JP2000234541A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the time to reach a rich air-fuel ratio in rich spike operation. SOLUTION: An NOx occulsion reduction catalyst 7 is arranged in an exhaust passage 2 of an internal combustion engine 1 having inner cylinder injection valves 111 to 114. NOx in the exhaust gas is absorbed by the catalyst 7 by operating the engine under a lean air-fuel ratio stratification combustion mode. Then the engine is operated under a rich air-fuel ratio even mixture combustion mode. By this rich-spike operation, NOx absorbed by the catalyst 7 is reduced and purified. An electronic control unit(ECU) 30 sets an engine fuel injection amount under the rich air-fuel ratio even mixture combustion mode during rich-spike operation, based on an intaken air amount and an engine speed. Since the fuel injection amount is set according to the actual intake amount, it is possible to vary the engine air-fuel ratio to a specified rich value in a short time irrespective of variation retarding of the intake amount at the time of changeover of the modes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 according to a required engine load.

[0002]

2. Description of the Related Art An in-cylinder fuel injection valve for directly injecting fuel into each cylinder of an engine is provided. The operating air-fuel ratio of the engine is controlled to a lean air-fuel ratio and a rich air-fuel ratio as required. There is known an internal combustion engine that switches between a lean air-fuel ratio stratified combustion and a homogeneous mixture combustion.

[0003] In such a direct injection internal combustion engine, for example, when the engine is operating at light or medium load, fuel is injected from the direct fuel injection valve during the compression stroke of each cylinder, and a combustible air-fuel mixture is supplied to the vicinity of the ignition plug. The stratification makes it possible to operate the engine with an extremely lean air-fuel ratio as a whole. In addition, these engines can increase the engine output by performing fuel injection during the intake stroke of each cylinder during high-load operation and performing homogeneous mixture combustion to form a homogeneous mixture with a combustible air-fuel ratio throughout the combustion chamber. I have. That is, in these in-cylinder fuel injection engines, the operation mode of the engine is switched between a stratified combustion mode having a lean air-fuel ratio and a homogeneous mixture combustion mode in accordance with the engine load condition.

[0004] On the other hand, there is known an exhaust gas purifying apparatus provided with a NO _X storage reduction catalyst for purifying NO _X in exhaust gas having a lean air-fuel ratio. _The NO _X storage reduction catalyst absorbs NO _X in the exhaust gas when the air-fuel ratio of the exhaust gas flowing is lean, the air-fuel ratio is the stoichiometric air-fuel ratio of the exhaust gas flowing NO _X to or absorbed to become rich air-fuel ratio of the following, And has the property of reducing and purifying. In such an exhaust gas purification apparatus using the NO _X storage reduction catalyst, after operating at a lean air-fuel ratio, the engine is operated at a rich air-fuel ratio regardless of the load required for the engine, and the NO _X storage reduction is performed. to release NO _X absorbed from the catalyst, it is necessary to reduce and purify.

[0005] As an example of this kind of in-cylinder fuel injection type internal combustion engine,
For example, Japanese Patent Application Laid-Open No. 7-332071 describes
There are things. The engine of the publication discloses NO in the exhaust passage._XOcclusion return
Stratified combustion with extremely lean air-fuel ratio
Engine operation from combustion to homogeneous air / fuel mixture with rich air-fuel ratio
It is operated in a wide air-fuel ratio range accordingly. In addition, the
Seki is NO during lean air-fuel ratio operation _XAbsorbed by storage reduction catalyst
NO_XTo reduce and purify the lean air-fuel ratio
Load required by the engine when operation continues for some time
Engine operation mode for a predetermined time regardless of (engine operation state).
Mode to rich air-fuel ratio homogeneous mixture combustion mode
Perform a rich spike operation.

The engine disclosed in this publication has an electronically controlled throttle valve that operates independently of the driver's operation of the accelerator pedal. In the stratified combustion mode of the engine, the throttle valve opening is set to an almost full opening. Will be maintained. For this reason,
In the engine disclosed in the publication, in the stratified combustion mode, a control amount (for example, ignition timing, fuel injection amount, fuel injection timing, throttle valve opening, etc.) for controlling the engine operating state is determined by a driver's accelerator pedal depression amount (accelerator opening). The operating state of the engine is controlled by setting the relationship based on a predetermined relationship using the engine speed. Also, during a rich spike, when the operation mode is suddenly switched from the stratified combustion mode having a lean air-fuel ratio to the homogeneous air-fuel mixture combustion mode having a rich air-fuel ratio, a sudden change in engine output torque occurs due to a difference in the combustion mode and a change in the air-fuel ratio. There is. For this reason, in the engine of the publication, in order to prevent the torque fluctuation from occurring, the accelerator opening and the engine speed are set at the same time as in the stratified charge combustion mode even after shifting to the rich air-fuel ratio homogeneous combustion mode during the rich spike operation. And the control amount is gradually changed from a value in the stratified combustion mode to a value in the rich air-fuel ratio homogeneous mixture combustion mode.

[0007]

However, in the engine disclosed in Japanese Patent Application Laid-Open No. 7-332071, the control amount of the engine, particularly the fuel injection amount, is set based on the accelerator opening and the engine speed during the rich spike operation. May cause problems. That is, in the publication, the control amount of the engine including the fuel injection amount and the throttle valve opening during 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 this control amount determination, a map for a lean air-fuel ratio stratified combustion mode, a map for a rich air-fuel ratio homogeneous mixture combustion mode, and a map for an operation mode at an intermediate air-fuel ratio are prepared. When the air-fuel ratio is switched, the control amount is changed with time by sequentially switching the map to be used, so that the mode shifts from the lean air-fuel ratio stratified combustion mode to the rich air-fuel ratio homogeneous mixture combustion mode.

