During the rich spike operation when the engine is operated in the lean air-fuel ratio stratified combustion mode, the engine fuel injection is controlled by the second fuel injection control means while the engine is operated at the lean air-fuel ratio , engine fuel injection control apparatus for an internal combustion engine during the controlling fuel injection of the engine by said first fuel injection control means for operating in a homogeneous mixture combustion mode rich air-fuel ratio. The engine accessory, the release of NO _X exhaust air-fuel ratio is absorbed when it is rich exhaust air-fuel ratio flowing disposed engine exhaust passage flows to absorb NO _X in the exhaust gas when the lean, reducing and purifying NO _X is storage-reduction catalyst, the rich-spike operation is to release NO _X absorbed from _the NO _X storage reduction catalyst, fuel for an internal combustion engine according to claim 1 or claim 2 is performed when the reduction and purification of Injection control device. The engine combustion air-fuel ratio is further controlled to a predetermined air-fuel ratio based on an output of the air-fuel ratio sensor during the rich spike operation. Or the fuel-injection control apparatus of the internal combustion engine of Claim 2.

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