For this reason, for example, when the engine shifts from the lean air-fuel ratio operation to the rich air-fuel ratio homogeneous mixture combustion mode, the throttle valve opening and the fuel injection amount are obtained from the numerical map for the rich air-fuel ratio homogeneous mixture combustion mode. The value is immediately changed to a value determined based on the opening and the engine speed. However, in actual operation, the throttle valve opening changes relatively quickly and reaches a set value in a short time.
Since the amount of air actually taken into the engine is delayed with respect to the change in the throttle valve opening, the engine intake air amount may not be a value corresponding to the throttle valve opening immediately after the change in 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 air-fuel mode map based on the accelerator opening and the engine speed. And the fuel injection amount is similarly increased based on the map to achieve a predetermined rich air-fuel ratio. However, immediately after the switching, the actual engine intake air amount may not be sufficiently reduced to a value corresponding to the throttle valve opening after the change, and immediately after the switching, the fuel injection amount determined from the map may not satisfy the predetermined rich air-fuel ratio. It cannot be obtained, and the actual combustion air-fuel ratio of the engine may temporarily become a lean air-fuel ratio near the stoichiometric air-fuel ratio. _The NO _X storage reduction catalyst, the exhaust air-fuel ratio is a lean air-fuel ratio range to lower the storage capacity of more NO _X approaches the stoichiometric air-fuel ratio immediately after the rich air-fuel ratio uniform mixture combustion mode transition during the rich spike operation above As described above, when the state where the engine air-fuel ratio is temporarily operated at the lean air-fuel ratio near the stoichiometric air-fuel ratio occurs, the absorbed N
Some of O _X is in some cases been released without being purified.

For this reason, in the engine disclosed in the above publication, unpurified NO _X is released into the atmosphere every time the rich spike operation is performed, and there is a problem that 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 without switching the engine operation mode (for example, the lean air-fuel ratio). Even when the engine is operated in the homogeneous mixture combustion mode during operation), 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. In the same manner as described above, problems such as deterioration of exhaust characteristics due to a delay in change of the engine intake air amount occur.

[0010] Further, the rich spike operation of the engine is NO _X
From storage reduction catalyst in addition to when to emit NO _X, to be executed when there is a need for a brake actuation vacuum retention that will be described later, the stoichiometric air-fuel ratio of the vicinity to the NO _X occluding and reducing catalyst in this case lean air-fuel ratio exhaust gas flows unpurified NO _X may become to be discharged to the atmosphere. SUMMARY OF THE INVENTION 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
It 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 characteristics even when an _X storage reduction catalyst is used.

[0011]

According to the first aspect of the present invention, there is provided a fuel injection control device for an internal combustion engine for controlling an engine combustion air-fuel ratio in accordance with a required engine load. The first fuel injection control means controls the fuel injection of the engine based on the intake air amount and the engine speed, and the second fuel injection control means sets the fuel injection of the engine based on the required engine load and the engine speed. When the engine is operating at a lean air-fuel ratio, the engine performs a rich spike operation to operate the engine at a rich air-fuel ratio at the request of an engine accessory regardless of the required engine load, and switches the air-fuel ratio in the rich spike operation. Sometimes, while the engine combustion air-fuel ratio is lean, the second
A fuel injection control device for an internal combustion engine, wherein the fuel injection control means controls the engine fuel injection by the fuel injection control means and controls the fuel injection of the engine by the first fuel injection control means while the engine is operated at the rich air-fuel ratio. You.

That is, in the first aspect of the present invention, when the rich spike operation is performed, as long as the engine air-fuel ratio is lean, the engine fuel injection is performed based on the required engine load (eg, the accelerator opening) and the engine speed as in the related art. Control is performed, but when the combustion air-fuel ratio of the engine is switched to the rich air-fuel ratio, the fuel injection of the engine is controlled based on the intake air 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 is not a value corresponding to the throttle valve opening immediately after the transition to the rich air-fuel ratio homogeneous mixture combustion mode, the fuel injection amount is determined based on the actual intake air amount. The air-fuel ratio is set to a value that sets 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.

According to the second aspect of the present invention, a stratified fuel injection valve for directly injecting fuel into the cylinder is provided, and the fuel is injected during the compression stroke of each cylinder to perform stratified combustion with a lean air-fuel ratio. A fuel injection control device for an internal combustion engine that operates by switching between a combustion mode and a homogeneous mixture combustion mode in which fuel is injected during an intake stroke of each cylinder to perform homogeneous mixture combustion. First fuel injection control means for controlling based on the intake air amount and the engine speed, and second control for setting the fuel injection of the engine based on the required engine load and the engine speed.
Fuel injection control means for switching the operation between the stratified combustion mode and the homogeneous mixture combustion mode according to the required engine load, and irrespective of the required engine load, the rich air-fuel ratio During the rich spike operation when the engine is operated in the lean air-fuel ratio stratified combustion mode, while the engine is operating in the lean air-fuel ratio stratified combustion mode, while the engine combustion air-fuel ratio is lean, Controls the engine fuel injection by the second fuel injection control means, and controls the fuel injection of the engine by the first fuel injection control means while the engine is operated in the rich air-fuel ratio homogeneous mixture combustion mode. A fuel injection control device for an internal combustion engine is provided.

In other words, according to the second aspect of the present invention, during the execution of the rich spike operation, as long as the engine air-fuel ratio is lean, the engine fuel injection is performed based on the required engine load (for example, the accelerator opening) and the engine speed as in the prior art. Although the control is performed, when the operation of the engine is switched to the rich air-fuel ratio homogeneous mixture combustion mode, the fuel injection of the engine is controlled based on the intake air amount and the engine speed. For this reason, after shifting 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 when the actual engine intake air amount does not correspond to the throttle valve opening immediately after the transition to the rich air-fuel ratio homogeneous mixture combustion mode, the fuel injection amount is determined based on the actual intake air amount based on the actual engine intake air amount. Is set to a value that sets a predetermined rich air-fuel ratio, and a predetermined rich air-fuel ratio can be obtained immediately after switching to the rich air-fuel ratio homogeneous combustion mode.

According to the invention described in claim 3, wherein the engine accessory is an exhaust air-fuel ratio of the exhaust air-fuel ratio flowing disposed engine exhaust passage flows to absorb NO _X in the exhaust gas when the lean-rich the absorbed NO _X when it is released, a _the NO _X storage reduction catalyst for purifying the rich spike operation to release NO _X absorbed from _the NO _X storage reduction catalyst, is executed when the reduction and purification A fuel injection control device for an internal combustion engine according to claim 1 or 2 is provided.

That is, according to the third aspect of the invention, even when the rich spike operation is performed to release the NO _X absorbed from the NO _X storage reduction catalyst, the actual operation is performed immediately after switching to the rich air-fuel ratio homogeneous mixture combustion mode. Since the engine combustion air-fuel ratio becomes a predetermined rich air-fuel ratio, lean air-fuel ratio exhaust near the stoichiometric air-fuel ratio does not flow into the NO _X storage reduction catalyst, and the emission of unpurified NO _{X to} the atmosphere is prevented.

According to the fourth aspect of the present invention, there is further provided an air-fuel ratio sensor disposed in the engine exhaust passage for detecting the air-fuel ratio of the exhaust gas, and the engine combustion is performed based on the air-fuel ratio sensor output during the rich spike operation. A fuel injection control device for an internal combustion engine according to claim 1 or 2, wherein the air-fuel ratio is controlled to a predetermined air-fuel ratio. That is, in the invention of claim 4, the combustion air-fuel ratio of the engine 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]

Embodiments of the present invention will be described below 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 internal combustion engine for a vehicle. In FIG. 1, reference numeral 1 denotes an automobile internal combustion engine. In the present embodiment, the engine 1 is a four-cylinder gasoline engine having four cylinders # 1 to # 4, and 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 capable of operating in a wide range of air-fuel ratios from an air-fuel ratio higher than the stoichiometric air-fuel ratio (lean) to an air-fuel ratio lower than the stoichiometric air-fuel ratio (rich). I have.

In this embodiment, the cylinders # 1 to # 4 are grouped into two cylinder groups each including two cylinders whose ignition timings are not continuous. (For example, in the embodiment of FIG. 1, the cylinder ignition order is 1-3-4-2,
The cylinders # 1 and # 4 and the cylinders # 2 and # 3 each constitute a cylinder group. 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, 21a is # 1, # 4
The exhaust manifold 21b connects the exhaust ports of the cylinder group consisting of cylinders to the individual exhaust passages 2a, and the exhaust manifold 21b connects the exhaust ports of the cylinder group consisting of # 2 and # 4 cylinders to the individual exhaust passage 2b. In the present 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. The individual exhaust passages 2a and 2b are S
It joins the common exhaust passage 2 on the downstream side of C.

On the common exhaust passage 2, a NO _X storage reduction catalyst 7 described later is arranged. FIG. 1 shows 29a and 29b.
Indicate the air-fuel ratio sensors 3 and 3 arranged upstream of the start catalysts 5a and 5b of the individual exhaust passages 2a and 2b.
Reference numeral 1 denotes an air-fuel ratio sensor disposed downstream of the NO _X storage reduction catalyst 7 in the exhaust passage 2. Air-fuel ratio sensor 29
Reference numerals a, 29b, and 31 denote so-called linear air-fuel ratio sensors that output voltage signals corresponding to the exhaust air-fuel ratio in a wide air-fuel ratio range.

In FIG. 1, reference numeral 10b denotes an intake manifold for connecting the intake port of each cylinder of the engine to an intake passage 10.
a is a surge tank provided in the intake passage 10. In this embodiment, the individual exhaust passages 2b of the # 2 and # 3 cylinders are used.
Tank 5 in the upstream of SC5b and engine intake passage 10
0a is connected with the EGR passage 43. Further, EG
Provided on the R passage 43 is an EGR valve 41, which is a flow control valve for controlling the flow rate of exhaust gas flowing from the exhaust passage 2b to the intake passage 10 through the EGR passage. EGR valve 41
Is provided with an actuator 41a of an appropriate type such as a stepper motor or a negative pressure actuator that operates in accordance with a control signal from the ECU 30, which will be described later.

Further, in this 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, and is driven by an appropriate type of actuator 15a such as a stepper motor or the like, and has an opening in accordance with a control signal from an ECU 30 described later. Reference numeral 30 in FIG. 1 denotes an electronic control unit (ECU) of the engine 1. In the present 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. Also,
In the present embodiment, in addition to performing the above-described basic control, the ECU 30 performs the in-cylinder injection valve 1 according to the engine operating state as described later.
Performs a control to change the operating air-fuel ratio changes to the engine fuel injection mode from 11 to 114, further lean air-fuel ratio operation of the engine in order of the NO _X release operation or the brake vacuum retention from _the NO _X storage reduction catalyst 7 A rich spike operation is performed during which the operating air-fuel ratio is switched to the rich air-fuel ratio.

The input ports of the ECU 30 are provided with the start catalysts 5a, 5b from the air-fuel ratio sensors 29a, 29b.
A signal representing the exhaust air-fuel ratio at the inlet and an air-fuel ratio sensor 3
1 to a signal representing the exhaust air-fuel ratio at the outlet of the NO _X 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 engine intake manifold (not shown). A pulse signal is input from the rotation speed sensor 33 disposed near the engine crankshaft (not shown) at every constant rotation angle of the engine crankshaft. Further, in the present embodiment, a signal indicating 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 arranged near an accelerator pedal (not shown) of the engine 1. Have been.
The ECU 30 performs AD conversion on the output of the intake pressure sensor 35 and the output of the accelerator opening sensor 37 at predetermined intervals to obtain the intake pipe pressure PM and the accelerator opening ACCP in the RAM of the ECU 30.
And the engine speed NE is calculated from the interval of the pulse signal from the speed sensor 33,
M in a predetermined area. The output port of the ECU 30 is connected to the fuel injection valves 111 to 114 of the respective cylinders via a fuel injection circuit (not shown) in order to control the amount and timing of fuel injection into each cylinder.
The throttle valve 15 is connected to an actuator 15b of the throttle valve 15 via a drive circuit (not shown) to control the opening of the throttle valve 15.

The ECU 30 is connected to an actuator 41a of the EGR valve 41 via a drive circuit (not shown).
EGR that controls a degree of opening of the GR valve 41 and recirculates a part of the exhaust gas from the exhaust passage 2 b to the intake passage 10 according to the engine operating state.
Perform the operation. In the present embodiment, during normal operation of the engine 1 (when a later-described rich spike operation is not performed), the ECU 30 operates the engine 1 in one of the following five modes according to operating conditions.

Lean air-fuel ratio stratified combustion (compression stroke single injection) Lean air-fuel ratio weak stratified combustion (intake stroke / compression stroke twice injection) Lean air-fuel ratio homogeneous mixture combustion (intake stroke single injection) Stoichiometric air-fuel ratio homogeneous mixing Air Combustion (Single-Injection Injection Injection) Rich Air-Fuel Ratio Homogeneous Mixture Combustion (Single-Intake Injection Injection) That is, in the light load operation region of the engine 1, the lean air-fuel ratio stratified combustion in the above mode 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 a cylinder, and an intake valve having a normal straight port, and an intake passage communicating with the straight port. By adjusting the opening of a swirl control valve (SCV) (not shown) provided in the cylinder, it is possible to control the amount of intake air flowing into the cylinder from the swirl port. When performing stratified charge combustion, the SCV opening is fully closed to increase the amount of intake air from the swirl port and generate strong swirl 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 near the cylinder ignition plug. Further, the fuel injection amount in this operating state is extremely small, and the air-fuel ratio as a whole in the cylinder becomes about 25 to 30 or more.

Further, when the load increases from the state of the above-mentioned mode to enter a low-load operation range, the lean air-fuel ratio weak stratified combustion in the above-mentioned mode is performed. As the engine load increases, the amount of fuel injected into the cylinder increases.However, in this load region, in addition to the fuel injection in the latter half of the compression stroke, the target amount of fuel is previously injected into the cylinder by injecting fuel in the first half of the intake stroke. I am trying to supply. The fuel injected into the cylinder in the first half of the intake stroke produces an extremely lean homogeneous mixture by the time of ignition. In the latter half of the compression stroke, fuel is further injected into this extremely lean homogeneous mixture to form a layer of ignitable combustible mixture near the spark plug. At the time of ignition, the combustible air-fuel mixture layer starts burning, 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 the mode, but the air-fuel ratio as a whole becomes slightly lower (for example, about 20 to 30 in air-fuel ratio).

When the engine load further increases, the engine 1 performs the lean air-fuel ratio homogeneous mixture combustion in the above mode. 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 performed only once in the first half of the intake stroke, and the fuel injection amount is further increased from the above mode. In this state, the homogeneous mixture generated in the cylinder has a lean air-fuel ratio relatively close to the stoichiometric air-fuel ratio (for example, an air-fuel ratio of about 15 to 25).

When the engine load further increases and enters the engine high load operation region, the fuel is further increased from the mode state,
The stoichiometric air-fuel ratio homogeneous mixture operation in the above mode 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 becomes full load operation, the fuel injection amount is further increased from the mode state, and the rich air-fuel ratio homogeneous mixture operation in the mode 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 in air-fuel ratio).

In the present embodiment, the optimal operation mode (from the above) is set in advance based on experiments and the like according to the accelerator opening (the amount of depression of the accelerator pedal by the driver) and the engine speed. The map is stored in the ROM using the accelerator opening and the engine speed. During operation of the engine 1, the ECU 30 determines which of the above operation modes should be currently selected based on the accelerator opening detected by the accelerator opening sensor 37 and the engine speed, and according to each mode. A control amount for controlling an operating state of the engine, such as a fuel injection amount, a fuel injection timing and the number of times, an ignition timing, a throttle valve opening, an EGR amount (EGR valve opening), is determined.

When the mode (stoichiometric air-fuel ratio homogeneous mixture combustion) is selected, the ECU 30 further uses the fuel injection amount calculated above as an air-fuel ratio sensor so that the engine exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio. Air-fuel ratio control for performing feedback correction based on the outputs of 29a and 29b is performed. More specifically, the mode from above (lean air-fuel ratio combustion)
Is selected, the ECU 30 calculates the fuel injection amount, the fuel injection timing, the throttle opening, the EGR amount, the ignition timing, etc. from the accelerator opening and the engine speed based on the maps prepared in advance for each mode from the above. Is determined.
The accelerator opening represents the engine load required by the driver. Therefore, in the mode, the values of the control amounts such as the fuel injection amount are set based on the required engine load and the engine speed.

When the above mode (stoichiometric air-fuel ratio or rich air-fuel ratio homogeneous mixture combustion) is selected, the ECU 30 opens the throttle valve based on a map prepared for each mode. Degree and engine speed,
And a control amount such as a fuel injection amount based on 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. The engine intake air amount and the engine speed are used as parameters representing the engine load state. For this reason, in the mode, each control amount such as the fuel injection amount is necessary to obtain a desired air-fuel ratio in consideration of the engine speed in addition to the engine intake air amount determined from the engine speed and the intake pipe negative pressure. Is set to an appropriate value. That is, in the present embodiment, in the mode of the homogeneous mixture combustion operation, the values of the respective control amounts such as the fuel injection amount are set based on the engine intake air amount and the engine speed.

In the mode, the opening of the throttle valve 15 is controlled in accordance with the accelerator opening in a region close to full opening. In this region, when the accelerator opening decreases, the throttle valve opening also decreases.However, since this is a region equivalent to the throttle valve being fully opened, the intake pipe pressure becomes substantially constant even when the throttle valve opening changes, and the intake throttle is almost completely closed. Does not occur. On the other hand, in the mode, the throttle valve opening is controlled to an opening substantially equal to the accelerator opening. That is, when the accelerator opening (accelerator pedal depression amount) is 0, the throttle opening is also 0
At (fully closed), when the accelerator opening is 100% (when the accelerator pedal is fully depressed), the throttle opening is also set to 100% (fully open).

The opening of the EGR valve 41 is set so that a relatively large amount of EGR gas is recirculated in the mode.
Control is performed so that the EGR gas amount decreases as the mode is changed. In the mode, EGR is almost stopped. Next, the NO _X storage reduction catalyst 7 of the present embodiment will be described. The NO _X storage-reduction catalyst 7 of this embodiment uses, for example, alumina as a carrier, and on this carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, or cesium Cs, or an alkaline earth such as barium Ba or calcium Ca. , Lanthanum La, cerium C
e, carrying at least one component selected from rare earths such as yttrium Y and a noble metal such as platinum Pt. When the air-fuel ratio of the inflowing exhaust gas is lean, the NO _X storage-reduction catalyst reduces the NO _X (NO ₂ ,
The NO) nitrate ions NO ₃ ^- is absorbed in the form of inflow exhaust gas is performed to absorbing and releasing action of the NO _X that releases NO _X absorbed and becomes rich.

In this embodiment, the engine 1 capable of operating at a lean air-fuel ratio is used. When the engine 1 is operating at a lean air-fuel ratio, the NO _X storage reduction catalyst absorbs NO _X in the exhaust gas flowing into the engine. . Further, when the engine 1 is operated at a rich air-fuel ratio, NO _X occluding and reducing catalyst 7 is absorbed NO _X
Releases, it reduces and purifies the released was NO _X with HC, CO components in the exhaust gas of a rich air-fuel ratio. In this embodiment,
When the lean air-fuel ratio _the amount of NO _X absorbed in the NO _X occluding and reducing catalyst 7 during operation increases, performs the rich spike operation for switching to a rich air-fuel ratio for a short time the engine air-fuel ratio from a lean air-fuel ratio from _the NO _X storage reduction catalyst release that to perform the reduction and purification of NO _X.

Next, the rich spy of the engine 1 of this embodiment is described.
A description will be given of the lock operation. In the present embodiment, the ECU 30
Is NO_XNO by increasing or decreasing the counter value _XOcclusion
NO retained by the reduction catalyst 7_XEstimate the amount. N
O_XNO absorbed by the storage reduction catalyst 7 per unit time
_XNO_XFlows into the storage reduction catalyst per unit time
NO in exhaust_XQuantity, ie per unit time at institution 1
NO generated in_XIt is proportional to the quantity. On the other hand,
NO generated per unit time_XAmount of fuel to the engine
Engine operation because it is determined by the amount, air-fuel ratio, exhaust flow
NO if conditions are determined_XNO absorbed by the storage reduction catalyst_X
You can know the quantity. In this embodiment, the engine operation is performed in advance.
Conditions (accelerator opening, engine speed, intake air amount, intake pipe
Pressure, air-fuel ratio, fuel supply, EGR, etc.)
NO generated per unit time_XMeasure the amount, NO
_XNO absorbed by the storage reduction catalyst 7 per unit time_X
The engine load (fuel injection amount) and the engine speed.
Stored in the ROM of the ECU 30 in the form of the numerical map used
I have. The ECU 30 operates at regular intervals (each of the above unit times).
This map is based on engine load (fuel injection amount) and engine speed.
NO per unit time using_XAbsorbed by storage reduction catalyst
NO_XCalculate the quantity, NO_XSet the counter to this NO_XSucking
Increase by yield. This makes NO_XThe counter value is
Always NO_XNO absorbed by storage reduction catalyst 7_XTable of quantity
I will be. The ECU 30 performs a lean air-fuel ratio operation of the engine.
In the above NO_XThe counter value has increased beyond the specified value
When the short-time engine is in the aforementioned mode (rich air-fuel ratio
Perform rich spike operation that operates with homogeneous mixture combustion).
U. Thereby, NO_XNO absorbed from the storage reduction catalyst
_XIs released and reduced and purified. In addition, the engine is rich empty
When the fuel-ratio operation is performed, the amounts of HC and CO in the exhaust gas increase, and N
O_XNO from the storage reduction catalyst_XIs released and H in the exhaust
It is reduced by C and CO. Here, per unit time
NO_XHC and CO in exhaust gas released from the storage reduction catalyst
NO reduced by_XIs determined by the air-fuel ratio of the exhaust
HC and CO amounts) and the exhaust flow rate. This embodiment
Then, the engine operating conditions (accelerator opening, engine speed,
Intake air amount, intake pipe pressure, air-fuel ratio, fuel supply amount, EGR
The engine is operated at a rich air-fuel ratio_X
Released from the storage reduction catalyst 7 per unit time, reduced and purified
NO_XMeasured during operation of the engine at rich air-fuel ratio
O_XNO released per unit time from the storage reduction catalyst 7
_XFor example, the engine load (fuel injection amount) and the engine speed
Stored in the ROM of the ECU 30 in the form of a numerical map using
ing. ECU 30 is constant during rich air-fuel ratio operation of the engine
Engine load (fuel injection amount) every time (each unit time above)
Per unit time using this map from the
NO_XNO released from the storage reduction catalyst_XCalculate quantity
And NO_XSet the counter to this NO_XReduce the amount absorbed
You. At the time of the rich spike operation, this NO_XMosquito
Ends rich spike operation when counter value reaches 0
I do.

That is, in this embodiment, the lean air-fuel ratio operation of the engine 1 continues, and the NO stored in the NO _X storage reduction catalyst 7 continues.
O _X amount rich spike operation is performed to operate independently of the engine at a rich air-fuel ratio and increasing the engine load required from the engine operating condition to a predetermined amount. Moreover, the rich spike operation is sometimes separately performed from the occluded amount of NO _X in _the NO _X storage reduction catalyst. That is, in the engine of the present embodiment, the negative pressure of the intake pipe is low (absolute pressure is high) in the lean air-fuel ratio operation from the mode, since the throttle valve 15 has an opening close to full open. On the other hand, when using a booster using negative pressure for vehicle braking,
It is necessary to always maintain a negative pressure for booster operation.However, during lean air-fuel ratio operation, negative pressure is supplied from the intake passage downstream of the throttle valve to the booster because the intake pipe negative pressure is low. Can not be introduced. 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. When the pressure in the negative pressure tank increases (negative pressure decreases) due to the operation of the booster, the same rich spike operation as described 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 of the throttle valve 15 decreases, and a large negative pressure is generated downstream of the throttle valve 15. In the present embodiment, even when the negative pressure of the negative pressure tank or the like that supplies the negative pressure to the booster drops, the rich spike operation is performed irrespective of the required load of the engine. If the engine load increases due to acceleration or the like from the lean air-fuel ratio stratified combustion operation mode during normal operation, the engine operation mode takes a certain time from the engine operation mode,
Mode is switched to the rich air-fuel ratio mode. At the time of the rich spike operation, it is necessary to switch the air-fuel ratio to rich as soon as possible. However, when the mode is switched from the lean air-fuel ratio stratified combustion operation to the direct mode rich air-fuel ratio homogeneous mixture combustion, the combustion mode changes (stratified combustion). Therefore, both the change in the air-fuel ratio and the change in the air-fuel ratio (from the lean air-fuel ratio to the rich air-fuel ratio) occur at the same time, so that the output torque of the engine greatly varies. Therefore,
Normally, even during the rich spike operation from the lean air-fuel ratio stratified combustion operation (mode), the mode is changed to the rich air-fuel ratio homogeneous mixture combustion operation (mode), and the operation is performed at about the number of revolutions of the engine to gradually increase the air-fuel ratio. The operation mode is switched. As described above, in the normal operation mode (rich air-fuel ratio homogeneous mixture combustion), the control amount such as the fuel injection amount of the engine is the engine intake air amount and the engine speed (the engine intake pipe negative pressure and the engine speed). However, since the operation time of the mode during the rich spike operation is usually short, the mode engine operation during the rich spike operation requires the required engine load and the engine speed (the accelerator opening and the (Engine speed) to simplify the control. That is, conventionally, a numerical map is separately prepared for the mode during the rich spike operation (lean air-fuel ratio homogeneous mixture air-fuel ratio combustion), and when the mode is switched from the mode to the rich spike mode, the required engine load continues. Each control amount including the fuel injection amount has been determined based on the engine speed and the engine speed (accelerator opening and engine speed).

In this case, however, 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. Since the amount of air taken into the engine changes later than the change in the throttle valve opening, a slight time delay occurs until the air amount reaches a value corresponding to the changed throttle valve opening. Therefore, when switching to the mode, the actual engine intake air amount does not immediately decrease even if the throttle valve opening immediately decreases. On the other hand, the fuel injection amount is changed to a value corresponding to the throttle valve opening immediately after switching to the mode, so immediately after the switching, the actual engine intake air amount becomes larger than the fuel injection amount, and the actual engine air-fuel ratio becomes smaller. There is a problem that the target value (rich air-fuel ratio) is shifted to the lean side.

For this reason, the engine is operated in a lean air-fuel ratio region (for example, an air-fuel ratio of 20 or less) near the stoichiometric air-fuel ratio immediately after the engine air-fuel ratio is switched to the rich air-fuel ratio (mode) during the conventional rich spike operation. In some cases, unpurified NO _X is released to the atmosphere due to a decrease in the storage capacity of the NO _X storage reduction catalyst. 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 the present embodiment, when the engine operation mode is switched to the rich air-fuel ratio homogeneous mixture combustion mode during the rich spike operation, the actual fuel injection amount is determined from the intake pipe pressure detected by the intake pressure sensor and the engine speed. Is set to a value to obtain a predetermined rich air-fuel ratio (for example, an air-fuel ratio of 12 to 14) based on the engine intake air amount and the engine speed. For this reason, 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 at which a predetermined rich air-fuel ratio is obtained with respect to the actual engine intake air amount. Thus, a stable rich air-fuel ratio can be obtained immediately after the switching.

FIG. 2 is a timing chart 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 this embodiment. As shown in FIG. 2, when the rich spike operation is started from the mode (lean air-fuel ratio stratified combustion), the operation mode is switched to the mode via the mode. At this time, the throttle valve opening TA is set to the mode, the accelerator opening and the engine speed (required engine load and engine speed) based on the numerical map for each operation mode at the time of rich spike operation when the mode is switched to the mode. Can be switched to a value determined from. In this case, FIG.
As shown in (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.
The air volume in the steady state of the mode is reached.

Also in this embodiment, since the fuel injection amount QINJ is set based on the accelerator opening and the engine speed from the mode, the operation mode is switched to the operation mode as shown in FIG. Every time, it changes stepwise similarly to the throttle valve opening TA. However, in this embodiment, when the operation state is switched from the mode to the mode, the fuel injection amount QINJ is set according to the engine intake air amount and the engine speed (the intake pipe negative pressure and the engine speed). Immediately after the mode switching, the value temporarily increases to a value corresponding to the actual intake air amount, and then the intake air amount (PM)
Decrease in accordance with the decrease of For this reason, 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 the mode to the mode.

On the other hand, the dotted line in FIG. 2 indicates the fuel injection amount QINJ immediately after the start of the mode when the fuel injection amount is set based on the required engine load and the engine speed during the operation in the mode at the time of the rich spike as in the prior art. And engine air-fuel ratio A /
The change from F is shown. In this case, as shown by the dotted line in FIG. 2, when the mode is switched to the mode, the fuel injection amount QINJ changes stepwise according to the change in the throttle valve opening TA and is maintained at a constant value during the operation of the mode. Is done. However, as described above, since the engine intake air amount actually changes with a delay with respect to the change in the throttle valve opening TA, the intake air amount is not sufficiently reduced immediately after the start of the mode operation. For this reason, the intake air amount becomes excessive with respect to the fuel injection amount, and the engine air-fuel ratio A / A is maintained until the intake air amount is sufficiently reduced to a value corresponding to the throttle valve opening.
F does not have a sufficient rich air-fuel ratio. Therefore, the time the engine air-fuel ratio remains in the lean air-fuel ratio range of the near stoichiometric air-fuel ratio is increased, unpurified from _the NO _X storage reduction catalyst NO _X
Will be released.

FIG. 3 is a flowchart showing the operation for calculating the above-described fuel injection amount QINJ. This operation is performed by the ECU 30
Is performed as a routine executed at regular intervals. In FIG. 3, in step 301, the current operation mode (mode to) of the engine is read. Then, in step 303, the current operation mode read in step 301 is the mode (normal stoichiometric air-fuel ratio homogeneous air-fuel mixture combustion) in the normal operation (operation other than the execution of the rich spike operation).
Or the mode (rich air-fuel ratio homogeneous mixture combustion) is determined. If neither is the case, then in step 305, the current mode is changed to the mode during rich spike operation (rich air-fuel ratio homogeneous mixture). Is determined.

In step 303, the current engine operation mode is the normal operation mode or step 305.
If the current operation mode is the mode during the rich spike operation, step 307 is executed, and the value of the fuel injection amount QINJ is determined by the intake pipe pressure PM detected by the intake pressure sensor 35 (FIG. 1) and the engine speed. It is determined from a numerical map prepared in advance based on the number NE. As a result, the fuel injection amount QINJ is set to a value at which a predetermined rich air-fuel ratio can be obtained 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.

On the other hand, if the current engine operation mode is neither the normal operation mode nor the rich spike operation mode in steps 303 and 305, step 309 is executed, and the fuel injection amount QINJ is set to the accelerator open state. It is set based on the accelerator opening ACCP detected by the degree sensor 37 and the engine speed. Thus, in the mode, the fuel injection amount QINJ is always set to a value corresponding to the required engine load and the engine speed.

[0045] In this embodiment, since immediately the engine air-fuel ratio when the operation mode is performed at the time of the rich-spike operation as described above which changes to a predetermined rich air-fuel ratio, NO _X from storage reduction catalyst unpurified NO _X is Release is prevented. Further, for example, deterioration of the NO _X occluding and reducing catalyst, N
The determination can be made based on the time required from the time when the exhaust air-fuel ratio flowing into the O _X storage reduction catalyst changes from lean to rich to the time when the exhaust air-fuel ratio at the NO _X storage reduction catalyst outlet changes to rich. That is, since the HC in the exhaust gas and NO _X absorbed from _the NO _X storage reduction catalyst during the rich spike operation is released, CO components are oxidized by the released NO _X, the exhaust air in _the NO _X storage reduction catalyst outlet The fuel ratio does not immediately change to the rich air-fuel ratio, but is maintained near the stoichiometric air-fuel ratio while NO _X is being released from the NO _X storage reduction catalyst, and changes to the rich air-fuel ratio at the same time as the release of NO _X is completed. . Therefore, when the engine air-fuel ratio is switched from lean to rich during the rich spike operation,
By _the NO _X storage reduction catalyst 7 exhaust gas air-fuel ratio detected by the air-fuel ratio sensor 31 on the downstream side to measure the time until the change to the rich air-fuel ratio, calculated amount of NO _X absorbed in the NO _X occluding and reducing catalyst And the calculated NO _X
Absorbed amount of NO _X in the storage reduction catalyst is reduced _the NO _X storage ability of the NO _X occluding and reducing catalyst when lower than the predetermined value, i.e., it can be determined that _the NO _X storage reduction catalyst has degraded.

However, if the fuel injection amount is set based on the required engine load and the engine speed during the rich spike operation as in the prior art, the operation mode of the engine is switched to the rich air-fuel ratio homogeneous mixture combustion mode. Even if it is, the actual air-fuel ratio does not immediately change to the rich air-fuel ratio, and the air-fuel ratio of the exhaust gas flowing into the NO _X storage reduction catalyst varies. For this reason, there is a problem that when the deterioration of the NO _X storage reduction catalyst is determined by the above method, an error is caused in the determination of the deterioration.

On the other hand, in the present embodiment, when the rich air-fuel ratio homogeneous mixture operation is performed during the rich spike operation, N
O _X occluding air-fuel ratio of the exhaust gas flowing into the reduction catalyst it is possible to prevent the error of the deterioration determination for changing a stable rich air-fuel ratio. In the present embodiment, the actual engine intake air amount is obtained based on the intake pipe pressure and the engine speed. For example, when an air flow meter is provided in the intake passage, the intake air amount directly detected by the air flow meter is obtained. 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 and the engine speed.

In this embodiment, the rich spike operation is performed.
During the combustion of a homogeneous rich air-fuel mixture, the fuel injection
It is set based on the intake air amount and the engine speed.
NO _XAir-fuel ratio sensor in the exhaust passage upstream of the storage reduction catalyst 7
The exhaust air-fuel ratio detected at 29a, 29b is a predetermined rich air
Based on the engine intake air amount and the engine speed, the fuel
The fuel injection amount set based on the air-fuel ratio sensor 29
If the correction is made based on the outputs of a and 29b,
The air-fuel ratio is accurately specified during the switch spike operation.
The ratio can be controlled.

As described above, in the above-described embodiment, the fuel injection amount is set based on the engine intake air amount and the engine speed during the combustion of the rich air-fuel ratio homogeneous mixture during the rich spike operation. The time during which the engine air-fuel ratio changes to a predetermined rich air-fuel ratio when switching to the rich air-fuel ratio is reduced. However, while setting the fuel injection amount based on the required engine load and the engine speed as in the past,
It is also possible to shorten the time.

As described above, when switching from the lean air-fuel ratio to the rich air-fuel ratio, the delay in reaching the predetermined rich air-fuel ratio is caused by the delay in following the change in the actual engine intake air amount with respect to the change in the throttle valve opening. Depending on. Therefore, for example, when the throttle valve opening changes during the rich spike operation (when switching from the mode), the fuel may be increased according to the changing speed of the throttle valve opening. In this case, for example, when the change speed (decrease speed) 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 rate of change of the degree increases.

FIG. 4 is a flow chart for explaining the fuel injection amount correction operation in the case of performing the 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, in step 401, the throttle valve opening degree TA,
The engine speed NE and the current engine operation mode (from the mode) are read.
It is determined whether or not the current engine operation mode read in 1 is a mode during a rich spike operation (a rich air-fuel ratio homogeneous mixture combustion mode). If the operation is being performed in the mode in which the rich spike operation is currently being performed, the process proceeds to step 405, where the change amount ΔTA of the current throttle valve opening TA from the previous operation execution time is set as ΔTA = TA−TA _OLD. Is calculated. TA _OLD is the throttle valve opening read in step 401 during the previous execution of the operation. And
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 by the accelerator opening and the engine speed. The value multiplied by fdlta is newly set as QINJ. As described above, the increase coefficient fdlta becomes larger as ΔTA becomes a larger negative value, and fdlta>
It is set to be 1. If ΔTA is the same, the value of fdlta increases as the engine speed increases.

After correcting QINJ as described above, step 4
At 11, the value of TA _OLD is updated using the current value of TA, and the operation is terminated. By performing the operation in FIG. 4, the rich air-fuel ratio homogeneous mixture combustion mode is set during the rich spike operation, and the fuel injection amount is increased when the throttle valve opening TA is reduced, so that the actual engine intake air amount is sufficient. The actual air-fuel ratio of the engine immediately changes to the rich air-fuel ratio even if it has not been reduced to a low value, and the emission of unpurified NO _X from the NO _X storage reduction catalyst is prevented.

Instead of increasing the fuel in accordance with the throttle valve opening change amount ΔTA as described above, the target mode 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. The air-fuel ratio may be set further to the rich side. Rich air-fuel ratio By setting the target air-fuel ratio further rich for a predetermined time immediately after the change of the homogeneous air-fuel mixture combustion mode, the engine air-fuel ratio becomes a lean air-fuel ratio near the stoichiometric air-fuel ratio even when the intake air amount change does not sufficiently decrease. since it is possible to prevent, that the NO _X unpurified from _the NO _X storage reduction catalyst is released is prevented.

[0054]

According to the invention described in each claim, the engine air-fuel ratio can be changed from the lean air-fuel ratio to the rich air-fuel ratio in a short time during the rich spike operation.
O _X occluding and reducing catalyst to NO _X unpurified rich spike operation early even when used it becomes possible to prevent 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 a direct injection type internal combustion engine for a vehicle.

FIG. 2 is a timing chart illustrating an example of a rich spike operation of the present invention.

FIG. 3 is a flowchart illustrating a rich spike operation in FIG. 2;

FIG. 4 is a flowchart illustrating another example of a rich spike operation.

[Explanation of symbols]

1 ... internal combustion engine 2 ... exhaust passage 7 ... NO _X occluding and reducing catalyst 15 ... electronic control throttle valve 111 to 114 ... cylinder injection valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) F02D 41/34 F02D 41/34 EF Term (Reference) 3G091 AA02 AA11 AA12 AA17 AA24 AA28 AB03 AB06 BA14 BA33 CB02 CB03 DA04 DC01 EA00 EA01 EA03 EA05 EA06 EA07 EA34 FB10 FB12 GB02W GB03W GB06W GB17X HA11 HA12 HA36 3G301 HA01 HA04 HA09 HA16 HA17 JA00 JA25 JB09 MA01 MA13 MA19 MA26 NC02 ND01 NE02 NE13 NE23 PA01ZPA07ZPZ PDZZ

Claims (4)

[Claims] 1. A fuel injection control device for an internal combustion engine that controls an engine combustion air-fuel ratio according to a required engine load, wherein a first fuel injection control device controls an engine fuel injection based on an engine intake air amount and an engine speed. Fuel injection control means, and second fuel injection control means for setting the fuel injection of the engine based on the required engine load and the engine speed. When the engine is operated at a lean air-fuel ratio, A rich spike operation for operating the engine at a rich air-fuel ratio in response to a request from an engine accessory regardless of an engine load is performed. At the time of switching the air-fuel ratio in the rich spike operation, the second spike operation is performed while the engine combustion air-fuel ratio is lean. The fuel injection control device of the internal combustion engine controls the fuel injection of the engine by the fuel injection control means, and controls the fuel injection of the engine by the first fuel injection control means while the engine is operated at the rich air-fuel ratio. Place. 2. A stratified combustion mode including a direct fuel injection valve for injecting fuel directly into a cylinder, injecting fuel during a compression stroke of each cylinder to perform a lean air-fuel ratio stratified combustion, and an 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 in which fuel is injected and a homogeneous mixture combustion is performed, wherein fuel injection of the engine is controlled by an engine intake air amount and an engine speed. First fuel injection control means for controlling the fuel injection of the engine based on the required engine load and the engine speed, and the second fuel injection control means for setting the fuel injection of the engine based on the required engine load and the engine speed. While performing operation switching between the combustion mode and the homogeneous mixture combustion mode, perform a rich spike operation of operating the engine in the homogeneous mixture combustion mode with a rich air-fuel ratio at the request of the engine auxiliary machine regardless of the required engine load, During the execution of the rich spike operation when the engine is operated in the lean air-fuel ratio stratified combustion mode, while the engine combustion air-fuel ratio is lean, the engine fuel injection is controlled by the second fuel injection control means, A fuel injection control device for an internal combustion engine, wherein the first fuel injection control means controls fuel injection of the engine while the engine is operated in a homogeneous air / fuel mixture combustion mode with a rich air-fuel ratio. Wherein said engine accessory is, NO _X exhaust air-fuel ratio of the exhaust air-fuel ratio flowing disposed engine exhaust passage flows to absorb NO _X in the exhaust gas when the lean absorbed when they become rich releasing, _the NO _X storage reduction catalyst for purifying the rich spike operation to release NO _X absorbed from _the NO _X storage reduction catalyst, according to claim 1 or claim 2 is performed when the reduction and purification A fuel injection control device for an internal combustion engine. 4. An air-fuel ratio sensor disposed in an engine exhaust passage and detecting an air-fuel ratio of exhaust gas, wherein the engine combustion air-fuel ratio is set to a predetermined air-fuel ratio based on the air-fuel ratio sensor output during the rich spike operation. 3. The fuel injection control device for an internal combustion engine according to claim 1, wherein the control is performed.